Although the limits of the velocity and pressure are met, the PV value exceeds the allowed limit for self-lubricated sintered bronze bearing material, where the PV limit is 110,000 psi-ft=min. | direction is P Fa A where A p D - D2 This is the shoulder area that supports the thrust load. Substituting yields 4Fa 4 x 600 _ . p D2 - D2 p - 12 Psi This is within the allowed limit of Pallowed 2000 psi. b. Calculation of Average Surface Velocity of Thrust Bearing Vth. The average velocity of a thrust bearing is at the average diameter D1 D 2 Vth Rav o Dr where o 2pN rad min. Substituting yields Vth 2pNRav 2pN D1 D D1 D Substitution in the foregoing equation yields Vth x 1000 rev min ft ft min This is well within the allowed limit of Vallowed 1180 ft min. c. Calculation of Actual Average PV Value for the Thrust Bearing PV 1736 psi x ft min 500 x 103 psi-ft min Remark. The imperial units for PV are of pressure in psi multiplied by velocity in ft min. Conclusion. Although the limits of the velocity and pressure are met the PV value exceeds the allowed limit for self-lubricated sintered bronze bearing material where the PV limit is 110 000 psi-ft min. b. Radial Bearing Calculation of Average Pressure P - fa Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. where A LD is the projected area of the bearing. Substitution yields P f 1200 lbf 1200 psi LD 1 in. x 1 in. Calculation of Journal Surface Velocity. The velocity is calculated as previously however this time the velocity required is the velocity at the surface of the 1-inch shaft D 2. Vr o 2rcny p x 1000 rev min x ft 261 ft min Calculation of Average PV Value PV 1200 psi x 261 ft min 313 x 103 psi-ft min In a similar way to the thrust bearing the limits of the velocity and pressure are met however the PV value exceeds the allowed limit for sintered bronze bearing material where the PV limit is 110 000 psi-ft min. Example Problem 1-2 Calculation of Bearing Forces In a gearbox a spur gear is mounted on a shaft at equal distances from two supporting bearings. The shaft and gear turn together at a speed of 600 RPM. The gearbox is designed to transmit a maximum power
