Types Of Greases
Lithium, Calcium, Soda, Aluminium, Complex and Mixed soap base Greases, Soap free Grease, PTFE, Silicone and Molybdenum modified Greases, Specialty and Synthetic Greases.
The original Definition of ASTM of Grease was "A” solid or semi solid combination of petroleum products and a soap or mixtures of soaps with or without fillers, suitable for certain types of lubrication.
Subsequent technological advances have led to the use of synthetic lubricating fluids on the one hand and non-soap thickener’s on the other hand.
Current - Modified Definition of Grease is "A solid or semi solid product of dispersion of thickening agent in liquid lubricant. Other ingredients imparting special properties may be included”. Most greases are in fact is a combination of petroleum oils and metallic soaps.
Grease is a lubricant of higher initial viscosity than oil, consisting originally of a calcium, sodium or lithium soap jelly emulsified with mineral oil.
Greases are typically used in areas where a continuous supply of oil cannot be retained, such as open bearings or gears.
Grease is a fine dispersion of an oil-insoluble thickening agent - usually soap in a fluid lubricant which is generally mineral lubricating oil. The soap is made up of fatty acid, tallow or vegetable oil saponified with alkali which can be hydrated lime, caustic soda, lithium hydroxide or aluminum hydroxide. The lubricating oil component is refined base oil-naphthenic, of medium viscosity index, or cylinder oil stock. Structurally grease is a “water-in-oil” emulsion. Its appearance is smooth, mostly translucent, soft or hard.
Properties essential for performance of grease are structural stability, lubricating quality, low and high temperature performance (which are provided by the selected lube oil base stock), where as properties such as water resistance, high temperature quality, resistance to break down through continuous use and ability of grease to stay in place are provided by the soap.
Additives e.g. Graphite, modified clay, asphalt, oxidation and corrosion inhibitors, extreme pressure additives molybdenum disulphide etc. are used to impart specific properties as required by end application.
Factors to be considered when selecting greases are the type of grease, which in turn depends on operating temperatures, water resistance, oxidation stability etc. The second factor, no less important, are the grease's characteristics, including viscosity and consistency.
Basic Types Of Grease
SOAP TYPES GREASES
Metallic soaps + Lubricating Oils + Additives for imparting Special properties
NON SOAP THICKNER GREASES
Thickening Agent + Lubricating Fluid (Synthetic oils) + Additives for imparting Special properties
The value of plastic lubricants has been recognized since very early times when animal fats were used for Axles and the like. In general any lubricating fluid can be gelled by means of a suitable thickness to form a lubricating Grease. In practice mineral oils are almost exclusively used. For soap type Greases mineral oils of relatively low viscosity index 60 are preferred since the greater solvency of the more aromatic oils for soaps makes manufacture easier and gives greases with lower soap contents and with better properties.