The National Lubricating Grease Institute, NLGI defines lubricating grease as: "A solid to semi-fluid dispersion of a thickening agent (thickener) in a liquid lubricant. Additives imparting special properties maybe included". Lubricating grease is a mixture of three main components: lubricating fluid, thickener, and performance inhancing additives.

Some people thought the thickener is the main lubricating part of the grease, but oil is main actually. Oil (mainly) play lubricant role, thickener like "a structure" to "holds the oil in the place". This is most commonly described as "the sponge that holds the base oil plus additives". Understanding of the grease basics thoroughly will help us study about grease more easily, which factors will impact on quality? How impact? Which properties must be considered when choosing grease suitable for specific machinery, for specific production?

A. COMPONENTS OF LUBRICATING GREASE

I. Base oil

Almost base oil is mineral or synthetic oil

II. Thickener

Thickener classified into two major families: soap and non-soap. Soap geases are more widespread.

1. There are thress types of soap-based thickeners:

• Simple soap: from the reaction of one fatty acid and a metallic hydroxide
• Mixed soap (less common): from the reaction of a fatty acid with two metallic hydroxides
• Complex soap: from reaction of blend of a fatty acid and a short chain complexing acid with metallic hydroxide.

2. Non-soap includes: bentonite, Polyurea, silica, Polytetrafluoroethylene (PTFE’s), ...

III. Additives

Additives for enhancing properties of grease such as: antioxidant, rust inhibitor, antiwear, friction-reducing , extreme pressure, extreme spead, high-load, water resistance,...

B. CLASSIFICATION BY PENETRATION

Besides classification by type of thickenner, grease can be classified by consistency, penetration. The National Lubricating Grease Institute categorize grease into NLGI grade from 000 to 6:

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