专业英语第8课全文及翻译 滚动轴承

Lesson 8

Rolling Bearings

Rolling bearings can carry radial, thrust or combination of the two loads. Accordingly, most

rolling bearings are categorized in one of the three groups: radial bearings for carrying loads that

are primarily radial, thrust bearings for supporting loads that are primarily axial, and angular conta

ct bearings or tapered roller bearings for carrying combined radial and axial loads. Figure 8.1a sh

ows a common single-row, deep groove ball bearing. The bearing consists of an inner ring, an out

er ring, the balls and the separator. To increase the contact area and. hence permit larger loads to b

e carried, the balls run in curvilinear grooves in the rings called raceway. The radius of the racewa

y is very little larger than the radius of the ball. This type of bearing can stand a radial load as well

as some thrust load. Some other types of rolling bearings are shown in Figs. 8. 1b, 8. lc and 8. 1d.

Figure 8.1

Some type: of rolling bearings: (a) deep groove ball bearing; (b) thrust ball bearing;

(c) tapered roller thrust bearing;(d) needle roller bearing.

The concern of a machine designer with ball and roller bearings is fivefold as follows: (a) life

in relation to load; (b) stiffness, i. e. deflections under load; (c) friction; (d) wear; (e) noise. For m

oderate 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 become impo

rtant where loads are high, although this is usually of less magnitude than that of the shafts or othe

r components associated with the bearing. Where speeds are high special cooling arrangements be

come necessary which may increase frictional drag. Wear is primarily associated with the introdu

ction 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 bearings depends on quantity production,

the task of the machine designer becomes one of selection rather than design. Rolling bearings are

generally made with steel which is through-hardened to about 900 HV

. Owing to the high stresses

involved, a predominant form of failure should be metal fatigue, and a good deal of work is curren

tly in progress intended to improve the reliability of this type of bearing. Design can be 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 per cent of a batch will exceed a life of one million re

volutions.

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 t

o be performed by the bearing and be concerned not only with bearing selection but with the condi

tions for correct installation.

The fit of the bearing rings onto the shafts or onto the housings is of critical importance beca

use of their combined effect on the internal clearance of the bearing as well as preserving the desir

ed degree of interference fit. Inadequate interference can induce serious trouble from fretting corr

osion. The inner ring is frequently located axially by abutting against a shoulder. A fillet radius at t

his point is essential for the avoidance of stress concentration and the inner ring is provided with a

corner radius or chamfer to allow 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

g capacity

ry or subject to slight swiveling motions, without impairing its running qualities for subsequent rot

ational motion. This has been determined by practical experience as the load which when applied t

o a bearing results in a total deformation of the rolling element and raceway at any point of contact

not exceeding 0.01 per cent of the rolling-element diameter. This would correspond to a permanen

t deformation of 0.0025 mm for a ball 25 mm in diameter.

The successful functioning of many bearings depends upon providing them with adequate prote

ction against their environment, and in some circumstances the environment must be protected fro

m lubricants or products of deterioration of the bearing surfaces. Achievement of the correct functi

oning of seals is an essential part of bearing design. Moreover, seals which are applied to moving

parts for any purpose are of interest to tribologists because they are components of bearing system

s and can only be designed satisfactorily on the basis of the appropriate bearing theory. Notwithsta

nding their importance, the amount of research effort that has been devoted to the understanding o

f the behavior of seals has been small when compared with that devoted to other aspects of bearin

g technology.

Words and Expressions

radial bearing

向 心轴承

(

主要用于承受径向载荷的滚动轴承

)

thrust bearing

< br>推力轴承

(

主要用于承受轴向载荷的滚动轴承