Analysis of the influence of small quantity secondary lubricant on water lubrication

The use of water-lubricated bearings has increased dramatically in recent years because of environmental concerns. However, due to its low viscosity water generates easily broken lubrication film, which may cause wear and noises when water-lubricated bearings are subjected to short-time sever working conditions, e.g., low speeds and impact loads. A block-on-ring test rig is used in our work to simulate working conditions of water-lubricated bearings under the mixed lubrication regime and the coefficient of friction (COF) is monitored during the experiment. After the COF is stable between the rubber block and the stainless-steel ring lubricated by water, a small quantity of secondary lubricating medium (#5 white oil) is injected into the contact region. The COF decreases accordingly and its stable value is smaller than that under water-lubricated condition. The flow of water and #5 white oil, as well as the interaction between these two phases, are examined by CFD simulation. The results show that #5 white oil can break though the reverse water flow at the inlet and enter into the contact region to participate into the lubrication, and small oil droplets are formed during the injection, which are distributed throughout the contact area and stuck on the block and the ring to improve the lubrication performance. Therefore, the injected #5 white oil could enhance the film-forming ability of water, reduce the COF and improve the tribological behaviors of the water-lubricated contacts. Our work thus provides a new lubrication method to alleviate the friction and wear of water-lubricated bearings when subjected to short-time severe working conditions.