tailieunhanh - LUBRICATION OF MACHINE ELEMENTS P1

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. | CHAPTER 21_ LUBRICATION OF MACHINE ELEMENTS Bernard J. Hamrock Department of Mechanical Engineering Ohio State University Columbus Ohio SYMBOLS 508 LUBRICATION FUNDAMENTALS 512 Conformal and Nonconformal Surfaces 512 Bearing Selection 513 Lubricants 516 Lubrication Regimes 518 Relevant Equations 520 HYDRODYNAMIC AND HYDROSTATIC LUBRICATION 523 Liquid-Lubricated Hydrodynamic Journal Bearings 524 Liquid-Lubricated Hydrodynamic Thrust Bearings 530 Hydrostatic Bearings 536 Gas-Lubricated Hydrodynamic Bearings 545 ELASTOHYDRODYNAMIC LUBRICATION 556 Contact Stresses and Deformations 558 Dimensionless Grouping 566 Hard-EHL Results 568 Soft-EHL Results 572 Film Thickness for Different Regimes of Fluid-Film Lubrication 573 Rolling-Element Bearings 576 BOUNDARY LUBRICATION 616 Formation of Films 618 Physical Properties of Boundary Films 619 Film Thickness 621 Effect of Operating Variables 621 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