Millwright and operator shorthand for the converging film that forms under a rotating shaft in a plain bearing. As the journal turns it drags oil into the narrowing gap, pressure builds in the wedge and lifts the shaft so metal never touches metal. Losing the wedge, through low oil, overheating or turning too slowly under load, is how a babbitt bearing gets wiped.
Don't bar it over dry, there's no oil wedge at that speed and you'll drag the shaft right across the babbitt.
Also heard as
- oil film wedge
Related terms
Hydrodynamic lubrication
Full-film lubrication in which motion drags oil into a narrowing gap and builds enough pressure to float the load.
Babbitt
Soft tin- or lead-based alloy that lines plain bearings so they tolerate dirt and brief contact.
Wipe
To smear the soft babbitt lining of a plain bearing when the oil film fails, ruining the bearing.
Viscosity
A fluid's resistance to flow, the lubricant property that sets how thick an oil film can build.