Most idler rolls in cast-link belt furnaces today are 11 inches in diameter with smooth surfaces.

Their job is to support the belt on the charge end and provide take-up pressure. A smooth surface works best. If the belt is even and everything is aligned, the belt stays centered. If the belt is uneven or rolls are misaligned, the belt will drift to one side. The smooth idler shows this tracking problem early, like a warning, so repairs can be made.

Some furnaces use toothed idler rolls for better tracking. This works only if all other issues are fixed. If problems remain, the stress damages the belt—usually by breaking pins from fatigue.

Idler rolls are built like drive drums, with trunnions inserted one diameter deep. Omega Castings keeps trunnion diameters at or below four inches to avoid metal fatigue from take-up pressure.