General knowledge of compressor oil: compressor (divided into air compressor and various gas compressors), refrigerator and vacuum pump (mainly referring to mechanical vacuum pump), there are great similarities between the basic actions such as compression generating pressure, compression expansion refrigeration, compression evacuation and lubrication requirements. For example, it is necessary to bear the sealing effect of compressed gas between the piston and the cylinder wall at the lubrication position (i.e. lubricating cylinder, piston, valve, bearing, sliding plate, etc.), and also have the performance that does not work with compressed gas.
1、 Use characteristics of compressor oil
1. High temperature oxidation: when the compressor is running, the lubricating oil entering the cylinder contacts with high temperature gas and high temperature metal surface. If the temperature in the gas is higher, the oxidation speed of the lubricating oil will be faster. Experiments show that when the temperature of compressor oil increases 10 ℃, the oxygen absorption speed of oil increases 1.5 times.
The lubricating oil oxidizes violently at high temperature (the lubricating oil in the compression chamber of piston air compressor is mainly thin-layer oxidation) and deteriorates rapidly, forming carbon deposits on the exhaust valve and other exhaust system pipe walls.
2. High oxygen partial pressure: the oxidation speed of compressor oil is not only proportional to the oxidation temperature and time, but also proportional to the oxygen concentration. The oxidation rate of lubricating oil in air is only 1 / 5 of that in oxygen. At the same time, the oxidation rate of lubricating oil in air is about the same at 0.1MPa.
3. Oil mist: in the piston compressor, the lubricating oil is splashed to the lower part of the cylinder by the crankcase splash method, and then brought into the upper part of the cylinder by the piston ring (for the compressor without crosshead), or into the cylinder by the pressure oil feeding method (for the compressor with crosshead). In a rotary compressor, oil is injected directly into the cylinder. The oil droplets that enter the internal lubrication system together with the gas are crushed into oil mist in different parts under the impact of high-speed airflow pulse. Although the oil mist can evenly distribute on each moving part and play a good role in lubricating and effectively cooling high-temperature gas, due to the large surface area of the oil mist, the chance of contact with high-temperature gas is increased, which increases the oxidation speed of the lubricating oil. On the other hand, due to the speed of air flow, the process of oil mist deposition into oil drops is delayed, which leads to the decrease of oil-gas separation efficiency of oil-gas separator in compressor exhaust system, the increase of oil content in exhaust gas, and the increase of oil consumption and air pollution.
4. Large amount of circulating oil: Although the temperature of the contact between oil droplets and gas in the oil injection internal cooling rotary compressor is not as high as that in the piston compressor, and the proportion of oil gasification to oil vapor is small in the compression process, the exhaust temperature of the first stage oil cooling vane compressor with severe working conditions can sometimes reach about 120 ℃. Another working feature of the oil injected internal cooling rotary compressor is the large amount of circulating oil. The lubricating oil is continuously heated by high temperature gas in the air chamber and cooled in the cooler, and at the same time, it repeatedly contacts with the metal surface and is catalyzed by the metal. Therefore, the oxidation catalysis of the lubricating oil is accelerated, the oil is rapidly aging, and the oil change period is shortened.
5. Condensate: there is a certain amount of water vapor in the air, which flows into the air cavity of compressor with air or other gases. When it is cold, it condenses into water drops and stays on the parts or mixed with oil, which makes the parts rusty and oil emulsified.
6. Pollution gas: in addition to compressed air, the compressor also compresses other gases, such as hydrogen, oxygen, petrochemical gas, natural gas, gas and other acid gases. When these gases are mixed with corrosive substances, they will have different degrees of corrosion on the metal surface contacting the compressor parts. At the same time, the suspended dust particles in the air constantly enter the compressor, and these impurities are often strong oxidation catalysts, which not only make the lubricating oil rapidly aging, promote the generation of carbon deposits in the exhaust system and the pollution of the cylinder and aftercooler, but also increase the wear of the parts.