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40.为什么拖拉机要进行试运转?拖拉机有许多重要的相对运动零件,如气缸套与活塞环、曲轴颈与轴瓦以及各种传动齿轮等,它们都在较大的压力作用下高速摩擦。在制造或修理过程中,这些零件虽都经过精细的加工,有较高的加工精度和光洁度,看上去也很光滑,但实际上零件表面仍留下了凹凸不平的加工痕迹。因此零件装配后(有装配误差)突际接触面积比设计计算的要小得多,单位面积上受力比设计计算的要大得多。此时如果让拖拉机全负荷工作,这些局部接触点会受到巨大的集中载
40. Why the tractor to be commissioned Tractor has many important moving parts, such as cylinder liner and piston rings, crankshaft and bearing bush and a variety of transmission gears, which are under high pressure friction under high speed. In the manufacturing or repair process, although these parts are finely processed, with high machining accuracy and finish, looks very smooth, but in fact the surface of the parts still leave rough machining traces. Therefore, after the assembly of parts (with assembly error) sudden contact area is much smaller than the design calculation, the force per unit area is much larger than the design calculations. At this point if the tractor to work at full capacity, these local contacts will be a huge concentration