From the point of view of lubrication, the oil injected internal cooling compressor is the most widely used type at present. In this kind of air compressor, the lubricating oil is pressed into the air compressor by the oil pump to lubricate the bearings and screws respectively. The lubricating oil is directly injected into the air compressor and mixed with the compressed air in the form of mist to absorb the compressed heat in the air. At the same time, an oil film is formed on the rotor cylinder and the covering surface to play the role of sealing and lubrication, and then discharged into the gas storage tank together.

　　The requirement of air compressor for lubricating oil is very strict. Therefore, the correct selection of air compressor oil for reasonable lubrication is an important measure to ensure the safe and stable operation of air compressor, and the factors that determine the quality of compressor oil usually come from the following aspects:

　　1. Quality of base oil

　　The base oil of air compressor oil generally accounts for more than 95% of the product oil, so the quality of base oil is directly related to the quality level of air compressor oil, and the quality of base oil is directly related to the refining depth. The heavy aromatics and gum content of the deep refining base oil are less, the carbon residue is low, the sensitivity of antioxidant is good, the tendency of carbon deposition in the air compressor system is small, and the oil-water separation is good. Base oil has a great influence on the performance of screw air compressor oil, so high quality hydrogenated mineral oil or synthetic oil is generally selected as base oil.

　　2. Oxidation stability

　　In the process of recycling, oil products are in constant contact with the high temperature and high pressure oxygen in the compressed air, which is easy to be oxidized and metamorphosed to produce various acids, resins, asphaltenes and other substances, so that the color of oil products becomes darker, the acid value increases, the viscosity increases and deposits appear, so as to reduce the injection amount of oil, increase the temperature of oil products and machines, and generate excessive wear. Therefore, screw air compressor oil must have excellent oxidation stability to ensure long-term safe use of oil. Coking tendency

　　The anti coking tendency of compressor oil is very important for the reliable operation of compressor oil. The main materials that are easy to form carbon residue in oil products are asphaltene, gum and polycyclic aromatic hydrocarbon. Most of the above substances can be removed after deep refining of lubricating oil. Generally, the carbon residue value of low viscosity and deep refined lubricating oil is low, so it is not easy to deposit carbon in use. The coking tendency performance of oil products is the comprehensive performance of various indexes, and there are many influencing factors, among which the additive should also be ash free.

　　3. Oil water separation

　　During the operation of the air compressor, it constantly meets with the condensed water in the air and is stirred violently, which is easy to produce emulsification phenomenon, resulting in unclear oil-gas separation and increased oil consumption. As the oil is emulsified, the oil film is damaged, resulting in wear. Emulsified oil will disperse dust, grit and sludge, affect the function of valve, increase friction, wear and oxidation. Therefore, high quality air compressor oil has good demulsibility and oil-water separation performance.

　　4. defoaming property

　　When the screw air compressor oil is used in circulation, the circulation speed is fast, and the oil is in a state of intense mixing. When the compressor oil starts or depressurized, the oil in the oil pool is also bubbling easily. A large number of oil bubbles are poured into the oil and gas separator, which makes the resistance increase and fuel consumption increase, which will cause serious overloading, overheating and other abnormal phenomena. Therefore, the excellent rotary compressor oil must have excellent defoaming performance to ensure that the foam tendency of the oil product (i.e. foaming) is small and foam stability (i.e. defoaming) is good.

　　5. Rust and corrosion resistance

　　The oil cooling and other parts of air compressor are made of copper or copper metal, which is easy to be corroded and will cause early oxidation and deterioration of oil products, resulting in oil sludge. This requires that oil products should have good corrosion resistance. The moisture in the air is easy to be cooled in the screw machine operated intermittently, which is not good for lubrication and can produce corrosion, so it is required that the compressor oil should have a good anti rust effect.

　　Of course, according to the characteristics of different air compressor oil, different working conditions and different environments, the oil products required by different manufacturers will be different. Here are some common types of screw air compressor oil.

　　Compared with ordinary air compressor oil, high-quality air compressor oil has the following customer benefits:protect the compressor parts to prevent wear and prolong the service life of the parts greatly reduce maintenance, spare parts costs and downtime losses, and lower operating costs. wide range of operating temperature, one kind of oil can be used in all-weather and different areas, and it can still work under severe conditions longer oil change period, maintenance free low oil consumption, fuel saving, energy saving and greatly reduced lubrication cost.