4.10 Grease Classification

Today s grease is petroleum or synthetic oil based, and consists of a chemical soap thickening agent dispersed within the liquid lubricant to make it semi-solid A good analogy for grease would be a sponge soaked in oil. The word grease itself is derived from the Latin word crassus which means fat. Grease relies on pressure to move it around and although it is termed semi-solid, it can range from very fluid to brick hard.

Unlike oil, grease is lucky to have a single standard grading system named the NLGI (National Lubricating Grease Institute) grading system. The corresponding number identifies the grease s consis tency. To test for consistency, the ASTM D217 core test is used in which a special cone is dropped into the grease from a specified height, at a temperature of 25 C (77 F), and its depth of penetration is measured in 0.1mm increments as shown in Figure 4.10a. Most industrial applications will utilize an NLGI number one or number two grade grease. Figure 4.10b shows that an NLGI #1 rated grease is very soft in appearance and feel.

Figure 4.10a: ASTM D-217 Cone Test for Grease

Note: Centralized grease lubrication delivery systems are only rated for NLGI #1 and less. Always check with the delivery system supplier and lubricant supplier for compatibility.