Evaluation Method of Friction and Wear Performance of Heavy Load Bearing Grease Using SRV Test Machine

As an important part of rolling bearing, grease is very important to improve the performance of rolling bearing, it is very important for the reliability of bearing and equipment to select the suitable lubricating grease. In order to improve the efficiency of low-speed and heavy-duty grease formula selection and save the cost of bearing bench test, a new method of low-speed and heavy-load grease friction and wear performance test based on SRV fretting friction and wear test machine is proposed. Based on the linear reciprocating motion form of SRV fretting friction and wear testing machine, the method simulates the operating conditions of low-speed and heavy-duty bearings: AISI 52100 bearing steel cylindrical roller with φ6 mm×8 mm, hardness 60±2 HRC, roughness R_a 0.025± 0.005 µm was used for the top specimen roller. AISI 52100 bearing steel disk with φ24 mm× 7.88 mm was used for the bottom specimen disk. Hardness 62±1HRC, roughness 0.035 μm<R_a<0.050 μm; The contact line of the cylindrical top specimen roller/bottom specimen disk was at an angle of 10° with the reciprocating direction. In this paper, four kinds of low-speed and heavy-duty grease were used as test samples to study the correlation between SRV fretting friction and wear test results of low-speed and heavy-load grease and those of FE-8 bearing wear bench test. The influences of load, temperature, reciprocating frequency and stroke on the test method for measuring friction and wear properties of low-speed and heavy-duty grease with the roller-disk geometry using SRV test machine were investigated. In this paper, Pearson correlation coefficient method of correlation analysis method was used to analyze the correlation between the results of different friction and wear test methods. The optimal test parameters of the method were determined: temperature 25 ℃, load 1 kN, stroke 1 mm, frequency 50 Hz, and the repeatability of the established test method was determined by using the Bessel formula under optimal conditions. The results showed that: the correlation between the self-built SRV test method and the results of FE8 bearing bench test was better than that of SH/T 0204-1992 Four-ball machine method and NB/SH/T 0721-2016 high-frequency linear vibration machine. The correlation coefficient between FE8 bearing bench results was 9.59, and the reliability was strong. The wear morphology obtained by four-ball testing machine method, SRV ball/disc test method and the SRV cylindrical roller/disc test method were observed with metallurgical microscope and three-dimensional profile instrument. It can be seen that the wear morphology obtained by the SRV cylindrical roller/disc test method is narrow and long. It is more similar to the fretting sliding wear morphology of cylindrical roller bearings produced along the axial direction during service. This method was used to carry out repeatability test on four samples, and the variation coefficient of grease A was 5.26%, that of grease B was 6.02%, that of grease C was 4.75%, and that of grease D was 6.61%. The variation coefficient of test results was far less than 10%, which indicated that the test results of this test method had a small degree of dispersion and good repeatability. The friction performance evaluation method of low speed and heavy duty bearing greases based on SRV had high resolution, good sensitivity, high matching degree with the service performance requirements of bearing greases and good compatibility in high working conditions. The establishment of this method was helpful to promote the upgrading of wear performance testing technology of bearing greases. It provided technical support for establishing a more perfect and more efficient characterization system of bearing grease anti-wear property.