Why measure the oil separation of greases? What are the test methods for determining the oil separation of greases? What is the difference?

Grease is made from base oil thickened by thickeners such as soaps, organic or inorganic substances. The solubility of various thickeners in base oil is very small, so the thickener is suspended in the base oil in a colloidal state. Among them, its properties are similar to emulsions or suspensions. When external conditions such as ambient temperature, acceleration of gravity and pressure change, or even if the grease is placed for a long time, the original stability of the grease colloidal structure will be destroyed, and the thickener with a specific gravity greater than the base oil will precipitate from the base oil. Therefore, the measurement results of grease oil separation can be used as the basis for judging the stability of the colloidal structure of grease under certain conditions.

According to the different test conditions, the determination methods of grease separation can be divided into pressure separation, storage separation, centrifugal separation and steel mesh separation, etc., as shown in the following table: