How dose self lubricating plastic bearings work?

Self-lubricating bearings are bearings in which the rolling elements, inner and outer races or cages are treated with special materials and can work normally without adding oil or lipid lubricants. From the lubrication mechanism, self-lubricating bearings can be divided into two types: bearings with self-lubricating properties produced by self-lubricating materials and bearings with self-lubricating properties produced by sintered microporous materials.

Self-lubricating materials mainly refer to some solid lubricants. The composite coating co-deposited by particles of solid lubricant and metal has small friction coefficient and less wear of the coating itself. Solid lubricants include MoS2, graphite fluoride (CF)n, polytetrafluoroethylene (PTFE) and so on. The following is a detailed introduction of PTFE, a common self lubricating plastic bearings material.

PTFE self lubricating plastic bearings is an engineering polymer with the lowest friction coefficient among plastics (μ=0.04), good self-lubrication and corrosion resistance.

 

When the bearing cage is made of PTFE-based composite material, when the self lubricating plastic bearings rotates, friction is generated between the steel ball and the cage due to the spin motion of the steel ball. Because of the repeated contact and extrusion of the micro-protrusions on the contact surface of the rolling element, small band-shaped grooves will be formed on the contact surface of the PTFE structural cage. Because the PTFE self lubricating plastic bearings structure is a strip-shaped structure, the adhesion force is much smaller than that of the metal. In the process of friction, PTFE strip fragments are continuously adhered-flattened-re-adhered-re-flattened, and gradually form a transfer film, which has a certain thickness (about 100-130 μ m) and its structure is a small band-shaped additional layer. Similarly, in the process of friction, PTFE transfer film can be formed in the raceway of the inner ring and outer ring on the surface of steel ball. Because of the micro-unevenness of the surface, PTFE film is plowed and squeezed to produce small pieces, which are adhered to the raceway surface, and then flattened and extended to gradually form PTFE lubrication transfer film. The thickness of the transfer film in the raceway is only 1/3 ~ 1/2 of that of the roller. When a certain thickness of self-lubricating transfer film is formed in the inner and outer race of the rolling element, the friction coefficient of PTFE decreases sharply. This is the self lubricating plastic bearings principle of operation.

In Japan, because the temperature of hydrogen in engine fuel liquid is very low, engineers and technicians use cylindrical material impregnated with PTFE glass fiber cloth to make bearing cage, in which PTFE content is 62% and glass fiber content is 38%. This kind of cage material makes full use of the self-lubricating property of PTFE in extreme environment such as low temperature and vacuum. At the same time, due to the laminated glass fiber cloth structure, the mechanism strength and wear resistance are extremely high.

The self lubricating plastic bearings will be applied to a wider field.

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