Lubricant Distributions and Lubrication State under Regular and Quantitative Oil Supply

The high-speed spindles equipped in the machine tool have been developed to meet the demands for machining efficiency and surface quality. The rolling bearings assembled in the high-speed spindles always suffer from starvation because of inadequate lubricant supply. In the traditional lubrication methods, a large amount of lubricant was fed into the bearing, causing churning loss but still in starvation states after a period of running. Alternately, a new lubricant method with regularly and quantitatively lubricant feeding was proposed to deliver to the bearing in time replenish the lost lubricant from the rolling track. To fundamentally validate this concept, lubricant was fed to the EHL contacts with a high-precision micro-dosage syringe pump. An optical ball-on-disc apparatus was used to observe the lubricant distributions and lubrication states under different oil supply conditions. By regulating the oil feeding parameters, such as the oil supply time τ, the oil supply interval time T, the number of oil supply n, and the single oil supply volume q, different oil supply conditions were obtained. In this paper, the effects of these parameters on the lubrication states were observed. The lubrication states under different oil supply methods were also compared to represent the advantages of the new method. The results showed that the oil supply time τ was the main factor determined the shape of the oil reservoir and the lubrication state. With the increase of the oil supply time τ, the inlet distance and the lubrication state of the contact area were improved. There existed a critical oil supply time that made the lubricant reached a feed-loss balance, beyond which the increase in the oil supply time had little effect on the lubrication state. Under the same total oil supply amount, the increase in the single oil supply time within a certain range would significantly improve the lubrication state. After the contact reached a stable state, the lubrication duration could be extended by extending oil supply interval. In another words, the consumption of lubricant amount could be reduced for the same lubrication time. Under a proper oil supply time τ and oil supply cycles n, the oil supply interval T became less important. However, the increase of the oil supply interval T meant that the amount of lubricant was reduced within the same lubricating time t. Compared with the previous method of single droplet lubricant supply, the present method could effectively improve the lubrication states. The main reason was that the present lubricant supply method formed higher oil ridges to facilitate lubricant replenishment. In addition, the lubricant supply position affected the time that the contacts reached an equilibrium state and the lubricant consumption. If the oil supply position was set on the right side of the raceway, the amount of lubricant and the lubrication time reached the feed-loss balance would be increased due to the restriction of lubricant replenishment. With the increase in oil supply amount, the oil reservoir on the right side gradually migrated to the left and finally reached a symmetry oil reservoir. Capillary force contributed to the lubricant transportation. It showed that the regular and quantitative oil supply method could efficiently improve lubricant state, extent lubrication duration, and reduced lubricant consumption.