Plain bearings are simple mechanisms consisting of two sliding components used for linear, axial, and pivotal motion. They can be bushings, integral, or split and made from various materials such as bronze, graphite, cast iron, Babbitt metal, solid plastics, and ceramics. The soft component supports the harder one, and plain bearings require low friction, heat, and corrosion resistance.
A plain bearing is a simple mechanism consisting of two sliding components. This lightweight, compact and economical bearing is used extensively in many types of equipment and is sometimes referred to as a Babbitt, bushing or journal bearing. A plain bearing can be used for three basic types of motion: linear, axial and pivotal. The basic types of plain bearings are bushings, integral or split. Bearings can be made from many types of materials.
Plain bearings used for linear motion can consist of a round bearing and shaft assembly or two matching surfaces that slide against each other. Axial plain bearings allow rotation between two parts by supporting an axial load. Pin motion bearings typically consist of a rotating shaft within a stationary bearing. A pivot movement is the most common type of movement in which a plain bearing is used.
A bush bearing is a separate piece that is mounted within a housing to provide a replaceable bearing surface. Bushings are generally the most common type of plain bearing application. An integral bearing is actually built into the equipment for which it is used. Integral bearings typically consist of a hole machined directly into the piece of equipment with a steel shaft passing through it. Two-piece bearings are commonly used for large diameter applications such as crankshafts and connecting rod assemblies.
A plain bearing must be constructed of a durable material that provides low friction and is resistant to both heat and corrosion. Plain bearings usually consist of two separate components. One bearing component is usually made of a soft material while the other is much harder. In most applications, the soft bearing component is used to support the harder one. A wide variety of materials are used to make plain bearing components.
Bronze is typically used in bushing bearings in conjunction with a polished and hardened steel shaft. The softer bronze bush supports the shaft and can be easily replaced when worn. An alloy of graphite and copper is typically used for plain bearing applications in furnaces and dryers. The graphite material in the alloy acts as a dry lubricant for the bearing. Cast iron generally provides a long life material in combination with steel shafts in thrust bearing applications.
Babbitt metal is often used as a bore lining for integral style bearings to collect lubricant contaminants and prevent pin damage. Solid plastics typically provide a durable bearing material that requires no lubricant. Plastic polymer materials are also corrosion resistant and generally maintenance free. The hard ceramic material used in some plain bearings is usually capable of grinding sand and grit contaminants into a fine powder while providing continuous and smooth operation.
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