Basic Composition of Lubricating Grease

Basic Composition of Lubricating Grease

Lubricating grease primarily consists of three components: a thickener, base oil, and additives. Typically, grease contains approximately 10%–20% thickener, 75%–90% base oil, and less than 5% additives and fillers.

1. Base Oil

Base oil acts as the dispersion medium within the grease structure and significantly influences its performance. Most greases use medium- to high-viscosity petroleum oils as base oils. To meet the demands of harsh operating conditions—such as extreme temperatures or heavy loads—synthetic oils like esters, silicones, and polyalphaolefins (PAOs) may also be used.

2. Thickener

The thickener is a critical component that forms the structural framework of the grease, holding the base oil in place. It largely determines the grease's water resistance and temperature tolerance. Thickeners fall into two main categories: soap-based (metal salts of fatty acids) and non-soap-based (hydrocarbons, inorganic compounds, or organic materials).

Soap-based thickeners are further classified into simple soaps (e.g., calcium soap), mixed soaps (e.g., calcium-sodium soap), and complex soaps (e.g., complex calcium soap). Approximately 90% of greases are produced using soap-based thickeners.

3. Additives and Fillers

Certain additives are unique to grease formulation. These include structure stabilizers (such as glycerin or water), which enhance the stability of the thickener-base oil mixture. For example, water is essential in calcium-based grease—without it, the structure breaks down and the grease cannot form. Glycerin, used in sodium-based grease, helps adjust consistency.

Other additives are similar to those used in lubricating oils, such as antioxidants, anti-wear agents, and rust inhibitors, though they are often used in higher proportions in greases. Examples include phosphate esters, ZDDP, Elco extreme pressure additives, composite additives, and dropping point improvers.

Additionally, fillers like graphite, molybdenum disulfide, or carbon black may be incorporated to improve adhesion, enhance load-carrying capacity, and reinforce lubrication performance.