Hydrostatic bearings and hydrodynamic bearings are fluid film bearings that rely on a film of oil or air to create a clearance between the moving and stationary elements. They are different than basic bearings, machine components that reduce friction between supports in order to move loads. Typically, hydrostatic bearings and hydrodynamic bearings are used whenever one machine part comes in contact with another. Without bearings, machine parts would need to be constantly replaced from the wear of friction. The two primary types of bearings are antifriction bearings such as roller bearings and ball bearings, and plain bearings such as journal bearings and trust bearings. An antifriction bearing reduces friction by removing sliding between surfaces and replacing part contact with rolling components. A plain bearing uses a lubricant to reduce the friction between the sliding surfaces.
Hydrostatic bearings and hydrodynamic bearings are a type of plain bearing. With hydrostatic bearings and hydrodynamic bearings, the generation of heat during machine operation is due to oil shear. A hydrostatic bearing employs a positive pressure supply that maintains clearance between the rotating stationary elements. With a hydrostatically lubricated bearing, the lubrication is introduced under pressure between the moving surfaces. Hydrostatic bearing spindles feature high stiffness and long bearing life, and are often used for fine machining and finishing. Because hydrostatic lubrication does not depend on relative motion to maintain the lubrication film, it can accommodate heavy loads at low speeds. A hydrodynamic bearing is typically a low-clearance assembly that relies on a film of oil (and occasionally air) that develops clearance while the spindle is rotating. Machines that use hydrodynamically lubricated bearings should not be endure high load during start up.
There are several different types of hydrostatic bearings and hydrodynamic bearings. The three basic types of hydrodynamic bearings are circumferential groove bearings, pressure bearings, and multiple groove bearings. Hydrodynamic bearing spindles feature high stiffness and long bearing life, and are often used for fine machining and finishing. Suppliers of hydrostatic bearings and hydrodynamic bearings can assist customers in product selection.