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Journal Bearings
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Journal Bearing (Oil filmed Bearings):-
A journal bearing, simply stated, is a cylinder which surrounds the shaft and is filled with some form
of fluid lubricant. In this bearing a fluid
is the medium that supports the shaft preventing metal to metal
contact. The most common fluid used is oil, with special applications using water or a gas.
This application
note will concentrate on oil lubricated journal bearings. |
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Hydrodynamic Bearing:-
A Hydrodynamic Bearing, which are active as the shaft rotates, create an
oil wedge that supports the
shaft and relocates it within the bearing
clearances. In a horizontally split bearing the oil wedge will lift
and support
the shaft, relocating the centerline slightly up and to one side into a normal
attitude position
in a lower quadrant of the bearing. The normal attitude angle
will depend upon the shaft rotation direction
with a clockwise rotation having
an attitude angle in the lower left quadrant. External influences, such as
hydraulic volute pressures in pumps or generator electrical load can produce
additional relocating forces
on the shaft attitude angle and centerline
position. |
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Hydrostatic Bearing:-
Hydrostatic bearings provide accurate, highly damped, friction free linear
and rotary motion. These
bearings also average the form errors of the surfaces
that make up the bearing components. This
averaging allows the bearings to
exhibit smaller error motions than would otherwise be possible. The
small error
motions attainable when hydrostatic bearings are used make them the bearing
technology of
choice for ultra precise ways and spindles for instruments and
machines.
Hydrostatic bearings are used when operating
conditions require full film lubrication that cannot be
developed
hydro dynamically. The hydrostatically lubricated bearing is supplied with
lubricant under
pressure from an external source. Advantages of the hydrostatic
bearing over bearings of other type are
lower friction, higher load capacity,
higher reliability, and longer life.
Hydrostatic
bearings rely on an external pump. The power for that pump is arguably part of
overall
bearing friction. Better seals can reduce leak rates and pumping power,
but may increase friction. |
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