Grease & Speciality Greases
Grease is a semisolid lubricant obtained by thickening lubricating oil with the addition of a metallic soap. It is used where the temperature and the speeds are not high and in sealing arrangements where oil does not offer satisfactory results. Grease consists of a dispersion of soap in lubricating oil. By varying the quantity and quality of soap, oil and additives, it is possible to produce greases for a wide variety of applications. Hence grease is manufactured by the combination of three components: oil, thickener and additive.
Generally, mineral oil is used for the manufacture of grease in industries. The viscosity of oil used depends upon the application of grease. Synthetic oil is used as base oil when grease is used for high temperature applications
(b) Thickener
The thickener, such as metallic soap, is used in the grease. Most commonly used metallic soaps are calcium, sodium and lithium.
(I) calcium GreaseThese greases do not dissolve in water but cannot be used at a temperature above 60 °C. These greases also provide a protection against salt water.
(ii) Sodium GreaseThese are not water-resistant as these are soluble in water and can be used at a temperature above 150 °C.
(iii) Lithium GreaseTheir ability is to adhere to metal, and their stability at high temperature is excellent. These greases are used in wet conditions where the temperature is too high for calcium grease.
(iv) Synthetic-based GreaseThese consist of synthetic lubricating oil such as polymer alpha-olefins, ester and silicon. They do not oxidise as rapidly as the mineral oils to which the various thickeners such as lithium soap are added. These greases are often used where the temperature is -7 °C.
These are added to the grease to improve the properties like
Oxidation.
rust inhibitors.
pour-point depressants.
extreme pressure additives.
Antiwear additives, etc.
molybdenum disulphide and graphite may also.
be added to grease to improve the load-carrying capacity.