The 4 Most Common Conveyor Idlers

People walk past them every day in plants and mines and barely notice, those little round rollers, spinning under the belt are just doing their job but if one's wrong or worn out, you'll notice real quick because the belts start sagging, drifting or tearing. I've seen million dollar systems slowed to a crawl because of a few bad idlers, so picking the right type and putting them in the right spot always matters more than folks think.

Trough Idlers:More even load distribution

These are the workhorses, three rollers set in a V-shape sometimes called 35° or 45° forming a shallow pocket that cradles the belt and that trough shape keeps material from sliding off and spreads the weight across the whole belt width. In heavyduty mining where rock chunks can be the size of a football, trough idlers keep the load balanced so the middle doesn't get chewed up faster than the edges.

I've once seen belts fail in months when flat rollers were used where a trough should be, the center stretched, the splice tore and the belt started cupping. Swapping in proper trough idlers fixed the wear patternm and the key is to match the trough angle to your material flow and belt speed because too steep and you'll stress the belt edges then too shallow and material starts spilling.

Flat Return Idlers: Prevent stretching, sagging and failure of conveyor belt

You'll find these under the empty side of the belt, just one roller and straight across. Sounds simple but without them spaced right, the belt will sag between frames and that sag stretches the carcass and puts uneven tension on your drive pulley then over time, you get cracks in the top cover or worse the splice starts peeling.

However in waste sorting plants I've serviced, long conveyors with poorly spaced return idlers caused the belt to whip during start up but once we re-spaced them and upgraded to rubber-coated returns in wet areas and the belt tracked straight and stayed tighter. Don't just think of these as “non-load” rollers because they're tension control devices in disguise.

Impact Idler: Absorbs the continuous impact of falling materials

If you're dropping 50 kg of material from three meters up, you better have something under the belt to soften that blow. Impact idlers do this with rubber rings around the roller absorbing the shock so the belt surface doesn't shatter or gouge and they're usually placed right after chutes or hoppers and nowhere else.

I once walked into a quarry before where they had no impact idlers under the main feed chute just steel returns and the belt lasted two weeks before it ripped across the width. Rubber-ring impact rollers aren't cheap but compared to shutting down a 500-ton-per-hour plant they're nothing.

Training Return Idlers: Detect and correct belt misalignment

Belts like to wander like heat, load changes and frame misalignment can push them off-center. Training idlers have a swivel mount or tilt action that nudges the belt back toward the middle when it starts straying so you mostly see them on the return side though some sit on the carry side in tricky spots. In packaging facilities misalignment can ruin product spacing and jam discharge points and installing a couple of training returns after the loading area can cut daily adjustments in half. The trick is don't overuse them, so if you need one every five meters there's a bigger alignment problem upstream.