As their name suggests, self-lubricated sleeve bearings provide their own lubrication without any repetitive reapplications of solid lubricants or lubricating oil to their assembly. As such, they're usually referred to as maintenance-free bearings that work by having lubricants impregnated within their bearing surfaces.

For example, oil-impregnated bronze bearings rely on capillary action to create a lubricating film that grants low friction coefficient, high precision, and high speeds. This contrasts with the lubrication systems on rotary bearings, including but not limited to ball bearings, roller bearings, and linear bearings. These usually rely on external lubrication to operate.

Without an external lubricant, which is mostly grease or graphite for ball bearings, the balls or rollers within the bearing would cause irreparable damage and catastrophic failures. Many manufacturers overcome this flaw in the bearing design by adding oil-impregnated seals to the ends of the bearing's housing.

Types of Self-Lubricating Bearings

There are two main types of self-lubricating bearings categorized by the type of bearing material:

• Metallic — self-lubricating bushings and plain bearings are usually made of sintered bronze, copper, and aluminum alloys, lead, and sintered iron and copper.
• Non-metallic bearings — include a whole variety of polymer bearings (PTFE), including those made of Polyacetal, Polyethylene, resin-based plastics, Teflon compounds, woven fibers (such as composite bearings), and carbon graphite.

How Do Self-Lubricating Bearings Work?

A liquid or a solid lubricant is infused within the sliding layer of the self-lubricating bearing. As the bearing performs its function, the bearing lubrication is released through the material's pores into the bearing surface, thus reducing the coefficient of friction within the assembly.

Since the lubricant is evenly distributed throughout the sliding surface, even if the sliding layer starts to wear, the performance of low friction bearings remains unaffected. In order to offer low friction bearing performance at startup before the impregnated lubricant reaches the bearing surface, a "running-in" surface is also typically incorporated at the top of the sliding layer.

What are Self-Lubricating Bearing Applications?

Self-lubricating bearings are mostly used in the automotive and aerospace industry. Aerospace applications in particular require resilient, low friction bearings to help minimize risks of having a malfunction at 10,000 feet or more above the ground. Additionally, many of the components in an aircraft are difficult to access and service and thus benefit significantly from the self-lubricating bearings' long service lives.

Common Misconceptions

Advertisements often claim that self-lubricating bearing systems don't require any additional lubrication during their operational life, which isn't true—there isn't an indefinitely lubricated bearing. Most of these systems self-lubricate via integrated lubrication, which eventually runs out or becomes ineffective over time.

This means that these self-lubricated and "lubed-for-life" systems aren't really lubed for life but rather for a very, very long time. It pays to have these systems lubricated during each inspection or maintenance of your machine assemblies.

Summary

The ability of the bearing to transfer minute amounts of substance, typically a PTFE (Teflon)-based substance, to the mating surface—often a shaft or rail—defines self-lubricating bearings. If you want to learn more about bearings, visit Reid Supply to access their extensive library of professional literature and industry news.