What are the additives in the lubricating oil (Part 2)

3、 Oily and extreme pressure antiwear agents

1. Extreme pressure antiwear agent refers to an additive that can form a high melting point chemical reaction film with the metal surface under the boundary lubrication state of high temperature and high pressure to prevent fusion, biting and scratching. Its function is that the products decomposed under high friction temperature can react with the metal to generate compounds with lower shear stress and melting point than pure metal, so as to prevent the bite and welding melting of the contact surface and effectively protect the metal surface. Extreme pressure antiwear agents are mainly used in industrial gear oil, hydraulic oil, guide rail oil, cutting oil and other lubricants with extreme pressure requirements to improve the extreme pressure antiwear performance of oil products.

Extreme pressure antiwear agents are generally divided into organic sulfide, phosphide, chloride, organic metal salt and borate extreme pressure antiwear agents. The main varieties of extreme pressure antiwear agents are: chlorinated paraffin, dibutyl acid phosphite, nitrogen-containing derivatives of sulfur phosphoric acid, Trimethylphenol phosphate, sulfurized isobutene, dibenzyl disulfide, lead naphthenate, borate, etc.

2. Any additive that can make the lubricating oil increase the oil film strength, reduce the friction coefficient, improve the anti-wear ability and reduce the friction and wear between moving parts is called oily agent.

Oily agent is a kind of surfactant. One end of the molecule has a polar group and the other end is an oil-soluble hydrocarbon group. The substance containing this polar group has a strong affinity for the metal surface. It can firmly and directionally adsorb on the metal surface and form a protective film similar to a buffer between the metals to prevent direct contact with the metal surface and reduce friction and wear.

Oily agents have high interfacial activity, and they produce physical or chemical adsorption on the metal surface. Physical adsorption is reversible. Physical adsorption works when the temperature is low and the load is small; Under high temperature and high load, the adsorbent will desorb and lose its function. In addition to physical adsorption, fatty acid based oily agents also have chemical adsorption. They form metal soap with metal surface at lower temperature to improve wear resistance.

The commonly used oily agents are higher fatty acids (such as stearic acid, palmitic acid, oleic acid, lauric acid, palmitic acid, ricinoleic acid, etc.), esters of fatty acids (such as ethyl stearate, butyl oleate, etc.), fatty acid amines or amide compounds (such as stearic acid amine, N, n-di (polyethylene glycol) octadecylamine, stearamide, etc.), sulfurized whale oil, sulfurized cotton seed oil, dimeric acid Benzotriazole fatty amine salt and acid phosphate, etc. Oily agent is mainly used for industrial lubricating oil, hydraulic oil, guide rail oil, gear oil, etc.

4、 Viscosity index improver

Viscosity index improver, also known as tackifier or viscosity agent, its output is second only to detergent dispersant. Viscosity index improver is an oil-soluble chain polymer with molecular weight ranging from tens of thousands to millions.

Viscosity index improvers are dissolved in lubricating oil. At low temperature, they exist in the form of silk rolls, which has little effect on the viscosity of lubricating oil. With the increase of lubricating oil temperature, the silk rolls stretch, the effective volume increases, and the flow resistance of lubricating oil increases, resulting in a relatively significant increase in the viscosity of lubricating oil.

Because the viscosity index improver has different forms at different temperatures and has different effects on viscosity, it can increase viscosity and improve viscosity temperature performance. Therefore, the viscosity index improver is mainly used to improve the viscosity index, viscosity temperature performance and viscosity of lubricating oil. Viscosity index improver can be used to prepare thickened engine oil, so that the prepared oil has excellent viscosity temperature performance, good low-temperature starting performance, low fuel consumption and certain anti-wear effect.

Viscosity index improver is widely used in internal combustion engine oil, mainly in the production of multi-stage gasoline and diesel engine oil, as well as hydraulic oil and gear oil. Commonly used viscosity index improvers include polyisobutylene, polymethacrylate, ethylene / propylene copolymer, styrene and diene copolymer and polyethylene n-butyl ether.

5、 Pour point depressant

When the oil temperature drops to a certain extent, it will lose fluidity and solidify. The function of pour point depressant is mainly to reduce the freezing point of oil and ensure that oil can flow at low temperature. Oil contains wax. At low temperature, high melting point paraffin hydrocarbons are often precipitated by needle or sheet crystallization, and interconnected to form a three-dimensional network structure to form a crystalline skeleton, which adsorbs and surrounds the low melting point oil, especially a water absorbing sponge, resulting in the loss of fluidity of the whole oil. Pour point depressant has two functions: adsorption and eutectic. Although pour point depressant can not prevent the precipitation of wax crystals, it can change the structure of wax.

The adsorption of pour point depressant on the wax crystal surface or eutectic with it can change the shape and size of wax crystal and prevent the connection of wax grains to form a three-dimensional network structure, so as to maintain the fluidity of oil products at low temperature. Pour point depressants are widely used in all kinds of lubricating oils, typically alkyl naphthalene, polymethacrylate and polyacrylate α Olefins.

6、 Rust inhibitor

The function of antirust agent is to form a firm adsorption film on the metal surface to inhibit the contact between oxygen and water, especially water, and prevent the metal from rusting. Antirust agents as petroleum additives must have sufficient adsorption on metals and solubility in oil. Therefore, antirust agents are composed of strong polar groups and appropriate lipophilic groups. At present, sulfonates (calcium sulfonate, sodium sulfonate and barium sulfonate), carboxylic acids and their salts (dodecenylsuccinic acid, zinc naphthenate, N-oleoyl sarcosine octadecylamine salt), organic phosphates, imidazoline salts, ester antirust agents (lanolin and lanolin soap, benzene-60 or 80, stone oxide grease) Heterocyclic compounds (benzotriazole), organic amines, etc.

Water soluble antirust agents mainly include: sodium nitrite, potassium dichromate, trisodium phosphate, diammonium hydrogen phosphate, sodium benzoate, triethanolamine, etc. Antirust agents are mainly used in industrial lubricants, metal processing cooling lubricants, metal protective oils, etc.

7、 Anti emulsifier

Oil products will be polluted by water during use, such as water leakage of mechanical equipment, spraying a large amount of cooling water in order to cool processed parts, etc., which will enter a certain amount of water in the oil, which requires that the oil products have certain water separation and will not be emulsified into w / O (water / oil) emulsion. Because the lubricating oil will lose fluidity (w / O emulsification will double the viscosity of the oil) and lubricity after emulsification or its poor anti emulsification, it will also cause metal corrosion and wear. Industrial gear oil, turbine oil and hydraulic oil (such as oil containing zinc salt) are easy to be polluted by water, so these oil products have high requirements for anti emulsification performance.

There are many reasons for poor water separation or emulsification of lubricating oil.

1) High viscosity oil will contain some polar components;

2) Various additives are added to industrial lubricating oil, especially detergent dispersant, antirust agent and extreme pressure anti-wear agent. Most of these additives are surfactants, which should reduce the anti emulsification of oil after adding;

3) The oil is oxidized to produce easily emulsified compounds such as carboxylic acid, which makes the anti emulsification of the oil worse.

Deepening the refining depth of base oil and selecting appropriate additives are the first consideration, but adding anti emulsifier is the main way to improve the anti emulsification of lubricating oil. The addition of anti emulsifier in oil can change the oil / water interfacial tension, so as to improve the anti emulsification of oil. Because the barrier to the combination of dispersed phase droplets (i.e. the protective film outside the droplets) can be eliminated after the addition of anti emulsion, so that the droplets can be easily combined. In addition, the anti emulsifier can change the phase of the emulsion from w / O type to O / W type to achieve the purpose of water separation. The commonly used anti emulsifiers include polyoxypropane derivatives, etc.

8、Anti foam agent.

A small amount of polar substances will remain after refining the lubricating oil base oil, and with the use of various additives to meet the high-performance requirements of various mechanical equipment, foaming will occur in the circulating lubrication system, which will not only affect the pumping of lubricating oil, but also damage the strength and stability of oil film, resulting in undue wear accidents, Or make the machine unable to operate normally, such as oil cut-off, air resistance, sintering and other phenomena will continue to occur.

The function of anti foaming agent is to inhibit foam production, so as not to form stable foam. It can adsorb on the bubble film and form unstable film, so as to achieve the purpose of destroying the foam. The commonly used antifoam agent is methyl silicone oil antifoam. It is insoluble in oil and is highly dispersed in oil by means of colloidal grinding. Its dosage is generally 1-100ppm. In addition, there is a non silicon antifoaming agent, which belongs to polyacrylate polymer ester. Compared with silicone oil, it can effectively improve the air release of oil products.

9、 Compound additive

With the improvement of oil quality grade, functional additives gradually change from single agent to composite agent. The performance of composite additives not only depends on the improvement of the quality of a single additive, but also determines the essence of the interaction of additives through the study of the compound law of additives, so as to obtain a composite agent with good comprehensive performance. The use of composite additives can reduce the difficulty of formula screening, reduce the cost of lubricating oil production and stabilize the quality of oil production. Now, the position of compound additives in lubricating oil is becoming more and more important.