问题描述:
求人类翻译呀 机械工程专业英语
Although wear generally alters a part's surface topography and may result in severe surface damage, it also can have a beneficial effect. The running-in period for various machines and engines produces this type of wear by removing the peaks from asperities(fig. 16.3). Thus, under controlled conditions , wear may be regarded as a type of smoothing or polishing process.
Lubrication is a process by which the friction and wear between two solid surfaces in relative motion is reduced significantly by the interposing a lubricant between them. There are four types of fluid lubrication that are generally of interest in engineering practice(Fig. 16.4):
1. In thick-film lubrication,the two surfaces are completely separated from each other by a continuous fluid film. The fluid film can be developed either hydrostatically or, more often by the wedge effect of the sliding surfaces in the presence of a viscous fluid at the interface.
2. As the load between the two surfaces increases or as the sliding speed and viscosity of the fluid decrease, the lubricant film becomes thinner(thin-film lubrication). This condition raises the friction at the sliding interfaces and results in slight wear.
3. in mixed lubrication.although the contacting surfaces are separated by a thin lubricant film,asperity contact also may take place.the total applied load is thought to be carried by asperity contacts and partly by hydrodynamic action.
4. in boundary lubrication ,the load is supported by contacting surfaces covered with a boundary film of lubricant(fig.16.4d).this is a thin(molecular)lubricant layer that is attacted physically to the metal surfaces,thus preventing direct metal-to-metal contact of the two bodies and reducing wear.
Although wear generally alters a part's surface topography and may result in severe surface damage, it also can have a beneficial effect. The running-in period for various machines and engines produces this type of wear by removing the peaks from asperities(fig. 16.3). Thus, under controlled conditions , wear may be regarded as a type of smoothing or polishing process.
Lubrication is a process by which the friction and wear between two solid surfaces in relative motion is reduced significantly by the interposing a lubricant between them. There are four types of fluid lubrication that are generally of interest in engineering practice(Fig. 16.4):
1. In thick-film lubrication,the two surfaces are completely separated from each other by a continuous fluid film. The fluid film can be developed either hydrostatically or, more often by the wedge effect of the sliding surfaces in the presence of a viscous fluid at the interface.
2. As the load between the two surfaces increases or as the sliding speed and viscosity of the fluid decrease, the lubricant film becomes thinner(thin-film lubrication). This condition raises the friction at the sliding interfaces and results in slight wear.
3. in mixed lubrication.although the contacting surfaces are separated by a thin lubricant film,asperity contact also may take place.the total applied load is thought to be carried by asperity contacts and partly by hydrodynamic action.
4. in boundary lubrication ,the load is supported by contacting surfaces covered with a boundary film of lubricant(fig.16.4d).this is a thin(molecular)lubricant layer that is attacted physically to the metal surfaces,thus preventing direct metal-to-metal contact of the two bodies and reducing wear.
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