COMMISSIONING PROCEDURE 1.1 Belt Starting
This is the most important aspect of belt conveyor erection. As a matter of fact, a good erection eliminates to a great extent the difficulty in belt training while a bad erection may cause untoward problems in training the belt. 1.2
General Checks before Operating a Conveyor
(a) Check the conveyor structure is perfectly straight & correctly levelled. (b) Check the correct direction of rubber lagging-groove (Herring bone groove) on drive pulleys. (c) Check that all the pulleys are correctly mounted, such that they are in level and with their axes perpendicular to the centre of conveyor belt. (d) Ensure that all the carrying & return idler sets are correctly mounted with their axes perpendicular to the centre line & that all rollers are rotating freely. (e) Ensure that self-aligning idle sets, when fitted, are pivoting freely. (f) In the case of gravity take up ensure that take up assembly is square & free to move. (g) In the case of screw take up, ensures that take up is adjusted initially to remove under slack from belt & that equal tension is applied on each side, such that pulley is correctly perpendicular to the line of belt. (h) Ensure all the parts of conveyors are greased and /or oiled where necessary. (i) Ensure the skirt board seal strips are correctly fitted and adjusted. (j) Check along length of the conveyor & ensure that there are no items left lying about which could obstruct & cause damage to
moving equipment and especially between the chutes, skirt, scraper etc. (k) Ensure that the transmission machinery like motor, gear boxes, couplings, etc.have been properly aligned. (l) Check the direction of rotation before locking the backstop & tighten the backstop after confirming the direction of rotation of the belt run. (m) Check the tension of the belt, which should be sufficient at the start-up. (n) Ensure the gear box/ geared motor is filled with recommended grade of oil up to the correct level. Please see the manufacturer's catalogue for the direction before first fill. (o) Remove coupling bolts between motor & gearbox & ensure that the direction of rotation of the motor is correct. (p) Now the conveyor is ready for empty run and the following procedure may be adopted for first trail run. 1.Start the motor foe 3/4 seconds & stop. 2.Check the belt sway. 3.Where the belt has swayed adjust the idlers. 4.Check for any other interruption. 5.Start conveyor again for 30-40 seconds & if minor corrections are required adjust the idlers. 6.Now start the conveyor for 1 to 2 minutes & if there is no other problem continue this operation for 15 minutes. 7.After stopping the conveyor, check once again for any problem. 8.Check spliced joint for edge opening if any. 9.Check any mark on the belt or wear on the belt surface.
(q) Run the belt continuously on no load for 8 hrs. (r) During this run, make readings for voltmeter, wattmeter & ammeter for empty belt. These readings should be recorded for future reference. This information will be valuable in case of problem at a later date.
(s) After 8 hrs. run, carry out a thorough check of all fasteners of tightness. Check for excessive heating of bearings, Gearbox & motor. Check for oil leakage from Gearbox. (t) Rectify/repair all the defects found during no-load test. (u) Checks chute for trajectory of product flow & correct the flow as required with the help of Deflector plate. (v) Now the conveyor is ready for continuous operation load. (w) Start loading the belt with quarter load. Ensure that the materials are fed on the belt without excessive impact and at uniform feed rate. Check whether loading takes place at centre. If it is out of centre too much, correct the feed chute. Gradually increase the load to half the rated capacity. Check the motor current. (x) Check belt run away from its centre with loading. (y) Ensure that the material spilled during loading is not allowed to accumulate around the idlers, pulleys & other related components. (z) Run the conveyor in this condition, continuously for 8 hrs. (aa) During the above period, check proper loading on the belt & discharge( clogging of chute) (bb) Stop the conveyor & recheck for tightness of all fasteners. (cc) If everything is okay, the conveyor can be run continuously by gradually increasing the load to full load (dd) The voltmeter, ammeter & wattmeter reading should be taken every day. Proper records should be maintained. (ee) For a few days, a continuous check shall be make on all fasteners for tightness, heating of bearings, wear & tear of components oil leakage. 1.3
Belt tracking
When belt conveyors are installed within accepted conventional alignment limits with idlers & pulley parallel, belt spliced square & true and material loaded centrally the belt will track correctly without the need of special training & tracking devices.
In practice, these ideal conditions are seldom achieved and corrective device and accessories are required to maintain satisfactory training. A number of more common causes of poor belt tracking are set out below. Corrective action necessary for each of these is readily ascertained when the particulars cause (causes) is identified. 1. Misplaced or twisted components in the conveyor structure. 2. Driving & idler pulleys are not normal to the conveyor centre line & not parallel to each other. 3. Carrying & return idlers are not set normal to the conveyor belt centre line( This point is of particular concern for reversible belt conveyors) 4. Out-of-round or 'stiff' idler rollers giving belt contact forces asymmetrical to the belt centre line. 5. Poor belt splicing giving a transverse bend to the centre line at the splice. 6. Asymmetrical loading of burden. 7. Pulley diameters are not symmetrical about the centre line of the belt. 8. Build up of material on pulleys, idler and/ or belt. 9. Transverse forces applied to the belt such items as angled belt scrapers. 10. Excessive tensioning of belt which is precluding all idlers from assisting in belt 'steering'. 11. Under-tensioning of belt which precludes pulleys from controlling drift. 12. Belt take-ups not taking up slack effectively during running & acceleration. 13. Belt take-ups not travelling in line with belt centre line. 14. Belt take-ups giving different forces on opposite sides of the belt this can occur during take-up motion & is prevalent with hydraulic take-ups. 15. Jammed idlers or extraneous jammed articles along the conveyor.
A newly installed belt must be lined up to run on centre of pulleys and idlers. The tail end, take up pulleys and all idlers should be squared up so that they are at 90 degree. with the centre line of the conveyor. Belt can be aligned properly, only by adjusting the carrying and return idlers. Self-aligning rollers are supplied with an actuating swivel base, which will be bolted to the bottom side of the idler frame and will tilt the idler in proper direction to centralise the belt (fig.-1). Adjust idlers to one side
Tail Pulley.
Roller
Head
pulley. Belt
1.4
Fig.-1 : BELT TRAINING. Important Tips
(a)When starting a new belt for the first time, run it slowly and intermittently and check the entire length to ensure that it is not running off at any point to an extent that it will damage the belt. (b) Do not attempt to train the belt by adjusting head end pulley. (c)The return run should be checked first for belt alignment. When a belt runs off a return roller, the edge may get damaged. To train the return belt, start at the head end. In general the adjustments are made 3 to 4 meters behind the point where the belt runs off.
(d) All troughing idlers are provided with slotted holes for the hold down bolts to permit the shifting of the ends for the belt alignment. To adjust the idlers loosen the hanger bracket bolts slightly and move the idler slightly forward or backward. The belt will shift to the side where it touches the roller first. (e)For training the belt on carrying side start with the tail pulley & follow the procedure as explained above. (f) Do not try to collect belt alignment by extreme shifting of one idler but rather by slightly changing the number of idlers. Proper alignment of idlers at the head end will train a belt to run on the centre of the head pulley. (g) If the belt does not run centrally after adjustment of idlers and take up screws, check to ensure that the belt lacing is square. (h) Conveyor take up should be adjusted to provide enough tension for the belt to operate under load without slipping. Correct belt alignment must be maintained while tension adjustments are made. When correctly aligned and adjusted, the belt will be centred on the tail pulley while the conveyor is operated. The amount of tension is correct when the belt sags slightly between return idlers. (i) Do not apply excessive tension because it results in damaging the belt & bearing. After the belt has been run on, tension should be checked at frequent intervals and take up adjusted when necessary. 1.5
Loading of Conveyor Belt
To ensure maximum life, the following conditions for loading of the conveyor should be met. The material should be fed in the same direction in which the belt travels. Also material should be loaded at an angle, moving approximately at the same speed as of the belt, whereby the cover wear is minimised. Conversely, if the material were loaded at an angle of 90 degree traversely to the direction of the belt travel, the wear of rubber covers would be maximum. Also if the material has no velocity in the direction of the belt travel or has negative cove wear would be maximum.
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Free fall of material on the belt should not be more than 500mm. A properly designed loading chute & closely spaced impact idlers, also reduced free fall, minimise cover belt. Loading area of the belt should be horizontal or should have a slope of not more than 8 degree. If the slope were more than 8-degree cover wear would be high. For very abrasive materials, grizzly screen should be used so that fine are placed on the belt first and provide a bed for larger lump. Cover wear for general purpose belt is minimum i.e. where the material conveyed does not react chemically with the belt & has a maximum temperature of 70 degree. C. For reactive material or hot material, special covers are provided but their wear resistance is relatively lower. By means of skirt board, spillage on the return side of the belt may be prevented.
