1、 Lubricating oil is a liquid lubricant used in various types of machinery to reduce friction and protect machinery and processing parts. It mainly plays the roles of lubrication, cooling, rust prevention, cleaning, sealing and buffering. Lubricating oil accounts for 85% of all lubricating materials, with a wide variety of brands. Now the annual consumption in the world is about 38million tons. The general requirements for lubricating oil are:

(1) Reduce friction and wear, reduce friction resistance to save energy, reduce wear to prolong mechanical life and improve economic benefits;

(2) For cooling, the friction heat shall be discharged from the machine at any time;

(3) Sealing, and it is required to prevent leakage, dust and gas channeling;

(4) Corrosion resistance and rust prevention. It is required to protect the friction surface from oil deterioration or external erosion;

(5) Clean and wash, and it is required to clean and remove the scale on the friction area;

(6) Stress dispersion buffer, load dispersion, impact mitigation and shock absorption;

(7) Kinetic energy transmission, hydraulic system, remote control motor and friction stepless speed change.

2、 Lubricating oil composition

Lubricating oil is generally composed of base oil and additives. Base oil is the main component of lubricating oil, which determines the basic properties of lubricating oil. Additives can make up for and improve the performance of base oil, endow some new properties, and are an important part of lubricating oil.

1. Lube base oil

Lube base oils are mainly divided into mineral base oils and synthetic base oils. Mineral base oil is widely used with a large amount (about 95% or more), but in some applications, the products blended with synthetic base oil must be used, so the synthetic base oil has developed rapidly. Mineral base oil is refined from crude oil. The main production processes of lube base oil include atmospheric and vacuum distillation, solvent deasphalting, solvent refining, solvent dewaxing, clay or hydrorefining. In 1995, China's current lube base oil standards were revised, mainly the classification method was revised, and two special base oil standards of low pour point and deep refining were added. For the production of mineral lubricating oil, it is important to select good crude oil. The chemical composition of mineral base oil includes high boiling point, high molecular weight hydrocarbon and non hydrocarbon mixture. Its composition is generally alkanes (straight chain, branched chain, multi branched chain), cycloalkanes (monocyclic, bicyclic, polycyclic), aromatics (monocyclic aromatics, polycyclic aromatics), cycloalkyl aromatics, as well as oxygen-containing, nitrogen-containing, sulfur-containing organic compounds, resins, asphaltenes and other non hydrocarbon compounds.

2. Additives

Additives are the essence of modern high-grade lubricating oil. Correct selection and reasonable addition can improve its physical and chemical properties, endow lubricating oil with new special properties, or strengthen its original

It has certain performance to meet higher requirements. According to the quality and performance requirements of lubricating oil, careful selection, careful balance and reasonable deployment of additives are the key to ensure the quality of lubricating oil. Commonly used additives include: viscosity index improver, pour point depressant, antioxidant, detergent dispersant, friction moderator, oily agent, extreme pressure agent, anti foam agent, metal passivator, emulsifier, anti-corrosion agent, rust inhibitor, demulsifier.

3、 Basic properties of lubricating grease

Lubricating oil is a technology intensive product, which is a complex mixture of hydrocarbons, and its real performance is the comprehensive effect of complex physical or chemical changes. The basic properties of lubricating oil include general physical and chemical properties, special physical and chemical properties and simulation bench test.

General physical and chemical properties

Each type of lubricating grease has its common general physical and chemical properties to indicate the internal quality of the product. For lubricating oil, these general physical and chemical properties are as follows:

(1) Appearance (chroma) the color of an oil product can often reflect its refining degree and stability. For base oil, the higher the refining degree is, the cleaner the oxide and sulfide of hydrocarbon are removed, and the lighter the color is. However, even if the refining conditions are the same, the color and transparency of base oils produced by crude oils from different oil sources and base genera may also be different. For new finished lubricating oil, due to the use of additives, color has lost its original significance as an indicator to judge the refining degree of base oil.

(2) Density density is a simple and commonly used physical property index of lubricating oil. The density of lubricating oil increases with the increase of the amount of carbon, oxygen and sulfur in its composition. Therefore, under the same viscosity or the same relative molecular weight, the lubricating oil with more aromatics, more gum and asphaltene has higher density, the lubricating oil with more cycloalkanes is in the middle, and the lubricating oil with more alkanes is small.

(3) Viscosity viscosity reflects the internal friction force of an oil product and is an indicator of the oiliness and fluidity of an oil product. Without any functional additives, the higher the viscosity, the higher the oil film strength and the worse the fluidity.

(4) Viscosity index viscosity index indicates the degree to which oil viscosity changes with temperature. The higher the viscosity index is, the less the oil viscosity is affected by temperature, the better its viscosity temperature performance is, and vice versa.

(5) Flash point flash point is an indicator of oil evaporation. The lighter the distillate, the greater the evaporation and the lower the flash point. On the contrary, the heavier the distillate, the smaller the evaporation, and the higher the flash point. At the same time, the flash point is an indicator of the fire risk of petroleum products. The danger level of oil products is divided according to the flash point. The flash point below 45 ℃ is flammable, and the flash point above 45 ℃ is flammable. It is strictly prohibited to heat the oil products to its flash point temperature during the storage and transportation of oil products. With the same viscosity, the higher the flash point, the better. Therefore, users should choose lubricating oil according to the operating temperature and working conditions of lubricating oil. It is generally believed that the flash point is 20-30 higher than the operating temperature

℃, which is safe to use.

(6) Freezing point and pour point the freezing point refers to the high temperature at which the oil product stops flowing under the specified cooling conditions. The solidification of oil products is very different from that of pure compounds. There is no definite solidification temperature for oil products. The so-called "solidification" only loses fluidity as a whole, and not all components become solids. The freezing point of lubricating oil is an important quality index that indicates the low temperature fluidity of lubricating oil. It is of great significance for production, transportation and use. Lubricants with high pour point cannot be used at low temperatures. On the contrary, it is not necessary to use lubricants with low freezing point in areas with high temperature. Because the lower the freezing point of lubricating oil, the higher the production cost, causing unnecessary waste. Generally speaking, the freezing point of lubricating oil should be 5~7 ℃ lower than the low temperature of the operating environment. However, it should also be mentioned that when selecting low-temperature lubricating oil, the freezing point, low-temperature viscosity and viscosity temperature characteristics of the oil should be considered comprehensively. The low temperature viscosity and viscosity temperature characteristics of low freezing point oil may also not meet the requirements. Freezing point and pour point are indicators of low-temperature fluidity of oil products. There is no principle difference between them, but the determination method is slightly different. The pour point and pour point of the same oil are not exactly the same. Generally, the pour point is 2 ~ 3 ℃ higher than the pour point, but there are exceptions.

(7) Acid value, base value and neutralization value acid value is an indicator of acidic substances in lubricating oil, and the unit is mgkoh/g. The acid value can be divided into strong acid value and weak acid value, and the combination of the two is the total acid value (Tan for short). What we usually call "acid value" actually refers to "total acid value (tan)". The base number is an indicator of the content of alkaline substances in lubricating oil, and the unit is mgkoh/g. The base number is also divided into strong base number and weak base number, and the combination of the two is the total base number (TBN). What we usually call "base number" actually refers to "total base number (TBN)". Neutralization value actually includes total acid value and total base value. However, unless otherwise noted, generally speaking, "neutralization value" only refers to "total acid value", and its unit is also mgkoh/g.

(8) Moisture moisture refers to the percentage of water content in lubricating oil, usually the weight percentage. The presence of water in the lubricating oil will damage the oil film formed by the lubricating oil, worsen the lubricating effect, accelerate the corrosion of organic acids on metals, rust equipment, and make the oil easy to produce sediment. In short, the less water in lubricating oil, the better.

(9) Mechanical impurities mechanical impurities refer to the precipitates or colloidal suspensions in lubricating oil that are insoluble in gasoline, ethanol, benzene and other solvents. Most of these impurities are sand, stone and iron filings, as well as some organic metal salts that are difficult to dissolve in solvents brought by additives. Generally, the mechanical impurities of lubricating base oil are controlled below 0.005% (mechanical impurities below 0.005% are considered as none).

(10) Ash and sulfuric acid ash ash refers to the non combustible substance left after burning under the specified conditions. The composition of ash is generally considered to be some metal elements and their salts. Ash has different concepts for different oil products. For base oil or oil products without additives, ash can be used to determine the refining depth of oil products. For oil products (new oil) with metal salt additives, ash content has become a means to quantitatively control the amount of additives added. Sulfuric acid ash is used to replace ash in foreign countries. The method is to add a small amount of concentrated sulfuric acid after burning the oil sample and before burning and ashing to convert the metal elements of the additive into sulfate.

(11) Under the specified experimental conditions, the coke black residue formed after heated evaporation and combustion of carbon residue oil is called carbon residue. Carbon residue is an important quality indicator of lube base oil, and it is a specified item for judging the nature and refining depth of lube oil. The amount of carbon residue in lube base oil is not only related to its chemical composition, but also to the refining depth of the oil. The main substances that form carbon residue in lube oil are gum, asphaltene and polycyclic aromatic hydrocarbons in the oil. Under the condition of insufficient air, these substances are subject to strong thermal decomposition and condensation to form carbon residue. The deeper the refining depth, the smaller the carbon residue value. Generally speaking, the smaller the residual carbon value of blank base oil, the better. Nowadays, many oil products contain additives of metal, sulfur, phosphorus and nitrogen elements, and their residual carbon value is very high, so the residual carbon of additive oil has lost the original significance of residual carbon determination. Mechanical impurities

Moisture, ash and carbon residue are all quality indicators reflecting the purity of oil products and the refining degree of lubricating base oil.

Special physical and chemical properties

In addition to the above general physical and chemical properties, each lubricating oil should also have special physical and chemical properties that characterize its use characteristics. The higher the quality requirements or the stronger the specificity of the oil, the more outstanding its special physical and chemical properties. The test methods reflecting these special physical and chemical properties are briefly introduced as follows:

(1) Oxidation stability: oxidation stability indicates the anti-aging performance of lubricating oil. Some industrial lubricating oils with long service life have this index requirement, so it has become a special performance required by these kinds of oils. There are many methods to determine the oxidation stability of oil products. Basically, a certain amount of oil products are oxidized at a certain temperature for a certain time in the presence of air (or oxygen) and metal catalysts, and then the acid value, viscosity change and sediment formation of oil products are determined. All lubricating oils have different tendency of automatic oxidation according to their chemical composition and external conditions. Oxidation occurs with the use process, thus gradually generating some aldehydes, ketones, acids, resins, asphaltenes and other substances. Oxidative stability is the performance of inhibiting the formation of the above substances that are not conducive to the use of oil products.

(2) Thermal stability: thermal stability refers to the high temperature resistance of oil products, that is, the resistance of lubricating oil to thermal decomposition, that is, the thermal decomposition temperature. Some high-quality anti-wear hydraulic oils and compressor oils have put forward the requirements of thermal safety. The thermal stability of oil products mainly depends on the composition of base oil. Many additives with low decomposition temperature often have adverse effects on the stability of oil products; Antioxidants can not significantly improve the thermal stability of oil products.

(3) Oiliness and extreme pressure: oiliness refers to that the polar substances in lubricating oil form a solid physicochemical adsorption film on the metal surface of the friction part, thus playing the role of high load resistance and friction and wear resistance, while extreme pressure refers to that the polar substances in lubricating oil decompose under high temperature and high load, and react with the surface metal to form a soft (or plastic) extreme pressure film with low melting point, thus playing the role of impact resistance and high load high temperature resistance.

(4) Corrosion and rust: due to the oxidation of oil products or the action of additives, it often causes the corrosion of steel and other non-ferrous metals. The corrosion test is generally to put the red copper bar into oil, place it at 100 ℃ for 3 hours, and then observe the change of copper; The corrosion test is that the steel surface will rust under the action of water and steam. The determination of rust resistance is to add 30ml of distilled water or artificial sea water to 300ml of test oil, then place the steel bar in it, mix it at 54 ℃ for 24 hours, and then observe whether the steel bar has rust. The oil product should have the effects of metal corrosion resistance and rust prevention. In the industrial lubricating oil standard, these two items are usually required to be tested.

(5) Anti foaming property: during the operation of lubricating oil, due to the presence of air, foam will often be generated, especially when the oil contains additives with surface activity, it is easier to generate foam, and the foam is not easy to disappear. The foam generated in the use of lubricating oil will damage the oil film, cause the friction surface to sinter or increase wear, promote the oxidation and deterioration of lubricating oil, and also make the lubrication system air resistance, affecting the circulation of lubricating oil. Therefore, anti foaming property is an important quality index of lubricating oil.

(6) Hydrolytic stability: hydrolytic stability characterizes the stability of oil products under the action of water and metals (mainly copper). When the oil has a high acid value or contains additives that are easy to decompose into acidic substances in water, this indicator is often unqualified. Its measurement method is to add a certain amount of water to the test oil, mix and stir the copper strip at a certain temperature for a certain time, and then measure the acid value of the water layer and the weight loss of the copper strip.

(7) Demulsibility: industrial lubricating oil is often inevitably mixed with some cooling water in use. If the demulsibility of lubricating oil is not good, it will form emulsion with the mixed water, making it difficult for the water to be discharged from the bottom of the circulating oil tank, which may cause poor lubrication. Therefore, demulsibility is a very important physical and chemical property of industrial lubricants. Generally, 40ml of test oil and 40ml of distilled water are vigorously stirred at a certain temperature for a certain time, and then the time for oil layer water layer emulsion layer to separate into 40-37-3ml is observed; The industrial gear oil is to mix the test oil with water, mix it for 5 minutes at a certain temperature and 6000 rpm, and place it for 5 hours, and then measure the milliliters of oil, water and emulsified layer.

(8) Air release value: there is this requirement in the hydraulic oil standard, because in the hydraulic system, if the air dissolved in the oil cannot be released in time, it will affect the accuracy and sensitivity of hydraulic transmission, and in serious cases, it will not meet the use requirements of the hydraulic system. The method for measuring this performance is similar to that for anti foaming, but it is to measure the release time of air (MIST) dissolved in the oil.

(9) Rubber tightness: most of the hydraulic system uses rubber as seals. Oil products in machinery inevitably contact with some seals. Oil products with poor rubber tightness can swell, shrink, harden and crack the rubber, affecting its tightness. Therefore, oil products and rubber are required to have good adaptability. The hydraulic oil standard requires the rubber sealing index, which is measured by the change of a certain size of rubber ring after immersion in oil for a certain time.

(10) Shear stability: during the use of the oil added with viscosity enhancer, due to the effect of mechanical shear, the high polymer in the oil is sheared, so that the viscosity of the oil decreases,