Why do GRAPHALLOY bushings have oversize OD and ID dimensions relative to my housing and shaft diameters?
A. A GRAPHALLOY bushing needs to be retained in its housing via an interference fit. The coefficient of thermal expansion of GRAPHALLOY material grades is low relative to steel and other housing materials. In order to maintain retention at elevated temperatures, the initial press fit needs to be sufficient to overcome this difference. Graphalloy is also fully elastic and the interference between the bushing OD and the housing ID will close up the bushing ID upon installation in the housing. The bushing also needs to have a clearance with the rotating shaft to allow movement. If the housing and shaft are similar materials and are heated to similar temperatures, then the clearance in the bushing ID will increase slightly through the temperature range (the compression fit becomes relieved and the bushing ID follows the expansion of the housing ID).
