In addition to the above general physical and chemical properties, each lubricating oil shall also have special physical and chemical properties that characterize its service characteristics. The higher the quality requirements, or the stronger the specificity of the oil, the more prominent 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 lubricants with long service life have this index requirement, which has become a special performance required by these types 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 catalyst, and then the acid value, viscosity change and sediment formation of oil products are measured. All lubricants have different automatic oxidation tendency according to their chemical composition and external conditions. Oxidation occurs along with the use process, so some aldehydes, ketones, acids, colloids, asphaltenes and other substances are gradually generated. Oxidation 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 safety quality refers to the high temperature resistance of the oil, that is, the resistance of the 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 means that the polar substances in the lubricating oil form a solid physical and chemical adsorption film on the metal surface of the friction part, thus playing the role of high load resistance and friction and wear resistance. Extreme pressure means that the polar substances in the lubricating oil decompose on the metal surface of the friction part 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, it has the lubrication function of impact resistance and high load and high temperature resistance.

(4) Corrosion and rust

Due to the oxidation of oil or the action of additives, steel and other non-ferrous metals are often corroded. Generally, the corrosion test is 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 to add 30ml distilled water or artificial seawater to 300ml test oil, and then place the steel bar in it, stir it at 54 ℃ for 24 hours, and then observe whether the steel bar is corroded. The oil product should have the function of resisting metal corrosion and rust. In the industrial lubricating oil standard, these two items are usually required to be tested.

(5) Antifoam property

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

(6) Hydrolytic stability

Hydrolytic stability indicates the stability of oil 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 when meeting water, this index is often unqualified. Its measuring 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 anti emulsifying property of the 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. For general oil products, 40ml of test oil and 40ml of distilled water are violently stirred at a certain temperature for a certain time, and then the time when the oil layer, water layer and emulsion layer are separated into 40-37-3ml is observed; The industrial gear oil is to mix the test oil with water, stir it for 5 minutes at a certain temperature and 6000 rpm, place it for 5 hours, and then measure the milliliters of oil, water and emulsion layer.

(8) Air release value

The hydraulic oil standard has this requirement, 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 determining this property is similar to that for anti foaming, but it is to determine the release time of air (MIST) dissolved in the oil.

(9) Rubber tightness

Most hydraulic systems use rubber as seals. Oil products in machinery inevitably contact with some seals. Oil products with poor rubber sealing can cause rubber to swell, shrink, harden and crack, affecting its sealing. Therefore, oil products are required to have good adaptability to rubber. The hydraulic oil standard requires the rubber sealing index, which is measured by the change of a certain size of rubber ring after being immersed in oil for a certain time.

(10) Shear stability

During the use of the oil added with the tackifier, the high molecular polymer in the oil is cut off due to the effect of mechanical shear, which reduces the viscosity of the oil and affects the normal lubrication. Therefore, shear stability is a special physical and chemical property of this kind of oil. There are many methods to determine the shear stability, including ultrasonic shear method, nozzle shear method, Vickers pump shear method and FZG gear turbine shear method. These methods ultimately determine the viscosity decline rate of oil products.

(11) Solubility

Solubility is usually expressed by aniline point. The solubility limit aniline point of different grades of oil to composite additives is different. The limit value of low ash oil is greater than that of super alkaline oil, and the limit value of single-stage oil is greater than that of multi-stage oil.

(12) Volatility

The volatility of base oil is related to oil consumption, viscosity stability and oxidation stability. These properties are particularly important for multigrade oils and energy-saving oils.

(13) Rust resistance

This refers specifically to the special physical and chemical properties of antirust grease. Its test methods include humidity test, salt spray test, lamination test, water displacement test, shutter box test, long-term storage test, etc.

(14) Electrical performance

Electrical performance is the unique performance of insulating oil, mainly including dielectric loss angle, dielectric constant, breakdown voltage, pulse voltage, etc. The refining depth, impurities and moisture of the base oil have a great impact on the electrical performance of the oil.

(15) Special physical and chemical properties of lubricating grease

In addition to the general physical and chemical properties of lubricating grease, special purpose grease has its special physical and chemical properties. For example, the grease with good water resistance requires water spray test; Low temperature torque shall be measured for low temperature grease; Multi effect grease shall be tested for extreme pressure abrasion resistance and rust resistance; Long life grease shall be subject to bearing life test, etc. There are also corresponding test methods for the determination of these properties.

(16) Other special physical and chemical properties

In addition to the general performance, each oil product should have its own unique special performance. For example, the cooling rate of quenching oil shall be measured; Emulsion stability shall be determined for emulsified oil; Anti creep coefficient shall be measured for hydraulic guide rail oil; Spray lubricating oil shall be tested for oil mist diffusivity; Measure the coagulation point of the refrigerator oil; For low-temperature gear oil, the groove forming point shall be measured. These characteristics need special chemical composition of base oil or some special additives to ensure.