TROUGHING IDLER SET
A troughing idler set is a frame of three carrying rollers — one horizontal centre and two inclined wings at 20/30/35/45° — that shapes the belt into a trough cross-section to maximize material-carrying capacity.
The troughing idler set is the canonical carrying-side support arrangement for bulk-material belt conveyors. Three rollers — a horizontal centre roller and two outer 'wing' rollers angled upward at the chosen [trough angle](/glossary/trough-angle) — are mounted on a single base frame, evenly spaced along the conveyor at the design idler pitch. As the belt passes over the frame, it conforms to the trough shape, dramatically increasing the cross-sectional area available for material compared with a flat-supported belt.
Trough angles of 20°, 30°, 35° and 45° are standard. Higher angles give more capacity but require a more flexible belt (the carcass must bend twice the trough angle on every revolution). The centre roller carries roughly 65–75 % of the loaded mass; the wing rollers carry the balance and also do most of the work of trough shaping. Roller diameter is selected against the belt speed × belt mass duty per [CEMA idler class](/glossary/cema-idler-class) (89 mm to 219 mm) — heavier duty needs larger rolls and stiffer bearings.
Two- and five-roll variants exist. The two-roll V-trough is used on light-duty narrow belts where a fully troughed three-roll set would be excessive. The five-roll garland set (suspended on chains) provides extreme flexibility at impact zones and on belts that handle very large lump material. The standard three-roll set, however, remains the default and accounts for the vast majority of installed troughing idlers worldwide.
Related products
Related engineering tools
Related terms
- Trough Angle
Trough angle is the angle between the outer (wing) idlers and the horizontal centre idler in a three-roll troughing set, typically 20°, 30°, 35° or 45°, which controls belt cross-section and capacity.
- CEMA Idler Class
CEMA idler class (A, B, C, D, E, F) is the U.S. standard rating system that groups conveyor idler rolls by shell thickness, bearing size and maximum load — A is lightest duty, F is heaviest.
- Return Idler
A return idler is a single roller (or V-shaped two-roller set) below the carrying strand that supports the empty return belt at typical spacing of 3 m, with self-cleaning variants used in dirty applications.
- Transition Idler
A transition idler is an adjustable idler frame placed near the head and tail pulleys whose wing rolls gradually flatten from the design trough angle down to horizontal, easing the belt onto the flat pulley face.