Experimental Study On The Performance Of Lubricating Films In Ball-on-ring Contacts

A simple ball-on-disc configuration is widely used to simulate and conduct fundamental research on rolling bearing lubrication.In fact,the ball-on-ring configuration is preferable since the contact geometry is more like the prototype of a real bearing.However,researches using the ball-on-ring contact is quite limited mainly due to the difficulties in the glass ring manufacturing,the layer coating and the optical design.In addition,the varies in the contact geometry and forces on the lubricant will affect the lubrication behaviors,which is expected to be further explored.It is therefore necessary to develop a new ball-on-ring apparatus to experimentally study the lubrication performance of this contact type.In view of film thickness and friction force are two key factors to character lubrication performance,the present ball-on-ring apparatus is designed to simultaneously measure the film thickness and friction force.To simulate the contact of rolling element and outer race of a bearing,the steel ball-glass ring configuration is employed.By using the transparent glass ring,the film thickness can be measure via the dichromatic interference intensity modulation approach.To obtain different rolling-sliding motions,the steel ball and the glass ring are independently driven.A pre-press operation is imposed at both sides of the loading lever so as to accurately capture the friction force.Observation of different lubrication behaviors induced by differences in contact geometries between ball-on-ring and ball-on-disc.Under the same operation conditions,both film thickness and friction in the types of contacts were compared.It is found that under pure rolling conditions,the film thickness in the ball-on-disc contact is larger than that of the ball-on-ring contact.Under rolling-sliding conditions,the value of friction from ball-on-ring contact is greater than that of the ball-on-disc contact.This probably attributes to the differences in elliptical ratios and orientations of centrifugal forces.Influence of surface roughness of ball-on-ring contact pair on lubrication performance.Both friction force and film thickness of with different surface roughness were measured.With steel ball-steel ring,it is found that the friction coefficient reduces to an almost constant value over test cycles under the same working conditions.In steel ball-glass ring contacts,the friction coefficient will become higher if the surface roughness of the steel ball increase in the mixed lubrication regime,whilst in the full film regime the effects of roughness on the friction are inconsiderable.Influence of lubricant structure on lubrication performance in ball-steel ring contacts.Experiments were conducted to measure friction coefficient under different operating conditions.The effects of entrainment velocity,the rolling-sliding ratio,the viscosity,and the molecular chain structure on the friction coefficient were discussed.The results show that the lubricant structure strongly affects the friction coefficient.The friction coefficient of the lubricant with ring molecular structure oil is higher than that of lubricant with long chain molecular structure.According to the results,the underlying mechanisms were analyzed.