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Mechanism of Common Lubricating Oil Additives

2020-01-17 14:37:32  Knowledge

With the development of industrial technology, high speed, high performance, high automation, high efficiency, and long life required by modern equipment, it is challenging to meet the requirements of lubrication with mineral oil alone. Adding a small number of other substances to the lubricating material can improve its performance and give it new characteristics. These substances are called additives for lubricants.

engine oil cleaner additive

Do oil additives really help?

Adding different additives to oil is the most economical and effective way to improve oil quality. Generally speaking, the quantity and quality of lubricants often depend on the variety and quality of the additives. Therefore, the development of the production and use of additives has become a meaningful way to rationally and effectively use resources, improve equipment performance, and save energy.

Lubricant additives can be divided into engine oil cleaner additive, antioxidant and antiseptic, oily and anti-friction oil additive, antioxidant and metal deactivator, viscosity index improver, rust inhibitor, pour point depressant, Foaming agents and other groups, the following introduces the action mechanism of common lubricant additives.

1.Engine oil cleaner additive

Engine oil cleaner additives include detergents and dispersants. Mainly used in internal combustion engine oils (steam engine oil, diesel engine oil, railway diesel locomotive oil, two-stroke engine oil, and marine engine oil). Its primary function is to keep the inside of the engine clean, and to make the insoluble matter in a colloidal suspension state, so as not to further form carbon deposits, paint films or sludge. Specifically, its role can be divided into four aspects: acid neutralization, solubilization, dispersion, and washing.

1) Acid neutralization: engine oil cleaner additive generally has specific alkalinity, and some are even highly alkaline. It can neutralize the organic and inorganic acids produced by the oxidation of lubricating oil, preventing its further condensation, thus making the paint. The reduced membrane also prevents these acidic substances from corroding engine components.

2) Solubilization: engine oil cleaner additives are all surfactants, which can solubilize solid or liquid substances that are not soluble in oil in the center of micelles composed of 5-20 surfactant molecules In use, it will solubilize oxygen-containing compounds containing hydroxyl, carbonyl, and carboxyl groups, containing nitro compounds, moisture, etc. into the micelles to form colloids, prevent further oxidation and condensation, and reduce harmful deposition on engine components Formation and aggregation of objects.

3) Dispersion: It can adsorb the small solid particles such as carbon deposits and paint films that have been formed, and make it a colloidal solution dispersed in oil, preventing these substances from further condensing into massive particles and adhering to the machine, or depositing For sludge.

4) Washing effect: The paint film and carbon deposits that have been adsorbed on the surface of the component can be washed and dispersed in the oil to keep the engine and metal surfaces clean.

The structure of the engine oil cleaner additive is composed of three groups: lipophilic, polar, and hydrophilic. Due to the different structures, the performance of the detergent dispersant is different. Generally speaking, the detergency of ash additives Preferably, the dispersibility of the ashless additive is outstanding.

The typical representatives of engine oil cleaner additive are sulfonate, alkyl phenate, salicylate, succinimide, succinate, and polymer. The first three are also called ash cleaning dispersants, and the last three are called ashless cleaning dispersants.

anti friction oil additive

2. Antioxidants

Antioxidants and antioxidants can inhibit the oxidation of oil products and are mainly used in industrial lubricants, internal combustion engines, and process oils. Antioxidants can be divided into two types according to their principle of action: 1) chain reaction terminator; 2) peroxide decomposition agent. Typical shielding phenolic and amine compound antioxidants are chain reaction terminators, which can form stable products (ROOH or ROOA) with peroxide groups (ROO.), Thereby preventing the oxidation reaction of hydrocarbon compounds in lubricating oils. Such as 2,6 phenol, 4,4 methylenebisphenol, α-naphthylamine, N, N-di-sec-butyl-p-phenylenediamine, and the like.

The peroxide decomposition agent can decompose the peroxide generated in the oxidation reaction of the oil so that the chain reaction cannot continue to develop and play an antioxidant role; it can cause an inorganic complex during the thermal decomposition process, and form a protective film on the metal surface. It has an anti-corrosion effect; under extreme pressure conditions, a chemical reaction occurs on the metal surface to form a vulcanized film with the load-bearing capacity to play an anti-wear impact, so it is a multi-effect additive. The main varieties of antioxidants and antiseptics are zinc dialkyl dithiophosphate (ZDDP), zinc thiophosphinoyl zinc, zinc thiophosphinobutyl octyl, and their products.

Phenol and amine antioxidants are mostly used in transformer oils, industrial lubricants, turbine oils, and hydraulic oils. The zinc dialkyl dithiophosphate and other compounds containing sulfur, phosphorus, or organic selenium are often used in handicraft lubricants, internal combustion engine oils, and process oils. But dithiophosphate-containing lubricating oil is not suitable for silver-plated toggle pin diesel locomotive and lubricating the top of the connecting rod steel sleeve of the engine. Dialkyldithiocarbamate can meet the requirements of silver-plated parts Machine use requirements.

3. Oil and extreme pressure anti-wear agent

1) An intense pressure anti-wear agent refers to an additive that can form a high melting point chemical reaction film with the metal surface under high temperature and high-pressure boundary lubrication conditions to prevent fusion, seizure, and scratching. Its function is that the products decomposed under the high temperature of friction can react with the metal to generate compounds with lower shear stress and melting point than pure metals, thereby preventing the contact surface from engaging and welding, and effectively protecting the metal surface. Extreme pressure anti-wear agent is mainly used in industrial gear oil, hydraulic oil, guide rail oil, cutting oil and other lubricants with excessive pressure requirements to improve the intense pressure anti-wear performance of oil products.

Extreme pressure anti-wear agents are generally divided into organic sulfides, phosphides, chlorides, organometallic salts, and borate type radical pressure anti-wear agents. The main varieties of radical pressure anti-wear agents are chlorinated paraffin, acid dibutyl phosphite, thiophosphoric nitrogen derivative, tricresol phosphate, isobutylene sulfide, dibenzyl disulfide, lead naphthenate, borate Wait.

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 an oily agent.

An oily agent is a surface-active agent with a polar group at one end of the molecule and an oil-soluble hydrocarbon group at the other end. Substances containing this extreme group have a strong affinity for metal surfaces. It can be firmly adsorbed on metal surfaces in a targeted manner, forming a protective film similar to a cushion between metals, preventing direct contact with metal surfaces. To 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. At low temperature and low load, physical adsorption works; under high heat and high pressure, the adsorbent will desorb and lose its effect. In addition to physical adsorption, fatty acid-based oily agents also have chemical adsorption. Metal soaps are formed on metal surfaces at lower temperatures to improve abrasion resistance.

Common oily agents are higher fatty acids (such as stearic acid, palmitic acid, oleic acid, lauric acid, palmitic acid, ricinoleic acid, etc.), fatty acid esters (such as ethyl stearate, butyl oleate, etc.), Fatty acid amines or amide compounds (such as amine stearate, N, N-di (polyethylene glycol) stearylamine, ceramide, etc.), sulfurized whale oil, sulfurized cottonseed oil, dimer acid, benzotriazole fat Amine salts, and acid phosphates. The oily agent is mainly used in industrial lubricants, hydraulic oil, guide rail oil, gear oil, etc.

4. Viscosity index improver

The viscosity index improver is also called tackifier or viscosity agent, and its yield is second only to detergent and dispersant. Viscosity index improvers are oil-soluble, chain-like polymers with molecular weights ranging from tens of thousands to millions.

Viscosity index improvers are dissolved in the lubricating oil. They exist in the form of coils at low temperatures, which has little effect on the viscosity of the lubricant. As the heat of the lubricant increases, the reels expand the effective volume increases, and the oil flows — the increased resistance results in a relatively significant increase in the viscosity of the lubricant.

As the viscosity index improver has different forms and has different effects on viscosity at different temperatures, it can increase thickness and improve viscosity-temperature performance. Therefore, the viscosity index improver is mainly used to increase the viscosity index of lubricants, improve viscosity-temperature performance, and increase viscosity. Viscosity index improver can be used to formulate thickened motor oil so that the formulated oil has excellent viscosity-temperature production, good low-temperature stability, low fuel consumption, and a specific anti-wear effect.

Viscosity index improvers are widely used in internal combustion engine oils, mainly used in the production of multi-grade gasoline and diesel engine oils, as well as hydraulic and gear oils. Universal viscosity index improvers are polyisobutylene, polymethacrylate, ethylene/propylene copolymer, styrene and diene copolymer, and polyethylene n-butyl ether.

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5. Pour point depressant

After the temperature of the oil drops to a certain level, it will lose fluidity and solidity. The role of the pour point depressant is mainly to reduce the freezing point of the oil and ensure that the oil can flow at low temperatures. The oil contains wax. At low temperatures, high-melting paraffin hydrocarbons are often precipitated as needle-like or plate-like crystals, which are connected to form a bulk network structure to create a crystalline skeleton. The low-melting oil is adsorbed and surrounded, especially as a water-absorbing oil. Sponges, causing the entire fat to lose fluidity. Pour point depressant has two functions of adsorption and eutectic. Although depressants cannot prevent the precipitation of wax crystals, it can change the structure of wax.

Adsorption of the pour point depressant on the crystal surface of wax or forming a co-crystal with it, changing the shape and size of the wax crystal, preventing the wax crystals from forming a three-dimensional network structure, thereby maintaining the fluidity of the oil at low temperatures. Pour point depressants are widely used in various types of lubricating oils. Typical representatives are alkyl naphthalene, polymethacrylate, and polyalphaolefin.

6. Rust inhibitor

The role of the rust preventive agent is to form a strong adsorption film on the metal surface to inhibit the contact of oxygen and water, especially water, to the metal surface so that the metal will not rust. As rust preventive for petroleum additives, it must have sufficient adsorption to metals and solubility in oil. Therefore, rust preventives are composed of active polar groups and appropriate lipophilic groups. At present, the following types are widely used and have sound effects: sulfonates (calcium sulfonate, sodium sulfonate and barium sulfonate), carboxylic acids and their salts (dodecyl succinate, zinc naphthenate), N-oleoyl sarcosine octadecylamine salt), organic phosphates, imidazoline salts, ester-type rust inhibitors (lanolin and lanolin soap, stilbene-60 or 80, oxidized petroleum grease), Heterocyclic Compounds (benzotriazole), organic amines, etc.

Water-soluble rust inhibitors include sodium nitrite, potassium dichromate, trisodium phosphate, diammonium hydrogen phosphate, sodium benzoate, and triethanolamine. Rust inhibitors are mainly used in industrial lubricants, metal processing cooling lubricants, metal protective oils, etc.

7. Anti-emulsifier

Oil products will be contaminated by water during use, such as mechanical equipment leaks, large amounts of cooling water must be sprayed to cool processed parts, etc., all will enter a certain number of water in the oil, which requires that the oil products have a distinct water separation. It is not emulsified by water into W / O (water/oil) type emulsion. After emulsification or weak emulsification resistance of lubricating oil, it will lose fluidity (W / O type emulsifier will increase oil viscosity doubled) and loss of lubricity. It will also cause metal corrosion and wear. Industrial gear oil, steam turbine oil, hydraulic oil (such as oil containing zinc salt) are susceptible to water pollution, so these oil products have higher requirements for anti-emulsification performance.

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

1) High viscosity oil will contain some polar components;

2) Various additives are added to industrial lubricating oils, especially detergent and dispersant, rust inhibitor, and extreme pressure anti-wear agents. Most of these additives are surfactants, and the anti-emulsification of the oil should be reduced after the addition.

3) The oil is oxidized during use to form easily emulsified compounds such as carboxylic acid, which makes the oil anti-emulsification worse.

Deepening the refining depth of the base oil and selecting the appropriate additives is undoubtedly a problem that should be considered first, but adding anti-emulsifiers is the primary way to improve the anti-emulsification of lubricating oils. After adding an anti-emulsifier to the oil, the oil/water interfacial tension can be changed to achieve the purpose of enhancing the anti-emulsification of the oil. Because the addition of the anti-emulsion can eliminate the obstacle of the dispersed phase droplets binding (that is, remove the protective film outside the droplets), and make the droplets easily bind together. Also, the anti-emulsifier can make the emulsification phase inversion effect, it is O/W type to O/W type, to achieve the purpose of water separation. More commonly used anti-emulsifiers are polyoxypropane type derivatives.

8. Defoaming agent

After refining the lubricating base oil, there will still be a small number of polar substances remaining. As the lubricating oil uses various additives to meet the high-performance requirements of different mechanical equipment, foaming will occur in the current lubrication system. Not only does it affect the pumping of the lubricating oil, but it also destroys the strength and stability of the oil film, causing unnecessary abrasion accidents, or making the machine unable to operate normally. Such phenomena as oil cut-off, air blocking, sintering will continue to occur.

The role of the antifoaming agent is to suppress the generation of foam, so as not to form a stable foam. It can adsorb on the foam film and create an unstable movie, thereby achieving the purpose of destroying the foam. The most commonly used antifoaming agent is methyl silicone oil antifoaming agent. It is insoluble in oil and is distributed in the oil in a highly dispersed state by means such as colloid mill. Its dosage is generally 1-100ppm. There is also a non-silicone antifoaming agent, which belongs to polyacrylate type polymer ester. Compared with silicone oil, it can effectively improve the air release of oil products.

graphene

9. Compound additives

With the improvement of oil quality grade, functional additives are gradually changing from a single agent to a compound agent. The performance of composite additives depends not only on the improvement of the quality of the single additive agent but also through the study of additive compounding rules to determine the nature of the cooperation of the additives to obtain the composite agent with the best overall 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 lubricants is becoming more and more critical.


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