Tham khảo tài liệu 'friction and lubrication in mechanical design episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | RollinglSliding Contacts 255 which suggests that the elasticity of the rollers causes the minimum film thickness to increase by approximately 100 times. Dowson and coworkers 4 6 approached the problem from first principles and simultaneously solved the elasticity and the Reynolds equations. Their formula for the minimum film thickness is given in a dimensionless form as H 16 IF013 where 4 a u speed parameters heI e G material parameter aEe p IF load parameter EeR Using the same dimensionless groups suggested by Dowson and Higginson 4 the Grubin solution can be given as GƯ 073 What is particularly significant in the EHD theory is the very low dependency of the minimum film thickness on load. The important parameters influencing the generation of the film are the rolling speed the effective radius of curvature and the oil viscosity. Consequently Dowson and Higginson suggested the following simplified formula for practical use hữ 5 r 0UReỸ 2 where hữ minimum film thickness in. inlet oil viscosity poise Re effective radius in. u rolling speed in. sec 256 Chapter 7 FRICTION IN THE ELASTOHYDRODYNAMIC REGIME The EHD lubrication theory developed over the last 50 years has been remarkably successful in explaining the many features of the behavior of heavily loaded lubricated contacts. However the prediction of the coefficient of friction is still one of the most difficult problems in this field. Much experimental work has been done 7 21 and many empirical formulas have also been proposed based on the conducted experimental results. Plint investigated the traction in EHD contacts by using three two-roller machines and a hydrocarbon-based lubricant 14 He found that roller surface temperature has a considerable effect on the coefficient of friction in the high-slip region thermal regime . As the roller temperature increases the coefficient of friction falls linearly until a knee is reached. With further increase in temperature the .
