Study of fittings of silicon nitride bearings

摘要

Ceramic bearings made of silicon nitride were implemented for the purpose of producing bearings capable of operating under severe conditions where traditional rolling bearings made of steel could not operate. However, when all-ceramic bearings in which inner and outer rings and rolling elements are made of silicon nitride are attached to a steel shaft, a difference in the coefficient of linear expansion of steel and silicon nitride results in the expansion of a steel shaft due to a temperature rise during the operation and, in the worst cases, the development of excessive stress and damage of the inner ring made of silicon nitride. In the present work, static fitting tests by heating a silicon nitride ring attached to a steel shaft were performed with the purpose of establishing the limit interference at the failure of the silicon nitride ring and dynamic tests by attaching an all-ceramic bearing to a steel shaft were performed by supplying a heated lubricant during its rotation. Three types of shafts (solid, hollow, and spline) were used in tests of both types. Obtained results allowed that clarification that the application of a hollow shaft and a spline shaft in both static and dynamic tests resulted in an increase in the limit interference by about 1.3, compared to that established for a solid shaft. It was additionally found that the interference limit under dynamic conditions amounted to about 60% of that established under static conditions.