The conveyor belt slips on the drive pulley under load. You tighten the tensioner and it helps for a week, then slips again. The belt isn’t stretching. The problem is the wrap angle on the drive pulley.
Friction needs wrap, not just tension
A belt transmits torque through friction between the belt and the drive pulley. The amount of friction depends on the coefficient of friction and the angle of wrap. More tension helps, but it also stretches the belt and wears the bearings. A bigger wrap angle gets more traction without cranking the tensioner.
On a small pulley, the belt wraps 180 degrees. Add a snub roller on the return side and the wrap goes to 210 or 220 degrees. That extra 30 percent of wrap can double the friction without adding belt tension. For a slipping drive, this is the first thing to check before you crank the tensioner.
Too much tension is its own problem
Overtensioned belts stretch, wear the pulley bearings, and tear at the fasteners. The drive pulley wears a groove where the belt runs. The belt edges fray. If you’re tightening the tensioner every month, the belt was never right. Set it to the minimum tension that doesn’t slip under full load, then leave it.
A new belt stretches the first week. Tension it once after the first 8 hours of run-in, then leave it. If it still slips after run-in, the problem is wrap angle or pulley condition, not tension.
Pulley lagging
A bare steel pulley is smooth. A lagged pulley has a rubber or ceramic coating that grips the belt. On wet or dirty conveyors, lagging is the difference between traction and slip. Smooth lagging works for light duty. Diamond lagling bites into the belt for heavy loads. Replace the lagging when it’s worn smooth; it’s cheaper than a new pulley.
The tail pulley is a drive problem too
If the tail pulley is crowned wrong or the belt wanders, the belt pulls to one side and edges the pulley. The effective wrap on the drive pulley drops because the belt isn’t centered. Fix tracking before you fix tension. A mistracked belt slips because it’s riding the edge, not because the tension is low.
Bottom line
When a belt slips, check the wrap angle and the pulley lagging before you tighten the tensioner. More tension is a band-aid that shortens belt and bearing life. Fix the friction, not the stretch.
