Machinery's Handbook, 31st Edition
Journal Bearings
2415
c) a minimum of 750 × 10 − 6 inches for larger bearings. More conservative designs would increase these requirements 2) Determine the minimum acceptable c d based on a maximum Δ t of 40 ° F from the oil temperature rise curve (Fig. 11). 3) If there are no requirements for maintaining low friction horsepower and oil flow, the possible limits of diametral clearance are now defined. 4) The required manufacturing tolerances can now be placed within this band to optimize h o as shown by Fig. 11. 5) If oil flow and power loss are a consideration, the manufacturing tolerances may then be shifted within the range permitted by the requirements for h o and Δ t .
Oil Feed Hole
2.3 ”
l.9 ”
Fig. 12. Full Journal Bearing Example Design. Example: A full journal bearing, Fig. 12, 2.3 inches in diameter and 1.9 inches long, is to carry a load of 6000 pounds at 4800 rpm, using SAE 30 oil supplied at 200 ° F through a single oil hole at 30 psi. Determine the operating characteristics of this bearing as a function of diametral clearance.
1) Diameter of bearing, given as 2.3 inches. 2) Length of bearing, given as 1.9 inches. 3) Bearing pressure: . . p 1 19 23 6000 b # # =
1372lbs. per sq. in. = 4) Diametral clearance: Assume c d is equal to 0.003 inch from Fig. 6 on page 2410 for first calculation. 5) Clearance modulus: . . . m 23 = 0 003 = 0 0013 inch 6) Length-to-diameter ratio: . 23 = 19 = 083 7) Assumed operating temperature: If the temperature rise Δ t a is assumed to be 20 ° F, t F 200 20 220 b ° = + = 8) Viscosity of lubricant: From Fig. 6 on page 2403, Z = 7.7 centipoises 9) Bearing-pressure parameter: . . . . P 77 4800 69 13 1372 043 2 # # # ′ = = 10) Eccentricity ratio: From Fig. 7, 1 1 − ε = 6.8 and ε = 0.85 d l . .
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