Bearing Grease - High Temperature Greases & Lubricants

Grease is defined as a semi-solid lubricant, however it also is used to describe rendered fat of animals. In the context of lubrication however, the term grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil.

The characteristic feature of all greases, the one that makes them so useful, is that they possess a high initial viscosity, which upon application provides the necessary lubrication to the bearing etc.

The main application for greases are for mechanisms which can only be lubricated infrequently and where a normal lubricating oil would not stay in place.

Another advantage / use for grease is that they also act as a sealant, thus preventing ingress of water etc.

The Properties of Greases

A true grease consists of a base oil and/or other fluid lubricant that then mixed with a thickener, normally a soap, to form a solid. Here the term soap is used in the chemical sense (nothing like a household soap at all) [a metallic salt of a fatty acid, which forms an emulsion with the base oil] .

Greases are a member of the family ' shear-thinning or pseudo-plastic fluids'. All of this group demonstrate a viscosity that is reduced under the pressure of shear.

To explain, once a sufficient force to shear the grease has been applied, the viscosity drops and approaches that of the base oil lubricant. Grease is often applied using a 'grease gun', the pressure used in the application allowing the grease to become viscous enough to force the solid grease into the spaces in the part.

Types of Greases

There are many types of greases available, the properties of which varying greatly depending on the additives and the base oil. Grease is also known by its colour, there being:-

• White Grease
• Red Grease
• as well as named and application types
• Moly Grease
• High Temperature Grease

Additives in Grease

Bearing and Gear greases most often consist of rosin oil, thickened with lime and mixed with mineral oil, with a varying amount of water.

Other special purpose greases use glycerol and sorbitan esters. These are used in low-temperature conditions, while others, labeled "EP", (Extreme Pressure) are used where high pressures or shock loadings are anticipated.

EP grease most often contains a solid lubricant, usually graphite and/or molybdenum disulfide, this being required to provide protection under heavy loadings. These solid lubricants actually bond to the surface of the metal, thus preventing damaging metal-to-metal contact.

As you can see there is a lot to the selection of the right greases and we would advise that if you are unsure in this matter that you contact us so that our experts can ensure that you make the right choice of oil.