GREASE BASES USED IN THE MANUFACTURE OF LUBRICANTS
A lubricating grease is defined as a solid or semiliquid product representing a dispersion of a thickener in a liquid lubricant. Grease is used where it is required to hold the lubricating oil and appropriate additives together to lubricate those applications where an oil cannot be contained. Most greases are made in large kettles by mixing oils with various types of base materials called "soaps". While "mineral oil base" greases are predominant, synthetic oil base greases are made for many severe or exotic applications.
As grease is used, the oils in the greases are gradually degraded by temperature and pressure in the work piece being lubricated. This process will continue until the oil becomes carbonized, unless fresh lubricant is applied periodically. As the oil oxidizes in service, it becomes a contaminant and mixes with the collapsing and degrading base to become "Used grease", which will be extruded regularly as fresh grease is added to the bearing.
Sometimes synthetic greases are required. They are generally made with synthetic fluids rather than petroleum. They are affected in service in many of the same ways as are greases made from petroleum oils. Advantages of synthetic greases include high and/or low temperature capabilities and longer service life. The extent of these capabilities depends largely on the type of synthetic base fluid, thickener type and additive formulation. These lubricants are generally used for exotic or extreme type applications.
AUTOMOVE GREASE SOAP TYPE
Calcium-A hydrated lime, alkaline-type material used as a soap base makes a water repellent grease of smooth, buttery texture and is excellent for use under heavy churning action and around wet or highly humid environments up to around 175°F. (79°C.) operating temperatures. Mineral oils thickened with calcium soap or "cup greases" constituted the first type of lubricating grease produced in any volume. They were the only products available for years. Although they continue to be relatively popular, they are being replaced by newer products.
Sodium base greases are fibrous and have a fairly high melting point suitable for antifriction bearings and other high speed centrifugal-operating conditions. It is an extremely good type of grease for use in heavy-duty applications taking shock-loading and pounding. Although sensitive to water, they have found their own niche. They can be used in dry conditions at temperatures 100°F. (38°C.) above the calcium base greases and are often more shear stable than the aluminum sterate and calcium soap greases. Sodium grease have been replaced by greases which are more water resistant and have equal or better heat resistance.
Lithium 12-Hydroxystearate - The latest and best of the simple soap based greases to evolve were the lithium-more specifically, lithium 12-hydroxystearate. These greases combine the heat resistance of sodium soap greases with the water resistance of calcium soap greases. They also display excellent mechanical stability and low temperature pumpability.
Most of the grease requirement in automobile segment varies from NLGI-2 to NLGI-3 consistency for Anti Friction Bearings and NLGI-1 for Chassis lubrication due to pumpability to hard to reach and lubricated place.