What are ep additives?

Time：

2025-11-17

What are ep additives?

Before learning about ep additives, we should first understand load-carrying additives. Load-carrying additives are various additives that can reduce friction and wear and prevent sintering of friction surfaces. Load-carrying additives are classified into oily additives, anti-wear additives and extreme pressure additives according to their function.

Extreme pressure additives (EP additives) are important lubricant additives used in gear oils to prevent sintering, wear, and scratches on the surfaces of interacting metal parts under extreme pressure conditions. Their primary application is in gear oils, especially with the rapid development of hypoid gears. To meet the enormous load transmission requirements between hypoid gears, sulfur-containing, chlorine-containing, and phosphorus-containing extreme pressure additives, among others, have been developed.

Development of ep additives

Extreme pressure additives developed alongside gears, especially hypoid gears. The earliest extreme pressure additives were animal and vegetable oils, and the first element used was sulfur. In the early 20th century, hypoid gears were widely used due to their high load-transfer capacity and resistance to gear damage, thus placing very high demands on gear oils. Traditional animal and vegetable oils could no longer fully meet these requirements, leading to the use of sulfur-chlorine extreme pressure additives. However, their application in truck gears revealed persistent wear. Subsequently, phosphorus was introduced, forming sulfur-phosphorus-chlorine type extreme pressure anti-wear agents to simultaneously meet the needs of both automotive and truck gears. Later, sulfur-phosphorus extreme pressure anti-wear agents were used to improve thermal stability and antioxidant properties. In recent years, with the increasing severity of environmental issues, the use of phosphorus has been gradually reduced, and borates and hyperalkaline sulfonates have been increasingly adopted.

Types of ep additives

Chlorine-containing extreme pressure additives
- Chlorinated paraffin(Chlorcosane) has good extreme pressure properties and is inexpensive, making it suitable for metalworking fluids. Its disadvantage is that it is harmful.
- Chlorinated paraffins(Chlorcosane) are classified into short-chain chlorinated paraffins(SCCP) and medium-chain chlorinated paraffins(MCCP).
Sulfur-containing extreme pressure additives
- Mainly sulfurized olefins, sulfurized isobutylene, sulfurized fatty acids, and sulfurized triglycerides, etc.
Phosphorus-containing extreme pressure additives
- Widely used alkyl phosphites, phosphate esters, acidic phosphate esters, acidic phosphate ester amine salts (phosphorus and nitrogen extreme pressure agents), and thiophosphate ester amine salts (sulfur, phosphorus, and nitrogen extreme pressure additives) are among them.
Organometal salt extreme pressure additives
- MoDDP and MoDTC are important
Borate extreme pressure additives
- Borate extreme pressure additives have excellent thermal stability, do not corrode copper, are non-toxic and odorless, and are well-suited for rubber seals. They are suitable for gear oils, hydraulic oils, lubricating greases, or metalworking fluids, but because they are slightly soluble in water, they are not suitable for use in water-contact environments.
Overbased sulfonate extreme pressure additives
- Overbasedcalcium sulfonate is the most commonly used additive, also known as PEP inert extreme pressure agent. It is a multifunctional additive with detergency, dispersion, acid neutralization, corrosion prevention, wear resistance, oxidation resistance, and extreme pressure properties.

Keywords:

extreme pressure additives

ep additives

extreme pressure oil additives

extreme pressure additives for lubricants

extreme pressure additives in gear oils

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Polyisobutylene succinimide

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Polyisobutylene succinimide