Đang chuẩn bị liên kết để tải về tài liệu:
LUBRICATION OF MACHINE ELEMENTS P2

Test Fluid Advanced ester Formulated advanced ester Polyalkyl aromatic Polyalkyl aromatic + 10 wt % heavy resin Synthetic paraffinic oil (lot 3) Synthetic paraffinic oil (lot 4) Synthetic paraffinic oil (lot 4) + antiwear additive Synthetic paraffinic oil (lot 2) + antiwear additive C-ether Superrefined naphthenic mineral oil Synthetic hydrocarbon (traction fluid) Fluorinated polyether | 21.2 HYDRODYNAMIC AND HYDROSTATIC LUBRICATION 523 Table 21.4 Pressure-Viscosity Coefficients for Test Fluids at Three Temperatures From Ref. 17 Temperature C 38 99 149 Test Fluid Pressure-viscosity Coefficient m2 N Advanced ester 1.28 x 10 8 0.987 X 10 s 0.851 x IO 8 Formulated advanced ester 1.37 1.00 .874 Polyalkyl aromatic 1.58 1.25 1.01 Polyalkyl aromatic 10 wt heavy resin 1.70 1.28 1.06 Synthetic paraffinic oil lot 3 1.77 1.51 1.09 Synthetic paraffinic oil lot 4 1.99 1.51 1.29 Synthetic paraffinic oil lot 4 antiwear additive 1.96 1.55 1.25 Synthetic paraffinic oil lot 2 antiwear additive 1.81 1.37 1.13 C-ether 1.80 .980 .795 Superrefined naphthenic mineral oil 2.51 1.54 1.27 Synthetic hydrocarbon traction fluid 3.12 1.71 .939 Fluorinated polyether 4.17 3.24 3.02 2 f f p x y dx.dy 8 x y --------77 -----------737773 ttE J J x - X 2 y - yj 2 1 2 A 21.11 where 21.12 and v Poisson s ratio E modulus of elasticity N m2 Therefore Eq. 21.6 is normally involved in hydrodynamic lubrication situations while Eqs. 21.7 - 21.11 are normally involved in elastohydrodynamic lubrication situations. 21.2 HYDRODYNAMIC AND HYDROSTATIC LUBRICATION Surfaces lubricated hydrodynamically are normally conformal as pointed out in Section 21.1.1. The conformal nature of the surfaces can take its form either as a thrust bearing or as a journal bearing both of which will be considered in this section. Three features must exist for hydrodynamic lubrication to occur 1. A viscous fluid must separate the lubricated surfaces. 2. There must be relative motion between the surfaces. 3. The geometry of the film shape must be larger in the inlet than at the outlet so that a convergent wedge of lubricant is formed. If feature 2 is absent lubrication can still be achieved by establishing relative motion between the fluid and the surfaces through external pressurization. This is discussed further in Section 21.2.3. In hydrodynamic lubrication the entire friction arises from the shearing of the lubricant