How self-lubricating bearings work

Self-lubricating bearings commonly used in linear and profile rails are made of oil-impregnated plastic. Figure 1 shows a self-lubricating cartridge that might be pressed onto each end of a pillow-block housing of a round rail.

 Figure 1

In the design illustrated, the micro-porous polymer section is saturated with oil, which gets diffused when the carriage is in motion, thank to the capillary action of a wire spring that is in continuous contact with the rail. This capillary action ensures that there is always a film of lubricant between all rolling elements and races.

When motion stops, the micro-porous polymer acts as a sponge to reabsorb the oil, preventing excessive buildup of the lubricant on the shaft and eliminating the messy dripping that comes with manual oil applications. A double-lip, nitrile seal provides further protection from oil loss. Figure 2 illustrates a comparable self-lubricating assembly on a profile rail.

 Figure 2 

Specifying self-lubricating bearings
Whether you are an OEM motion designer seeking to design a maintenance-friendly system or a maintenance engineer replacing a bearing that requires manual lubrication, the design and application factors you must consider are similar. Maintainability adds a critical dimension to the specification matrix, impacting, or being impacted by, almost every variable. Self-lubrication options should be considered for just about every profile or linear guide specification and evaluated based on the following criteria.

Availability of maintenance support — Where end-user maintenance resources are limited, lubrication-free bearings are an easy choice. Independent testing showed that self-lubricating bearings exhibited no need for maintenance or addition of lubrication to the lube block during a three-million-cycle deflection test.