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Friction and Lubrication in Mechanical Design Episode 1 Part 10

Tham khảo tài liệu 'friction and lubrication in mechanical design episode 1 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Design of Fluid Film Bearings 2Ơ5 30 000 LÚ flt p tn I tr 20 000 ŨL s D s X s 10 000 5000 10 000 15 000 20 000 SPEED RPM Figure 6.35 Maximum oil pressure in optimum bearings. Figure 6.36 Frictional loss. 206 Chapter 6 SPEED RPM Figure 6.37 Merit value for optimum designs. upon at low speeds to maintain the required film thickness. As the speed increases and the journal eccentricity becomes smaller the optimal viscosities drop in order to satisfy the stability criterion. This trend continues as speed increases until the lower limit set on the viscosity is reached. Although longer bearings may have higher merit values according to the design criterion under consideration the drop in the optimum L D ratio with increasing speed is primarily induced by stability requirements. Figure 6.33 shows an increase of temperature rise of the optimum bearing with increased speeds and loads. A similar trend can be seen in Fig. 6.34 for the quantity of oil to be fed to the bearing. The maximum oil film pressure. Fig. 6.35 generally increases with increasing load at any speed. For any particular load the changes in maximum film pressure with speed are influenced by the corresponding changes in radial clearance. The frictional power loss Fig. 6.36 and the value of the objective function Fig. 6.37 increase with increased loads and speeds. The effect of the weighting factor k on the final design is illustrated for the case where w 10001b and N 166.66 rps. The results are given in Table 6.2. It can be seen that by taking k 1 5 and 10 respectively the temperature rise for the optimum bearings are 3.77 11.0 and 14.44 F respectively. Design of Fluid Film Bearings 207 Table 6.2 Effect of Weighting Factor k on the Optimum Design H7 100 lb N 166.6 rps Weighing factor k c L D Ar F Q in.3 sec 1 max psi HP loss 1 1 X 10 7 3.4 X 103 0.36 3.77 4.88 7600 0.147 5 1 X 107 2.55 X 10-3 0.325 11.00 2.15 8500 0.175 10 1 X 10 7 1.5 X 10 3 0.313 14.44 1.67 6500 0.185 The corresponding values of the oil flow