Belt conveyors are continuous conveyors used to convey materials horizontally or with a (small) degree of inclination. They are a subgroup of belt conveyors (when a “belt conveyor” is used as a generic term).
In belt conveyors, endless belts that are used both as pulling and carrying elements are directed by means of pulleys at the points where the conveyor’s line of motion changes. Normally, the pulley on the discharge side is the drive pulley, while the feeding side is used as a tensioning station. Idlers are usually used to support the belt between these pulleys. Normally, the material being conveyed lays on the belt’s top strand.
Belt conveyors can be used both for unit goods (i.e., pallets, boxes, etc.) and for bulk material. The belt is driven by means of friction – drive pulleys that are frequently fitted with special friction linings are used for this purpose. In order to keep the stress exerted on the conveyor belt as low as possible, the drive station should be arranged in such a way that the load-bearing strand is being pulled. Because of this, the drive station is normally the delivery station as well, and the same pulley is often used to perform these two tasks. In the case of long belt conveyors, however, it is often necessary to use several drive pulleys in order to be able to transmit the required driving power.
At the turn station, the belt is deflected from the top strand to the bottom strand by a non-driven pulley. This pulley is usually also used as a tensioning station. On one hand, the belt must be pretensioned in order to restrict the belt’s sag between the idlers. On the other hand, a minimum amount of pretension is necessary in the belt in order to be able to transmit the driving forces at the drive station.
Idlers are an essential part of a belt conveyor, since the belt that is moving in a loop between the head and tail pulleys needs to be supported. Also, the load-bearing top strand must be supported by more idlers than the bottom strand. The placement of idlers below the belt makes it possible to adjust the latter’s troughing. The bottom strand can also be pulled on top of a smooth surface without the use of any idlers. Moreover, the type and number of idlers used plays an extremely important role in defining the conveyor’s power requirements.
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