1. Viscosity: Viscosity is a main performance index of frozen oil. Different refrigerants have different requirements on viscosity. For example, R12 and frozen oil can dissolve each other, which will reduce the viscosity of the frozen oil. Therefore, the viscosity of the frozen oil should be selected. Compression The viscosity of the frozen oil in the machine is too large and too small. The viscosity is too large to increase the frictional power and friction heat of the compressor, the starting torque is increased, and the machine efficiency is reduced. If the viscosity is too small, the required oil film cannot be established. Accelerate the wear of bearings, etc. Therefore the viscosity must be moderate. The viscosity of the frozen oil varies greatly with temperature (for example, when the temperature is raised from 50 ° C to 100 ° C, the viscosity of the mineral oil is reduced to 1/3 of the original value. -1/6). Therefore, the temperature should be selected to have a small effect on the viscosity of the frozen oil.
2. Cloud point: The cloud point of the refrigerating oil is the temperature at which the precipitation of paraffin (ie, the chilling oil becomes turbid) begins when the temperature is lowered to a certain value. The refrigerating oil used in the refrigerating compressor, The cloud point should be lower than the evaporation temperature of the refrigerant. Especially in the fluorine system, a part of the refrigerant oil is dissolved in the refrigerant and flows to the refrigeration system with the refrigerant. If paraffin is precipitated in the oil, it will accumulate in the throttle valve. Causing blockage, or accumulated in the heat transfer surface of the evaporator, reducing heat transfer.
3. The freezing point of the freezing oil under the test conditions, cooling to the temperature at which the flow stops, called the freezing point. For the refrigeration oil of the refrigeration compressor, the freezing point should be as low as possible. The general freezing point should be lower than -40 ° C. When the frozen oil and When the refrigerant dissolves with each other, the freezing point will decrease.
4. Flash point: When the frozen oil (in the open oil sump) is heated until its steam is in contact with the flame, the lowest temperature at which the flash fire occurs is called the flash point. The freezing oil used in the refrigeration compressor should have a flash point that is more than the exhaust steam. The temperature is 25-35 °C, so as not to cause the combustion and coking of the frozen oil. The freezing oil for ammonia, R12 and R22 should be above 160-170 °C.
5. Learning stability and oxidation resistance Refrigerated oil should have good chemical stability and oxidation resistance. Otherwise, under the catalysis of high temperature or metal, contact with refrigerant and other reactions will produce harmful substances such as coke and acid.
6. Water content and mechanical impurities: The frozen oil should not contain water, because the water will not only lower the evaporation pressure, but also increase the evaporation temperature, and it will aggravate the chemical change of the oil and the role of corrosive metals. The water is still in the Freon compressor. It will cause "plating phenomenon", causing copper parts to react with Freon to decompose copper and accumulate on the steel surface of bearings, valves and other parts. As a result, the thickness of these tables is increased, the gap of the bearing is broken, and the machine is broken. Poor operation. This phenomenon occurs in closed and semi-hermetic compressors. Generally, new oils do not contain moisture and mechanical impurities, because the refrigeration oil used in refrigerators undergoes strict dehydration during production. Treatment. However, the dehydrated frozen oil has strong hygroscopicity. Therefore, when storing and transporting, it should be avoided to contact with air. The frozen oil is dissolved and diluted with gasoline or benzene, and the residual material after filtering with filter paper is called frozen oil. Mechanical impurities. Mechanical impurities in the frozen oil will accelerate the wear of the parts and reduce the insulation performance of the oil, blocking the refrigeration oil passage, so the impurities are as small as possible, generally not exceeding 0. .01%.
7. Breakdown voltage: The breakdown voltage is an indicator of the insulation performance of the refrigeration oil. The pure refrigeration oil has good insulation performance, but when it contains impurities such as moisture, fiber, dust, etc., the insulation performance will be reduced. Semi-closed and Fully enclosed compressors generally require a breakdown voltage of the refrigerating oil above 25kV. Because the refrigerating oil is in direct contact with the motor windings.