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Friction and Lubrication in Mechanical Design Episode 2 Part 3

Tham khảo tài liệu 'friction and lubrication in mechanical design episode 2 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 280 Chapter 7 7.7.4 Effective Viscosity Using the notation Tf absolute bulk disk temperature e.g. Tb 273.16 C ATS temperature rise for steel-steel contact A T temperature rise from Eq. 7.27 using the material properties of the contacting surfaces for steel-coating contact AT ATC ATS temperature rise difference between the steel-coating contact and the steel-steel contact ATe effective temperature rise difference between the steel-coating contact and the steel-steel contact Then ATr AT p 7.31 where p is the coating thickness factor from the previous section. Then Te Tb ATe is used to calculate the viscosity for that coating conditions and the viscosity is then substituted into Eq. 7.24 to calculate the corresponding coefficient of friction. The viscosity of 10W30 oil is calculated by the ASTM equation 27 logics 0.6 a - h log T 7.32a therefore viscosity 10 - 0.6 0 7.32b 7.32c where Te is the absolute temperature K or cS is the kinematic viscosity centistokes a 7.827. b 3.045 for 10W30 oil. For some commonly used oil a and b values are given in Table 7.3. 7.7.5 Coating Thickness Effects on Modulus of Elasticity For the reasons mentioned before the effective modulus of elasticity for coated surface is desirable. Using the well-known Hertz equation one calculates the Hertz contact width for two cylinder contact as 27 b . 7.33 RollingỊSliding Contacts 281 Table 7.3 Values of a and b for Some Commonly Used Lubricant Oils Oil a b SAE 10 11.768 4.6418 SAE 20 11.583 4.5495 SAE 30 11.355 4.4367 SAE 40 11.398 4.4385 SAE 50 10.431 4.0319 SAE 60 10.303 3.9705 SAE 70 10.293 3.9567 where E7 1 2 1 - r E and V are the modulus of elasticity and Poisson s ratio. Coating material properties are used for 2 and because coating thickness is an order greater than the deformation depth this can be seen later . Therefore the deformation depth is calculated by Fig. 7.18 hd R sin 0 tan Ớ 0 is very small therefore hd Ree R a R R R 7.34 The variation of the deformation depth with load is shown .