Plain bearing

A plain bearing, or more commonly sliding contact bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing), is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore, the journal (i.e., the part of the shaft in contact with the bearing) slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests on or the ways on the bed of a lathe. Plain bearings, in general, are the least expensive type of bearing. They are also compact and lightweight, and they have a high load-carrying capacity. The design of a plain bearing depends on the type of motion the bearing must provide. The three types of motions possible are: Journal (friction, radial or rotary) bearing: This is the most common type of plain bearing; it is simply a shaft rotating in a hole. In locomotive and railroad car applications a journal bearing specifically referred to the plain bearing once used at the ends of the axles of railroad wheel sets, enclosed by journal boxes (axleboxes). Axlebox bearings today are rolling-element bearings rather than plain bearings. Linear bearing: This bearing provides linear motion; it may take the form of a circular bearing and shaft or any other two mating surfaces (e.g., a slide plate). Thrust bearing: A thrust bearing provides a bearing surface for forces acting axial to the shaft. One example is a propeller shaft. Integral plain bearings are built into the object of use as a hole prepared in the bearing surface. Industrial integral bearings are usually made from cast iron or babbitt and a hardened steel shaft is used in the bearing. Integral bearings are not as common because bushings are easier to accommodate and can be replaced if necessary. Depending on the material, an integral bearing may be less expensive but it cannot be replaced.