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Engineering Tribology Episode 2 Part 9

Tham khảo tài liệu 'engineering tribology episode 2 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Solid Lubrication and Surface Treatments 425 various test machines were also increased by the addition of suspended molybdenum disulphide 49 50 . Although in most cases 1 concentration by weight of molybdenum disulphide in oil is sufficient improvements were still obtained at higher concentrations reaching 5 49 . FIGURE 9.15 Comparison of the durability of a gold lubricant film produced by different coating techniques under fretting conditions 46 . However an increase in wear when molybdenum disulphide is added to oil has also been reported 51 . under moderate conditions of sliding speed and load where molybdenum disulphide is not expected to improve lubrication abrasive impurities in the solid lubricant can cause rapid wear 51 . Silica in particular accentuates wear when in concentrations above 0.01 and pyrites iron sulphide are also destructive 51 . The quality i.e. cleanliness of the solid lubricant added to oil is therefore critical. Although solid lubricant additives are suitable for extremes of loads and speeds they are not suitable for reducing wear under moderate conditions. Molybdenum disulphide suspensions provide a limited reduction in friction and wear when added to an oil containing sulphur based additives or zinc dialkyldithiophosphate. on the other hand the presence of detergents or dispersants in the oil such as calcium sulphonate inhibits the lubricating action of molybdenum disulphide 48 50 . The mechanism of lubrication by molybdenum disulphide dispersed in oil has unfortunately received very little attention. it is widely believed however that molybdenum disulphide provides a complimentary role to surfactants. Where there is a worn surface devoid of surfactant it is hypothesized that molybdenum disulphide particles adhere to form a lubricating film. A conceptual model of solid lubrication by molybdenum disulphide which occurs only when there are no surfactants to block adhesion by lamellae of solid lubricant to the worn surface is illustrated .