tailieunhanh - Engineering Tribology 2E Episode 10

Tham khảo tài liệu 'engineering tribology 2e episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Boundary And Extreme Pressure Lubrication 381 which offer a much wider freedom of chemical specification systematic optimization of the heat of adsorption may eventually become practicable. HIGH TEMPERATURE - MEDIUM LOAD LUBRICATION MECHANISMS There has always been much interest in oil based lubrication mechanisms which were effective at high temperatures. The primary difficulty associated with lubrication is temperature whether this is the result of process heat . a piston ring or due to frictional energy dissipation . a high speed gear. once the temperature limitations of adsorption lubrication were recognized the search began for high temperature mechanisms . Although these mechanisms have remained elusive some interesting phenomena have been discovered. Two basic mechanisms involved in high temperature lubrication at medium loads have been found chain matching and formation of thick films of soapy or amorphous material. chain matching is the modification of liquid properties close to a sliding surface in a manner similar to the low temperature - low load mechanism but effective at far higher temperatures and contact pressures and dependent on the type of additive used. The thick colloidal or greasy films are deposits of material formed in the sliding contact by chemical reaction. They separate the opposing surfaces by a combination of very high viscosity and entrapment in the contact. Chain Matching chain matching refers to the improvement of lubricant properties which occurs when the chain lengths of the solute fatty acid and the solvent hydrocarbon are equal. This is a concept which is not modelled in detail but which has periodically been invoked to explain some unusual properties of oil-based lubricants. In a series of four-ball tests the scuffing load was found to increase considerably when the dissolved fatty acid had the same chain length as the carrier fluid lubricant 43 . An example of scuffing load data versus chain length of various fatty .