Care of Belting Rev 01
Care of Belting Rev 01
Care of Belting Rev 01
Section 1 Care of Belting Ozone and Ultra Violet Light Heat Oil and Solvents Abuse Handling of Conveyor Belt Rolls Correct Storage Procedures Section 2 Protection of Conveyor Belting Section 3 Conveyor Belt Training Section 4 Conveyor belt service difficulties Section 5 Chutes
Heat
Rubber compounds are degraded by heat. Some polymers withstand the effects of heat better than others but all are degraded. Additives can be added to the cover rubber of conveyor belts to enable them to perform under conditions of prolonged high temperature. These are termed 'heat resistant' conveyor belts. Conveyor belting should not be stored in a hot environment as it will seriously effect the life expectancy. Ideal storage temperature for conveyor belting is between 10C and 25C.
Abuse
One of the most common enemies of the conveyor belt is abuse of one kind or another. Abuse arises either through ignorance or the desire for ever increasing achievement. The consequences of abuse are vast. Between 80% and 90% of all belts are replaced due to physical damage before they have worn out.
Section 2
Protection of Conveyor Belting
The conveyor structure should be assembled so that the belt runs true on both the carry and return strands. The loading of the material onto the belt should not affect the true running. Clearances between the belt and structure should be sufficient to prevent fouling at all points. International standards for straight running of belting allow a movement of 5% of the belt width or 75mm whichever is the smaller, a larger clearance is required in the conveyor structure. Conveyor structure should have sufficient clearance to accommodate belt movement. Movement of the structure will require that regular inspection and adjustment is carried out to ensure that the belt always runs true and free. Long conveyors with high installed power are prone to extensive damage when foreign objects become jammed between belt and structure. Many belts have been ripped from end to end in such circumstances. Long conveyors should therefore be provided maximum protection.
Section 3
Conveyor Belt Training
The important factor for continuous central belt training is stable alignment of the conveyor Alignment
1. The conveyor structure must be true. 2. All pulleys and idlers must be centred on the centre line 3. Pulleys must be perpendicular to the centre line. 4. Idler bases must be perpendicular to the centre line. 5. All idler bases or brackets must be horizontal. 6. Gravity take-ups and trippers must move centrally on the centre line and the moving pulleys must remain parallel to the other pulleys on the system. 7. All idler rolls and non-driven pulleys must rotate freely. 8. There must be no build up of material on idler rolls or pulleys. 9. The belt joins must all be true. 10. The belt must not be so stiff as to prevent troughing when empty. 11. The load must be placed centrally on the belt. If the basic alignment factors are thoroughly checked there should be no difficulty training the belt.
A horizontal troughed idler set causes equal and opposite resultant forces acting outwards.
Non horizontal idler set causes unequal resultant forces. A greater resultant force acts on the higher side.
3. 4.
2. 3. 4.
Too much lateral movement of take-up carriage Tension unevenly applied by take-up
Wind influences belt tracking Material loaded off centre Belt bowed Mis-aligned splice
Build up on pulleys
Section 4
Conveyor belt service difficulties
Typical service difficulties that can be experienced with conveyor belts are tabled below. This table lists possible causes of the difficulty in order of precedence with the most likely cause having the highest precedence. Diagnosis criteria are given to help determine which cause is responsible for the particular difficulty.
Difficulty
Worn Covers Top Cover wears out quicker than predicted by the Dunlop belt wear formula.
Causes
Diagnosis
Remedy
Relatively narrow strips of wear occur along line of skirt seals in contact with the belt.
Replace worn skirtboard sealing material. Install wider skirtboard sealing material or more efficient skirtboard seals so that pressure can be reduced for the same sealing efficiency. Increase gap between skirtboard and belt surface. Increase tension applied by the take-up to reduce sag between the idlers at the loading point. Reduce the incline angle at the loading point. Split the material feed so that fine material is fed onto the conveyor first.
Wear is concentrated in the centre of the belt. Material accumulates at the loading point. Little or no material velocity in the direction of belt travel. Cover cut and gouged at line of skirt- board contact with belt.
Alter gap between skirtboards and belt to prevent material entrapment. Increase inter-skirt board width. Install garland impact idlers at the loading point. Install wider skirtboard sealing material or more efficient skirtboard seals. Increase the ground or floor clearance of the conveyor. Most commonly the problem is associated with a low ground clearance at the tail pulley. Replace worn skirtboard sealing material. Increase troughing angle at the loading points. Extend the length of the skirtboards. Improve house keeping. Install blocked chute detector with alarm condition and belt trip. Increase clearances in the discharge chute. If the conveyor discharges to another conveyor install interlock between the two. Install efficient belt scrapers at all discharge points. Replace worn belt scraper blades. Adjust belt scraper to improve cleaning efficiency. Adjust belt scraper to meet the manufacturer's specifications. Replace worn scraper blades. Clean accumulated material from the belt scraper blades and blade mounting bracket. Replace faulty torsion mountings. Replace seized idler rolls. Replace or repair idler brackets or frames that cause idler rolls to jamb. Locate idler rolls correctly in the idler brackets or frames. Align return idlers as described in section 3. Ratio of top to bottom cover thickness should not be greater than 3 to 1.
Wear occurs across the full width of the belt. Longitudinal cuts and gouges into the cover. Very often more severe wear and damage to cover occurs nearer belt edges. Material accumulated under the conveyor to the extent that it makes contact with the return belt. Longitudinal cuts and gouges across the full belt width. Cover torn from the belt carcass.
Excessive material carry back on the return side. Poorly adjusted belt scraper or belt scraper incorrectly installed.
Material build up on return idlers and pulleys in contact with the carry side of the belt. Piles of material accumulate under return idlers. Sinusoidal wear pattern. Width of wear pattern related to the width of the scraper blades.
Longitudinal wear coinciding with position of faulty idler rolls. In severe cases the idler shell is worn through resulting in cutting of the cover. Even wear across the width of the belt. Poor tracking of the return belt. Belt curls up at edges. Top cover wears near edge because of concentration of weight at the edge.
Badly aligned return idlers. Excessively high ratio between thickness of top\and bottom covers.
Difficulty
Bottom cover worn.
Causes
Material build up on deck plates.
Diagnosis
Wear in centre third of belt width. Longitudinal cuts and gouges in the cover. Material spillage at loading point.
Remedy
Replace worn skirtboard sealing material. Increase troughing angle at the loading points. Extend the length of the skirtboards. Increase tension applied by the take-up to reduce sag between carry idlers at the loading point. Improve house keeping. Install vee return scrapers to prevent material carry back into pulleys. Adjust scraper blades of existing vee return scrapers. Replace worn vee return scraper blades. Replace seized idler rolls. Remove material that may cause idler rolls to jamb. Replace or repair idler frames that cause idler rolls to jamb. Locate idler rolls correctly in the idler frames. Lag drive pulleys or replace worn drive pulley lagging. Use grooved pulley lagging if water is present. Increase force applied by the take-up. Ensure that the take-up pulley moves freely along its travel length. Align idlers and pulleys as described in Section 3. Replace the affected belt join. Correct the alignment of the conveyor structure. Alter the load chute angle. Increase the vertical velocity of material through the load chute thereby increasing the effective angle of impingement.
Material trapped between belt and a pulley in con- tact with the bottom cover. Seized or jammed carry idler rolls.
Punctures into the cover. Wear across the full belt width. Excessive noise in vicinity of pulley.
Wear coincides with position of the seized or jammed idler rolls. In severe cases the idler shell is worn through resulting in cutting of the bottom cover. Cover worn across the full belt width. Very often this is an intermittent problem resulting in intermittent wear along the belt length. Belt fouls the conveyor support structure. Belt in close proximity to a join, fouls the conveyor support structure. Belt fouls the conveyor structure at the position of misaligned structure. Effective angle of impingement with the belt cover between 18 and 28 . Material cuts the cover as it strikes the belt. Many random cuts in the centre third of the belt width. Belt surface takes on an appearance similar to a well used chopping board. Longitudinal cuts in top cover along line of skirtboard contact with the belt. Seized or jammed idler rolls. Cuts in cover coincide with seized idler rolls.
Misaligned idlers or pulleys. Misaligned belt join. Misaligned belt structure. Material impinging with belt at a critical angle.
Cut Cover.
Inadequate clearance between skirtboard and belt. Worn idler roll shell.
Increase gap between skirtboard and the belt surface. Replace worn idler rolls. Remove material causing idler roll jambs. Replace or repair idler brackets which have poor clearance between idler roll and bracket. Alter position of idlers at the load point in relation to the material flow path. Increase spacing of idlers at the load point. Alter arrangement at the load point. Increase gap between skirtboards and impact bars. Skirtboard gap must increase in direction of belt travel. Alter angle of material feed to reduce velocity difference between belt and material.
Large material lump size. Material flow path directly onto an idler roll. Insufficient idler spacing to accommodate material lump size at the loading point. Impact bars installed at load point having insufficient clearance to prevent entrapment of material. Large material lump size. Large velocity difference between belt and material being loaded.
Difficulty
Cover swelling.
Causes
Oil, grease or solvent contamination. Belt fouls with belt structure or chutes. Belt slip on a pulley.
Diagnosis
Soft cover in the area of the swelling. Belt curl induced by the cover swelling. Relatively high belt speed. Distinctive smell of 'burning rubber'. Most commonly on drive pulley during starting but can also result from a jammed pulley. Loud screeching noise. Intermittent areas of soft cover on surface in contact with pulley. Top cover smeared with soft, sticky rubber. Often smear occurs along width coinciding with width of single scraper blade. Embrittlement of the cover rubber. Non heat resistant cover compound or material temperature exceeds temperature rating of SBR heat resistant cover compound. Fine surface cracks. Fine surface cracks. Fine surface cracks. Belt left standing in the same position for long periods.
Remedy
Remove the source of contamination or change belt to a type that is not affected by the contaminant. Provide sufficient clearance between the belt and conveyor structure. Rectify jammed pulley. Increase take-up force to prevent belt slip during starting.
Badly adjusted belt scraper. Pressure between scraper blade and belt too high. Cracks in the belt cover. Material conveyed is excessively hot.
Adjust scraper blade pressure. Replace blades that have worn. Ensure even contact pressure across the belt width. Change belt specification to one that is more appropriate for the temperature.
Protect the belt from direct sunlight. Screen the belt against exposure to ultraviolet light. During storage of the belt keep changing its position and rotate the roll at regular intervals. While on the conveyor the belt should be turned regularly. Reduce vertical fall in the loading chute or break the fall with drop boxes in the load chute. Alter position of idlers in the loading area. Increase thickness of top cover. Reduce number of plies in the belt carcass or increase the belt class. Increase the cord diameter if the belt has a steel cord carcass. Install or adjust vee return plow to prevent material carry back.
Cuts and gouges in top cover. Material flow path directly onto idler roll or impact bar. Materials loaded onto the belt have a high vertical velocity component.
Most commonly associated with the tail pulley and material spillage at the load point. High modulus belt carcass. Punctures in the cover which is in contact with the offending pulley face. Carcass breaks at the edges. Rapid wear of pulley lagging where the belt edges contact the pulley.
Reduce the troughing angle of the idlers in the transition zone. Increase the distance between terminal pulley and the closest troughing idler. Remove obstructions to the belt path. Correct belt alignment.
Ply separation
Ply se paration confine d to belt edges. Cover separated from the carcass at the belt edges. Edges badly worn. In most i nstances there will be sections where the covers have been torn from the carcass. Ply separation coincides with the idler junctions. Ply separation coincides with the idler junctions.
Vertical alignment of idlers varies excessively. Spacing of idlers in convex curve too large.
Profile idlers to within a 3 mm vertical alignment tolerance. Check that all idler sets are in place. Decrease idler spacing in the convex curve so that maximum change of angle at any particular idler is within specification. Replace belt with a construction that provides adequate load support. This is normally achieved by increasing the number of plies or increasing the belt class.
Difficulty
Causes
Pulley diameter smaller than required minimum.
Diagnosis
Ply separation across full width of belt. Belt splices fail regularly.
Remedy
Replace all pulleys that are smaller than the recommended minimum. Reduce the number of plies to suit the installed pulley diameters checking first that the replacement belt will provide adequate load support. Remove source of contamination. Correct alignment of conveyor structure. Replace the belt join.
Rubber soft and swollen in the vicinity of ply separation. All sections of the belt run off at the misaligned section of the conveyor. Belt runs off in close vicinity of the join at all points of the conveyor structure. Belt runs off in the vicinity of the pulley. One section of belt runs off at all points of the conveyor.
Belt mis-tracking
Build up on pulleys.
Clean the pulley face. Soft rubber pulley lagging (40 shore hardness) will assist in prevention of build up on pulleys. Avoid storing belts in telescoped condition. In some instances the bowed section of belt can be straightened by applying additional force in the take-up. Beware of exceeding the pulley shaft and bearing load capabilities.
Belt bowed.
Section 5
70
Chutes
The primary purpose of chutes are to: 1. Deposit the material centrally and evenly on the receiving conveyor at a velocity approaching the belt velocity. 2. Receive the material from the discharge point of a conveyor and direct it to the required location. Well designed chutes meet the following requirements: 1. All chute openings are large enough to provide unrestricted flow of the material. 2. Material degradation is minimised 3. The discharge chute collects all the material including that which is removed by the belt scraper. 4. Conveyor loading chutes direct the material at an angle and velocity which minimises belt wear.
60
DUNLOP BELTING PRODUCTS
50 Rate of Wear 40 30 20 10 0
Angle of impingement of the material with the belt cover also effects the rate of wear of the cover. A critical angle occurs at about 22 where the wear rate is up to 100 times greater than an angle of 0 or 90 .
Rate of Wear
20 0 0 10 20 30 40 50 60 70 80 90 Angle of Impingement