Research On The Lubricating Characteristics And Mechanisms Of Aqueous Emulsions

Although the water-based lubricant has a wide application in many fields, such as metal processing, biological lubrication, micromachine, and so on, the film formation characteristics and mechanism are still dubious. As to the oil-in-water emulsion, which has been widely used in metal working, the film formation mechanism needs further discussion and research in spite of numerous previous studies.In this study, a testing set-up system has been developed for observation and film-thickness measurement of water-based lubrication, and the relative optical interference intensity technique has been validated and improved. By using this system, thickness and the state of the lubricant film at nanometer scale under point contact with different sliding ratios can be measured and real-time traced. The loading and rotating systems both can be automatically controlled. The locating measurement for the film thickness was also developed. Thus, measurement with high resolution and precision can be obtained. Therefore, the testing system lays the foundation of the study on water-based lubrication in point contacts.In the research for the lubrication of water with micro content of oil, different surfaces and liquid feeding modes were adopted. A relatively high film thickness was obtained in the experiment although the oil volume concentration was extremely low (<1×10^-3%), which does not agree with the traditional EHL (elastohydrodynamic lubrication) theory. The film forming ability attributes to the the micro content of oil contamination. The competitive wetting behavior of water and oil on the surface was investigated to explain the mechanism, which premises for the feasibility of micro-content-oil lubrication.The film formation of oil-in-water emuslion under point contact was found to be sensitive to the feeding mode, rolling speed, emulsifier and oil concentration. The critical speed of film thickness was detected to be effected significantly by the oil concentration by ultilizing emulsion with micro content of oil. The observation of the emulsion flow surrounding the contact area was carried out for direct explanation of the film formation mechanism. Reemulsification effects near the contact area were raised for the film formation mechanism based on the modeling validation. During the investigation, good film formation ability can be obtained when the oil concentration is lower than 0.5%. An emulsion film about 80nm can be obtained at 1m/s when the oil concentration is 0.0005%, which provides effective experiemental evidence for the micro-oil-content lubrication.