Vacuum pump (mainly refers to mechanical vacuum pump), compressor (air compressor, various gas compressors) and refrigerator have special requirements for lubricating oil. The vacuum pump oil is used in the mechanical vacuum pump in the vacuum system. The compressor oil is mainly used in the lubrication of reciprocating piston type gas compressor, exhaust machine and piston pump's cylinder and piston friction parts and inlet and exhaust valves. When it is used in the automatic oil feeding lubrication system, it also lubricates the compressor's main bearing, connecting rod bearing, crosshead, sliding plate, etc, Low viscosity is also used in all kinds of rotary compressors. Refrigeration oil is mainly used in compressor to compress refrigerant.
The three have different uses, but they have many things in common. For example, in addition to the lubrication of the cylinder, piston, valve, bearing, sliding plate and other parts, they also have to bear the sealing function of preventing the compressed gas from channeling between the piston and the cylinder wall, and also have the chemical stability that does not work with the compressed gas.
Vacuum pump oil is a special lubricating oil for mechanical vacuum pump. Although there are different types of pumps, the requirements for oil quality are the same. During the operation of the vacuum pump, the oil in the pump cavity on the one hand plays a sealing role, making the pump obtain the necessary vacuum degree; on the other hand, the oil in the pump cavity is affected by friction, temperature and pressure reduction, and the components with high vapor pressure evaporate into the vacuum space, polluting the vacuum system and limiting the improvement of vacuum degree. In addition to proper viscosity, high viscosity index, good oil-water separation and excellent thermal oxidation stability, the most important quality requirement of vacuum pump oil is low saturated vapor pressure and extremely strong limit to ensure high vacuum degree. Therefore, in the production of vacuum pump oil, in addition to selecting the appropriate base oil type, a single narrow fraction oil or pure chemicals should be used instead of blending several fractions as far as possible.
For reciprocating compressor, because the discharge temperature of compressed gas is higher than that of suction, it needs better viscosity temperature performance, suitable viscosity and better anti-oxidation stability. It is usually made of deeply refined base oil (preferably naphthenic base oil) and additives with anti-oxidation, corrosion and anti-wear properties (generally, pour point depressant and viscosity reducer are not allowed). For the rotary compressor oil, its working condition and lubrication mode are quite different from that of reciprocating compressor, so it puts forward more stringent requirements on the quality of lubricating oil. In addition to lubricating, cooling and sealing the parts, the rotary compressor oil also plays a prominent role in cooling the compressed gas. In the process of use, the oil mist is separated from the gas after mechanical collision and adsorption medium, The oil is easy to be polluted and aged due to repeated circulation. At the same time, in order to overcome the rotary centrifugal force, the oil needs good adhesion, and the bearing does not need the lubricating oil with too high viscosity. Therefore, the rotary air compressor oil is generally produced with the base oil of deep refining narrow fraction, and the additives of compound antioxidant, antirust, anti-wear, demulsification and defoaming are added.
In addition to meeting the above basic requirements, the refrigerator oil should have excellent low temperature performance and good separation from refrigerant or water. Therefore, the general refrigeration engine oil is produced by deep refining low freezing point naphthenic base oil. It is worth noting that when SO2 is used as refrigeration engine oil, the deep refining lubricating oil (such as white oil) without aromatics and sulfur oxides should be selected. Otherwise, gum precipitation will be generated, which will affect the operation of the refrigerator. When chloroethane is used as refrigerant, petroleum will be dissolved, and glycerin and castor oil are generally used for lubrication; When ammonia or carbon dioxide is used as refrigerant, lubricating oil without fatty oil should be used, because fatty oil is easy to emulsify, which is not conducive to water separation and freezing, and the thermal conductivity of fatty oil is small, which leads to the decrease of freezing efficiency.
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