CONVEYOR MAINTENANCE & BELT REPAIRS

Transcription

1 CONVEYOR MAINTENANCE & BELT REPAIRS INTRODUCTION The topic for this presentation is Conveyor Maintenance and Belt Repairs. Although belt repairs could be included in the general conveyor maintenance section, the subject is sufficiently specialized to warrant its own section. The Conveyor Maintenance section lists the various components of the unloading system that require ongoing maintenance in order to maximize your unloading efficiency. All conveyor components and the cargo being unloaded must work in harmony to allow for quick, trouble-free unloading. If the equipment is permitted to deteriorate, you should expect problems and costly delays. The key to effective maintenance is the inspection frequency. Inspections provide information on what components need maintenance repairs. Most maintenance work should be done as soon as the need is detected. This will help to avoid major problems. Proper maintenance, both during the shipping season and at lay-up, will allow the vessel to move more tons of cargo per year and make life easier for both the crew and the fleet engineers. Belt Repairs are needed as a part of the conveyor maintenance program and in response to situations when the unexpected happens. The smaller repairs, such as filling cover gouges and re-bonding frayed belt edges, can be done by either your crews or by an outside service company. Minor belt damage should be repaired as quickly as possible since it could develop into a major problem with surprising speed. Emergency tear repairs can be done by your crews as a temporary fix to permit the completion of the unload. Major repairs of holes, major gouges, and tears should be done by the hot vulcanized method. Normally, this requires the services of an outside service company. With major repairs, time is of the essence. The longer major damage is allowed to go without repair, the greater the chance that a catastrophic failure will occur. The information provided in these two sections is meant as a guideline only. Each vessel has unique conditions which warrant individual analysis for effective maintenance. Your conveyormen, who work with the systems on a daily basis, are the best source of information on their systems. They have learned what is most effective for their conveyors under the everchanging conditions presented by cargo and weather variations. They also know what they are capable of in providing ongoing maintenance. It will not do the conveyor system any good if a maintenance program is instituted that can not be accomplished by the personnel involved. As managers, every chief engineer and fleet engineer should develop a maintenance program that is realistic for the unloading system and personnel available. You can help your conveyormen to keep your systems running smoothly by providing support in manpower and in information on new develops in conveyor technology. Page 1 of 14

2 CONVEYOR MAINTENANCE The various factors that affect the efficient unloading of cargo via the conveyor system include the weather, the cargo itself, the hold, and the conveyor system. The weather can create problems with temperature, rain, ice, and wind interfering with the unload. These variable mainly affect the boom conveyor's performance. Adverse weather conditions can create belt tracking problems, freeze the belt to the idlers, cause lower unload speeds, or prevent the unload altogether if unloading into a hopper. Although certain steps can be taken to minimize the impact of the weather, we do not have a means of controlling it. Ideally, the cargo is dry, free flowing, of uniform size, of uniform shape, and free of any foreign material that can cause problems with the unload. All too frequently, this is not the case and the crew must react to troublesome materials. As with the weather, the ship's crew can not completely control what is placed in the cargo hold. This is unfortunate as oversized material and foreign material, such as lumber and steel, can do substantial damage to the unloading system. This forces the crew to be vigilant while unloading and to stop the system whenever a potentially system damaging item tries to pass through a gate. The cargo hold allows for the proper flow of whatever material it was originally designed for. For those vessels which carry multiple cargos, some materials may not exit the hold easily. If this happens, extraordinary measures may be required. Under normal conditions, the major maintenance considerations for the cargo hold include replacement of the cargo hold cover seals as they wear out; repair of hold wear areas (for unlined holds); replacement of cargo hold lining materials (for lined, or partially lined, holds); the repair or replacement of worn gate components; and the maintenance of the gate operating mechanism. The maintenance of the wear components should be done at least on an annual basis, or more frequently if it is noted that certain areas wear quickly. This maintenance should include an inspection (to see what is happening), an inspection report (to advise the chief engineer and the fleet engineer so that a decision can be made as to what steps should be taken), and repair or replacement of the worn components as directed by the chief engineer and fleet engineer. The maintenance of the gate operating mechanism should be done on a frequent scheduled basis that is appropriate for the vessel. This could be prior to every unload or every fifth unload - your experience will dictate whatever is appropriate. Typical maintenance steps for the gate operating mechanisms include the inspection and lubrication of moving components, and the inspection and repair of the hydraulic system for fluid levels and leaks. The conveyor system is designed to move the cargo from the gates to the hopper or pile on shore. Maintenance of the conveyor system should be done on a regular basis to ensure that the conveyor system is kept operational and efficient. As there are many components to the Page 2 of 14

3 conveyor system, maintenance can be a time consuming activity. The following list provides a description of the various conveyor components, describes their function, details what could happen if the component fails, and suggests maintenance action steps. Loading chutes The loading chutes for most conveyors aboard vessels include the cargo hold with its gates and any transfer chutes in the unloading system. The purpose of these chutes is to receive the cargo and to place it on the receiving conveyor belt in a controlled manner. This control includes both the rate of material flow and the location of the material on the belt. As the flow rate of transfer chutes is controlled by the feed rate of preceding conveyors, these chutes provide cargo direction (placement) only. The important considerations for the gates are that they must be capable of controlling the flow speed of the cargo and that they must deposit the cargo centrally on the belt. If the gates are not functioning properly, the cargo being deposited on the hold belt(s) can be either too little or too much. If too little, the unload efficiency is diminished. If too much, spillage, belt overloading, idler damage, or belt failure could result. If the gate lips are worn or damaged, the cargo could be deposited on the belt in the wrong area. This could cause the belt to mis-track with potential cargo spillage, belt edge wear, side guide roller wear, or structural damage (as the belt "saws" through the conveyor's supports). The cargo hold and gates should be maintained as described previously. The important considerations for the transfer chutes are that they must be capable of accepting the cargo from the previous belt and then deposit it on the next belt in a controlled manner. Normally, this means that the cargo is to be fed to the center of the belt, in the direction of the belt's movement, and with as little vertical drop force as possible. Typical components of the chute include the metal housing, impact pads, and deflection plates. The chute housing is what contains and determines the general flow pattern of the material. The impact pads, which could be flat or profiled act to protect the chute from wear and to absorb energy from the material so that it does not damage the receiving belt. The deflection plates act to direct the material flow to the desired point on the receiving belt. If the deflection plates wear out, or become misaligned, the material could be placed on the receiving belt incorrectly. This could result in spillage or mis-tracking of the receiving belt. If the impact pads or chute housing wear out, spillage or material mis-direction are likely to occur. As the impact pads wear, the material approaches the deflection plates at a different angle. If they wear out completely, the chute housing is left unprotected and can wear out quickly. If the chute housing wears out in the impact area, the material would go through the chute instead of being redirected by it. This would cause a spillage problem. To avoid these potential problems, maintenance of the chutes is required. This involves regular inspection of the chute and replacement of the wear components as required. The frequency of inspection should be once per unload. Page 3 of 14

4 Drive System The drive system, which includes the motors, the gear reducers, shafts, and all control mechanisms, is what provides the motive power to move the conveyor belt. As I am not conversant with the maintenance requirements of these systems, I can not elaborate on their special maintenance needs. Drive Pulley The drive pulley is the pulley which transfers the energy of the drive system to the conveyor belt. This is accomplished by means of friction between the face of the pulley and the bottom cover of the belt. The efficiency of this power transference is determined by the degree of wrap of the belt around the pulley, by the coefficient of friction between the belt surface and the pulley surface, and by good contact between the belt and the pulley face. Frequently a drive snub pulley is used to increase the wrap, or amount of belt to pulley contact. Also, it is common to use lagging to increase the coefficient of friction. Lagging which has a groove pattern is also used to channel water and dirt away from the belt/pulley interface to improve power transference and to maintain tracking. The tightness of the belt against the drive pulley is normally controlled by the take-up system. As most drive pulleys are lagged, the maintenance concerns are with the lagging, the pillow block bearings, and with the structural integrity of the pulley. If slippage develops between the drive pulley and the belt, it is possible that mis-tracking of the belt will result. This could cause damage to the edges of the belt and the belt could "saw" through the conveyor support structure. In the more extreme cases of slippage, the belt could stop moving while the pulley continues to turn. This would result in a frictional heat build-up that could destroy the belt and pulley lagging. A worst case scenario would be the separation of the belt. The slippage can be caused by overloading of the belt prior to start-up, which is an operational - not a maintenance issue; by the loss of take-up pressure (discussed in the take-up system section); or by the deterioration of either the lagging surface or belt bottom cover surface. If the bearings fail, it is possible that they would seize and that either the pulley assembly or the drive system would sustain major damage. If the structural integrity of the pulley were to fail, it is likely that the pulley would be destroyed and that the belt would be damaged. Maintenance actions include the inspection of the pulley seams and taper locks on a regular basis; inspection of the pillow blokes during each unload; and inspection of the pulley lagging before each unload. If the pulley shows signs of structural weakening, corrective action should be taken immediately. If the bearings are overheating or making noise, they should be monitored during the unload and repaired or replaced as soon as possible. If the lagging is wearing, it should be monitored and replaced at a convenient time (normally during lay-up). If the lagging is Page 4 of 14

5 glazed, it should be monitored and have its surface buffed at a convenient time. If the grooves in the lagging are plugged with contaminants, it should be cleaned as soon as possible. If the grooves in the lagging are not capable of removing water, they should be widened or deepened, depending on the amount of rubber available in the lagging. If the bottom cover of the belt is glazed or hardened, slippage can occur. The bottom cover should be either roughened or the belt should be replaced. Whenever there is a problem with either the lagging surface or the belt's bottom cover, extra care should be taken during each start-up to help prevent slippage between the belt and the drive pulley. Take-up System The conveyor's take-up system provides the belt tension required to allow the belt to be moved by the drive system when there is no load on the belt. The take-up system utilizes a take-up pulley which is either fixed in place, as with screw take-ups, or allowed to float with a predetermined holding or tensioning force, as with hydraulic and gravity take-ups. Excessive take-up force is detrimental to both belt training and the pulleys. Insufficient take-up force will result in the belt not having enough contact with the drive pulley to move the belt. This could result in damage to both the belt and the drive pulley's lagging. The maintenance actions required for the take-up system include the inspection and repair, as needed, of the take-up force mechanism (screw threads, gravity box, or hydraulic system). These should be inspected on a periodic basis for screw and gravity systems, and on a frequent basis for hydraulic systems. Also required is the periodic inspection and repair, as needed, of the take-up pulley guide rails and rollers (or wheels). Finally, the take-up pulley itself needs to be inspected regularly for pulley structural integrity, for alignment, and for pillow block bearings. As a number of take-up pulleys are now lagged to both extend the life of the pulley and to improve belt training, maintenance inspections of the lagging should also be done frequently. If the lagging is showing signs of loosening or wear, corrective action should be taken. This includes rebonding of loose pulley lagging seams or edges and relagging. Pulleys The various pulleys, other than the drive and take-up system, are used to redirect the belt's movement on the conveyor. As the pulleys are forcing the belt to go through an arc, they must be of sufficient diameter to permit the belt to bend without doing damage to the belt's carcass (fabric strength component). Frequently, these pulleys have lagging on them which performs two functions. The lagging extends the life of the pulley by eliminating wear of its metal shell and the lagging also helps prevent belt mistraining by channeling dirt and water away from the belt/pulley interface. Page 5 of 14

6 Maintenance actions include the inspection of the pulley seams and taper locks on a regular basis; inspection of the pillow blokes during each unload; and inspection of the pulley lagging before each unload. If the pulley shows signs of structural weakening, corrective action should be taken immediately. If the bearings are overheating or making noise, they should be monitored during the unload and repaired or replaced as soon as possible. If the lagging is wearing, it should be monitored and replaced at a convenient time (normally during lay-up). If the grooves in the lagging are plugged with contaminants, it should be cleaned as soon as possible. If the grooves in the lagging are not capable of removing water, they should be widened or deepened, depending on the amount of rubber available in the lagging. A broken, or frozen, pulley is capable of doing damage to both the conveyor system and the belt. Worn lagging or metal shell can create severe belt training problems. Idlers (Carry & Return) The purpose of the carry idlers is to support the belt and the bulk material along the conveyor. The carry idlers are also used to shape the belt to provide enhanced material holding properties. The purpose of the return idlers is to support the belt along the return run of the conveyor. As the belt is in motion, the idlers must rotate. If the bearings in an idler should seize, the idler would not be capable of moving and it would be strapped by the belt. This would result in a stationary roller which has a sharp edge which could cut the belt. If an idler gets worn at one, or more, isolated point (as is typical with return idlers), the shell of the idler could separate from the shaft and bearings. This would result in a loss of support or a potential cutting edge against the belt. If the seals of an idler permit grease to drop on the belt surface, the rubber will be attacked and it will separate from the fabric. This would result in the loss of protection that the rubber is meant to provide the carcass. It could also result in belt slippage at the drive pulley. Maintenance actions include scheduled lubrication of the idler bearings, with care being taken not to over lubricate, inspection of the idlers to confirm that they turn freely, and inspection of the idlers for wear. The inspections should take place during each unload. If an idler does not turn freely, it should be repaired or replaced. If an idler shows signs of wear, it should be monitored or replaced. If there is evidence of over lubrication, in the form of grease on the belt, the idler should be repaired or replaced and the lubrication technique should be altered to prevent blown seals. Impact Idlers & Impact Slider Beds Impact idlers and slider beds perform the same roll as regular idlers plus provide a cushioning function at load points. This energy absorbing function helps to prevent damage to the belt when the cargo is being dropped on it. Impact idlers have the same maintenance concerns of regular idlers. Impact slider beds, however, do not rotate. Therefore, lubrication and freedom of Page 6 of 14

7 movement are not concerns. Impact slider beds should be inspected for wear of their UHMW pe (Ultra High Molecular Weight polyethylene) runners to ensure that they are not overly worn. These should be replaced as they wear. Side Guide Rollers Side guide rollers are vertical, or angled, rollers that engage the belt edge if the belt should mistrain. Their purpose is to prevent the belt from cutting into the conveyor's structure or from running off the system. If a side guide roller should freeze of wear out, it could do damage to the belt as well as failing to perform its function. The maintenance steps for side guide rollers are the same as for idlers. Training Idlers The purpose of a training idler is to keep belts which tend not to run straight within the conveyor boundaries. The training idler is useful in countering belt or structural deficiencies which are still within commercial tolerances. Training idlers are also effective tools to compensate for running differences encountered from one cargo to another. Some training idlers are fixed while others have pivot points that allow the it to react to changes in the belt's movement. The maintenance steps for training idlers are the same as those used for regular idlers. Belt The conveyor belt's purpose is to support the cargo from its loading point on the belt to the discharge point. To do this, the belt must be of sufficient width and strength for the design capacity of the system. As the belt must navigate the conveyor system continuously, it needs to be endless. The three components of the conveyor belt are its carcass, its top cover, and its bottom cover. The carcass provides the belt's strength and load carrying capability. The top cover provides cut, gouge, wear, and impact protection for the carcass. The bottom cover provides wear protection for the carcass and provides a friction surface against the drive pulley to improve belt motion. In those belts which have multiple fabric plies in the carcass, a rubber layer is used between each layer of fabric. This rubber permits the plies to move around pulleys without separating and also provides additional impact resistance. If the belt should fail, the cargo could not be moved to its desired location. Also, it is likely that any cargo on the belt at the time of failure would spill. In a catastrophic belt failure, damage to other conveyor components could result. Page 7 of 14

8 Maintenance actions for the conveyor belt include inspections prior to and during each unload to determine if there is any damage to the belt or its splice. If there is damage, repairs should be made as quickly as possible and the cause of the damage should be eliminated, if possible. Severe damage should be repaired immediately. Inspections that are made during the unload are done to confirm that the belt is training, or tracking, properly and that there is no belt threatening problems with the conveyor system or cargo. If the belt is mistraining, but staying within the system, it should be monitored throughout the unload and corrections should be made when possible. If the belt is seriously mistraining, corrective action should be taken immediately. The type of repair to be used on a belt with damage depends on the nature of the damage. Longitudinal and transverse tears can be temporarily repaired by using mechanical fasteners. This will permit the unload to continue. General belt repair methods are discussed in the "Belt Repair" section of this paper. Skirting Skirting is used to contain the cargo within the belt boundaries. Normally, skirting is used only a the loading point and for a sufficient length to allow the cargo to settle on the belt. In some cases, skirting is used along the whole length of the conveyor's carry side. To be effective, the skirting must make contact with the belt surface. If the skirting wears or otherwise deteriorates it will not prevent cargo from spilling. If the skirting is positioned to tightly, it can do damage to both itself and the belt. Maintenance actions for skirting include an inspection prior to and at the start of each unload to ensure that the skirting is not worn and is positioned properly. If the skirting is partially worn, it should be repositioned to make proper contact. If it is worn, it should be replaced. If the skirting is too tight, it should be repositioned. Do not employ belting as a skirting material as the fabric can trap cargo which will rapidly abrade the conveyor belt. Belt Cleaners Belt cleaners, both wipers and scrapers, are used to clean the surface of the belt after it deposits the cargo. This prevents carry-back of material which could create housekeeping problems or which could foul idlers and pulleys. V -plow and angle plow belt cleaners are used on the bottom cover of the belt to prevent unwanted material from getting between the belt and a pulley. These cleaners direct the material to the side of the system where it can do no harm. A wiper is a Page 8 of 14

9 flexible material, normally rubber, which provides a squeegee like cleaning action. A scraper is a rigid material, normally metal or polyurethane, which scraps foreign material from the belt surface. Other belt cleaning devises include water sprays, air knives, and rotating brushes. If the belt cleaner does not function properly, the belt will not be cleaned. This could be detrimental to the conveyor belt as the carryover material could cause belt mistraining or could damage the carcass or cover of the belt. Belt cleaners that are improperly positioned can also cause damage to the belt by digging into it. Maintenance actions for belt cleaners include an inspection prior to and at the start of each unload to ensure that the cleaner is not worn and is positioned properly. If the cleaner is partially worn, it should be repositioned to make proper contact. If it is worn, it should be replaced. If the cleaner is too tight or misaligned, it should be repositioned. BELT REPAIRS Repairs to the conveyor belt are necessary whenever there is sufficient damage to the belt to interfere with its function or to weaken its resistance to further damage. There are times when the level of damage is too great to warrant repairs and it is more cost effective to replace the belt. In this section, common belt injuries are listed and repairs methods are given. As a general rule, injuries that involve damage to the belt carcass should be repaired by the hot vulcanization method. Injuries not involving damaged fabric can be repaired with cold cure repair materials or by the hot vulcanization method. Emergency temporary repairs of longitudinal and transverse tears in the belt can be done by using mechanical fasteners. Edge Delamination This condition is the separation of the rubber covers and the carcass, or the separation of the carcass plies at the edge of the belt. Typically, this is caused by the belt mistraining and rubbing against side guide rollers. With older belts, this condition can occur when the belt edges run on the return rollers. If this condition is not repaired, the depth of the delamination can increase to the point where the various layers of the belt separate completely, or the frayed belt edge gets caught by a belt cleaner and rips. As with most damage, a repair should be made as soon as possible. Edge delamination can be repaired by rebonding the separated components together. This can be done by cold cure or hot vulcanization methods. Whichever method is used, a key requirement to the repair is the application of pressure while rebonding is being done. The cold cure method utilizes a cement which is compatible with the carcass and the rubber. The hot vulcanization method utilizes fresh cement and rubber. Care must be taken with the hot vulcanization method to avoid the induction of a bow in the belt. Page 9 of 14

10 Gouges Without Fabric Damage This condition is the loss of top or bottom cover rubber in a localized area. A gouge without fabric damage could extend to the first fabric layer. Typically, gouges are caused by pieces of cargo or foreign material being driven into the rubber cover. This can occur at the loading point; at pulleys, if material gets trapped between the pulley and the belt; at belt cleaners, if material gets caught; at chute back stop rubber pads, if material gets caught; and along the skirting, if material gets caught. In some systems, gouging occurs due to turbulence of the cargo as the belt goes through direction changes. Obviously, some cargoes are more likely to cause gouges then others. Gouges can be repaired by using cold cure repair materials or by the hot vulcanization process. Generally, it is more cost effective to use cold cure repair materials. There are many types of cold cure materials available and the user must decide which one is best suited for the application. Gouges With Fabric Damage A gouge with fabric damage is worse than one without as the fabric provides the belt strength. Anything which compromises the integrity of the designed overall strength of the belt should be avoided. These gouges are typically caused by the same actions as what causes those gouges which do not have fabric damage. Gouges which have fabric damage should be repaired using the hot vulcanized method where fresh fabric is applied. As this method is fairly involved and a proper repair for a small gouge which damages one ply of fabric will extend at least 8 inches, many operators choose to rely on the safety factor built into the belts and do cold cure repairs for the smaller gouges. The danger involved with the cold cure repair method is that the damaged ply, or plies, are covered and the injury is forgotten. If enough of these "quick fix" repairs are concentrated in one area, the strength of the belt can be seriously undermined. Regardless of which repair method is used, any repair is better than letting the injured fabric go unprotected. Gouges with fabric damage should be repaired as soon as possible. Holes A hole is an injury which goes completely through the belt. Therefore, every fabric ply has been damaged. Holes are typically caused by cargo or foreign materials being forced through the belt. Another typical cause of a hole is the wearing away of exposed fabric from a gouge that has gone untreated. The strength of the belt, along the hole path, is completely lost. That is, a small hole anywhere along the length of the belt destroys the strength of the belt by whatever the width of the hole is. A one inch wide hole in a belt which is 50 inches wide, reduces the belt's total Page 10 of 14

11 strength by 2%. Also, a hole which is left unrepaired is likely to become larger. Holes should be repaired using the hot vulcanized method where fresh reinforcing fabric is installed. Cold cure repairs utilizing fabric reinforced sheeting can also be used. Holes which are covered over with cold cure repair materials will be protected somewhat, but there is no correction to the loss of strength. Score Lines A score line is a longitudinal groove cut into the cover of the belt, and sometimes into the carcass. These can be caused by the skirting being too tight; by material being trapped under skirting that is too loose; by misaligned belt cleaners; by material being trapped by the cleaners; by material being trapped between the belt cover and a pulley; or by some foreign material which is allowed to stay in hard contact with belt surface. Score lines can be very thin or quite wide - it depends on what caused the wear. Unless the fabric is exposed, score lines are normally not repaired. If the carcass is exposed or damaged, the typical repair method is to use cold cure repair materials. Cuts & Tears A cut or a tear in the belt is normally caused by a foreign material of sufficient strength being jammed against the belt to the point where it goes through the belt and stays in place while the belt is still in motion. Typically, these tears and cuts are located in the center part of the belt. Edge cuts, or fractures, which are common in innerloop belts are caused by fatigue of the carcass at the high stress point at the edge. The cut or tear that is located in the load carrying part of the belt should be repaired immediately. As these normally occur during an unload, the most commonly used method of repair is to bridge the tear with a series of solid plate mechanical fasteners. These hold the tom edges together so that the unload can continue. Once the unload is finished, the tear can be repaired by the hot vulcanization repair method. If the tear is a transverse one which goes across the belt for a length greater than one third of the total belt width, the belt should be respliced. In some instances, a saddle section may be required. An edge cut which is short in length should be repaired as soon as possible. The preferred repair method is the hot vulcanization one, but success has been accomplished with cold cure repair materials if the leading edge of the tear is relieved with a boring bit. Edge tears which are long should be repaired using the hot vulcanization repair method. Page 11 of 14

12 Blisters A blister is the separation of the cover rubber from the top ply in a localized area of the belt. It differs from edge delamination in that there is bonded rubber on all side of it. Typically, blisters form when the rubber is attacked by grease to the point where the grease penetrates to the bond interface and destroys the adhesion. Blisters are predominately a bottom cover phenomenon. Blisters on the top cover can be formed through unusual flexing of the belt or by imbedded pieces of cargo that are worked by normal belt movement to the point where the bond interface surrounding it is destroyed. Blisters should be repaired by removing the expanded rubber that forms the blister and then replacing it with either cold cure repair materials or by fresh rubber which is hot vulcanized in place. A blister which is left will normally expand until it is broken. Once broken, it could be caught and additional cover rubber could be ripped from the belt. Wear Areas Wear areas are sections, normally full belt length, of cover that have a greater degree of abrasion than the rest of the belt cover. Typically, this occurs in the center path of the belt due to the normal abrasion caused by carrying the cargo. Sometimes, this can be caused by trapped material as discussed with score lines. Sometimes, this can be caused by uneven pressure on the cover rubber when either the belt or the system is unbalanced. Wear areas are normally not repaired unless they are relatively small in area. For those wear areas which are isolated, cold cure repair materials are typically used. When the wear area is extensive, the belt should be monitored and plans should be made for a change-out during the lay-up. Glazed & Hardened Covers Glazed and hardened covers are normally a sign of age in the rubber. The rubber has lost most of its flexibility. With this loss of flexibility is the lowering of the rubber surface's coefficient of friction. This can increase the chance of slippage on the drive pulley. A further potential problem is that the rubber will be more prone to gouges. Although there is no repair method for this condition, slippage problems can be alleviated by buffing the bottom cover of the belt. It is possible to extend the effective service life of the belt in this manner. Page 12 of 14

13 Weatherchecking Weatherchecking of a belt's cover rubber is normally restricted to boom belts as these belts are exposed to the weather. This is an attack by ozone on rubber which is being stretched. The rubber is being cleaved on a molecular level. Generally, the condition looks worse than it actually is as the weatherchecking cuts tend to take a number of years to reach the carcass. Weatherchecking is similar to hardened covers in that the rubber has lost much of its flexibility. As this tends to happen on the bottom cover of the belt, there is an increased chance of slippage against the drive pulley. Although there is no repair method for this condition, sealing the affected area with a neoprene cement helps to slow the process. Also, buffing the surface of the rubber can help avoid slippage problems. Pulley Burns Pulley bum wear areas are caused when the drive pulley spins against the bottom cover of the belt and abrades the bottom cover rubber. The damage is normally confined to the rubber, but there have been cases where the fabric has been damaged. The repair method normally used for rubber only damage is to remove any glazed rubber by buffing the surface. If the rubber is worn to the fabric, the fabric should be sealed with cold cure materials. The repair method used for those cases where fabric is damaged is the hot vulcanized method. Where there is severe fabric damage, a splice or a saddle section with two splices may be required. Splice Fill Strip Problems The most common splice problems are cracks forming in the middle or at the edges of the fill strips. A crack which forms at the edge of the strip is normally caused by the flexing action of the belt as it goes around pulleys. Normally, the only damage with this type of injury is the loss of bond between the edge of the fill strip and the cover rubber. That is, the fill strip is still well bonded to the belt fabric. A crack which forms in the middle of the fill strip is indicative of a bond separation at the first ply. This is a warning sign that the splice may be starting to open. This problem is also caused by the flexing of the belt as it goes around the conveyor system. The repair method for a fill strip which has cracks at the edges is to apply a cold cure filler to the cracks. This seals the cracks to prevent dirt, or other foreign material, from staying in the crack and enlarging it to the point where the fill strip starts to lift. Page 13 of 14

14 The repair method for a fill strip which has cracks in the center is to remove the fill strip in the area around the crack, or completely; examine the adhesion of the first step; repair any adhesion problem; and apply fresh breaker and rubber. This repair method requires the hot vulcanization process. CONCLUSION The various belt problems mentioned above are the most common ones that a belt experiences. The methods given to correct these problems are rather loosely classified as either cold cure repair or hot vulcanization. The reason for referring to the repair methods in this manner is that there are a wide variety of cold cure repair materials available. Which repair material is best suited for a particular application is dependent on both the application and the personnel applying the material. Also, cost and time considerations could have a bearing on what material should be used. As a general rule, the preparation and application technique are as important, if not more important, to a successful cold cure repair as the actual material used. It is obvious that the area being repaired must be cleaned prior to the application of the cold cure repair material. What is not obvious, is that the solvent used to clean the area may have a deleterious affect on the bond. Therefore, care must be taken to ensure that the cold cure materials are used properly. Other considerations for the proper application of cold cure repair materials include the temperature and the set-time. These materials must be applied in favorable conditions to work properly. Also, they must have sufficient time to set up before the belt can be moved. Page 14 of 14