Although a lubricant primarily controls friction and wear, it can and ordinarily does perform numerous（许多） other functions, which vary with the application and usually are interrelated（相关的）.
Friction control: The amount and character of the lubricant made available to sliding surfaces have a profound effect upon the friction that is encountered. For example, disregarding such related factors as heat and wear but considering friction alone between two oil-film lubricated surfaces, the friction can be 200 times less than that between the same surfaces with no lubricant. Under fluid-film conditions, friction is directly proportional to the viscosity of the fluid. Some lubricants, such as petroleum derivatives, are available in a great range of viscosities and thus can satisfy a broad spectrum of functional requirements. Under boundary 1 frication condition, the effect of viscosity on friction becomes less significant than the chemical nature of the lubricant. For instance, delicate instruments must not be lubricated with fluids that would attack and corrode the finer metals.
Wear control: Wear occurs on lubricated surfaces by abrasion, corrosion, and solid-to-solid contact wear by providing a film that increases the distance between the sliding surfaces, thereby lessening the damage by abrasive contaminants and surface asperities.
Corrosion wear is generally caused by the products of oxidation of petroleum lubricants. Use of oxidation inhibitors reduces deterioration of petroleum lubricants, and the addition of corrosion preventives protects metal surfaces from any oxidation products that do form.
Temperature control: lubricants assist in controlling temperature by reducing friction and carrying off the heat that is generated. Effectiveness depends upon the amount of lubricant supplied, the ambient temperature, and the provision for external cooling. To a lesser extent, the type of lubricant also affects surface temperature.
Corrosion control: The role of a lubricant in controlling corrosion of the surfaces themselves is twofold. When machinery is idle, the lubricant acts as a preservative. When machinery is in use, the lubricant controls corrosion by coating lubricated parts with a protective film that may contain additives to the thickness of the lubricant film remaining on the metal surfaces and the chemical composition of the lubricant. Additives that react with the sliding surfaces enhance the corrosion control of the lubricant.
Vocabulary
1.lubricant n. 润滑剂
2.derivative v. 引出的 n.派生的事务
3.available a. 可利用的；有用的
4.encounter v. & n. 遭遇；遭到
5.fluid-film 流体润滑膜
6.viscosity n. 粘性；粘度
7.boundary n. 边界
8.significant a. 有（特殊）意义的
9.delicate a. 精密（巧、细）的
10.abrasion n. 擦伤、磨损之处
11.inhibitor n. 抑制剂；防腐蚀剂
12.petroleum n. 石油（产品）
13.spectrum n. 范围；光谱
14.boundary n. 边界
15.corrosion n. 腐蚀
16.combat n. 斗争；竞争
17.contaminant n. 杂质；污物
18.asperity n. 粗糙（度）；凹凸不平
19.oxidation n. 氧化
20.deterioration n. 变坏（质）
21.ambient a. 周围的；环境的
22.provision n. （预防）措施
23.preservative a. 防腐的；防腐剂[料]
24.neutralize v. 使中和；使失效
25.react v. 起反应；回复原状
26.enhance vt. 增强
27.additive a. 附加的；添加剂
28.oxidation n. 氧化
