T - SU552 Conveyor Maintenance Technical Paper T - SU552 BASIC CONVEYOR DESIGN & MAINTENANCE By Neil Schmidgall
CONTENTS ABSTRACT.....................................................................2 DESIGNING FOR MAINTENANCE............................................2 MATERIAL CHARACTERISTICS..............................................2 BELT WIDTH, SPEED, AND CAPACITIES....................................3 SELECTING THE BELT........................................................4 IDLER SELECTION............................................................7 PULLEY AND SHAFT SELECTION...........................................8 BELT CLEANERS..............................................................9 TAKE-UPS.....................................................................11 TRANSFER POINTS.........................................................12 SKIRTBOARDS...............................................................13 IMPACT ABSORBING SYSTEMS............................................13 EMERGENCY STOP SWITCHES AND CONVEYOR GUARDING.........14 CONVEYOR MAINTENANCE SAFETY......................................14 GENERAL SAFETY GUIDELINES...........................................15 GENERAL CONVEYOR MAINTENANCE....................................17 IDLER MAINTENANCE.......................................................18 INSTALLING A CONVEYOR BELT...........................................19 CONVEYOR BELT TRAINING................................................20 LOADING THE BELT.........................................................22 BELT TIGHTENING AND REPAIR...........................................22 TROUBLESHOOTING........................................................22 CONCLUSION................................................................24 1
ABSTRACT Maintenance is an important part of the life span of any piece of equipment. The harsh operating conditions experienced by aggregate conveyor systems not only increase the need for proper maintenance but also create a need for design considerations that facilitate proper maintenance. In many cases, proper design considerations may reduce the cost and time involved with conveyor maintenance. Design considerations are not able to eradicate maintenance altogether however, in order to achieve longevity of the equipment maintenance must be performed correctly and according to the recommended maintenance schedule. DESIGNING FOR MAINTENANCE Producers and bulk material handlers spend millions of dollars every year maintaining conveyor systems. Oftentimes conveyor design does not provide the means for ease of maintenance, and as a result, maintenance may not be performed correctly, on time, or at all. This eventually leads to a greater risk of component failure and a resulting loss of production. Designing a conveyor to be maintenance friendly means providing adequate provisions for necessary service from the onset. This means eliminating problems such as inadequate spacing, inaccessible positions, and other nonrepairable configurations. The following sections will illustrate some of the design considerations that may deter or aid in conveyor maintenance. MATERIAL CHARACTERISTICS When designing a conveyor, the type of material to be conveyed is the first item to be taken into consideration. The flowability of a material affects the size of the cross-section of material load that can be carried on a given belt width. Flowability is affected by material characteristics such as: size and shape of the fine particles and lumps, roughness or smoothness of the material particle surface, the proportion of fines and lumps present, and material moisture content. Considerations should also be given to the weight per cubic foot of material, abrasiveness, 2
and temperature. (Table 1) gives the weight per cubic foot, surcharge angle (Figure 1), and maximum conveying angle (Figure 2) of some commonly conveyed materials. BELT WIDTH, SPEED, AND CAPACITY For a given speed and material density, the wider the conveyor belt the higher the capacity of the conveyor. A belt must be wide enough so that the combination of fines and lumps do not push the lumps too close to the edge of the belt. (Table 2) shows the belt width necessary for a specific lump size, various proportions of lumps and fines, and various surcharge angles. Conveyor belt speeds depend upon the material characteristics, the capacity desired, and belt tensions. Heavy material with sharp edges should be conveyed at moderate speeds. The sharp edges will cause wear to the belt, particularly if the loading velocity of the material in the direction of belt travel is lower than the belt speed. Light, powdery materials must also be conveyed at lower speeds to reduce dust particles, especially at loading and discharge points on the conveyor. Fragile materials may degrade at loading and discharge points, as well as when moved over idlers. Therefore, these types of materials should also be conveyed at lower speeds. (Table 3) recommends maximum belt speeds for commonly conveyed materials. As stated previously, belt capacity increases with the increase of belt width. It is important to know the tons per hour of material an end user 3
expects to move with a conveyor. If there is uniform feed to the conveyor, a cross section of the material loaded on the belt is used in calculating the capacity of a conveyor. The cross section of material must meet the following two conditions. First that the material does not extend beyond to the belt edge or the distance recommended by CEMA, and secondly that the top of the load does not exceed the surcharge angle of loading (Figure 1). SELECTING THE BELT The three elements of a conveyor belt are the carcass, top cover, and bottom cover. The carcass of the belt must have the tensile strength to withstand the load on the belt, and it must also have the strength to withstand the impact of materials in loading areas. Most carcasses consist of multi-ply woven fabrics (Figure 3 & 4). Heavier duty belt carcasses may contain steel cables for reinforcement. The yarns of a belt carcass that run parallel to the conveyor are called wrap yarns. These bear 4
the tension of the belt. The cross yarns of the belt carcass are called weft yarns and aid in impact resistance and fabric stability. There are four types of belt carcasses. They are: multi-ply belt carcasses, reduced-ply belting, steel-cable belting, and solidwoven belts. The multi-ply carcass is usually made up of three or more plies cemented together by a rubber compound. Strength and load support depend on the number of layers, which is usually limited to eight at the most. Reduced ply belting may be used in place of multi-ply belting. It consists usually of fewer layers than the multi-ply, but the layers are made of synthetic fabrics of higher unit strength. A steel-cable belting carcass consists of a single layer of steel cables imbedded in rubber. The all-gum type has only cables and cable rubber, while the fabric-reinforced type has one or more layers of fabric above or below the steel cables (Figure 5). This type of carcass is best used for applications where the tensions required go beyond ply carcasses, and where take-up travel is not long enough to compensate for the high elasticity of ply carcasses. Solidwoven belts consist of a single ply of solid woven fabric usually covered with a top and bottom cover made of PVC material. This type of carcass aids in abrasion resistance. The main purpose of the top and bottom cover is to protect the carcass from wear and impact damage. They also provide a friction surface to aid in the driving of the belt. (Table 4) provides a guide to the required thickness of the top and bottom belt cover. 5
The required length of a belt can be computed by multiplying the conveyor length by 2 and adding the length needed to wrap around the head and tail pulleys (Table 5). A gravity take-up on a channel frame conveyor will require an additional 6 feet of belt, while a gravity take-up on a truss frame conveyor will require an additional 10 feet of belt. The ends of a conveyor belt must be joined together (spliced) to create a continuous belt. The two most common ways of splicing a belt are vulcanizing and using mechanical fasteners. There are two types of vulcanization: hot and cold. Using the hot method, the layers of the belt are stripped in a stair-step manner and overlapped with glue and rubber. A heated press is then used to vulcanize the belt, creating an endless loop (Figure 6). The cold method laps the belt's layers with glue that cures at room temperature. The advantages to vulcanizing belt ends are an improvement in splice strength, longer belt life, and a lack of interference with belt cleaners, idler rolls, or skirting. The vulcanized splice will eliminate material sifting through the splice as happens with mechanical fasteners. The vulcanized splice also has some disadvantages, including initial cost and time required to create the splice. A vulcanized splice takes longer than using mechanical fasteners and therefore increases the conveyor down time. 6
Although vulcanized splices are more expensive and time-consuming, for permanent splicing of a conveyor belt vulcanizing is the best choice. The most important step in using mechanical fasteners to splice a belt is to recess the top and bottom splice pieces. The top and bottom covers are removed down to the carcass. This does not endanger the belt strength or integrity. The recess is needed to keep the fasteners from interfering with potential catch points. Mechanical fasteners (Figure 7) are less expensive than vulcanization and more easily applied. They are also the preferred method for making repairs to the belt in the field, such as adding belt length and patching holes or tears. Material leakage through mechanical fasteners is inevitable. Over time, this may cause clean up problems and will create the potential for damage to other conveyor components. IDLER SELECTION All belt conveyor idlers have the same purpose. They provide shape and support for the belt and minimize the power needed to transport material. Idler spacing affects both the shape and support of the conveyor belt. Idlers placed too far apart will not properly support the belt or enable it to maintain the desired profile. Idlers that are placed too close together will provide the necessary support and profile, but may add a prodigal expense to the conveyor. The main influences in idler selection are belt weight, material weight, idler load rating, belt sag, idler life, belt rating, and belt tension. (Table 6) cites suggested idler spacing recommendations under relatively normal operating conditions when the amount of belt sag is not specifically limited. This table also shows the recommended spacing for return idlers. Proper idler roll diameter and size of bearing and shaft selection is based on load carried, belt speed, and operating conditions. To aid in the selection of idlers, various designs have been assigned classifications illustrated in (Table 7). 7
PULLEY AND SHAFT SELECTION The standardization of pulleys lends itself to the ease of choosing the correct pulley for a given application. The most commonly used pulley is the standard steel pulley shown in (Figure 8). Plain steel drum pulleys are best used in dry clean environments where traction is not critical, and when no foreign material is present on the return belt. Conveyor pulleys may also be covered with rubber, fabric, or other material. This is referred to as lagging. Lagging on a drive pulley provides an increase in the friction between the belt and the pulley. Lagging is also used to reduce abrasive wear to the face of the pulley and to create a self-cleaning action on the surface of the pulley. (Figure 9) illustrates a vulcanized lagged drum pulley. Typical grooving patterns include Herringbone, Chevron, and Diamond. Plain rubber lagging on drum pulleys is typically used in snub applications where traction is not critical (Figure 10). Replaceable lagging is also available. The lagging strips are welded to the face of the pulley, and can easily be replaced in the field (Figure 11). Wing pulleys are typically used in tail pulley applications to reduce the build up of material between the belt and pulley (Figure 12). Trapped materials fall through the paddle-like formations of the pulley. Lagged winged pulleys (Figure 13) are used in applications with abrasive material present on the return side of the belt. It is natu- 8
ral under these conditions for the wing tips to wear prematurely. The rubber lagging will add life to the pulley. Shafting is commonly considered to be a part of the pulley assembly since the strength and rigidity of the assembly depends on both of these components. When choosing shaft diameter, it is important to consider both the shaft diameter required for strength and shaft diameter required for deflection. Depending on the pulley assembly, either strength or deflection may be the deciding factor of shaft diameter. BELT CLEANERS Carry back is the fugitive material that sticks to the belt after the belt passes over the head pulley and subsequently creates fugitive material piles along the underside of the conveyor. Fugitive material is a costly problem, considering that many man-hours are spent cleaning fugitive material piles. In order to correct carry back, a belt cleaner is used. This is usually a form of wiper or scraper device mounted near the discharge (head) pulley. A common type of belt cleaner is the pre-cleaner. This is often referred to as the primary cleaner and functions by scraping off most of the carry back leaving only a thin layer of fines on the belt. The pre-cleaner is mounted on the face of the head pulley just below the discharge trajectory. This allows the material scraped from the belt to fall with the discharge materials. (Figure 14) shows a typical precleaner. 9
Multiple cleaner systems are the preferred method for eliminating carry back. The multiple systems consist of a pre-cleaner and one or more secondary cleaners. In addition to the improvement in belt cleaning, multiple belt cleaner systems increase the time interval between scheduled maintenance times. Belt cleaners should be positioned as close to the head end as possible (Figure 15). Secondary cleaners are designed to remove the thin layer of fines left by the precleaner. It's best to place the secondary cleaner in contact with the belt while it is still against the head pulley. This enables the cleaner to scrape against a firm surface. There are several types of belt cleaners available to eliminate carry back. The brush type can be driven by the pulley motion or motorized (Figure 16). This type is effective on dry materials, as the bristles of the brush sweep the belt clean. The disadvantage to brush type cleaners is the potential for build up on the brush's bristles. Pneumatic type belt cleaners send a stream of air across the face of the pulley to blow off the carry back materials. They are best utilized when moving dry materials. The disadvantages of the pneumatic cleaners are the expense of the continual air stream, and the creation of airborne dust as the carry back is not deposited in the discharge pile (Figure 17). 10
There are two styles of washtype cleaners that use water to clean the belt (Figure 18). The first is a system that spays a misting of water on the belt in order to make the scraping process easier. The second type uses a high-pressure wash to completely remove carry back. Problems occur with these types of cleaning systems with the removal of the sludge that is created. However, in some cases, the water-material mixture can be returned to the material load. These systems also have the potential for trouble under cold operating conditions. Return belt cleaner systems, also known as v-plows, are used to prevent large objects and tramp iron on top of the return belt from damaging conveyor components. A low pressure mechanical scraping is used to remove the material from the belt (Figure 19). TAKE-UPS All conveyors need some form of take-up device in order to ensure proper belt tension at the tail to prevent spillage of materials due to belt sag between the idlers, and to provide enough tension to prevent slippage between the belt and the drive pulley. They also compensate for belt shrinkage or stretch, and allow for extra belt length storage for making replacement splices in the belt. The required take-up movement length is determined by the type of mechanism being used to start and stop the conveyor, the frequency of starts and stops with a loaded belt, stretch characteristics of the belt, and running tensions. 11
There are two types of take-up systems, manual and automatic. The manual systems are preferred when an automatic take-up is impractical. They are also preferred for use on short, light conveyors where take-ups are not as critical. The take-ups shown here are most commonly found on belt conveyors. Window style takeups (Figure 20) are best utilized on conveyors less than 150 feet in length. The travel length of the take-up can be up to 36 inches. Telescoping Tube type take-ups (Figure 21) can be used on conveyors up to 150 feet in length where headroom may be a concern. The travel length of the take-up can be up to 36 inches. The Scissors type vertical gravity take-up (Figure 22) is also used when headroom is a concern. The travel length on this take-up can be up to 8 feet. Gravity take-ups (Figure 23) are used on stationary conveyors over 150 feet long and where vertical headroom is of no concern. TRANSFER POINTS A transfer point is any point on the conveyor where material is loaded onto or unloaded from the conveyor belt. The ideal transfer point would be designed to load the belt in the center and at a uniform rate. They should also reduce the impact of the material falling on the belt and maintain a minimum angle of inclination of the belt at the loading point. The design of discharge chutes and other loading equipment should take these topics into consideration. Other factors such as 12
capacity, size, characteristics of material handled, speed, and inclination of the belt should also be considered. SKIRTBOARDS Skirtboards are used to keep transfer material on the belt after it leaves the loading chute until it reaches belt speed. They are usually an extension of the loading chute and extend for some distance along the conveyor (Figure 24). The distance between the skirtboard and the conveyor belt is critical. Skirtboards need to be placed high enough so that they never come into contact with the belt. The gap between the belt and skirtboards should be as small as allowable. The closer they are together the easier it is to maintain a seal between them. The gap between the bottom edge of the skirtboard and the belt is usually sealed by a flexible rubber strip attached or clamped to the exterior of the skirtboard. Skirtboard length can be based on a rule-of-thumb of 2 to 3 feet per 100 feet per minute of belt travel. The material should be traveling the same speed as the belt when it leaves the load area. IMPACT ABSORBING SYSTEMS Transfer point structures can rapidly deteriorate due to loading zone impact from heavy objects or material with sharp edges. Loading zone impacts also cause wear and damage to the conveyor belt, weakening the belt carcass. To aid in the prevention of this damage, transfer points should be designed to lessen the height of the material drop. There are also devices made to reduce impact at transfer points. Impact idlers may be used at the transfer point; these are troughing idlers that have rubber-cushioned rollers to absorb impact. Impact cradles can also be positioned under the conveyor belt to absorb impact at loading areas. 13
EMERGENCY STOP SWITCHES AND CONVEYOR GUARDING Emergency stop switches consist of a pull-cable that runs along the side of the conveyor and is connected to a switch approximately every 100 feet of the conveyor's length (Figure 25). The emergency stop switch either shuts down the conveyor system or sounds an alarm if the cord is pulled, providing an extra safety device for operators and conveyor maintenance workers. Another safety device important in conveyor design is guarding. Machine guarding provides a safer working environment. Some examples are shown below. Drive guards are used to cover v-belt drives, rotating shafts, and jackshafts (Figure 26). Return roll guards (Figure 27) are used to guard return idlers that are less than 7 feet from the ground or accessible by operators or maintenance personnel. Side guards (Figure 28) are used on transfer points to prevent access to pinch points and rotating components. CONVEYOR MAINTENANCE SAFETY Before performing maintenance on a conveyor, it is important to be aware of general safety guidelines that will help protect operators and maintenance personnel from injury. The first step is to read the conveyor manufacturer's operations manual. Manuals have instructions specific to each conveyor on maintenance schedules, procedures, and requirements. The following sections discuss safety procedures that should be followed before and during conveyor maintenance. 14
GENERAL SAFETY GUIDELINES Do not allow anyone to operate or perform maintenance on a conveyor until they have read the manufacturer's operations manual and are completely familiar with all safety precautions. Do not allow the following people to operate or maintain the conveyor... - Children - Persons unfamiliar with the equipment, or unfamiliar with safe operating and maintenance procedures for the equipment. - Persons under the influence of alcohol, medications, or other drugs that can impair judgment or cause drowsiness. Make sure everyone is clear of the conveyor before starting the belt, during operation, or maintenance. Never allow anyone to ride on the conveyor. Do not leave conveyor unattended while in operation. Do not wear loose hanging clothes, neckties, or jewelry. Long hair is to be placed under a cap or hat. These precautions will help prevent you from becoming caught in the moving parts of the conveyor. Wear safety glasses, ear protection, respirators, gloves, hard hats, safety shoes, and other protective clothing when required. Requirements for personal protective equipment will vary depending upon conveyor placement and material to be conveyed. It is the responsibility of conveyor operators to be certain they make use of all necessary personal protective equipment. Buildup of materials on pulleys or idlers will lead to belt misalignment or damage. When removing such materials, the conveyor must be stopped 15
and power controls must be locked out or tagged out. The conveyor should not be used to handle materials other than those specified as part of its design and manufacture. It is the operator's responsibility to be aware of the conveyor system capacities and operate the conveyor accordingly. Make sure the operator's area is clear of any distracting objects. Keep work areas clean, and free of grease and oil to avoid slipping or falling. Periodically check all guards, shields, and structural members. Replace or repair anything that could cause a potential hazard. When the belt is moving, the material travels at a speed sufficient to cause injury. Do not start the conveyor until you are certain no one is exposed to the moving parts or to the material being discharged from the end of the conveyor. When doing maintenance work on structural parts or repairing any moving parts: - Disconnect and lockout or tagout all power sources. Know OSHA requirements. - When welding is required, disconnect all power sources and connect ground to point closest to welding area. - Block all wheels to prevent the conveyor from moving, and block any extended hydraulic cylinders to prevent them from moving or retracting. If any safety devices are not functioning properly, do not use the conveyor. Remove it from service until it has been properly repaired. Do not replace components or parts with other than factory-recommended service parts. To do so may decrease the effectiveness of the unit. Do not lubricate parts while the conveyor is running. Before starting engines within enclosed areas, be certain ventilation is sufficient to avoid buildup of exhaust fumes. Relieve any and all pressure before opening, repairing, or removing any air pressure lines, hydraulic lines, valves, fittings, or seals. In the event of a hydraulic line rupture, stay clear of the area until pressure has been relieved. Clean up any spilled fluid before performing repairs in the area. It is the operator's responsibility to be aware of equipment operation and work area hazards at all times. Operators are responsible to know the location and function of all controls and indicators, including electrical power panels, hydraulic controls, motor controls, incline indicators, fuel and oil level indicators, belt scale controls, etc. Operators are responsible to know the location and function of all guards and shields including but not limited to drive guards, pulley guards, and nip guards; and are responsible to make certain that all guards are in place when operating the conveyor. 16
Operators are responsible to be aware of safety hazard areas and follow instructions on warning, caution, or danger decals applied to the conveyor. Safety hazard areas may include but are not limited to: - Pinch points at fold hinge areas - Pinch points at fold support areas - Pinch points where locking pins are used - Electrical control panels - Moving parts hazards on drives - Moving parts hazards where contact with belts and idlers is possible GENERAL CONVEYOR MAINTENANCE Carefully read through all safety instructions in the owner's manual. Return and trough idlers are either greaseable or non-greaseable. Check greaseable idlers to be sure they are filled with grease. Check to be sure the reducer is filled to the proper oil level. Check all other fluid levels. Check to be sure that skirtboards at loading points are installed and adjusted. Check equipment wiring-any and all wiring must be done by a qualified electrician. Loosen and remove the v-belts by adjusting the torque arm reducer or motor mount tension bolts. Turn the driven sheave by hand to determine the direction of rotation. Run the drive motor or use a phase rotation indicator to determine the drive sheave direction of rotation. If both sheaves are not rotating in the same direction, the unit must be rewired by a qualified electrician. Adjust the torque arm reducer or motor mount tension bolts to set v- belts at proper tension. If conveyor has multiple motors, steps should be taken to ensure the conveyor load is shared equally between the motors. Use amperage meters to measure the current drawn by the motors. Adjust the tension of the v-belts on the drives until the readings from the motors are equal. Be certain not to over tighten the v-belts. The drives should be checked periodically to see if the motor load is still balanced. When a belt scraper is used, be sure that it is properly installed, tensioned, and working. Be certain all guards and safety devices are in place and in working order. Visually inspect all hoses, lines, and belts for leaks, wear, and damage. Check and remove all tools and any foreign objects from the belt, particularly on the return run side where they may get between the pulleys and belt. Grease on the belt should be removed immediately as it will deteriorate the belt. Make certain no parts of the conveyor power, hydraulics, or moving parts have been locked out or tagged out. If they have, determine who placed the lockouts, and have them remove the lockouts or tagouts before starting the conveyor. Walk completely around the conveyor, making certain no other personnel are under, on top of, or next to the conveyor. Warn anyone nearby that you are starting up the conveyor. 17
After starting the conveyor, check all controls and indicators or gauges to be certain they are in working order. Check the operation of safety stop lines and switches, if applicable, after starting the conveyor. IDLER MAINTENANCE All regreaseable idler series use the same principle: One shot-grease through, with a standard alemite 1627-B on one end and a bushing-pressure relief fitting combination on the other end. If a change in the greasing side of the idler is needed after the idler is installed, the fittings are interchangeable. The idler rolls are filled with grease at the factory. Idlers that have been stored for longer periods of time need to be purged and re-filled with grease. Idlers should be re-lubricated every 800-1000 hours unless running in extremely dirty or wet conditions where more frequent greasing would be required. Do not over-grease! More idlers fail from over-greasing than from lack of grease. Make sure all fittings are cleaned before and after greasing. Re-lubrication should not be done when outside temperature is below freez ing. Grease is sluggish and stiff at these temperatures and may cause inter nal damage. Roller grease seals are designed to hold in grease while there is pressure in the idler lubrication system. When grease passes through all three rolls, the pressure relief fit restricts the flow, causing internal pressure that results in grease being purged through the bearings. At a maximum pressure of 25 lbs., the relief fitting releases; thus protecting seals from excessive pressure. Leakage may occur around the outside ring of the seals. This is known as star burst or starring. This will flush the contaminants away from the bearing. General guidelines for greasing idlers: Mild Conditions: Inside, protected from weather, dry material being conveyed. Grease every 1000 hours. Normal Conditions: Exposed to weather, but only dry material being conveyed. Grease every 800-1000 hours. Severe Conditions: Exposed to weather with water in material being conveyed. Grease every 100-200 hours. Extreme Conditions: Grease after every 40 hours of operation or more often if necessary. 18
INSTALLING A CONVEYOR BELT Belts are customarily packaged in crates that can be rolled from place to place. Crates and rolls are usually marked with an arrow that shows the direction in which they should be rolled. When hoisting the belt roll, a bar should be passed through the hole in the center of the roll. Fasten chain or cable to the ends of the bar for lifting, and use a spreader bar above the roll to prevent damage to the edge of the belt. Always store the belt roll suspended on a tube or bar, or resting on the face width of the belt. Storing the belt roll with weight on one edge may stretch the belt, making it difficult to square at assembly and train during the initial operation. Belts should be stored in a dry, cool building. Never drop the belt or store it on its edges. Installation of the belt begins with building a suitable stand behind the conveyor and then aligning the belting roll with the conveyor frame (Figure 29). If the area behind the conveyor will not permit this method of threading, the roll of belting can be suspended above the conveyor frame for threading. Next, check the position of the side take-up bearings to make sure they are positioned all the way to the retracted position. This will give you maximum take-up ability after belt installation. Then check the belt to make sure the load side (side with the thickest rubber covering) is facing up. Most belting is shipped from the factory cut to length with additional allowance for squaring ends for the splice. The molded edges on new belts are not always straight and parallel. Whenever practical, it is recommended to square ends of belt with the centerline of the belt. Mark the center point of the belt using a light colored chalk or pencil (Figure 30). Then draw an average centerline using these points as 19
a guide. Locate two center points on the belt such that arcs will overlay. Draw the arcs on the belt. Using a steel straight edge, draw the square line through the two arc intersecting points (A). Measure an equal distance (B) on both sides of belt from square line to the cut line. Next, position the fastener manufacturer's template on the belt (or fashion one yourself given the manufacturer's recommendation for fastener spacing) and punch holes in the end of the belt for the fasteners. Always follow the manufacturer's recommendations as to the proper size of fasteners to be used on any belt. Attach a clamping plate onto the end of the belt to enable an even pull for threading the belt onto the conveyor. Place the pulling plate on the bottom side of the belt so it will pass more easily over the troughing idlers. Bolt the clamping plate to the belt through the fastener holes. The number of bolts should be proportionate to the amount of pull exerted. Connect a cable or rope to the clamping plate. A braking system can be made by using a belt clamp mounted on the conveyor frame to prevent belt runaway while threading. Slowly pull the belt into position (near the tail section for easy access) with a block and tackle or similar equipment. Attach 2 stretcher clamps roughly 3 feet from each end of the belt. Make sure the stretcher clamp on the squared end of the belt is parallel with the belt end. Remove the clamping plate and firmly attach the parallel stretcher clamp to the conveyor frame. Evenly draw the belt ends together, using a cable-jack or similar means, and pull the unsquared end of the belt over the top of the squared end until the correct belt tension is obtained. Maintaining this tension, create a centerline following the procedure described earlier, and mark a squared line where the belt must be cut for the splice. Place a wooden plank under the splice point to facilitate the cutting and punching of holes in the belt. Cut the belt, position the fastener manufacturer's template on the belt end, and punch holes for the fasteners. The use of belt tape under the belt fasteners is recommended to help reinforce the splice area. Refer to instructions included with the belt fasteners for proper installation. CONVEYOR BELT TRAINING Belt training is a process of adjusting idlers and loading conditions in a manner that will correct any tendency of the belt to run off of center. Never attempt to train the belt by unequal adjustment of take-ups. The take-ups are only to be used for keeping the tail pulley square with the conveyor frame and to maintain belt tension. The training of a conveyor belt causing it to travel over the center area of troughing idlers, pulleys, and return idlers is vitally important to trouble-free operation and low maintenance cost. Unless a belt itself is warped and curved from improper manufacture, use, or storage, it is possible to train it for central running. The following recommendations are basic to belt training procedures: 1. Level all frames crosswise as gravity will force the belt off-center if one side of the conveyor frame is lower than the other (Figure 31). 20
2. Square the tail pulley with the frame. Locate and mark point A at the midpoint of a conveyor cross member. Next, measure an arbitrary distance from point A to locate a point X on the edge of the conveyor frame. Then measure the same distance from point A to measure a point Y on the other edge of the conveyor frame. Line XY should now be square with the conveyor frame. On the other side of the square line (line XY), locate a point B at the midpoint of a cross member. Measure the distance of BX and BY to verify that line XY is square. Line BX and BY should be equal. Clamp a straight edge to the conveyor frame directly on top of the square line. Any component on the conveyor can now be squared by measuring from the straight edge equal distance on each side (Figure 31, distance C). 3. Square all troughing and return idlers with the frame by measuring from the straight edge on both sides of the conveyor and tighten the attachment bolts. 4. Check the belt splice for squareness. Check the belt run on the return run side of the conveyor, or place a large plywood board under the belt on the load side to get accurate measurements. 5. Run the conveyor empty and at reduced speed if possible. If the belt should show a side creep at only the splice area and this progressed along the conveyor instead of remaining at one point on the frame, the splice may not be square and may have to be redone. If necessary, resplice the belt. If you don't have sufficient belt length to resplice after squaring the belt ends, you will have to add a section of belt. When adding belt sections, remove enough length from the original belt to allow for a minimum distance of 3 feet between belt splices. Once you have determined the splice is square, examine the return run side of the conveyor for side creep first, beginning at the head end and working down to the tail. Make adjustments where side creep occurs as follows: A. The point of maximum side creep (D) requires adjustment of a preceding idler (E) when you are facing in the direction of belt travel. B. Loosen the bolts and pivot the idler (E) around its midpoint just as you would turn a steering wheel to bring an automobile back to the center of its lane. Make these adjustments in small amounts; tighten the bolts and make a test run after each adjustment to see the effect on side creep. Run the belt at least three revolutions for the adjustment to take effect. If the point of maximum side creep changes, adjust the idler that precedes that new point. C. When the slow running belt is centered, change to a higher speed (if possible). Load the belt with material and continue testing until normal operating conditions cause no deviation from central running. 21
6. Examine the load run side of the conveyor following the belt travel from tail to head end. Make the same adjustments where side creep occurs. LOADING THE BELT After the conveyor has been thoroughly checked over and all belt training completed, the conveyor can be loaded. Start with a light load and gradually work up to the load that the conveyor was designed to handle. When stopping the conveyor, operate until the belt is clear of material, especially at the end of each working day. During cold weather, material remaining on the belt will freeze to the belt and may cause damage. Rubber skirtboards are bolted to the trough to form the load centrally on the belt, to prevent side spillage, and to prevent material from spilling out the back or bottom of the trough. Larger material spilling out the back of the trough has potential to catch in the belt or damage the tail pulley. Skirtboards will require adjustment or replacement as they wear. Material should be stilled on the belt before it reaches the end of the skirtboards. If the material particles are still tumbling as they pass the skirtboard ends, belt speed may need to be adjusted, feed arrangement or rate may need to be adjusted, or the skirtboards may need to be extended in order to avoid side spillage of material. BELT TIGHTENING AND REPAIR Conveyors with manual take-ups are equipped with side adjusting bolts at the tail end to maintain the necessary belt tension. With a wrench, loosen the take-up side adjusting bolts to move the sliding bearing assemblies forward. Apply the proper tension to the belt to prevent slippage and excessive belt sag between troughing idlers, and then re-tighten the take-up side adjusting bolts. Fasteners can be used to make quick repairs to belt tears or to replace belt sections with new pads of the same belting. Coat all exposed edges or cuts with rubber cementing compound to prevent any moisture or foreign material from entering the belt carcass and causing further damage. TROUBLESHOOTING The following is a troubleshooting guide with suggested solutions to some common conveyor problems. Match troubleshooting table (Table 8) to the corresponding number on the troubleshooting key. 22 23
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