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Lubricating Grease

Grease is a semi-solid lubricant consisting of a base oil and a thickener.
It should be remembered that different brands of the same type of grease may have different properties.

(1)  Base Oil
Mineral oils or synthetic oils such as silicone or diester oil are mainly used as the base oil for grease.
The lubricating properties of grease depend mainly on the characteristics of its base oil. Therefore, the viscosity of the base oil is just as important when selecting grease as when selecting an oil. Usually, grease made with low viscosity base oils is more suitable for high speeds and low temperatures, while greases made with high viscosity base oils are more suited for high temperatures and heavy loads.However, the thickener also influences the lubricating properties of grease; therefore, the selection criteria for grease is not the same as for lubricating oil.

(2)  Thickener
As thickeners for lubricating grease, there are several types of metallic soaps, inorganic thickeners such as silica gel and bentonite, and heat resisting organic thickeners such as polyurea and fluoric compounds. The type of thickener is closely related to the grease dropping point (1); generally, grease with a high dropping point also has a high temperature capability during operation. However, this type of grease does not have a high working temperature unless the base oil is heat-resistant. The highest possible working temperature for grease should be determined considering the heat resistance of the base oil.

The water resistance of grease depends upon the type of thickener. Sodium soap grease or compound grease containing sodium soap emulsifies when exposed to water or high humidity, and therefore, cannot be used where moisture is prevalent.
 

(3)  Additives
Grease often contains various additives such as antioxidants, corrosion inhibitors, and  extreme pressure additives to give it special properties. It is recommended that extreme pressure additives be used in heavy load applications. For long use without replenishment, an antioxidant should be added.

(4)  Consistency
 Consistency indicates the"softness"of grease. The relation between consistency and working conditions.

(5)  Mixing Different Types of Grease
In general, different brands of grease must not be mixed. Mixing grease with different types  of thickneners may destroy its composition and physical properties.
Even if the thickeners are of the same type, possible differences in the additive may cause detrimental effects.