2022年毕业设计论文外文文献翻译机械设计制造及其自动化轴承的摩擦与润滑中英文对照.docx

Friction , Lubrication of BearingIn many of the problem thus far , the student has been asked to disreAgactrudaollryn,eglect friction . friction is present to some degree whenever two parts are in contact a. nTdhemtoevremon each other friction refers to the resistance of two or more parts to movement.Friction is harmful or valuable depending upon where it occurs. friction is necessary for fastening devices such as screws and rivets which depend upon friction to hold the fast.eBn eltand the parts together drivers, brakes, and tires are additional applications where.friction is necessaryThe friction of moving parts in a machine is harmful because it reduces the mechanical advantage of the device. The heat produced by friction is lost energy becauseAnlsoow, ogrrkeatatekrespopwlaecrei.srequired to overcome the increased friction. Heat is destructive in that it causes expansion. Expansion may cause a bearing or sliding surface. tIof afitgtrigehat ernough pressure builds up because made from low temperature materials may melt.There are three types of friction which must be overcome in moving parts: 1starting, 2sliding, and3rolling. Starting friction is the friction between two solids that tend to resist movement. When two part are at a state of rest, the surface irregularities of both parts tend to interlock anod form a wedging action. T produce motion in these parts, the wedge-shaped peaks and valleys of the stationary surfaces must be ma to slide out and over ea.cThhoethroeur gher the two surfaces, the greater is starting friction resulting fromtheir movement .Since there is usually no fixed pattern between the peaks and valleys of two mating parts, the irregularities do not interlock once the parts are in motion but .sTlidhee ofrvicetrioenacohf tohtehetwr osurfaces is known as slidingAfsrischtiow.n in figure ,starting friction is always greater than sliding friction .Rolling friction occurs when roller devces are subjected to tremendous stress which cause the parts to change shape or deform. Under these conditions, the material in front of a roller tends to pile up and forces the object to roll sliugphhtliyll. This changing of shape , known as deformation, causes a movement ofmoleculeAss. a result ,heat is produced from the added energy required to keep the parts turning andovercome friction.The friction caused by the wedging action of surface irregularities can be overcome partly by the precision machining of the surfaces, .eHveonwethveesre smooth surfaces may require the use of asubstance between them to reduce the friction still more. This substance is usually a lubricant which provida fine, thin oil film. The film keeps the surfaces apart and prevents the cohesive forces of the surfaces from coming in close contact and producing heat .Another way to reduce friction is to use different materials for the bearing surfaces and rotating parts.This explains why bronze bearingss,saonfdt aclolopyper and tin iolite bearings are used with both soft and12 / 10hardened steel shaft. The iolite bearing is porous. Thus, when the bearing is dipped in oil, capillary action carries the oil through the spaces of the bearing. This type of bearing carries its own lubricant to the points where the pressures are the greatest.Moving parts are lubricated to reduce f,riactniodnh, ewaet.aTr he most commonly used lubricants areoils, greases, and graphite compounds. Each lubricant serves a different purpose. The conditions under which two moving surfaces are to work determine the type of lubricant to be used and the system selected for distributing the lubricant.On slow moving parts with a minimum of pressure, an oil gsruofofivceieinst utosudaislltyribute the required quantity of lubricant to the surfaces moving on each other .A second common method of lubrication is the splash system in which parts moving in a reservoir of lubricant pick up sufficient oil which is then distributed to all moving parts during each cycle. This system is used in the crankcase of lawn-mower engines to lubricate the crankshaft, connecting rod ,and parts of the piston.A lubrication system commonly used in industrial plants is the pressure system. In this system, a pump on a machine carries the lubricant to all of the bearing surfaces at a c.onstant rate and quantityThere are numerous osttheemr syof lubrication and a considerable number of lubricants available for any given set of operating conditions. Modpearnysingdruesattreyr attention to the use of the properlubricants than at previous time because of the increased speeds, pressures, and operating demands place equipment and devices.Although one of the main purposes of lubrication is reduce friction, any substance-liquid , solid , or gaseous-capable of controlling friction and wear between sliding surfaces can be classed as a lubricant.Varieties of lubricationUnlubricated sli.dMinegtals that have been carefully treated to remove all foreign materials seize and weld to one another when slid. Itnogtheethaebr sence of such a high degree of cleanliness, adsorbed gases,water vapor ,oxides, and contaminants reduce frictio9n and the tendency to seize but usually result in sevewea；r this is called“ unlubricated” or dry sliding.Fluid-film lubrica.tIinotnerposing a fluid film that comseppleatrealtyes the sliding surfaces results in fluid-film lubrication. The fluid may be introducedaisnttehnetioinl ainllythe main bearing of anautomobile, or unintent,ioansainllythe case of water between a smooth tuber tire and a wet pavement.Although the fluid is usaulaiqlluyid such as oil, wanadtear gas. The gas most comemmopnlloyeyd is a. irwide range of other materials, it may also be aBoundary lubrica.Atiocnondition that lies between unlubricated sliding and fluid-film lubrication isreferred to as boundary lubrication, also defined as that condition of lubrication in which the friction betwee surfaces is determined by the properties of the surfaces and properties of the lu. bricant other than viscosity Boundary lubrication encompasses a significant portion of lubrication phenomena and commonly occurs during the starting and stopping off machines.Solid lubricatiSoonli.d such as graphite and molybdenum disulfide are widely used when normal lubricants do not possess sufficient resistance to load or temperature extremes. But lubricants need not tak only such familiar forms as fats, powder；s, eavnedngsaosmese metals commonly serve as slidingsurfaces in some sophisticated machines.Function of lubricantsAlthough a lubricant primarily controls friction and ordinarily does perform numerous other functions, which vary with the application anadreusinutaelrlyrelated .Friction con.trTohle 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 hea and wear but considering friction alone between the same surfaces with on lubricant. Under fluid-film conditions, friction is encountered. In a great range of viscosities and thus can satisfy a broad spectrum of functional requirements. Under boundary lubrication conditions , thoenefrfficetciot nofbveisccoomseitsyless significant than the chemical nature of the lubricant.Wear contr.owlear 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.Temperature con.tLroulbricants assist 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 contro corrosion by coating lubricated parts with a protective film that may contain additives to neutralize corrosive materials. The ability of a lubricant to control corrosion is directly relatly to the thickness of the lubricant film remaining on the metal surfaces and the chermical composition of the lubricant.Other functionsLubrication are frequently used for purposes other than the reduction of friction. Some of these applications are describe.d belowPower transmis.sLiounbricants are widely employed as hydraulic fluids in fluid transmission devices.Insulatio. nIn specialized applications such as transformers and switchgear , lubricants with high dielectric constants acts as electrical insulators. For maximum insulating properties, a lubricant must be kefree of contaminants an.d waterShock dampen. iLnugbricants act as shock-dampening fluids in energy transferring devices such as shock absorbers and around machine parts such as gears that are subjected to high intermittent loads.Sealin.gLubricating grease freqpueernfotlryms the special function of forming a seal to retain lubricants or to exclude contaminants.The object of lubrication is to reduce friction ,wear , and heating of machine pars which move relative to each ot.hAelrubricant is any substance which, when inserted between the moving surfaces, accomplishes these purposes. Most lubricants are liquidssuch as mineral oil, silicone fluids, and water,but they may be solid for use in dry bearings, greases for use in rolling element bearing, or gasessuch as air for use in gas bearings. The physical and chemical interaction between the lubricant and lubricating surfaces must be understood in order to provide the machine elements with satisfactory life.The understanding of boundary lubrication is normally attributed to hardy and doubleday , who found the extrememly thin films adhering to surfaces were often sufficient to assist relative sliding. They conclude that under such circumstances the chemical composition of fluid is important, and they introduced the term “ boundary lubrication”. Bouisndaat rtyheluobpripcoastiioten end of the spectrum from hydrodynamiclubrication.Five distinct of forms of lubrication that mayabheydderofidnyenda；m:(c) elastohydrodynamic dbo；unedasroylid film.icbhydrost；aticHydrodynamic lubrication means that the load-carrying surfaces of the bearing are separated by a relatively thick film of lubricant, so as to prevent metal contact, and that the stability thus obtained can be explained by the laws of the lubricant under pressure ；,thboutgiht ditomesayrebqeuire the existence ofan adequate supply at aTllhteimfeilms. pressure is created by the moving surfaces itself pulling the lubricantunder pressure, though it maybe. The film pressure is created by the moving surface to creat the pressure necessary to separate the surfaces against the load on the bearing . hydrodynamic lubrication is also called film ,or fluid lubrication .Hydrostatic lubrication is obtained by introducing the lubricant ,which is sometime air or water ,into the load-bearing area at a pressure high enough to separate the suthrfiacckefilwmithofalurberlaictaivnetl.ySo ,unlikedhryodynanmic lubrication, motion of one surface relative to another is not required .Elasohydrodynamic lubrication is the phenomenon that occurs when a lubricant is introduced between surfaces which are in rolling contact, such as mating gears or rolling bearings. The mathematical explanatio requires the hertzian othf econytact stress and fluid mechanics.When bearing must be operated at exetreme temperatures, a solid film lubricant such as graphite or molybdenum disulfide must be use used because the ordinary mineral .oMilsusatrerensoetasrcahtisfactoryis currently being carried out in an effort, too, to find composite bearing materials with low wear rates as weas small frictional coefficients.In a journal bearing, a shaft rotates or oscillates within the bearing , and the relative motion is sliding . i an antifriction bearing, the main relative motion is rolling . a follower may either roll or slide on the cam.Gear teeth mate with each other by a combination of rolling and sliding . pistions slide within their cylinders All these applications require lubrication to reduc,eanfrdichtioenat,inwge.arThe field of application for journal bearing s is immense. The crankshaft and connecting rod bearings of an automotive engine must poerate for thousands of miles at high temperatures and under varying load conditions . the journal bearings used in the steam turbines of power generating station is said to have reliabilities approaching 100Aptetrhceenother extreme there are thousands of applications in which theloads are light and the service relatively unimportant. a simple ,easily installed bearing is required ,suing litt or no lubrication. In such cases an antifriction bearing might be a poor answer because because of the cost the close ,the radial space required ,or the increased inertial effects. Recent metallurgy developments in bearing materials , combined with increased knowledge of the lubrication process, now make it possible to design journal bearings with satisfactory lives and very good reliabilities.参考文献：1. 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Douglas M Bryce, 1997,“ Plasti-cMionljdecdteiosnigmn ofuldnindgamentals-12”0 , v2, pp 1轴承的摩擦与润滑现在看来，有很多这种情形，很多同学在被问到关于摩擦的问题时，往往都没引起足够的重视，甚至是忽视它；实际上，摩擦从某种程度上说，存在于任何两个相接触并有相对运动趋势的部件之间；而摩擦这个词，本身就意味着，两个或两个以上部件的阻挡相对运动趋势；在一个机器中，运动部件的摩擦是有害的，由于它降低了机械对能量的充分利用；由它引起的热能是一种铺张的能量；由于不能用它做任何事情；仍有，它仍需要更大的动力来克服这种不断增大的摩擦；热能是有破坏性的；由于它产生了膨胀；而膨胀可以使得轴承或滑动表面之间的协作更紧密；假如由于膨胀导致了一个足够大的积压力，那么，这个轴承就可能会卡死或密封死；另外，随着温度的上升，假如不是耐高温材料制造的轴承，就可能会损坏甚至融解；在运动部件之间会发生很多摩擦，如1. 启动摩擦2. 滑动摩擦3. 转动摩擦；启动摩擦是两个固体之间产生的倾向于组织其相对运动趋势的摩擦；当两个固体处于静止状态时，这两个零件表面的不平度倾向于相互嵌入，形成楔入作用，为了使这些部件“动”起来；这些静止部件的凹谷和尖峰必需整理光滑，而且能相互抵消；这两个表面之间越不光滑，由运动造成的启动摩擦（最大静摩擦力）就会越大；由于，通常来说，在两个相互协作的部件之间，其表面不平度没有固定的图形；一旦运动部件运动起来，便有了规律可循，滑动就可以实现这一点；两个运动部件之间的摩擦就叫做滑动摩擦；启动摩擦通常都稍大于滑动摩擦；转动摩擦一般发生在转动部件和设备上，这些设备“抵触”极大的外作用力，当然这种外力会导致部件的变形和性能的转变；在这种情形下，转动件的材料趋向于积累并且强迫运动部件缓慢运动，这种转变就是通常所说的形变；可以使分子运动；当然，最终的结果是，这种额外