The chemical reaction of fatty acids, fats or esters with an alkali metal to form the metallic salt. This salt is commonly called soap.
A form of wear that resembles scratches along the direction of motion of sliding surfaces. Causes include contaminated or insufficient lubrication, excessive loads, vibration and lack of anti-wear or extreme pressure additives in lubricant.
A form of wear that resembles a dull or matte area on sliding surfaces. Causes include contaminated or insufficient lubrication, excessive loads, vibration and lack of anti-wear or extreme pressure additives in lubricant.
A type of damage that occurs when rolling surfaces overheat suddenly or rapidly, and metal surfaces such as bearings and raceways soften, melt and deform. Causes include inadequate or contaminated lubrication, excessive speed or load, and inadequate clearances
In manufacture of a lubricating grease, the change from a fluid to a semi-fluid or plastic state.
The word â€œSETTâ€ is uniquely applied to a particular type of product, i.e., Cold Sett greases, which change from a fluid to a semi-fluid or plastic state after component combination and often after packaging.
The rate of a slip within a substance engaging in flow. The average or mean shear rate in a pipe or tube is proportional to the average velocity divided by the radius of the tube. It, therefore, has the dimensions of the reciprocal of the time and is usually expressed in the unit of reciprocal seconds (sec-1). The mean shear rate is reported in the determination of apparent viscosity in ASTM D1092.
The ability of a lubricating grease to resist changes in consistency (hardness) during mechanical working. Working may be in any of several types of laboratory machines or may be in actual service. This may also be called Mechanical Stability.
The force per unit area tending to cause shearing in a substance. In fluids, the ratio of the shear stress to the shear rate is the viscosity of the substance.
Slipping or sliding of one part of a substance relative to an adjacent part. In a solid, such action involves cutting or breaking of the crystal structure, but in a fluid or plastic, shearing does not necessarily destroy the continuous nature of the substance.
Simple soaps are grease thickeners that are prepared by reacting a single organic acid with one or more inorganic bases. Complex soaps are prepared from two or more organic acids.
See Thickener; Complex Soap; Saponification.
See Soap Thickener
Many greases are prepared by reacting organic acid(s) and inorganic base(s) in base fluid to form salt crystals. These crystals are partially soluble in base fluid and form colloidal particles or fibers dispersed in the fluid. These particles or fibers are responsible for the semi-solid consistency of grease, and they are referred to as soap thickeners.
A suspension of particles of colloidal dimensions in a liquid. These systems possess the gross properties of a liquid.
That state of lubrication in which surfaces thickly coated or flooded with lubricant move toward each other at sufficient speed to develop fluid pressure sufficient to support a load of short duration. Because of viscosity (or apparent viscosity), the lubricant cannot immediately flow away from the area of contact. This action occurs, for example, between gear teeth and between wrist pins and their bushings.
A fluid is described as undergoing steady-state flow when its properties at any given point are unchanging, which is the case during laminar flow.
In general, a stearate is a salt or ester of stearic acid. Stearic acid is a fatty acid with chemical formula C18H36O2 or CH3-[CH2]16-COOH. Stearate greases are made by reacting stearic acid with an inorganic base to form a salt, i.e., soap thickener.
Loss of liquid lubricant from a lubricating grease due to shrinkage or rearrangement of the structure. The shrinkage may be due to either physical or chemical changes in the thickener. Syneresis is a form of oil separation.
A grease composition in which the liquid lubricant is other than mineral or vegetable oil.