Seven Major Lubricant Additives in Hydraulic Oil

Hydraulic fluid plays a role in energy transmission, lubricity, cooling, and anti-corrosion in the hydraulic systems of construction machinery, machine tools, and aviation. In order to satisfy the demands of different performances, adding multi-functional additives to the hydraulic oil is an important way to improve stability and service.

 

• Anti-oxidation additive: delays the aging and deterioration of oil products.

Antioxidant is used for improving the anti-oxidation performance and prolonging oil service life, is also called oxidation inhibitors.

The engine oil in the operation process will undergo a series of chemical changes, like oxidation, aggregation, and decomposition, because of the oxygen in the air, by-products from fuel combustion, high temperature, and metals on the friction surfaces. This will lead to engine bearing corrosion, piston ring adhesion, formation of paint film and sludge, increased oil viscosity, and decreased thermal efficiency, which influence the equipment's normal operation. To improve the oxidation stability of engine oil, antioxidants must be added.

 

Zinc Dioctyl Primary Alkyl Dithiophosphate (ZDDP) has good anti-oxidation, extreme pressure anti-wear performance, and hydrolytic stability. Used in the high grade engine oil, it can inhibit oxidation, prevent oil viscosity from increasing, and efficiently reduce cam follower wear. And ZDDP can also be used in the hydraulic fluid.

Butylated hydroxytoluene Antioxidant T501 has a good anti-oxidation performance and performs well below 100 ℃. It is used in industrial gear oil, anti-wear hydraulic oil, turbine oi and transformer oil.

 

• Antiwear additive: reduce metals wear and friction

In the process of metal cutting, when the load increases to a certain extent, the oil film on the metal surface will be completely extruded, and the metal surface will come into direct contact. Under such boundary lubrication conditions, the EP antiwear additive begins to function effectively. The active components in the EP additive can react with metal under a certain temperature and form a chemical film to separate and lubricate the metal surface.

 

These EP anti-wear additive common contains sulfur, phosphorus, chlorine, and other elements. In high temperatures, these elements will form a corresponding molecular film to prevent the connection between metals, to avoid welding and scraping.

 

For example, zinc dioctyl alkyl dithiophosphate T203 can react with iron under high temperature and form a protective film. Phosphorus-containing antiwear additive can form a highly plastic phosphate film at low temperature, and it's helpful to improve surface flatness.

 

• Anti-rust additive: prevents metal surfaces from corrosion

Rust is a compound of oxides and hydroxides formed on the metal surface due to the action of oxygen and water. Sometimes, it also contains carbonates formed by the connection with air and carbon dioxide.

 

To avoid rust, one of the most common methods is to use anti-rust oil. When the oil product with rust preventive additives connects with metal, the polar group in the anti-rust additive molecule has a high absorption force and forms a tight monomolecular or multi-molecular protective layer on the metal surface to prevent the corrosion medium from connecting with metals.

 

Anti-rust additive Dodecenylsuccinic Acid T746 can form a strong oil film on the metal surface to prevent the metal from corrosion. It's suitable for turbine oil, hydraulic oil, and gear oil.

 

• Viscosity improver index: promote the viscosity temperature performance

The viscosity of oil decreases with temperature increases. Viscosity Index (VI) is used to measure the viscosity change with temperature. The VI of oil is bigger, the viscosity change with temperature is smaller.

 

Due to the viscosity index of mineral oil usually at 96-100, when producing multi-grade internal combustion engine oil with excellent viscosity temperature performance and other high index industrial lubricants, it is better add VII or use synthetic lubricating oil.

 

The internal combustion engine oil, gear oil, and hydraulic oil formulated by VII have excellent low-temperature starting performance and high-temperature lubricity. It can satisfy the multiple viscosity grades and is suitable for use all year round.

 

PMA T602HB in Chorus is a typical VII that can promote the hydraulic oil viscosity index from 90 to 140, which is helpful to guarantee the smooth operation of equipment in a wider temperature range.

 

• Pour point depressant (PPD): promotes the liquidity under low temperatures

At low temperatures, the paraffin component in hydraulic fluid may precipitate and cause solidification. PPD can decrease the pour point by changing the shape and size ofthe paraffin crystal. The commonly used pour point depressant is Pour Point Depressant (PPD) T248 For Lubricant Oils​​​​​​, which can decrease the hydraulic pour point from -10 ℃ to -40℃ to ensure the normal operation of equipment in a cold environment.

 

• Demulsifier: promotes oil and water separation

The water is mixed into the hydraulic system, which may form an emulsion, which influences the lubricity and leads to corrosion. Demulsifier can damage the oil-water interface film and accelerate water deposit and separation.

For example, the sulfonate demulsifier has a good effect that can shorten the oil-water separation time from 30 mins to 5 minutes to maintain the system stability.

 

• Anti-foam additive: inhibits the formation and accelerates the elimination of foam.

In the circulation of hydraulic fluid, it's easy to mix with air and form foam, which influences the system stability and leads to cavitation. An anti-foam oil additive can reduce the lubricant oil surface tension and make the foam break up quickly.

Anti-foam additive AF-3 is the commonly used antifoam in chorus; the amount is usually at 0.001%-0.01%. That's beneficial to decrease the generation of foam.

After adding the antiform additive, AF-3 can improve the stability of hydraulic system pressure control.

 

The improvement of hydraulic fluid depends on various additives.

Anti-wear additives, anti-rust additives, anti-oxidation, defoam additives, VII, PPD, and demulsifier play their role in reducing wear, preventing corrosion, prolonging aging, maintaining viscosity, and improving liquidity.

Choosing and proportioning the lubricant additives reasonably can prolong the life span of the hydraulic system, but also reduce maintenance costs and improve the operation efficiency.