Abstract: The purpose of this paper is to study the influence of lubrication and cleanliness on the life of rolling bearings. The method is: through the statistics of the existing research results at home and abroad, and the analysis and comparison of the experimental data, the control variable method is used to analyze the influence of lubrication and cleanliness on the bearing life. The results are as follows: bearing life is proportional to lubricant viscosity and bearing cleanliness when bearing type, material, size, working conditions and other factors are consistent, and bearing life correction coefficient is closely related to viscosity coefficient. It is concluded that ensuring the viscosity and cleanliness of the rolling bearing lubricant can effectively extend the service life of the rolling bearing. In this paper, a new calculation method for the life of rolling bearings and a comparison of the influence of lubrication and cleanliness on bearing life under different working conditions are used to reveal the degree of influence of lubrication and cleanliness on bearing life, thus proving the importance of reasonable lubrication and seal design.

Key words: rolling bearing; Lubrication; cleanliness

0 Introduction

With the continuous improvement of product quality, as well as the continuous progress of bearing design, application and other technologies, as well as the gradual improvement of individual requirements for bearing application performance and service life of enterprises and individuals, the impact of rolling bearing service life on mechanical equipment is increasingly apparent. Among the factors that affect the service life of rolling bearings, lubrication and cleanliness are the two main reasons. In this paper, the influence degree of lubrication and cleanliness on rolling bearing life is analyzed and discussed, and illustrated by an example.

1  Influence of lubrication on fatigue life of rolling bearing

Improve the overall efficiency of the system. Rolling bearings use the concentration of rolling contact to carry loads and increase local pressure and stress, so good lubrication and contact surfaces are required to avoid further stress concentration. Therefore, the lubrication directly affects the service life of the rolling bearing, but when the bearing is in the state of boundary lubrication, continue to extend the service time, it will produce direct contact between the metals, in the absence of lubricants, the mutual friction between the metals will shorten the service life of the bearing, and the damage to the bearing is great. On the contrary, when the lubricant is sufficient, the metals are completely separated by the lubricant, which will reduce the mutual friction between the metals and extend the service life of the bearing. In 1967, American scholar Taillian conducted a series of studies on ball bearings and Skurka conducted a series of studies on roller bearings in 1970, initially revealing the relationship between bearing life and lubricating oil film thickness ratio under different lubrication conditions, and then determining that with the increase of film thickness ratio, the service life of rolling bearings can be multiplied. The main failure form of rolling bearings is fatigue pitting [1].

Improving the contact fatigue life of rolling bearings has always been the key research object of scholars at home and abroad. However, in addition to the influence of bearing material and structure on fatigue pitting, lubricant performance also has a great influence on it. However, in lubricants, the correlation of different types of additives and lubricant properties to contact fatigue pitting corrosion is least studied. Some researchers have made a preliminary study on the influence of some additives on contact fatigue by using the contact fatigue tester modified by the four-ball machine friction tester. As relevant scholars at home and abroad have different test methods and test forms, the types of additives studied are also diverse, the relevant mechanism of action is also very different, and the final conclusions are not the same, so far, no consistent results have been obtained [2].

2  Influence of lubricant cleanliness on bearing life

Pollutants, dust, debris generated by wear, alumina and silicon dioxide and other small particles adsorbed on the bearing lubrication surface without special protection will form abrasive type friction, which will cause serious wear on the contact part between the bearing rolling body and the raceway, which greatly reduces its service life. There are three main sources of dust pollution, one of which is that the lubricant used does not meet the relevant requirements, the filtration accuracy is not enough, and the mechanical particles exceed the standard. Nowadays, in China, quantitative research on the impact of pollution degree on bearing fatigue life has achieved certain results [3]. In foreign countries, relevant research has been carried out for a long time and has achieved fruitful results. In 1981, Bhachu et al of Imperial College London on roller bearings, and Loewenthal et al of NASA Lewis Research Center from 1978 to 1982 on ball bearings, all carried out a certain analysis of the degree of change in the life of bearings when using different precision filtered lubricant. Then a method of calculating bearing life based on the filter effect of lubricant is proposed. Finally, it is concluded that the lubricant guarantees good filtration effect and can effectively improve the life of the bearing.

Under the same operating conditions, the lower the vibration and noise level of the bearing, the longer its fatigue life, and one of the important indicators of bearing inspection is vibration and noise [4]. On the bearing vibration measuring instrument, the bearing rotation running test, the speaker will emit intermittent clicking sound, the vibration pulse on the oscilloscope presents a wave type, the main reason for this is that dust and other small particles with the lubricant into the rolling contact area of the rolling bearing, thereby triggering vibration pulse and issuing abnormal sound. Therefore, through a large number of studies and tests on this problem, the small particles brought in by the unrefined lubricant are the main cause of bearing abnormal sound.

3 Comprehensive consideration of lubrication and cleanliness affect life methods

The traditional life calculation method is the L-P equation proposed by Landberg and PAM Green and adopted by the ISO organization, which is based on the relevant data obtained in the bearing life test, and then observe the bearing ultra-long life phenomenon, and summarize a new set of bearing life calculation equations:

Where: α1 is the reliability system. When the reliability is 90%, 95%, 96%, 97%, 98%, 99%, its value is 1, 0.62, 0.53, 0.44, 0.33, 0.21, respectively.α23 is a comprehensive life correction factor reflecting the influence of lubrication conditions on the life of rolling bearings. This is based on the viscosity of the lubricant K=V/V1. In 1989, SKF Engineering Research Center revised this equation and introduced SKF comprehensive life coefficient αSKF to put forward a new revised life calculation equation, namely:

The method of determining αSKF for all kinds of bearings in SKF samples is also published, that is, αSKF is obtained by K and (P1/P).

The deep groove ball bearing 6210 of SKF company is taken as the research object. Rated dynamic load C=35.1kN, speed n = 4000r/min, reliability is 90%(i.e. α=1).

Through experimental comparison and calculation by the above formula, bearing life coefficient is directly proportional to the viscosity and cleanliness coefficient of lubricant when bearing type, material, size, working conditions and other factors remain consistent, and the corrected rated life of bearing is closely related to the viscosity coefficient through life correction coefficient [5]. When the bearing is in full film elastohydrodynamic lubrication, the lubricant is sufficient, and the metals are completely separated by the lubricant, so there is no direct friction between the metals, and there is almost no wear, which extends the service life of the bearing. At the same time, the higher the cleanliness of the bearing, and the fewer particles adsorbed by the metal parts of the bearing, the lower the wear caused to the bearing, and the better the service life of the bearing can be extended. Therefore, it can be seen that good lubrication and high cleanliness can improve the service life of the bearing a lot, the use of lubricants and filtration should be strictly implemented in accordance with the relevant standards, strictly control the accuracy of filtration, so that dust, pollutants and other particles will not enter the bearing with the lubricant. Maintain good cleanliness, timely clean up the pollutants in the bearing part, reduce the wear degree of the metal in the bearing part, thus extending the service life.

4 Conclusion

With the bearing material manufacturing technology more and more mature, and the processing technology level is getting higher and higher, the traditional ISO281:2007 proposed basic rated life calculation method has been gradually replaced, the traditional calculation of bearing life can not be suitable for the development of The Times. Considering that the service life of the bearing is closely related to its working conditions, the change of lubricant viscosity, cleanliness and other factors will have a serious impact on the bearing life, so when the lubricant lubrication is not in place, the lubricant viscosity is insufficient, the lack of lubrication film protection between the bearing and other metals causes direct friction, thus accelerating the aging of the bearing, resulting in reduced service life. For some devices with special requirements, such as wind power gearboxes, nuclear power gearboxes, and transmission systems on high-speed locomotives, when the operating condition deteriorates, the bearing life will be greatly reduced. Therefore, for some devices with special requirements and devices with a harsh operating environment, it is necessary to strengthen the control of the filtration accuracy of the lubricant, so as to prevent particles from entering the bearing of the device with the lubricant.

【 Reference 】

[1] Li Xinglin, Zhang Yangping, Cao Maolai, et al. Practice of monitoring and diagnosis technology of rolling shaft bearing life and Reliability test [J]. Equipment Management and Maintenance, 2014,12 (S1):47-50.

[2] Zhu Liangliang, Lin Sumin, Ji Xiaomin. Research and Analysis on Development of Life Calculation Method of Rolling Bearing [J]. Harbin Bearing, 2014,09 (03):3-6.

[3] Liao Yinghua, Zhang Liangdong, Li Zhirong, et al. Bearing wear Life Prediction of Travelling Star Gear Transmission System Based on Dynamics [J]. Mechanical Transmission, 2013,09 (10):41-45.

[4] Guan C. Cleanliness of Rolling bearing: A New method of Environmental Protection [J]. China Medical Device Information, 2013,06 (08):14-19. (in Chinese)

[5] Zhu Liangliang, Lin Sumin, Lv Qiushuo, et al. Optimization of Calculation Method for Rolling Bearing Life [J]. Machinery, 2015,03 (02):20-24.