O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

additives are divided depending on the purpose into:
1) detergents - to remove oil oxidation products from friction surfaces. They are surfactants that help keep solid particles in suspension in the oil;
2) antioxidant - to slow down the oxidation of oils;
3) extreme pressure - for the formation of strong films on friction surfaces that prevent seizure;
4) anti-corrosion - to protect metals from corrosion;
5) antifriction - to reduce the coefficient of friction (animal and vegetable oils, organic compounds of sulfur, phosphorus, metals, etc.);
6) anti-wear - to reduce wear (barium salts, zinc, etc.);
7) antifoam - to eliminate the foaming of oils in engine lubrication systems;
8) multifunctional.
Tribopolymerizable additives constitute a special group. They initiate the cross-linking of oil molecules or self-form high-molecular compounds under the action of friction, which leads to the formation of separating films on the friction surfaces. The latter have high adhesion to metals and strength. They have an anti-wear and anti-friction effect, do not dissolve in oil and are regenerated as they wear.
Water-based lubricating compositions contain glycols or glycerin, as well as a water-soluble thickener, which gives the composition the desired viscosity. They began to be developed due to the shortage of oil raw materials. The compositions have the structure of sols - liquid colloidal systems with particles of the dispersed phase - micelles. Micelle - in this case, a molecule of glycol or glycerol, surrounded by a layer of water molecules or ions of its constituents. During the adsorption of micelles on friction surfaces, films with good load and lubricity are formed.
Lubricant composition concentrates are used as technological materials in the processing of metals by pressure. Their aqueous solutions (5-10%) are used in friction units of machines and as drilling fluids during the drilling of oil and gas wells.
Liquid metals are used as lubricants mainly in vacuum systems, where they provide lubrication and sealing of friction units. Potassium, mercury, eutectic alloys of gallium with indium and tin are used to seal the input of rotating shafts into spacecraft. In movable seals of vacuum equipment, fusible inserts made of Wood's alloy, tin, silver, and indium are used.
Greases are semi-solid or solid products consisting of a mixture of mineral or synthetic oil and soaps or other thickeners. A feature of their structure is the presence of a framework formed by thickener particles, in the cells of which oil is enclosed. Due to the framework, plastic materials under normal conditions are solids. Under load, the frame collapses, and they flow like oil. When the load is removed, the frame is restored, the material solidifies and is held on the part.
As a thickener, soaps are most often used - salts of fatty acids. Depending on the composition of the soap, greases are divided into calcium, sodium, mixed calcium-sodium, etc.
Calcium lubricants ( greases ) contain free and bound water, do not dissolve in water. They have a lubricating effect in a humid environment, the maximum operating temperature is +55 ⁰ C. When melted, they lose water and decompose into oil and soap. After cooling, the original structure of the grease is not restored.
Sodium greases ( constalines ) melt in the range of +100 - 200 ⁰ C. Solidifying after melting, they restore the original lubricating parameters. Easily soluble in water at elevated temperatures.
Calcium-sodium greases combine the advantages of these two classes of materials. They are used at high temperatures and low humidity.
Lithium greases have become widespread in recent decades. Lithium soaps are practically insoluble in water and are effective thickeners. Lithium is a waste product of the nuclear industry and is readily available. The material with the trade name lithol is widely used in the main friction units of domestic cars.
Paraffin, ceresin, petrolatum, polymers, etc. are also used as thickeners. They are used mainly for the production of conservation (gun grease, technical petroleum jelly) and sealing lubricants.
Anti-friction plastic materials according to GOST 23258 - 78 are divided into groups: general purpose, multi-purpose, heat-resistant, frost-resistant, anti-wear and extreme pressure, chemically resistant, instrument, gear, running-in, highly specialized, briquette.
Solid lubricants are used in the form of powders or thin films. In composition, these are organic or inorganic substances, or combinations thereof.
Inorganic materials are divided into several groups. The first of these are graphite, molybdenum disulfide MoS ₂ , tungsten disulfide WS ₂ , diselenides NbSe ₂ , TaSe _{2 ,} etc., difluorides CaF ₂ , etc. They are characterized by high adhesion to structural materials and unequal strength in different directions, i.e. have anisotropy. Their crystal lattice has a layered structure (Fig. 10.2) with strong bonds between atoms in the plane of the layer and weak bonds between the layers.
These materials are mined as minerals or can be synthesized. They are relatively cheap and available.
Molybdenum disulfide or molybdenite has a low coefficient of friction in high vacuum (10 Pa
⁰ С) and high (up to +700 ⁰ С) temperatures. Its lubricating effect is weakly affected by ionizing radiation. Therefore, molybdenite is a part of lubricating compositions used in space, cryogenic and nuclear technology.
Graphite is less versatile as a lubricant. The intermolecular interaction of its layers is strongly influenced by the sorption of environmental components, in particular, water. Low molecular weight components are located between the layers and reduce their attraction. Therefore, in high vacuum, when they are removed, the lubricity of graphite becomes significantly worse. The strength of graphite increases with increasing temperature. It has high thermal and electrical conductivity. The friction coefficient of graphite depends little on the sliding speed. Graphite has good adhesion to metal oxides and cast iron, forming a stable film during friction, in which the crystalline layers are oriented parallel to the friction surface. Optimal applications for graphite are high temperature lubrication and sliding electrical contacts.
The second group of inorganic solid lubricants consists of non-ferrous and rare metals (lithium, lead, cadmium, silver, gold, etc.), which are used as coatings. The mechanism of their lubricating action resembles that of oil lubrication. Metallic coatings are used in conditions unacceptable for oils: wire drawing, tube rolling, large temperature differences, etc.
Organic materials - soaps, waxes, fats, polymers.
Soaps - salts of higher fatty acids, in particular, salts obtained from fat substitutes - synthetic fatty acids, tall oil, naphthenic and resin acids. Waxes are fat-like substances of animal or vegetable origin.