機(jī)械專(zhuān)業(yè)畢業(yè)設(shè)計(jì)外文翻譯5-其他專(zhuān)業(yè)(已改無(wú)錯(cuò)字)
2023-03-03 12:29:55 本頁(yè)面
【正文】 ts to deflect under their separate systems of with one another. Flexible couplings can also serve to reduce the intensity of shock loads and vibrations transmitted from one shaft to another. Virtually all shafts contain rolling contact bearings. The concern of a machine designer with ball and roller bearings is fivefold as follows:(a) life in relation to load。 (b) stiffness ,. deflections under load。 (c) friction。 (d) wear。 (e) noise. For moderate loads and speeds the correct selection of a standard bearing on the basis of load rating will usually secure satisfactory performance. The deflection of the bearing elements will bee important where loads are high, although this is usually of less magnitude than that of the shafts or other ponents associated with the bearing. Where speeds are high special cooling arrangements bee necessary which may increase frictional drag. Wear is primarily associated with the introduction of contaminants, and sealing arrangements must be chosen with regard the hostility of the environment. Because the high quality and low price of ball and roller bearings depends on quantity production, the task of the machine designer bees one of selection rather than design. Rollingcontact bearings are generally made with steel which is throughhardened to about 900HV, although in many mechanisms special races are not provided and the interacting surfaces are hardened to about 600 HV. It is not surprising that, owing to the high stresses involved, a predominant form of failure should be metal fatigue, and a good deal of work is currently in progress intended to improve the reliability of this type of bearing. Design can be 5 based on accepted values of life and it is general practice in the bearing industry to define the load capacity of the bearing as that value below which 90 percent of a batch will exceed a lift of anew million revolutions. Notwithstanding the fact that responsibility for the basic design of ball and roller bearings rests with the bearing manufacturer, the machine designer must form a correct appreciation of the duty to be performed by the bearing and be concerned not on
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