Journal bearing

A journal bearing is a plain sliding bearing that supports a rotating shaft on a thin pressurized film of oil, with no rolling elements. The shaft journal turns inside a cylindrical shell lined with whitemetal; oil drawn into the converging wedge generates a hydrodynamic film that lifts the journal off the surface, so steady-state running is metal-on-oil, not metal-on-metal. Marine main bearings, crankpin bearings, and turbocharger bearings are journal bearings fed by the forced-lubrication system. Load capacity rises with speed and oil viscosity and falls with clearance and temperature. Starting and stopping pass through boundary contact, which is when most wear occurs.