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Unformatted text preview: W. Gregory Sawyer 1 Thierry A. Blanchet Department of Mechanical Engineering, Aeronautical Engineering and Mechanics, Rensselaer Polytechnic Institute, Troy, NY 12180 Vapor-Phase Lubrication in Combined Rolling and Sliding Contacts: Modeling and Experimentation The in situ vapor-phase lubrication of M50 steel, in combined rolling and sliding contacts at 540°C using nitrogen atmospheres containing acetylene, is achieved. Acetylene partial pressures of 0.05 atmospheres are capable of providing continuous lubrication to com- bined rolling and sliding contacts through pyrolytic carbon deposition. In these tests, friction coefficients as low as m 5 0.01 are found for contacts at 2.0 m/s rolling speed, 10 cm/s sliding speed, 100 N load (1.3 GPa Hertzian contact pressure), and ambient tem- perature of 540°C, with even lower values observed at more modest sliding speeds. One example of a model for vapor phase lubrication of combined rolling and sliding contacts is developed which predicts the lubricant steady-state fractional coverage of the contact surfaces, and from this makes friction coefficient predictions using a linear rule-of- mixture. Friction coefficient responses to step changes in acetylene partial pressure, sliding speed, and disk wear-track diameter are measured. Increased partial pressure of acetylene and increased area available for deposition are observed to be beneficial, while increased sliding speed is detrimental to lubrication performance. Shapes and trends of steady-state friction coefficient versus acetylene partial pressure, sliding speed, and disk wear-track diameter are described and curve-fit by the model. In combined rolling and sliding this example model predicts large regions of operating conditions over which friction coefficient is independent of rolling speed, as well as regions of independence of vapor partial pressure. In the special case of pure sliding, a region of friction coefficient independence of a ratio of partial pressure to sliding speed and another region of inde- pendence of a ratio of partial pressure to the product of sliding speed and normal load are predicted. @ DOI: 10.1115/1.1308039 # Introduction The conditions in many future high temperature bearing appli- cations will require the use of a lubricant that can endure high sliding speeds, high contact stresses, and extreme operational tem- peratures ~ up to 700°C and higher are often discussed ! . Because predeposited lubricant coatings wear during operation, their life- times are limited. ‘‘Vapor-phase lubrication,’’ as used here, is a general term which encompasses a broad range of approaches by which bearing surfaces interact with their gaseous environment to form solid lubricating deposits. As these deposits are being re- plenished even as existing solid lubricant is being worn away, vapor phase lubrication is a candidate approach under extended durations of such extreme condition @ 1,2 # . Numerous variations of vapor phase lubrication exist. For example, tricresyl phosphatesvapor phase lubrication exist....
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.
- Spring '08
- Mechanical Engineering