A plain bearing with an inner diameter of 40 mm and a width of 30 mm carries a radial load of 1.2 kN, and the shaft turns at 600 rpm. Taking the bearing pressure P as the load divided by the projected area (inner diameter × width) and the sliding speed v as the surface speed of the shaft, which is closest to the PV value?

Answer: B. About 1.3 MPa·m/s

The bearing pressure is P = 1.2×10³/(0.040×0.030) = 1.0×10⁶ Pa = 1.0 MPa and the surface speed is v = π×0.040×600/60 ≈ 1.26 m/s, so PV ≈ 1.0×1.26 ≈ 1.3 MPa·m/s. Frictional heat generated per unit area is μPV, so the PV value is a guide to temperature rise and wear in a bearing, and allowable values are set for each material in polymer bearings and sintered oil-impregnated bearings. About 75 MPa·m/s is the value obtained by using 600 as is without converting the rotational speed to revolutions per second. About 0.40 MPa·m/s is the value obtained by dividing the load by the circumferential area πDL instead of the projected area. Even when the PV value is within its limit, also check that P and v each stay below their own limits.