The diagram below of a conveyor used in the mining industry shows all the components.
Conveyor Idlers:
Idlers can be of various types: Carrying Idlers, Return Idlers, Impact Idlers, Training Rollers
Carrying Idlers: Carrying Idlers are free-rotating units designed to support the conveying surface, usually a conveyor belt. Idlers are constructed of three main components: frame, rollers (or cans), and rolling element bearings. Assembled, carrying idlers are designed to trough the carrying surface. The figure below illustrates how a conveyor belt rides in the idler trough. Idler rollers are generally available in diameters ranging from four to seven inches. Situating the outer cans at predefined angles to the center roller forms the idler trough. Generally, idlers come standard in three degrees of trough: 20°, 35°, and 45°. The trough allows the loaded material to be transferred with the least amount of spillage. Depending upon the application requirements, most idlers are spaced three to four feet apart on center. This allows ample load support to the conveyor belt. It is important that the belt makes contact with all rollers to ensure proper belt tracking and training, as well as load support.
Return Idlers: Return Idlers are positioned below the conveyor system structure and provide a surface for carrying the conveyor belt in the opposite direction of the carrying side of travel. Like the carrying idler, the return idler consists of three components: frame (idler supports), roller (or “can”), and rolling element bearings. Depending upon the application requirements, most return idlers are spaced 10 feet apart on center.
Impact Idlers: Impact Idlers are specially designed to absorb the energy produced upon impact of the product being conveyed to the conveyor’s carrying surface. Identical to traditional troughed idlers, impact idler rollers are engineered to absorb the impact by coating the rollers in rubber or affixing semi-pneumatic impact rings.
Training Rollers: Training Rollers are used to keep the conveyor belt centered on the conveyor system. Training rollers are affixed to the frame of the carrying or return idlers. The perpendicular positioning of the training roller to the belt keeps the belt from tracking off the carrying idler.
Gearboxes
Gearboxes, or speed reducers, are necessary in a conveyor application to reduce the prime mover output RPM to a speed more suitable for the conveyor application
Pulleys
Pulleys are of various types in conveyor applications: Drum Pulleys, Winged Pulleys, Lagged Pulleys, and Lagged Pulleys
Drum Pulleys: These are used as a point of angle change for the conveying surface. Used as a head, tail, take-up, or snub, the drum pulley is usually larger in diameter than an idler roller (ranging from 10” to 42” in diameter in normal applications). Due to the fact that a minimum bend radius limits conveyor belts, pulley diameter becomes a factor when upgrading or replacing an existing belt.
Winged Pulleys: These are used as a point of angle change for the conveying surface. Similar to the drum pulley, winged pulleys can be used as a head, tail, or take-up. Also like the drum pulley, the winged pulley is usually larger in diameter than an idler roller (ranging from 10” to 42” in diameter in normal applications). The differentiating characteristic of the winged pulley is the construction. The carrying surface is not smooth like a drum pulley. Instead, the winged pulley, in profile view, appears to have spokes emanating from the hub center, forming gaps on the carrying surface. These gaps allow trapped material (between the pulley and the belt) to escape at the end of the pulley. Material, such as rocks, when caught between the pulley face and the conveyor belt, can produce belt punctures. Apart from large rocks, material buildup on a drum pulley can cause abrasive wear to the bottom cover of the belt and poor belt tracking.
Lagged Pulleys: These are used as a point of angle change for the conveying surface. The lagged pulley is nothing more than a drum pulley with a layer of rubber or ceramic tiles bonded to its surface. This rubber surface provides a higher coefficient of friction between the conveyor belt and the pulley, reducing slippage on startup, in heavily loaded applications, and where wet or slippery conditions are of concern. Also like the drum pulley, the lagged pulley is usually larger in diameter than an idler roller (ranging from 10” to 42” in diameter in normal applications).
Take-up system
Conveyor belts stretch over time due to many different factors: drive location, moisture, loaded starts, frequency of starts, braking, etc. In addition, belts experience periods of momentary elongation, such as when a conveyor system starts. As the initial load is accelerated to speed, the belt eventually returns to its initial length. Belting manufacturers know this and provide stretch and elongation factors to be calculated into the conveyor operation. By providing elongation factors as a percentage, the conveyor engineer can anticipate how much the belt will grow over time. To compensate for this belt growth, the extra belt must be either removed or the conveyor travel distance must be able to compensate. As an example, if a belt is calculated to stretch 2%, then a 1000’ belt will stretch twenty feet over its useful life. As a result, the belt becomes loose, slips on the drive pulley, and does not track on the conveyor system properly.
Take-up systems can be of various types: Take-up pulleys, Screw take-ups, and Gravity take-ups
Take-up pulleys remove this slack from the conveyor belt. There are many types of conveyor belt take-up pulleys, but the two most popular are screw and gravity.
Screw take-ups are most commonly located at the mid-section or the tail of the conveyor system, and use a screw mechanism on each side of the take-pulley to reduce belt slack.
Gravity take-ups are usually located toward the head/drive pulley. The gravity pulley is attached to a weight, as determined by the belt manufacturer, and rides in a vertical motion to compensate for overall belt stretch as well as periodic temporary elongation during start-up. The gravity take-up is also useful in preventing serious damage to a system during a jam.
Tripper Arrangements
As application demands vary, some conveyors must have the capability to change where the load is discharged without physically moving the entire conveyor structure. Obvious examples of changing discharge location are seen in the sand and gravel industry, where the same conveyor systems are used to build multiple piles of material. To do this, a tripper is used. A tripper conveyor has the ability to discharge material at any point before that material gets to the head pulley. It can also discharge the material to the left or right side of the conveyor structure as well as back onto the conveyor itself.
Back-stops
Mounted usually within the speed reducer of a conveyor drive system, the backstop prevents the conveyor from reversing direction during a power outage under a loaded condition. In some instances, the backstop prevents a conveyor belt from coming off the conveyor system should the belt itself break
Emergency Stops / Cords
Emergency stops/cords are cables that run the length of the conveyor system and are designed to stop the conveyor from running when pulled during an emergency.
Belt Cleaners
“Carry-back” the portion of material left on the conveyor belt after material has been offloaded or discharged, has always been a problem in conveyor operation. Carry-back is messy, as it accumulates along the return run and requires manpower to remove it. Carry-back tends to wear return idlers and pulleys. More importantly, carry-back falling off conveyors can draw fines from the EPA.
There are two types of belt cleaners: brush and blade. Yet, while there are many styles of each type, the objective is the same: keep material from sticking to the belt on the return run.
V-guides may be used to keep a conveyor belt centered on a system. A v-guide is a polymer extrusion in the shape of a v, welded or chemically bonded to the bottom cover of a conveyor belt. This v-guide rides, firmly seated, in a specially cut groove in the pulleys and rollers, thus keeping the entire belt centered.
Skirtboard
During the conveyor loading process, a hopper fills the conveyor belt. If not properly handled, not all the material will make its way directly to the belt. Depending upon the angle and slope of the hopper, material can end up everywhere but where it belongs. The skirtboard is a rubber strip, clamped into place at the point where the hopper comes into contact with the belt. The skirtboard, in essence, seals the loading area. While many use old pieces of conveyor belting as a skirtboard, most belting manufacturers advise against it. Fabric plies and rubber durometer of an old belt skirtboard can cause damage to the conveyor belt itself. Check with your local supplier for the skirtboards suitable for your application.
Belt Training
Moving or adjusting idlers and pulleys to achieve proper, central running of the conveyor belt through the system trains the conveyor belt.
It takes time for new conveyor belts to run in properly. Run-in is the point at which the conveyor belt follows the system without running significantly to either side. When a conveyor belt consistently runs to the side of a system, either at one point or throughout the entire run, chances are that there is either a change in the alignment of the structure (or its components), or a change in the material loading. This kind of operating condition can result in material spillage or even damage to the belt itself.
While many at first believe that a poorly tracking system is the product of a belt defect or belt-slitting problem, be assured that this (while possible) is highly unlikely. Experience indicates that structural or application changes are the cause of the problem. There is also the possibility of an improperly aligned splice. Check with your conveyor belt supplier for specific training assistance.
Dimensional Specifications
All conveyor belting manufacturers have specialized programs for calculating proper belt sizes, based upon application and system features. Likewise, conveyor manufacturers have software to make conveyor design simple.
Gearboxes
Gearboxes, or speed reducers, are necessary in a conveyor application to reduce the prime mover output RPM to a speed more suitable for the conveyor application. Read more details on the gearbox in the Gears section.
Motors
One most essential parts of the conveyor system is the prime mover. While steam and internal combustion engines are used as prime movers, the electric motor, by far, is the most commonly used with conveyor systems. Electric motors range from fractional (1/4 hp) for very light conveyor applications, to very heavy-duty application, high-horsepower motors (5000 hp).
Conclusion
As can be seen, the conveyor system is nothing more than a few basic components. The optimum objective is to synchronize these components into one harmonious material-moving instrument. This is sometimes very difficult to do, considering the potential size, material being conveyed, and the environment in which the system is expected to operate.
In heavy-duty conveying systems, most of the individual components (motors, gearboxes, and conveyor belts) can be very expensive. Normally, if one component fails, the odds that it will damage another component are high. A proactive and preventative maintenance program will pay for itself over time, should it keep the operator from replacing one of these expensive components. Obviously, preventative maintenance must be weighed against the potential loss of not only components, but also lost production.