固液界面对流体动压润滑膜厚的影响

Effects of the Liquid/Solid Interface on Thickness of Hydrodynamic Lubricating Films

目的研究固液界面对流体动压润滑油膜厚度的影响。方法在面接触润滑油膜光学测量装置中,旋转的光学玻璃圆盘和静止的微型滑块平面构成面接触摩擦副。实验选取PAO6和80%甘油水溶液作为润滑剂,而滑块使用的表面材料为钢和二氧化硅两种。实验中分别利用同种润滑液体与不同滑块表面材料组合,以及不同润滑液体与同种滑块表面材料组合成不同界面组。针对不同界面组进行不同条件下的膜厚-速度关系曲线的测量。各界面的亲和性通过液体对固体的接触角评价。结果 PAO6/钢界面与PAO6/SiO_2界面产生的膜厚-速度曲线无明显差别,并与经典润滑理论计算值保持一致。而PAO6对钢表面和二氧化硅表面的接触角分别为17.5°和21.9°,两界面的亲和性差别不大。当界面组内各界面亲和性差别较大时,对应的膜厚表现出差别。亲和性较弱,或对应液体在固体的接触角较大时,膜厚相对较低。对于文中实验条件,界面效应随载荷的增加表现明显。初步分析表明,载荷的增加会加大摩擦副出口处油膜的剪切应变率,诱发滑移,从而使得界面效应明显。结论在流体动压薄膜润滑条件下,固液界面亲和性可以对膜厚产生明显的影响。

The work aims to investigate the effects of liquid/solid interface on thickness of hydrodynamic lubricating film. In an optical surface-contact lubricating film thickness tester, the surface-contact friction pair was composed of a rotary optical glass disc and a stationary micro slider. PAO6 and 80% glycerol aqueous solution were used as lubricants while steel and SiO_2 were used as the surface materials of sliders. In the test, one lubricant was combined with different surface materials of sliders and different lubricants were combined with one surface material of sliders to constitute different interface groups. For each interface group, film thickness-speed curves were measured under different conditions. The affinity of various interfaces was assessed by the liquid-solid contact angles. Results indicated that the PAO6/steel interface and the PAO6/SiO_2 interface showed negligible difference in film thickness-speed curves, and the curves agreed well with theoretical predictions. The contact angle of PAO6 on these two slider surfaces were 17.5° and 21.9° respectively, showing strong affinity but less difference between the two. However, in case of large affinity difference in the interface groups, the film thickness also showed difference. When the interface affinity was weak, or corresponding liquid-solid contact angle was large, the film thickness was relatively low. Under the present experimental conditions, interfacial effects varied significantly with the increase of load. Preliminary analysis indicated that load increase would induce slippage and therefore enhance interfacial effects since it would increase shear rate of oil film at the outlet of friction pair. Provided with hydrodynamic lubrication, the affinity of solid/liquid interface can have obvious influence on the film thickness.