TROUGH ANGLE

The trough angle is the inclination of the wing rolls in a troughing idler set, measured from horizontal. A flat (single-roll) idler has 0° trough angle; the three-roll set used on most bulk-handling conveyors uses 20°, 30°, 35° or 45° wings. The angle shapes the belt cross-section from flat into a shallow trough that holds more material per unit belt width while still allowing the belt to flex over the centre roll without overstressing the carcass at the edges.

Higher trough angles deliver more capacity for the same belt width and speed: a 35° trough typically carries roughly 10–15 % more than a 30° trough, and 45° carries 25–30 % more than 30°. This is why steep-trough idlers are popular on high-capacity bulk systems. The trade-offs are heavier idler frames, more stringent belt flexibility requirements (the belt must bend through twice the trough angle on every revolution without internal damage), and a larger minimum drive pulley diameter so the carcass relaxes back to flat without delamination at the splice.

Capacity in a troughed belt is calculated by combining the cross-sectional area of the trough itself with the area of the material heap above the rim (governed by the surcharge angle). For full design intent, the trough angle is one of three coupled choices — width, trough angle and speed — that together set the throughput Q (m³/h or t/h) of the system.