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Lithium complex greases possess many of the properties of simple lithium soap greases and also have higher dropping points, allowing the greases to be used at higher temperatures.

According to the 2012 NLGI Grease Production Survey, 58% of the grease produced worldwide is based on either simple lithium soap and 19% on lithium complex thickener. You might ask, “Why are those thickener types so popular?” and “How do I decide which one is best for my application?” This article will provide answers to these and a few other questions.

Lithium complex greases were developed in the late 1940s. U.S. Patent 2,417,428 was granted to Lester W. McClennan on March 18, 1947. This is one of the first patents to describe complex soap greases. However, it wasn’t until the early 1980s that lithium complex greases entered the market in large volumes and started to displace the simple lithium soap greases that had been the mainstay of the industry since the 1950s.

1. The dropping point of lithium complex greases is higher than that of simple lithium soap greasesand is above 260°C due to the presence of a second thickener component, known as the complexing agent. Modern lithium complex greases typically use a shorter chain-length difunctional carboxylic acid, such as azelaic acid or adipic acid. The lithium salt of these materials is typically present in a significantly lower proportion compared to the simple lithium soap thickener. An alternate material used as a complexing agent is boric acid. The use of this material also results in an elevated dropping point.

 

1. Table

Properties of Lithium and Lithium Complex Greases

   

Lithium Complex grease MC-BLUE 1510

2. Mechanical stability, also known as shear stability, is the ability of grease to maintain consistency when subjected to mechanical shear forces. Simple lithium greases have good resistance to breakdown due to shear, and lithium complex greases also exhibit good resistance to shear. This property makes both simple lithium and lithium complex greases popular for use in a wide range of applications.

3. The water resistance of simple lithium and lithium complex greases is related to the solubility of the thickener. Lithium hydroxide has limited solubility in water (about 10 percent), and the thickeners based on it also have limited solubility. This provides good resistance to both washing by water and the absorption of water.

4. The oil separation properties of a grease relate to both the product’s lubrication ability and storage stability. The grease must release enough oil in the contact zone of the application (bearings, gears), while not releasing so much oil during storage to cause the product to become unusable. If the oil separates excessively during storage, the grease may not be able to be remixed and used.