tailieunhanh - Handbook of Lubrication part 3

Tham khảo tài liệu 'handbook of lubrication part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 72 CRC Handbook of Lubrication c UNWRAPPED FIGURE 3. Journal bearing oil-film relations. Short Journal Bearing The three factors essential for a hydrodynamic slider bearing velocity viscosity and a converging film are all contained in the right side term of the Reynolds equation 6 pU dh dx . The required convergent film is also formed when a shaft and bushing become eccentric as shown in Figure 3b. The unwrapped film shape is shown in Figure 3c. A positive superambient pressure is generated in the convergent left portion of the film. Since liquids cannot withstand substantial subambient pressure the fluid film ruptures in the divergent right section forming discontinuous streamers which flow through this region at approximately ambient pressure. These streamers contribute nothing to load carrying capacity. When the bearing is narrow . its length is less than its diameter Reynolds equation can be simplified to h3 -g- 6 ƯM dy dx 8 Neglecting the pressure gradient term for the x direction attributes circumferential flow primarily to the motion of the journal surface expressed by the right side of the equation. Axial flow and leakage are due entirely to the pressure gradient term on the left side of the equation. This short bearing version of Reynolds equation can be integrated twice in the y direction because h is not a function of y to give the pressure function 9 Copyright 1983 CRC Press LLC Volume II 73 Table 3 SHORT JOURNAL BEARING Quantity Formula Load capacity Attitude angle 7T 1 -e2 1 2 tan ự L 4 e Friction force _ ceW sin ự 27rgưrL f 2r C 1 - e2 1 2 Oil flow from ends of bearing Q UcLe where y is measured from the bearing center plane. This distribution satisfies the pressure boundary conditions of P 0 at both y L 2 and y -L 2. Axial pressure distribution is shown by this equation to approach a simple parabolic shape. Because the fluid film thickness is much smaller than the journal radius h c 1 - e cos0 . When substituted into the pressure equation 3 .

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