Bearings, Lubrication, and Seals
Bearings
Antifriction bearings (ball, cylindrical roller, tapered roller, spherical roller, needle, thrust) carry load through rolling elements; plain or sleeve bearings carry load on an oil film. The rotating ring is normally the press fit and the stationary ring the slip fit, so the ring that turns relative to the load creeps correctly. Never hammer a bearing on - use an induction heater, oil bath, or a press on the proper ring.
Failure signatures
Spalling and fatigue from overload; brinelling (true, from impact) versus false brinelling (vibration while stationary); fluting from electrical current; discoloration from overheating; smearing from inadequate lubrication. Reading the pattern tells you the cause.
Lubrication
Viscosity is the primary selection criterion, and it must suit speed, load, and temperature. Grease is oil in a thickener; NLGI grade number rises with stiffness. Over-greasing is a real failure mode - it blows seals and churns the grease. Never mix incompatible thickeners, and keep everything clean; most bearing failures start with contamination.
Seals
Lip seals have the lip facing the medium being retained, with a light film of grease on the lip at installation. Labyrinth seals are non-contacting and need no lubrication. Mechanical seals need clean flush, correct spring compression, and no dry running. Packing must drip slightly to run cool.
Worked example
A bearing rated C = 10,000 lb carries P = 2,000 lb. L10 = (C/P)³ × 10⁶ revolutions = 5³ = 125 × 10⁶ revolutions. Double the load to 4,000 lb and life falls to about 15.6 × 10⁶ revolutions.