plain bearings
plain bearings
Author :Admin | Publish Date:2013-05-24 10:16:35
The distance from one parting edge to the other is slightly larger than the
corresponding distance in the housing so that a light amount of pressure is
required to install the bearing. This keeps the [plain
bearings] in place as the two halves of the housing are installed. Finally,
the shell's circumference is also slightly larger than the housing circumference
so that when the two halves are bolted together the bearing crushes slightly.
This creates a large amount of radial force around the entire bearing which
keeps it from spinning. It also forms a good interface for heat to travel out of
the bearings into the housing.
Plain bearings must be made from a material that is durable, low friction,
low wear to the bearing and shaft, resistant to
elevated temperatures, and corrosion resistant. Often the bearing is made up of
at least two constituents, where one is soft and the other is hard. The hard
constituent supports the load while the soft constituent supports the hard
constituent. In general, the harder the surfaces in contact the lower the
coefficient of friction and the greater the pressure required for the two to
seize.
Solid plastic plain bearings are now increasingly popular due to
dry-running lubrication-free behavior. Solid polymer plain bearings are low
weight, corrosion resistant, and maintenance free. After studies spanning
decades, an accurate calculation of the service life of polymer plain bearings
is possible today. Designing with solid polymer plain bearings is complicated by
the wide range, and non-linearity, of coefficient of thermal expansion. These
materials can heat rapidly when used in applications outside the recommended pV
limits.
Most plain bearings have a plain inner surface, however some are grooved.
The grooves help lubrication enter the bearing and cover the whole
journal.Self-lubricating plain bearings have a lubricant contained within the
bearing walls. There are many forms of self-lubricating bearings. The first, and
most common, are sintered metal fag bearings,
which have porous walls.
The porous walls draw oil in via capillary action and release the oil when
pressure or heat is applied. Another form is a solid one-piece metal bushing
with a figure eight groove channel on the inner diameter that is filled with
graphite. A similar bearing replaces the figure eight groove with holes that are
plugged with graphite; this allows the bearing to be lubricated inside and out.
The last form is a plastic bearing, which has the lubricant molded into the
bearing. The lubricant is released as the bearing is run in.
Bearings that are made from bearing grade materials always run in the dry
condition. The other two classes of plain bearings can run in all three
conditions; the condition in which a bearing runs is dependent on the operating
conditions, load, relative surface speed, clearance within the bearing, quality
and quantity of lubricant, and temperature (affecting lubricant viscosity). If
the plain bearing is not designed to run in the dry or boundary condition it
will wear out and have a high coefficient of friction. Dry and boundary
conditions may be experienced even in a fluid koyo
bearing when operating outside of its normal operating conditions; e.g., at
startup and shutdown.
BRING SKF RMS 14 (1 3/4 X 4 1/4 X 1 1/16)
BRING SKF RMS 16 (2 X 4 1/2 X 1 1/16)
BRING SKF RMS 18 (2 1/4 X 5 X 1 1/4)
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