What a Five-Roll Idler Set Does
A five-roll idler set is a support assembly that carries the conveyor belt on the load side using five rollers arranged in a trough shape. Instead of the common three-roll arrangement, this set adds two extra rolls to spread the belt load over a wider contact area. In quarry, iron ore, and cement plant operations, that extra support can help control belt sag and reduce stress on the belt edges when wide belts carry dense material. The assembly is also known as a five-roller trough idler set, and it belongs to the troughing idler family. It is not a drive pulley, tail pulley, or bend pulley, and it does not replace those components.
Construction and Roller Layout
The set typically consists of five idler rollers mounted in a steel frame with conveyor brackets at each end. The two outer rolls are angled upward to form the trough, while the center rolls sit lower to support the middle of the belt. Common roller diameters for this type include Ø89, Ø108, Ø127, Ø133, and Ø159 mm, though the final size depends on belt width and load. Roller surfaces may be steel tube, nylon, ceramic, or rubber rings; rubber rings are often chosen for impact zones near a crusher or transfer point. Bearings such as 6205, 6305, 6308, or 6310 are used according to the roller diameter and duty. The trough angle is usually 20, 30, 35, or 45 degrees, and a slight forward tilt of about 1.5 to 2 degrees may be used on training idlers, not on every set.
Where It Fits in the Conveyor Line
These sets are most often installed in the carrying run of long overland conveyors, plant feed lines, and stockyard conveyors. In a limestone mine or sand and aggregate line, a five-roll set can be used where the belt is wide and the material load is heavy. In a coal washing plant or power plant coal handling system, the set helps keep the belt centered and stable. A typical five-roll idler set is not a substitute for a return idler, impact idler, or self-aligning idler; those are separate subtypes with different jobs. For comparison, a three-roll trough idler set is lighter and more common on moderate belt widths, while the five-roll version adds support for wider belts and higher loads.
Common Reference Dimensions
The table below gives common reference values, not fixed combinations. Roller length varies with belt width, trough angle, and frame design, and side rolls may differ from center rolls.
| Belt width | Typical roller length (three-roll reference) | Common roller diameter range |
|---|---|---|
| B500 | 200 mm | Ø63 to Ø89 mm |
| B650 | 250 mm | Ø76 to Ø108 mm |
| B800 | 315 mm | Ø89 to Ø127 mm |
| B1000 | 380 mm | Ø108 to Ø133 mm |
| B1200 | 465 mm | Ø108 to Ø159 mm |
| B1400 | 530 mm | Ø127 to Ø159 mm |
| B1600 | 600 mm | Ø133 to Ø178 mm |
| B1800 | 670 mm | Ø159 to Ø194 mm |
| B2000 | 750 mm | Ø159 to Ø219 mm |
These values are examples only. A five-roll set may use different roll lengths because the extra rolls change the geometry. Always confirm dimensions with the conveyor design.
Buyer Checklist
- Match the idler set to the actual belt width and trough angle, not to a catalog guess.
- Check the roller diameter and bearing size against the load and speed of the conveyor.
- Confirm the frame and bracket dimensions fit the existing conveyor stringers.
- For dusty or wet conditions, review seal type and roller surface finish.
- Remember that a five-roll idler set works with the conveyor belt and does not replace the conveyor pulley or drive components.
Whether the plant handles EP conveyor belt or a steel cord conveyor belt, the idler set should be selected for the belt’s load and width. In a cement plant or mining conveyor belt system, a well-matched five-roll idler set can help extend belt life and keep material moving smoothly.
