Industrial oils are commonly used to lubricate various equipment and machinery. These oils are usually used in relatively low temperatures: below 100°С, most commonly at 40-60°С, and without direct contact with steam, hot air or any other factors of changing the chemical composition and physical properties of the hydrocarbons in the oil. Industrial oils become contaminated by atmospheric dust, metal particles (especially if lubricating metal-working equipment), fibers (in the case of textile industrial machinery), in the course of abrasive wear of parts, clogging of oil conduits and purification devices, intensification of corrosion, increased vulnerability of the oil to foaming and oxidation.
The moderate temperature of industrial oil application makes the oxidation rate relatively slow.
At the same time, industrial oils tend to accumulate resin and asphaltenes, formed in the process of oxidation, catalyzed by metal particles; the process generates sludge, which can foul up equipment and piping.
The degree of industrial oil aging can be apparent by the darkening color, appearance of sharp acidic smell, thickening and the formation of sludge in the oil. There are three kinds of sediment:
1) dark, grainy, similar to fine coal particles;
2) relatively light, rather viscous materials, which can solidify into a dense varnish like substance with heating and oxygen;
3) dark, with sometimes large grains, usually form in the presence of water, which enters the lubrication system.
The first type of sediment includes asphaltenes, carbenes and carboids. The sediment in industrial oils used in various machines and equipment is made up mostly of asphaltenes.
The second types of sediment is mixture of substances, referred to as oxyacids: with high ester numbers due to the presence of lactonic and estolid groups. Besides, these products contain ketoacids. The higher the temperature of the lubricated parts, the more estolids (the products of oxyacid condensation) there are, and the denser the sediment. The products of deep estolide condensation are high molecular asphaltogenic acids, which then transform into carbon-line state; the elementary composition is similar to humic compounds of coals. This path of oxyacid condensation is also possible with long oil use at lower temperatures around 50-100°С.
The products of oxyacid condensation settle in the form of varnish on various equipment surfaces, hindering operation of the machinery.
The third type of sediment consists of iron, copper, lead and other salts of organic acids(carbon and oxyacids), formed in the process of reaction between these acids and metals in the presence of water and oxygen. The third type of sediment in the oil leads to formation of stable emulsions in oil tanks.