A regime in which sliding surfaces are fully separated by a pressurized oil film generated by their own motion. In a journal bearing the shaft runs slightly off center, pulls oil into the converging wedge and lifts itself on a film several to a few tens of microns thick. Wear is close to zero while speed, viscosity and load stay in balance, but the film collapses at very low speed, so large machines add jacking or lift oil for start-up and turning gear.
Once the turbine's off turning gear and up to speed the journals are fully hydrodynamic and the lift pumps can drop out.
When a sleeve bearing shows wear, ask when the film was lost: start-up, shutdown, overload or low oil. A healthy hydrodynamic film wears nothing.
Also heard as
- full-film lubrication
- thick-film lubrication
- HD lubrication
Related terms
Oil wedge
Shop name for the tapered, pressurized film of oil that lifts a shaft off a sleeve bearing.
Babbitt
Soft tin- or lead-based alloy that lines plain bearings so they tolerate dirt and brief contact.
Stribeck curve
Plot of friction against viscosity times speed over load, showing the boundary, mixed and full-film regimes.
Viscosity
A fluid's resistance to flow, the lubricant property that sets how thick an oil film can build.