Linear Bearings and Lubricants

Linear Bearings - Design and Considerations

Linear Bearings - Cleanliness: As with any linear bearings, precautions are recommended to exclude foreign matter, such as chips, grit, plastic dust, fibers, or other airborne material. Hard chips in the path of the balls cause ball spalling or fracture and can damage the races. Any dirt or grit between race and rolling elements produces wear, and the balls or rollers suffer progressive lapping that results in increased play. Plastic dust and fibers are particularly bad in recirculating linear bearings because the material tends to pack into the recirculating channels and eventually prevents movement of the balls or rollers.

Bellows-type enclosures are best for keeping foreign material away from critical parts of the linear bearings. Telescoping tubes or cover plates also can be used to protect critical elements.

Some linear bearings have integral rubber-lip seals that avoid the need for extended housings (to accommodate outboard seals) and which also simplify seal retention.

For round linear bearings, a clock-spring arrangement is sometimes used -- the inner coil is attached to the end of the shaft and the outer coil is attached to the OD of linear bearings. Some machine tool installations use a window-shade arrangement with way-covering material of heavy rubber or synthetic material stored on a roller arrangement at the ends of the bed.

If none of these methods are feasible, wipers or scrapers should be used. These are commercially available for flat or round surfaces and are made of felt, leather, or plastic with spring-loaded fingers for positive sealing. Enclosures for ball splines are usually custom designed and are generally more effective at keeping out large chips than dust.

Linear Bearings - Lubrication: For low-friction operation, a thin film of oil keeps surfaces lubricated. The oil also inhibits rust, which causes problems. If the atmosphere is particularly corrosive, stainless steel or some other special alloy must be used as the material for any linear bearings. Surface coating and plating are not recommended for any linear bearings. Unusual temperatures are not really a problem, but special high-temperature or low-temperature lubricants are available.

Linear Bearings