机电技术专业英语 教学课件 作者 徐起贺 张庆良pata a lesson Eleven.pptVIP

* 机电技术专业英语 Lesson Eleven Text Virtually all machines contain shafts. The most common shape for shafts is circular and the cross section can be either solid or hollow (hollow shafts can result in weigh savings). Rectangular shafts are sometimes used, as in screw driver blades, socket wrenches and control knob stems. A shaft must have adequate torsional strength to transmit torque and not be over stressed. It must also be torsionally stiff enough so that one mounted component does not deviate excessively from its original angular position relative to a second component mounted on the same shaft. Generally speaking, the angle of twist should not exceed one degree in a shaft length equal to 20 diameters. Shafts and Couplings Lesson Eleven Shafts are mounted in bearing and transmit power through such devices as gears, pulleys, cams and clutches. These devices introduce forces which attempt to bend the shaft; hence, the shaft must be rigid enough to prevent overloading of the supporting bearings. In general, the blending deflection of a shaft should not exceed 0.01 in. per ft of length between bearing supports. In addition, the shaft must be able to sustain a combination of bending and torsional loads. Thus an equivalent load must be considered which takes into account both torsion and bending. Also, the allowable stress must contain a factor of safety which includes fatigue, since torsional and bending stress reversals occur. Lesson Eleven New Words and Expressions Lesson Eleven Lesson Eleven Lesson Eleven Lesson Eleven Lesson Eleven 参考译文 实际上，几乎所有机器中都装有轴。轴的最常见的形状是圆形，其截面可以是实心的，也可以是空心的（空心轴可以减轻重量）。有时也采用矩形轴，例如，螺丝起子的头部、套筒扳手和控制旋转的杆。 为了在传递扭矩时不发生过载，轴应该有适当的抗扭强度。轴还应该有足够的抗扭刚度，以使在同一轴上的两个传动零件之间的相对转角不会过大。一般来说，在长度等于轴的直径的20倍时，轴的扭转角不应该超过1°。 轴安装在轴承中，通过齿轮、皮带轮、凸齿和离合器等零件传递动力。通过这些零件传来的力可能会使轴产生弯曲变形。因此，轴应该有足够的刚度以防止支撑轴承受力过大。总而言之，在两个轴承支撑之间，轴在每英尺长度上的弯曲变形不应该超过0.01英寸。 此外，轴还必须能承受弯矩和扭矩的组合作用。因此，要考虑扭矩与弯矩的当量载荷。因为扭矩和弯矩会产生交变应力，所以在许用应力中也应该有一个考虑疲劳现象的安全系数。 轴和联轴器 谢谢观赏 相关词汇