机械专业英语中文翻译
stress and strain 应力与应变
In any engineering structure工程结构the individual components独立构件or members will （be subjected to）受到，被附加external forces外力arising from由。。引起the service conditions工作环境or environment in which the component works.
在任何的工程结构中，每个零件，构件将会受到来自工作环境的外力的作用。
If the component or member is in equilibrium平衡, the resultant合力of the external forces外力will be zero but, nevertheless不然的话, they together place a load on the member which tends to deform使变形that member and which must be reacted作用by internal forces内力set up within the material由材料提供.
如果这构件是处于平衡状态的话，外力的合力是为零。但是他们必须由材料提供的内力来平衡。
There are a number of different ways in which load负载can be applied作用to a member. Loads may be classified分类with respect to time:
负载作用于构件有许多的形式。相对于时间可以将负载分类为：
(a) A static静态load负载is a gradually逐渐applied作用load for which equilibrium is reached in a relatively相对short time.
静态负载是逐渐作用的可以在相对较短的时间内达到平衡的负载。
(b)A sustained load持续载荷is a load that is constant维持不变over a long period of很time, such as the weight of a structure构件重力. This type of load is treated处理，对待in the same manner as a static load静态载荷; However for some materials对一些材料，and conditions of temperature and stress, the resistance抵抗力to failure may be different under short time loading and under long time loading.
持续载荷是可以维持很长时间不变的载荷。比如构件的重力。这种类型的载荷和静态载荷是同样的处理方法。但是对于某种材料，在某些特定的温度和外部压力的作用下，构件抵抗失效的能力是不同的。
(c) An impact冲击load is a rapidly很快的迅速的applied load (an energy load). Vibration震动normally results from an impact load, and equilibrium平衡is not established确定until the vibration振动is eliminated消除, usually by natural damping forces阻尼力.
冲击载荷是一种快速作用的载荷。振动常常是有冲击载荷引起。在振动被消除之前，平衡是很难稳定的。而消除振动的一半都是靠阻力。
(d) A repeated load重复载荷is a load that is applied作用and removed移动many thousands of times.
持续作用很多次，移动很多次的载荷称为持续载荷。
(e) A fatigue or alternating load交变载荷is a load whose magnitude and sign are changed with time.
狡辩载荷是大小和符号都在不断变化的载荷。
It has been noted above that external force applied to a body in equilibrium is reacted by internal forces set up within the material.
上述的外力作用于物体时将会被材料提供的内力抵消而达到平衡。
If, therefore因此, a bar棒子，零件is subjected to作用a uniform统一的，制服tension拉
伸or compression压缩, i.e. 也就是说 a force, which is uniformly applied across the cross-section截面, then the internal forces set up are also distributed分布uniformly and the bar is said to be subjected to a uniform normal stress正应力, the stress being defined定义as: 因此，如果零件受到统一的拉伸或者压缩，也就是说，力均匀的分布在截面上，此时内力也同样是均匀分布，此时我们就说哦这个构件受到了正应力的作用。这种应力定义为：
stress=press/area=P/A
Stress б may thus be compressive or tensile depe nding on the nature of the load and will be measured衡量in units单位of newtons牛顿per square meter每平方米(N/m2)or multiples 倍数of this.
这个力是压力还是拉力由构件所受的载荷确定。同时，此力可以用牛顿每平方米或者它的倍数来衡量。
If a bar is subjected to an axial load轴向载荷, and hence因此a stress, the bar will change in length. If the bar has an original length L and changes in length by an amount δL, the strain应变produced产生的is defined as follows:
如果构件受到轴向的载荷，此时构件的长度会发生变化。如果构件的本身长度是L，改变了&L则，产生的应变定义为：
strain=chang in lengyh/original length=&l/l
Strain is thus a measure度量of the deformation变形of the material and is non-dimensional无量纲的, i.e. it has no unit没有单位; it is simply a ratio比例，比率，比值of two quantities数量，数值with the same unit.
因此，应变是材料形变的度量，而且它是无量纲的。也就是说它没有单位。它只是两个有相同的单位的数值之间的比值。
Tensile stress张应力and strain拉应力are considered被认为是positive正的in sense在某种程度. Compressive压应力stress and strain are considered negative负的in sense. Thus a negative strain produces a decrease in length.
张应力和拉应力在被定义为正的，而压应力被认为是负的。因此负的压应力造成长度的减少。
A material is said to be elastic有弹性的if it returns to its original, unloaded dimensions大小when load is removed.
如果材料在外力卸去的时候长度回复到了受力前的正常情况，我们就说这种材料有弹性。
A particular特别的form形式of elasticity弹性which applies to a large range of engineering material工程材料, at least over part of their load range负载范围, produces deformations变形which are proportional to成比例的the loads producing them.
很多材料都有这种特性，至少在一定范围内，变形与负荷是成正比的。
Since loads are proportional to成比例the stress they produce and deformations are proportional to the strains, this also implies意味着that, whilst material are elastic, stress is proportional to strain. Hooke’s law胡克定律therefore states that
负载可以产生成比例的应力，而应力又可以产生成比例的形变。也就意味着材料有弹性。用胡克定律表示
This law is obeyed服从within certain limits by most ferrous alloys铁基合金and it can even
be assumed理论上to apply to other engineering materials such as concrete混凝土, timber木材and non-ferrous alloys有色金属with reasonable合理的，可接受的accuracy准确性，精度.
此定律适用于大部分的铁基合金，理论上还可以用于其它工程材料，例如混凝土，木材，有色金属。并且精度还可接受。
Whilst同时a material is elastic the deformation produced by any load will be completely recovered when the load is removed; there is no permanent deformation残留变形，永久变形. 如果材料是弹性的，那如果负载去掉之后，由负载造成的变形将会完全消失不会留下残留变形。
Within the elastic limits of materials, i.e. within the limits in which Hooke’s law applies, it has been shown that
在材料的弹性极限内，也就是说，在胡克定律允许的范围内，表现为：
stress/strain=E
This constant常数is given the symbol符号E and termed被称为the modulus of elasticity 弹性模量or Young’s modulus杨氏模量. Thus
这个常数由符号E表示，并被称为弹性模量或者杨氏模量。
Young’s modulus E is generally assumed假定to be the same in tension or compression and for most engineering materials has a high numerical value数值. Typically代表性的, E=200*109N/m2 for steel钢, so that it will be observed观察from Eq.(2.5) that strains are normally very small.
一半假设杨氏模量E在拉压时是相同的。对大多数的材料来说，它的数值都比较大，代表性的，钢的是200*109，从仪器中观察到的是2.5，应变是很小的。
In most common engineering applications应用strains rarely exceed很少超过0.1%. The actual 真实的value of Young’s modulus for any material is normally determined by carrying out a standard test on a specimen of the material.
As we look around us we see a world full of “things”: machines, devices设备, tools; things that we have designed, built, and used; things made of wood, metals, ceramics陶瓷, and plastics. We know from experience that some things are better than others; they last longer, cost less, are quieter, look better, or are easier to use.
当我们环顾四周，我们可以看到世界充满了“东西”。机器，设备，工具；我们设计，建造，使用的东西；用木头，金属，陶瓷，塑料制造的东西。我们凭借经验可以知道，一些东西比另一些东西更好，更便宜，更持久，更漂亮和更易于使用。
Ideally理想的, however, every such item项目has been designed according to some set of “functional requirements”功能要求as perceived感知by the designers — that is, it has been designed so as to answer the question, “Exactly what function should it perform执行?” In the world of engineering, the major function frequently频繁的is to support some type of loading due to weight, inertia惯性, pressure, etc.
然而，理想的化的，每个项目都是根据设计者的感知到的功能要求来设计的。也就是说，它是设计来解决一些问题，那么它们需要执行什么功能呢？在工程界中，最频繁的功能就是用来支持各种形式的由重力，惯性，压力引起的载荷。
From the beams衡梁in our homes to the wings of an airplane, there must be an appropriate melding结合of materials, dimensions规模，大小, and fastenings连接件to produce structures
that will perform their functions功能reliably可靠的for a reasonable cost over a reasonable lifetime.
从家里的衡梁到飞机的翅膀，都必须由合适的材料，规模，连接件的配合，从而生产出有可靠功能和合理寿命的结构设备。
In practice实际上, engineering mechanics工程力学，机械工程methods are used in two quite different ways:
事实上，工程力学方法被用于两个截然不同的方面：
(1) The development of any new device装置，设备requires an interactive交互式的, iterative反复的consideration of考虑form, size, materials, loads, durability耐久性, safety, and cost.
装置的发展要求有对形状，尺寸，材料，负载，耐久性，安全和消费的交互式的反复的考虑。
(2) When a device fails (unexpectedly失效) it is often necessary to carry out a study to pinpoint查明the cause of failure and to identify鉴定potential潜在的corrective measures补救措施. Our best designs often evolve进化，发展through a successive elimination逐次消元of weak points.
当一个产品失效的时候，应该去找出失效的原因，并且看看是否有潜在的补救措施。我们的最好的设计常常是通过不断减少弱点来得到的。
To many engineers, both of the above processes过程can prove to be absolutely 绝对的fascinating迷人的and enjoyable, not to mention更不必说lucrative有利可图.
对于设计师来说，上面的两个过程都是非常的迷人，有趣的。更不必说它还是有利可图可以赚钱的。
In any “real” problem there is never sufficient足够good, useful information; we seldom know the actual loads and operating conditions工作条件with any precision精度, and the analyses are seldom exact.
在任何现实的情况中，都没有足够的信息，我们很少知道真实的载荷，工作条件。精度和分析几乎没有什么保证。
While our mathematics数学运算may be precise精确, the overall analysis全分析is generally only approximate近似的, and different skilled people can obtain获得different solutions. In the study of engineering mechanics, most of the problems will be sufficiently “idealized理想化的” to permit允许unique solutions唯一解, but it should be clear that the “real world” is far less idealized, and that you usually will have to perform some idealization in order to obtain a solution.
就算我们的数学运算是完全精确的，全非西也就只能是近似。用不同的方法可以获得不同的结果。在工程机械的研究中，我们经常需要用到理想化的思想，来允许唯一解。但是我们要知道，现实世界远非理想，我们经常要用这个思想来解决问题。
The technical工艺的areas we will consider are frequently频繁的called “statics” and “strength of materials,” “statics” referring to the study of forces acting on stationary devices, and 搒trength of materials?referring to the effects of those forces on the structure (deformations, load limits, etc.).
While a great many devices are not, in fact, static, the methods developed here are perfectly applicable to适用于dynamic situations动态情况if the extra loadings associated with与。。有关the dynamics are taken into account 被考虑(we shall briefly短暂的mention how this is done). Whenever the dynamic forces动力are small relative to the static loadings, the system is
usually considered to be static.
大部分设备并不是静态的，这里提出的方法适用于动态，如果与动态有关的额外载荷被考虑进去。。任何时候只要动力与静态载荷有任何的关系，那么系统就被认为是静态的。
In engineering mechanics, we will appreciate欣赏到the various各种各样types of approximations近似法that are inherent in固有的any real problem:
在工程机械中，我们可以欣赏到各种各样形式的近似法来解决固有的问题。
Primarily首先, we will be discussing things which are in “equilibrium,” i.e., not accelerating加速的. However, if we look closely enough, everything is accelerating. We will consider many structural members结构部件to be “weightless” — but they never are. We will deal with forces that act at a “point” —but all forces act over an area. We will consider some parts to be “rigid坚硬的” — but all bodies will deform under load.
首先，我们讨论处于平衡中的物体，也就是说没有加速的。然而，如果我们仔细观察，可以看到所有物体都是运动的，我们会认为构件是没有重量的，但是他们总有重量。我们会认为力作用在点上，但是力总是作用在面上的，我们认为一些部分是坚硬的，但是任何物体在力的作用下都会变形。
We will make many assumptions假定that clearly are false. But these assumptions should always render the problem easier, more tractable易处理的. You will discover that the goal is to make as many simplifying assumptions as possible without seriously degrading退化the result. 我们会假定一些显然是错误的东西。但是这些假设会使问题变得简单，更易处理。你会发现我们的目的是找到尽量简单的假设，只要不使结果严重变形。
Generally there is no clear method to determine确定how completely, or how precisely, to treat a problem: If our analysis is too simple, we may not get a pertinent相关的answer; if our analysis is too detailed详细, we may not be able to obtain得到any answer. It is usually preferable to start with a relatively simple analysis and then add more detail as required to obtain a practical solution.
During the past two decades, there has been a tremendous growth in the availability of computerized methods for solving problems that previously were beyond solution because the time required to solve them would have been prohibitive. At the same time the cost of computer capability and use has decreased by orders of magnitude. We are experiencing an influx of “personal computers” on campus, in the home, and in business.
Lesson 6 Shaft轴Design
A shaft is a rotating旋转or stationary固定的member零件，构件, usually of circular圆形的cross section横截面, having mounted安装upon it such elements as gears齿轮, pulleys滑轮, flywheels飞轮, and other power-transmission传动装置elements.
轴类零件一般都是固定的或者是旋转体。截面一般都是圆形，并且有齿轮，滑轮，飞轮或者其他的传动装置安装在上面。
If a shaft carries安装several gears or pulleys齿轮或者滑轮, different sections截面of the shaft will be subjected to承受different torques力矩, because the total power delivered to传递the shaft is taken off piecemeal分散成片at various points. Hence one must note记录the amount of torque力矩on each part of the shaft. Then study the distribution分布of the bending moment弯矩, preferably较好的sketching草图( freehand is all right) the shear force切应力and bending moment diagrams弯矩图.
如果轴上安装了几个齿轮和滑轮，不同的截面将会承受不同的力矩。因为传递到轴上的总力被分散到了不同的点。因此我们必须分别记录不同部分的力矩，然后研究弯矩的分布，较好
的画出切应力和弯矩的图。
From this preliminary examination预备考试，预先检查, which is a problem in mechanics, we note the section截面where the bending moment弯矩is a maximum and the section where the torque扭矩is a maximum. If these maximums occur at the same section, the diameter直径needed for that section is determined- and used for the entire整个的shaft when the diameter is to be constant恒定. If the maximums do not occur at the same section, determine the diameter for the section of maximum torque and also for the section of maximum bending moment, and use the larger value.
从之前的检查我们可以知道，我们在工程中注意弯矩和扭矩达到最大的截面。如果这些截面重合，那么我们就说当此直径恒定的时候，截面的的直径也就定了，当然此轴的尺寸也就定下来了。如果两个面没有重合，那么我们就取其中大的那个。
The diameter of shaft is often varied from point to point , sometimes for structure reasons. In this case, check the stress or determine the size needed for each section. The designer makes certain that all sections of the shaft are subjected to safe stresses, taking due note of holes, keyways, and other stress raisers应力集中装置.
轴各部分的直径常常是不同的。一些是结构的原因。这种时候，我们要检查上面的应力并且决定所需面的尺寸。设计师要特别注意孔，键槽和其他的应力集中装置，确保所有的截面所受的力都在允许范围内。
Hollow洞round shafts园轴sometimes serve a useful purpose, usually in large sizes, though they are more expensive than solid ones. They have the advantage of being stronger and stiffer 更硬的, weight for weight, because the outer fibers外部纤维are more effective in resisting the applied moments, and they respond better to heat treatment because quenching淬火can proceed outward as well as inward.
孔轴常常可以发挥重要的作用，它们的尺寸一般都比较大，而且比一般的实心轴更贵。它们的优点是等质量的情况下更加的硬，因为外部的纤维更有利于承受应力，而且由于它们可以内外同时进行热处理所以效果可以更好。
Deflection偏差is a significant重大的consideration in the design of shafts. Criteria标准条件for the limiting torsional deflection扭转变形vary from 0.25 degree per meter of length for machinery shafts to 1 degree per meter or 1 degree in a length of 20 diameters for transmission shafting传动轴. Even short shafts become special problems in rigidity硬度when the load is applied in impulses脉冲, as on an automobile crankshaft汽车机轴. The impulses脉冲produce a torsional vibration扭转变形, usually compensated by torsional-vibration dampers扭转减震器in an automotive engine汽车发动机.
在轴的设计中，偏差将会被着重考虑。传动轴的标准扭转变形范围是每米0.25度到1度。就算是微小的偏差如果加载上脉冲负载都会严重影响轴的硬度。就比如汽车的机轴，就需要汽车发动机中的扭转减震器来消除脉冲造成的扭转变形。
Data on permissible values允许值of deflections变形are rare, probable because the range范围of values would be large and each situation has its own peculiarities独特性. An old rule of thumb检验的法则for transmission shafting传动轴is that the deflection should not exceed 0.0005L, where L is the shaft length between supports; although greater stiffness may be desired 需要.
变形的允许值很小，也许是因为每种特定的情况都有其独特性。旧时后的检验法则表示就算需要更高的强度变形也不能超过轴长的0.0008倍。
Preferably较好的, on transmission shafts, the pulleys and gears should be located close to bearings轴承in order to minimize最小化moments. If journal bearings径向轴承with “thick film” lubrica tion润滑are used, the deflection偏向across the bearing width轴承宽度should be only a small fraction部分of the oil-film thickness油膜厚度; if the slope斜坡is excessive过多here, there will be “binding粘合” in the journal轴颈. A self-aligning bearing球面轴承may eliminate消除this trouble if the deflection is otherwise acceptable.
传动轴的较好的设计是将齿轮和滑轮放在靠近轴承的地方。如果使用的是涂有润滑油的径向轴承那么轴承宽度方向的偏向只能是油膜厚度的一小部分。如果斜坡过多那么就要在轴颈上涂上粘合剂。但是当变形在可接受范围内时球面轴承可以消除这种问题。
On machine tools, rigidity硬度is a special concern because of its relation to accuracy准确性. If a shaft supports a gear, deflection is more of a consideration than if it carries a V-belt pulley皮带轮.
在机械工具中，硬度被特别关注。因为他反应了其精度。装了齿轮的轴比装了皮带轮的轴更加强调偏差。
The center of mass质心of symmetric匀称的, rotating旋转body does not coincide with与一致its center of rotation. This is because (a) it is impossible from a practical实际viewpoint to get the mass uniformly distributed分布式about the geometric几何学center of the body and (b) the shaft on which the body rotates deflects under load, thus moving the center of mass away from the true axis, which passes through通过the center line of the bearings.
均与的旋转体的质心与其旋转中心不重合。因为从实际情况看，质量是不可能按照其几何形状均匀分布的。因此将质心移动离开其轴心，
Rotation循环may begin about the geometric axis几何中心, but at some speed, the centrifugal force离心力of the displaced取代center of mass质心will equal the deflecting forces偏转力on the shaft; the shaft with its attached附加的bodies will then vibrate震动violently猛烈的, since the centrifugal force changes its direction方向as the shaft turns. This speed is termed术语是the critical speed临界转速. Above the critical speed, a smooth-running state光滑运行状态of equilibrium平衡is again reached when the body is then rotating旋转virtually事实上about its mass center质心(centrifugal forces离心力balance).
循环也许会绕着几何中心进行。但是在某些速度的情况下，被取代了的质心的离心力会与轴上的偏心力平衡，带着附加物件的轴将会猛烈的震动。知道离心力方向改变成与转动方向一致。这个速度被称为是临界转速。在此速度时，工件将会再次达到平衡的光滑运行状态。High-speed turbines高速涡轮机often operate运转above the critical speed临界转速. Additional附加的critical speeds, higher than the first, are successively相继的attained得到, but the amplitudes振幅of the corresponding相应的vibrations震动progressively逐渐的decrease.
高速涡轮机经常在临界转速运转。更加高的附加的临界转速也常常被运用。但是相应的震动的振幅也就逐渐的减少。
Many shafts supported by three or more bearings, which means that the problem is statically 静态的indeterminate不确定的. Texts on strength of materials材料强度give methods of solving such problems. The design effort设计工作should be in keeping with与。。相关联the economics经济学of a given situation. For example, if one line shaft supported by three or more bearings is needed, it probably would be cheaper to make conservative assumptions保守假设as to moments and design it as though it were determinate. The extra cost of an oversize shaft may be less than the extra cost of an elaborate复杂的design analysis.
许多的轴承上装了三个甚至三个以上的齿轮，也就意味着，这个问题是不确定的。材料强度手册给出了解决这个问题的方法。设计工作应该随时与经济情况相联系。例如，如果需要在轴上加上三个或者以上的齿轮时，去直接买设计好了的比设计一个复杂的设计分析还要省钱。
In addition to除了gears, belts皮带and chains链条are in widespread use. Belts and chains represent代表了the major types of flexible灵活的power transmission能量传输elements. Fig.8.1 shows a typical典型的industrial application应用of these elements combined with a gear-type speed reducer减速装置. This application illustrates阐明where belts, gear drives, and chains are each used to best advantage.
除了齿轮，皮带，链条也是广泛的运用。它们代表了绝大部分的灵活能量传输机构。他展示了这些包含了减速装置的元素的典型的运用。这个运用阐明了皮带，齿轮和链条的每个的优点。
Rotary旋转power能量is usually developed by the electric motor电动机, but motors typically典型的operate运行at too high a speed and deliver传送too low a torque转矩to be appropriate for适合于the final drive application最终执行应用程序. For a given power transmission, the torque is increased in proportion to成比例the amount that rotational转动的speed is reduced.
电动机一般输出旋转能量，但是典型的电动机进行高速的运转，并且输出低速的转矩来适应最终执行应用程序。经过一个能量转换器来成比例的增加转矩和减少转速。
So some speed reduction减速is often desirable令人满意的. In general, belt drives皮带传动are applied where the rotational speeds转速are relatively相当high, as on the first stage of speed reduction减速from an electric motor or engine. A smaller driving pulley皮带轮is attached to附属于the motor shaft电机轴, while a larger diameter直径pulley is attached to a parallel平行的shaft that operates操作at a correspondingly相应的lower speed. Pulleys皮带轮for belt drives皮带传动are also called sheaves捆绑. The linear speed线速度of a belt is usually 10-30m/s, which results in导致relatively相对的low tensile forces拉力in the belt.
一部分减速是比较令人满意。一般皮带轮适用于将高速运动转变成为低速运动。连丽如电动机和马达的第一步减速过程。皮带轮是附属于电机轴同时一个大直径的皮带轮附属于一平行的在相应的低速运行的轴。
These are four main belt types: flat, round, V, and synchronous同步的同时的. Flat and round belts may be used for long center distances between the pulleys in a belt drive. On the other hand, V and synchronous belts are employed for负责limited shorter center distance. Excluding 除了synchronous belts, there is some slip滑到between the belt and the pulley, which is usually made of cast iron铸铁or steel.
以下是四个主要的皮带形式：平皮带，圆形皮带，v型和同步皮带。平型和圆形皮带适用于皮带传动中中心距较远的两个皮带轮之间。同时，v型和同步皮带比较适合于较短中心距的情况。除了同步皮带在皮带和皮带轮之间也会有铸铁或者钢做成的滑轮。
A widely used type of belt, particularly in industrial drives工业传动and vehicular 车辆applications应用, is the V-belt driveV型皮带传动. The V-belt causes the belt to wedge楔入tightly紧紧的into the groove of the sheave滑轮的槽, increasing friction摩擦力and allowing high torques力矩to be transmitted传输before slipping滑动occurs.
在工业传动和车辆应用中v型皮带被广泛的运用。v型皮带紧紧的楔入滑轮的槽中，提供了大的摩擦力和力矩用于传输，以避免滑动的发生。
Flat belt drives produce very little noise and absorb more vibration from the system than either V-belt or other drives. A flat belt drive has an efficiency效率of around 98%, which is nearly the same as for a gear drive. A V-belt drive can transmit more power than a flat belt drive. However, the efficiency of a V-belt drive varies between 70% and 96%.
平带比其他各种传动发出的噪声都要少，而且能够吸收更多的震动。平带的效率大约是98%，和齿轮传动的效率差不多。v型皮带传动可以传输更多的能量，但是他的效率只有70%到96%。
A synchronous belt, sometimes called timing belt, has evenly均匀的spaced teeth on the inside circumference圆周(see Fig.8/2). A synchronous belt does not slip and hence transmits power at a constant恒定的angular velocity ratio角速度比.
同步皮带也成为同时皮带，在内圆周有均匀的齿轮空间。同步皮带传动不会打滑并且传递着恒定的角速度比。
However, if very large ratios比率of speed reduction减速are required in the drive, gear reducers are desirable理想的because they can typically代表性的accomplish large reductions in a rather small package很小的空间. The output shaft of the gear-type speed reducer is generally at low speed and high torque. If both speed and torque转矩are satisfactory满足for the application应用. It could be directly直接coupled to耦合the driven machine从动机.
但是如果要求传递大比率的减速那么齿轮传动是代表性的理想方式。他可以在很小的范围内完成大范围的速度减少。输出轴如果能满足速度和转矩要求，一般是低速高转矩。还可以直接耦合从动机。
Since gear reducers齿轮减速箱are available only at discrete离散的reduction ratios减速比, the output must often be reduced more before meeting the requirements of the machine. At the low-speed, high-torque condition, chain drives链传动become desirable. The high torque causes high tensile forces拉力to be developed in the chain. The elements of the chain are typically metal, and they are sized to withstand抵挡the high forces. When transmitting power between rotating shafts回转轴, the links of chains are engaged in从事于toothed wheels齿轮called sprockets齿轮链to provide positive (no slip) drive. Fig.8.3 shows a typical chain drive.
由于齿轮减速箱只适用于离散的传动比，输出常常会达不到机器的要求。在低速高转矩条件时，比较适用链传动。大的转矩在传动链中造成了大的拉力。在回转轴间的传动，如果链连接作用与齿轮就称为是齿轮链用以提供正作用。
Chain drives combine some of the more advantageous features特色of belt and gear drives. Chain drives provide almost any speed ratio速度比. Their chief主要，首席advantage over gear drives is that chain drives can be used with arbitrary任意的center distances. Compared with belt drives, chain drives offer the advantage of positive drive强制驱动(no slip) and therefore greater power capacity.动力能量
链传动比皮带传动和齿轮传动有更多的特色。链传动基本上可以提供任何的传动比。相对于齿轮传动，链传动最大的好处是可以在任何中心距上工作。和皮带传动比较，链传动可以提供强制驱动并从而得到更大的动力能量。
The most common type of chain is the roller chain滚子链, in which the roller on each pin provides exceptionally特别的low friction摩擦between the chain and the sprockets. Of its diverse不同的applications, the most familiar is the roller chain drive on a bicycle. A roller chain is generally made of hardened steel硬化钢and sprockets链齿轮are generally made of steel or
cast iron. Nevertheless然而, stainless steel不锈钢and bronze青铜chains are obtainable能得到的where corrosion resistance抗腐蚀性is needed.
One of the important considerations注意事项in material selection材料选择is their physical properties物理性质(that is, density密度, melting point, specific heat比热, thermal conductivity导热性, thermal expansion热膨胀, and corrosion resistance抗腐蚀性). Physical properties化学特性can have several important influences on manufacturing and the service life of components零件.For example, high-speed machine高速钻机tools require lightweight components to reduce inertial forces惯性力and, thus, keep machines from excessive过多的vibration.震动
在材料选择中，要注意材料的物理性质和化学性质。物理性质包括：密度，熔点，比热，导热性，热膨胀和抗腐蚀性。化学性质对零件的寿命和工作能力会有很大的影响。例如，高速钻机就要求使用轻质的零件来减少惯性，从而消除多余的震动。
1. Density密度The density of a material is its mass per unit volume单位体积的质量. Another term is specific gravity比重, which expresses a mat erial’s density in relation to that of water, and thus, it has no units. Weight saving is important particularly for aircraft and aerospace structures, for automotive bodies车身and components, and for other products where energy consumption能量损耗and power limitations局限性are major concerns. Substitution代替of materials for the sake of为什么的利益weight saving and economy is a major factor主要因素in the design both of advanced先进的equipment and machinery and of consumer products消费品, such as automobiles.
材料的密度就是材料单位体积的质量。另一种叫法是比重，表示金属密度与水密度的比值，因此是没有单位的。对于飞行器和航空器，减少重量是异常重要的。对于车身零件，和其他一些主要关心能量损耗和能量局限性的装置时，设计中主要用减轻重量的材料代替。不论是在先进装备的设计还是消费品的设计。
2. Melting Point The melting point of a metal depends on the energy required to separate its atoms原子. The melting temperature of a metal alloy金属合金can have a wide range (depending on its composition) and is unlike that of a pure metal, which has a definite melting point. The temperature range within which a component or structure is designed to function is an important consideration in the selection选择of materials.
材料的熔点与材料融化需要的能量有关。金属合金的溶解温度可能是在一个范围内。与纯金属有恒定的溶解温度不同。零件的允许工作范围对于零件材料的选择是非常重要的指标。
The melting point熔点of a metal has a number of indirect effects间接效应on manufacturing operations生产过程. Because the recrystallization temperature再结晶温度of a metal is related to its melting point, operations such as annealing退火and heat treating and hot working热加工require a knowledge of the melting points of the materials involved.
金属的熔点对于生产过程有许多的间接效应。这是因为再结晶温度与金属的熔点有关，退火加工和热处理还有热加工时都需要金属的熔点信息。
3.Specific Heat比热 A material’s specific heat is the energy required to raise the temperature of a unit mass by one degree. Alloying element have a relatively minor effect on the specific heat of metals. The temperature rise in a workpiece工件resulting from machining operation制造
加工is a function of the work done and of the specific heat of the workpiece material. Temperature rise升温in a workpiece, if excessive, can decrease product quality by adversely不利的affecting its surface roughness表面粗糙度and dimensional accuracy空间准确性, can cause excessive tool wear工具磨损, and can result in undesirable metallurgical金相changes in the material.
金属的比热是金属单位质量上升一度需要消耗的能量。合金元素有利于降低材料的比热。制造加工合一使工件的温度升高。如果温度升高过多的话会影响工件表面粗糙度和空间准确性，还能增加工具的磨损并且造成金相的不当改变。从而影响工件的质量。
4. Thermal Conductivity Thermal conductivity indicates the rate at which heat flows within and through a material. Metals generally have high thermal conductivity, while ceramics and plastics have poor conductivity.
导热系数代表着温度在材料中传导速度的估计值。金属一般都有很好的导热性，而陶瓷和塑料的传导性就很差。
When heat is generated by制作plastic deformation塑性变形or due to friction摩擦力, the heat should be conducted引导away at a rate比率high enough to prevent防止a severe剧烈rise in temperature. The main difficulty experienced in machining titanium钛, for example, is caused by its very low thermal conductivity. Low thermal conductivity can also result in high thermal gradients and, in this way, cause inhomogeneous不同的deformation变形of workpieces in metalworking processes金属加工过程.
如果是由于塑性变形或者摩擦产生热量，这样的热量要迅速的被引导走，以免产生剧烈的温度起伏。例如，对于钛来说，最难的是由于它的低导热率。低导热率很容易引起高的热梯度。因此金属加工过程中会产生不均匀的变形。
5.Thermal Expansion热膨胀The thermal expansion of materials can have several significant effects, particularly the relative expansion相对膨胀or contraction收缩of different materials in assemblies装配such as moving parts in machinery that require certain clearances for proper functioning正常运行.
材料的热膨胀有几个很有意义的影响，特别是装配中的金属相对膨胀和收缩。
Shrink fits热配合utilize利用thermal expansion热膨胀and contraction收缩. For example, a part, such as a flange, is to be installed安装over a shaft. It first is heated and then slipped over 套上a shaft which is at room temperature. When allowed to cool, the part shrinks收缩and the assembly装配effectively becomes an integral component.
热配合就利用了热膨胀和热收缩。例如，一部分，例如法兰会安装在轴上，首先将它加热，任何套入一个室温的轴上。等到回到室温时，就装配完成了。
6. Corrosion Resistance抗腐蚀性Metals, ceramics, and plastics all are subject to服从forms of corrosion. The word corrosion itself usually refers to the deterioration of metals and ceramics, while similar phenomena现象in plastics generally are called degradation退化. Corrosion leads not only to surface deterioration恶化of components and structures but also reduces their strength and structural integrity结构完整性.
金属，陶瓷，和塑料都有抗腐蚀性。腐蚀这个词表示了金属和陶瓷变质现象。在塑料中我们
常常叫做退化。腐蚀不仅仅会使表面质量变差，还能降低材料的强度和结构完整性。Corrosion resistance腐蚀抗性is an important aspect方面of material重要selection选择for applications应用in the chemical, food, and petroleum industries石油工业, as well as in manufacturing operations制作过程. In addition to除之外various possible chemical reactions 化学反应from the elements and compounds present现在, environmental corrosion of components and structures is a major concern, particularly at elevated temperatures升温and other transportation vehicles运输车辆.
在化学，食品，制造过程和石油工业里，抗腐蚀性是材料选择时要着重考虑的一方面。
Resistance to corrosion depends on the composition of the material and on the particular environment. Corrosive media may be chemicals (acid, alkalis, and salts), the environment (oxygen, moisture, pollution, and acid rain), and water (fresh or salt water). Nonferrous metals, stainless steels, and nonmetallic materials generally have high corrosion resistance, Steels and cast irons usually have poor resistance and must be protected by various coatings and surface treatments.
The usefulness有效性of some level of oxidation氧化is exhibited展出in the corrosion resistance抗腐蚀性of aluminum铝, titanium, and stainless steel不锈钢. Aluminum develops a thin (a few atomic layers), strong, and adherent hard-oxide film (Al2O3) that better protects the surface from further environmental corrosion. Titanium develops a film of titanium oxide (TiO2).
A similar phenomenon occurs in stainless steels, which (because of the chromium present in the alloy) develop a protective film on their surfaces. When the protective film is scratched and exposes the metal underneath, a new oxide film begins to form.
Drilling钻孔involves producing through or blind holes in a workpiece by forcing a tool, which rotates around its axis, against the workpiece. Consequently, the range of cutting from that axis of rotation is equal to the radius of the required hole.
钻孔指在工件表面利用工具的对表面的旋转来钻通孔和盲孔。因此，所得的孔的半径的大小是由刀具的半径决定的。
Cutting Tools for Drilling Operations
In drilling operations, a cylindrical cutting tool, called a drill, is employed. The drill can have either one or more cutting edges and corresponding flutes, which can be straight or helical. The function of the flutes is to provide outlet出口passages for the chips generated生产during the drilling operation and also to allow lubricants润滑油and coolants冷却剂to reach the cutting edges and the surface being machined. Following is a survey of the commonly used drills
在钻孔操作中，一种圆柱形的叫钻的工具不断的运行。钻可以有一个或多个刃口，既可以是直的，也可以是螺旋的。平面刀具的功能是切除材料，生成碎屑，螺旋面的功能是让切下来的碎屑可以流到外界，同时让润滑油和冷却剂可以流进去到工件的加工平面。下面是一些常用的钻头。
Twist Drill 麻花钻
The twist drill is the most common type of drill. It has two cutting edges and two helical flutes that continue over the length of the drill body. The drill also consists of a neck and a shank that can be either straight or tapered.
麻花钻是最常用的钻。在钻身上有两个切削刃和两个螺旋形排削槽。还包括一个颈和一个柄，他们既可以是锥形的也可以是直的。
carbide tipped drill硬质工具刀头钻
Most of drills are made of high-speed steel. However, for machining hard materials as well as for large volume production, carbide tipped drill are available. As shown in Fig.24.1, the carbide tips of suitable geometry适当的几何学are clamped夹紧to the end of the tool to act as the cutting edges.
大部分的钻是高速钢做的。然而当材料是硬质材料或者是大批量生产时，硬质工具刀头钻常常更加适合。如图所示，适当的形状的硬质钻被夹紧到工具的末端作为刀具。
Core Drills中心钻，扩孔钻 A core drill consists of the chamfer凹槽, body, neck, and shank. A core drill has flat end. The chamfer can have three or four cutting edges. Core drills are employed for enlarging放大previously之前made holes and not for originating holes. This type of drill is characterized by greater productivity, high machining accuracy, and superior quality of the drilled surfaces
中心钻包括凹槽，钻身，颈部和柄部。中心钻是平头的。凹槽可以有三到四个切割刃。扩孔钻是用来扩大之前已有的孔，而不能自己钻原始孔。这类钻的特点是生产效率高，机器精度高，孔的表面质量好。
Other Types of Drilling Operations其他类型的钻
In addition to conventional drilling, there are other operations that are involved in the production of holes in the industrial practice. Following is a brief description of each of these operations.
除了传统的钻，在工场实际中还包括别的类型的生产孔的方法。以下是对其中一些的简介。Boring 镗孔
Boring involves enlarging a hole that has already been drilled. It is similar to internal turning and can, therefore, be performed on a lathe. There are also some specialized machine tools for carrying out boring operations. Those include the vertical boring machine, the jig boring machine, and the horizontal boring machine.
钻孔包括扩大已有的孔，类似于车削，因此可以在车床上操作。还有其他的特殊的机器可以用来钻孔。包括：立式镗床，坐标镗床和水平镗床。
counterboring扩孔
Already existing holes in the parts can be further machined by counterboring as shown in Fig.24.3(a). In the counterboring operation, the hole is enlarged with a flat bottom to provide a space for the bolt head螺栓头or a nut螺母, so it would be entirely below the surface of the part.
如图所示已经存在的孔还可以进行锪孔操作。在这次锪孔操作中，这个孔被放大出一个平底来留出螺栓头或者是螺母的空间，这样他们才能完全没入工件。
Countersinking
As shown in Fig.24.3(b), countersinking is done to enable accommodating适合the conical seat of a flathead screw平头螺栓so that the screw does not appear above the surface of the part.
如图所示，这个操作是为了给平头螺栓创造一个位置，这样他就不会出现在表面了。
Spot facing 锪孔
Spot facing operation removes only a very small portion of material around the existing hole to be provide a flat surface square to the hole axis, as shown in Fig.24.3(c). This has to be done only in case where existing surface is not smooth and is usually performed on casting or forgings.
锪孔只会从已存在的孔的表面切除少量的材料，使得孔的表面变得光滑，而且提高了同轴度，如图所示，这种操作往往是在工件表面不平整或者是锻铸出来的孔时用。
Reaming铰孔
Reaming is an operation used to make an existing hole dimensionally在尺寸上more accurate than can be obtained by drilling alone. As a result of a reaming operation, a hole has a very smooth surface. The cutting tool used in this operation is known as the reamer.
铰孔是为了使已存在的孔在尺寸上可以比锪孔得到的更加的准确。铰孔得到的工件表面会变得非常的光滑，所用的刀具就叫做铰刀。
Tapping攻丝
Tapping is the process of cutting internal threads内螺纹. The tool is called a tap.
攻丝的过程就是制作内螺纹，刀具是叫丝锥。
Drilling operations can be carried out by using either electric hand drills or drilling machines. The latter differ in shape and size. Nevertheless the tools always rotates around its own axis while the workpiece is kept firmly fixed. This is contrary to相反the drilling operation on a lathe, where the workpiece is held in约束and rotates旋转with the chuck卡盘. Following is a survey of the commonly used types of drilling machines.
钻孔工序既可以用手提电钻也可以用机器电钻。后者的不同是在于形状和尺寸。但是，当工件固定的时候，刀具总是绕着他自己的轴转动。（工件固定而刀具旋转）这与车床的工作原理相反。车床是把工件约束固定住，然后旋转卡盘。以下是一些常用的钻床的介绍。
Bench-type drilling machines are general-purpose, small machine tools that are usually placed on benches. This type of drilling machine includes an electric motor电动机as the source来源of motion, which is transmitted传送via pulleys由。滑轮and belts皮带to the spindle, where the tool is mounted. The feed is manually手动的generated进行by lowering a lever handle手柄, which is designed to lower (or raise) the spindle.主轴
工作台型的钻床是多功能的，小型的工件一般会用这个加工。这种钻床是电动作为动能的来源，能量由滑轮，皮带传送到轴上工件安装的轴上。进给是通过控制专门设计的手柄达到的。The workpiece is mounted on the machine table, although a special vise虎钳is sometimes used to hold the workpiece. The maximum height of a workpiece to be machined is limited by the maximum gap间隙between the spindle and the machine table
工件被固定在机床的平台上，有时用虎钳固定。允许加工的工件的最大高度是由刀具到钻
床平台的距离决定的。
Upright Drilling Machines 立式钻床
Depending upon the size, upright drilling machine tools can be used for light, medium, and even relatively heavy jobs. It is basically similar to bench-type machines, the main difference being a longer cylindrical column fixed to the base.
由于形状，立式钻床可以用于轻型的，中型的甚至是较大型的工件。他与台式机床差不多，不同是长圆柱固定在底座上。
Along that column is an additional, sliding table for fixing the workpiece which can be locked in position at any desired height. The power required for this type is more than that for the bench-type drilling machines.
Radial Drill摇臂钻床 A radial drill is particularly suitable for drilling holes in large and heavy workpieces that are inconvenient to mount on the table of an upright drilling machine. A radial drilling machine has a main column, which is fixed to the base. The cantilever guide arm, which carries the drilling head spindle and tool, can be raised or lowered along the column and clamped at any desired position. The drill head slides along the arm and provides rotary motion and axial feed motion. Again, the cantilever guide arm can be swung, thus enabling the tool to be moved in all directions according to a cylindrical coordinate system.
摇臂钻床特别适合在又大又重的工件上钻孔
After lathes, milling machines are the most widely used for manufacturing applications. In milling, the workpiece is fed into a rotating milling cutter, which is a multi-edge tool as shown in Fig.28.1. Metal removal金属切削is achieved through combining the rotary motion of the milling cutter and linear motion of the workpiece simultaneously.
车之后铣床被最广泛用于制造应用。铣削加工工件旋转输入铣刀,如图所示是一个多刃刀具。旋转运动与直线运动相结合，实现金属的切削加工。
Each of the cutting edges of a milling cutter acts as an individual single-point cutter when it engages with the workpiece metal. Therefore, each of those cutting edges has appropriate rake and relief angles. Since only a few of the cutting edges are engaged with the workpiece at a time, heavy cuts can be taken without adversely affecting the tool life. In fact, the permissible cutting speeds and feeds for milling are three to four times higher than those for turning or drilling. Moreover, the quality of surfaces machined by milling is generally superior to the quality of surfaces machined by turning, shaping, or drilling.
每个切削刃铣刀与金属接触时是单点切削。因此，每一个刀刃具有适宜的斜度与后角。因为同时有不止一个刀刃与工件接触，所以重力切削也不会对刀具产生大的影响，影响其寿命。事实上,其允许切削速度和进料速度是车削和钻孔的三到四倍。此外,由铣削加工表面质量通常比钻孔，刨削和车削要佔优势。
The milling process is characterized by:
铣削过程的特征是:
(1)Interrupted cutting.
适合间断性切割
Each of the cutting edges removes material for only a part of the rotation of the milling cutter. As
a result, the cutting edge has time to cool before it again removes material. Thus the milling operation is much cooler compared to the turning operation.
每个刀刃旋转一次只切除一小部分的材料，因此，切削刃在下次切除材料之前有足够的时间冷却。因此相对于车削加工，铣削加工的刀片温度更加低。
(2)Small size of chips.体积小Though the size of the chips is small, in view of鉴于，由于the multiple多重cutting edges in contact a large amount of material is removed and as a result the component is generally completed in a single pass unlike the turning process which requires a large number of cuts for finishing.
虽然刀片的尺寸小，但是由于有多重切削刃与工件接触，有很大量的材料在仅仅是一次玩完整的过刀中被切下来。而不像车削那样，为了达到最终要求需要切很多次。
(3)Variation in chip thickness.碎片厚度的变化This contributes to the non-steady不稳定state状态cyclic conditions循环条件of varying cutting forces during the contact of the cutting edge with the chip thickness varying from zero to maximum size or vice versa反之亦然. This cyclic variation循环变化of the force can excite激发any of the natural frequencies固有频率of the machine tool system and is harmful to the tool life and surface roughness generated.
这是有利于那种不稳定状态循环条件
变化的切削力在切削刃与切削厚度之间的接触从零变到最大或者反之亦然。这个循环变化的力量能够激发任何机床系统的固有频率并且这是有害于表面粗糙度和刀具寿命的。
As far as the directions of cutter rotation and workpiece feed are concerned, milling is performed by either of the following two methods.
至于刀具旋转方向以及材料进给方向的关系,铣削由以下二种情况。
Up milling (conventional milling). In up milling the cutting tool rotates in the opposite direction to the table movement, the chip starts as zero thickness and gradually increases to the maximum size as shown in Fig.28.2(a). This tends to lift the workpiece from the table. There is a possibility that the cutting tool will rub the workpiece before starting the removal. However, the machining process involves no impact loading冲击载荷, thus ensuring smoother operation of machine tool.
逆铣(传统的，惯用的铣)。铣削刀具与工作平面以相反方向运动，切削的厚度从零开始，逐步增加到的最大值,如图Fig.28.2(a)。这可能会把工件弄出工作平台。有可能，在切削开始之前刀具就与工件接触。然而，加工过程不包括冲击载荷，因此需要确保机器工具的平稳工作。
The initial rubbing最初的摩擦of the cutting edge during the start of the cut in up milling tends to dull the cutting edge and consequently因此have a lower tool life. Also since the cutter tends to cut and slide alternatively, the quality of machined surface obtained by this method is not very high. Nevertheless, up milling is commonly used in industry, especially for rough cuts粗削.
在你洗开始的阶段的这种摩擦会弄顿刀刃因此这种刀的寿命会缩短。还有由于此时切割与打滑刀具要选其一，加工件的表面质量又得不到保证很高。然而，不过逆铣在生产中只要不是粗削都常用这个。
Down milling (climb milling). In down milling the cutting tool rotates in the same direction as that of the table movement, and the chip starts as maximum thickness and goes to zero thickness gradually as shown in Fig.28.2 (b). This results in a kind of impact影响, or sudden loading. Therefore, this method cannot be used unless the milling machine is equipped with a backlash eliminator on the table lead screw. The maximum depth of cut is achieved directly直接as the cutter刀具engages参与with the workpiece and this gives a large force, which will have to be taken care of by a rigid严格lead screw导螺杆for table feeding工作台进给.
顺铣。铣削刀具与工作平面以相同方向运动，切削的厚度从最厚开始，逐步减少到的零。用这种方法会有突如其来的载荷。因此除非在在机床导螺杆上装了齿轮消除装置，不然这样不好。刀具与工件刚刚接触的时候就达到了最大切割深度，而有了最大的力。因此必须严格遵循导螺杆调节进行工作进给。
The advantages of this method include higher quality of the machined surface and easier clamping of workpiece, since cutting forces act downward. Down milling also allows greater feeds per tooth and longer cutting life between regrinds than up milling. But, it cannot be used for machining castings or hot rolled steel, since the hard outer scale will damage the cutter.
这种方法的优点包括高质量的机械加工面还有工件更易夹持。因为切削力大小是下滑的。顺铣可以有更大的进给量和更长的寿命。但是不能用于铸件加工还有热轧钢。因为坚硬的表面会伤害刀刃。