TOOLS · GLOSSARY
Idlers & Rollers — Belt Conveyor Glossary
45 terms on Idlers & Rollers, each with its working definition, the governing symbol or formula where one exists, and a link to the standard behind it.
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45 terms
Idler (idler set)
Rotating belt-support unit; a set forms the carrying or return trough.
Carrying (troughing) idler
Load-side idler set that shapes the belt into a trough under the material.
Return idler
Flat idler set supporting the empty returning belt.
Impact idler
Cushioned idler set under the loading point that absorbs the drop energy of the material.
Training (self-aligning) idler
Idler set that automatically corrects belt drift, usually through angled or pivoting rollers.
Garland idler
Flexible suspended idler set used on heavy mining conveyors.
Spiral (helical) idler
Return idler with a helical surface that self-cleans sticky carry-back.
Disc / rubber-disc idler
Rubber-ringed idler that cushions impact and sheds build-up; common under chutes.
Idler roll
The rotating tube-and-shaft unit of one idler position.
Idler diameter
Tube outer diameter (89 / 108 / 133 / 159 mm typical); a larger diameter lasts longer and runs at lower rpm.
Idler spacing
Distance between idler sets; carrying side ≈ 1000–1500 mm, return side ≈ 2500–3000 mm.
Idler bearing
Rolling bearing inside the roll, commonly 6204–6306 series; sealed for life on good idlers.
Bearing housing
Sealed housing that locates and protects the bearing inside the roll.
Labyrinth seal
Non-contact multi-path seal that keeps grease in and dust or water out.
Idler shell (tube)
The outer tube of an idler roll; wall thickness sets wear life under abrasive duty.
Idler shaft
Fixed axle on which the roll turns; cold-drawn or turned steel.
Idler runout (concentricity)
Total indicated runout of the rotating roll; a key quality and noise indicator.
Rotational resistance
Torque needed to turn an unloaded idler; low drag saves energy and extends life.
Idler bracket / frame
Bracket or frame that mounts idler sets to the structure at the correct troughing angle.
Belt tracking (centring)
Keeping the belt centred on the idlers while running; corrected by training idlers or self-aligning rollers.
Troughing idler 20°
Carrying idler set with a 20° trough angle; used for wide belts and easy-flowing material.
Troughing idler 35°
The most common trough angle worldwide; best balance of capacity and belt life.
Troughing idler 45°
Deep-trough carrying idler giving the largest cross-section area per belt width.
Deep-trough idler set
Idler set with a trough angle above 45°, or a 5-roll garland, for maximum capacity and spillage control.
Flat carrying idler
Single-roll idler for unit loads and flat belts rather than bulk troughing.
V-return idler set
Two-roll return set at a shallow V that helps keep the belt centred.
Forward-tilted idler
Carrying idler with side rolls tilted a few degrees forward to steer the belt to centre.
Offset-centre idler
Idler set whose centre roll is offset to improve tracking and smooth the belt run.
Variable-trough idler
Idler set whose trough angle can be adjusted on site to suit the material.
Ceramic-lagged idler
Idler roll with a ceramic or hard-faced shell for extreme abrasion and sticky material.
UHMW-shell idler
Roll sleeved with ultra-high-molecular-weight polyethylene to shed sticky fines.
Rubber-disc (impact) roll
Roll with stacked rubber discs that cushions impact and resists build-up under chutes.
Spiral (helical) return roll
Return roll with a helical surface that self-cleans and sheds carry-back.
Self-aligning return idler
Pivoting return set that corrects belt drift on the empty side.
Friction (brake) idler
Return idler that resists rotation to help hold an inclined belt and cut run-away risk.
Idler roll length
Face length of the roll; the three rolls of a troughing set sum to roughly the developed trough width.
Idler shaft diameter
Shaft size (commonly 20, 25 or 30 mm) set by the load on the roll.
Idler bearing series
Bearing size inside the roll — 6204, 6205, 6305, 6306 are typical.
Idler axial clearance
End float of the roll on its shaft; kept small to avoid noise and seal wear.
Idler life (L10)
Rated service life at which 10 % of a batch is expected to have failed.
Idler water resistance (IP)
Ingress-protection rating of the bearing housing; good idlers reach IP65 or better.
Idler dust resistance
Ability of the seal to keep airborne dust out; decisive in coal and cement duty.
Idler shell thickness
Wall thickness of the roller tube. Below 2 mm the roll dents permanently under impact and loses balance.
Idler roll diameter
Nominal outer diameter of the roll. Larger diameters suit wider belts, higher speeds and abrasive material.
Idler roll runout
Radial wobble of the rotating shell; out-of-tolerance runout shakes the belt and shortens bearing life.
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