TAILIEUCHUNG - Handbook of Lubrication part 5

Tham khảo tài liệu 'handbook of lubrication part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 154 CRC Handbook of Lubrication FIGURE 14. Typical contact area patterns for longitudinally oriented isotropic and transversely oriented rough surfaces. Micro-Elastohydrodynamic Lubrication Micro-EHL69 deals with local pressure and film fluctuations around asperities or furrows within a macro-EHL conjunction. For pure rolling local pressure and film thickness distributions at asperities are governed mainly by the normal approach action. As an ellipsoidal asperity approaches the opposing surface the lubricant at the asperity center becomes highly pressurized and entrapped to form a central pocket as it travels through the Hertzian 70 For pure transverse ridges the normal approach action in pure rolling causes the lubricant in the Hertzian region ahead of the asperity to become extremely viscous. Subsequently the asperity becomes frozen together with the lubricant and is transported through the Hertzian conjunction as an integral Copyright 1983 CRC Press LLC Volume II 155 FIGURE 15. Effect of surface roughness on the average film thickness of EHL contacts Po E pure rolling aE 3333 and Ơ R X 10-5. For sliding EHL contacts micro-EHL film thickness is controlled largely by entrainment of lubricant at the inlet of an asperity. For tranverse asperities a lower limit of film thickness can be estimated by applying the classical EHL film thickness formulas to a sliding asperity in a low pressure ambient. For longitudinal asperities very little is available to estimate minimum film thickness. For a pair of transverse asperities colliding in a lubricant of low ambient pressure microEHL film thickness can be estimated with existing 73 If collision takes place in a high-pressure ambient micro-EHL film is expected to increase considerably but cannot be predicted quantitatively. COMPLIANT HYDRODYNAMIC JOURNAL AND THRUST BEARINGS In hydrodynamic journal and thrust bearings EHL effects can become significant if deformation of the bearing

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