Friday, 16 May 2014

Bearing Lubrication - the importance of lubricant selection for ball bearings

You may not have given it much thought, but what's inside your bearing can be crucial to it's future survival...


When a bearing must perform under demanding conditions, the lubricant selection becomes critical. Lubrication will affect life, torque, speed, noise, grease migration out gassing, temperature and rust prevention of the bearing.

Two basic types of lubricants available are oil and grease.

Applications that require extremely low torque or narrow range of torque variation are suited to use oil as a lubricant. Depending on the application, it is possible that an oil lubricant may not meet a specific requirement. Grease is an oil to which a thickener has been added.

A technician adds oil lubricant to a bearing

Oil

Oil is the basic lubricant for ball bearings. Previously most lubricating oil was refined from petroleum. Today, however, synthetic oils such as diesters, silicone polymers, and fluorinated compounds have found acceptance because of improvements in properties.
Compared to petroleum base oils, diesters in general have better low temperature properties, lower volatility, and better temperature/viscosity characteristics. Silicones and fluorinated compounds possess even lower volatility and wider temperature/viscosity properties.

Grease

Grease is an oil to which a thickener has been added to prevent oil migration from the lubrication site. It is used in situations where frequent replenishment of the lubricant is undesirable or impossible. All of the oil types mentioned here can be used as grease bases to which are added metallic soaps, synthetic fillers and thickeners.
The operative properties of grease depend almost wholly on the base oil. Other factors being equal, the use of grease rather than oil results in higher starting and running torque and can limit the bearing to lower speeds.
Grease additives include rust inhibitors, extreme pressure additives (EP), oxidation preventatives, etc. Because of the wide variety and complexity of additives, the characteristics of similar greases change considerably from one manufacturer to another.
Some of our grease lubricant

And just when you think you've got the hang of it, there are also:

Dry Lubricants 
Used primarily in vacuum applications or where standard lubricants are unsuitable. AT SMB we use graphite based dry lubricants and also molybdenum disulfide for their hardwearing and low friction properties and the fact that they insoluble in water and dilute acids. It is also effective within a wide temperature range of -180 to +300°C.   

Molybdenum disulfide powder - before it is applied
By burnishing the balls and raceways of a bearing, friction is reduced allowing higher speeds than with dry bearings. This also gives improved performance in vacuum applications.


At SMB we take lubricant selection very seriously & all our bearings come lubricated as standard with high quality lubrication. We can also assist with specialist lubrication requirements, using our on-site re-lubrication facilities - to handle everything from food safe applications to low torque conditions. We regularly supply our bearings or the customers' own bearings with:
  • dampening greases 
  • dry lubricants 
  • food safe greases 
  • high temperature lubricants 
  • low temperature lubricants 
  • low torque lubricants 
  • molybdenum disulphide coating 
  • perfluorinated lubricants 
  • radiation-resistant lubricants 
  • vacuum lubricants 
  • waterproof greases
Please contact us if you'd like any more information about the re-lubrication of your bearings.
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