What Is Lithium Grease?
Lithium grease is a soap-based lubricant made by dispersing lithium salt of lithium stearate or hardened fatty acid of castor oil in raw base oil as a thickening agent.
In the past, calcium grease (water resistance) and sodium grease (heat resistance) were used separately. Still, since the development of lithium grease in 1938, which has excellent water and heat resistance, it has been used in many fields as an all-purpose grease.
Lithium grease can be compared to aluminum complex grease and non-soap-based urea grease, developed for use under high-temperature conditions.
Uses of Lithium Grease
Not limited to lithium grease, grease is used to smoothly lubricate bearings and prevent wear in automobiles, home appliances, and machine tools.
Lithium grease is also called “universal grease,” since it is used for general purposes, it is widely available at home centers. Although lithium grease is versatile, it is necessary to select the appropriate grease by checking its heat resistance temperature, water resistance, strength, shear stability, and other properties. In addition, care must be taken when mixing with different types of grease, as mixing with other types of grease may result in reduced performance.
Manufacturing Method of Lithium Grease
Dissolve the thickener in the base oil and add an alkaline solution. The thickener is generally 5-20% of the base oil. Heating and stirring the solution causes a saponification reaction, resulting in soap formation. As soon as the soap is formed, it forms a three-dimensional network structure (micelle structure) and takes in the base oil. The form is a semi-solid shape characteristic of grease.
Then, necessary additives such as molybdenum are mixed, and the length and thickness of the soap fibers are aligned and smoothed in the milling process. Finally, air bubbles in the lithium grease are removed, and foreign matter is removed through a filter before filling the can to completion.
Characteristics of Lithium Grease
The heat resistance temperature of lithium grease is approximately 130°C. It has excellent water resistance and mechanical stability, which are inferior to non-soap-based urea grease. However, some urea greases harden or soften under high temperatures or shear, requiring careful selection, so lithium grease is generally used unless the application is unique. Another characteristic of lithium complex grease is that it is suitable for use at a wide range of rotational speeds, from low to high.
Other Information about Lithium Complex Grease
- Lithium Complex Grease
Lithium complex grease is a lithium grease with improved heat resistance. Lithium complex grease is a grease that uses complex lithium soap, a soap made by reacting lithium hydroxide with fatty acids and dibasic acids, as a thickening agent.
Compared to lithium grease, it has improved heat resistance, and other performances are at the same level. In terms of heat resistance, the performance is close to urea grease. In some applications, the lubricating performance is superior to urea grease.
In Japan, urea grease is the second most widely produced grease after lithium grease, but in some regions overseas, lithium complex grease is the second most commonly made grease. If you need better performance than lithium grease, you should consider both lithium complex grease and urea grease as candidates.
- Differences in Properties of Lithium Grease Depending on Base Oil
Lithium grease derives from the thickening agent, but its properties vary depending on the base oil (base oil). The types of base oils can be broadly classified into mineral oil, synthetic oil, ether, and fluorine-based oils. Synthetic oils generally include diester oil, silicone oil, polyglycol oil, hydrocarbon oil, and silicone oil. Here is an example of a base oil for lithium grease commonly used in bearings.
- Mineral Oil Mineral oil is the most common base oil. It is widely distributed because it is inexpensive, and many retailers carry mineral oil-based lithium grease. Lubricating performance is standard, and its heat resistance and oxidation stability are inferior to synthetic oils. Aggressiveness to rubber and resins is at a slightly acceptable level.
- Ester Oil Ester oils have superior lubricity, heat resistance, and low-temperature properties compared to mineral oils. Therefore, ester-based lithium grease is suitable for high-speed operation over a wide temperature range. It is necessary to check the materials of oil seals and other parts around the point of use because of their high aggressiveness to rubber and resin.
- Silicone Oil Lithium grease based on silicone oil is more resistant to higher and lower temperatures than ester oil-based lithium grease. Therefore, it can be used in a broader temperature range. It is less aggressive to rubber and resins and has less impact on the surrounding area where it is used. However, it cannot be used under high loads due to its low steel-to-steel boundary lubricity.