A straight-faced pulley is the same diameter across the face of the pulley. A crown-faced pulley changes in diameter from the outer edges to the center of the pulley, with the center being slightly larger than the edges.
Crowned pulleys are sometimes used at the conveyor tail as it is widely believed that the crowned face will improve the tracking of the belt as it goes around the pulley and into the loading zone. However, this is not always true, and there are instances where the crown face of the pulley can actually damage the belt.
Crown-faced pulleys should never be used in a high-tension area of the belt. This is usually the driven pulley. The driven pulley may be at the head end, the tail end, or, with a center drive, anywhere along the return side of the conveyor. In these high-tension areas, the additional diameter in the center of the pulley adds additional stress to the center of the belt and may cause carcass and lagging damage. The exception to this is when the rated tension of the belt is 35 kilonewtons per meter (200 PIW) or less; then a crowned pulley may be used anywhere in the system.
In lower tension areas of the belt, crowned-faced pulleys may have a slight influence on belt tracking. However, if there are serious problems with the belt such as belt cupping, belt camber, or idler-junction failure, no amount of pulley crown will track the belt. It is always best to identify the cause of mistracking and cure the problem.
Crown pulleys also present problems with belt cleaners mounted on the face of the discharge pulley.