The straight tracking of the belt may be compromised by the type of conveyed material, especially when this material is sticky and thereby adheres easily to the belt surface. In this case, material is also deposited on the return rollers that support the belt, adding an irregular addition of scale to the roller itself. Consequently, not only wear and tear of the belt occurs, but forces are brought into play to move the belt away from its correct track.
Return rollers with spaced rubber rings contribute largely to eliminating the build-up of scale that forms in certain conditions on the belt surface. The rings are pointed, assembled at intervals, in the central part of the roller, where they have the scope to break up the scale which normally is present at the belt centre; meanwhile flat rings mounted in groups at the extremities of the belt, support and protect the belt edges, also in cases of limited belt wandering. Return rollers with rings should not be used as belt tensioning devices.