Machinery's Handbook, 31st Edition
2420 Thrust Bearings 3) Radial pad width, a. Equal to one-half the difference between the inside and outside diameters. a D D 2 2 1 = − 4) Pitch line circumference, B. Found from the pitch diameter. B D a 2 = π − ^ h 5) Number of pads, i. Assume an oil groove width, s . If the length of pad is assumed to be optimum, i.e., equal to its width, i a s B app = + Take i as nearest even number. 6) Length of pad, b. If number of pads and oil groove width are known, b i B i s # = − ^ h 7) Actual unit load, p. Calculated in pounds per square inch based on pad dimensions. p iab W = 8) Pitch line velocity, U. Found in feet per minute from U BN = 12 where N = rpm 9) Friction power loss, Pf. Friction power loss is difficult to calculate for this type of bear ing because there is no theoretical method of determining the operating film thickness. However, a good approximation can be made using Fig. 3. From this curve, the value of M , horsepower loss per square inch of bearing surface, can be obtained. The total power loss, P f , is then calculated from P iabM f = 10) Oil flow required, Q. May be estimated in gallons per minute for a given temperature rise from . Q c t P 424 f ∆ = where c = specific heat of oil in Btu/gal/ ° F Δ t = temperature rise of the oil in ° F Note: A Δ t of 50 ° F is an acceptable maximum. Because there is no theoretical method of predicting the minimum film thickness in this type of bearing, only an approximation, based on experience, of the film flow can be made. For this reason and based on practical experience, it is desirable to have a minimum of
one-half of the desired oil flow pass through the chamfer. 11) Film flow, Q F . Calculated in gallons per minute from . Q Z iVh p 15 10 F s 2 5 3 = ^ h^ h where V = effective width-to-length ratio for one pad, a/b Z 2 = oil viscosity at outlet temperature h = film thickness Note: Because h cannot be calculated, use h = 0.002 inch.
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