Rolling Contact Wear of Hybrid Ceramic Bearings with Refrigerant Lubrication.

Abstract

Silicon nitride Si3N4 bearing elements have shown practical advantages over traditional steel elements due to their mechanical and physical properties. Leading technology and demands for high efficiency have caused loading bearing contacts in all kinds of machinery to be subjected to high speeds, high contact stresses and severe conditions of lubrication. In addition the introduction of a new generation of hydrocarbon refrigerants in various systems, where these rolling contact silicon nitride bearing elements are employed raises further demands to evaluate the rolling contact fatigue performance of these elements with refrigerant lubrication. Obtaining material wear properties of these refrigerants used in mechanical applications is difficult due to high saturation pressure of the refrigerants. It is important to investigate the influence of these refrigerants as lubricants on the rolling contact fatigue performance of ceramic bearing elements. This research responds to the need for bench testing of rolling contacts using the new generation refrigerants as lubricants. A novel pressurised chamber was designed to achieve a liquid state of the refrigerant as fluid for the rolling contact fatigue experiments. A high-speed rotary Tribometer was used for rolling contact fatigue tests. Experimental study of the influence of the liquid refrigerant lubrication on rolling contact wear of the silicon nitride/steel elements is presented. Investigations of the lubricated contact of silicon nitride rolling elements using the pressurised chamber reveal that wear rate is affected by the nature and geometry ofthe induced defect. A residual stress survey was also performed on failed ceramic elements. Analysing the relationship of residual stress with rolling contact fatigue is an important study which will provide guidelines on the design process and manufacturing of these elements. The residual stress field analysis shows that residual stresses are relieved due to sub-surface damage and are inversely related to stress cycles. Maximum tensile stresses at the edges of the contact path cause a weaker residual stress field at the sub-surface crack front.