Grease was first used on chariot axles more than 3,000 years ago. Today more than 80% of bearings are lubricated with grease. Lithium soap greases, the most prevalent, were introduced in the early 1940s. Lithium complex greases, introduced in the 1960s, are becoming the most prevalent in North America.

A soap is, by definition, a metal salt of a fatty acid. The National Lubricating Grease Institute defines grease as, “a solid to semi-solid product of dispersion of a thickening agent in a liquid lubricant. Additives imparting special properties may be included.”

Grease-making is a relatively simple time-temperature process: a one-pot batch method. For soap grease, fatty acids are added; if it is non-soap, the other constituents are put into base oil. Common acids include high-molecular-weight fatty acids, stearic acid 12-hydroxystearic acid, and short-chain complexing acids such as tallow, azelaic acid, and sebacic acid. Once the acid gets up to temperature (i.e., the fatty acid melts) the metal base is added. The process is called sa

It is a highly versatile, multipurpose grease invented in the 1940s. The product consists of mineral or synthetic oil and hardened castor oil fatty acids called lithium stearate or lithium salt. Lithium soap-based grease:

• Has a wide temperature range
• Is very mechanically stable
• Has a high water resistance

In almost all industrial sectors, it is the most preferred bearing grease.

Benefits of a Lithium Soap-Based Grease

Lithium soap is the thickener that turns the base oil into grease. So, it is best to compare lithium soap-based grease to those using other thickeners, such as sodium and calcium soap thickeners. In most cases, lithium soap-based greases offer so many advantages that the additional cost is easily offset by increased performance.

A few of its benefits include:

• A high dropping point of 190-200°C (374-392°F)
• Depending on the base oil, a good low-temperature function
• Perfect for almost all types of bearings
• Highly water-resistant
• A high degree of shear stability
• Exceptional thermal stability
• Long-term storage stability
• A long useful life
• Pumpable
• Smooth structure
• Available as an extreme pressure (EP) grease, which adds high load and anti-wear abilities.

The Disadvantages of Lithium Grease

While lithium soap-based grease has a long list of benefits, it also has a few disadvantages, including:

• Due to its high production and raw material costs, lithium grease is more expensive than other greases.
• The dropping point of 190-200°C (374-392°F) is not high enough for several high-temperature applications.
• It has lower adhesion properties, so it is not suitable for sliding or reciprocating applications.
• Calcium greases have a higher water resistance than lithium grease.
• Anticorrosion additives are specifically needed.

Lithium vs. Lithium Complex Grease

Simple lithium soap-based greases had been the mainstay of the industry until lithium complex greases became popular in the early 1980s. Compared to lithium soap-based grease, lithium complex grease is more resistant to heat, water, and rust. Since lithium complex greases contain a second thickener component, the complexing agent, the dropping point is higher than that of simple lithium soap greases. Moreover, this higher dropping point than simple lithium soap-based greases, allows you to use lithium complex grease at higher temperatures.

Property Lithium Soap-Based Grease Lithium Complex Grease

Dropping Point 385°F / 195°C 500°F / 260°C

Oil Separation Resistance Good Excellent

Mechanical Stability Good Excellent

Water Resistance Good Excellent

Mechanical Stability

The first major characteristic is mechanical stability, or shear stability, which is the ability of the grease to remain consistent under mechanical shear forces. Both lithium soap-based grease and lithium complex grease exhibit good shear resistance. This makes them an excellent choice for a variety of applications.

Water Resistance

The solubility of the thickener determines the water resistance of lithium complex and simple greases. Water is still soluble in lithium hydroxide, but only in small amounts. So, lithium hydroxide-based thickeners have the same properties. As a result, it is resistant to both the absorption of water and washing by water. Other thickeners such as calcium and barium are more water resistant than lithium and lithium complex thickeners, but their negative qualities make them less desirable in a wide variety of applications. Furthermore, small amounts of polymer additives can be added to lithium complex and lithium soap-based greases to improve their water resistance.

Oil Separation

Lubricating ability and storage stability are both influenced by the oil separation properties of grease. For grease to be helpful, it must release enough oil in the contact zone on bearings or gears. However, it shouldn’t remove too much oil during storage. Over time, if the oil separates too much in storage, it may be impossible for the grease to be reconstituted for use.

The Best Applications for Lithium Soap-Based Grease

Lithium soap-based grease is such a multipurpose grease that you can use it for many applications. Here are a few of the suitable uses:

• Industrial, automotive, and marine use
• Suitable for use at temperatures up to 130°C (266°F)
• Low, medium, and high-speed bearing grease
• Bearings with plain or rolling elements
• Gear lubrication for open and enclosed gears
• Automobile chassis lubrication
• A variety of industrial equipment including agricultural, mining, construction machinery, pumps, conveyors, elevators, chains, pulleys, cranes, shafts, wire ropes, and automotive applications require good thermal stability and water resistance.

How to Choose the Right Lithium Soap-Based Grease

There are many factors to consider when choosing lithium soap-based grease. They perform well in a wide range of applications due to their versatility. But, what is the best option for your application? Lithium complex greases are commonly used as general-purpose lubricants, and that’s a good approach since they have a higher temperature range. However, simple lithium soap-based greases are often the most economical choice for specific applications. At the end of the day, the most important thing is to select the right grease for the application. Temperature, environment, and type of equipment all need to be considered when making a selection.

pontification or soap making. So basically acid + base = soap + water.

Then, because there needs to be very little water in lubricants, all the water is removed. Once that is done, the material is cooled and gelled—this is the point where the mixture becomes a grease. Next, the mixture is adjusted for consistency by adding base oil (additives might be added, as well). It may have to be reheated, cooled, and tested several times to get the consistency that is required for the product. Most people think grease is primarily thickener, but in actuality, it is mostly oil. Soap concentration in oil is typically 10%-20%.