Concerns for Ceramic Bearings
We all know that bearing products can be made of various materials. And among all the different kinds, the ceramics have special features. They show some practical advantages over traditional bearing steels when they are used as materials for rolling contact bearing components. The properties of ceramics, specifically low density and high stiffness, are important features as to gas turbine and machine tools. High hardness, low coefficient of thermal expansion and high temperature capability are properties also suited to rolling element materials.
According to the research which is made on structure, quality control and manufacturing techniques, ceramic materials are suitable alternative to steel for rolling contact bearing design. This is especially true for hybrid ball bearings, i.e. precision angular contact ball bearings using ceramic rolling elements are now offered as standard components with in the ball bearing manufacturing industry. As a result, an expansion in the use of ceramic bearings necessitates guidelines for the choice of bearings or rolling elements. More and more people pay much attention to this material.
However, nothing is described about rolling contact fatigue behavior, which is fundamental information to assess the lifetime of the material. Due to the lack of such information, some concern for the reliability of ceramic bearings still remains. Thus, it also deserves our study. Rolling contact fatigue is the surface damage process due to the repeated application of stresses when the surfaces of two bodies roll on each other. It is encountered most often in rolling element bearings and gears.
The failure process of rolling contact fatigue involves fatigue crack initiation and propagation, which is related to the characteristics of the surface quality, stress distributions and lubrication condition. Surface crack defects are considered as a main factor that causes rolling contact fatigue failure at the present. It is difficult to detect these surface cracks during high volume production processes and hence it is crucially important to understand their influence and the fundamental mechanism of the failures they cause.
It is common that there are still many other causes which lead to the failure of products except for the rolling contact fatigue. We can draw a conclusion that we should always take other aspects which can affect the service life of products into consideration even if those products made of ceramics have many advantages.
