Just now, we explored with you the common types of extreme-pressure and anti-wear additives.
Release time:
2020-11-23
Author:
Goncord Oil
Common types of extreme-pressure and anti-wear additives: Extreme-pressure and anti-wear additives are important lubricant grease additives, most of which are compounds containing sulfur, phosphorus, chlorine, lead, or molybdenum. Under normal conditions, chlorine- and sulfur-based additives enhance the load-carrying capacity of the grease and prevent metal surfaces from seizing, galling, or scratching under high-load conditions; meanwhile, phosphorus-based additives and organic metal salts exhibit superior anti-wear performance, helping to prevent or reduce wear on metal surfaces under moderate-load conditions.
Common types of extreme-pressure and anti-wear additives: These are important grease additives, typically comprising compounds containing sulfur, phosphorus, chlorine, lead, or molybdenum. In general, chlorine- and sulfur-based additives enhance the grease’s load-carrying capacity, preventing metal surfaces from seizing, galling, or scratching under high‑load conditions. Meanwhile, phosphorus‑based compounds and organic metal salts offer superior anti‑wear performance, helping to prevent or reduce wear on metal surfaces under moderate‑load conditions. In practical applications, blending different types of extreme‑pressure and anti‑wear additives in specific proportions usually yields better overall performance.
1: Organochlorine compounds
Organochlorides exhibit a low coefficient of friction under extreme-pressure conditions and impart grease with superior extreme-pressure performance compared to anti-wear properties; however, their extreme-pressure performance deteriorates at elevated temperatures and in the presence of water, and they can also cause metal corrosion and rusting. Typical addition levels range from 1% to 10%. Chlorinated paraffin is one of the earliest extreme-pressure additives; it appears as a light‑yellow to yellow, viscous liquid and is classified into three grades—chlorinated paraffin 42, chlorinated paraffin 50, and chlorinated paraffin 52—depending on its chlorine content. When heated above 120°C, chlorinated paraffin decomposes slowly, releasing hydrogen chloride gas; therefore, it is often used in combination with metallic sulfonate‑based rust inhibitors.
2: Organic Sulfides
Organic sulfur compounds offer superior load‑carrying performance compared to chlorinated additives. The film formed by sulfidized animal oils remains effective even at high temperatures of 700°C and exhibits excellent hydrolytic stability, though it has a relatively high coefficient of friction. Typical addition levels range from 1% to 5%. Representative products include:
Sulfurized lard exhibits excellent oil solubility, enabling lubricating oils to maintain a stable oil film under heavy loads. It is suitable for use in cutting fluids, guideway oils, gear oils, hydraulic and guideway oils, engine break-in oils, greases, and other applications.
Sulfurized cottonseed oil is a reddish‑brown, transparent liquid that exhibits excellent oil solubility, extreme‑pressure properties, and antioxidant performance, while also reducing the coefficient of friction. The typical addition level is 1%–3%.
Sulfurized olefin cottonseed oil is a deep‑red, transparent, viscous liquid that readily dissolves in petroleum lubricants. It exhibits excellent extreme‑pressure, anti‑wear, and antioxidant properties, along with a low coefficient of friction, making it an ideal substitute for sulfurized whale oil. It is typically used in combination with other additives, at dosages ranging from 0.5% to 4%.
Isobutylene sulfide, prepared from isobutylene as the raw material, is first sulfurized with sulfur chloride, then desulfurized and further sulfidized using sodium sulfide, followed by purification with an alkali. It exhibits excellent oil solubility and extreme-pressure properties, with low corrosivity, and is widely used in extreme-pressure, anti-wear lubricants.
Dibenzyl disulfide, a white or slightly yellowish dendritic crystal, exhibits excellent extreme-pressure performance. It has relatively poor oil solubility and will precipitate when its concentration exceeds 2.8%; the typical addition level is 1%–2%.
3: Organophosphorus compounds
Phosphorus-containing compounds can enhance the anti-wear performance of lubricating greases. Although acidic phosphate esters exhibit superior load-carrying capacity compared to neutral phosphate esters, their high chemical reactivity makes them prone to causing metal corrosion, so they are seldom used. Commonly employed phosphates include tricresyl phosphate, triphenyl phosphate, triethyl phosphate, tributyl phosphate, and dibutyl phosphite, among others.
Tricresyl phosphate is a pale yellow, oily liquid that is toxic and has a pour point of −35°C. It is insoluble in water but soluble in alcohols, ethers, benzene, and other organic solvents. It exhibits flame retardancy and excellent anti‑wear properties, and is often used in combination with other extreme‑pressure additives to enhance these characteristics. Typical addition levels range from 0.5% to 5%.
Dibutyl phosphite is a colorless, transparent liquid that is insoluble in water and exhibits acidic properties. During use, an appropriate amount of alkaline rust inhibitor may be added to mitigate corrosion of metals. It is often compounded with sulfur‑containing extreme‑pressure additives to enhance its extreme‑pressure and anti‑wear performance.
Triphenyl phosphate is a white or slightly yellowish needle‑shaped crystalline substance with an aromatic odor; it is toxic, insoluble in water, slightly soluble in alcohols, and readily soluble in benzene, chloroform, and acetone, as well as in vegetable oils. It is primarily used as a flame‑retardant plasticizer for cellulose and, when employed as an anti‑wear additive in lubricating greases, is typically added at levels of 0.5% to 1%.
4: Organometallic Salts
Organic molybdenum, antimony, and lead salts not only effectively enhance the extreme-pressure and anti-wear properties of greases but also improve their oxidation stability and rust‑prevention performance. However, their oil solubility is relatively poor, so these additives are typically dispersed uniformly in the grease through specialized dispersion techniques. Common examples include dialkyl dithiocarbamates, dialkyl dithiophosphates, and lead naphthenates. Typical addition levels range from 1% to 5%.
Lead naphthenate is a yellow, semi-solid, viscous substance with a melting point close to 100°C. It is insoluble in water but soluble in diethyl ether, benzene, and methyl compounds. It readily undergoes emulsification and hydrolysis, forming precipitates in acidic oils. It exhibits poor thermal stability, decomposing at temperatures above 80°C. Due to its heavy‑metal content, it poses environmental hazards and has been banned in many industries.
5: Borates and Borate Esters
Borate-based extreme-pressure additives exhibit significantly superior EP performance compared to sulfur-phosphorus and chlorinated lead‑based additives, making them a new generation of EP additives for lubricating greases. An oil‑soluble dispersion is prepared by dispersing amorphous microspherical borates in lubricating oil; it is odorless and non‑toxic. This formulation offers excellent EP and anti‑wear properties as well as thermal stability, and it is non‑corrosive to copper. Slightly soluble in water, it is suitable for gear oils and greases that do not come into contact with water.
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