Defining Industrial Lubricant Stiffness
In industrial and automotive lubrication, grease is used when liquid oils won't stay in place. However, not all greases are created equal. Some flow like a syrup, while others are as hard as a bar of soap. The **National Lubricating Grease Institute (NLGI)** established a consistency numbering system to quantify this physical property.
The Penetration Test
To determine a grease grade, a sample is placed in a grease worker machine. A standard cone (typically 102.5 grams) is allowed to drop into the grease for exactly 5 seconds at 25°C. The depth of the penetration is measured in tenths of a millimeter. A higher penetration value means the grease is softer, resulting in a lower NLGI number.
NLGI 2: The Universal Standard
Approximately 90% of the world's lubricant applications utilize **NLGI 2** grease. It has a physical consistency similar to peanut butter or lard. It is ideal for roller bearings because it provides enough stiffness to stay in the casing while being soft enough to be distributed by the rolling elements within the bearing.
NLGI Grease Grade Reference Table
| NLGI Number | Worked Penetration (0.1mm) | Consistency Like... |
|---|---|---|
| 000 | 445 - 475 | Cooking Oil / Syrup |
| 0 | 355 - 385 | Brown Mustard |
| 2 | 265 - 295 | Peanut Butter |
| 4 | 175 - 205 | Ice Cream |
| 6 | 85 - 115 | Bar of Soap |
Related Science Utilities
Frequently Asked Questions
What is an NLGI grade?
An NLGI grade is a measure of the relative hardness of a grease. It is based on a "penetration value" determined by allowing a standard cone to drop into the grease at 25°C.
What is the most common grease grade?
NLGI 2 is the "standard" multi-purpose grease, with a consistency similar to peanut butter. It accounts for the vast majority of grease applications.
What happens if I use the wrong grease grade?
If a grease is too thin, it may leak out of the bearing. If it is too thick, it may not flow into the load zone, resulting in heat buildup and premature wear.