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Lubrication

The following sub-sections provide general support and guidelines about lubrication for each material type. The complexity makes it impossible to include all the information needed to cover every conceivable application. For additional information about lubrication, contact the SKF application engineering service.
Solid bronze bushings
SKF solid bronze bushings can be lubricated with either oil or grease. The lubricant not only improves the sliding properties, but also reduces wear and prevents corrosion. While oil is used in exceptional cases, solid bronze bushings are typically grease lubricated.
To protect the bushing and lubricant, SKF recommends using seals in highly contaminated environments.
All bushings with a bore diameter d > 14 mm incorporate an axial lubrication groove.

Sintered bronze bushings
SKF sintered bronze bushings are impregnated with a lubricant. Therefore, when storing or mounting, the bushing should never come in contact with absorbent material as it may wick the oil away very quickly. Additional lubrication is usually not necessary.

Wrapped bronze bushings
The sliding surface of an SKF wrapped bronze bushing contains diamond shaped pockets (fig. 1) that should initially be filled with grease. The pockets act as reservoirs to progressively release lubricant during operation. Whether grease or oil is used, a good quality lubricant reduces friction and wear by separating a wrapped bronze bushing from its shaft. To protect the bushing and lubricant in highly contaminated environments, SKF recommends using seals.

PTFE composite bearings
PTFE composite bearings have good dry sliding characteristics and do not require lubrication. However, the presence or continuous supply of oil or other fluid may be advantageous. Even fluids not normally associated with lubrication, such as water, kerosene or paraffin, may be used. Lubrication improves the removal of heat from the bearing position and the formation of a hydrodynamic lubricating film. Therefore, lubrication has a very favourable effect on the wear behaviour of the bearing and considerably extends bearing life.
Periodic relubrication with grease to enhance sealing or to protect the counter surface against corrosion also can extended bearing service life.
However, a single initial application of grease when mounting PTFE composite bearings may have a negative influence on bearing life, as the grease can form a paste-like mixture together with the wear particles produced during running-in and increase bearing wear.
Age-resistant lithium base greases are preferred for operating temperatures up to 80 °C, while at higher temperatures, silicone greases should be used. Greases containing solid lubricants such as molybdenum disulphide are totally unsuitable.

POM composite bearings
SKF POM composite plain bearings are designed to operate under marginal lubrication conditions. Its sliding surface contains grease reservoirs (fig. 2) that should be filled prior to installation. It is not necessary to relubricate these plain bearings, but the presence of a lubricant can extend bearing service life considerably.
To protect the mating surface against corrosion, grease can be applied periodically. For this reason, POM composite bushings wit a bore diameter d ≥ 10 mm and a width of B ≥ 12 mm are manufactured as standard with a lubrication hole. The hole dimensions and position are in accordance with DIN 1434:1983.
Age-resistant lithium base greases are preferred for operating temperatures up to 80 °C, while at higher temperatures, silicone greases should be used. Greases containing solid lubricants such as molybdenum disulphide are totally unsuitable.

PTFE polyamide bushings
SKF PTFE polyamide bushings are designed for dry operation. A lubricant can, however, improve the performance of these bushings. With an adequate supply of grease, oil, water or other liquid, the operating speed of these bushings can be increased.
SKF PTFE polyamide bushings are resistant to most lubricating oils and greases.

Filament wound bushings
SKF filament wound bushings have excellent dry sliding characteristics due to its unique sliding surface. The low friction sliding surface does not require additional lubricant.
In cases where lubrication is needed, for example because the shaft requires protection against corrosion or adjacent components (e.g. a thrust washer) require lubrication, the lubricant usually has no negative effect on the bushing under normal operating conditions. However, with lubrication the advantage of maintenance-free operation gets partly lost under conditions of high-frequency load changes with heavy load levels.
SKF recommends using seals when the bushing is to be used in a highly contaminated environment.

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