Ch11 - bud21932_ch11_549-596 05:50 AM Page 549 CONFIRMING...

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11 Rolling-Contact Bearings Chapter Outline 11–1 Bearing Types 550 11–2 Bearing Life 553 11–3 Bearing Load Life at Rated Reliability 554 11–4 Bearing Survival: Reliability versus Life 555 11–5 Relating Load, Life, and Reliability 557 11–6 Combined Radial and Thrust Loading 559 11–7 Variable Loading 564 11–8 Selection of Ball and Cylindrical Roller Bearings 568 11–9 Selection of Tapered Roller Bearings 571 11–10 Design Assessment for Selected Rolling-Contact Bearings 582 11–11 Lubrication 586 11–12 Mounting and Enclosure 587 549
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550 Mechanical Engineering Design The terms rolling-contact bearing, antifriction bearing, and rolling bearing are all used to describe that class of bearing in which the main load is transferred through elements in rolling contact rather than in sliding contact. In a rolling bearing the starting friction is about twice the running friction, but still it is negligible in comparison with the starting friction of a sleeve bearing. Load, speed, and the operating viscosity of the lubricant do affect the frictional characteristics of a rolling bearing. It is probably a mistake to describe a rolling bearing as “antifriction,” but the term is used generally throughout the industry. From the mechanical designer’s standpoint, the study of antifriction bearings differs in several respects when compared with the study of other topics because the bearings they specify have already been designed. The specialist in antifriction-bearing design is confronted with the problem of designing a group of elements that compose a rolling bearing: these elements must be designed to fit into a space whose dimen- sions are specified; they must be designed to receive a load having certain character- istics; and finally, these elements must be designed to have a satisfactory life when operated under the specified conditions. Bearing specialists must therefore consider such matters as fatigue loading, friction, heat, corrosion resistance, kinematic prob- lems, material properties, lubrication, machining tolerances, assembly, use, and cost. From a consideration of all these factors, bearing specialists arrive at a compromise that, in their judgment, is a good solution to the problem as stated. We begin with an overview of bearing types; then we note that bearing life cannot be described in deterministic form. We introduce the invariant, the statistical distribution of life, which is strongly Weibullian. 1 There are some useful deterministic equations addressing load versus life at constant reliability, and we introduce the catalog rating at rating life. The reliability-life relationship involves Weibullian statistics. The load-life-reliability relationship, combines statistical and deterministic relationships giving the designer a way to move from the desired load and life to the catalog rating in one equation.
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Ch11 - bud21932_ch11_549-596 05:50 AM Page 549 CONFIRMING...

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