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How to choose refrigerant oil for refrigeration compressor and unit?

Number of visits: Date:2017-07-07 16:59:42
The lubricant in a refrigerator is different from other mechanical equipment, and the choice of lubricant is also different due to the different conditions of use and refrigerant. The requirements of refrigeration oil are as follows:
1. viscosity: lubricating oil viscosity is an important parameter in the characteristics of the oil, the use of different refrigerants to choose different refrigerant oil. In addition, the viscosity of the lubricating oil is also related to the temperature of the refrigerator. When the temperature rises, the viscosity of the oil decreases. The viscosity of lubricating oil in refrigeration equipment through the general assembly of mechanical friction power, friction and heat starting torque increases, if the viscosity is too small, it will make the moving parts can form oil film required, can not due to lubrication and cooling effect.
2. cloud point: the cloud point of lubricating oil is when the temperature drops to a certain value, the lubricating oil begins to separate the wax and makes the lubricant become cloudy. The evaporation temperature of refrigeration equipment for lubricating oil should be lower than the cloud point of refrigerant, or when the precipitation of paraffin lubricating oil, will accumulate in the throttle valve, throttle plug, heat transfer surface or may be stored in the evaporator, the heat transfer performance influence.
3. freezing point: the temperature at which lubricating oil is cooled to stop flow is called freezing point. In the refrigeration system, heat exchange equipment and pipelines, usually work at low temperature, and the pipe wall are more or less oil film, the freezing point of how high oil will affect the refrigerant flow, increase flow resistance, effect of heat transfer effect. Generally speaking, for freezing equipment, the freezing point should be as low as possible, such as R-22 compressor, refrigeration oil should be below -55 degrees celsius. If used in cryogenic installations, the freezing point should be lower.
4. flash point: This is the minimum temperature that occurs when the lubricant is heated to its flame. The lubricating oil used in refrigeration equipment must be more than 15~30 degrees higher than the exhaust temperature so as not to cause combustion and coking of the lubricating oil. Usually R-12 and R-22 lubricants, flash point requirements above 160 degrees celsius.
5. chemical stability and oxygen resistance: pure lubricating oil, chemical composition, stable, non oxidation, will not corrode the metal. However, when the lubricant contains refrigerant or water, it will produce corrosive effect, lubricating oil will produce acid after oxidation, corrosion of metal. When the oil is in high temperature, Coke will appear. If the material is attached to the valve plate, it will affect the normal operation of the valve and cause clogging of the filter and throttling valve. Therefore, it is necessary to choose a refrigerator lubricant with good chemical stability and oxidation resistance.
6. moisture and mechanical impurities: if the oil contains moisture, it will exacerbate the chemical changes in oil, oil metamorphism, causing corrosion of the metal, but also in the throttle or expansion valve at the "ice jam"". And lubricating oil contains mechanical impurities, will aggravate the friction surface of moving parts wear, and soon plug the filter and throttle valve or expansion valve, so the refrigerator lubricant should not contain mechanical impurities.
7. insulation performance: in the semi closed and closed in the freezer, freezing lubricating oil and refrigerant directly and the winding of the motor and the terminal contact, thus lubricating oil has good insulating properties, high breakdown voltage. Pure lubricating oil insulation performance is better, but contain moisture, impurities and dust, its insulation performance will drop, general refrigerator lubricant requirements breakdown voltage is above 2.5KV.
8. due to different characteristics of various types of refrigerant, the refrigeration system working temperature difference, the refrigerator oil generally can be selected: equipment of low speed, low temperature freezing can be used lubricating oil low viscosity, low freezing point and high speed air conditioning equipment; or under the condition of freezing should be used lubricating oil viscosity, freezing point high.
According to the refrigeration oil 40 degrees viscosity size is divided into N15, N22, N32, N46 and N68 five viscosity grade, selection of refrigeration oil mainly depends on the type of refrigerant, compressor types and operating conditions (evaporation temperature, condensation temperature), generally in accordance with the requirements specified by the compressor.

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