In bulk material handling, belt conveyors move coal, cement, clinker, grain, fertiliser and countless other materials over long distances. The belt gets most of the attention, but the idlers that support it are just as important. Poor idler selection or maintenance shortens belt life, increases power consumption and causes spillage that costs time and money to clean up.
What Idlers Do
Idlers are the rollers that support the belt along its length. On the carrying side, troughing idlers shape the belt into a trough so material stays on it. On the return side, flat return idlers support the empty belt. Special idlers handle impact at loading points and help keep the belt tracking straight.
Types of Idlers
- Troughing idlers: usually three rolls set at an angle, commonly 20, 35 or 45 degrees.
- Impact idlers: rubber-ringed rolls at loading zones that absorb shock from falling material.
- Return idlers: flat rolls under the return belt, sometimes with rubber discs to shed sticky material.
- Self-aligning or training idlers: pivoting assemblies that steer the belt back to centre.
- Transition idlers: set at intermediate angles near pulleys to protect the belt edges.
Choosing the Trough Angle
A deeper trough carries more material and reduces spillage, but it requires a more flexible belt. Light, free-flowing materials may only need a 20-degree trough, while bulky materials on heavy-duty conveyors often use 35 or 45 degrees. The belt and idlers must be specified together.
Idler Spacing
Spacing affects belt sag. Too much space between idlers allows the belt to sag, causing material to shift and spill, and increasing power consumption. Spacing is usually closer at loading points and wider on return runs. Heavier materials require closer spacing.
Roller Quality
Good idlers rotate freely with well-sealed bearings. Seals keep dust and moisture out, which is especially important in cement, coal and fertiliser environments. A seized idler rubs against the belt, causing wear and sometimes generating heat that can be a fire risk with combustible materials.
Shell and Material Options
Steel rolls are standard for most applications. In corrosive environments, such as fertiliser plants or coastal locations, HDPE or rubber-lagged rolls may last longer. Lightweight materials also reduce noise and make replacement easier.
Maintenance Tips
- Walk the conveyor regularly and listen for noisy bearings.
- Replace seized idlers promptly.
- Keep loading zones clean to prevent material building up around rollers.
- Check belt tracking and adjust training idlers when needed.
- Record replacements to identify sections with repeated failures.
Belt Cleaners and Skirting
Idlers suffer when material falls off the belt and builds up around them. Effective belt scrapers at the head pulley remove carry-back from the return belt, while skirt boards and sealing rubber at loading points keep material on the belt. These components are inexpensive compared with the cost of replacing idlers and belts early. When surveying a conveyor, look closely at the area under the head pulley and around the tail; heaps of spilled material there usually point to cleaner or skirting problems that are also shortening idler life.
Designing for Reliability
Many idler problems start at the design stage, with spacing or impact protection that does not match the material. When planning a new conveyor, provide your supplier with full details of material type, lump size, capacity and operating conditions.
Hilden designs belt conveyors and bulk material handling systems for industrial plants, selecting idlers and layouts that keep belts running reliably and reduce maintenance over the conveyor’s life.
