Question

A 3-inch diameter ground shaft rotates at 1000 rev/min in a lathe turned full journal bearing, which is 3 in long. SAE Grade 20 lubricant is used and the lubricant sump has a steady-state temperature of 100°F. The maximum lubricant temperature must not exceed 200°F. Analyze the assembly assuming average clearance and a H8/f8 clearance fit. Determine the following: a. The maximum radial load that the journal can carry and still operate under thick-film lubrication conditions. (6 points) b. The corresponding magnitude and location of the minimum oil-film thickness. (1 points) c. The corresponding total lubricant volumetric flow rate and the power loss. (2 points) d. The maximum oil-film pressure and its angular location. (2 points)

Answer 1

Given diameter d = 3 inch = 3 (2.54 cm) = 7.62 cm = 76.2 mm speed n = 1000 rev/m = 1000 rpm length l = 3 inch = 76.2 mm steady state temperature = 100 degree f = 37.7 degree C max temperature = 100 degree f = 37.7 degree c max temperature = 200 degree f = 93.3 degree c Given lubricants is SAE Grade 20 degree so from the viscosity temperature relationship the absorbed viscosity at 93.3 degree c for SAE Grads 20 is around 7.5 to 8 cp Therefore Z = 8cp Given fit is clearance fit of H_8 f_8 Now the limits for the hole and that one shaft limits (76.2 + 0.000) and (76.2 + 0.046) mm shaft limits (76.2 - 0.076) and (76.2 - 0.030) mm when the process of manufacturing is cleared the average size of the hole and that will be 76.223 and 76.147 mm respectively Therefore diametric Clarence = 76.2233 - 76.147