Grease or lubricant definition
In order to maximize the number of bearing running hours, it is most important to use good quality grease. Below information shows the main points in choosing the right grease.
WORKED PENETRATION AND NLGI NUMBER
The Worked penetration and NLGI number (sometimes called “NLGI grade”) expresses a measure of stiffness or relative hardness of a grease used for lubrication.
ASTM worked penetration
(60 strokes at 25 °C)NLGI numberAppearance“Thickness” consistency food analogy
| 445-475 | 000 | fluid | cooking oil |
| 400-430 | 00 | semi-fluid | apple sauce |
| 355-385 | 0 | very soft | brown mustard |
| 310-340 | 1 | soft | tomato paste |
| 265-295 | 2 | “normal” grease | peanut butter |
| 220-250 | 3 | firm | vegetable shortening |
| 175-250 | 4 | very firm | frozen yoghurt |
| 130-160 | 5 | hard | smooth pate |
| 85-115 | 6 | very hard | cheddar cheese |
A high value for the worked penetration (or low NLGI number) means the grease is more fluid and will easier run from the bearings. For a grab “normal grease” is recommended.
DROPPING POINT
The dropping point of lubricating grease is the temperature at which it passes from a semi-solid to a liquid state. It is an indication of the type of thickener used, and a measure of the cohesiveness of the oil and thickener of grease. The dropping point has limited significance for performance of the grease as it is always far above the high temperature performance limit (HTPL).
WATER RESISTANCE
The water resistance of a grease indicates the change in the grease after contact with water and is reported as a value between 0 (no change) and 3 (major change).
EMCOR RUST TEST
The purpose of the Emcor rust test is to measure the ability of grease to protect a bearing against corrosion even in the presence of water. During the Emcor test, bearings are lubricated with a mixture of grease and distilled water. At the end of the test, a value between 0 (no corrosion) and 5 (very severe corrosion) is given.