Machine Elements翻译.doc

Machine Elements机械零件Complex machines are made up of moving parts such as levers, gears, cams, cranks, springs, belts, and wheels. Machines deliver a certain type of movement to a desired location from an input force applied somewhere else. Some machines simply convert one type of motion to another type (rotary to linear). While there is a seemingly endless variety of machines, they are all based upon simple machines. Simple machines include inclined planes, levers, wheel and axle, pulleys, and screws.复杂的机器是由运动部件如杠杆，齿轮，凸轮，曲柄，弹簧，皮带，和车轮。机从施加别的地方的输入力提供某一类型的运动到所需位置。有些机器只是一种类型的运动转换为另一种类型（旋转到线性）。虽然是一个看似无穷无尽的各种机器，它们都是基于简单的机器。简单的机器包括倾斜面，杠杆，轮轴，滑轮，和螺钉。Inclined Plane and the Lever倾斜面和杠杆An inclined Plane decreases the force required to raise an object a given height by increasing the distance over Which a force must be applied(see figure 1.1.1). You can imagine lifting something twice your Would be much easier. For example,if lifting a 300-kilogram machine two and one-half meters into a truck,then750 meter-kilograms of work is required. If you use an inclined plane as a loading ramp ,which is l0 meter long, and neglect the small friction force,then 75 kilograms of force will be required to roll the machine up to the ramp. The total work is still 750 meter-kilograms, but the effort has been model fed so that the maximum force required is only 75 kilograms and not 300 kilograms.一倾斜平面而减小，通过增加在其上的力必须施加（见图1.1.1）的距离，以提高物体的给定的高度所需的力。你可以想像的东西抬起你的两次会容易得多。例如，如果举起300公斤重机两个和一个半米远的卡车，然后工作750米一公斤是必需的。如果你用一个斜面作为装卸跳板，这是10米长，而忽略了小的摩擦力，再用75公斤的力量将被要求滚机到坡道。的总工作仍然750米 - 公斤，但努力已经模型馈送，使得所需的最大的力只有75公斤，而不是300千克。图片 half effort but twice the distance半力，但距离的两倍 Full effort 全力 inclined plane斜面Inclined planes are commonly put to use in cutting devices(e.g.an axe) and often two inclined planes are put back-to-back to form a wedge.In a wedge，forward movement is converted into a parting movement acting perpendicularly to the face of the blade. A zipper is simply a combination of two lower wedges for closing and an upper wedge for opening,as shown in Figure1.1.2.倾斜面通常放置在切割装置（e.g.an斧）和常两个倾斜平面以使用被放回到后端以形成楔。在一个楔，向前运动被转换成垂直作用于叶片的表面的脱模运动。拉链仅仅是用于闭合两个下楔块和用于开口的上部楔的组合，如图1.1.2。There are three factors in manipulating a lever:the fulcrum the load,and the effort applied lever. The fulcrum is the point around which the lever pivots rotationally. The load is what we wish to manipulate with the lever, and usually is described by its position relative to the fulcrum,and the force (magnitude and direction) it exerts at that point. The is also a force that has a magnitude and a direction,and a position with respect to the fulcrum.A lever is used to change the direction of movement,and to change the magnitude of the effort.有三个因素在操纵杠杆：支点的负荷，并努力施加杠杆。支点是围绕该杆枢转转动的点。负载是我们希望与杆来操纵，并且通常是由相对的位置来描述的支点，和力（大小和方向）它施加在该点。的是还具有一个幅度和一个方向，并且相对于所述支点的位置的力。杠杆用于改变运动的方向，并且以改变的努力的幅度。图片 the inclined plane at work 在工作时倾斜面 axe 斧头 zipper 拉链As shown in Figure1.1.3 there are three different classes of levers defined by the relative positions of the fulcrum, effort, and load. A first class lever has the fulcrum positioned between the effort and the load. Examples of first class levers include: a balance, a crow bar, and scissors. In a second class lever the load is placed between the fulcrum and the effort. Examples of second class levers include: a wheelbarrow, a bottle opener, and a nutcracker. Third class levers place the effort between the fulcrum and the load. Examples of a third class lever are a hammer, a fishing rod, and tweezers. Most machines that employ levers use a combination of several levers, often of different classes.如图.3所示，有三种不同的类别由支点，努力和负载的相对位置定义的杠杆。第一类杠杆具有位于该工作和负载之间的支点。一流的杠杆的例子包括：平衡，乌鸦酒吧和剪刀。在第二类杠杆负载被放置在支点和努力之间。第二类杠杆的例子包括：独轮车，开瓶器，和胡桃夹子。第三类杠杆放置支点和负载之间的努力。的第三类杠杆的例子是一个锤，钓竿和镊子。雇用杠杆大多数机器经常使用的不同类别的几个杠杆的组合。图片 fulcnm centered 支点为中心的 fulcnm cffcenter 支点中心load effort功first class levers一流的杠杆this end of the lever moves twice as far as the other end moves 杠杆的一端移动到另一端移动的两倍 Effort applied 3 times one third the force futher from fulcrum: three times the distance努力应用3次三分之一力进一步从支点的距离的三倍Load will move 3 times the distance that the effort is applied moves at a greater speed负载将移动3倍的距离，这一努力是适用于更大的速度移动Wheel and Axle轮与轴Both the inclined plane and levers could 1ower the force required for a task at the price of having to apply that force over a longger distance.With wheels and axles the same is true: a force and movement of the axle is converted to a greater movement,but less force, at the circumference of the whee1. In a circular geometry, torque is a more useful concept than force and distance.The wheel and axle can be thought of as simply a circular lever, as shown in Figure3.8. Many common items rely on the wheel and axle such as the screwdriver, the steering wheel, the wrench, and the faucet,etc.两斜面和杠杆可以降低在应用力在较长距离价格任务所需的力，车轮和车轴同样是真实的：一个轴的受力和运动转化为一个更大的动作，但力度较小，在车轮的周长。在一个圆形的几何形状，力矩是一个比力和距离更有用的概念。轮轴可以被认为是简单的圆杆，如图3.8所示。许多普通的物品都依赖于车轮和车轴，如螺丝刀、方向盘、扳手、水龙头等。Pulley滑轮Pulleys can be used to simply change the direction of an applied force or to provide a force/distance tradeoff in addition to a directional change, as shown in Figure3.10. Pulleys are very flexible because they use ropes to transfer force rather than a rigid object such as a board or a rod. Ropes can be routed through virtually any path. They are able to abruptly change directions in three-dimensions without consequence. Ropes can be wrapped around a motors shaft and either wound up or let out as the motor turns.滑轮可以用来简单地改变作用力的方向或提供另外一个方向变化的力/距离的权衡，如图3.10所示。滑轮是非常灵活，因为他们用绳索传递力而非刚性物体如板或杆。绳索可以通过几乎任何路径路由。他们能够在三个维度中突然改变方向而无结果。绳索可以缠绕在马达的轴上，或者绕着一个马达转动，或者把绳索放出来。图片 load 加载 effort 力 rope is attached to the bottom of pulley努力绳连接在滑轮的底部Wrench 扳手 movement of axle 轴运动 movement of wheel车轮运动 the wheel and axle is like a circular lever轮子和轴像一个圆形杠杆Figure1.1.6illustrates how a compound pulley trades force for distance through an action/reaction force pair. In a double pulley, as the rope passes over the pulley the force is transmitted entirely but the direction has changed. The effort is now pulling up on the left side of the bottom pulley. Now, for a moment forget that the end of the rope is tied to the bottom of the top pulley. The mechanics are the same if the rope is fixed to the ceiling. The important thing is that the end of the rope is immobile. The effort is once again transmitted entirely as the rope passes over the bottom pulley and there is a direction change. The end of the rope is attached to the ceiling so the rope is pulling down on the ceiling with the force of the effort (and half of the force of the load). We assume that the ceiling holds up, so this must mean that there is a force balancing out this downward force. The ceiling pulls up on the rope as a reaction force. This upward force is equal to the effort and now there is an upward force on the right side of the bottom pulley. From the perspective of a free-body diagram the compound pulley system could be replaced by tying two ropes to the load and pulling up on each with a force equal to the effort.图1.1.6说明复合滑轮业力距离通过行动/反应力对。在一个双滑轮，当绳子穿过滑轮的力量是完全的传输，但方向改变了。现在的努力是在底部的滑轮的左侧拉动。现在，暂时忘记了绳子的一端系在顶部滑轮的底部。如果钢丝绳固定在天花板上，力学是相同的。重要的是绳子的末端是不动的。当绳子穿过滑轮底部时，这一努力再次被传送，并有一个方向改变。绳子的末端被连接在天花板上，这样绳子就在天花板上被用力拉下来，用力的用力（荷载的一半）。我们假设天花板要有，所以这就意味着有一种力平衡向下的力量。天花板上的绳子是一种反应力。这种向上的力量是平等的努力，现在有一个向上的力量在底部滑轮的右边。从一个自由车身图的角度来看，复合滑轮系统可以被替换为一个由两个绳系到负载，并在每一个与力相等的努力。图片 the rope pulls down on the bottom of the top pulley with the force of the effort绳子在顶部滑轮的底部，用力的用力The bottom of the pulley pulls up on the rope with a force of the magnitude (a reaction force)滑轮的底部用一个力的大小（一个反应力）在绳子上拉起来Top pulley simply changes the direction of the effort运算滑轮只需改变努力的方向The end of the rope pulls down on the bottom of the top pulley, which is immobile绳子的末端在顶部滑轮的底部，这是不动的There is a reaction force from the bottom pulley pulls up on the rope with the force of the effort有一个反应力从底部滑轮拉绳上的力量的努力The disadvantages of pulleys, in contrast to machines that use rigid objects to transfer force, are slipping and stretching. A rope will permanently stretch under tension, which may affect the future performance of a device. If a line becomes slack, then the operation of a machine may change entirely. Also, ropes will slip and stick along pulley wheels just like belts. One solution to the problems associated with rope is to use chain. Chain is pliable like rope, and is able to transfer force through many direction changes, but the chain links are inflexible in tension, so that the chain will not stretch. Chains may also be made to fit on gears so that slipping is avoided.滑轮的缺点，相反，机器使用刚性物体传递力，是滑动和伸展。一根绳子将永久性拉伸，这可能会影响未来的性能的设备。如果一条线变得松弛，机器的操作可能会完全改变。同样，绳索也会滑倒，沿着滑轮的轮子，就像皮带一样。一个解决的问题与绳子的问题是使用链。链柔韧如绳，并能够通过多方向变化的力传递，但链紧张僵化，使链不会拉长。链条也可以在齿轮上安装，以避免打滑。Screw螺杆The screw is basically an inclined plane (see Figure3.12) wrapped around a cylinder. In an inclined plane, a linear force in the horizontal plane is converted to a vertical lifting force. With a screw, a rotary force in the horizontal plane is converted to a vertical lifting force.When a wood screw is turned, the threads of the screw push up on the wood. A reaction force from the wood pushes back down on the screw threads and in this way the screw moves down even though the force of turning the screw is in the horizontal plane. Screws are known for high friction, which is why they are used to hold things together.A worm gear is sometimes used in machines, it also has high friction that can waste considerable power.螺纹基本上是一个倾斜的平面（见图3.12）缠绕气瓶。在倾斜平面上，在水平面上的线性力被转换为垂直的“提升”力。随着螺杆，水平面上的旋转力被转换为垂直的“提升”力，当一个木螺钉被转动时，螺杆的螺纹就被推上了木头。来自木材的反应力推后在螺杆上，并以这种方式，螺杆向下移动，即使在螺杆的力量是在水平面。高摩擦，这就是为什么他们是用来把东西放在一起。一个蠕虫齿轮有时被用来在机器，它也有高摩擦，可以浪费相当大的力量。图片a screw is simply a spiraled inclined plane螺杆是一个简单的螺旋斜面 effect of wedge楔形效应Raw effort 原力 force on wood 木材受力 effect影响Comprehension Exercises理解练习Write a T in front of a statement if it is true or write an F if it is false according to the text.写一个在前面的语句，如果它是真的或写一个如果它是假的根据文本。(1) The function of an inclined Plane is to save energy and increase efficiency.斜面的功能是节约能源，提高效率。(2) A lever consists of the load,the effort and the fulcnm.杠杆由负载的努力和支点。(3) Both effort and load are means with which people can manipulate the ever.这两种力和负载都意味着人们可以操纵的永远(4) The fulcrum is always situated between the effecting points of both effort and load on a lever.在一个杠杆上，该支点始终位于两个努力和负载的作用点之间。(5) The wheel and axle can convert a powerful force and movement to a greater movement,but less force.车轮和车轴可以将一个强大的力量和运动转化为更大的运动，但较少的力量。(6) The disadvantages of pulleys are slipping and stretching of the rope.滑轮的缺点是的滑绳。(7) A pulley uses rigid objects to transfer force.滑轮使用刚性物体来传递力。(8) Both a screw and an inclined plane work under the same principle.在同一原则下，螺钉和斜面工作。Tolerances and Fit公差与配合Machine parts are manufactured so they are interchangeable.In other words,each part of a machine or mechanism is made to a certain size and shape so it will fit into any other machine or mechanism of the same type.To make the part interchangeable,each individual part must be made to a size that will fit the mating part in the correct way.It is not only impossible,but also impractical to make many parts to an exact size.This is because machines are not perfect,and the tools become worn.A slight variation from the exact size is always allowed.The amount of this variation depends on the kind of part being manufactured.For example,a part might be made 1.5 inches in diameter with a variation allowed 0.001 inch,above and below this size.Therefore,the part could be 1.499 to 1.501 inches and still be the correct size.These are known as the limits.The difference between upper and lower limits is called the tolerance.机器生产零件,所以他们是可以互换的。换句话说,每一部分机器或机制是一种特定的大小和形状,它能塞进其他机器或机制相同的类型。可互使部分换的,每个人都必须做出部分尺寸适合交配,参加了正确的方法。它不仅是不可能的,但也不让很多地方到一个精确的尺寸。这是因为机器还很不完善,工具磨损。一个稍微变化的大小正好合适总是允许的。这一差异的数量取决于类型的部分正在制造的。例如,一个部份可能是使1.5英寸直径变化允许0.001英寸,上面和下面的尺寸。因此,部分可能是1.499到1.501英寸,仍然是正确的尺寸。这些被称为非限制。区别上下限,叫做宽容。Quality and accuracy are major considerations in making machine parts.Interchangeable parts require suitable accuracy to fit together.Both of dimensions of parts given on engineering drawings and manufactured dimensions should be exactly the same and fit properly.Unfortunately,it is impossible and unnecessary to make things to an exact shape or dimension.Most dimensions have a varying degree of accuracy and means of specifying acceptable limitations in dimensional variance that an object will tolerate and still have its function.质量和精度的主要考量使机械零件。可互换的零件精度要求适当配合。两个维度的部分工程图纸制造了尺寸应该完全相同,而且合适。不幸的是,这是不可能的,不必要的做一个确切的形状和尺寸。大多数维度有不同程度的准确性和可接受的方式限制规定一个物体在空间方差会容忍,还有它的功能。Size, Tolerance and Allowance尺寸、公差及余量Size usually includes nominal,basic,design,and actual size,etc.大小通常包括名义、基本设计和实际尺寸等。Nominal size generally identifies the overall size of an object without any error.一般公称通径识别物体的总体规模没有任何错误。Basic size in the size from which the limits of size are derived by the application of allowances and tolerances.基本尺寸的大小,范围的大小,得出应用津贴和公差。Design size is the size from which you derive the limits of size by the use of tolerances.设计尺寸是你从中获得的尺寸公差的大小。Actual size is the manufactured size of the object that may be larger or smaller than the nominal size. See Figure1.2.1.实际尺寸是可以大于或小于公称尺寸的对象的制造尺寸。看到图1.2.1。图片 indicating object size 指示对象的大小 basic size基本尺寸 actual size 实际尺寸 design size设计尺寸Tolerance is the tota1 permissible variation in the size of a part or the tota1 amount of a specific dimension that may vary from a minimum limit to a maximum limit.公差是零件或一个特定的尺寸可能会有所不同从一个最低限制到最大限度的总金额大小的结构允许偏差。Unilateral tolerances indicate variation from the basic size in one direction.注重从单向公差指示变化在一个方向上的基本尺寸。Bilateral tolerances indicate variation from the basic size in both directions. See Figure 1.2.2.双边公差表明在两个方向的基本尺寸的变化。见图1.2.2。Allowance is the intentional difference between the maximum material limits of mating parts (a hole and a shaft) . This is a minimum clearance(positive allowance) or maximum interference (negative allowance) between mating parts.津贴是对交配部分（一个孔和一个轴）的最大物质限制的故意的区别。这是一个最小的间隙（正津贴）或最大干扰（负补贴）之间的交配部分。图片indicating tolerance 指示公差 unilateral tolerance 单边公差 bilateral tolerance双侧公差Fit配合Fit is the general range of tightness resulting from the application of a specific combination of allowance and tolerances in the design of mating parts.How mating parts or assemblies fit together with component parts could be referred to as different fits: clearance fit, interference fit, or transition fit.配合零件的设计中，公差与公差配合使用的一般范围是紧密结合的，配合零件或装配件配合的零件或装配件可以称为不同的配合：间隙配合、干涉配合或过渡配合。Clearance fit. it is a fit enabling a clearance between the hole and shaft in the coupling. The lower limit size of the hole is greater or at least equal to the upper limit size of the shaft.间隙配合。这是一个适合使孔和轴之间的间隙耦合。该孔的下限大小是更大或至少等于轴的上限大小。Transition fit. It is a fit where (depending on the actual sizes of the hole and shaft) both clearance and interference may occur in the coupling. Tolerance zones of the hole and shaft partly or completely interfere.过渡配合。这是一个适合在那里（根据实际大小的孔和轴）的间隙和干扰可能会出现在耦合。孔和轴公差带部分或完全干涉。Interference fit. It is a fit always ensuring interference between the hole and shaft in the coupling. The upper limit size of the hole is smaller or at least equal to the lower limit size of the shaft.过盈配合。这是一个合适的总是确保在耦合的孔和轴之间的干扰。该孔的上极限尺寸较小，或至少等于该轴的下极限尺寸。Figure 1.2.3 illustrates the difference among three fits.图三说明了在适合的差异的前提下。图片the difference among clearance fit,transition fit,and interference fit 间隙配合、过渡配合和过盈配合差 clearance fit间隙配合 transition fit过渡配合 interference fit过盈配合Basic hole system基本孔系The basic hole system is a system of fits in which the design of the hole is the system basic size and the allowance applies to the shaft. When specifying the tolerances for a hole and cylinder and determining their dimensions, we should begin calculating by assuming either the minimum (smallest) hole or the maximum (largest) shaft size if they are to fit together well.Figure 1.2.4 illustrates the basic hole system.基本的孔系是一个适合于该系统的设计，该系统的基本尺寸和余量适用于轴。当指定的公差和缸孔和确定其尺寸，我们应该开始计算假设最低（最小）孔或最大（最大）轴尺寸是否适合。图1.2.4说明了基孔制。In the illustration, the minimum hole size is the basic size. To calculate the maximum diameter of the shaft, assume an allowance of 0.003 and subtract that from the basic hole size.在插图中，最小的孔尺寸是基本尺寸。要计算出轴的最大直径，假设一个0.003的余量，并减去从基本孔尺寸。图片the basic hole system(tolerance=0.002)基本孔系（公差= 0.002）If selecting a tolerance of 0.002 inch,apply the tolerance to both the hole and the shaft.This gives a maximum hole (1.502 inches) and minimum shaft (1.495 inches). The minimum clearance fit is the difference between the smallest hole (1.500 inches) and the largest shaft (1.497 inches) that is 0.003 inch. The maximum clearance fit is the difference between the largest hole (1.502 inches) and the smallest shaft (1.495 inches) that is 0.007 inch.如果选择一个公差为0.002英寸，适用于孔和轴的公差，这给出了一个最大的孔（1.502英寸）和最小轴（1.495英寸）。最小的间隙配合是最小的孔（1.500英寸）和最大的轴（1.497英寸），是0.003英寸之间的差异。最大间隙配合是最大的孔（1.502英寸）和最小的轴（1.495英寸），是0.007英寸之间的差异。Determine the maximum shaft size of an interference fit by adding the allowance (0.003 inch) to the basic hole size (1.500 inches),wh