Loom: A loom is a machine use to produce fabric from two series of yarn namely warp and weft. The warp yarn stays along the length direction and weft yar n remains across the width way. A loom can be very simple and is made of wood and it can also be very sophisticated like micro processor controlled. Types of loom: loom
non-automatic
primitive loom
semi automatic loom
automatic
ordinary loom
shuttleless loom
shuttle loom
airjet/ waterjet
rapier
projectile
multiphase
Loom motion:
shedding
primary
picking
beat up
motion of loom
stop motion tertiary/ auxilary
temple, leno motion take up
secondary let off
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Primary motion: Shedding, picking, beat up are called primary motion and w ithout primary motion it is not possible to produce fabric.
Shedding: This is the motion use to separate the warp yarn into two shed so that the shuttle /weft can be inserted between them.
tappet shedding
dobby jacquard
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Classification:
Hand Loom
1. Vertical loom: Damask, Tapestry. 2. Pit loom. 3. Frame loom. 4. Chittarangan/ Semi-automatic loom; Take up automatic but let off manually. 5. Hattersley loom. 6. Natural Source/ Ordinary power loom: I) Water wheel was until 1950 II) Steam engine III) Diesel engine 7. Electric power loom; 1st power loom 1784 1st weaving mill with power loom 1789 I) Large single motor II) Large group motor III) Individual motor with 1930 8. Modern loom: I) Projectile II) Rapier III) Air Jet IV) Water Jet V) Multiphase
Loom drive Power development/ Loom drive:
1. Hand loom: Human power drive. 2. Power loom: I) Water Wheel. II) Steam engine. III) Diesel engine. IV) Electric motor.
Large common motor (200 loom/motor) Group motor e.g. 200 loom/motor Individual motor: 1930 i)Direct drive. II) Indirect drive Multiple motor: for each modern loom.
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Disadvantages of common source of power/ common motor drive:
I) Chance of power loss: On average 20% loom can not run for various reasons: Absenteeism of worker Shortage of raw materials Shortage of work order Style change Shortage of spare parts Natural calamities Load-shedding Political disturbance II) Clumsy shed condition: As motion is transferred from main shaft via belts and shafts so in some cases they are in irregular manner and that is why, a clumsy appearance of shed occurs. III) Poor visibility: Due to more shafts and belts. IV) Dirt, oil and danger from driving shafts and belts i.e. possibility of accident. Advantages:
I) II) III) IV) V)
Minimum cable required. Less man power required. Less fire hazard. Less initial cost. Less electric complexity.
Disadvantages of grouped motor:
Risk of fire hazard Cost of electrical items More investment cost
Advantages:
Saves power energy Less risk of accident Reduce complex transmission of driving system
Advantages of individual motor drive:
Randomly power supply Power saving Simple driving system Least amount of production
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Disadvantages:
Higher initial cost More cable required More possibility of fire hazard Maximum electric personnel required Distribution & sub distribution board required Complexity of electric cable line High manpower
Loom drive: Methods of power drive in weaving/loom:
1. Direct drive 2. Indirect drive 1. Direct drive: Loom driven directly by on-off system of motor High initial torque is required Saves energy No side-way thrust is required High initial cost Used in Jute loom, Modern loom No use of clutch High power consumption of motor 2. Indirect drive: Clutch declutch system i.e. At first motor drive, the clutch drive and loom runs Low initial torque Apply undesirable side-way thrust (special thrust bearing) Wear of main shaft bearing Loss of power Used in cotton/conventional loom Low initial cost Low power consumption of motor How energy is saved in direct drive:
In running condition of loom, the loom is stopped due toExhausting of the pirn Weft breaks Warp breaks Mechanical draft The motor does not run instantly due to stop of the loom. So power is not consumption.
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Shedding Shedding:
Dividation of warp threads into two parts for insertion of weft threads is called shed and the mechanism of shed is called shedding, it is the first primary motion of weaving. Types of shed:
1. Bottom close shed 2. Centre close shed 3. semi-open shed 4. Open shed 1. Bottom close shed: This type of shedding is produced by giving motion only to threads that are to form the upper line. Under this condition, the warp is level on the bottom line. Hence in order to form a top shed, it is necessary to move some threads through a space equal to twice the depth of a shed, once up and down, before a fresh selection is made. A shed of this kind is known as stationary bottom with a rising and falling top. A Bottom line of warp B Rising and falling line C An arrow showing the space passed through
Advantages:
I) II) III)
Alternate tightening and slackening the warp threads produce a covered cloth Produce fire fabric (silk) Used in hand loom
Disadvantages:
I) II) III) IV) V) VI) VII)
More stress or tension on the top warp line and less tension on the bottom warp line. More chance of breakage on top warp line Unequal warp tension produces poor quality fabric Loom speed/ waving speed is slower Not possible to produce compact fabric More power consumption More time required
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2. Centre close shed: This type of shed is produced by imparting an upward movement to those threads which are to form the top line and the downward movement to the threads which are to form the bottom line. Then after inserting a pick, both the lines meet at the center between the highest and lowest lines of a divided warp.
A Closed warp line B, C Upper and lower lines of a divided warp respectively D Arrow showing the half distance of a shed in an upward direction E Arrow showing the half distance of a shed in a downward direction Advantages:
I) Equal tension on the top and bottom warp line II) Less time required so high production III) Less wear of the m/c IV) Less power consumption V) Less tear of the threads Disadvantages: I) II) III)
Beat up takes place in the closed shed condition There is chance of weft being moved backward Compact fabric can not be produced by this shed
3. Semi-open shed: In this shed, the stationary bottom is retained but threads for the top line either passes to bottom at one movement and again carried to the top mid way and again carried to top. In this shed close and open shed occurred simultaneously. In it the stationary bottom line is retained, but threads for the top line either pass to the bottom at one movement, or are arrested midway and again carried to the top. Such a shed can be formed as expeditiously as an open shed, for the upward movement begins and ends with the downward through movement, and the arrested downward movement is converted into an upward movement immediately the falling threads are in the same plane as the rising ones. They all reach the top together but the strain upon them is not equally distributed.
A Stationary bottom line B Top point C The point where downward movement ceases in threads D, E Showing the movement of through healds F Arrow showing the threads which are to lift for the next pick
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Advantages:
I) II) III) IV) V) VI) VII) VIII) IX) X)
Equal tension on the top and bottom warp line All the warp yarns are not required to move up and down in every pick Beat up takes places in the cross-shed condition The loom can run at a faster speed Possible to produce compact fabric Less complexity or disturbance in the shedding mechanism Used in power, dobby & jacquard loom For fancy fabric Less power consumption Less tear of threads
Disadvantages:
I)
Unusable movement
4. Open shed: In open shed, the warp threads form two stationary lines, the top line and the bottom line and changes are made by carrying the threads from one fixed line to the other without any interval. A, B Stationary warp line C, D Arrows which show the movement warp to equal the distance between A & B
of rising and falling
Advantages:
I) Beat up takes place in cross-shed condition II) Equal tension on the top and bottom warp line III) The loom can run at a fastest speed IV) Extensively used in tappet shedding mechanism V) Basic fabric (twill, sateen, plain) can be produced. VI) Less power consumption VII) Less wear of the weaving m/c Disadvantages: I) II)
High breakage rate If higher no of healds are used then the warp in back healds are more strained than the front ones III) Leveling apparatus should be added to open shed to place the headls in one plane.
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Tappet shedding Tappet:
A type of cam to which a rotary motion is given for the purpose of producing reciprocating motion in rods and levers by sliding contact. When the rod is to receive a series of lifts, with intervals of rest and thus forms a shed called tappet.
Basic shedding mechanism:
1. 2. 3. 4. 5.
Padel/Treadle Hand loom Tappet Dobby Power loom Jacquard Combined i) Tappet + Dobby ii) Tappet + Jacquard iii) Dobby + Jacquard iv) Treadle + Dobby v) Treadle + Jacquard extensively used
Power loom Cost of loom: Tappet < Dobby < Jacquard Design capacity: # Simplest(Tappet) # Medium(Dobby) # Elaborate(Jacquard) Speed: Tappet > Dobby > Jacquard Cost of production: # Lowest(Tappet) # Lower(Dobby) # Low(Jacquard) Scope of Tappet: 12 heald shaft
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Principle of Tappet shedding:
In the figure, a pair of shedding tappet is connected to bottom shaft or tappet shaft and two treadle lever is pivoted When two tappets rotate/moves due to rotation of bottom shaft, nose of tappets pushes ispringes continuously the anti friction bowl on treadle lever. As one end of the treadle lever is pivoted, the other end of treadle lowered.
This treadle lever is joined with heald shaft or frame by using rope or chain. And heald shaft is joined with top rollers by rope. For this the heald frame lowered with warp yarn. The other heald shaft moves upwards due to lowered of other heald frame As a result, the warp yarn from a shed and continuously shedding operation performed.
Auto reversing system:
Fig: Auto reversing system
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Difference between Tappet & Ordinary cam: Tappet 1. It gives motion to a shaft to receive a series of lifts with intervals of rests. 2. It is mainly used to produced shed 3. All tappets are cam
Ordinary cam 1. It gives a continuous reciprocating motion 2. It may be used for many purposes 3. All cams are not tappet
Conditions of good shedding:
A shed should be as small as the nature of the work to be done Healds should be placed at right angles with the warp threads Exact vertical movement of the heald shafts are required Perfect leveling of the heald shaft The heald shafts must begin to move slowly
Describe a shedding mechanism which will produce open shed:
Ratio between top shaft RPM and bottom shaft RPM = 2:1 2 tappets on tappet/bottom shaft on plain weave and the ratio between top and bottom shaft is 2:1
When top shaft rotates two times, then bottom shaft rotates one time. Then 2 times shedding and 1 time picking. Bottom shaft does not contain more than 2 tappets. If bottom shaft contains 3 tappets, produce 3 times beating and 3 times picking which is not real. i.e. picking mechanism is always mounted on the bottom shaft and picking takes place alternatively from the opposite side for each revolution of bottom shaft, 2 picks are inserted. That’s why, the RPM if crank shaft is twice than that of bottom shaft.
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Types of shedding tappet:
Various kinds of shedding tappets are in use in the industry. They are constructed on two principlesi) ii)
Negative shedding tappet. Positive shedding tappet.
i) Negative shedding tappet: All negative shedding tappets require the addition of pullers, stocks and bowls, springs or dead weights to reverse either pulls the heald down or lifts it.
Lifting Mechanically Lowering Spring The negative shedding tappets are the following
The ordinary plain and twill weave shedding tappets. Jamiesons tappets, and The barrel tappet
ii) Positive shedding tappet: The positive shedding tappets give both upward and downward movements to healds without the aid of any additional mechanism. But pulleys and stocks and bowls are based on compensating principle
Lifting and Lowering Mechanically The positive shedding tappets are the following
Woodcrafts section tappet The oscillating tappet Nutralls chain tappet, and Scroll tappets
Position of fixation of tappets:
1. Over or Under one end of the heald shaft 2. Over or Under the middle of heald shaft 3. Outside of the loom frame
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1. Over or under one end of the heald shaft: When tappets are placed over or under one end of the heald shaft then pressure is applied at only one side of heald shaft. Hence connecting cards should be used on two sides. Advantages:
I) easy access for fixing or mounting of the tappets and other relative parts relative parts and connections. Disadvantages:
I) Unbalanced loading or unequal shedding. II) If the tappets are mounted over the heald frames, then there will be possibilities of oil dropping on the warp yarn. III) It is possible but not practice. 2. Over or under the middle of heald shaft: When the tappet is placed over the centre of heald shafts then the oil, grease etc applied to treadle bowl for antifriction property may fall on the fabric and contaminate it when placed under the heald shafts, some difficulties may arise while cleaning. Advantages:
I) Equal loading or shedding II) Extensively used for conventional loom Disadvantages: I) Difficult access for tappet mounting, fixing or other settings. II) Oil dropping if tappet is over the heald frame. 3. Outside of the loom frame: In this system, its easy to clear the tappets and to apply grease, oil to treadle bowl and easy maintenance can be done. But it requires more space. Advantages:
I)
Though the tappets are mounted at one end of heald frame it works perfectly due to excellent mechanical setting. II) Positive tappets shedding mechanism is used for this kind of system III) Easy access for maintenance and setting Disadvantages:
I)
Initial investment cost is higher
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Advantages of tappet shedding:
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Simplest Cheapest of all shedding motions. If conveniently employed, it gives the best result within its capacity. Action is certain It is capable of lifting heavy weights with less wear and tear of the m/c than other shedding appliances Less wear and tear I t can move healds at high speeds Dwell period may be adjusted to suit the type of fabric to be woven Puts less strain upon the warp threads consumes less power and give greater output It causes fewer defects to the fabric
Defects of tappet shedding:
1. 2. 3. 4. 5. 6. 7.
Over shedding strains and breaks the warp threads Under shedding does mot permit the passage of the shuttle through the shed Sometimes unequal shedding by lifting one end of the shaft more than the other Missed shedding Unsuited dwell period May impart jerky motion Half a revolution contact time between bowl and tappet gives severe blow to the healds
Dwell period:
Dwell is the stationary period when the heald frames do not change their position and the shade remains open to allow the passage of the shuttle from one shuttle box to the other Factors affecting dwell of tappet/Points to be considered with dwell period:
If the loom width is lower, then dwell period will lower. Weave structure: complex structure DP↑ Simple structure DP↓ Reed space lower and dwell period lower No. of warp yarn per inch/ self ends per inch – Shorter dwell period Higher picking force – Shorter dwell period Type of yarn: for, Finer yarn, shorter dwell period And for, coarser yarn, higher dwell period
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Construction of shedding Tappet: For plain weave:
Points to be taken under consideration:1. Weave design:
1 1
plain
2. Lift of the tappet: 4″ 3. The distance from the center of the driving shaft to the nearest point of contact with the treadle bowl - 2″ 4. Diameter of the treadle bowl - 2″, Radious of the treadle bowl - 1″ 5. Dwell period =
1 3
of a pick
Construction:
1. A circle ‘A’ is drawn of 2 in radius representing the distance from the centre of the driving shaft or bottom shaft to the nearest point of contact with the treadle bowl. 2. A circle ‘B’ is drawn by adding radius of treadle bowl with A i.e. A = 2, B=A+1=3 3. A circle ‘C’ is drawn of 7. 4 are added for the lift of the tappet. i.e. C=B+4=7 4. The pattern being a plain one, the circles must be divided into two equal parts and each half circle will then represent one pick indicated by the line DE
Center: O
5. Each half circle is divided into three equal parts by lines FK, GH 6. Each of FOH and GOK is divided into six equal parts 7. A semicircle L is drawn between B and C at a radius of half of the lift of the tappet (i.e. 2) Page | 15
8. Divide the circumference of the semicircle into six equal parts (30 DEGREE) 9. Draw perpendicular from the dividing points of the semicircle on the line GO. This gives six unequal divisions on the lift to obtain the desired eccentric shape of the tappet. 10. From the corners of these unequal spaces and with the radius (1”) of the treadle bowl, the drawn circles represent the position of the treadle bowl at different parts of its movement. 11. The curved lines are drawn touching the extremities of the treadle bowl. This gives the outline of the plain weave tappet.
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Timing of tappet loom:
The timing in loom cycle generally refers to the position of sley. Timings are described in relation the angular position of the crank shaft from the reed derive their motion. The path traced by the crank pins represent the crank cycle. It is then graduated in depended starting from the forward most position to represent a timing diagram. The circle of timing is typical on most tappet looms the direction of rotation of crank shaft is generally anticlockwise. In the following timing diagram, the position for the timing of the sley. Shedding & picking have been located in over pick and in under pick tappet looms. In various angles: At 0° and 360°:
Heald are level Cranks are in top centre Sley in the mid position between the back and front centers Warp threads are parallel with the floor in oven pick looms Cone is in contact with picking disc. i.e. shuttle is at dwell
At 90°:
Healds are crossed in over pick loom Cone is in contact with picking disc. i.e. shuttle is at dwell Crank is at the front centre Reed is in contact with the fell of the cloth Fastest movement of the sley Beating up occurs
At 120°:
Shed is open Dwell period of tappet begins
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From 120° to 240°:
Shed remains open
It is the dwell period of tappet. i.e.
1 3
rd area of a pick cycle
At 150°:
Picking nose is in initial contact with the cone The shuttle begins to move in the box in over pick loom
At 180°:
Shed remains fully open Picking nose tip is in the final contact with the cone Shuttle leaves the box in over pick loom Crank is at the bottom centre Sley is in the mid point between the front and back centre
At 210°:
Shuttle enters the warp in over pick loom Shuttle leaves the box in under pick loom
At 240°:
Shed begins to close Changing period of healds begins in tappet Shuttle enters the warp in under pick loom
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Compare between Tappet, Dobby and Jacquard shedding:
1. 2. 3. 4.
Tappet shedding Design capacitysimplest Cost of loom- most costly Loom speed- very high Maximum no. of heald shafts- 14
5. Tappet is placed generally below the loom 6. Cost of productionlowest 7. For different designs different tappets are fitted to bottom shaft
8. Production is more than the dobby
Dobby shedding 1. Medium i.e. complex
2. Less
Jacquard shedding 1. Elaborate i.e. very complex 2. Very less
3. Medium to high
3. Slow
4. Theoretically it can controls maximum 48 heald frames. In wool, practically 36 heald In cotton, 24 5. Above the loom
4. Theoretically it can control any no. of warp thread individually
5. Above the loom
6. Lower
6. Low
7. For different designs, different design of pegging legs are placed on cylinder/pattern drum 8. Less production
7. For different design, different designed pinched cards are places on cylinder
8. Less production
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