Bearing Classification

Bearing Classification

Machines could not operate at high speed in their familiar way without some

means of reducing friction and the wear of moving parts. Several important

engineering inventions made it possible to successfully operate heavily loaded

shafts at high speed, including the rolling-element bearing and hydrodynamic,

hydrostatic, and magnetic bearings.


1. Rolling-element bearings are characterized by rolling motion, such as
in ball bearings or cylindrical rolling-element bearings. The advantage
of rolling motion is that it involves much less friction and wear, in
comparison to the sliding motion of regular sleeve bearings.


2. The term hydrodynamic bearing refers to a sleeve bearing or an
inclined plane-slider where the sliding plane floats on a thin film of
lubrication. The fluid film is maintained at a high pressure that supports
the bearing load and completely separates the sliding surfaces. The
lubricant can be fed into the bearing at atmospheric or higher pressure.
The pressure wave in the lubrication film is generated by hydrodynamic
action due to the rapid rotation of the journal. The fluid film acts
like a viscous wedge and generates high pressure and load-carrying
capacity. The sliding surface floats on the fluid film, and wear is
prevented.



3. In contrast to hydrodynamic bearing, hydrostatic bearing refers to a

configuration where the pressure in the fluid film is generated by an

external high-pressure pump. The lubricant at high pressure is fed into

the bearing recesses from an external pump through high-pressure

tubing. The fluid, under high pressure in the bearing recesses, carries

the load and separates the sliding surfaces, thus preventing high

friction and wear.


4. A recent introduction is the electromagnetic bearing. It is still in
development but has already been used in some unique applications.
The concept of operation is that a magnetic force is used to support the
bearing load. Several electromagnets are mounted on the bearing side
(stator poles). The bearing load capacity is generated by the magnetic
field between rotating laminators, mounted on the journal, and stator
poles, on the stationary bearing side. Active feedback control keeps the
journal floating without any contact with the bearing surface. 

The advantage is that there is no contact between the sliding surfaces, so
wear is completely prevented as long as there is magnetic levitation.