The function of a lubricant in a rolling element bearing is to prevent metal to metal contact between components, prevent wear and protect against corrosion. Two methods of lubrication are normally employed grease and oil. In the case of SRB Split Bearings grease lubrication is most often employed.
Grease Lubrication
Greases can be used to lubricate SRB split roller bearings under most normal conditions. Grease is the preferred method of lubrication because it can be more easily retained within the bearing enclosure and housing, the latter simplifying sealing arrangements. Greases are essentially oils thickened usually with a metal soap, a third ingredient are additives such as rust inhibitors, or extra pressure additives. The oils employed may be mineral or synthetic depending upon the application.
SRB bearings are heat treated to retain dimensional stability up to 140ºC. At temperatures up to 100ºC, standard high quality greases may be used. We suggest good quality lithium soap or complex based greases having extra pressure additives and a penetration number of 3. It is important to note that all values given in this catalogue for axial capacity assume the use of a grease with extra pressure (EP) additives. If EP additives are not present then axial capacity is reduced by 50%.
At temperatures exceeding 100ºC care must be taken to ensure that the correct thickener and viscosity of base oil are selected. The performance of grease at such temperatures is dependent on a stable thickener and the temperature/ viscosity ratio of the base oil. A stable base oil and soap thickener are important as is the ability of the oil to offer adequate viscosity at an elevated temperature.
In cases of water splash, calcium soap based greases may be used, these are particularly resistant to water wash out. Care should be taken when mixing greases with different soap thickeners and base oil types. Please contact SRB Technical Services for further advice.
For initial lubrication the bearing should always be well filled with grease. The remaining housing space should be
filled as follows:-
- At low speeds, not exceeding 25% of catalogue speed rating, we suggest that the remaining housing space be fully filled with grease.
- At medium speeds, between 25 and 50% of catalogue speed rating, the remaining housing space may be 1/3 to 1/2 filled with grease.
- At high speeds, exceeding 50% of catalogue speed rating, the remaining housing space should be left empty.
Re-lubrication
The re-lubrication intervals will be dependent on the prevailing operating conditions.
Greases age and oxidise due to a number of considerations these include load, speed, temperature, cleanliness, presence of water and even airflow through the bearing.
For retained type bearings, initial re-lubrication intervals for guidance purposes would be 2 – 4 weeks with 3 – 6 mls added. For expansion type bearings, initial re-lubrication intervals would be 3 – 4 months with 3 – 6 mls added. More accurate intervals and quantities should be established from observations taken during bearing operation.
If re-lubrication can be carried out whilst the bearing is in operation, this will allow for even distribution of the grease. This means of re-lubrication should only be undertaken if it is safe to do so.
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