轴承的摩擦与润滑 机械类毕业设计外文翻译

轴承的摩擦与润滑 -机械类毕业设计外文翻译 毕业设计论文外文翻译毕业设计论文题目 工具盒盖注塑模具设计 外文题目 Friction Lubrication of Bearing 译文题目 轴承的摩擦与润滑 系 部 机 械 系 专业班级机械设计制造及其自动化学生姓名 指导教师 外文文献原文 Friction Lubrication of BearingIn many of the problem thus far the student has been asked to disregard or neglect friction Actually friction is present to some degree whenever two parts are in contact and move on each other The term friction refers to the resistance of two or more parts to movementFriction 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 fastener and the parts together Belt 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 because no work takes place Also greater power is required to overcome the increased friction Heat is destructive in that it causes expansion Expansion may cause a bearing or sliding surface to fit tighter If a great enough pressure builds up because made from low temperature materials may meltThere are three types of friction which must be overcome in moving parts 1 starting 2 sliding and 3 rolling Starting friction is the friction between two solids that tend to resist movement When two parts are at a state of rest the surface irregularities of both parts tend to interlock and form a wedging action To produce motion in these parts the wedge-shaped peaks and valleys of the stationary surfaces must be made to slide out and over each other The rougher the two surfaces the greater is starting friction resulting from their 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 slide over each other The friction of the two surfaces is known as sliding friction As shown 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 slightly uphill This changing of shape known as deformation causes a movement of molecules As a result heat is produced from the added energy required to keep the parts turning and overcome frictionThe friction caused by the wedging action of surface irregularities can be overcome partly by the precision machining of the surfaces However even these smooth surfaces may require the use of a substance between them to reduce the friction still more This substance is usually a lubricant which provides a 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 bearings soft alloys and copper and tin iolite bearings are used with both soft and hardened 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 greatestMoving parts are lubricated to reduce friction wear and heat The most commonly used lubricants are oils 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 lubricantOn slow moving parts with a minimum of pressure an oil groove is usually sufficient to distribute 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 pistonA 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 constant rate and quantityThere are numerous other systems of lubrication and a considerable number of lubricants available for any given set of operating conditions Modern industry pays greater attention to the use of the proper lubricants than at previous time because of the increased speeds pressures and operating demands placed on equipment and devicesAlthough 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 sliding Metals that have been carefully treated to remove all foreign materials seize and weld to one another when slid together In the absence 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 severe wear this is called unlubricated or dry slidingFluid-film lubrication Interposing a fluid film that completely separates the sliding surfaces results in fluid-film lubrication The fluid may be introduced intentionally as the oil in the main bearing of an automobile or unintentionally as in the case of water between a smooth tuber tire and a wet pavement Although the fluid is usually a liquid such as oil water and a wide range of other materials it may also be a gas The gas most commonly employed is airBoundary lubrication A condition that lies between unlubricated sliding and fluid-film lubrication is referred to as boundary lubrication also defined as that condition of lubrication in which the friction between surfaces is determined by the properties of the surfaces and properties of the lubricant other than viscosity Boundary lubrication encompasses a significant portion of lubrication phenomena and commonly occurs during the starting and stopping off machinesSolid lubrication Solid 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 take only such familiar forms as fats powders and gases even some metals commonly serve as sliding surfaces in some sophisticated machines Function of lubricantsAlthough a lubricant primarily controls friction and ordinarily does perform numerous other functions which vary with the application and usually are interrelated 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 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 the effect of viscosity on friction becomes less significant than the chemical nature of the lubricantWear 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 asperitiesTemperature control Lubricants 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 controls 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 described belowPower transmission Lubricants are widely employed as hydraulic fluids in fluid transmission devicesInsulation In specialized applications such as transformers and switchgear lubricants with high dielectric constants acts as electrical insulators For imum insulating properties a lubricant must be kept free of contaminants and waterShock dampening Lubricants 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 loadsSealing Lubricating grease frequently performs the special function of forming a seal to retain lubricants or to exclude contaminantsThe object of lubrication is to reduce friction wear and heating of machine pars which move relative to each other A lubricant is any substance which when inserted between the moving surfaces accomplishes these purposes Most lubricants are liquids such 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 gases such 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 lifeThe 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 concluded that under such circumstances the chemical composition of fluid is important and they introduced the term boundary lubrication Boundary lubrication is at the opposite end of the spectrum from hydrodynamic lubricationFive distinct of forms of lubrication that may be defined a hydrodynamic b hydrostatic c elastohydrodynamic d boundary e solid filmHydrodynamic 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 though it may be but it does require the existence of an adequate supply at all times The film pressure is created by the moving surfaces itself pulling the lubricant under 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 full 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 surface with a relatively thick film of lubricant So unlike hydrodynanmic 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 explanation requires the hertzian theory of contact stress and fluid mechanicsWhen 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 oils are not satisfactory Must research is currently being carried out in an effort too to find composite bearing materials with low wear rates as well as small frictional coefficientsIn a journal bearing a shaft rotates or oscillates within the bearing and the relative motion is sliding in 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 reduce friction wear and heatingThe 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 100 percent At the other extreme there are thousands of applications in which the loads are light and the service relatively unimportant a simple easily installed bearing is required suing little 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 Chambers T L Parkinson A R 1998 揔nowledge Representation and Conversion of HybridExpert SystemsTransactions of the ASME v 120pp 468-4742 Koelsch James R 1999 揝oftware boosts mold design efficiencyMolding Systemsv57 n 3p 16-233 Lee Rong -Shean Chen Yuh-Min Lee Chang-Zou1997 揇evelopment of a concurrent molddesign system A knowledge-based approach Computer Integrated Manufacturing Systems v 10n 4 p 287-3074 Steadman Sally Pell Kynric M 1995 Expert systems in engineering d esign An application forinjection molding of plastic partsJournal of Intelligent Manufacturing v6 p 347-3535 Fernandez A Castany J Serraller F Javierre C 1997 揅ADCAE assistant for the design ofmolds and prototypes for injection of thermo plastics 揑nformation Technological v 8 p 117-1246 Douglas M Bryce 1997 扬lastic injection molding -Material selection and product design v 2pp 1-487 Douglas M Bryce 1997 扬lastic injection molding-Mold design fundamentals v2 pp 1-120 中文译文 轴承的摩擦与润滑 现在看来有很多这种情况许多学生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止相对运动趋势 在一个机器中运动部件的摩擦是有害的因为它降低了机械对能量的充分利用由它引起的热能是一种浪费的能 量因为不能用它做任何事情还有它还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因为它产生了膨胀而膨胀可以使得轴承或滑 动表面之间的配合更紧密如果因为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升高如果不是耐高温材料制造的轴承就可能会损坏甚至融化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须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因为通常来说在两个相互配合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改变在这种情况下转动件的材料趋向于堆积并且强迫运动部件缓慢运动这种改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的能量产生了热能这是必需的因为它可以保证运动部件的运动和克服摩擦力由运动部件的表面不平度的楔入作用引起的摩擦可以被部分的克服那就需要靠两表面之间的润滑但是即使是非常光滑的两个表面之间也可能需要一种物质这种物质就是通常所说的润滑剂它可以提供一个比较好的比较薄的油膜这个油膜使两个表面分离并且组织运动部件的两个表面的相互潜入以免产生热量使两表面膨胀又引起更近的接触减小摩擦的另一种方式是用不同的材料制造轴承和转动零件可以拿黄铜轴承铝合金和含油轴承合金做例子进行解释也就是说用软的或硬的金属组成表面含油轴承合金是软的这样当轴承在油中浸泡过以后因为毛细管的作用将由带到轴承的各个表面这种类型的轴承把它的润滑剂带到应力最大的部位对运动部件润滑以减小摩擦应力和热量最常用的是油脂还有合成剂每一种润滑剂都有其各自不同的功能和用途两个运动部件之间的运动情况决定了润滑剂的类型的选择润滑剂的分布也决定了系统的选择在低速度运动的部件一个油沟足以将所需要的数量的润滑剂送到相互运动的表面第二种通用的润滑方法是飞溅润滑系统在每个周期内这个系统内一些零件经过润滑剂存储的位置带起足够的润滑油然后将其散布到所有的运动零件上这种系统用于草坪修剪机中发动机的曲轴箱对曲轴连杆和活塞等零件进行润滑在工业装置中常用的有一种润滑系统是压力系统这种系统中一个机器上的一个泵可以将润滑剂带到所有的轴承表面并且以一种连续的固定的速度和数量关于润滑还有许多其他的系统针对各种类型的润滑剂对不同类型的运动零件是有效的由于设备或装置的速度压力和工作要求的提高现代工业比以前任何时候都更注重选用适当的润滑剂尽管润滑的主要目的之一是为了减小摩擦力任何可以控制两个滑动表面之间摩擦和磨损的物质不管是液体还是固体或气体都可以归类于润滑剂 润滑的种类 无润滑滑动经过精心处理的去除了所有外来物质的金属在相互滑动时会粘附或熔接到一起当达不到这么高的纯净度时吸附在表面的气体水蒸气氧化物和污染物就会降低摩擦力并减小粘附的趋势但通常会产生严重的磨损这种现象被称为无润滑摩擦或者叫做干摩擦流体膜润滑在滑动面之间引入一层流体膜把滑动表面完全隔离开就产生了流体膜润滑这种流体可能是有意引入的例如汽车主轴承中的润滑油也可能是无意中引入的例如在光滑的橡胶轮胎和潮湿的路面之间的水尽管流体通常是油水和其他很多种类的液体它可以是气体最常用的气体是空气为了把零件隔离开润滑膜中的压力必须和作用在滑动面上的负荷保持平衡如果润滑膜中的压力是由外源提供的这种系统称为流体静压润滑如果滑动表面之间的压力是由于滑动面本身的形状和运动所共同产生的这种系统就称为流体动压力润滑边界润滑处于无润滑滑动和流体膜润滑之间的润滑被称为边界润滑它可以被定为这样一种润滑状态在这种状态中表面之间的摩擦力取决于表面的性质和润滑剂中的其他性质边界润滑包括大部分润滑现象通常在机器的启动和停止时出现固体润滑当普通润滑剂没有足够的承受能力或者不能在温度极限下工作时石墨和二硫化钼这一类固体润滑剂得到广泛应用但润滑剂不仅仅以脂肪粉末和油脂这样一些为人们所熟悉的形态出现在一些精密的机器中金属也通常作为滑动面 润滑剂的作用尽管润滑剂主要是用来控制摩擦和磨损的它们能够而且通常也确实起到许多其他的作用这些作用随其用途不同而不同但通常相互之间是有关系的控制摩擦力 滑动面之间润滑剂的数量和性质对所产生的摩擦力有很大的影响例如不考虑热和磨损这些相关因素只考虑两个油膜润滑表面见的摩擦力它能比两个同样表面但没有润滑时小200倍在流体润滑状况时摩擦力与流体黏度成正比一些诸如石油衍生物这类润滑剂可以有很多黏度因此能够满足范围宽广的功能要求在边界润滑状态润滑剂黏度对摩擦力的影响不象其化学性质的影响那么显著磨损控制磨蚀腐蚀与固体和固体之间的接触就会造成磨损适当的润滑剂将能帮助克服上述提到的一些磨损现象润滑剂通过润滑膜来增加滑动面之间的距离从而减轻磨料污染物和表面不平度造成的损伤因此减轻了磨损和由固体与固体之间接触造成的磨损控制温度润滑剂通过减小摩擦和将产生的热量带走来降低温度其效果取决于润滑剂的用量和外部冷却措施冷却剂的种类也会在较小的程度上影响表面的温度控制腐蚀润滑剂在控制表面腐蚀方面有双重作用当机器闲置不工作时润滑剂起到防腐剂的作用当机器工作时润滑剂通过给被润滑零件涂上一层可能含有添加剂能使腐蚀性材料中和的保护膜来控制腐蚀润滑剂控制腐蚀的能力与润滑剂保留在金属表面的润滑膜的厚度和润滑剂的化学成分有直接的关系 其他作用 除了减小摩擦外润滑剂还经常有其他的用途其中的一些用途如下所述传递动力润滑剂被广泛用来作为液压传动中的工作液体绝缘在象变压器和配电装置这些特殊用途中具有很高介电常数的润滑剂起电绝缘材料的作用为了获得最高绝缘性能润滑剂中不能含有任何杂质和水分减振在象减振器这样的能量传递装置中和在承受很高的间隙载荷的齿轮这样的机器零件的周围润滑剂被作为减振液使用密封润滑脂通常还有一个特殊作用就是形成密封层以防止润滑剂外泻和污染物进入润滑的目的就是为了减小摩擦力降低能量损耗减少机器的热量产生热量就是因为表面的相互间的相对运动造成的润滑剂可以是任何一种物质这样的物质被填充到发生相对运动的两个表面之间实现这一目的大部分的润滑剂是液体比如说油脂合成剂等但它们有时也可能是固体用在干轴承上有的用在旋转基体的轴承上或者也可能是气体如空气等它是用在空气轴承上在润滑剂和润滑表面之间这种化学的和物质的相互渗入作用就是为了提供给机器一个良好的工作状态对润滑剂边界的理解往往是比较硬的而且是流动的非常薄的一层帖附在被润滑的表面这些表面通常是要发生相对滑动有些人推断按这种理解液体的这种化学合成是十分重要的它们提出了这样的词边界润滑边界润滑是和流体润滑相对的另一种润滑关于润滑的五种不同的润滑形式主要有1无润滑润滑剂2流体膜润滑3干润滑4边界润滑5固体润滑无润滑润滑剂是指轴承的工作表面被一种相对比较厚的液体润滑剂分隔开于是阻止了金属表面的直接接触这样得到的这种稳定性就可以用一种理论来解释润滑液在外压力下工作的理论尽管这只是一种可能但确实需要在任何时候都得提供的足够充分这种挤压力是运动表面本身施加给润滑剂而产生的当然这仍然是一种可能这种由运动表面产生的挤压力产生了必要的压力来分隔工作表面来抵抗加在轴承上的载荷所以这种润滑也可以被叫做液体润滑还有一种润滑方式那是一种特别的润滑剂它有时是空气或水当加在轴承上的外载荷足够高时它就会以一种比较厚的状态分隔开相互相对运动的工作表面所以不象上面的那种润滑方式并不需要两种工作表面一定发生相对运动第三种润滑方式是一种现象这种现象是一种润滑剂是用在发生相对转动的工作表面之间比如说齿轮或者是滚动轴承从数学上的解释就需要接触压力和流体机械的理论当轴承不得不在较高的温度下工作的时候固体润滑剂例如合成物等必须被使用因为通常使用的润滑油在这种情况下都不能工作目前在这方面的研究正在实施为了寻找到合成轴承的材料并且有低损耗和小的热量产生的性能在有的轴承上摇杆旋转或在轴承上转动相对运动就是滑动在一个自锁的轴承装置中这种相对运动就是转动其他的装置也可能是旋转或滑动齿轮的齿啮合是转动与相对滑动的合成活塞是相对于刚体的滑动所有的这些应用都需要润滑剂来减小摩擦降低能耗减少热量的产生在有些轴承的应用领域是不太成熟的有些有连接杆的轴承比如说汽车发动机上的必须在几千度高的高温下和各种不同性质的载荷下工作这种轴承用在汽轮发动设备上可以说是稳定性接近100还有另一种极端的情况在有些轴承有几千种应用应对各种不同的载荷其他的辅助设施就相对不重要了需要的是一个简单的容易安装的轴承需要很少的甚至是不需要润滑剂在这种情况下有的轴承并不是最好的选择因为成本和相近的公差最近在轴承材料上的研究已有了一定的突破随着对润滑的研究的知识的积累设计出有良好工作状况和较高的稳定性的轴承已不是很遥远了参考文献1 钱伯斯 T L帕金森 A R 知识代表及专家系统的混合转换 美国机械工程师学会1998120468-4742 凯尔其詹姆斯R软件升压模具设计效率的成型系统1999 316-233 李荣显陈育民邹昶开发一个并行模具设计系统以知识为基础的办法计算机集成制造系统19974287-3074 斯特德曼萨利佩尔M在工程设计专家系统一种注塑成型的塑料件的应用智能制造发动机19952347-3535 费尔南德斯A卡斯塔尼J赛尔 F CAD CAE 信息的模具和热塑性塑料注射原型设计的信息技术1997117-1246 道格拉斯M 布莱斯塑料注射成型材料选择和产品设计19971-487 道格拉斯M 布莱斯塑料注射成型模具设计基础199721-12011