轴类加工工艺外文翻译@中英文翻译@外文文献翻译

Shaft Solid shafts. As a machine component a shaft is commonly a cylindrical bar that supports and rotates with devices for receiving and delivering rotary motion and torque .The crankshaft of a reciprocating engine receive its rotary motion from each of the cranks, via the pistons and connecting roads (the slider-crank mechanisms), and delivers it by means of couplings, gears, chains or belts to the transmission, camshaft, pumps, and other devices. The camshafts, driven by a gear or chain from the crankshaft, has only one receiver or input, but each cam on the shaft delivers rotary motion to the valve-actuating mechanisms. An axle is usually defined as a stationary cylindrical member on which wheels and pulleys can rotate, but the rotating shafts that drive the rear wheels of an automobile are also called axles, no doubt a carryover from horse-and-buggy days. It is common practice to speak short shafts on machines as spindles, especially tool-carrying or work-carrying shafts on machine tools. In the days when all machines in a shop were driven by one large electric motor or prime mover, it was necessary to have long line shafts running length of the shop and supplying power, by belt, to shorter couter shafts, jack shafts, or head shafts. These line shafts were assembled form separate lengths of shafting clampled together by rigid couplings. Although it is usually more convenient to drive each machine with a separate electric motor, and the present-day trend is in this direction, there are still some oil engine receives its rotary motion from each of the cranks, via the pistons and connecting roads (the slider-crank mechanisms) , and delivers it by means of couplings, gears, chains or belts to the transmission, camshaft, pumps, and other devices. The camshafts, driven by a gear or chain from the crankshaft, has only one receiver or input, but each cam on the shaft delivers rotary motion to the valve-actuating mechanisms. An axle is usually defined as a stationary cylindrical member on which wheels and pulleys can rotate, but the rotating shafts that drive the rear wheels of an automobile are also called axles, no doubt a carryover from horse-and-buggy days. It is common practice to speak short shafts on machines as spindles, especially tool-carrying or work-carrying shafts on machine tools. In the days when all machines in a shop were driven by one large electric motor or prime mover, it was necessary to have long line shafts running length of the shop and supplying power, by belt, to shorter coutershafts, jackshafts, or headshafts. These line shafts were assembled form separate lengths of shafting clampled together by rigid couplings. Although it is usually more convenient to drive each machine with a separate electric motor, and the present-day trend is in this direction, there are still some situation in which a group drive is more economical. A single-throw crankshaft that could be used in a single-cylinder reciprocating engine or pump is shown in Figure 21. The journals A and B rotate in the main bearings, C is the crankpin that fits in a bearing on the end of the connecting rod and moves on a circle of radius R about the main bearings, while D and E are the cheeks or webs. The throw R is one half the stroks of the piston, which is connected, by the wrist pin, to the other end of the connecting rod and guided so as to move on a straight path passing throw the axis XX. On a multiple-cylinder engine the crankshaft has multiple throws-eight for a straight eight and for a V-8-arranged in a suitable angular relationship. Stress and strains. In operation, shafts are subjected to a shearing stress, whose magnitude depends on the torque and the dimensions of the cross section. This stress is a measure of resistance that the shaft material offers to the applied torque. All shafts that transmit a torque are subjected to torsional shearing stresses. In addition to the shearing stresses, twisted shafts are also subjected to shearing distortions. The distorted state is usually defined by the angle of twist per unit length； i.e., the retation of one cross section of a shaft relative to another cross section at a unit distance from it. Shafts that carry gears and pulleys are bent as well as twisted, and the magniude of the bending stresses, which are tensile on the convex side of the bend and compressive on the concave side, will depend on the load, the distance between the bearings of the shaft cross section. The combination of bending and twisting produces a state of stress in the shaft that is more complex than the state of pure shears produced by torsion alone or the state of tension-compression produced by bending alone. To the designer of shaft it is important to know if the shaft is likely to fail because of an excessive normal stress. If a piece of chalk is twisted, it will invariably rupture on a plane at about 45 degrees to the axis. This is because the maximum tensile stresses act on this plane, and chalk is weak in tension. Steel shafting is usually designed so that the maximum shearing stress produced by bending and torsion is less than a specified maximum. Shafts with circular cross sections are easier to produce in the steel mill, easier to machine, and easier to support in bearings than shafts with other cross section； there is seldom any need for using noncircular shapes. In addition, the strength and stiffness, both in bending and torsion, are more easily calculated for circular shafts. Lastly, for a given amount of materials the circular shafts has the smallest maximum shearing stress for a given torque, and the highest torsional rigidity. The shearing in a circular shaft is highest at the surface and drops off to zero at the axis. This means that most of the torque is carried by the material on and near the surface. Critical speeds. In the same way that a violin string vibrates when stroked with a bow, a cylindrical shaft suspended between two bearings has a natural frequency of lateral vibration. If the speed of revolution of the shaft coincides with the natural frequency, the shaft experience a whirling critical speed and become noisy. These speeds are more likely to occur with long, flexible shafts than with short, stiff ones. The natural frequency of a shaft can be raised by increasing its stiffness. If a slender rod is fixed to the ceiling ta one end and supports a heavy disk at the other end, the disk will oscillate back and forth around the rod axis like a torsion pendulum if given an initial twist and let go. The frequency of the oscillations will depend on the torsional stiffness of the rod and the weight of the disk； the stiffer the rod and the lighter the disk the higher the frequency. Similar torsional oscillations can occur in the crankshafts of reciprocating engines, particularly those with many crank throws and a heavy flywheel. Each crank throw and part of the associated connecting rod acts like a small flywheel, and for the crankshaft as a whole, there are a number of ways or modes in which there small flywheels can oscillate back and forth around the shaft axis in opposition to one another and to the main flywheel. For each of these modes there corresponds a natural frequency of oscillation. When the engine is operating the torques delivered to the crankshaft by the connecting rods fluctuate, and if the crankshaft speed is such that these fluctuating impulses are delivered at a speed corresponding to one of the natural torsional frequencies of the shaft, torsional oscillations will be superimposed on the rotary motion of the shafts. Such speed are known as torsional critical speeds, and they can cause shaft failures. A number of devices to control the oscillations of crankshafts have been invented. Flexible shafts. A flexible shaft consists of a number of superimposed tightly wound right-and left-hand layers of helically wound wires wrapped about a single center wire or mandrel. The shaft is connected to source of power and the driven member by special fittings attached to the end of the shaft. Flexible easings of metallic or nonmetallic materials, which guide and protect the shaft and retain the lubricant, are also available. Compared with solid shafts, flexible shafts can be bent to much smaller radii without being overstressed. For transmitting power around corners and for considerable distances flexible shafts are usually cheaper and more convenient than belts, chains, or gears. Most speedometers on automobiles are driven by flexible shafts running from the transmission to the dashboard. When a valve, a switch, or other control devices is in a hard-to-reach location, it can be operated by a flexible shaft from a more convenient position. For portable tools such as sanders, grinders, and drilling machines, flexible shafts are practically indispensable. KEY, SPLINES AND PINS Keys, splines, and pins. When power is being transmitted from a machine member such as a coupling, a gear, a flywheel, or a pulley to the shaft on which it is mounted, means must be provided for preventing relative motion between the shaft and the member. On helical and bevel gears, relative movement along the shaft caused by the thrust(axial) loads is prevented by a step in the shaft or by having the gear contact the bearing directly or through a tubular spacer. When axial loads are incidental and of small magnitude, the members are kept from sliding along the shaft by means of a set screw. The primary purpose of keys, splines, and pins is to prevent relative rotary movement. A commonly used type of key has a square cross section and is sunk half in the shaft and half in the hub of the other member. If the key is made of steel(which is commonly the case)of the same strength as the shaft and has a width and depth equal to one fourth of the shaft diameter(this proportion is closely approximated in practice) then it will have the same torque capacity as the solid shaft if its length is 1.57 times that of the shaft diameter. Another common type of key has a rectangular cross section with a depth to width ratio of 0.75. Both of these keys may either be straight or tapered in depth. The straight keys fit snugly on the sides of the key ways only, the tapered keys on all sides. Gib-head keys are tapered keys with a projection on one end to facilitate removal. Woodruff keys are widely used on machine tools and motor vehicles. The key is a segment of a disk and fits in a keyway in the shaft that is with a special milling cutter. Though the extra depth of these keys weakens the shaft considerably, it prevents any tendency of the key to rotate or move axially. Woodruff keys are particularly suitable for tapering shaft ends. Because they weaken the shafts less, keys with straight or tapered circular cross sections are sometimes used in place of square and rectangular keys, but the keyways, half in the shaft and half in the shaft and half in the hub, must be cut with a drill after assembly,and interchangeability of parts is practically impossible. When a large gear blank is made by shrinking a high-strength rim on a cheaper cast center, circular keys, snugly fitted, are frequently used to ensure a permanent connection. Splines are permanent keys integral with the shaft, fitting in keyways cut in the hub. The dimensions of splined fittings are standardized for both permanent (press) fits and sliding fits. The teeth have either straight or involute profiles；the latter are stronger, more easily measured, and have a self-centring action when twisted. Tapered circular pins can be used to restrain shaft-mounted members from both axial and rotary movement. The pin fits snugly in a reamed tapered hole that is perpendicular to the shaft surface. A number of straight pins that grip by deforming elastically or plastically when driven into straight holes are commercially available. All the keys and pins that have been described are standard driving devices. In some cases they inadequate, and unorthodox means must be employed. For driving small gear in which there is no room between the bore and the roots of the teeth for a longitudinal keyway, a transverse radial slot on the end of the gear can be made to fit a radial protuberance on the shaft. For transmitting moderate loads, a cheaper and effective connection can be made by forming a series of longitudinal serrations on the shaft with a knurling tool and pressing the shaft into the hole in the driven member, it will cut grooves in the hole and provide, in effect, a press-fitted splined connection. Press and shrink fits are also used, and they can provide surprisingly firm connections, but the dimensions of the connected member must be closely controlled. 轴 实心轴 轴作为机械零件通常是一根圆柱形杆，用来支 撑部件并随部件一起转动以接受和传递转动和扭矩。往复式发动机的曲轴接受每一根曲轴通过活塞和连杆（滑块 -曲柄机构）传来的转动，并通过联轴器、齿轮、链条或皮带把转动传递到变速箱、凸轮轴、泵和其它装置。由曲轴通过齿轮或链条驱动的凸轮轴只有一根受力轴即输入轴，但轴上的每一个凸轮都能把转动传递给气门的传动机构沟。 轮轴通常的定义是车轮和皮带轮能在其上旋转的一根固定的圆柱形构件，但驱动汽车后轮的旋转轴也叫轮轴，这可能是从过去马车时代传下来的。通常习惯上把机器上的短轴叫做主轴（或心轴），特别是指机床上安装刀具和工件的轴。 在以前一个车间里所有的机器都由一个大电动机或原动机的，这样就必须有一根同车间一样长的主传动轴（即天轴）通过皮带把动力供给较短的副轴、中间轴或顶轴。这种主传动轴是用一节节的轴装配起来的，用刚性联轴器固定在一起。尽管一般说来用单独的电动机来驱动每一台机器更为方便，并且现代的趋势也是按照这个方向发展的，但现在仍有某些场合采用分组传动更为经济。 应力和变力 轴在转动时承受剪应力，其大小取决于扭矩和断面的尺寸。这个剪应力是轴的材料对作用扭矩所产生的抗力的一种量度。所有传递扭矩的轴都承受扭转剪应力。 除剪应力之外，传 递扭矩的轴还会产生剪切变形。扭转的状态通常用每单位长度的扭转角来表示，即用轴的某一截面所转过的角度来表示。 安装齿轮和皮带轮的轴不但会产生扭矩，而且还会产生弯矩，弯曲应力（在凸面是拉应力，在凹面是压应力）的大小取决于两轴承间的距离及轴的截面尺寸， 弯曲和扭转综合起来使轴内所产生的受力状态比单纯扭转所产生的纯剪切状态或单纯弯曲所产生的拉伸压缩状态更为复杂。 对轴的设计工作者来说，重要的是要知道轴是否可能产生过大的发向应力或过大的剪应力以致损坏。如果扭转一支粉笔，它必定在同轴线成 45角的平面上而不是在与轴线 垂直的平面上断裂。这是因为最大的应力就作用在这个平面上，而粉笔的抗拉强度是很差的。通常在设计钢轴时要使弯曲和扭转产生的最大剪应力小于规定的最大设计应力。 圆形截面的轴与其它截面的轴相比，在扎钢上更易于扎制，且更易于加工，同时也易于支撑在轴承上。因此，在实际应用中很少使用非远行截面的轴。此外，圆轴的强度和刚度，无论是在弯曲或是扭转时，都较易与计算。最后，对一定量的材料来说，圆轴对一定的扭矩所产生的最大剪应力最小，而抗扭刚度则最大。 圆轴内的剪应力在表面最大，而在轴线部分则降到零。这就是说大部分扭矩是由表面和靠 近表面的材料来承受的。 临界转速 用弓拉小提琴时琴弦会发生振动，同样，支撑在两轴承之间的圆轴也有一个自然的横向振动频率。如果轴的转速与自然频率重合，轴就处于临界转速并发出噪音。多半长的挠性轴比短的刚性轴更容易出现临界转速。轴的自然频率可随其刚度的增加而提高。 如果把一根细长杆的一端固定在天花板上，另一端支撑一个很重的圆盘，如果给圆盘一个起始的扭矩就把手松开，圆盘就会像扭摆一样绕杆轴来回振动。振动的频率取决于杆的抗扭刚度和圆盘的重量；杆的刚度越大且圆盘越轻则频率越高。往复式发动机的曲轴也会产生类似的扭转振动 。特别是多拐曲轴和带有很重飞轮的曲轴更是如此。每一个曲拐和与之相联的连杆部分的作用就像一个小飞轮，并且对作为一个整体的曲轴来说，这些小飞轮能按很多种方式彼此安相反的方向与主飞轮反反方向地绕轴线来回振动。 当发动机