Lagging is the rubber or ceramic layer bonded to a pulley shell. Its job is to raise the friction coefficient between belt and pulley, and to protect the shell from wear. Both benefits matter most on the drive pulley — and much less elsewhere.
Where lagging is essential
On the drive pulley, available friction determines how much tension the drive can transmit before slipping. A bare steel shell in wet conditions can lose half its effective friction. Diamond-grooved rubber lagging restores it and channels water away from the contact area.
Where it is usually unnecessary
Tail, bend and snub pulleys transmit little or no torque. Unless the conveyor handles sticky material that builds up on the shell, plain pulleys are adequate and cheaper to maintain.
Rubber, ceramic or nothing
- Plain rubber (herringbone or diamond): general duty, wet or dry, moderate tension.
- Ceramic (dimpled tiles): high-tension drives, very wet or abrasive duty; roughly three to five times the service life of rubber at a higher initial cost.
- None: low-tension non-drive pulleys in dry, clean applications.
Thickness and drum diameter interact
Lagging adds to the effective pulley diameter, which changes belt speed slightly and — more importantly — must be included when checking the belt's minimum bending diameter. A 12 mm lagging on a 400 mm shell gives a 424 mm effective diameter.
When a drive slips, the reflex is often to increase take-up tension. That raises stress on splices, bearings and the belt carcass. Correct lagging solves the same problem without adding tension.
