Idlers are the cheapest component on a conveyor and the most expensive to ignore. A single seized roller can groove through a belt bottom cover in a matter of shifts.
1. Noise that changes with load
A dry bearing announces itself before it fails. Rumbling that rises with belt load usually means the bearing has lost lubrication; a rhythmic knock suggests shell damage.
2. Flat spots on the shell
A roller that has stopped turning develops a flat wear face. Once flat, it grinds rather than rolls, and the belt bottom cover pays the price.
3. Material build-up on return rolls
Carry-back accumulating on return idlers changes their effective diameter and pushes the belt off-track. It is a cleaning-system symptom as much as an idler symptom.
4. Belt mistracking that moves along the route
If the belt wanders at one specific frame, suspect that frame's idler alignment before adjusting the whole conveyor.
5. Shell wall thinning
Measure the shell wall at the mid-point. Once wear approaches half the original wall thickness, the roller should be scheduled for replacement rather than monitored.
A practical inspection interval
For quarry duty, a walking inspection every week and a measured inspection every quarter catches nearly all failures before they reach the belt. Record findings by frame number so wear patterns become visible over time.