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Lubricant Classroom-Glossary of Lubricant


Viscosity is the major property of lubricant. The measure of inner friction of flow of fluid is called viscosity. Viscosity is decreased along with the rise of temperature. The light body or heavy body of fluid as called generally refers to high or low of viscosity. The strength of film of lubricant is roughly proportional to viscosity. The higher the viscosity is the stronger the lubricant film. So, viscosity is one of the most important factors must be considered in selecting correct lubricant for machinery. In recent years, with the promotion of metric system, most of them have been changed to kinetic viscosity of dynamic viscosity

Dynamic Viscosity

This is a measure of inner friction when a fluid is flowing under a specific shearing stress, and the value is the ratio between shearing stress and shearing speed. In the statute measuring unit of ROC, it is Pa * s and the unit frequently used is Cp and iCp=10-3Pa*s

Kinetic Viscosity

This is a measure of inner friction of fluid flowing under effect of gravity and the value is the ratio between dynamic viscosity and the concentration under same temperature. In our statutory measuring unit, it is m2/s and it is frequently in cst and 1 cst =imm2/s

● Flash point

Flash point is the minimum level of temperature that a combustible liquid or evaporating solid combustible substance is heated to that temperature and the vapor mixed with air would flash when there is fire source is approaching.

● Pour point

Also known as flow point is that under certain conditions, when a fluid cooled to certain temperature will lose its fluidity. Flow point of lubricant is better be 10℉(5℃)below the lowest ambient temperature in winter time.

Specific Gravity

The Specific Gravity (SG) of a lubricant is usually used to calculate the mass and weight of it. The specific gravity of the fluid changes with temperature, when temperature is high, the fluid would expand and the mass becomes bigger but not the weight, and specific gravity is become smaller.