What are the additives in the lubricating oil (Part I)

With the development of industrial technology, the high speed, high performance, high automation, high efficiency and long service life required by modern equipment are difficult to meet with mineral oil lubricating materials alone. Adding a small amount of other substances to the lubricating material can improve its performance and give it new characteristics. These substances are called additives to lubricating oils.

Adding different additives to oil products is a means to improve oil quality. Generally speaking, the variety and quality of lubricating oil often depend on the variety and quality of additives. Therefore, developing the production and use of additives has become an important way to make rational and effective use of resources, improve equipment performance and save energy.

Lubricating oil additives can be divided into detergent dispersant, antioxygen and anticorrosive agent, extreme pressure antiwear additive, oiliness agent and friction modifier, antioxidant and metal deactivator, viscosity index improver, antirust agent, pour point depressant, anti foam agent and so on.

1、 Detergent dispersant

Detergent dispersants include detergent and dispersant. It is mainly used for internal combustion engine oil (steam engine oil, diesel engine oil, railway diesel locomotive oil, two-stroke steam engine oil and marine engine oil). Its main function is to keep the interior of the engine clean and make the insoluble substances generated in colloidal suspension, so as not to further form carbon deposition, paint film or oil sludge. Specifically, its functions can be divided into four aspects: acid neutralization, solubilization, dispersion and washing.

1) Acid neutralization: the detergent dispersant generally has a certain alkalinity, and some are even highly alkaline. It can neutralize the organic and inorganic acids generated by the oxidation of lubricating oil and prevent them from further condensation, so as to reduce the paint film and prevent the corrosion of these acidic substances to engine components.

2) Solubilization: detergent dispersants are surfactants, which can solubilize solid or liquid substances that cannot be dissolved in oil in the micelle center composed of 5-20 surfactant molecules. In the process of use, it solubilizes oxygen-containing compounds containing hydroxyl, carbonyl and carboxyl groups, nitro compounds and water into micelles to form colloids, Prevent further oxidation and condensation and reduce the formation and accumulation of harmful deposits on engine components.

3) Dispersion: it can adsorb the generated solid small particles such as carbon deposit and paint film, make them become a colloidal solution state and disperse in the oil, and prevent these substances from further condensing into large particles and adhering to the parts, or depositing into oil sludge.

4) Washing function: it can wash the paint film and carbon deposit adsorbed on the surface of components and disperse them in oil to keep the engine and metal surfaces clean.

The structure of detergent dispersant is basically composed of lipophilic, polar and hydrophilic groups. Due to different structures, the performance of detergent dispersant is different. Generally speaking, the detergency of gray additives is better, and the dispersion of ashless additives is prominent.

Typical representatives of detergent dispersants are sulfonate, alkyl phenol salt, salicylate, succinimide, succinate and polymer. The first three are also called ash cleaning dispersants, and the last three are called ash free cleaning dispersants.

2、 Antioxidant

Antioxidants and anti-oxidation and anti-corrosion agents can inhibit oil oxidation. They are mainly used in industrial lubricants, internal combustion engines and process oils. Antioxidants can be divided into two types according to their action principle: 1) chain reaction terminator; 2) Peroxide decomposing agent. Common shielding phenolic and amine compound antioxidants belong to chain reaction terminators, which can form stable products (ROOH or rooa) with peroxide groups (roo), so as to prevent the oxidation reaction of hydrocarbon compounds in lubricating oil, such as 2,6 phenol, 4,4 methylene bisphenol α- Naphthylamine, N, n-di sec butyl p-phenylenediamine, etc.

Peroxide decomposing agent can decompose the peroxide generated in oil oxidation reaction, so that the chain reaction can not continue to develop and play an anti oxygen role; It can produce inorganic complexes in the process of thermal decomposition and form a protective film on the metal surface; Under extreme pressure, chemical reaction takes place on the metal surface to form a sulfide film with bearing capacity, which plays an anti-wear role, so it is a multi effect additive. The main varieties of antioxidant and anti-corrosion agents include zinc dialkyl dithiophosphate (ZDDP), alkyl zinc thiophosphate, butyl octyl zinc thiophosphate and their series products.

Phenolic and amine antioxidants are mostly used in transformer oil, industrial lubricating oil, steam turbine oil and hydraulic oil. Zinc dialkyl dithiophosphate and other sulfur, phosphorus or organic selenium compounds are commonly used in handicraft lubricating oil, internal combustion engine oil and process oil. However, lubricating oil containing dithiophosphate is not suitable for diesel locomotives with silver plated toggle pins and steel sleeves on the top of connecting rods of lubricating engines. Dialkyl dithiocarbamate can meet the requirements of machines with silver plated parts.