What Is a Hub Flange?

A hub flange is a device used to support a wheel, pulley or sprocket on a machine. Consisting of a flat, steel plate fitted with mounting studs around the perimeter, the hub flange provides a location for the pulley, wheel or gear to be mounted while also providing a bearing location to allow the flange to rotate smoothly. It is common for a hub flange to be used as a component in a bearing assembly, making changing a bad bearing a simple, one-step procedure. The purpose of a hub flange is not only to house the mounting studs for the wheel, pulley or sprocket, but to also provide a flat and smooth surface that is machined perfectly plumb to provide a straight-running attachment that will track correctly. By creating the flange perfectly flat and plumb, the wheel or sprocket will not wobble or run off-center when mounted onto the hub assembly. This increases efficiency and adds greatly to the life expectancy of the bearing in the assembly. In the case of a belt or chain, these components also receive added life by running straight on the assembly and not experiencing premature wear by rubbing against the side of a wobbly assembly.
In order to create a hub flange that is part of a bearing assembly, the flange is often cast or machined as either the inner or outer bearing race, depending on the application. This type of manufacturing design, popular in both machine and automobile manufacturing and design, adds greatly to the total strength of the flange assembly and lowers the manufacturing cost of building the assembly. This cost savings can be passed onto the customer, making the design popular among discount auto supply stores as well as automobile and machinery manufacturers. While some hub flange designs use a greaseable bearing hub, the vast majority do not. The sealed bearing used in the non-greaseable design allows the unit to operate for long periods with no maintenance needs. The downside of this type of assembly is that once a problem is detected with the unit, the entire assembly must be changed. With a greaseable unit, the bearing is lubricated before and during every work cycle. This not only provides the proper amount of lubrication to give the hub flange a long working life, it also forces the worker to look at the assembly and check it for issues at every start-up.