Rolling Bearings

Rolling BearingsRolling 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 contact bearings or tapered roller bearings for carrying combined radial and axial loads. Figure 8.1a shows a common single-row, deep groove ball bearing. The bearing consists of an inner ring, an outer ring, the balls and the separator. To increase the contact area and. hence permit larger loads to be carried, the balls run in curvilinear grooves in the rings called raceway. The radius of the raceway is very little larger than the radius of the ball. This type of bearing can standa 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 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 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 frictional 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 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 currently 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 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 only with bearing selection but with the conditions for correct installation.The fit of the bearing rings onto the shafts 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 ring is frequently located axially by abutting against a shoulder. A fillet radius at this 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 "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 applied to 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 permanent deformation of 0.0025 mm for a ball 25 mm in diameter.The successful functioning of many bearings depends upon providing them with adequate protection against their environment, and in some circumstances the environment must be protected from lubricants or products of deterioration of the bearing surfaces. Achievement of the correct functioning 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 systems and can only be designed satisfactorily on the basis of the appropriate bearing theory. Notwithstanding their importance, the amount of research effort that has been devoted to the understanding of the behavior of seals has been small when compared with that devoted to other aspects of bearing technology.Words and Expressionsradial bearing向心轴承(主要用于承受径向载荷的滚动轴承)thrust bearing推力轴承(主要用于承受轴向载荷的滚动轴承)angular contact bearing角接触轴承tapered roller bearing圆锥滚子轴承deep groove ball bearing深沟球轴承thrust ball bearing推力球轴承(滚动体是球的推力滚动轴承)tapered roller thrust bearing推力圆锥滚子轴承(滚动体是圆锥滚子的推力滚动轴承)needle roller bearing滚针轴承(滚动体是滚针的向心滚动轴承)fivefold a.;ad.五倍(的)，五重的stiffness ['stifnis} n.刚性，刚度，稳定性deflection n.偏差，偏移，弯曲，挠度frictional a.摩擦的，由摩擦产生的drag v.拖，牵引，摩擦，拖着，阻碍;n，阻力，摩擦力，阻尼wear v. n.磨损，磨蚀，消耗，耗损contaminant n.沾染，杂质，污染物质，污染剂sealing n.密封，封接hostility n. 敌视，敌意，敌对through-harden v.整体淬火HV= Vickers hardness维氏硬度notwithstanding prep.; ad.; conj. 虽然，尽管……(还是)clearance n.间隙，裕度，空隙，余地，间距interference n.干涉，干扰，妨碍，过盈，相互影响fret v.侵蚀，腐蚀，磨损，损坏fretting n.松散，微振磨损abut v.邻接，毗连，倚着，支撑;n.端，尽头，支架chamfer n.;二在……开槽，倒棱，倒角，圆角swivel n.旋转轴承，转体;v.旋转，用活节连接raceway n.轴承座圈，滚道lubricant n.润滑剂，润滑材料;a.润滑的deterioration n.变质，退化，恶化，变坏tribology n.摩擦学Notes1. through-hardened意为“整体淬火的，，。