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.

PHG25MMH100

7010CD/P4ADRA ITALY V 703 347D

T310