1.?for diameters less than 3 in, the usual shaft material is cold-rolled steel containing about 0.4 percent carbon. shafts are either cold-rolled or forged in sizes from 3 in to 5 in. for sizes above 5 in, shafts are forged and machined to size. plastic shafts are widely used for light load applications. one advantage of using plastic is safety in electrical applications, since plastic is a poor conductor of electricity.
直径小于3英寸的轴可以选用含碳量大约为0.4%的冷轧钢，直径在3~5英寸之间的轴可以选用冷轧钢或铸造毛坯。当轴的直径大于5英寸时，则需求选用铸造毛坯，然后经过机械加工抵达所需求的标准。轻载时，广泛选用塑料轴，因为塑料是电的不良导体，在电气中选用塑料比照平安。

2.?components such as gears and pulleys are mounted on shafts by means of key. the design of the key and the corresponding keyway in the shaft must be properly evaluated. for example, stress concentrations occur in shafts due to keyways, and the material removed to form the keyway further weakens the shaft.
齿轮和带轮等零件经过键联接在轴上。在对键及轴上与之相对应的键槽的方案中，有必要进行细心的核算。例如，轴上的键槽会致使应力会集，因为键槽的存在会使轴的横截面积减小，会进一步削弱轴的强度。
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3.?if shafts are run at critical speeds, severe vibrations can occur which can seriously damage a machine. it is important to know the magnitude of these critical speeds so that they can be avoided. as a general rule of thumb, the difference between the operating speed and the critical speed should be at least 20 percent.
假定轴以临界速度滚动，将会发生激烈的振荡，可以会损坏整台机器。晓得这些临界速度的巨细是很重要的，因为这样可以避开它。一般凭经历来说，作业速度与临界速度之间至少大约相差20%。
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4.?many shafts are supported by three or more bearings, which means that problem is statically indeterminate. texts on strength of materials give methods of solving such problems. the design effort should be in keeping with the economics of a given situation.
许多轴需要三个或更多的轴承来支撑，这就意味着它是一个超静定疑问。材料力学教科书介绍了求解这类疑问的办法。可是，方案作业大约与特定场合的经济性相契合。
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5.?for example, if one line shaft supported by three or more bearings is needed, it probably would be cheaper to make conservative assumptions 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 design analysis.
例如，需要一根由三个或更多个轴承来支撑的主传动轴，可以对力矩做出保存的假定，依照静定轴对其进行方案，其本钱可以会更低一些。因为轴的标准增大所需的本钱可以会比进行凌乱、精密的计区剖辨作业所多花费的本钱要低一些。
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6.?another important aspect of shaft design is the method of directly connecting one shaft to another. this is accomplished by devices such as rigid or flexible couplings.
轴的方案作业中的另一个重要方面是一根轴与另一根轴之间的直接连接办法。这是由刚性或许弹性联轴器来完成的。

7.?a coupling is a device for connecting the ends of adjacent shafts. in machine construction, couplings are used to effect a semipermanent connection between adjacent rotating shafts. the connection is permanent in the sense that it is not meant to be broken during the useful life of the machine, but it can be broken and restored in an emergency or when worn parts are replaced.
联轴器是用来把相邻的两个轴端联接起来的设备。在机械规划中，联轴器被用来完成相邻的两根转轴之间的半耐久性联接。在机器的正常运用时刻内，这种联接一般不必拆开，在这种意义上，可以说联轴器的联接时耐久性的，可是在紧迫的情况下，或许在需要替换已磨损的零件时，可以先把联轴器拆开，然后再联接上。
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8.?there are several types of shaft couplings, their characteristics depend on the purpose for which they are used. if an exceptionally long shaft is required in a manufacturing plant or a propeller shaft on a ship, it is made in sections that are coupled together with rigid couplings.
联轴器有几品种型，它们的特性随其用处而定。假定制造工厂中或许船舶的螺旋桨需要一根特别长的轴，可以选用分段的方法将其制造出来，然后选用刚性联轴器将各段联接起来。
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9.?a common type of rigid coupling consists of two mating radial flanges (disks) that are attached by key driven hubs to the ends of adjacent shaft sections and bolted together through the flanges to form a rigid connection. alignment of the connected shafts is usually effected by means of a rabbet joint on the face of the flanges.
一种常用的联轴器是由两个配对的法兰（盘）构成，这两个法兰盘凭仗靠键传动的轴套联接到相邻两节轴的两端，然后用螺栓穿过法兰联接起来构成刚性接头。彼此联接的两根轴一般是靠法兰面上的槽口来对齐的。
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10.?in connecting shafts belonging to separate devices (such as an electric motor and a gearbox), precise aligning of the shafts is difficult and a flexible coupling is used. this coupling connects the shafts in such a way as to minimize the harmful effects of shaft misalignment.
在把归于不一样的设备（例如一个电动机和一个变速箱）的轴联接起来的时分，要把这些轴精确地对准是比照困难地，此时可以选用弹性联轴器。这种联轴器联接轴当地式可以把因为被联接的轴之间的轴线不重合所构成的有害影响削减到最低程度。
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11.?flexible couplings also permit the shafts to deflect under their separate systems of loads and to move freely (float) in the axial direction without interfering with one another. flexible couplings can also serve to reduce the intensity of shock loads and vibrations transmitted from one shaft to another.
弹性联轴器也答应被联接的轴在它们各自的载荷体系作用下发生偏斜或在轴线方向安适移动（起浮）而不至于发生彼此烦扰。弹性联轴器也可以用来减轻从一根轴传到另一根轴上的冲击载荷和振荡的强度。

12.?sprocket: any of various toothlike projections arranged on a wheel rim to engage the links of a chain.
链轮：在轮缘上有牙状杰出物，与链条相啮合的轮子。
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13.?universal joint: a joint or coupling that allows parts of a machine not in line with each other limited freedom of movement in any direction while transmitting rotary motion. also called universal coupling.
万向接头：一种接头或联轴节，能使彼此不在一条线上的机械零件在传输旋转运动时在任意方向上具有有限的运动安适度。也称作universal coupling。
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14.?the term shaft usually refers to a relatively long member of round cross section that rotates and transmits power. one or more members such as gears, sprockets, pulleys, and cams are usually attached to the shaft by means of pins, keys, splines, snap rings, and other devices.
轴一般是指有圆形截面的相对较长的构件，轴旋转并传递动力。一个或多个比方齿轮，链轮，皮带轮和凸轮等类的构件一般凭仗于销、键、花键、卡环或其它设备联接到轴上。
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15.?a shaft can have a non-round cross section, and it need not necessarily rotate. it can be stationary and serve to support a rotating member, such as the short shafts that support the non-driving wheels of an automobile. the shafts supporting idler gears can be either rotating or stationary depending on whether the gear is attached to the shaft or supported by it through bearings.
轴也可以对错圆截面的而且不必定要旋转。它可所以固定的去支撑一个回转构件，就像轿车里支撑从动轮的短轴相同。支撑换向齿轮的轴可以旋转也可以中止不动，这取决于这个换向齿轮是联接在轴上仍是经过轴承（由轴）支撑的。
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16.?it is apparent that shafts can be subjected to various combinations of axial, bending, and torsional loads, and that these loads may be static or fluctuating.
很显着，轴将承受轴向、曲折、改变等载荷的各种组合的作用。而且，这些载荷可所以静态的，也可所以不坚决的。
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17.?typically, a rotating shaft transmitting power is subjected to a constant torque (producing a mean torsional stress) together with a completely reversed bending load (producing an alternating bending stress).
典型地，一根传递动力的旋转轴遭到一个平稳的扭矩（发生一个均匀的改变应力）和一个完全的交变曲折载荷（发生一个交变曲折应力）的一起作用。
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18.?in addition to satisfying strength requirements, shafts must be designed so that deflections are within acceptable limits. excessive lateral shaft deflection can hamper gear performance and cause objectionable noise. the associated angular deflection can be very destructive to non-self-aligning bearings (either plain or rolling).
除了满足强度需求之外，所方案轴的挠度也有必要在可承受的极限规模内。过大的侧向挠度会阻止齿轮的功能并发生厌烦的噪声。有关的角向挠度对非调心轴承（滑动轴承或翻滚轴承）来说极具损坏性。

19.?torsional defection can affect the accuracy of a cam or gear driven mechanism. furthermore, the greater the flexibility (either lateral or torsional) the lower the corresponding critical speed.
扭改动形会影响凸轮或齿轮传动机构的精度。此外，柔性（横向的或改变的）越大，则相应的临界转速就越低。
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20.?a simpler attachment for transmitting relatively light loads is provided by pins. pins provide a relatively inexpensive means of transmitting both axial and circumferential loads.
更简略的用来传递相对较轻载荷的联接的是销。销供给了一种能一起传递轴向和周向载荷的较廉价的办法。
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21.?an excellent and inexpensive method of axially positioning and retaining hubs and bearings onto shafts is by means of retaining rings, commonly called snap rings. shaft snap rings require grooves that weaken the shaft, but this is no disadvantage if they are located where stresses are low.
一种极好的又很廉价的使轮毂和轴承在轴上轴向定位并固定的办法是用定位环，一般叫卡环。轴卡环需要（在轴上）开槽，这会使轴的强度降低，但假定槽开在应力较小的当地这也不算啥缺陷。
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22.?perhaps the simplest of all hub-to-shaft attachments is by means of an interference fit (hub bore is slightly smaller than shaft diameter, with assembly being made with a press, or by thermally expanding the hub —— sometimes also contracting the shaft, as with dry ice —— prior to making a quick assembly before the temperatures equalize).
凭仗于过盈协作来完成的联接可所以轮毂与轴之间的最简略的固定方法。轮毂孔比轴径稍小，用压装法或使轮毂热胀大——有时也用干冰让轴冷缩——在它们温度相同之前快速设备。
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23.?the strongest provision for torque transmission is usually by means of mating splines cut in the shaft and hub.
最佳的传递扭矩的方法使凭仗于在轴和轮毂上加工出来的配套的花键来完成的。
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24.?with respect to lateral vibration and critical speeds, the practicalities of manufacturing and operation are such that the center of mass of a rotating system can never coincide exactly with the center of rotation. hence as the shaft rotating speed is increased, centrifugal force acting at the mass center tends increasingly to bow the shaft. the more the shaft bows, the greater the eccentricity and the larger the centrifugal force. below the lowest (or fundamental) critical speed of rotation, the centrifugal and shaft elastic forces balance at a finite shaft deflection. at the critical speed, equilibrium theoretically requires an infinite displacement of the mass center.
关于横振荡和临界速度，制造和运用的实习是回转体系的质心历来不会和回转中心重合。因而当轴的转速添加，作用在质心的离心力也添加然后使轴曲折。轴曲折得越多，偏疼越凶狠，离心力也越大。在最低临界转速以下，离心力和轴的弹力在一个有限的轴挠度的情况下抵达平衡。在临界转速时，这个平衡理论上需求轴的质心有无限的偏移量。
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25.?damping causes equilibrium to occur at a finite displacement. however, this displacement is often large enough to break the shaft. rotation sufficiently above the critical speed results in a satisfactory equilibrium position by moving the mass center toward the center of rotation. in unusual situations (as some high-speed turbines), satisfactory operation is provided by quickly going through the critical speed (not allowing sufficient time for an equilibrium deflection to be reached) and then running well above the critical speed.
阻尼使这个平衡在有限的偏移下呈现。可是，偏移量常常大到足以损坏轴。充分大于临界速度的旋转经过将质心移向回转中心会得到令人满足的平衡方位。在特别情况下（如一些高速涡轮机），经过快速经过临界转速（不给抵达平衡挠度满足的时刻）可以抵达满足的作用，并顺畅使转速跨越临界转速。
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26.?clutch: any of various devices for engaging and disengaging two working parts of a shaft or of a shaft and a driving mechanism.
聚散器：一种使一根轴的两个作业有些或一根轴与机械驱动设备处于相接合或别离状况的设备。
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27.?friction is the resistance to motion of two moving objects or surfaces over each other.
冲突是两个彼此触摸的物体当有彼此运动或彼此运动趋势时，在触摸面发生的阻止运动的作用。
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28.?friction: a force that resists the relative motion or tendency to such motion of two bodies in contact.
冲突力：一种阻止两个相触摸物体之间发生相对位移的力。
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29.?chain: a connected, flexible series of links, typically of metal, used especially for holding objects together or restraining or for transmitting mechanical power.
链：一系列相连的，可折叠曲折的环节，一般为金属，用来将物体联合到一同或限制物体的方位或用来传递机械能。
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30.?belts, clutches, brakes and chains are examples of machine elements that employ friction as a useful agent. a belt provides a convenient means for transferring power from one shaft to another. belts are frequently necessary to reduce the higher rotative speeds of electric motors to the lower values required by mechanical equipment.
带、聚散器、制动器和链是使用冲突力的机械元件的比方。带供给将动力从一根轴传向另一根的简练办法。带常用于将电机的较高转速降低为机械设备需要的较低转速。
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31.?clutches are required when shafts must be frequently connected and disconnected. the function of the brake is to turn mechanical energy into heat. the design of frictional devices is subject to uncertainties in the value of the coefficient of friction that must necessarily be used. chains provide a convenient and effective means for transferring power between parallel shafts.
聚散器用于轴需要常常联接和断开的场合。制动器的功用是将机械能转化为热能。冲突设备的方案遭到有必要运用的冲突系数值得不断定性影响。链供给一种在平行轴间传递动力得便利而有用的办法。
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32.?the rayon and rubber v-belt is widely used for power transmission. such belts are made in two series: the standard v-belt and the high-capacity v-belt. other types of belts are available for power transmission purposes. the teeth of so-called timing belt will keep shafts completely synchronized.
人工纤维和橡胶v带广泛用于动力传动。这种皮带有两个系列：标准v型皮带和高容量v型皮带。其他类型的皮带可用于动力传输意图。所谓的同步带的齿将坚持轴完全同步。
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33.?when designing a v-belt drive it is a good plan to calculate the cost of two or three different layouts of belts and pulleys to determine which has the smallest overall cost. the catalogs of the various manufacturers of v-belts contain much practical information.
当方案v带传动时最佳核算两个或三个不一样规划的皮带和带轮的本钱以抉择哪种具有最小的全体本钱。v带制造商的目录包富含更多的实践信息。
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34.?the v-belt is an important element in the field of power transmission. it is continually being improved by the various manufacturers and loading values are revised from time to time. the designer generally is guided by the current literature for the particular brand of belt be expects to use. the forgoing development should be considered a method that shows how the fatigue life of a belt is influenced by factors such as bending, centrifugal effects, and power transmitted.
v带在动力传输领域中是一个重要的元件。各制造商的不断改进，负荷值也不时地得到批改。方案者一般以预期运用的特定品牌的带的其时文献为辅导。即便不打开也应思考一种办法，标明皮带的疲惫寿数如何遭到曲折、离心效应和传递功率等要素的影响。
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35.?a clutch is a device for quickly and easily connecting or disconnecting a rotatable shaft and a rotating coaxial shaft.
聚散器是一个用来使从动轴与位于同一轴线上的主动轴进行快速和顺畅的联接或脱开的设备。
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36.?clutches are usually placed between the input shaft to a machine and output shaft from the driving motor, and provide a convenient means for starting and stopping the machine and permitting the driver motor or engine to be started in an unloaded state.
聚散器一般位于机器的输入轴和驱动电机的输出轴之间，以供给一个便利地建议和中止机器的办法，并使得驱动电机或建议机在无载荷的状况下建议。
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37.?the rotor (rotating member) in an electric motor has rotational inertia, and a torque is required to bring it up to speed when the motor is started. if the motor shaft is rigidly connected to a load with a large rotational inertia, and the motor is started suddenly by closing a switch, the motor may not have sufficient torque capacity to bring the motor shaft up to speed before the windings in the motor are burned out by the excessive current demands.
电机中的转子有滚动惯量，当电机建议时需要一个转矩股动其作业。假定电动机的轴与具有很大滚动惯量的负载刚性地联接在一同，当合上开关使电动机俄然建议时，有可以在电动机没有来得及发生满足的扭矩，使电动机的轴抵达应有的转速之前，电动机内的线圈就会因为过大的电流而被焚毁。
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38.?a clutch between the motor and the load shafts will restrict the starting torque on the motor to that required to accelerate the rotor and parts of the clutch only. on some machine tools it is convenient to let the driving motor run continuously and to start and stop the machine by operating a clutch.
电机和负载轴之间的聚散器会捆绑电机的建议转矩，使其仅为加速转子和聚散器部件所需的扭矩。在一些机床上让驱动马达持续作业而经过操作聚散器使机器启停是便利的。
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39.?control of motion in machines. this category represents the majority of spring applications such as operating forces in clutches and brakes. also, springs are used to maintain contact between two members such as a cam and its follower.
控制机构运动。这类使用占弹簧用处的首要有些，如在聚散器和制动器中起操作力的作用。弹簧也被用来坚持凸轮与从动件触摸。
reduction of transmitted forces as a result of impact or shock loading. applications here include automotive suspension system springs and bumper springs.
缓冲和减振。这类使用包括轿车悬架体系弹簧弛缓冲弹簧。
storage of energy. applications in this category are found in clocks, movie cameras and lawn mowers. many parking meters use spring mechanisms which perform the timing function.
储存能量。这类弹簧使用于挂钟、拍摄机和割草机中。在许多轿车泊车计时器中选用弹簧机构来完成计时功用。
measurement of force. scales used to weigh people is a very common application for this category.
测量力的巨细。用来称体重的秤就是这类使用中最多见的一种。
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40.?most springs are made of steel, although silicon bronze, brass and beryllium copper are also used. springs are universally made by companies which specialize in the manufacture of springs. the helical coil spring is the most popular type of spring; torsion bars and leaf springs are also widely used.
大有些弹簧是选用钢来制造的，但也有一些弹簧选用硅青铜、黄铜和铜铍合金制造。弹簧一般由专业出产弹簧的厂家制造。圆柱螺旋弹簧是最常用的弹簧，扭杆和板簧也有广泛的使用。
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41.?if the wire diameter (assuming a helical coil spring) is less than 8 mm, the spring will normally be cold-wound from hard-drawn or oil-tempered wire. for larger diameters, springs are formed using hot-rolled bar.
假定钢丝直径（假定圆柱螺旋弹簧）小于8 mm，，一般选用冷拔钢丝或许油回火钢丝经过冷卷法制成。假定弹簧丝直径较大，选用热轧钢筋卷制弹簧。

42.?it is good practice to consult with a spring manufacturing company when selecting a spring design, especially if high loads or temperatures are to be encountered, or if stress reversals occur or corrosion resistance is required. to properly select a spring, a complete study of the spring requirements, including space limitations, must be undertaken. many different types of special springs are available to satisfy unusual requirements or applications.
选择弹簧，特别是在遇到重载、高温、需要承受交变应力或许需要具有抗腐蚀性的时分，大约向弹簧制造厂家进行征询。为了正确地选择弹簧，大约对弹簧的各种运用需求，包括空间捆绑进行全部地研讨。有许多不一样品种的专用弹簧可以满足一些特别的需求或用处。
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43.?melting point: the temperature at which a solid becomes a liquid at standard atmospheric pressure.
熔点：在标准大气压力之下固体熔化成液体的温度。
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44.?specific heat: the ratio of [the amount of heat required to raise the temperature of a unit mass of a substance by one unit of temperature] to [the amount of heat required to raise the temperature of a similar mass of a reference material, usually water, by the same amount].
比热：将一单位质量的物质的温度前进一单位所需的热量与将一具有类似质量的对照材料，一般为水，前进相同单位的温度所需的热量之比。
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45.?specific gravity: the ratio of [the mass of a solid or liquid] to [the mass of an equal volume of distilled water at 4℃].
比重：一种固体或液体的质量与温度为4℃的同体积的蒸馏水的质量之比。
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46.?one of the important considerations in material selection is their physical properties (that is, density, melting point, specific heat, thermal conductivity, thermal expansion, and corrosion resistance). physical properties can have several important influences on manufacturing and the service life of components. for example, high-speed machine tools require lightweight components to reduce inertial forces and, thus, keep machines from excessive vibration.
材料选择中要思考的重要方面是它们的物理功能（即密度、熔点、比热、导热系数、热胀大和抗腐蚀性等）。物理功能对制造和组件的作业寿数有几个重要影响。例如，高速机床需要选用分量轻的部件以削减惯性力，使机床不会发生过大的振荡。
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47.?the density of a material is its mass per unit volume. another term is specific gravity, which expresses a material’s density in relation to that of water, and thus, it has no units.
材料的密度是单位体积的质量。另一个词是比重，用来标明相关于水的密度，因而，比重没有单位。

48.?the melting point of metal depends on the energy required to separate its atoms. the melting temperature of a metal alloy 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 of materials.
金属的熔点取决于别离原子所需的能量。合金的熔化温度可所以一个宽的规模（取决于它的构成），不像纯金属那样有一个固定熔点。元件或规划的作业温度规模在材料选择时大约要点思考。
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49.?the melting point of a metal has a number of indirect effects on manufacturing operations. because the recrystallization temperature of a metal is related to its melting point, operations such as annealing and heat treating and hot working require a knowledge of the melting points of the materials involved.
金属熔点对制造加工有许多直接影响。因为金属的再结晶温度与熔点有关，退火和热处置以及热加工这些操作需要有关材料熔点的常识。
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50.?a brake is similar to a clutch except that one of the shafts is replaced by a fixed member. the basic function of a brake is to absorb energy (i.e., to convert kinetic and potential energy into friction heat) and to dissipate the resulting heat without developing destructively high temperatures.
除了把一根轴换成固定构件外，制动器和聚散器很类似。制动器的功用是吸收能量（即：将动能与势能转化为冲突热）并散热使之不会抵达损坏性的高温。
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51.?clutches also absorb energy and dissipate heat, but usually at a lower rate. where brakes (or clutches) are used more or less continuously for extended periods of time, provision must be made for rapid transfer of heat to the surrounding atmosphere. for intermittent operation, the thermal capacity of the parts may permit much of the heat to be stored, and then dissipated over a longer period of time. brake and clutch parts must be designed to avoid objectionable thermal stresses and thermal distortion.
聚散器也吸收能量并散热，只是一般功率较低。在制动器（聚散器）或多或少持续运用的情况下，有必要有将热量快速传向周围大气的避免办法。对间歇操作来说，零件的热容量可以储存更多的热量，并在较长的时刻里散热。制动器和聚散器的方案有必要能避免厌烦的热应力和热变形。
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52.?the rate at which heat is generated on a unit area of friction interface is equal to the product of the normal pressure, coefficient of friction, and rubbing velocity.
在冲突面的单位面积上所发生热的速率等于正压力，冲突系数和冲突速度三者的乘积。
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53.?manufacturers of brakes and of brake lining materials have conducted tests and accumulated experience enabling them to arrive at empirical values of pv (normal pressure times rubbing velocity) and of power per unit area of friction surface, that are appropriate for specific types of brake design, brake lining material, and service conditions.
制动器及其内衬材料的制造商有进行实验和经历堆集，使他们能得到pv（标准压力乘冲突速率）和冲突表面的单位面积功率的经历值，适用于特定类型的制动器方案，制动器内衬材料以及作业条件。
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54.?chain drives combine some of the more advantageous features of belt and gear drives. chains provided almost any speed ratio for any practical shaft separation distance. their chief advantage over gears is that chains can be used with arbitrary center distances. compared with belts, chains offer the advantage of positive (no slip) drive and therefore greater power capacity.
链传动组合了带传动和齿轮传动的一些利益。链在任意实践的轴间隔上几乎可以完成任意的传动比。与齿轮比较它们最首要的利益是链能在任意的中心距情况下运用。与带传动比较，链传动的利益是强行（无滑动）传动，因而具有更大的传递动力的才能。
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55.?an additional advantage is that not only two but also many shafts can be driven by a single chain at different speeds, yet all have synchronized motions. primary applications are in conveyor systems, farm machinery, textile machinery, and motorcycles.
还有一个利益是一根单链可以驱动两根以上的轴以不一样的转速作同步运动。首要使用在运送体系，农机，纺织机械和摩托车上。
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56.?in its simplest form a chain drive consists of two sprockets of arbitrary size and a chain loop. sprockets are wheels with external teeth shaped so that they can fit into the links of the drive or driven chain. the shape of the teeth varies with the number of teeth. in some recent automotive applications, tooth shape and size is modified to reduce noise generation.
最简略的链传动由两个任意标准的链轮和一圈链构成。链轮是带有外部齿廓的轮子，它能嵌入到主动链或被逼链的链节中。齿的形状随齿数改变。在新近的一些轿车使用中，齿形和标准被批改以削减噪声的发生。
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57.?chains are available in a range of accuracies extending from precision to non-precision. non-precision chains are low in cost and intended primarily for non-critical drives of less than 40-kw power ratings. precision chains, by contrast, are designed for high speeds and power capacity.
链可在从精密到一般的精度规模中运用。一般链的本钱低，首要用于额定功率在40kw以下的非要害性传动中。与之相反，优质链被方案用于高速和传递大功率的场合。
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58.?nut: a small block of metal with a central, threaded hole that is designed to fit around and secure a bolt or screw.
螺母：中部有带螺纹的孔，用于与螺栓或螺钉相协作并将其紧固的小金属块。
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59.?rivet: a rivet is a metal pin with a head used to fasten two or more materials together.
铆钉：铆钉是一头有帽的金属钉，用来将两种或多种材料紧固在一同。
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60.?spring: an elastic device, that regains its original shape after being compressed or extended.
弹簧：一种弹性设备在被紧缩和拉伸后仍能恢恢复来的形状。

61.?fasteners are devices which permit one part to be joined to a second part and, hence, they are involved in almost all designs. the acceptability of any product depends not only on the selected components, but also on the means by which they are fastened together.紧固件是将一个零件与另一个零件进行联接的零件。因而，几乎在一切的方案中都要用到紧固件。我们关于任何产品的满足程度不只是取决于其构成部件，而且还取决于其联接方法。
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62.?the principal purposes of fasteners are to provide the following design features:
紧固件为产品方案供给了以下特性：
(1)?? disassembly for inspection and repair;
为查看和修补供给拆开的便利；
(2)?? modular design where a product consists of a number of subassemblies.
为由许多部件构成的模块化方案供给便利。
(3)?? modular design aids manufacturing as well as transportation.
选用模块化方案有助于出产制造和运送。
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63.?there are three main classifications of fasteners, which are described as follows:
紧固件可以分为以下三类：
(1)?? removable. this type permits the parts to be readily disconnected without damaging the fastener. an example is the ordinary nut-and-bolt fastener.
可拆式。选用这种紧固方法联接的零件很简略被拆开，而且不会对紧固件构成损害。例如一般的螺栓螺母联接。
(2)?? semipermanent. for this type, the parts can be disconnected, but some damage usually occurs to the fastener. one such example is a cotter pin.
半耐久式。选用此类紧固件联接的零件尽管能被拆开，但一般会对所用的紧固件构成损害，如开口销。
(3)?? permanent. when this type of fastener is used, it is intended that the parts will never be disassembled. examples are riveted and welded joints.
耐久式。选用这种紧固件就标明所联接的零件不会被分隔，如铆接和焊接。
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64.?the following factors should be taken into account when selecting fasteners for a given application:
关于一个特定的使用，在选择紧固件时应思考以下几个方面：
(1)?? primary function; 根柢功用;
(2)?? appearance; 外观；


(3)?? a large number of small size fasteners versus a small number of large size fasteners (an example is bolts);
关于选用许多的小型紧固件仍是选用少量的大型紧固件（螺栓可以作为一个比方）；
(4)?? operating conditions such as vibration, loads and temperature;
比方振荡、载荷和温度等作业条件；
(5)?? frequency of disassembly; 装拆频率；
(6)?? adjustability in the location of parts; 零件方位的可调性；
(7)?? types of materials to be joined; 被联接零件的材料品种；
(8)?? consequences of failure or loosening of the fastener.
紧固件失效或许松脱构成的成果。
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65.?the importance of fasteners can be realized when referring to any complex product. in the case of the automobile, there are literally thousands of parts which are fastened together to produce the total product. the failure or loosening of a single fastener could result in a simple nuisance such as a door rattle, or in a serious situation such as a wheel coming off. such possibilities must be taken into account in the selection of the type of fastener for the specific application.
经过任何一个凌乱的产品，都可以知道到紧固件在其间的重要性。以轿车为例，它是由数千个零件联接在一同而变成一辆整车的。一个紧固件的失效或松脱可以会带来像车门嘎嘎响这类小费事，也可以构成像车轮掉落这种严峻的成果。因而，在为一个特定的用处选择紧固件时，大约思考到上述的各种可以性。
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66.?springs are mechanical members which are designed to give a relatively large amount of elastic deflection under the action of an externally applied load. hookes law, which states that deflection is proportional to load, is the basis of behavior of springs. however, some springs are designed to produce a non-linear relationship between load and deflection.
弹簧是一种可以在外载荷作用下，发生恰当大的弹性变形的机械零件。描绘变形与载荷成正比的胡克规则表面了弹簧的根柢功能。可是，也有一些弹簧在其方案时所断定的载荷与变形之间的联络即对错线性的。
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67.?specific heat: a materials 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 resulting from machining operations is a function of the work done and of the specific heat of the workpiece material. temperature rise in a workpiece, if excessive, can decrease product quality by adversely affecting its surface roughness and dimensional accuracy, can cause excessive tool wear, and can result in undesirable metallurgical changes in the material.
比热：材料的比热是单位质量的材料温度升高一度所需的能量。合金元素对金属比热的影响相对较小。在机械加工进程中，工件温度的升高是所做的功和工件材料比热的函数。工件的温升过高会因对表面粗糙度和标准精度的晦气影响而降低产质量量，会致使刀具过度磨损，也能致使材料金相的不良改变。
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68.?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：导热系数指热量在资猜中流经的速率。金属一般导热系数高，而陶瓷和塑料的导热性较差。

69.?when heat is generated by plastic deformation or due to friction, the heat should be conducted away at a rate high enough to prevent a severe rise in temperature. the main difficulty experienced in machining titanium, 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 deformation of work pieces in metalworking processes.
当热由塑性变形或冲突发生时，热大约以满足高的速率传导开去以避免急剧升温。举例来说，在加工钛金属时遇到的首要困难就是由它非常低的导热系数发生的。低导热率可以发生高的温度梯度，因而，在金属加工进程中会致使工件的不均匀变形。
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70.?thermal expansion: the thermal expansion of materials can have several significant effects, particularly the relative expansion or contraction of different materials in assemblies such as electronic and computer components, glass-to-metal seals, and moving parts in machinery that require certain clearances for proper functioning. the use of ceramic components in cast-iron engines, for example, also requires consideration of their relative expansions.
热胀大：材料的热胀大有几个重要的影响，特别是在设备件中不一样材料的相对胀大和缩短，如电子和核算机元件，玻璃-金属密封件(gtms)和那些为了正常作业需求必定间歇的机械的运动零件。例如，在铸铁引擎中使用陶瓷元件也需求思考它们的相对胀大。
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71.?shrink fits utilize thermal expansion and contraction. for example, a part, such as a flange, is to be installed over a shaft. it first is heated and then slipped over a shaft which is at room temperature. when allowed to cool, the part shrinks and the assembly effectively becomes an integral component.
冷缩协作使用热胀大和缩短。例如，一个像法兰那样的零件，被设备到轴上。它首要被加热然后套在处于室温的轴上。当答应冷却时零件缩短，设备件有用地变成一个全体元件。
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72.?corrosion resistance: metals, ceramics, and plastics all are subject to forms of corrosion. the word corrosion itself usually refers to the deterioration of metals and ceramics, while similar phenomena in plastics generally are called degradation. corrosion leads not only to surface deterioration of components and structures but also reduces their strength and structural integrity.
抗腐蚀性：金属、陶瓷和塑料都遭到腐蚀的作用。腐蚀这个词常常指金属和陶瓷的退化，塑料的类似表象一般叫做降解。腐蚀不单会致使元件和规划的表面退化，而且降低它们的强度和规划无缺性。
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73.?corrosion resistance is an important aspect of material selection for applications in the chemical, food, and petroleum industries, as well as in manufacturing operations. in addition to various possible chemical reactions from the elements and compounds present, environmental corrosion of components and structures is a major concern, particularly at elevated temperatures.
抗腐蚀性在化学制品、食物、石油工业和制造加工使用中是选材料的重要方面。除了存在的元素和化合物的各种可以的化学反应之外，组件和规划的环境腐蚀是重视的要点，特别是在高温情况下。
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74.?resistance to corrosion depends on the composition of the material and on the particular environment. corrosive media may be chemicals (acids, alkalis, and salts), the environment (oxygen, moisture, pollution, and acid rain), and water (fresh or salt water).
抗腐蚀性取决于材料的成分和特定的环境。腐蚀前言可所以化学品（酸、碱和盐），环境（氧、湿润、污染和酸雨）和水（清水或盐水）。
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75.?nonferrous metals, stainless steels, and non-metallic materials, generally have high corrosion resistance. steels and cast irons usually have poor resistance and must be protected by various coatings and surface treatments.
有色金属、不锈钢和非金属材料一般有高抗腐蚀性。钢和铸铁一般抗腐蚀性差，有必要有各种涂层和表面处置维护。
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76.?the usefulness of some level of oxidation is exhibited in the corrosion resistance of aluminum, titanium, and stainless steel. aluminum develops a thin (a few atomic layers) strong, and adherent hard-oxide film (al2o3) that better protects the surface from further environmental corrosion.
一些氧化的用处体如今铝、钛和不锈钢的抗腐蚀性上。铝发生一层薄的 (只需几层原子)健壮的附着氧化膜（al2o3）以维护表面不进一步的腐蚀。
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77.?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.
钛发生一层氧化钛（tio2）膜。不锈钢也有类似的表象，(因为合金中有铬)表面发生一层维护膜。当维护膜擦损并显露金属里层时，一层新的氧化膜又初步构成了。
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78.?basic size: the theoretical size, from which limits or deviations are calculated.
根柢标准：理论标准，是核算极限标准和误差的开始标准。
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79.?deviation: the difference between the hole or shaft size and the basic size.
误差：孔的标准或许轴的标准减去根柢标准所得的差值。
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80.?international tolerance (it) grade: a series of tolerances that vary with basic size to provide a uniform level of accuracy within a given grade.
世界公役 (it) 等级：一系列随根柢标准改变，并在规则等级内供给相同精度的公役。
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81.?todays technology requires that parts be specified with increasingly exact dimensions. many parts made by different companies at widely separated locations must be interchangeable, which requires precise size specifications and production.
现代技能需求零件的标准越来越精确。不一样公司在不一样地址制造的许多零件有必要可交换，这需要精确的标准标准和出产。

82.?the technique of dimensioning parts within a required range of variation to ensure interchangeability is called tolerancing. each dimension is allowed a certain degree of variation within a specified zone, or tolerance. for example, a parts dimension might be expressed as 20+0.50, which allows a tolerance (variation in size) of 1.00 mm.
在需求的改变规模内断定零件标准以保证交换性的技能称为公役。每个标准答应在指定区域或公役内有必定程度的改变。例如，零件的标准可以标明为20+0.50，这答应公役（标准改变）为1.00 mm。
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83.?a tolerance should be as large as possible without interfering with the function of the part to minimize production costs. manufacturing costs increase as tolerances become smaller.
在不影响零件功能的情况下，应当给标准尽可以大的公役，以把出产本钱降至最低。制造本钱会跟着公役的降低而升高。
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84.?there are three methods of specifying tolerances on dimensions: unilateral, bilateral, and limit forms. when plus-or-minus tolerancing is used, it is applied to a theoretical dimension called the basic dimension. when dimensions can vary in only one direction from the basic dimension (either larger or smaller), tolerancing is unilateral. tolerancing that permits variation in both directions from the basic dimension (larger and smaller) is bilateral.
有三种标明标准公役的办法：单向、双向和极限方法。当运用正负公役时，将它加到称为根柢标准的理论标准上去。当标准只能从根柢标准（较大或较小）的一个方向改变时，公役是单向的。答应根柢标准（较大和较小）在两个方向上改变的公役是双向的。
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85.?tolerances may also be given in limit form, with dimensions representing the largest and smallest sizes for a feature. some tolerancing terminology and definitions are given below.
公役也可以用极限方法给出，标明零件外形的最大和最小标准。一些与公役有关的术语和界说如下所述。
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86.?tolerance: the difference between the limits prescribed for a single feature.
公役：为某一单一要素所规则的上限与下限之间的差值。
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87.?upper deviation: the difference between the maximum permissible size of a part and its basic size.
上误差: 零件最大极限标准减去其根柢标准所得的差值。
lower deviation: the difference between the minimum permissible size of a part and its basic size.
下误差：零件最小极限标准减去其根柢标准所得的差值。
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88.?actual size: the measured size of the finished part.
实践标准：加工后零件的实测标准。

89.?fit: the tightness between two assembled parts. the three types of fit are: clearance, interference and transition.
协作: 两个设备在一同的零件之间的松紧程度。可以把协作分为3类：空位协作，过盈协作，过渡协作。
clearance fit: the clearance between two assembled mating parts.
空位协作：两个设备在一同的协作件之间留有空位的协作。
interference fit: results in an interference between the two assembled parts —— the shaft is larger than the hole, requiring a force or press fit, an effect similar to welding the two parts.
过盈协作：两个设备在一同的零件之间有过盈的协作——轴大于孔，需要用力或压力进行协作，具有类似于将两个零件焊接在一同的作用。
transition fits: may result in either an interference or a clearance between the assembled parts —— the shaft may be either smaller or larger than the hole and still be within the prescribed tolerances.
过渡协作: 在两个设备在一同的零件之间或许存在着过盈，或许存在着空位的协作——轴可以小于或大于孔，但仍在规则的公役内。
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90.?selective assembly: a method of selecting and assembling parts by trial and error and by hand, allowing parts to be made with greater tolerances at less cost, as a compromise between a high manufacturing accuracy and ease of assembly.
选择设备：经过手工试配来选择并设备零件的办法。经过这种办法，可以设备在较低的本钱下制造出来的公役较大的零件，它可作为高的制造精度和易于设备的零件之间的一种折中办法。
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91.?the basic hole system utilizes the smallest hole size as the basic diameter for calculating tolerances and allowances. the basic hole system is efficient when standard drills, reamers, and machine tools are available to give precise hole sizes. the smallest hole size is the basic diameter because a hole can be enlarged by machining but not reduced in size.
基孔制: 选用最小的孔的标准作为核算公役和加工余量根柢直径。中选用标准的钻头、铰刀和机床对孔进行精加工时，基孔制体系对错常有用的。选用最小的孔的标准作为根柢标准是因为孔的标准可以经过机械加工扩展，但不能减小。
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92.?the basic shaft system is applicable when shafts are available in highly precise standard sizes. the largest diameter of the shaft is the basic diameter for applying tolerances and allowances. the largest shaft size is used as the basic diameter because shafts can be machined to smaller size but not enlarged.
当轴可以依照非常的高精度的标准标准供给时，选用基轴制是适用的。核算公役和余量时，选用轴的最大直径作为根柢标准。这是因为轴可以经过加工变成较小的标准，但其标准不能增大。

93.?international tolerance grade (it) : a series of tolerances that vary with basic size to provide a uniform level of accuracy within a given grade. there are 20 it grades: it01, it0, it1, .... , it18.
世界公役(it)等级：一系列随根柢标准改变且在规则等级内供给均匀精度的公役。共有20个it等级: it01，it0，it1，...，it18。
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94.?tolerance symbols: notes giving the specifications of tolerances and fits; the basic size is a number, followed by the fundamental deviation letter and the it number, which combined give the tolerance zone; uppercase letters indicate the fundamental deviations for holes, and lowercase letters indicate fundamental deviations for shafts.
公役符号：符号给出了公役与协作的技能需求，根柢标准是一个数字，后边跟着标明根柢误差的字母和标明it等级的数字。它们一起抉择了公役带的巨细和方位。大写字母代表孔的根柢误差，小写字母代表轴的根柢误差。
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95.?because the surface texture (or surface finish) of a part affects its function, it must be precisely specified. surface texture is the variation in a surface, including roughness, waviness, lay and flaws.
因为表面描摹（即表面亮光程度）会影响零件的功能，因而对其巨细有必要精确地加以规则，表面描摹是表面上的差异，包括粗糙度，波度，加工纹路方向和缺陷。
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96.?roughness: the finest of the irregularities in the surface caused by the manufacturing process, used to smooth the surface. roughness height is measured in micrometers (μm) or microinches (uin).
粗糙度：由用来使工件表面光滑的加工技能所构成的最纤细的表面不平度。表面粗糙度的高度选用微米或微英寸进行测量。
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97.?waviness: a widely spaced variation that exceeds the roughness width cut off, measured in inches or millimeters; roughness may be regarded as a surface variation superimposed on a wavy surface.
波度：是跨越粗糙度宽度鸿沟的大间隔误差，选用英寸或毫米测量。可将粗糙度看作叠加在波度表面上的表面不平度。
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98.?lay: the direction of the surface pattern caused by the production method used.
加工纹路方向：由所选用的加工办法所发生的表面刀痕图像的方向。
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99.?flaws: defects occurring infrequently or at widely varying intervals on a surface, including cracks, blowholes, checks, scratches, and the like; the effect of flaws is usually omitted in roughness height measurements.
缺陷: 不常常呈现或许在很大区间内才会呈现的表面瑕疵，其包括裂纹，气孔，微细裂纹，划痕等。缺陷的影响一般在粗糙度的高度测量中被忽略。
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100. a coordinate measuring machine (cmm) is typically used to generate 3-d points from the surface of a part. it’s digitizing a part in three dimensions. however, it is often used to make 2-d measurements such as measuring the center and radius of a circle in a plane, or even one-dimensional measurements such as determining the distance between two points. typically, cmms are configured to measure in cartesian coordinates. there are also cmms that measure in cylindrical or spherical coordinates. they can measure any part surface they can reach.
三坐标测量机cmm特别用于生成零件表面的三维点。它在三个维度上对零件进行数字化。可是，它常用于做二维测量如在平面内测量圆心和半径，或许甚至是像测定两点间隔离这样的一维测量。一般，三坐标测量机是专门为在直角坐标系（笛卡尔坐标系）内进行测量而方案的。也有坐标测量机以圆柱或球面坐标测量。它们能测量能抵达的任何零件表面。