Belt Conveyors

Edition 12/08/98

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THE BELT CONVEYORS Knowledge & Adjustment

Continuous Professional Training Course of Mr. Marc des Rieux

 des RIEUX SAS au capital de 40 000 €uro Quartier St.Ruff 26000 VALENCE

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BELTS CONVEYORS

SUMMARY

I)

DEFINITION

1.1) The function 1.2) The means 1.3) The main element 1.4) The objective II)

MASTERING THE TRAJECTORY OF A CONVEYOR BELT

2.1) The elements of the conveyor  2.2) Interaction of the forces 2.3) The transported material 2.4) The elements to be neutralized 2.5) Factor that can perturb the trajectory of the belts. a) The deformation of the belt.  b) The deformation of the drum. c) The deformation of the support. d) Variation of the tension. 2.6) Other factors that can perturb the trajectory of the belt. a) The problems related to the presence of inlet chutes.  b) The problems related to the overflows of materials. III)

TERMINOLOGY OF THE MATERIALS

3.1) Longitudinal view. 3.2) Transversal view. 3.3) Particular cases. 3.4) Other elements that serve to define a conveyor. IV)

THE TRANSPORTED MATERIALS

4.1) Restraints due to materials. 4.2) Other imperatives imposed by the materials. 4.3) Calculation of a belt. 4.4) The outputs. 4.5) Influence of the materials on the belt. V)

THE ELEMENTS THAT CONSTITUTE THE CONVEYOR

5.1) The belts 5.2) The coatings 5.3) The frame 5.4) The gearbox group 5.5) System of tension

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5.6) The drums 5.6.1) Minimum diameter of the drums. 5.6.2) The forms of the drums. 5.6.3) The materials and surfaces of drums. 5.6.4) Zones of influence for the drums. 5.7) The supports 5.7.1) The supports of the slippage surface. a) The used materials. 5.7.2) The contact supports per bearing. a) Belts’ auto centering.  b) Coating of the rollers. c) Parasite forces. VI)

TRANSITION LENGTH

VII)

CONVEX CURVE

VIII) CONCAVE CURVE IX)

ADJUSTMENT OF A CONVEYOR BELT.

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THE BELT CONVEYORS

I)

DEFINITION

1.1) The function:

It is about realizing a handling of material, in bulk in a continuous manner. 1.2) The means :

The conveyors and the elevators with conveyor belt Commonly called: The belt conveyors. 1.3) The main element:

It is about well considering the belt like "main element" when we define the means that must realize the handling compare to the material to transport. The frames, motors and other elements, which constitute the transporters, must be considered as  being in service for the belt and therefore, they will be defined compare to the belt. 1.4) The objective:

Making the use of the belt " accurate and durable". For that, define its characteristics according to its use, the transported materials.. Choosing and adapting the materials that surround the belt in accordance with this one.  Attention::  Attention  It is very frequent to find installations for which the above rule has not been applied. These situations often end up to " dead-ends ", which turn out sometimes very onerous.

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II)

MASTERING THE TRAJECTORY OF A CONVEYOR BELT

Mastering the trajectory of a belt,

* It is to arrange the forces of the turning elements of the conveyor in the same direction; For that it is a must to determine the tolerance values of the forms and the positions of these elements. * It is to balance the right forces of  tension / left of the belt according to the axis of the conveyor. For that it is necessary to determine and to appreciate the importance of the parasite forces. 2.1) The elements of the conveyor:

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

The transported transporte d material The belt (belt, or carpet) The drive drum [+ its stressing drum] The drum of jetty [+ its stressing drum] The drums of the pouring trolleys The tension drum [+ its deviation drums] The tail drum (tail or discharge) The deviation drums The sliding supports or with rollers, return belt. The roller supports, return belt. The accessories: accessories: flanks, scrapers The annexes: feeding chutes(s)

* The frame must be considered that when it begets a variation of the position of one or of  the turning elements. 2.2) Reminder:

All those elements, the ones that compose the conveyor, generate or support forces. It is enough for one element to have a variable force so that the other elements see their forces fluctuate. Therefore the elements of the conveyor are " variables parameters". That state "unstable" leads to an " uncertain trajectory " of the belt, depending of the fact that those elements implicate forces of different directions. So, the conveyors are complicated machines, as far as physics is concerned. Mastering the trajectory of a belt, it is neutralize a maximum of variable then bring the conveyor  to the state of a simple machine, it means to tension towards a system of forces of the same direction. That notion of physics finds its mechanical expression "at the near tolerance". It is about considering here the tolerances of forms and positions of the elements of the mechanical system that the conveyor represents. The value that is affected for each tolerance can only fixed in accordance with a minimum general tolerance of good functioning and of the number of  interactive elements acting together (covered influence zones).

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2.3) The quantity:

The quantity of the transported material remains by force a variable parameter, it goes from 0 % to 100%. 2.4) The elements elements to neutralize:

present "together" forces forces of one one ∗ All the elements that have a movement of " revolution " must present

and same direction, They are drums and rollers, when they are included in same zone of  influence.

∗ All the couples of elements " in friction " must be decomposed in surfaces "pairs" and present a

symmetry of forces to the axis of the conveyor ; they are the couples belt/sole slipping, belt/ drum, belt/roller, material/belt, scraper/belt, mud flap /belt.

∗

All the elements that have a movement of revolution " with a related movement " must keep a constant of direction of forces; they are tension drums, the drums of the pouring trolleys, the drums are reserved from the belt. 2.5) Factors that can perturb the trajectory trajectory of the belts:

It is matter of considering the modification of the state of an element, such as its occasional or   permanent consecutive putting out of shape: - to an excessive excessive effort, - to a moderated and repeated effort (it is "fatigue"), - or due to a report or a retreat of material. We then consider the revolution of the state of one or several conveyor. We find, for illustrating that situation: a) The deformations of the belt under an important load of product, asymmetric to the axis of  the conveyor. ∗ In the case of slipping supports, that asymmetry of load is expressed by an asymmetry of 

friction resulting from the difference of the applied vertical force applied by the material on the belt by the material on the belt and which begets an unbalance of the pull forces.

∗ In case of roller supports, that asymmetry of load is expressed by an arrow of the belts

  between the supports, superior on one side compare to the other, then a resistance at the advance of the asymmetric belt. That resistant unbalanced factor is worsened by the crumbling of the materials pile on the belt, more important on one side then on the other and according to the cohesion of the material ( internal friction ) presenting a difference of  resistance to compression, more or less important, at the passage of each support, that factor  creates a supplementary unbalance of the pull forces.

∗ In the case of transition lengths that are too short and convex curves badly calculated, we

notice, at term of (# 1), a permanent deformation of the sides of the belt; that modification  brings a bigger sensitivity of the belt to the parasite forces (# 2). That deformation can be, on top of that, asymmetric which creates an imbalance of pull forces, that situation is worsened  by a big sensitivity of the belt to the parasite forces, like previously.

= after some hours with several months of work, according to the excess importance, in number and in value. #2 parasite forces = forces that are acting in different directions to the normal forces fo rces of the conveyor. #1 at term

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∗ In the case of a ratio "material width/total belt width" bending toward 0 %, with as

worsening factor the materials of high densities, the conveyors of long distance between the head and the tail drums, the ascending conveyors, the conveyors of concave curve, the belts whose carcass structure lacks « duitage », the belts functioning on drums which are too much convex.  b) The deformation of the drums under the applied loads, or for the addition of material in an asymmetric way, or the retreat of material, at the axis of the conveyor can lead to belt drifts: ∗ In the case of excessive loads for the drum, this one bends in a way that its outline, for the

 part under the belt support, describes, in longitudinal (transversal view compare to the belt), a " concave curve ".

∗ In the case of material plugging on the ferrule whose thickness, even very weak, does not

  present any symmetry to the conveyor axis. What we commonly call " spuds " is not considered in the worsening factors as far as the direct belt drifts are concerned. The presence of those spuds finally lead to a localized deformation, longitudinal of the carcass, that observation leads us to the belt drifts due to the deformation of this one.

less centered, more or less excessive. excessive. ∗ In the case of wear in shape of "diabolo toy", more or less

This type of deformation is the developer of abnormalities of the belt trajectory, it is matter of   permanent oscillations, of weak amplitudes; in that case it is interesting to look for the real causes of those drifts on top of the replacement of the defective drum. However there exists a particular case or the wear in "diabolo shape" of a drum is a worsening factor; that concerns the succession of three drums having wrapping angles close to 90°/180°/90°, in that case, the belt is alternatively drifted from right to left and conversely from a drum to another; once arrived at an extreme amplitude, the movement goes opposite again and so on. In that case, it is evident that the change of drums is a must ; a wear   presenting a bend of 5/10 mm is already significant, the first drum to be damaged is always one of the two drums of 90° of wrapping angle. The change of drums does not make exemption to searching and find a solution to the main problem, which allowed the beginning of the wear process for the drums.

c) The deformation of the roller supports and the state of the rollers properly called or the one of the soles and sliding skates truly bring disorders on the trajectory of the belts. The first handicap in the understanding of the drifts begotten by these elements is determined in the multitude of the elements to consider and the accumulative total of defaults for each element, knowing that that certain certain defaults defaults of the "supports" "supports" will be more or less active according according to the variation of other parameters like the material load on the belt, the vibration of one sieve, the wind. In annex, there is a list for the main changes of the state of the supports. d) The variation of the tension existing in the belts is a worsening factor for the situations of    precarious balance. balance. In fact, if the existing existing tension, during the the observed moment for a belt drift, cannot be the real cause, the direct cause of the drift, in the case of symmetry of the forces to the conveyor axis (in value and direction), it allows, by its simple variation, the ascendancy of the parasite forces, pre-existent, origin of the system unbalance. That observation values as much for variations toward superior forces as for the inferior forces to the initial values.

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∗ The conveyors ascending or descendant, of strong output, of long length, are more exposed to

 beget those variations of tension at the ends of the (conveyor) length. ∗ The conveyors equipped of pouring trolley present also important annoyances, especially if 

they are equipped of breaks placed at the head of the frame. For that type of material we should be afraid of the sagging of the belt between two supports at the foot of the concave curve (having the raising toward the drum at the top of the trolley) at a stopping moment, when the section of the belt preceding the rise toward the top of the trolley if fully loaded; therefore the material is poured out on the internal side of the return belt, then goes to pollute the extremity drum and this begets the drifting of the belt.

2.6) Other factors that can perturb the trajectory trajectory of the belt:

All the forces related to the passage of the material on the conveyor are sources of belt drifting. It is specified at the beginning of the text that the variation of output of the material is a variable factor that is inescapable whose effects must be limited by element that are sufficiently  proportioned. In this chapter "other factors" we have to consider the perturbations related to the  parasite forces that are generated by the handling of the material. We find, for illustrating that situation: a) The problems that are related to the presence of inlet chutes and/ or feeding hoppers, at the capacity banks, which beget "frictions" asymmetric to the axis of the conveyor in the case of   badly studied materials. The belt drifts are due: ∗ To the differences of the material flow, then of pressure in the hoppers or feeding chutes. ∗ To the differences of the material flow between the capacity banks. ∗ To the differences of pressure on the belt, generated by a granulometry segregation during the

 passage of chutes, in the case of feeding under an axis of different direction at the reception conveyor axis. Here it is matter of affecting the responsibility of belt drifting to the bad design of the chutes.

∗ To the incorrect material centering by the chutes. The 4 articles ,

here above, have in common, as factor of belt drift, a very important gap of the total forces on the right side of the conveyor axis compare to the ones on the left side. For  solving this type of problem, either we delete the cause by working on the geometry of the chutes, or we make the parasite forces insignificant compare the main forces by over sizing the elements of the conveyor, starting with the belt. These two solutions are not always easy to implement.

 b) The problems that are related to the overflows of materials. These overflows pollute the return  belt, They are transported up to the drums and they drift the belt. They are due: ∗ To the rebounds in the zone of putting the material in speed, either because the material

arrives so quickly (with too much energy) on the receiver belt, or because the speed of the receiver belt is very important compare to the speed of arrival of the material. The worsening factors are the conveyors that are strongly sloping, the rolling materials, the raised belts (rafters, battens), in this last case, the raised ones play like the whip of a kid who is striking his top (toy).

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transition that are too long. It is matter of considering considering the time of material ∗ To the lengths of transition

heap compare to the time that the belt takes to cover the distance from the last trough support (trough of the current length) to the drum of jetty. The worsening factors depend on the weak  cohesion of the materials, of the rolling materials.

∗ To the under-speeds of the belt, consecutive to a too much important output of material

(absorbed power superior to the installed available available power). In the same kind of default there is lateness of feeding output; In this case it is matter of problem of chute or/ and of speed related to material/ belt.

∗ There exists a case of overflow that is very particular on the sloping conveyors which is due

to the excessive presence of water in the material during the transport. The water builds up and piles up between the belt and the material until this one is lifted when the quantity of  water has reached a sufficient value, and the whole thing slips towards the tail of the conveyor.

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III)

TERMINOLOGY OF THE MATERIALS

Types and outlines of the conveyors: 3.1) Longitudinal View:

The conveyor is:

- straight horizontal - straight upward of x° (or x %) of slope - straight descendant of x° (or x %) of slope - straight vertical = elevator  - straight + 1 bend "concave" - straight + 1 bend "convex" - straight + 2 bends "concave and convex" - with multiple sections (straight, concave, convex, curved in the plan)

For all the conveyors, it is a must to know the total elevation height, the slopes and the radius of  the curves. An ascendant conveyor consumes energy. A descendant conveyor can produce energy.

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Elevation height Upward Straight conveyor 

Descendant Vertical Elevator  Belt width

Belt width

Conveyor length conveyor with bend Conveyor length Concave curve conveyor with double bend

convex

Elevation convex curve

Concave With multiple curves in the plan Top view

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3.2) Transversal view: The shape of the support(s)

The belt moves on a support (or on supports) " flat " The belt moves on a support (or on supports) " V " at 20°, 25°, 30° The belt moves on a support (or on supports) " trough " at 20°, 25°, 30°, 45° The belt moves on a support (or on supports) " deep trough " at 60°, 90° The troughs are regular (standard), deep or large. The nature of the support(s)

The support(s) is (are) constituted constituted by a slipping sole, by slides. The support(s) is (are) constituted constituted by rollers, by garland rollers  It is a must to use a form and a type of support that is adapted to the belt.

  Notably the slipping soles corresponding to belts of internal face without coating. The weak  coefficient of fabrics friction, associated to the relief of these ones, enable its functioning. Not retaining this rule has often as consequence destroying first the gearboxes, then the belt by a suction disc effect. We should make sure as well we do not use V or trough shapes for carcass belts, which is steep in grid. The preceding paragraph puts in evidence the distinction that is done between the shape and the nature of the supports.

Outline: support form

flat

In V for x°

In regular  trough with 3 rollers of  x°

In special trough

Type of support Turning supports Rollers

Supports with slipping surface

Sole

Sole

Bar or skate

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3.3) Particular cases: The measurers and weighers (weighbridges)

Their function: measure a quantity, a mass of material either in continuous movement, or in intermittent intermittent movement. They require a particular care as far as the homogeneity of the belt is concerned. The junctions must have a minimum effect on the weighing devices, for the measures. measure and weigher

The extractors:

Materials forbidden for commercial

Their function: extract directly the material under a hopper or silo. There is then no free space  between the two materials, the belt make therefore the bottom of the hopper or of the silo. The nature of the material, the section, the height of the column in support on the belt, the speed are determining for the choice of the components of the transporter. The drainage doors represent often traps in those materials. It is must, in principle, to give privilege to an important door opening height for a reduced speed of the belt advance. To define this type of application, there are particular calculations.

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3.4) Other elements that serve to define a conveyor:

The conveyors are defined as well by their width and their length. For the width, it is about the width of the belt in millimeters. The conveyor length is given in millimeter or meters. This measurement is not enough to know the length of the belt. In certain cases the width of the belt can be equal or superior to the conveyor length. Developed length, without end, of a belt (∅ t1 +∅ t2)  + (2 x conveyor length) = length without end 2 buying length = length without end + junction It is the manufacturer of the belt who, himself, must precise the necessary over-length for the junctions. He also must precise the number of belt reels to be delivered for the big conveyor lengths, which determines the number of junctions.

Drum 2

Drum 1 Conveyor 

Developped length = (∅t1 x π x α1)+( Rc x 2 x π x αc)+(∅t 2 x π x α2)+(∅t3 etc. jusqu'à t9) + 360° 36 0° 360° 360° 360° 36 0° EA1 + EA2 etc. up to EA9. In the case of an utilization "big cold", consider the retreat according to te nature of the carcass and ∆t temperature. Length. s real end = Lengths calculated end x ∆t. (t°u - t° 20° C) ∆t = coefficient coeff icient of expansion ex pansion per ° C per m. linear t°u = utilization temperature (even at stop)

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Direction of movement : The movement direction of a belt is defined by the direction of the material movement. We say that: - the belt is pulled when the drive drum is at the head. - the belt is pushed when the drive drum is at tail (tail). - the belt has double direction, then it is pulled and pushed alternately. In that case, a particular care is brought in the choice and the assembly of all the elements that compose the transporter (see paragraph belt, drums, supports). During the calculation of the conveyor, we have to " necessarily " proceed according to the two   possibilities belt "pulled" et "pushed"; that concerns notably the values to apply to the tension systems and to be determined according to the radius of the concave curves. The conveyors that are equipped of pouring trolley present often abnormalities of functioning having as origin partial calculations.

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IV)

THE TRANSPORTED MATERIALS

(compare to the belt)

4.1) Restraints due to the material

To determine a belt it is a must to know well, of course, the restraints that will be imposed to it. The transported materials will have on the belt some influences : PHYSICAL } CHEMICAL } or THERMAL }

a combination of all 3

The physical influences are:

The load, the abrasion, the punching, the cut, the fouling. The chemical influences are:

The range of the materials is so large that it is always careful to make tests. A aggressive material for a belt will make its mechanical resistances resistances drop down. The thermal influences:

Are as destructive destructive for low temperatures temperatures under 0° C (of the order order of -10°C, -20°C, -30°C an more); as for temperatures above 20° C (of the order of +70° C to +250°/+400° C and above). WE HAVE TO RETAIN OBSOLUMENT THAT ALL TECHNICAL CHARACTERISTICS, THE MECHANICAL RÉSISTANCES OF THE BELTS ARE GIVE ON DOCUMENTATION FOR A USE AT "20° C"

4.2) Other imperatives imposed by the materials:

We also have to consider supplementary factors when we determine a conveyor belt compare to the transported materials. We mean sanitary restraints, material fragility, the weight of the daily work, weekly work, incident frequencies (starting in full load), industrial risks (cost of production stop), manufacturing manufacturing standards. The objective being to move a material from a point A to a point B, we have to know the quantities in volume and in mass, for a peak output and for an average output, the distance and the height of elevation (or the difference in height) of the transport.

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.3) Calculation of a belt The standard standard to know: know: NF H 95-203 95-203

(ISO 5048)

Determination of a conveyor belt. Calculation of the forces, output and section. 4.4) The outputs outputs in "Volume", in "Mass"

The transported quantity is expressed by the output which is very often given in tons / hour.  In that case we should not forget, especially, to calculate the output in m³/ hour because before all a belt transports a " volume". volume".

For that, we have to know the density of the material when this one is in movement : It is the apparent density. This density may be very different from the "Physical" density, considering the presence of air in the pile: material of heterogeneous shapes and granulometry, material that emulsifies.  Not respecting that rule has always got as consequences consequences to see the material overflowing from the   belt and making the installation dirty, which has got as second consequence to provoke the dysfunction of the belt In that case, it will be useless to talk about belt adjustment. To adorn this problem, we can often increase the output by increasing the speed or / and the linear capacity which mean by increasing the trough value. But pay attention when modifying these parameters you can also make some new constraints to occur (abrasion, patination patination during during start etc.).

Tobacco leaves Density : 0.08

Zin ore Density : 5.5

1 masse unity Ratio between these 2 example densities: 68.75

1 mass unity

-

A belt, as all the " containers " carries before all all : A VOLUME The outputs are often given in tone/hour: t/h Always, we have to take care of calculating the output in cubic meter / hour: m 3/h for that we have to know the Density of the material in movement. when the density density reduces, reduces, the volume increases, increases, when the density increases, the volume reduces.

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4.5) Influence of materials on the trajectory of the belt :

In a belt drift due to a material that is badly centered, the amplitude of that drift is very uncertain;   because many factors intervene, it is difficult to have a situation that is foreseeable of  equilibrium (centered) for the belt trajectory and that this one is satisfying for the minimum outputs to the maximum one. By experience, despite the real report of a material that is badly centered on the belt, it turns out that a neutral position of the turning elements and a sufficient pre-tension of the belt reduce, even supersede, the belt drift. But pay attention, by modifying these parameters you can also make new restraints appear.

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V) THE ELEMENTS THAT CONSTITUTE THE TRANSPORTER :

5.1) The belts:

Description: The belts are composed of  carcass and coating(s) The types of carcass: There are "mono-pleat " carcass and "multi-pleats " carcass with an inter-pleats rubber assuring the liaison of the pleats. In the case of thick inter-pleats the rubber serves in addition to the  protection against shocks and punching. For information, There are belts without carcasses. The polyester (E), the polyamide (P), the cotton (C), the metal (S), the glass (G). Other materials: the Kevlar, the polyethylene, Nomex (aromatic polyamide) The carcass constituti constitution: on: The chain and grid cables cables are of the same material. material. The chain and grid cables cables are in different material. material. The grid cables are in mono-filament of big diameter (stiff). The weavings are straight, of SOLIDWOVEN type, with superposed chain and grid (steel carcass), with cable, then without grid (steel carcass). There are carcasses with pleats of different natures (example: Round Baller agricultural machine). E = polyester Abbreviations: P = polyamide Lengthening due to rupture: E = 15 % P = 23 % Lengthening of service of: E = 1,5 % (under 10% of load of rupture)

The metal, the glass has a lengthening lengthening of service of 0,25 %. Certain references of belt with metal carcass have a lengthening of service 0,6 to 0,8 %. The nature and the number of pleats have a direct influence influence on the diameters of the drums. The inter-pleats are of the same material like the coatings, or of different materials. They also contribute to the protection of the carcass; inter-pleats strong thickness will be more resistant against punching but will necessitate bigger drums; (see standard NF T 47-103). Standards of fabrics in resistance against rupture for lengthening  N/mm : 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630. We must consider these values at the junction in accordance to the type of junction.

THE CARCASS ENDURES THE TENSIONS AND THE CHOCS

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5.2) The coatings:

THE COATINGS PROTECT THE CARCASS The used materials:

The natural rubber = NR, the SBR, NBR, IIR, EPM, NCR, CR, PVC, PU, silicone, Teflon, leather, felt, PE, PP For information, there belts without coating. The coatings protect the carcasses against abrasion, punching, heat, cold, all sorts of chemical  products, fire, static electricity. They have a function of capacity in the case of rafters, battens and buckets, sides. They have a function of drive with the relief of bee nest type. A function of guidance with the trapezoid guides.

Calculation of tension for a belt and for i ts counterweight of tension:

(annex file)

THE CHOICE OF A BELT MAKES NUMEROUS PARAMETERS INTERVENE. IT IS THEN VERY IMPORTANT TO CLASS IN DECREASING ORDER  THE CHOICE CRITERIA FOR EACH APPLICATION. TO RECLASS THIS HIÉRARCHY AS THE EXPERIENCE ON THE FIELD GOES ALONG BY A MATERIALS’ FOLLOW-UP.

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THE BELT CONVEYORS Interaction of the components:

It is matter of determining the influences of all the components of a handling by belt conveyor, as well on the resistant forces, the absorbed powers as the utilization constraints that are specific to each component. 5.3) The frame

It is by definition the skeleton of the transporter and supports the whole of the elements that compose the transporter including the bulk (materials) to handle. Its first quality is to be stable in the time, as well in its form as in its dimensions. It must neither  fold, nor subside under the load. It is desirable that it is not sensitive to its environment; for example to the vibrations of a sieve, to the heat of an oven, to the wind blows, etc. 5.4 ) The gear box group

  No matter the used energy or or the model of material, the power* expressed in kW kW will be retained and if it is equipped of a system of progressive start. Do not neglect the systems of breaks which can have a "power" widely superior to the motorization, motorization, it is the case of the descendant transporters. ∗ From Installed Power: we have to know the efficiency of the group of command up to the

drum shaft. This efficiency is in general of 0,9 for the coaxial gear boxes, it can go down up to 0,45 for the gear boxes with wheels and screws.

The efforts of traction on the belt will be: - maximums in DIRECT start ( and superior to the ones of the stabilized movement regime ) - rising with an equipment "PROGRESSIVE" ( and will not overpass the ones of the stabilized movement régime.)

That information will be determining to evaluate the coefficient of security for the resistance against belt rupture. Knowing that that resistance against rupture is defined compare to the motor power and to the speed we also have to know the "Speed" given to the belt and expressed in meter/second (m/s).If  this one is fixed or variable, we are supposed to know the minimal and maximal values. The frequency of starts under load is to be considered as well. Note:

For a "given power " and a "given output " : - the more we increase the speed of the belt the more the necessary resistance against rupture reduces. - the more we reduce the speed of the belt the more the necessary resistance against rupture increases. (see § calculation).

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5.5 ) Tension systems:

They are classed in two categories. • The tensions whose run is " invariable in service " irrespective of the jolts of load applied on

the belt. They are for example the screw tensions.

• The tensions whose course is " variable in service " in accordance with the applied loads.

They are for example the counterweight tensions.

The function of a "system of tension" is to apply a defined force (calculated) (calculated ) and of a direction that is opposed to the forces resisting the traction of the drive drum. When we apply a force of traction on any material, we provoke its lengthening according to its nature and its size (section). The mechanical characteristics of the material under traction as well as other values will allow to determine the necessary course of the tension. The tension system is not used to adjust the belt, but practically it is true that in numerous cases the " tension system " totalizes these two functions. Manage the trajectory of the belt by an action on the geometric position of the tension drum often underlines the absence of the research of the defaults which are the origin of the problem. The tension can partially serve to catch up the over-length of the soft belt side. On the big conveyor lengths it is preferable to realize a pre-tension by the good care of your vulcanizer. Calculation of a tension:

(see calculation of a belt Paragraph 6.3.3)

AFNOR NF H 95-203

In the practice, very numerous belts function "over-tensioned". A good principle wants that we apply a tension that is equal to the 2/3 of the nominal value (value issued by calculation) and only in case of "slipping" we increase "if necessary" and progressively that tension after having, of course, eliminated the causes of slipping and without over passing the nominal tension; otherwise we should look for the error! Example: Example: Scraper, flanks in excessive pressure, belts and drums that are wet or have fat, the same for  certain dusts (case of the calculation with as conditions "clean environment"), unreliable drive drum, without rubber coating, wrongly assembled, belt in friction with the belt. Particular case: For the belts with double direction it is often necessary to tension them "to the maximum of the calculated value" in order to assure them a good guidance (only by the drums) by reducing (or  canceling) in this case the effects due to a load which is incorrectly shared out. In certain cases from elsewhere, we will use a type of belt superior to the calculated value. Example: calculated type 250 N/mm, recommended type 315 N/mm even 400 N/mm. Precautions: Precautions: On the transporters with counterweight tension notably, we often find a succession of drums that are close to one an other: the more the length of the drums is important, the less the uncertainty on their geometrical position will have influence on the trajectory of the belt.

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Run Run = 50 mm 100 mm Belt : F = 0.5

Belt : F = 0.5 Anchorage = 0.5 t Angle : superior to 5° = drum Angle : inferior to 5° = roller 

F=1t at the hook  -% of the efficiency ( 1%)

Anchorage = 0.5 t P = Spacing f = curve

Limits prescribed by the standard H95-203 #6.3.3  F = 0,5 at 2 % of P Value of the wrapping angle on the rollers  2.α  2. tangent line α = 2. f  Example For a spacing of 3000 mm  ½ P = 3000 = 1500 m 2 for a curve of 1%  f = 1 % of P = 30 mm the wrapping angle on the roller = 2 α α = tang. α = f = 30 = 0,02  1° 8' 26" meaning 2 α ½ P 1500

½P

2° 16' 52"

Measurement of the tension of a belt in accordance with the spacing of the rollers and of the belt curve, Measurement of its curve in accordance with the tension and with the spacing, Measurement of the spacing in accordance with the tension and with the curve:

Prescriptive reference: NF H 95-203 #6.3.3 (correspondence ISO: 5048) Calculation of the Tension T = P²x m x g 8xf

Calculation of the curve Calculation of the Spacing f = P²x m x g P = ⌦ T x 8 x f  8xT mxg

T : the tension applied on the belt "at the measurement place" = value in N P : spacing between two consecutive belts supports = value in m m : mass " at the measurement place " = value in Kg/m linear  either the mass of the belt alone / or belt + material / or belt + material + impact energy (feeding) 8 : factor in the expression of a parabola f : belt curve mesured at ½ supports spacing = value in m (Pay attention on frequent errors of conversion of the measurement unities)

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5.6 ) THE DRUMS

Standards ISO 3, 1536, 251, 583, 7590.  NF T 47-103, T 47-004, T 47-111

It is prudent to distinguish the drums and the rollers, their uses are different. - For the drums we have the high loads of geometric qualities with tighter tolerances. tolerances. - For rollers we have weak loads with medium geometric tolerances. Wrapping angle of the belt

180° and

Drums domain

 Near another 

Far from another 

Rollers domain

The name of the drums that correspond to the location that they occupy on the frame ; the order  of the goes from the drum that supports the strongest load to the weakest. The standard class them in three categories: A, B, C A Drive drum A Motor drum (it is a drive drum whose gear box is integrated in the ferrule of the drum.). A Head drum, drums for the pouring trolleys B or A Tale drum (for dismissal) dismissal) B or A Tension drum or counterweight drum C Stressing drum C Deviation drum C Bend drum

23

You will notice by yourself that this hierarchy goes from the drum to the strongest load towards the on with the weakest load is strongly respected in the technical manuals from the belt manufacturers. In fact, they indicate the diameters of rising values according to the above bill of  materials. The technical documentations always indicates the minimum diameters recommended compare to a belt reference which is well precise; that value is not forcibly suitable for two belts of the same type, meaning of the same resistance to rupture to the lengthening that is given in (N/mm) That minimum diameter corresponds for a use at 100% of the load capacity of the belt in reference. In certain case, it is possible to reduce that minimum diameter when we are sure that the belt will always be used with half load, as well in transported product as in traction force, but   pay attention to the temperature and fatigue factors (this one depends on the frequency of a flexion of the belt around a drum).

1: head drum 2: tale drum 3: tension or stressing drum 4: constraint drum 5: deviation or inflexion drum

Pulled Head drum = Drive Drive drum

Pushed Tail drum = Drive drum Drive drum on return belt

internal face ullin

carr carr in face face ullin ullin

run c : Tension run

Counterweight tension Bolt

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5.6.2) The forms of drums :

 NF T 47-004

In principle, a drum is a cylindrical form with a well centered axis. But, in order to obtain an effect of centering of the belts, a convex form is given to the ferrule. Actually, a convex drum enables to resist to the parasites forces which are superior to the cylindrical drum. The general rule is to keep a cylindrical form for 1/3 of the width of the belt in the middle of the drum (maximum 40% of the length of the drum), the adjacent parts, right and left having a form of a cone trunk. The standard AFNOR NF T 47-004 indicates: indicates: d = D - 1 % for belt carcasses That have an lengthening und load of reference, at 10 % of the rupture, of 0,8 % to 1,6 %. Example : the carcasses in polyester (E) The carcasses with weak lengthening in metal, glass , Polyamide, the convex is invalid ∅d= ∅D-0%  Note:: The width of the belt does not intervene at all in the value of the convex.  Note

25

Form of the drums called convex according to NF T 47-004 ∅d= or

∅ D x 0,99 ∅D-1%

value given for the carcasses whose lengthening under load of reference* is between 0, 8 % and 1, 6 % of lengthening.

* The lengthening under load of reference is an lengthening which is measured under a tension (a load) that is equal to 10 % of the tension (the load) of rupture, for example the belts with polyester carcass (E).

Len th of theDru heDrum Widt idth of the the Drum= Drum= B

In maximum 40% of the length of the drum

The belts with metal carcass, glass, Kevlar ® are excluded from this standard. Their

reference is of 0,25 %. The drums drums must be cylindrical. cylindrical. lengthening under load of reference

In the case of small diameter of the drum and of big width of the belt, the slope resulting from the difference of the diameters D and d is practically void, then without effect of " guidance ". In this case of big width (1200, 2000 mm and +) a multi- convex can be utilized. This method comes to consider that our belt is equivalent to a number "x" of belts. We can also increase the guidance efficiency of a convex form by increasing the friction coefficient (of adhesion) belt/drum by realizing a rubber coating. Particular case: case : The drums " squirrel cage ". These drums have their ferrule made of metallic barrettes, straight, arched (convex) or not, set on the circumference of the flasks with a spacing which is more or less tight. At the origin this type of drum was utilized on dirty installations to avoid plugging of the transported material on the drums. It would have, as it seems to us, been more convenient to improve the cleanness of the transporter (except in particular case: the elevators). The followers of this type of drum have the conviction to obtain a better drive for the belt. No scientific calculation with equal use has proved it. The elements to retain in order to determine the transmission factor:

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The factor of transmission corresponds to the drive capacity for the belt by the drum. It depends : - on the coefficient of adhesion belt/drum; which changes depending on the nature and the state of the present materials. - on the contact surface belt/drum; this one is equal to the width of the belt by the length of the wrapping angle on the drum, if this surface is full, and it is reduced from the surface of grooves or empties, if the surface of the drum is structured. - On the tension force that is applied applied to the belt; this one is measured measured near the drum (see NF H 95 203, # 6.3.3). Save a polygonal effect of the barrettes of the squirrel cage (then a certain increase of the "tension" factor), the other factor are widely unfavorable. The results " pull force " is then not more favorable with the drums of the squirrel cage type. In practice, we have often noticed that the belts turning on the transporters with drums of  "squirrel cage" type were over-tensioned. In the cases of normal tensions, the belt ware  presenting, internal face, important and significant significant traces for slippage on the drive drum . 5.6.3) The materials and surfaces of the drums:

The main role of the drums is to lead the belt, to tension it, to enable it to change direction. High loads correspond to those functions!

It is then evident to manufacture the drums in steel sheet of strong thickness. Their handicap is to have a coefficient of medium adhesion; on the other hand, when an object  passes between the belt and the drum it is the belt which suffers (punching by the internal face) if  that object is hard, if the object (material) is soft or of fine granulometry it will form “potatoes” or a dandruff of material which will drift the belt and will also deform the belt carcass. Facing those problems, it is very effective to garnish the drums with rubber, either with smooth surface*, or with structured surface (grooves). The most common quality is the natural rubber. According to the chemical restraints, thermal (hot or cold) or sanitary other qualities of coating are used. *smooth surface coating: this is justified only when we can guarantee a real cleanness of both surfaces in contact (belt and drum), which is practically a rare case; the we have to prefer the structured surface!

The hardness of the rubbers which is expressed in Shore A, for a drum coating, depends on the resistance to rupture at the lengthening of the belt, on its rate of utilization and of the category of  the drum (A,B,C). In general, we use rubbers of 45-50 Sh for the types up to 400 N/mm, above that we pass to the rubbers of 65-70 Sh. There again, the width of the belt is not to be retain as criteria of choice for the hardness of the rubber. As well the thickness of the coating follows the rules which are similar to the preceding  paragraph. It goes from 2 mm to 8 mm, even 12, 15, 20 mm. A weak thickness of drum coating, of medium hardness (45-50 Shore), foreseen for an installation that have a belt of strong resistance to the rupture, risk of getting stuck by " delaminating ". We notice the same  phenomenon with the rubbers of weak elasticity. (see table on the following page)

27

Table of hardness and thickness of the rubbers of drum coating, in accordance with the resistance to the rupture of the belt and its rate of utilization (% of the RMBT): Resistance to the rupture / rate of utilization at 100% RMBT -/- <60% RMBT

hardness -/- thickness of the c/c  ≤315N/mm 400 N/mm 500 N/mm

630 N/mm 800 N/mm 100 <60 100 <60 100 <60 100 <60 100 <60 % % % % % % % % % %  50 Sh A/B/ A/B/ B/C A/B/ B/C A/B/ C A/B/ B/C th.8 C C C C C 50 Sh B C ép.10 65 Sh B A A A th.8 65 Sh A A th.10 65 Sh th.12 65 Sh th.15 65 Sh th.20

Category of the drums :

1000 N/mm 100 <60 % % B/C

1250 N/mm 100 <60 % % C

C

1400 N/mm 100 <60 % % C

B

A B

1600 N/mm 100 <60 % %

B

C

C B

B

A

C B

A

A

A C B

A A

A

A = head drum, drive drum, motor drum, jetty drum

B = tail drum, dismiss dismiss drum, tension tension drum C = snub drum, deviation drum, bend drum

Remark : We perceive easily the role of the rubber, of a drum coating, in the increase of the coefficient of adhesion to the traction, of the anti-plugging and of the decrease of the risk of belt punching. We often forget the role of the rubber in the important improvement of the guidance of the belts due to its strong coefficient of adhesion and to the service life of its action due to its excellent running against the abrasion. If there is movement towards the center, there is drift, then friction, then wear. We can say that at equal pre-tension of the belt, this one will resist from parasites forces which are superior compare to a conveyor which is equipped of bare drums.  Note: In very rare cases, a trapezoid groove (or trapezoid  Note: trapezoid grooves) is (or are) used on the drums. To those gorges correspond trapezoid guide-profiles welded on the internal face of the belt. We must retain only that those grooves must imperatively have measurements that are slightly superior to the guide ones. Very often, the use of these systems of guide/ groove underlines a wrong problem. Examples of application with guides: - assembly of several belts on the same drum and subjected to a transversal effort. - narrow and long belts subjected to important transversal efforts. 5.6.4) Drums’ influence zone: Every drum applies a tension on the two blades (carrying and return belts) of the belt which adjoins it. The tension in each blade is equal no matter the wrapping angle for free drums. The tension is inferior or equal for the pushed  blade compare to the pulled blade, to the drive drum. The bigger that tension, that force, is, the longer will be the belt under the drum influence.

The interest of knowing that factor is that all the elements which can influence, positively or negatively, the trajectory of the belt, in that zone, will be modified. Concerning the adjustment of the belts, wanting to correct a belt trajectory, by the annex elements of the drum, will  be more difficult and uncertain than the tension noticed on the drum will be big. That rule goes the other way round for the first or the last station in trough tr ough adjoining to the drum, but with limited effects. Considering these remarks, it appears evident that the drums must present a good geometric quality for the form and the position.

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5.7) THE SUPPORTS

• Their function is to support, well of course, the belt and the bulk to be transported between the

different drums of the installation.

• Their influence on the wear of the belt must be as weak as possible. • They participate, in a way or anther, according to their types, to the good trajectory of the belt. Therefore the choice of one type of support, its intrinsic quality and its assembly are important.

There are two categories of support: 1. The supports with surface of  slippage . 2. The supports with contact by rotation (or turning)  Note : As we saw in the chapter " terminology of the materials", we have to distinguish well the nature of the shape of the supports. 5.7.1) The supports with surface of slippage:

• By definition, there is friction between belt and support. • The quality, of the couple belt/support, will be defined by the coefficient of friction resulting

from the two elements. • It is imperative to use a belt with an internal face that is adapted for that use. • A weak coefficient of friction implicates a weak absorbed power. • That coefficient of friction must be " homogeneous " and " invariable " on all the surface of  contact, for fear to create a "couple of force" like the way this is used by the caterpillar  machine for turning. In this category, we find the slipping soles and the slides or skates . • Irrespective of their form (seen in transversal cut) these supports must necessarily present a

symmetry (image mirror) compare to the longitudinal axis of the frame. • The two half plans, that they define, must be parallel to the theoretical plan that is limited by two consecutive drums, in order to enable a straight trajectory of the belt. In the case of the slides, or skates, in v or in trough, it is perfectly useless to give them a pinching in hope of  obtaining a better guidance of the belt, as there is no phenomenon of "couple of forces" between belt and support  (equality of the forces on the right side and the left one).

The only way to correct a belt trajectory with the supports with slippage is obtained by the correction of the heights (or incline) of the half-plans left and right. These corrections induce in fact a modification of the tensions (a re-stabilization) on the carcass of the belt, which enables to find a symmetry of forces at the level of the drums. It is frequent, in the case of sliding sole, to meet phenomena called " empty space of air " which do provoke an suction disc effect.

29

In the case of a normal functioning, there presence of air between the belt and the sole, even under important load. But in the case of " suction disc " effect, The necessary forces of traction for the moving do not much any more with the calculated values, for the fully loaded conveyor. These forces of traction depend, in this case, on the empty space of air; meaning, on a load which is equal to the atmospheric pressure by the surface of the belt under empty space of air plus, of course, the mass of the transported product (this value can be void). Example: Example: For an atmospheric pressure of 1013,33 HPa and a surface of contact belt/sole, with no load, of 2 m² (500 x 4000 mm) we obtain: 1013.33 x 2 = 2026.66 N = 206,6 kgf  With a mercury barometer a column of 760 mm corresponds to a pressure of 1013,33 Hpa (hectopascal) 1 HPa = 100 Pa = a pressure of 1 N/m² The necessary forces of traction for the movement of the belt are calculated for a fictitious load of the conveyor which is equal to 206 kg t (in this example), plus the load of the material to carry. In that case we notice first a heating of the gear box, which can go up to its putting out of  service. The only solution is to find a way that enables the air to circulate again between the belt and the slipping sole. When we use exclusively slides, it is preferable that they keep the belt moving continuously, for  example with a diagonally arrangement of these ones, rather than a arrangement in parallel lines, longitudinal which has got the disadvantage of provoking, with time, a located wear of the internal face of the belt. a) The materials used: The lack iron sheet, the inox, the wood, the agglomerate panels with coating in melanin or  stratified, the technical plastics like the polyethylene. In the case of the plastics, we should ignore the dimensional instabilities. We also have to consider the disturbances which are due to the loads of static electricity which are accumulated in the belt by the friction on the supports during the utilization of the electronic materials (metal detectors, weighing scales, etc.), without forgetting the risks of fire or  explosion, depending on the environmental characteristics.

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5.7.2) The supports with contact by rotation:

NF E 53-300  NF E 53-301

• By definition of the belt " rolls " on the support. • In this case we need a coefficient of minimum friction between the belt and the rollers in a

way that there is a drive of the rollers during the advance of the belt.

Once again the choice of rollers must be compatible with the belt. To help you, the manufacturers manufacturers of these materials have established standards as well for the dimensions (diameter, length, thickness of the sides) as for the bearings. The rules, that enable to choose such or such type of roller, always refer to the static loads, to the dynamic loads , to the speed and to the loads of work. Apart from the standard roller, there are roller with particular functions such as the shock  absorber patterns, anti-plugging, scrubbers, auto-centering apparatus, guides. A belt circulating circulating on perpendicular perpendicular rollers rollers compare compare to the frame axis will have a trajectory which gets confused with the axis of the frame, out of any other influence (parasite forces).

• In that case, the effect of the material, irrespective of its mass, is without effect on the

trajectory of the belt from the moment when it is spread in homogeneous way.

• In the case of a material that is badly spread, there is a difference of tension between the right

and the left side of the belt, like in the case of the sliding soles. Here, the increase of the resisting forces, for the side which is the most loaded, is related to the increase of the curve of  the belt between two supports (vertical forces due to the mass of the material and to the forces of internal frictions of the material at the passage of each; as the heap of the material got more or less crumbled between the supports, it must be reformed at the passage of the rollers.

• Also, for a vein of material which is well centered on the belt, we can have a belt drift if that

material is of " heterogeneous mass " and it got spread in an asymmetric way on that belt as far as the masses are concerned.

Example: Example: Material with very different granulometry granulometry (fine/ blocks). The separation of the blocks and the fine is often done during the feeding by successive belts at 90° from each other (ballistic law E = 1/2 m V²); we find then very clearly the extreme granulometries in opposed positions on the belt. Therefore, the mass difference makes the rule act on the differences of right and left tension at the level of the drums. * In the case of rollers presenting an  orientation in the plan compare to the frame axis, the belt  will have a uncertain trajectory , more or less "drifted" but not forcibly proportional to that orientation, because in that case several parameters intervene. The difference of the functioning principle, between the rollers and the sliding supports, are related to the fact that the rollers implicate a supplementary parameter of couple of forces. The trajectory of the belt is not influenced when the values of couples are equal to zero, meaning that the rollers are perpendicular to the axis of the conveyor.

31

 Note:  Note: You should not mistake orientation in the plan to raising. In the case of the elevation (a lateral roller is higher, more sloping, than the other) it is the rule of differences of tension which is applied at the level of  the drums. To draw the " parallelograms of forces " applied to the belt and by there define its trajectory, the first  parameter to retain depends on the forces related to the adhesion belt/rollers. These forces are essentially variable because they depend directly on the load of the material on the belt and of the "spacing" of the rollers. These forces of adhesion vary as well according to the coating of the inferior force of the belt, the nature of the face of contact of the rollers, the presence of strange things (water, grease, dust). The tension of the   belt also intervenes, its longitudinal stiffness, the forces that are generated by the drums, the material feeding and its position stabilized on the belt, the vibrations that are generated by the annex materials and other diverse disturbances (the wind etc.). We understand then the difficulty of mastering the trajectory of a belt due to parameters that are continuously variable.

a) auto-centering of the belts Despite all, that possibility of forces’ equilibrium has been put in place for the benefit of an autocentering of the belts. The auto-centering of the belts is only used for the installations in trough to " only one direction" of the belt. In fact, the lateral rollers of the supports present a slight pinching toward the front of 2° to 3° (NF ISO 1537) meaning an angle at the summit of  175°±1° , in such a way the right side of the belt intends to get directed towards the left side of the frame and the other way round for the left side of the belt. The forces are convergent to the axis of the conveyor.

1)

By assuming that a bigger belt width is on the right side of the frame, thanks to the pinching of the rollers compare to its direction of movement, the belt will go quickly to get recentered in order to restabilize the couple of force and therefore recover the symmetry of the belt widths right and left supported on the rollers. The assertion here above is only possible under condition that the parasites forces are inferior to the  forces of adhesion, convergent to the axis of the frame.

2) By considering this time that the lateral rollers make an angle at the summit of  185°±1° , compare to the movement direction ( case of the supports assembled upside down ), the least default of belt drifting will only get very quickly amplified because the forces are facing a direction that is divergent to the axis of the conveyor.

Therefore, the installations with double movement direction oblige the supports’ assembly "without  pinching ". This particular wording is also often forgotten in the orders to the suppliers like the "upside down" assembly, on the frame, of the supports with pinching for the simple movement direction (standard NF E 53-300 and E 53-301). The ones recommending, for the transporters with double movement direction, an alternating assembly of  the supports with pinching, in a direction, then in the other, have never considered the manufacture tolerances for these materials and, therefore, the have been able to demonstrate the efficiency of their  advice. We can only insist on the geometric quality of the assembly of the rollers’ supports and remind that their perfect symmetry to the axis of the frame is essential .

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Effect on the trajectory of the belt in accordance with the pinching NF ISO 1537. Rollers’ supports following the standard NF E 53-300 or E 53-301. I. Normal assembly, centered belt All the other parameters are considered as neutral and with no influence. II. Normal assembly, belt deported by a certain cause All the other parameters are considered to be with no influence.

Ex. I

 belt axis

frame axis

The forces are convergent and balanced. The belt is stable

Movement direction

The forces related to the rollers are convergent

Ex. II direction of drift

direction for the rollers’ friction

 belt axis

frame axis

Movement direction

Φ : 2° to 3° meaning a summit angle of 175° ± 1°

The belt is going to tighten towards the axis of the frame until it recovers the equilibrium F = F

33

III. Upside down assembly, centered belt All the other parameters are considered as neutral and with no influence. IV. Upside down assembly, belt drifted by a certain cause All the other parameters are considered to be with no influence.

Ex.

 belt axis

Movement

frame

But the equilibrium is precarious and uncertain

The forces related to the rollers are divergent Direction of the rollers’

Ex.

Direction of the initial drift

The drift is intensified

The belt is going to have its drift intensified by the unbalance of forces (F'>F"), It is an aggravating factor 

La bande va voir son déport accentué  par le déséquilibre des forces (F'>F"), C'est un facteur aggravant

Φ : 2° to 3° meaning a summit angle of 185° ± 1°

The forces related to the rollers are divergent

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 b) Coating of the rollers We often find rollers with coating or with rubber sleeves. These types of rollers have in principle  particular frictions (shock absorber, anti-plugging etc.), but people rarely think about their great efficiency for the guidance of the belts due to their stronger coefficient of friction. Attention: Attention: It is important to make the different between "coating" or " sleeves " and rubber " sleeves ". The systematic use of the rollers " with sleeves " is unfavorable to the guidance of the belt (too weak surface of contact). c) Parasite forces In the case of installation with problems we can increase the angle of pinching, then the forces of  centering, by tilting all the support towards the front. This type of assembly brings on the other  hand more important wear of the lateral rollers or/and of the inferior face of the belt. Considering those reports of " directional " effects brought by the rollers, the manufacturers of  the material do propose different patterns of "auto-centering apparatus " supports using the   physique principle of the " parallelogram of force" and implemented thanks to the forces of  adherence belt/roller. Designed as well as possible, this type of material will give a result that is proportional to the forces of adhesion belt/rollers, then essentially variable. Their correction efficiency will be also related to other present forces ( influence zone of the drums) and the longitudinal stiffness of the  belt. On the other hand, the corrections that they bring are also related to their location compare to the origin of the defaults (drifts). These materials, when they are worn out or in bad state, do not bring the foreseen correction any more; they can beget trajectory defaults; the solution by their use is worse than bad!

35

The guiding rollers Their functioning principle (of correction) is assimilated to an obstacle on which the belt come to stumble. Their revolution axis is perpendicular (vertical) to the plan of the belt. So, when this one comes in contact with the guiding rollers, it is the edge, the side of the belt that comes to " crush " against the rollers. This functioning principle is bluntly destroying for the belt.

Two possible cases: The necessary correction of the belt trajectory is minor, then the restraint applied by the guiding rollers on the sides of the belt will be weak and therefore weakly destroying. That means the trajectory problem is really minor and that a simple adjustment will be enough. Then you do not need guiding rollers.

The necessary correction is important, then the constraint applied on the belt side will be very  prejudicial and, anyway, the belt will continue to get "crushing" or "coming up" on the guiding roller and so continue to get drifted beyond this one. Especially, we should not use guiding rollers.

The only case where guiding rollers are used remains their assembly on the auto-centering apparatus supports having a revolution axis in their middle. The guiding rollers are used to transmit by the lever arm the movement of the belt drift and acting on the orientation of the support. These supports have no pinching. It is the very orientation of the support that defines in "the angle of pinching ", this one is directly proportional and of a direction that is opposed to the  belt drift. We have to be careful in order to avoid assembling these materials "upside down", a case that is relatively common; certain patterns are put upside down compare to themselves due to an accident (the stop of run end does not exist or is damaged), for example when they are installed in a concave curve. Once again the solution is worse than bad!

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Standard commerce manufacture « without Depending on the belt width and the standard E 53.300 or 

Standard commerce manufacture « with pinching » For the model « without pinching » = special order 

Reference measurement in accordance with the  belt width and its standard NF E 53.300 or E 53.301

37

Table of hardness and thickness of the rubbers of drum coating, in accordance with the resistance to the rupture of the belt and its rate of utilization (% of the RMBT): Resistance to the rupture / rate of utilization at 100% RMBT -/- <60% RMBT

hardness -/- thickness of the c/c  ≤315N/mm 400 N/mm 500 N/mm

630 N/mm 800 N/mm 100 <60 100 <60 100 <60 100 <60 100 <60 % % % % % % % % % %  50 Sh A/B/ A/B/ B/C A/B/ B/C A/B/ C A/B/ B/C th.8 C C C C C 50 Sh B C ép.10 65 Sh B A A A th.8 65 Sh A A th.10 65 Sh th.12 65 Sh th.15 65 Sh th.20

Category of the drums :

1000 N/mm 100 <60 % % B/C

1250 N/mm 100 <60 % % C

C

1400 N/mm 100 <60 % % C

B

A B

1600 N/mm 100 <60 % %

B

C

C B

B

A

C B

A

A

A C B

A A

A

A = head drum, drive drum, motor drum, jetty drum

B = tail drum, dismiss dismiss drum, tension tension drum C = snub drum, deviation drum, bend drum

Remark : We perceive easily the role of the rubber, of a drum coating, in the increase of the coefficient of adhesion to the traction, of the anti-plugging and of the decrease of the risk of belt punching. We often forget the role of the rubber in the important improvement of the guidance of the belts due to its strong coefficient of adhesion and to the service life of its action due to its excellent running against the abrasion. If there is movement towards the center, there is drift, then friction, then wear. We can say that at equal pre-tension of the belt, this one will resist from parasites forces which are superior compare to a conveyor which is equipped of bare drums.  Note: In very rare cases, a trapezoid groove (or trapezoid  Note: trapezoid grooves) is (or are) used on the drums. To those gorges correspond trapezoid guide-profiles welded on the internal face of the belt. We must retain only that those grooves must imperatively have measurements that are slightly superior to the guide ones. Very often, the use of these systems of guide/ groove underlines a wrong problem. Examples of application with guides: - assembly of several belts on the same drum and subjected to a transversal effort. - narrow and long belts subjected to important transversal efforts. 5.6.4) Drums’ influence zone: Every drum applies a tension on the two blades (carrying and return belts) of the belt which adjoins it. The tension in each blade is equal no matter the wrapping angle for free drums. The tension is inferior or equal for the pushed  blade compare to the pulled blade, to the drive drum. The bigger that tension, that force, is, the longer will be the belt under the drum influence.

The interest of knowing that factor is that all the elements which can influence, positively or negatively, the trajectory of the belt, in that zone, will be modified. Concerning the adjustment of the belts, wanting to correct a belt trajectory, by the annex elements of the drum, will  be more difficult and uncertain than the tension noticed on the drum will be big. That rule goes the other way round for the first or the last station in trough tr ough adjoining to the drum, but with limited effects. Considering these remarks, it appears evident that the drums must present a good geometric quality for the form and the position.

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5.7) THE SUPPORTS

• Their function is to support, well of course, the belt and the bulk to be transported between the

different drums of the installation.

• Their influence on the wear of the belt must be as weak as possible. • They participate, in a way or anther, according to their types, to the good trajectory of the belt. Therefore the choice of one type of support, its intrinsic quality and its assembly are important.

There are two categories of support: 1. The supports with surface of  slippage . 2. The supports with contact by rotation (or turning)  Note : As we saw in the chapter " terminology of the materials", we have to distinguish well the nature of the shape of the supports. 5.7.1) The supports with surface of slippage:

• By definition, there is friction between belt and support. • The quality, of the couple belt/support, will be defined by the coefficient of friction resulting

from the two elements. • It is imperative to use a belt with an internal face that is adapted for that use. • A weak coefficient of friction implicates a weak absorbed power. • That coefficient of friction must be " homogeneous " and " invariable " on all the surface of  contact, for fear to create a "couple of force" like the way this is used by the caterpillar  machine for turning. In this category, we find the slipping soles and the slides or skates . • Irrespective of their form (seen in transversal cut) these supports must necessarily present a

symmetry (image mirror) compare to the longitudinal axis of the frame. • The two half plans, that they define, must be parallel to the theoretical plan that is limited by two consecutive drums, in order to enable a straight trajectory of the belt. In the case of the slides, or skates, in v or in trough, it is perfectly useless to give them a pinching in hope of  obtaining a better guidance of the belt, as there is no phenomenon of "couple of forces" between belt and support  (equality of the forces on the right side and the left one).

The only way to correct a belt trajectory with the supports with slippage is obtained by the correction of the heights (or incline) of the half-plans left and right. These corrections induce in fact a modification of the tensions (a re-stabilization) on the carcass of the belt, which enables to find a symmetry of forces at the level of the drums. It is frequent, in the case of sliding sole, to meet phenomena called " empty space of air " which do provoke an suction disc effect.

39

In the case of a normal functioning, there presence of air between the belt and the sole, even under important load. But in the case of " suction disc " effect, The necessary forces of traction for the moving do not much any more with the calculated values, for the fully loaded conveyor. These forces of traction depend, in this case, on the empty space of air; meaning, on a load which is equal to the atmospheric pressure by the surface of the belt under empty space of air plus, of course, the mass of the transported product (this value can be void). Example: Example: For an atmospheric pressure of 1013,33 HPa and a surface of contact belt/sole, with no load, of  2 m² (500 x 4000 mm) we obtain: 101 333 x 2 = 202.666 N = 20.266, Kgf = 20,2 t With a mercury barometer a column of 760 mm corresponds to a pressure of 1013,33 Hpa (hectopascal) 1 HPa = 100 Pa = a pressure of 1 N/m² The necessary forces of traction for the movement of the belt are calculated for a fictitious load of the conveyor which is equal to 20,2 t (in this example), plus the load of the material to carry. In that case we notice first a heating of the gear box, which can go up to its putting out of  service. The only solution is to find a way that enables the air to circulate again between the belt and the slipping sole. When we use exclusively slides, it is preferable that they keep the belt moving continuously, for  example with a diagonally arrangement of these ones, rather than a arrangement in parallel lines, longitudinal which has got the disadvantage of provoking, with time, a located wear of the internal face of the belt. a) The materials used: The lack iron sheet, the inox, the wood, the agglomerate panels with coating in melanin or  stratified, the technical plastics like the polyethylene. In the case of the plastics, we should ignore the dimensional instabilities. We also have to consider the disturbances which are due to the loads of static electricity which are accumulated in the belt by the friction on the supports during the utilization of the electronic materials (metal detectors, weighing scales, etc.), without forgetting the risks of fire or  explosion, depending on the environmental characteristics.

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5.7.2) The supports with contact by rotation:

NF E 53-300  NF E 53-301

• By definition of the belt " rolls " on the support. • In this case we need a coefficient of minimum friction between the belt and the rollers in a

way that there is a drive of the rollers during the advance of the belt.

Once again the choice of rollers must be compatible with the belt. To help you, the manufacturers manufacturers of these materials have established standards as well for the dimensions (diameter, length, thickness of the sides) as for the bearings. The rules, that enable to choose such or such type of roller, always refer to the static loads, to the dynamic loads , to the speed and to the loads of work. Apart from the standard roller, there are roller with particular functions such as the shock  absorber patterns, anti-plugging, scrubbers, auto-centering apparatus, guides. A belt circulating circulating on perpendicular perpendicular rollers rollers compare compare to the frame axis will have a trajectory which gets confused with the axis of the frame, out of any other influence (parasite forces).

• In that case, the effect of the material, irrespective of its mass, is without effect on the

trajectory of the belt from the moment when it is spread in homogeneous way.

• In the case of a material that is badly spread, there is a difference of tension between the right

and the left side of the belt, like in the case of the sliding soles. Here, the increase of the resisting forces, for the side which is the most loaded, is related to the increase of the curve of  the belt between two supports (vertical forces due to the mass of the material and to the forces of internal frictions of the material at the passage of each; as the heap of the material got more or less crumbled between the supports, it must be reformed at the passage of the rollers.

• Also, for a vein of material which is well centered on the belt, we can have a belt drift if that

material is of " heterogeneous mass " and it got spread in an asymmetric way on that belt as far as the masses are concerned.

Example: Example: Material with very different granulometry granulometry (fine/ blocks). The separation of the blocks and the fine is often done during the feeding by successive belts at 90° from each other (ballistic law E = 1/2 m V²); we find then very clearly the extreme granulometries in opposed positions on the belt. Therefore, the mass difference makes the rule act on the differences of right and left tension at the level of the drums. * In the case of rollers presenting an  orientation in the plan compare to the frame axis, the belt  will have a uncertain trajectory , more or less "drifted" but not forcibly proportional to that orientation, because in that case several parameters intervene. The difference of the functioning principle, between the rollers and the sliding supports, are related to the fact that the rollers implicate a supplementary parameter of couple of forces. The trajectory of the belt is not influenced when the values of couples are equal to zero, meaning that the rollers are perpendicular to the axis of the conveyor.

41

 Note:  Note: You should not mistake orientation in the plan to raising. In the case of the elevation (a lateral roller is higher, more sloping, than the other) it is the rule of differences of tension which is applied at the level of  the drums. To draw the " parallelograms of forces " applied to the belt and by there define its trajectory, the first  parameter to retain depends on the forces related to the adhesion belt/rollers. These forces are essentially variable because they depend directly on the load of the material on the belt and of the "spacing" of the rollers. These forces of adhesion vary as well according to the coating of the inferior force of the belt, the nature of the face of contact of the rollers, the presence of strange things (water, grease, dust). The tension of the   belt also intervenes, its longitudinal stiffness, the forces that are generated by the drums, the material feeding and its position stabilized on the belt, the vibrations that are generated by the annex materials and other diverse disturbances (the wind etc.). We understand then the difficulty of mastering the trajectory of a belt due to parameters that are continuously variable.

a) auto-centering of the belts Despite all, that possibility of forces’ equilibrium has been put in place for the benefit of an autocentering of the belts. The auto-centering of the belts is only used for the installations in trough to " only one direction" of the belt. In fact, the lateral rollers of the supports present a slight pinching toward the front of 2° to 3° (NF ISO 1537) meaning an angle at the summit of  175°±1° , in such a way the right side of the belt intends to get directed towards the left side of the frame and the other way round for the left side of the belt. The forces are convergent to the axis of the conveyor.

1)

By assuming that a bigger belt width is on the right side of the frame, thanks to the pinching of the rollers compare to its direction of movement, the belt will go quickly to get recentered in order to restabilize the couple of force and therefore recover the symmetry of the belt widths right and left supported on the rollers. The assertion here above is only possible under condition that the parasites forces are inferior to the  forces of adhesion, convergent to the axis of the frame.

2) By considering this time that the lateral rollers make an angle at the summit of  185°±1° , compare to the movement direction ( case of the supports assembled upside down ), the least default of belt drifting will only get very quickly amplified because the forces are facing a direction that is divergent to the axis of the conveyor.

Therefore, the installations with double movement direction oblige the supports’ assembly "without  pinching ". This particular wording is also often forgotten in the orders to the suppliers like the "upside down" assembly, on the frame, of the supports with pinching for the simple movement direction (standard NF E 53-300 and E 53-301). The ones recommending, for the transporters with double movement direction, an alternating assembly of  the supports with pinching, in a direction, then in the other, have never considered the manufacture tolerances for these materials and, therefore, the have been able to demonstrate the efficiency of their  advice. We can only insist on the geometric quality of the assembly of the rollers’ supports and remind that their perfect symmetry to the axis of the frame is essential .

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Effect on the trajectory of the belt in accordance with the pinching NF ISO 1537. Rollers’ supports following the standard NF E 53-300 or E 53-301. I. Normal assembly, centered belt All the other parameters are considered as neutral and with no influence. II. Normal assembly, belt deported by a certain cause All the other parameters are considered to be with no influence.

Ex. I

 belt axis

frame axis

The forces are convergent and balanced. The belt is stable

Movement direction

The forces related to the rollers are convergent

Ex. II direction of drift

direction for the rollers’ friction

 belt axis

frame axis

Movement direction

Φ : 2° to 3° meaning a summit angle of 175° ± 1°

The belt is going to tighten towards the axis of the frame until it recovers the equilibrium F = F

43

III. Upside down assembly, centered belt All the other parameters are considered as neutral and with no influence. IV. Upside down assembly, belt drifted by a certain cause All the other parameters are considered to be with no influence.

Ex.

 belt axis

Movement

frame

But the equilibrium is precarious and uncertain

The forces related to the rollers are divergent Direction of the rollers’

Ex.

Direction of the initial drift

The drift is intensified

The belt is going to have its drift intensified by the unbalance of forces (F'>F"), It is an aggravating factor 

La bande va voir son déport accentué  par le déséquilibre des forces (F'>F"), C'est un facteur aggravant

Φ : 2° to 3° meaning a summit angle of 185° ± 1°

The forces related to the rollers are divergent

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 b) Coating of the rollers We often find rollers with coating or with rubber sleeves. These types of rollers have in principle  particular frictions (shock absorber, anti-plugging etc.), but people rarely think about their great efficiency for the guidance of the belts due to their stronger coefficient of friction. Attention: Attention: It is important to make the different between "coating" or " sleeves " and rubber " sleeves ". The systematic use of the rollers " with sleeves " is unfavorable to the guidance of the belt (too weak surface of contact). c) Parasite forces In the case of installation with problems we can increase the angle of pinching, then the forces of  centering, by tilting all the support towards the front. This type of assembly brings on the other  hand more important wear of the lateral rollers or/and of the inferior face of the belt. Considering those reports of " directional " effects brought by the rollers, the manufacturers of  the material do propose different patterns of "auto-centering apparatus " supports using the   physique principle of the " parallelogram of force" and implemented thanks to the forces of  adherence belt/roller. Designed as well as possible, this type of material will give a result that is proportional to the forces of adhesion belt/rollers, then essentially variable. Their correction efficiency will be also related to other present forces ( influence zone of the drums) and the longitudinal stiffness of the  belt. On the other hand, the corrections that they bring are also related to their location compare to the origin of the defaults (drifts). These materials, when they are worn out or in bad state, do not bring the foreseen correction any more; they can beget trajectory defaults; the solution by their use is worse than bad!

45

The guiding rollers Their functioning principle (of correction) is assimilated to an obstacle on which the belt come to stumble. Their revolution axis is perpendicular (vertical) to the plan of the belt. So, when this one comes in contact with the guiding rollers, it is the edge, the side of the belt that comes to " crush " against the rollers. This functioning principle is bluntly destroying for the belt.

Two possible cases: The necessary correction of the belt trajectory is minor, then the restraint applied by the guiding rollers on the sides of the belt will be weak and therefore weakly destroying. That means the trajectory problem is really minor and that a simple adjustment will be enough. Then you do not need guiding rollers.

The necessary correction is important, then the constraint applied on the belt side will be very  prejudicial and, anyway, the belt will continue to get "crushing" or "coming up" on the guiding roller and so continue to get drifted beyond this one. Especially, we should not use guiding rollers.

The only case where guiding rollers are used remains their assembly on the auto-centering apparatus supports having a revolution axis in their middle. The guiding rollers are used to transmit by the lever arm the movement of the belt drift and acting on the orientation of the support. These supports have no pinching. It is the very orientation of the support that defines in "the angle of pinching ", this one is directly proportional and of a direction that is opposed to the  belt drift. We have to be careful in order to avoid assembling these materials "upside down", a case that is relatively common; certain patterns are put upside down compare to themselves due to an accident (the stop of run end does not exist or is damaged), for example when they are installed in a concave curve. Once again the solution is worse than bad!

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Standard commerce manufacture « without Depending on the belt width and the standard E 53.300 or 

Standard commerce manufacture « with pinching » For the model « without pinching » = special order 

Reference measurement in accordance with the  belt width and its standard NF E 53.300 or E 53.301

47

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Mine type Standard roller

L A B

In accordance with the belt width

and its standard NF E 53.300 or E 53.301

Type Type LM 204 HY LM 205 HY LM 305 HY LM 206 HY

d NM 20 25

14 14 (18) 25 14 (18) 30 22

Bearin Bearings gs 6204 6205 6305

Join Joints ts

Dxe by reques requestt

70x2,9/89x3,2/133x4

63,5x2,9/102x3,6/108x3,6 89x3,2/133x4

HYPE R  OYO

89x3,2/133x4/159x4,5 102x3,6/108x3,6

6206

STANDARD:

Utilization Utilization Life duration

Dxe in stock stock

BY REQUEST:

-20°C
* (18) Rubber coating. Electro-zinc coating: tube, casings, deflector, axis

Rollers delivered crude oiled steel, following the above design

49

Roller 

Bearing

∅

63,5/70 89 133

159

6204 6204 6205 6204 6205 6206 6305 6206

"isolated load" Bearing

L

∅20-6204 ∅25-6205 ∅25-6305 ∅30-5206

Indicative table for the critical speeds in m/s 1 1,5 2 2,5 3 3,25 3,5 3,75 m/s m/s m/s m/s m/s m/s m/s m/s

track

4 m/s 4,25 m/s

4,5 m/s

prohibited

Rollers admissible maximum load per axis ∅ "d" in kg (on an indicative basis)

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

350 500 700 1100 1100

350 500 700 1100 1100

350 500 700 1100 1100

350 500 700 1100 1100

350 450 650 1100 1100

330 425 540 1100 1100

280 370 465 930 930

250 330 405 810 810

220 290 360 720 720

200 260 325 650 650

180 240 295 600 600

165 215 270 550 550

150 200 250 500 500

140 185 230 460 460

130 171 215 430 430

(On the conveyor return rollers, we must cut the values of the above table, the measurement A is superior) Approximate weight in kg

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Roller with rubbers rings called « Anti- plugging »

51

Roller assembled in garland

C

B A

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Garland roller for deep trough of « VACKEM » Type

3

Width

500 650 800 1000

Output m  /H* for crumbling slope

10° 10 ° 108 196 302 480

15° 15 ° 119 213 335 524 7 77 72

20° 20 ° 130 229 349 553 81 812

∅ Reel

L

H

530 580 730

302 372 420

920 110 100 0

510 555 55 5

120 200 0

690

1400

960

1110 1160 1170

620

1600

1270

1417 1500 1310

740

1800

1600

1702 1765 1490

805

2000

1830

2290 2350 1620

870

E

80 80 80 80 80 80 80 80 80 80 80 80 80 80 80

G

60 60 60 60 60 60 60 60 60 60 60 60 60 60 60

mm 89 89 89 89 133 133 159 133 159 133 159 133 159 159 193

Nbr of reel

8 8 8 8 8 8 8 8 10 10 10 10 10 10 10

Garland weight

∅ of the axis

Kg 9 11 13 15 23/25 28/30 33/35 37/39 42/44 42/46 47/51 43/45 50/54 56/60

mm 20 20 20 20 25-30 25-30 25-30 25-30 25-30 30-40* 30-40* 30-40* 30-40* 30-40* 30-40*

* For V = 1 m/s and Loading Slope < 4° or 7 % * For ∅ 40 consult us.

53

Surface for the selection of a standard through, composed composed of 3 regular

Example

Belt width 1200

Surface for the selection of a deep through, composed of one garland of « VACKEN » Type

Belt width 1200

The S2 presents a superior section of about 36% at the S 1 Drawings and keys extracted from a constructor document. It is good to remind that the standard NF H 95-203 indicates that the useful width of the belt is equal to [0,9 x B] – 50 mm, no matter the outline of the belt in transversal view; meaning for the above drawings [0,9 x 1200] – 50 = 1030 mm

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Support called « in inverted trough »

Support called « auto-centering » with pivot

(orientation in the plan)

Superior belt

Return belt or for Belt « flat »

Note:: Note

These materials are presented here because they exist, but their efficiency remains relative and uncertain

55

VI)

TRANSITION LENGTH:

AFNOR NF T 47-005, T 47-111 T 47-006

The transition length corresponds to the distance between a "plat" position of the belt, on the drum, and the form in V or in (maximum) (maximum) trough of this one on the supports. supports. There is an elevation of the sides of the belt; this implicates an over-length of these belt compare to the middle of the belt. The standard NF T 47-005 (or 006) underlines, precisely, that at that over-length corresponds a supplementary traction force . To the progression of the lengthening of all the materials, during a traction effort, corresponds a  proportional increase of traction forces, up to the critical point of " stricture " of the material. When that critical point is reached, there is a brutal decrease of the resistance to the traction of  the piece due to the decrease of the section of the material under effort; then if the effort of  traction is maintained on the piece we reach very quickly its rupture. We reach the same critical situation, without over passing a limit effort, by a phenomenon of  fatigue due to important and repeated efforts: it is matter of accelerated ageing of the material. In order to avoid that ageing, of course, that lengthening should remain in the acceptable limits in accordance with the type of belt used: it is the elastic limit . This "transition length" must be given by the manufacturer of the belt. It is a function of the nature of the carcass of the belt then of its elasticity module (standard NF T 47-111), of the value of the trough angle, of the belt width in elevation and of the tension existing in the belt at the  place observed in the most favorable conveyor working conditions. That length can be slightly shorter  if the bottom of the trough is at inferior level at the belt/drum

tangent line. People could assimilate this configuration, foreseen by the standard NF T47-005 or  006, to a concave curve . In this case of figure, - if the belt bends less under the load, the transition zone is lengthened up to the support in contact with the belt; - if the belt touches the rollers of the last support, due to the load, the sides of the belts get damaged. In that case, it is matter, most of time, of a design error ! That length is stronger  if

the bottom of the trough is above the belt/drum tangent line. In that case, it is matter of considering a " convex curve " built in the transition zone. In that case, the 2 standards NF T47-005 and DIN22-101 (TGL20.350 001) should be applied. This type of design often underlines a ignorance of the art rules . Particular case : If we consider, normally, the width of the belt to calculate the transition length, we take in the case of a belt " incorrectly centered " the maximum width of the belt in elevation on the trough. This detail has more importance when the lengthening of the belt under reference load is weak, for example with a metallic carcass at 0,25% of lengthening (against 1,6 % for the polyester).

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Ignoring that detail bring very quickly the destruction occult  (# 1) of the carcass in the belt edge, that is noticed by a permanent lengthening of this one; the belt festoons or even gets torn and then begets a unbalance of the right/left tensions. It is a worsening factor for the drift of the belt.

Morality: It is better to have a conveyor that is well adjusted, with a belt that is well centered.

Outlines of the conveyors in the transition zones

 Normal configuration: the tangency generators (belt/roller) (belt/roller) of the 2 rollers r ollers of troughs bottom are lined up with the superior superior tangency generator generator of the drum ( angle = 180° )

Convex curve in a transition zone: the

tangency generators (belt/roller) (belt/roller) of the 2 rollers of troughs  bottom are misaligned toward the top side with the superior tangency generator of the drum (angle > at 180° )

Concave curve in a transition zone: the tangency generators (belt/roller) (belt/roller) of the 2

rollers of  troughs bottom are misaligned downward with the superior tangency generator of the drum (angle < to 180° )

# 1 destruction occult: it is a destruction of the carcass that can not be seen with bare eye because it hidden by the belt coatings.

57

Conveyor Belts (standard T 47-005)

Formula of calculation for the distance of trough transition with 3 equal rollers. Foreword 

The present standard reproduces at some editorial modifications modifications to the international standard ISO 5293 published in 1981. Introduction The distance between the drum and the station of rollers of putting in trough placed at head or at the end of a belt conveyor is called distance of through transition. On that distance, the belt  passes progressively from a plat profile to a trough profile or conversely. It is important for this distance to have an adequate value allowing to avoid the tension in the sides with as resultant an excessive tension forcing the belt in the intersections of the trough rollers. Furthermore, it is convenient to avoid invalid or negative tensions in the center of the belt, as this can occur at the tail drum of certain conveyors. That is why it is requested to calculate the trough transition distances by means of the formula indicated by the present standard, by using appropriate values of the functions from the given tables and the value of the module of the belt given by the manufacturer. The level of the superior side of the drum is a significant factor. It is normally lined up with the horizontal roller of the trough stations with three rollers or with an imaginary line situated at 1/3 of the through section of the conveyor. The methods of calculation corresponding to each of those configurations are indicated. 1. Subject and application domain The standard specifies a calculation formula for the trough transition distances of the conveyor   belts. 2. Formula of calculation for the trough transition distance The formula of calculation for the trough transition distance, whose demonstration is given in annex, is as follows :  L1 = 0,707 v ( M ); ∆T 

where  L1

is the distance of trough transition, in meter;

v

is the maximum elevation of the side of the belt compare to the trough bottom (see figure 1), in meter;

 M 

is the elasticity module, measured to the maximum service tension of the belt, expressed in Newton per millimeter; millimeter;

Tn

is the maximum service tension of the belt expressed in Newton per millimeter;

∆T 

is the over-tension of the belt side at the trough trough transition, in Newton per millimeter. millimeter.

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The distances of trough transition so calculated allow

- to limit the tension of the sides at 130 % of the maximum service tension of the belt., - to avoid the ripples due to the longitudinal compression in the central part of the belt. Length of trough transition

B/3

v

v = b sin λ 3  b = we consider that the belt section in elevation is equal to 1/3 of its width, which is not 3 totally exact; In the case of the support in V (with 2 rollers), it is convenient to take b 2 On an indicative basis, we can calculate the transition length of a belt, in a simplified way; this method is convenient in most of cases. Belt with polyester carcass (E): L1 = v . 8,3 Belt with metallic carcass (S): L1 = v . 17

59

Calculations of a transition length according to the formulas of the standard NF T 47 005

Case of a convex curve in the transition zone: (see sketch on the previous page) 1. Calculation of a transition length 1.1 The drum is aligned with the horizontal roller of the trough.

Belt with polyester carcass from a manufacturer  manufacturer  L : transition transition length length

in m

 b : belt width v : trough deepness sin : trough angle M : elasticity module Tr : maximum service tension

 by the belt manufacturer  10 % of the rupture Tension or calculated tension.

∆T : belt side over-tension

Table of standard T 47 005

3.3

1200 mm = 1,20 m

en m 30°

Value of  T 

Calculating the tension of the belt in the transition zone and expressing it in proportion of TR (maximum service tension). Choosing the value of ∆T in accordance with TR following the table here below (interpolating if needed).

Belt tension ratio in the trough transition at TR  ex.2-6 ex.1 ex.3-4-5

The retained values of ∆T allow - to avoid sides tensions over-passing 130% of the admissible maximum service tension¹) - To avoid the ripples that are due to the compression in the central part of the belt. ²)

L = 0,707 . v . 1.1

( M ) ∆t 

If we consider that the the value of rupture is 870 N/mm (data by manufacturer), manufacturer), we find for L:

Tr calculated calculated = 80 N/mm* meaning Tr = 80 = 0,92 Tr maxi 87 maxi

M from manufacturer’s information = 7,6 7,6 = characteristic of the polyester  870: The manufacturer indicates a value of 870  N/mm of resistance against rupture, for a belt *Tr calculated calculated : example calculated value for one conveyor  of type 800 N/mm; N/mm; meaning meaning a maximum service tension, maximum T (=10% of the v = b . sin α = 1,20 . sin 30° = 0,2 m rupture tension ) of 87 N/mm

3 3 M = 7,6 x 870 = 6 612 N/mm In the table 3.3 of the standard ∆T = 0,35 . Tr = 0,35 . 87 = 30,45 meaning L = 0,707 . 0,2 .

(6612) = 2,08 m 30,45

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If we consider that the rupture value is 800 N/mm and not 870 N/mm (data from the manufacturer), manufacturer), we find for L: 1.2

Tr calculated calculated = 80 N/mm* meaning Tr = 80 = 1,00 Tr maxi 80 maxi

M from manufacturer’s information = 7,6 7,6 = characteristic of the polyester  800: we do not consider the value given by the manufacturer; we retain a value of 800 N/mm *Tr calculated calculated : example calculated value for one conveyor  of resistance against rupture, for a belt of type 800 N/mm; meaning a maximum service v = b . sin α = 1,20 . sin 30° = 0,2 m tension T, maximum maximum T (= 10% of the rupture tension ) of 80 N/mm 3 3 M = 7,6 x 800 = 6 080 N/mm In the table 3.3 of the standard ∆T = 0,30 . Tr = 0,30 . 80 = 24,00

Meaning L = 0,707 . 0,2 .

1.3

(6080) = 2,25 m 24

If we consider consider a rupture value value of 800 N/mm, a service service tension tension calculated calculated at the drum drum of 70 % of the maximum service tension, we find for L:

Tr calculated calculated = 80 .70% = 56 N/mm* meaning Tr = 56 = 0,70 Tr maxi 80 maxi

M from manufacturer’s information = 7,6

M renseignement renseigneof ment du fabricant = 7,6 7,6 =sur characteristic the polyester  7,6 du value polyester  800:=wecaractéristique do not consider the given by the manufacturer; we retain a value ofde800 800: on ne tient pas compte la N/mm valeur  of resistance *Tr calculated par  against rupture, for a belt of type calculated : example calculated value for one conveyor  donnée 800 N/mm; meaning a maximum servicede v = b . sin α = 1,20 . sin 30° = 0,2 m le fabricant; on retient un valeur tension T, maximum maximum T (= 10% of the 3 3 800 rupture N/mmtension ) of 80 N/mm M = 7,6 x 800 = 6 080 N/mm In the table 3.3 of the standard ∆T = 0,55 . Tr = 0,55 . 80 = 44,00 (6080) Meaning L = 0,707 . 0,2 . = 1,66 m 44

1.4

If we consider a rupture value value of 870 N/mm given by the manufacturer, manufacturer, a service service tension calculated at the drum of 70 % of the maximum service tension, we find for L:

Tr calculated calculated = 56 N/mm* meaning Tr = 56 = 0,64 Tr maxi 87 maxi

M from manufacturer’s information = 7,6

M renseignement renseigneof ment du fabricant = 7,6 7,6 =sur characteristic the polyester  7,6 du value polyester  870:=wecaractéristique do not consider the given by the 870:manufacturer; le fabricant we a indiqué une valeur de retain a value of 800 N/mm of resistance against rupture, for a belt of type *Tr calculated calculated : example calculated value for one conveyor  870 N/mm 800 meaning maximumpour service de N/mm; résistance à la arupture, une tension T, maximum maximum T (= 10% of the v = b . sin α = 1,20 . sin 30° = 0,2 m  bande typetension ) of 87 N/mm rupture 3 3 M = 7,6 x 870 = 6 612 N/mm In the table 3.3 of the standard ∆T = 0,55 . Tr = 0,55 . 87 = 47,85 (6612) Meaning L = 0,707 . 0,2 . = 1,66 m 47,85 61

If we consider a rupture value value of 870 N/mm given by the manufacturer, manufacturer, a service service tension calculated at the drum of 70 % of the maximum service tension and we consider a maximum drift of the belt (right and left) for a value 0,049 m, we find for L: 1.5

Tr calculated calculated = 56 N/mm* meaning Tr = 56 = 0,64 Tr maxi 87 maxi

M from information = 7,6= 7,6 M sur manufacturer’s renseignement renseignement du fabricant 7,6 = characteristic of the polyester  7,6 du value polyester  870:=wecaractéristique do not consider the given by the 870:manufacturer; le fabricant we a indiqué une de retain a value valeur of 800 N/mm *Tr calculated N/mm resistance against rupture, for a belt of type calculated : example calculated value for one conveyor  870 of 800 meaning maximumpour service  b = 1,20 + 0,049 + 0,049 = 1,298 m de N/mm; résistance à la arupture, une tension T, maximum m aximum T (= 10% of the  bande type rupture tension ) of 87 N/mm v = b . sin α = 1,298 . sin 30° = 0,216 m 3 3 M = 7,6 x 870 = 6 612 N/mm In the table 3.3 of the standard ∆T = 0,55 . Tr = 0,55 . 87 = 47,85

Meaning L = 0,707 . 0,216.

(6612) = 1,79 m 47,85

1.6 If we consider a rupture value value of 800 N/mm and not of

870 N/mm (data given by the the manufacturer) manufacturer) and we consider a maximum drift of the belt (right and left) for a value of  0,049m, we find for L:

Tr calculated calculated = 80 N/mm* Meaning Tr = 80 = 1,00 Tr maxi 80 maxi

M from information = 7,6= 7,6 M sur manufacturer’s renseignement renseignement du fabricant 7,6 = characteristic of the polyester  7,6 = caractéristique du polyester  800: we do not consider the value given by the 800:manufacturer; on ne tient pas compte de la we retain a value of valeur  800 N/mm *Tr calculated : example calculated value for one conveyor  donnée par  against rupture, for a belt of type calculated of resistance  b = 1,20 + 0,049 + 0,049 = 1,298 m 800 N/mm; meaning a maximum servicede le fabricant; on retient un valeur tension T, maximum m aximum T (= 10% of the 800 N/mm rupture tension ) of 80 N/mm v = b . sin α = 1,298 . sin 30° = 0,216 m 3 3 M = 7,6 x 800 = 6 080 N/mm In the table 3.3 of the standard ∆T = 0,30 . Tr = 0,30 . 80 = 24,00

Soit L = 0,707 . 0,216.

2.

(6080) = 2,43 m 24

Calculation of the radius of the convex curve

for the belts with polyester carcass the radius is equal to 125 times the trough deepness. r = 125 . v v = b . sin α = 1,20 . sin 30° = 0,2 m 3 3

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Current position Faulty (wrong) Trough 30° Position According to NF T 47005 Trough 30° Level : -50 mm

Position According to NF T 47005 + NF H 95-203 # 7 Trough 30° Level : -140 mm

63

Standard DIN 22-101 (TGL20.350 001) (in the case of belts circulating on supports in V or in trough) VII.

CONVEX CURVE:

We find here again the same restraints like in the preceding chapter. It is matter of considering the tension forces which are the most important in the sides of the belt, compare to its median  part due to a bigger radius in belt edge. This bigger radius is related to the elevation of the belt sides, in support on the supports in V or in trough. The convex curve described by the trough  bottom (or V) and the ones of the belts sides have the same center ''o''. The standard defines the minimum radius of the curve in accordance with the nature (the material) of the belt carcass compare to the trough deepness, this is in order to avoid over   passing the elastic limit of the belt. r = 125 x for the Polyester carcass r = 300 to 400 x v for the metallic carcass r = radius of the curve v = deepness of the trough  But,

If we observe precisely this curve, equipped of successive supports (roller or sliding skate supports) we notice that it is not matter of a continuous curve but several sectors of a polygon. To avoid localized over-tensions, the standard allows by the calculation, in accordance with the elasticity module of the belt, of the tension at the observed place, to determine the angular value of each polygon sector. From experience, we notice that that angular value varies, from belts which are strongly tight to belts which are weakly tight, between: 2°30’ and 4°30'  Example: • • • •

The two conveyor sections framing the convex curve make an angle of 16°. The belt is of polyester carcass. The trough deepness, measured, is of 133 mm. The belt is weakly tight in the zone of the curve (retained angular value: 4°).

We find a curve radius: 133 x 125 = 16 625 mm = 16,62 m

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To avoid a pinching of the belt in the trough bends, with roller supports, it is necessary to have supports that leave an empty space between the extremities of the lateral rollers and the central roller of 10 mm in maximum (see standard ISO 1537). The more the belt will be of " light " design the more we shall have a risk of pinching (of fold) at that place. It is important here to calculate well the values of the counterweights (or tension systems) in order to avoid over passing the admissible tension values in the curve. A bad appreciation of those parameters inevitably leads to important damages, and often occult, of the carcass, this happens very quickly. In the design of the conveyor, it is a wish to use to the best the means that allow a decrease of the  belt tension. We frequently frequently find conveyors conveyors that are equipped equipped of convex convex curve, with trough trough supports of a trough value that is inferior in the curve compare to the current conveyor length. This type of  assembly actually actually reveals a ignorance of the art rules. rules. For example, a current conveyor length equipped of trough at 30° for a convex curve equipped in trough at 20°. It is all the conveyor which should be in trough at 20°, if we do not notice any loss of material in that curve; conversely, we need troughs at 30° in the curve, if there is loss of  material at that place, by taking care of calculating the elements and their positions. We also find abnormalities to the consequences that are very prejudicial for the belt, when the convex curve was calculated for a polyester belt and, that following a change of belt, a belt with metallic carcass is installed.

65

VIII. CONCAVE CURVES:

In the case of the concave curves, we also need to put in profit the different solutions allowing a " minimum tension ". But the reason here is to avoid having the belt " taking off " from the frame as well at start as during the normal movement, empty, in partial or total load. If, in fact, the belt "takes off" from the frame, it is no longer " guided " and .... anything can happen. On the other hand, in load, on a trough installation, when the belt " takes off " this one is found "flat" then  presents a capacity (output) widely inferior to its position in trough. In that situation, the material will flow out on the installation. In a general manner, we should always prefer a "heavy" belt then of important mass per linear meter. When a conveyor is equipped of a break device for the belt, it is recommended to install that device on an upstream drum of the curve, for example on the tail drum. When that type of assembly is not respected, we can fear a sagging of the belt between two consecutive supports, at the beginning of the concave curve; this phenomenon leads to diverse disorders which are more or less important, these can go up to the breaking of the elements of the conveyor or/and of the belt. Radius of bend, choice of the belt: see calculation Determining the radius of a concave curve of a conveyor.

1. Simple method: - We know how to measure the angles αo and α1 with a declination meter, or by the sinus of the angle (Hyp./h= 0,..) Example: αc = α1 - αo = 15° (measured values) a = 109,90 m (measured value) angle of the curve in ° αc = R= radius of the curve in m a= length of the arch in m meaning R = (360° x a) : 2 x π) α R = (360 x 109,90) : 2 x 3,14) = 420 m

15 Hyp.

h

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2. Long method

Measured example from x = 112 .5 m from y = 15.1 m

C2

We know how to measure the projection to the floor of the curve length = x for 112,5 m We know how to measure the elevation height, in Y, from the end of the curve = y example 15,1 m

example for 

R = Hypotenuse of the rectangle triangle xC 2O, of angle αx = (90° - αc), whose adjacent side at αx = ½ c, or c = hypotenuse of the rectangle triangle of the sides x and y, that we have measured. c = √ x² = y² = √ 112,5² + 15,1² = 113,50 m 1 c = c = 113,50 = 56,75 m 2 2 2 cos αc = adjacent side = x = 112,5 = 0,991112  αc = 7°38' hypotenuse c 113,5 R = triangle hypotenuse xC 2O, whose angle αx = ½ αc = 90°-7°38' = 82°22'

cos ½ αc = 82°22' = 0,1330 cos ½ αc = hypotenuse  hypotenuse = adjacent side = ½ c = 56,75 = 426,7 m = R adjacent side cos ½ αc cos ½ αc 0,1330 67

Edition 12/08/98 IX.

ADJUSTMENT OF A CONVEYOR BELT

Before running to the adjustment screws of the drum (drums) or to the hummer to incliner the stations… we ( see here-below ) 1) Analysis of the default: • • • • •

• •

It is located or it is on all the conveyor. It presents symmetries. It is permanent, momentary, irregular, uncertain. It is weak or important (measurement of the amplitude). It is detrimental for the belt, the material, the frame. It is a drift on the right or/and on the left. A slippage during the movement.

2) The cause(s) is(are): • • •

old or new, unique or combined,  permanent or intermittent or periodical, direct or indirect, they implicate the transporter itself or its environment, like for example the time (in the sense of meteorology), upstream or downstream transports, a kiln, a sieve.

3) The different defaults of each constituent element

of the transporter and its environment are: (list

non-exhaustive here below) 3.1 the material: • • • • •

• • •

it plugs, it brings thermal problems (hot or cold), it chemically attacks the belt (inflates, hardens or softens, cracks), it pierces (punching by the carrying side, by the inferior side), it arrives on the belt, neither in i n the axis, nor with equal speed and in the same direction (static/dynamic  pressure), it stuffs at the reception, at the jetty, it jams in the edges, it diffuses (impregnates all the installation) or wets.

3.2) the belt: • • • • • • •

• •

festoons, is curved, the carcass is destroyed in the middle of the belt, at the junction without the coatings being torn, the side(s) are spoiled, the junction is not in the axis, not lined up, has slipped, it is open or cut, the grid is no longer perpendicular to the chain, the coating presents friction traces; all rips, perforations, inflations or grooves of the coatings and of  the carcass are to be taken is consideration, the belt circulates on a sole with an internal face coating, the surface of contact belt/rollers is not enough,

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• • •

• • • • • • •

the belt does not take the trough (to much steep in grid), The belt does not take the concave curve (not heavy enough or too much tight, too weak curve radius), It is torn crosswise: too small drum diameter, too weak transition length, convex curve of too weak  radius, it hangs on in the frame, materials passes between the drums and the belt. The internal face coating is prematurely worn out, It shows punching traces, It is plugged, The lengthening of the belt is excessive, The lengthening happens only on one side (it festoons), Or on the contrary has shrinked, The belt turns over itself.

3.3) the frame: • • • • • • • • •

•

Is twisted,  buckled, subsided, the longitudinal beams are asymmetric, it is not lined up, the two sides are not of the same level, it bends under the load, under the tension, it vibrates under indirect causes (sieve, the wind), metallic pieces have got unscrewed. Pay attention with the electrical cables which run in the frame (safety problem)

3.4) The drums: • • • • • • • • •

• • •

• • • • • •

They are worn out, the trace of the belt laid down does not correspond to the width of the new belt, The ferrule is arched. The middle of the ferrule is decentered compare to the axis of the frame, The bearings are loosened (the drum strolls), It has got a faulty round shape, it bends under the load, it has no convex, it has a convex that is incorrectly centered, it has a convex that does not correspond to the standards (out of sides, bi-conical, metallic carcass, glass, Kevlar), they have a diameter which is inferior to the standards of the belt, they have a width that is insufficient for the width of the belt, they are close to one another (case of tension drums and of the bend drums) which requests tolerances that are tighter as far as the shape and the position are concerned, the wrapping angle of the belt is insufficient, it is plugged, it is wrought, it is not coated (there are traces of melted rubber), it has a coating which is worn out, it has a coating which has a banderole (spiral in one direction), the drum axis is not perpendicular with the axis of the frame and the plane of the belt.

69

3.5) The slipping soles: • • • • • • •

they are worn out, they are deformed, they are torn, pierced, they are dirty, they are not in the level of the drum, the belt does not correspond to a slipping sole, there is a "saturation" between belt and sole which creates an empty space of air.

3.6) the rollers: (carrying belt (side), return belt (side), guides) • • • • • • •

• • • • • • •

they are worn out, cut, conical, they are blocked, the bearings are broken, they axis is twisted, they are plugged, their feather stuffing is worn out, the anti-plugging types have not enough sleeves, the belt gets jammed, subsided, and insufficiently guided, the shock absorbers have got their rubber fragmented, the shock absorbers are missing under the reception chute, they are not leveled, they do not match with the belt, they do not correspond to their station, they do not correspond to their working load, their geometric position is defective (see at station).

3.7) the knives: knives: or saber (fixed ( fixed axis or profile) • • • • •

they present wear problems, their geometric position is defective (orthogonal), (orthogonal), they present friction problems, they have a diameter and a wrapping angle which are not compliant the belt is not adapted to the knives.

3.8) the stations: V, trough, squares of return belt, auto-centering apparatus • • • • • • • • •

 pay attention to the assembly direction, we need stations without pinching in the case of belt with double direction of movement. They are twisted, They have a difference of trough angle from one side to the other, They do not match with the rollers, They are not posed in the axis of the frame, They are not orthogonal to this one and/or horizontal, Pay attention with the transition lengths, the auto-centering stations are blocked, clogged, wet.

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3.9) The scrapers and the mud flaps: They have a real influence on the belt, • they are worn out, • they are blocked, • they are too far from the drums and they do not have any counter support, • they are used as constraint drums or they have a pressure that is too strong. • They are unsuitable to the belt, to the material, to the motor power, • They are badly installed, • At a minor belt drift the mud flaps come out of this one, • They are forcing to much on the belt, • They quality does not comply with the belt. 3.10) the inlet chutes and the hoppers • • • • • • • • • • •

They do not put the material in the axis of the belt They allow a systematic pressure on the belt The provoke a cramming at the reception They provoke a cramming at the drainage (jetty) They do not put the material in speed They do not stop the big granulometry They do not let the small granulometry granulometry pass first, They are worn out, They are subsided, They transmit the vibrations, Their form do not correspond to the art rules.

4) The solutions

We shall establish first a hierarchy for the restraints. We shall not well the hierarchy in order to reorganize that hierarchy later  We shall use the means of cleaning (scraper, brush) We shall turn the return belt upside down, if possible (valid for the long conveyor lengths), We shall use a quality of belt that is appropriate to the material temperature, of the ambient area, We shall use a quality of belt that is appropriate chemically to the material, We shall use a quality of belt that is more qualified for the punching and/or we shall modify the edges, We shall use edges with mud flaps, We shall decrease the speed, We shall reduce the height of the chute at the reception., We shall install an over turning (aspiration or excess pressure) We shall cover the drums with grooved rubber coatings, We shall increase the wrapping angle, We shall increase the tension, We shall use an internal face belt adapted for the slipping soles, etc. Then, the installation will be put back in good state.

71

THE TOOLS AND THE MATERIALS OF THE PERFECT BELT ADJUSTER

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 triple metallic ribbon meter  1 metallic ribbon decameter  1 small ruler of 250 mm 1 metallic ruler 50 x 5 mm, long = belt width + 200 mm 1 angle protractor protractor (declination meter 360°) 1 spirit level for horizontal and vertical 1 lead thread 1 string (piano string) 2 V (des Rieux SARL ® pattern) 1 needle and its hummer  1 tracing pin 1 "écrimétal " tube chalks for rubber  1 small (hand) brush the tool box of the mechanic with the keys corresponding to the bolting system of the frame (10,13,17,19,21,22,24,27) (10,13,17,19,21,22,24,27) and notably : (1 quality toothed wheel key, opening 36 mm) 4 vice-pliers with big opening 2 solid clamps of good quality (2 pulling appliances of 1,5 t + chains and shackles) the necessary to move a bearing + a good eye look, a good sense of observation, of analysis, a lot of patience.                                      

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

                                     

+ a gifted companion of the same qualities. The thinking with 2 people is always profitable. For the extreme cases in the t he research of problems : call the technicians technicians of "des RIEUX SARL"

and BEFORE ANY ACTION ON THE TRANSPORTER : -  put OUT OF SERVICE the material on order table - affix your SAFETY PLAQUE to the CUTOUT SWITCH - forbid all faulty maneuvers by YOUR PADLOCK. These operations will be done in the presence of the head of the post. This one must inform you about the particular safety rules for his Establishment. See standards AFNOR in use notably EN 618 et EN 620.

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5. Methods of adjustment for drums and rollers NO ADJUSTMENT SHOULD BE DONE IN WORKING MOOD. In working mood we shall proceed later to the control of the belt trajectory.

The measurements of drift are done with the small ruler of 250 mm, because if in case it gets caught by the belt that will not last more than 2,5/10 of second in the case of a belt speed of 1 m/s. That time is so short for your hand to react and for you to try getting the small ruler back. If you had used a double ribbon meter, in the same circumstances, there are strong chances for  you to get trapped trapped in the the belt and ... it is an ACCIDENT.

Building or noticing the coordinates of a drum by geometric construction in the space. I. Measurement according to the axis of y

Lets consider the control of the drum horizontality. Spirit level

V

Drum

Drum length Distance between the housings’ axis

ruler 

Centered spirit level

Error on the horizontality

V

The thickness of the wedging to be inserted under the housing is equal to : eh x distance between the housings’ axis drum length

73

Edition 12/08/98 III. Measurement according to the axis of x

a) determining and materializing the 2 extremity points on a drum generator.

left Gd righ

 b) constructing the isosceles triangle "G dr MG MGg once the drum is adjusted, hit the guarantee points on the housings and the frame,  between leather and rostrum. right left Mc = summit of the triangle That must be isosceles M1 Gdr = M1 Gg or  Mt Gdr = Mt Gg If Mt has an error  of alignment on M1

or 

Conveyor axis

M1 = middle of the frame Mt = middle of the drum When the measurements MG (right and left) are stable, the drum is perpendicular to the axis of  the conveyor, or perpendicular and parallel and that axis when we consider the summit of the triangle Mt, under condition that the operations #1 and 2 are well done or the gaps balanced by wedging or measurement. measurement.

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IV. – Operations of adjustment for secondary or annex turning elements.

The stressing drum, adjoining to the main drum (reference drum) which has just been adjusted, is to put in level or in the same incline like its reference drum, centering it then adjusting it equidistant to its reference drum, by using the generator points which are materialized on the two drums. It is necessary to proceed the same way for the supports adjoining to the reference drum, by using the external notches of its supports and the generator points which are materialized on the reference drum. Left side

Right side

The right measurements must be stable with the lefts ones  by going from the original mark points G right and G left

75

V. Adjustment by geometric construction construction in the space of the position of a roller.

 Note : adjusting a roller with a square does not allow a geometric construction with a tight tolerance due to numerous hazards hazards on the measurement. measurement. That method of adjustment by geometric construction is identical to the one which is used for the drums. It is the only method that allows a tight tolerance on the position of the rollers. It is then  particularly effective in the case of the conveyors with double direction of movement, equipped of rollers. That method is applied as well for the adjustment of the return belt rollers, in the case of "short spacings"; a simpler method is used for the "long spacings" (see following pages).

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METHOD OF ADJUSTMENT BY "COMPARISON" OF RETURN ROLLERS OF A CONVEYOR

The Spacing of the return rollers: itit is in general of 2 to 3 m, no matter the belt. belt. In accordance with the standard NF H 95-203 paragraph 6-3-3, You would be able, in all cases of smooth belts, use a spacing of 6 to 9 m (see more according to the calculations).  Not to forget considering the admissible load of the rollers in order to determine the maximum spacing. In normal movement, when empty or loaded, the belt bend to obtain between two supports must  be between 0,5 % and 2 %; a bend > to 2 % absorbs more power. Preparation of the work: •

Laying down or putting out of service the fixed or turning accessories (scrapers, inverted stations, auto-centering auto-centering apparatus, guiding rollers, r ollers, flanks of the carrying belt, etc...)

•

Laying down the extra rollers (definitive laying down) by starting from the head of the conveyor and by going toward the tail. Adapt your remaining supports in accordance with the elements which must be conserved like the deviation drums of the tension systems.

 Note : It is frequent to lay down the stressing drum adjoining to the tail drum if its presence is not justified. It happens again often enough that we proceed the same way for the stressing drums associated to the head drum; "The less there are, the better we are!"

Releasing the belt in a way to obtain a bend of 3 to 4 % of the spacing of the supports; for  example for a spacing of 6 m, we shall endeavor to have 240 m. Making sure no fitting comes to perturb the testing or damage the belt. In the case where there a risk, preferring (if possible) the removal of the fittings if these ones present a discomfort with a bend of 2% to 0,5 % of the new spacing. In testing phase, with a bend of 2 % of the spacing, a belt rubbing on the transversal fitting, "horizontal" is not affected by that friction in its trajectory. If we consider the same friction in "exploitation" situation, this one will not affected more the trajectory of the belt; we shall simply have a wear of those fittings. In the case of " stapled " belt, no friction can be accepted   because it is the staple that takes the risk of catching on the fittings and therefore...break  everything!

•

•

Adjusting the two first rollers by geometric construction (the l st is at 6 m or 9 m of the head drum). With experience, that operation can be eliminated.

•

In the case where the rollers of the return rollers are of anti-plugging type with sleeves or  scrubbers with turns (actually all the patterns that are not cylindrical), we have to exchange them " IMPERATIVELY " by standard cylindrical rollers; they have a better tolerance of  manufacture an they offer a better support to the belt.

77

Trap: a belt which is supported all the 6 m, even 9 m, weighs 2 (to 3) times more, then at 3 m Trap: initial spacing. It is then careful to exchange first the sleeves rollers of the supports which must  be conserved, by standard rollers, before lay down the extra rollers, for fear to find oneself with 12 or 18 m of belt to lift. Trap:: replace the roller supports squares obliging a " unsettlement Trap unsettlement " during their later change, for  example during a future maintenance, with the application of safety devices (recommendations standard EN 618 and EN 620); this case of figure has the risk to be more and more frequent. When a conveyor is equipped of several belt sections, no matter their length, it is imperative to locate each section. In most of cases a water painting with quick seasoning is convenient in application on the side of the belt. Choosing lively colors and which are very contrasted amongst one another; especially for the belt with high speed of movement. We need half less colors than sections.

•

It is "IMPERATIVE" that the belt goes back centered on the head drum and comes out centered, including at the constraint drum. If that is not the case, we have to act on:

•

st 

: the head drum is compliant and well adjusted; we have to act on the last support for  carrying belt and note the initial position and the corrections which are brought. nd  2 case : the head drum does not respond to the rules of the art ; we have to put the compliant material and adjust it correctly. • At the beginning of the adjustment work, it is admitted for the belt to have An incorrect centering on the tail drum in the where case the belt is centered at the head.  Note:: In the phase of adjustment, we shall have the same considerations for all the drums that are  Note installed on the return belt. There is an imperative of good centering of the belt on the drums which precede a section of return belt supports. There is a tolerance which is related to the belt drift on the drums that follow a section of return belt supports. Safety: in the case where the belt has " come out " from the drum, we must recenter it manually. That operation will be performed " IMPERATIVELY I MPERATIVELY " belt stopped, installation installation and regime "out of service", shut down level: unbrocaded 1 case

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Adjustment of the return belt by comparison: •

Putting the installation in trying regime.

Safety:

•

The adjustments are done when the belt is stopped.. The measurements of belt trajectory are done "after" the rollers and especially not at the entrance in the belt on these ones (retractable point)

In the case where the belt gets drifted, but "remains on the conveyor", we start by making the  belt turn for one or two turns in order to appreciate the drift amplitude of each section of belt and to note the values and the direction of those drifts. That observation is done at the entrance of the head drum, above the belt (safety) and with the right of the two first rollers. r ollers.

Compare the direction and the amplitudes of drifts with the observations done before the head drum. Correct the adjustment of these first rollers in a way to have values that match with the measurements performed performed near the drum ; to see amplitude values of drifts reduced. In two tries, three in maximum, by comparison of the results of obtained trajectory correction, correction, in accordance with the incline corrections corrections (orientation in the plan) of the supports you must come to a correct trajectory ; otherwise look for the error ! Pay attention, attention, the corrections to bring on the roller supports are in millimeter order ! Example: if for 1 mm of orientation correction for the roller support, you obtain 23 mm of  trajectory correction and if beforehand to your action you must correct your belt trajectory by 60 mm, you will have to complete your correction by about 1,5 mm; meaning the rule of  three : 1 x 60 - 1 = 1,6 mm 23 •

An unreeling of 5 to 10 m of belt is enough to appreciate your action with accuracy. In the case of belt with several sections, you will use your statement of drift established at the head drum according to the "color" of each section. If for example, the belt section painted in green was presenting a left drift of 18 mm at the head drum, you consider the belt centered when, at the level of the rollers that you observe, the belt will be drifted by 18 mm on the left compare to the reference value.  Note: The less the belt will be tight, the longer will be the roller spacing, the more the orientation  Note: corrections for the supports will be proportional to the reductions of amplitudes of drift for belt trajectory. The more you come closer to a drum, the more the belt tension will increase, the less your  correction action will be proportional. You are in the " influence zone of the drum" ; be careful in your corrections, proceed millimeter by millimeter! •

Proceed like here above, for each pair of the following rollers, until you reach the tail drum. After every adjustment, make sure you observe the belt trajectory at the level of the last roller  that precedes the pair of rollers, subject for your action, before moving to the level of the following pair.

79

•

All the adjusted rollers, make one to two belt turns, in order to control your work. Make sure the tightening of all the bolts is good.

•

Put back a normal tension giving a bend of 0,5 % to 2 % of the spacing of the supports and make a control of trajectory.

Trick : for more speed, when the roller supports have two bolts per piece, do not tight in the "adjustment" phase more than one bolt out of two; but always the same one: the upstream or  the downstream, in order to reduce your working time. Reassembly: • Reassemble in place and fix the anti-plugging rollers or others without unsettling the supports. Start in the order, by pair, from the head toward the tail. Make the belt turn by 10 meter for  control. If the trajectory is perturbed, the solution is either to put back the standard rollers, or rectify* the sleeves rollers and without guarantee of result for that second solution. Often, a good scraper exempt the use of sleeve rollers. * the rectification of bag bag rollers has a dissuasive dissuasive cost !

Then, this is not not the solution.

You notice, yourselves, that the inverted stations and other materials called "auto-centering apparatus " has no more use; however, if you wish to use them, their adjustment must be  performed by geometric construction. For memory, this type of support is exclusively reserved for the external conveyors, not covered, sensitive to the wind. - Make a control of trajectory. It is frequent for the quality of your adjustment to put in evidence some belt defaults. According to the importance of those defaults, it will be convenient to change the sections out of tolerance.

des RIEUX SAS®

ANNEX 1

THE USEFUL STANDARDS STANDARDS FOR THE BELT CONVEYORS

n° NF

n° ISO

date

1537

August 1970

Particulars

class.indication / expulsion

E

E 53-301 r

 prEN 618  prEN 620

Belts and rollers: lateral plays - dimensions of the rollers – trough with 3 rollers ./ T 47-100 - angle of pinching Equipments and continuous handling system Equipments for the mechanical handling of the materials in bulk except the fixed transporters with belt. Equipments and continuous handling system. Fixed transporters with belt for material in bulk.

class.indication

class.indication

EN ISO 7622-1

Dec. 1995

Conveyor belts with steel cables Try of longitudinal pull- measurement of the lengthening

class.indication T 47-071

EN ISO 7622-2

Dec. 1995

Conveyor belts with steel cables Try of longitudinal traction - measurement of the resistance.

class.indication T 47-072

EN ISO 9856

Dec. 1995

Conveyor belts Determination of the elasticity module.

class.indication T 47-111

EN 20284

284

June 1993

Belts for transport. Electrical conductivity – Specification & trying method

class.indication T 47-109

  pr EN 27590

DIS 7590

Sept. 1994

class.indication T 47-100.3

H 95-200

TC 101

Oct. 1970

Conveyor belts with steel cables Method of determination of the total thickness of the belt and of the thickness of the coatings. Mechanical handling of materials in bulk. Bill of materials

H 95-202

3435-2

Nov. 1976

Machines for continuous handling. Classification and symbolization of the materials in bulk.

H 95-203

5048

Oct. 1986

Belt conveyor with carrying rollers. Rules of the calculation.

H 95-320

May 1988

H 95-330

Sept. 1987

Belt conveyor intended to be an instrument of continuous accumulator  weighing. (see decree 1975, decree 1976) Drums, shafts, housings-heavy series : dimensions

H 95-400

Oct. 1970

Handling of the isolated loads Bill of materials

251

Sept. 1988

Conveyor belts Dimensions, widths and lengths

252

Sept. 1988

Conveyor belts Adhesion between constituent elements.

class.indication T 47-101 ./ iso 36 et 6133

283

May 1991

Conveyor belts Resistance and lengthening by traction in full thickness.

class.indication T 47-102 ./ iso 3 = NF X 01-001, iso 433 = NF T 47-119, iso 471 = NF T 40-101

./ H 95-200 H 95-203 OIML RI 50 ./ A 49-112 /E 52-109 H 95-208 /H 95-209 ISO 1536 ./ A 49-112 /E 52-109 H 95-208 /H 95-209 ISO 1536 class.indication T 47-100.1

81

n° NF

n° ISO

date

Particulars

class.indication / expulsion

340

Feb. 1989

Conveyor belts Resistance against flame

432

Dec. 1989

Conveyor belts with superposed pleats Characteristics of construction.

class.indication T 47-108 ./ cf. EN 20340, DM/H50 iso 235, 426-2, 565, 835, 2194,3310-1, 3310-2 class.indication T 47-118 ./ iso 251 = T 47-100.1

433

Dec. 1991

Conveyor belts Marking

583

Nov. 1990

703

Sept. 1988

Conveyor belts with textile carcass class.indication T 47-100.2 / Tolerances on the total thickness and the thickness of the coatings – Method of  iso 4648 direct measurement. Conveyor belts - Ability for putting in through – Characteristic of transversal class.indication T 47-125 flexibility and trying method.

1535

Oct. 1975

Machine for continuous handling – Conveyor belts Widths of the belts and lateral plays before obstacle.

1536

Oct. 1975

Machine for continuous handling - Conveyor belts Drums: diameters, lengths

1537

Oct. 1975

Machine for continuous handling - Conveyor belts. Support rollers

E

T 46-012

2148

Machines for continuous handling - Bill of materials

3435

Machines for continuous handling - Classification and symbolization of  material in bulk.

class.indication T 47-119

H 95-330

3684

Sept. 1990

Conveyor belts Determination of the minimum diameters of the dru ms

class.indication T 47-103 iso 3; 583; 1536; 7590

4195-1

Dec. 1987

Courroies transport. Resistance against heat – Trying method.

9856

Dec. 1989

Conveyor belts Determination of the elasticity module.

10247

May 1991

Conveyor belts Characteristics of the coatings.

class.indication T 47-110.1 ./ iso 37 = NF T 46-002, iso 48 = NF T 46-003, iso 188=NF T 46-004 / 005 iso 471 = NF T 40-101, iso 4661-1 = NF T 46-001 class.indication T 47-111  NF T 47-005 iso 282; 283; 471;5293 class.indication T 47-007 iso 37; 188; 3435; 4649

4649

Oct. 1984

Determination of the resistance against abrasion of rubbers

Sept. 1995

Conveyor belts Maximum values of the convex of the drums

T 47-004

T 47-005

5293

April 1983

Conveyor belts Calculation of the transition distance

T 47-006

TR  10357

Feb. 1990

Calculation of the transition distance with three equal rollers- / New method

./ E 75-100 T40.101/T43.006 T45-002/103 T46.003/022/030

iso 1537; 5293; 9856

des RIEUX SAS®

n° NF

n° ISO

date

Particulars

class.indication / expulsion

E

T 47-007 1024 May Characteristics of the coatings 7 1991 Classification T 47-105 3870 1980 Textile conveyor belts – Course of adjustment T 47-106

July 1988 Feb. 1991

T 47-107

Conveyor belts with “ aramide” carcass- Resistance and elongations - Specifications and trying methods. Conveyor belt Resistance against flame / tries with burner in gallery

Feb. Conveyor belt 1989 Resistance against flame / specifications and trying method (method that is less constraining than T 47107) T 47-109 R 284 1963 Conveyor belt – electrical conductivity T 47-108

340

T 47-111 9856 1989 Conveyor belt - Determination Determination of the elasticity module T 47-119 1965 Conveyor belt - marking T 47-126

Aug. 1965 T 47-131 1120 Apr. 1983

Conveyor belt – Resistance against the spreading of  the curt in the carcass Conveyor belt Determination of the resistance of the stapled assemblies

T 47-132 2878 Jan.1 Materials with rubber grassroots – electrical conductivity 995 Method of measuring the electrical resistance.

T46.002/005/012 H 95-202

./ DM/H n°50 DM/STSS n°428 A 35.575/578 T 47-072/100.2 T 47-100.3 /102/ 106/118 ./ E 66-061/067/071/072 E 66-073/074 A 51-105 / 51-115 B 35-306 X 11-501/504/

./ T 47- 002/102/005 T 40-101 ./ T 47-108 / T 47-109

./ T 40-101 / T 47-102

class. indication T 47-109 / EN 20284

83

ANNEX 2

REMINDER OF THE FUNDAMENTAL MECHANICAL FORMULAS Force

A force is the product of the mass by an acceleration. F=Mxϒ The force is expressed in Newton (N) when the mass is expressed in kg and the acceleration in m/s2. Particular case of the weight The masses in vertical movement are submitted to the acceleration of the gravity (9,81 m/s 2) and exercises a force that is equal to 9,81 time their mass. That is where the confusion frequent between mass and weight comes from. 1 kilogram mass in the vertical direction gives a force of 1 kilogram force = 9,81 N. Moment

The moment of a force (or couple) is the product of a force F (in ( in Newton) by a radius of gyration R (in meters) and it is expressed in Newton meter (N.m). Example A force of 500 N is applied to a distance of 300 mm (0,3 m) to lead to a rotary cylinder. Moment of the force = 500 x 0,3 = 150 N.m Power

The power is a quantity of work supplied by a unit of time and it is expressed in Watts (W) or in kilowatts (kW). The power is sometime expressed in horses (CV or HP) 1 CV = 736 W = 0,736 kW The moment and the power are joined together by the following formulas where n is the speed of  rotation which is expressed in turn (rotation)/minute (rotation)/minute (min-1) M = 9550 x P x λ n M in N.m and P in kW

et

P=Mxn 9550 x λ

des RIEUX SAS®

ANNEX 3 Belt conveyors

Helps for the orientation of the calculations’ results in accordance with the choices for each  parameter. Interaction of the components: It is matter of determining the influences of all the components of a handling by belt conveyor, as well on the resistant forces, the absorbed powers as the specific utilization restraints of each component. Orientation table

The carried materials

The materials with very irregular density oblige to consider  resistant forces the strongest density in order to determine the absorbed  power.

=+

The weakest density have an influence on the capacity, the resistant forces carried volume.

= +

The sticky material on the belt will necessitate a high scraper  resistant forces  pressure.

= +

The materials that are very cohesive have flow difficulties. difficulties.

=+

resistant forces

The materials that striking the belts with a strong energy type of belt (heavy, in mass, having an important initial speed)

= +

The materials in cluster (example : measure, extractor)

= +

resistant forces

The materials that have an inescapable chemical influence type of belt on the belt require sometime belts of superior type, then heavier.

= +

The materials that present a very expensive industrial risk  type of belt (pollution, machine stopping) impose the utilization of belts of superior type , then heavier.

= +

The loads of daily work, weekly, etc., the frequency of the type of belt starts in full load, the materials which are difficultly accessible (on the site, at the end of the world) require higher  security coefficients. coefficients.

= +

85

Divers cases

The case of measures or weighing frames, it is the resistance type of belt at the junction that makes the reference, that can impose  belts of superior type.

= +

Transporters with double direction of movement, for  type of belt trajectory reasons, that can impose belts of superior type.

= +

Belts with high change frequency with aggressive materials type of belt and due to manufacture standards impose belts of superior  type.

= +

The pouring trolleys

= +

resistant forces

The frames

The frames, which are very fragile, can be the origin of belt resistant forces drifts and they lead intensive frictions; here it is a must to   bring a solution to the problem and not to install a belt of  superior type.

The gearboxes groups

= +

:

Too much strong installed power.

type of belt

= +

The direct starts

type of belt

= +

The progressive starts,

type of belt

= +

The breaks can have powers that are superior to the installed type of belt gearboxes.

= +

A high speed necessitates

type of belt

= +

A low speed necessitates

type of belt

= +

des RIEUX SAS®

The tension systems

The tensions with invariable run

type of belt

= +

The tensions with variable run

type of belt

= +

: the tensions with variable run which are blocked type of belt or out of service must be considered like tensions with invariable run

= +

 Attention : the overloaded tensions

types of belt

= +

The belts which are under-tensioned, bend superior to 2 %

resistant forces

= +

Wet drive drum, covered with dust

type of belt

= +

Squirrel Cage drum

type of belt

= +

Drums made with materials of weak friction coefficient. coefficient.

type of belt

=+

Drive drum coated with rubber

type of belt

= +

Drum with polymer concrete.

type of belt

= +

Drum that has a shape which is out of the standards and/or  type of belt incorrectly installed.

= +

 Attention

The drums

Stressing drum increases the wrapping angle

type of belt

Stressing drum:

pay attention to the plugging materials which will close a gangue, assembly forbidden for the belts with profile like (rafters, battens, fingers, sides, etc.)

= +

Divers drums: the accumulative total of their mass is to resistant forces consider in the resistant r esistant forces.

= +

The knives or sabers are very greedy in absorbed resistant forces  power.

= +

87

The supports

The slipping soles, in accordance with the belt/sole friction resistant forces coefficient compare to the rollers.

= +

 Attention

: The anomalies like rust, empty spaces of air  resistant forces which provoke a suction disc effect

= +

The slippage shock absorber skates, in accordance with the resistant forces  belt/sole friction coefficient and compare to the rollers.

= +

The rollers

The mass of rollers per frame meter is to be considered.

resistant forces

= +

The rollers pinching angle

resistant forces

= +

The rollers that are incorrectly adjusted and out of use.

resistant forces

=+

Spacing of the supports/bends of the belt > to 2 % (NF H 95 resistant forces 203)

= +

The belts

A heavy belt

resistant forces

= +

A light belt

resistant forces

= +

Too much short transition length and convex curve resistant forces incorrectly calculated. calculated.

= +

des RIEUX SAS®

89