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There are two main categories of conveyor idlers: carrying idlers and return idlers. Carrying idlers (sometimes also called trough idlers) support the belt that carries the material, while return idlers are designed to support the empty belt. Each of these categories has several sub-categories.
Carrying idlers generally consist of a welded steel frame with three equal-sized rolls (one centre and two concentrator or wing rolls). Normally, there are two at each end of the conveyor. Sub-categories include:
Troughing idlers, standard
These idlers generally consist of three steel rolls with the concentrator roll tilted at a fixed angle of 20, 35 or 45°. The idlers are fixed to the conveyor frame and normally spaced at 1,2 m [4 ft] intervals.
These are placed strategically along the conveyor to keep the belt running straight and on centre. Belt training (tracking) is vital to reduce spillage and damage to the belt and related structures.
Impact idlers (both troughing and flat)
These are used in the loading zone of the conveyor and act as a cushion to prevent belt damage. They comprise three equal-sized rolls with rubber tyres to absorb impact and are spaced at 0,305 m [1 ft] intervals.
These are often used for conveying grain, but also suitable for underground mining applications where height clearance is minimal. In contrast to the inline idlers described above, these idlers have an offset centre roll. The rolls staggered position supports a broader section of the belt and prevents spillage.
These idlers enable the belt to transition from a flat profile to a full trough profile at the head and tail ends of the conveyor. They consist of a single fixed centre roll and two concentrator rolls with inclines adjustable from 0° to 35°
Flat standard idlers
These idlers consist of a single roll placed between two brackets, fixed to the conveyor structure. They are generally located under feeders or in applications where material is picked off the belt manually. As with the standard troughing idlers, these are spaced at 1,2 m [4 ft] intervals.
Return idlers are used to support the return run of the belt and are available with steel or rubber disc rolls. Sub-categories include:
Standard flat idlers consist of a single steel roll mounted on brackets. As there is no material load on the return side, the idlers can be spaced farther apart, at 3 m [10 ft] intervals.
V return idlers
These idlers consist of two rolls in a v-shaped profile of either 10° or 15°. They are used in applications where high-tension fabric or steel cable belts are used. Their higher load rating enables wider spacing.
Flat rubber disc
These idlers are similar to standard return idlers but they have rubber as opposed to steel disc rolls. These help prevent material sticking to the belt, making them good for applications where sticky material is being transported.
Metso also offers other types of idlers such as garland (catenary), scale quality, live shafts and picking table.