Spherical plain bearings are used to accommodate shafts or rods with varying amounts of misalignment. They are designed to manage high radial loads and provide consistent performance under conditions of marginal lubrication, extreme speed and critical-application stress. Most spherical plain bearings consist of a plain bearing and ball bushing inside a lined, cylindrical housing that minimizes friction or provides self-lubrication. Lubrication-free spherical plain bearings are also available. Typically, metal balls and liners are made of steel, bronze or iron. Non-metallic balls and liners are usually made of plastic, nylon, or polytetrafluoroethylene (PTFE). Both metallic and non-metallic products provide superior performance to conventional steel, plastic or bronze plain bearings. For heavy-duty industrial applications, spherical plain bearings often include large bores or spherically shaped rollers that permit axial loading and relative misalignment between the housing and shaft.
Specifications for spherical plain bearings include physical dimensions, performance specifications, and special features. Important physical dimensions to consider include bore diameter, bearing thickness or length-through-bore, and outside diameter. Spherical plain bearings are usually measured in English units such as inches (in), or metric units such as millimeters (mm) or centimeters (cm). Performance specifications for include radial load capacity and maximum angular misalignment, the amount of bearing swing from the normal or aligned condition. In most cases, bearing motion is symmetric about the center. The maximum angular misalignment is half of the total side-to-side range. In terms of special features, many spherical plain bearings are self-lubricating, corrosion-resistant, or include a lubrication port. Bearings that are suitable for rotating shafts can rotate about an axis and accommodate misalignment.
Spherical plain bearings are relatively maintenance-free and suitable for a variety of applications that involve swivel movements, high alternating loads, high shock loads, and very high radial loads with unilateral load direction. Some spherical plain bearings are used in railway engineering, railway station construction, bridge building, construction machinery, hydraulic steel structures, or roof designs. Others are used in power generation, oil field exploration, mining and aggregate processing, wind turbines, gear drives, or rolling mills. The aerospace industry uses spherical plain bearings in wing flaps, engine mounts, and hatches and joints. Spherical plain bearings are also used in helicopters, trains and automobiles. Specialized products include spherical drive bearings, spherical thrust roller bearings, and miniature spherical bearings.
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Rod end bearings contain a bearing that can accommodate a shaft or rod with varying misalignment. They attach to a static rod via a threaded shaft.