机械外文翻译中英文

机械外文翻译中英文

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英文原文

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,ie.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 a load rating will become important where loads are high,although this is usually of less magnitude than that of the shafts or other components associated with the bearing. Where speeds are high special cooling arrangements become necessary which may increase fricitional drag. Wear is primarily associated with the introduction of contaminants,and sealing arrangements must be chosen with regard to the hostility of the environment.

Because the high quality and low price of ball and roller bearing depends on quantity production,the task of the machine designer becomes one of selection rather than design. Rolling-contact bearings are generally made with steel which is through-hardened to about

900HV,although in many mechanisms special races are not provided and the interacting surfaces are hardened to about 600HV. 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 based on accept values of life and it is general practice in bearing industry to define the load capacity of the bearing as that value below which 90 percent of a batch will exceed life of one million revolutions.

Notwithstanding the fact that responsibility for 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 only with bearing

selection but with the conditions for correct installation.

The fit of the bearing races onto the shaft or onto the housings is of critical importance because of their combined effect on the internal clearance of the bearing as well as preserving the desired degree of interference fit. Inadequate interference can induce serious trouble from fretting corrosion. The inner race is frequently located axially by against a shoulder. A radius at this point is essential for the avoidance of stress concentration and ball races are provided with a radius or chamfer to follow space for this.

Where life is not the determining factor in design, it is usual to determine maximum loading by the amount to which a bearing will deflect under load. Thus the concept of "static load-carrying capacity" is understood to mean the load that can be applied to a bearing, which is either stationary or subject to slight swiveling motions, without impairing its running qualities for subsequent rotational motion. This has been determined by practical experience as the load which when