Lesson 6 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, i.e.deflections under load; (e) 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. concern vt. 涉及, 关系到 n.( 利害 ) 关系, 关心, 关注, 所关心的是 Fivefold adj.adv. 五倍的（地）， 有五部分的 Threefold 三倍 stiffness n. 坚硬, 硬度

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. drag v. 拖, 拖曳, 缓慢而 费力地行动 n. 拖拉 thrust contaminant n. 致污物, 污染物 atmospheric ~ air ~ food ~ Arrangement n. 布置, 排列 [ 复 ] 安排, 准备, 装置 调节, 安装, 装配 电路 hostility n. 敌意, 恶意, 不友 善, 敌对, 对抗, 反对

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. Roiling- contact bearings are generally made with steel which is through-hardened to about 900 HV, although in many mechanisms special races are not provided and the interacting surfaces are hardened to about 600 HV. through- hardened 整体硬化淬火HV Vickers hardness

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 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 hatch will exceed a life of one million revolutions. predominant adj. 卓越的, 支配的, 主要的, 突出的, 有影响的 hatch n. 批, 孵化 hatch out 孵化出来 ; 想出 计划, 结果变成 hatch up 发明, 设计, 计划

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. notwithstanding prep. 虽然, 尽管 adv. 尽管, 还是 conj. 虽然, 尽管 rest vi. 休息, 静 止, 依靠, 搁在, 保持 ( 状态 ) 取决于 Appreciation n. 感谢, 感激, 正确 评价, 欣赏

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. Fit Fit 配合 housing 轴承座 Clearance n. 间空， 间隔；清理，清除； interference fit 干涉 配合 inadequate adj. 不充 分的, 不适当的 Induce vt. 劝诱, 促使, 导致, 引起, 感应 fretting corrosi 接触腐蚀； 摩擦腐蚀

Fretting Wear Fretting is a type of wear that has the appearance of corrosion. It is the result of relative motion between tightly fitted parts, such as bearing and axle components. These relative motions can lead to surface discoloration, pitting, and eventually, surface failure. (See Figure 3.) For a railroad application, this can mean costly axle damage; within the bearing assembly itself, it can lead directly to loss of the bearing's clamping force.

The inner race is frequently located axially by abutting 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 allow space for this. abutting adj. 邻接的 chamfer n. 斜面 倒角 v. 斜切

Shaft and housing shoulder dimensions

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. swiveling 转动的 impair v. 削弱 Subsequent adj. 后来的, 并发的

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 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 beating surfaces. adequate adj. 适当的, 足够的 Lubricant n. 滑润剂 deterioration n. 变坏, 退化, 堕落 Deteriorate v. ( 使 ) 恶化

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 bearing systems and can only be designed satisfactorily on the basis of the appropriate bearing theory. seal n. 封铅, 封条, 印, 图章, 密封 vt. 封, 密封 n. 海豹, 海豹毛 皮 Tribology n. 摩擦学 tribologist

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. Devote vt. 投入于, 献身

Rolling Elements of Bearings

Names of bearing parts

Radial and Thrust Ball Deep groove Filling notch Angular contact Shielded Sealed External Double row Self-aligning Thrust Self-aligning thrus self-aligning

Plain roller Helical roller Self-aligning Spherical roller spherical roller thrust Needle Tapered roller Tapered roller Steep angle thrust tapered roller

THEORETICAL AND EXPERIMENTAL LOAD- DEFLECTION STUDIES OF A MULTILEAF JOURNAL BEARIN Trippett, R. J.Trippett, R. J.; Oh, K. P.; Rohde, S. M. Oh, K. P. Rohde, S. M. Abstract: In this study the deflections of a multileaf bearing are measured under load on a rotor dynamics rig up to speeds of 40,000 rpm. The effects of rotor speed, leaf-housing attachment angle, and leaf thickness on the load-deflection characteristics of a multileaf bearing are measured.

An analytical model, representative of the type of bearing tested, is developed and comparisons of predicted and measured performance are presented. Results predicted by the model agree with the experimental finding that at zero speed this bearing has little recovery from load applications. The model predicts accurately the running bearing stiffness during loading for the thickest leaves tested. However, it does not predict the return of the journal to its measured unloaded running position.

The major contributor to fretting is bearing operations with high axle deflections (high loads) present. When an axle deflects or bends under a load, the journal's outside surface gets a little longer on the top and a little shorter on the bottom. Depending on many variables, the bearing parts may or may not maintain their original position on the journal. When they do not, sliding occurs between the parts and the journal surface. This sliding occurs on a very small, even microscopic scale and is therefore very difficult to observe directly.