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Mechanical Engineer´s Handbook P27

CHAPTER 21 LUBRICATION OF MACHINE ELEMENTS Bernard J. Hamrock Department of Mechanical Engineering Ohio State University Columbus, Ohio SYMBOLS 21.1 LUBRICATION FUNDAMENTALS 21.1.1 Conformal and Nonconformal Surfaces 21.1.2 Bearing Selection 21.1.3 Lubricants 21.1.4 Lubrication Regimes 21.1.5 Relevant Equations HYDRODYNAMIC AND HYDROSTATIC LUBRICATION 21.2.1 Liquid-Lubricated Hydrodynamic Journal Bearings 21.2.2 Liquid-Lubricated Hydrodynamic Thrust Bearings 21.2.3 Hydrostatic Bearings 21.2.4 Gas-Lubricated Hydrodynamic Bearings 508 512 512 513 516 518 520 21.3 ELASTOHYDRODYNAMIC LUBRICATION 556 21.3.1 Contact Stresses and Deformations 558 21.3.2 Dimensionless Grouping 566 21.3.3 Hard-EHL Results 568 21.3.4 Soft-EHL Results 572 21.3.5 Film Thickness for Different Regimes of Fluid-Film Lubrication 573 21.3.6 Rolling-Element Bearings 576 BOUNDARYLUBRICATION 21.4.1 Formation. | CHAPTER 21_ LUBRICATION OF MACHINE ELEMENTS Bernard J. Hamrock Department of Mechanical Engineering Ohio State University Columbus Ohio SYMBOLS 508 21.1 LUBRICATION FUNDAMENTALS 512 21.1.1 Conformal and Nonconformal Surfaces 512 21.1.2 Bearing Selection 513 21.1.3 Lubricants 516 21.1.4 Lubrication Regimes 518 21.1.5 Relevant Equations 520 21.2 HYDRODYNAMIC AND HYDROSTATIC LUBRICATION 523 21.2.1 Liquid-Lubricated Hydrodynamic Journal Bearings 524 21.2.2 Liquid-Lubricated Hydrodynamic Thrust Bearings 530 21.2.3 Hydrostatic Bearings 536 21.2.4 Gas-Lubricated Hydrodynamic Bearings 545 21.3 ELASTOHYDRODYNAMIC 21.4 LUBRICATION 556 21.3.1 Contact Stresses and Deformations 558 21.3.2 Dimensionless Grouping 566 21.3.3 Hard-EHL Results 568 21.3.4 Soft-EHL Results 572 21.3.5 Film Thickness for Different Regimes of Fluid-Film Lubrication 573 21.3.6 Rolling-Element Bearings 576 BOUNDARY LUBRICATION 616 21.4.1 Formation of Films 618 21.4.2 Physical Properties of Boundary Films 619 21.4.3 Film Thickness 621 21.4.4 Effect of Operating Variables 621 21.4.5 Extreme-Pressure EP Lubricants 623 By the middle of this century two distinct regimes of lubrication were generally recognized. The first of these was hydrodynamic lubrication. The development of the understanding of this lubrication regime began with the classical experiments of Tower 1 in which the existence of a film was detected from measurements of pressure within the lubricant and of Petrov 2 who reached the same conclusion from friction measurements. This work was closely followed by Reynolds celebrated analytical paper3 in which he used a reduced form of the Navier-Stokes equations in association with the continuity equation to generate a second-order differential equation for the pressure in the narrow converging gap of a bearing contact. Such a pressure enables a load to be transmitted between the surfaces with very low friction since the surfaces are completely separated by a film of fluid. In such a