Extreme pressure antiwear agent is a common type. Extreme pressure antiwear agent is an important grease additive, most of which are compounds containing sulfur, phosphorus, chlorine, lead and molybdenum. In general, chlorine and sulfur can improve the load resistance of grease and prevent metal surface from sintering, sticking and scratching under high load conditions; Phosphorus and organometallic salts have higher wear resistance, which can prevent or reduce the wear of metal surface under medium load condition. In practical application, it is usually better to mix different kinds of extreme pressure antiwear agents in a certain proportion.

1: Organic chloride

The friction coefficient of organic chloride is small under extreme pressure conditions, and the extreme pressure performance of lubricating grease is better than the wear resistance, but the extreme pressure performance will decrease under high temperature and water conditions. And cause metal corrosion and rust. The common addition amount is 1%-10%. Chlorinated paraffin is an older extreme pressure additive product, light yellow to yellow viscous liquid, because of the amount of chlorine is divided into three kinds, chlorinated paraffin 42, chlorinated paraffin 50 and chlorinated paraffin 52. Chlorinated paraffin heated to more than 120℃ will slowly decompose, release hydrogen chloride gas, so it is often used with metal sulfonate rust inhibitor.

2: organic sulfide

Organic sulfide can resist the load more effectively than chloride, and the film formed by sulfide animal oil does not fail at the high temperature of 700℃. The hydrolysis stability is good, but the friction coefficient is high. The addition amount is generally 1%-5%. Representative products are:

Vulcanized lard, with good oil solubility, can keep oil film lubrication under high load. It can be used for cutting fluid, guide oil, gear oil, hydraulic guide oil, engine running-in oil, grease, etc.

Vulcanized cottonseed oil, red and swollen color transparent liquid, has good oil solubility, extreme pressure, oxidation resistance, can reduce friction coefficient. The addition amount is generally 1%-3%.

Vulcanized olefin cottonseed oil, deep red clear viscous liquid, soluble in petroleum lubricating oil. With excellent extreme pressure, anti-wear, anti-oxygen and low friction coefficient, it is an ideal substitute for vulcanized whale oil. Often combined with other additives, the amount of addition is generally 0.5%- 4%.

Sulfide isobutene, isobutene as raw material, first sulfide with sulfur chloride, then sodium sulfide dechlorination sulfide, and alkali refined, has good oil solubility and extreme pressure, corrosion is small. Used for extreme pressure wear - resistant lubricating oils.

Dibenzyl disulfide, a white or yellowish dendritic crystal, has good extreme pressure properties and slightly poor oil solubility. It will be precipitated when the dosage exceeds 2.8%, and the addition amount is generally 1%-2%.

3: Organophosphate compounds

Phosphorous compounds can improve the wear resistance of grease. Although the carrying capacity of acid phosphate ester is stronger than that of neutral phosphate, acid phosphate ester is rarely used because of its strong chemical activity and easy to cause metal corrosion. Commonly used are: tricresol phosphate, triphenyl phosphate, triethyl phosphate, tributyl phosphate and din-butyl phosphite.

Tricresol phosphate, a light yellow oily liquid, poisonous, freezing point -35℃, insoluble in water, soluble in alcohol, ether, benzene and other organic solvents, flame retardant and good wear resistance, often used with other extreme pressure additives to enhance extreme pressure wear resistance. The addition amount is generally 0.5%-5%.

Din-butyl phosphite, for colorless transparent liquid, insoluble in water, acid, the use of alkaline rust inhibitor can be added to overcome the corrosion of metal, often with sulfur extreme pressure additives compound use, enhance the extreme pressure anti-wear effect.

Triphenyl phosphate, white or yellowish aciculate crystal, poisonous, aromatic, insoluble in water, slightly soluble in alcohol, soluble in benzene, chloroform and acetone, but also soluble in vegetable oil. It is mainly used as a flame retardant plasticizer for cellulose, as an anti-wear additive for grease, the addition amount is generally 0.5%- 1%.

4: organometallic salt

Organic molybdenum salt, antimony salt and lead salt can not only effectively improve the extreme pressure wear resistance of grease, but also improve the oxidation stability and rust resistance of grease. But the oil solubility is a little poor, often with the help of grease dispersion process will be evenly dispersed in the grease additives. Commonly used are dialkyl dithiocarbamate, dialkyl dithiophosphate and lead naphthenate. The addition amount is generally 1%-5%.

Lead naphthanate is a yellow semi-solid gunk with a melting point close to 100℃. It is insoluble in water, soluble in ether, benzene, methyl and so on. It is easy to emulsify and hydrolyze and precipitate in acidic oil. Poor thermal stability, temperature above 80℃ will decompose, due to the heavy metal lead, environmental pollution, is banned by many industries.

5: Borate and borate ester

Borate is a new type of extreme pressure additive for grease, and its extreme pressure resistance is much better than thiophosphorous and chloro-lead additives. An oil-like dispersion formed by dispersing amorphous microspheres of borate in lubricating oil. Tasteless and non-toxic. With good extreme pressure wear resistance and thermal stability, no corrosion to copper. Slightly soluble in water, can be used for gear oil and grease without contact with water.

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