What are the performance requirements of air compressor oil?

Summary:1. The quality of the base oil should be high The base oil of Rotary screw air compressoroil can be divided into two categories: mineral oil type and ...
1. The quality of the base oil should be high
The base oil of Rotary screw air compressoroil can be divided into two categories: mineral oil type and synthetic oil type. The production of mineral oil type compressor oil is generally obtained by solvent refining, solvent dewaxing, hydrogenation or supplementary refining of clay and other processes to obtain base oil, and then add a variety of additives to blend.
The base oil of compressor oil generally accounts for more than 95% of the refined oil, so the quality of the base oil is directly related to the quality level of the refined oil of the compressor oil, and the quality of the base oil is directly related to its refining depth. The base oil with deep refining depth has less heavy aromatics and gum content. Low carbon residue, good susceptibility of antioxidants, high quality of base oil, small tendency to deposit carbon in the compressor system, good oil-water separation, and relatively longer service life.
Synthetic oil type base oil is a lubricating oil made of organic liquid base oil obtained by chemical synthesis and then blended or added with various additives. Most of its base oils are polymers or high molecular organic compounds. There are many types of synthetic oils. The synthetic oils used as compressor oils mainly include synthetic hydrocarbons (polyα-olefins), organic esters (diesters), polyalkylene glycols, fluorosilicone oils and phosphate esters. The price of synthetic oil-based compressor oil is much more expensive than that of mineral oil-based compressor oil, but the comprehensive economic benefits of synthetic oil still exceed that of ordinary mineral oil. It has oxidation stability, low carbon deposition tendency, can be lubricated beyond the temperature range of ordinary mineral oil, and has a long service life, which can meet the application requirements that ordinary mineral oil type compressor oil cannot bear.
2. The base oil fraction should be narrow
The working condition of compressor oil is studied and it is concluded that improving the composition of base oil is the key factor to improve the quality of compressor oil. After the compressor oil prepared from the light and heavy components is injected into the compressor cylinder, the light components leave the working part in advance due to their high volatility and affect the lubrication effect, while the heavy components are less volatile. Do not leave the work site quickly after the work task, and it is easy to form carbon deposits under the action of heat and oxygen for a long time. Therefore, under such conditions, the lubricating oil should be a narrow-cut component oil, and a component oil mixed with multiple fractions should not be used.
Oil free air compressor oil is prepared with wide-distillate oil containing a large amount of residual components, and the compressor has a large amount of carbon deposits during use. Therefore, in order to improve the quality of the compressor oil, the residual components in the No. 19 compressor oil should be removed, and the narrow-cut base oil should be selected.
3. The viscosity should be appropriate
Under the condition of dynamic lubrication, the thickness of the oil film increases with the increase of the viscosity of the oil, but the friction force also increases with the increase of the viscosity of the oil. The lubricating oil with too low viscosity is not easy to form a strong enough oil film, which will accelerate the wear and shorten the service life of the parts. On the contrary, if the viscosity of the lubricating oil is too high, it will increase the internal friction force, which will increase the specific power of the compressor, so as to increase the power consumption and oil consumption, and also in the piston ring groove, on the valve, in the exhaust passage, etc. deposits are formed. Therefore, choosing the right viscosity is the primary issue in the correct selection of compressor oil. Xi'an Jiaotong University has proved through experiments that using the same test conditions on the same type of compressor, the use of oil with lower viscosity grades can reduce the specific power of the compressor by at most about 10% compared with the use of oil with high viscosity grades. There was no significant difference in the amount of wear. Therefore, under the premise of ensuring lubrication, the selection of oil products with suitable viscosity grades has a very important impact on energy saving and reliable operation of the compressor.
4. Better viscosity-temperature performance
Oil-injected, internally-cooled rotary air compressors are repeatedly heated and cooled during operation. Therefore, it is required that the oil viscosity should not change too much due to temperature changes, and should have good viscosity-temperature properties. The viscosity index of the refined compressor oil is above 90.
5. The flash point should be appropriate
Flash point refers to the temperature at which the vapor pressure formed by heating the oil under atmospheric pressure reaches the lower limit concentration when ignited by an open flame. If the flash point is too high, the oil fraction will be heavy, the viscosity will be high, the asphaltene content will be high, and it will be easy to deposit carbon during use. If the compressor oil with high flash point is pursued unilaterally, it will become an unsafe factor. Therefore, the flash point requirements of the compressor oil can be appropriate.
 Flash point is only one of the safety indicators for oil use. Generally, the flash point of compressor oil can be controlled safely above 200℃.
 6. The tendency of carbon deposition is small
How the compressor oil resists the carbon deposition tendency is crucial to the reliable operation of the compressor oil. In actual industrial use, it is not uncommon for large and medium-sized compressors to catch fire and explode due to carbon deposits.
The main substances that easily form carbon residues in oil products are asphaltenes, colloids and polycyclic aromatic hydrocarbons. Most of the above substances can be removed after the lubricating oil is deeply refined. Generally, low-viscosity and deep-refined lubricating oils have low carbon residue values ​​and are not easy to deposit carbon during use. Therefore, high-quality L-DAB compressor oils should be highly refined narrow-cut base oils that do not contain residues (bright stock). Additives should also try to use ashless additives.