What Is an Extreme Pressure Grease?
An extreme pressure grease is a grease that has excellent high-load lubricating, metal surface protection, and friction resistance performance. It also has a sealing performance, such as water resistance and adhesion. It is intended to lubricate and protect parts such as high-rotation bearings, metal sliding parts under high loads and high speeds, and gears under high loads.
Although it is necessary to further reduce viscosity to reduce clay resistance, viscosity is a general value in order to maintain the adhesion and sealing properties originally required for grease. Clay resistance can be freely adjusted by additives.
Uses of Extreme Pressure Greases
Extreme Pressure Grease is used to withstand conditions that exceed the normal lubricating capacity of the base oil. Examples of such extreme pressure conditions include gear galling, impacts that exceed the lubrication capacity of the base oil, and the presence of foreign matter such as sand. For this reason, they are used in the following applications:
1. Automobile Wheel Bearings
Automobile wheels are subjected to strong rotating forces. Extreme Pressure Grease plays a key role in reducing friction in this area and helping smooth rotation.
2. Machine Tool Gears
Machine tool gears are subject to high forces and cannot be adequately lubricated with ordinary grease. Extreme Pressure Grease is used to extend the life of gears and ensure efficient operation.
3. Agricultural Machinery
Agricultural machinery is used in an environment where dirt, sand, and other foreign matter can easily enter, so normal grease tends to degrade lubrication effectiveness. Extreme Pressure Grease maintains lubricating performance even under such severe conditions.
Principle of Extreme Pressure Greases
Unlike ordinary grease, Extreme Pressure Grease contains special ingredients called Extreme Pressure Additives. The lubrication range under normal conditions depends on the performance of the base oil and thickener. However, when extreme pressure occurs, there must be an intervening lubricant.
The inclusion of Extreme Pressure Additives provides high lubricating performance when extreme pressure occurs. Extreme Pressure Additives reduce friction by creating a thin protective film on the metal surface. When high pressure is applied, this protective film chemically reacts with the metal surface to form an even stronger film. This is the reason why Extreme Pressure Grease can maintain its lubricating effect even in areas subjected to high pressure.
Extreme pressure is the frictional resistance applied to a point or line of contact. Normal lubricant film becomes thinner as the load increases, causing metal-to-metal contact and increased wear and friction, resulting in seizure. The use of extreme pressure additives avoids seizure and makes it possible to maintain the thickness of the oil film.
Types of Extreme Pressure Grease
Extreme Pressure Grease is mainly classified into the following types. The characteristics differ depending on the thickener, which is the main component of the grease.
1. Lithium-Based
Lithium Extreme Pressure Grease is the most commonly used type of Extreme Pressure Grease. It has excellent performance at high and low temperatures and water resistance.
2. Calcium-Based
Calcium Extreme Pressure Grease has excellent water resistance and is often used in wet environments. However, it is weak against high temperatures.
3. Aluminum-Based
Aluminum-based Extreme Pressure Grease is more resistant to high temperatures than lithium-based grease. However, its water resistance is inferior to that of lithium-based grease.
4. Polyurea Type
Polyurea Extreme Pressure Grease is extremely resistant to high temperatures and has a long service life. It is used in applications that require continuous use at high temperatures and for long periods of time, such as electrical equipment and high-speed rotating equipment. However, its high price is a drawback.
Other Information on Extreme Pressure Grease
Extreme Pressure Additive
Contact surfaces under high loads are always accompanied by high temperatures, and these high temperatures trigger the reaction of Extreme Pressure Additives. Extreme Pressure Additives are stable at room temperature and relatively low temperatures and become active and react with metals at slightly lower temperatures before reaching higher temperatures where fusion can occur.
Extreme Pressure Additives are substances that generally contain sulfur, chlorine, or phosphorus. They include sulfide oils and fats, sulfide esters, sulfides, and chlorinated hydrocarbons, as well as lead naphthenate and compounds containing two or more of the elements in the same molecule.