1. basic information

Refrigeration Oil (Refrigerant Oil)

The oil used for the lubrication of the moving parts in the refrigeration compressor is called refrigeration oil. In the compressor, the refrigerant oil mainly plays the functions of lubrication, sealing, cooling and energy regulation.

2. function

In the compressor, the refrigeration oil mainly plays four roles: lubrication, sealing, cooling and energy regulation.

(1) Lubrication The refrigerating oil plays a lubricating role during the operation of the compressor to reduce the friction and wear of the compressor, thereby extending the service life of the compressor.

(2) Sealing refrigeration oil plays a sealing role in the compressor, so that the piston in the compressor and the cylinder surface, and the rotating bearings are sealed to prevent refrigerant leakage.

(3) Cooling When the refrigerating oil is lubricated between the moving parts of the compressor, it can take away the heat generated during the working process and keep the moving parts at a lower temperature, thereby improving the efficiency and reliability of the compressor.

(4) Energy adjustment For a refrigeration compressor with an energy adjustment mechanism, the oil pressure of the refrigeration oil can be used as energy to adjust the power of the machine.

3. POE and PAG Meaning

In order to protect the ozone layer, the refrigerant of air conditioning equipment has been restricted in the world, and various alternative refrigerants have appeared, and the refrigeration oil has also changed accordingly. The alternative refrigerants for air conditioning are R134a and R410a/R407c, which are replaced by PAG and POE respectively.

POE is the abbreviation of Polyol Ester, also known as polyester oil, which is a kind of synthetic polyol ester oil. PAG is an abbreviation of Polyalkylene Glycol, a synthetic poly (ethylene) glycol-based lubricating oil. Among them, POE oil can be well used not only in HFC refrigerant systems, but also in hydrocarbon refrigeration. PAG oil can be used as HFC, hydrocarbon and ammonia as refrigerant in the refrigeration system of lubricating oil.

4. requirements

Due to the use of different occasions and refrigerants, refrigeration equipment on the choice of frozen oil is not the same. The requirements for refrigeration oil are as follows:

(1) Freezing point The temperature at which the freezing oil cools to stop flowing under the experimental conditions is called the freezing point. The freezing point of the refrigeration oil used in the refrigeration equipment should be as low as possible (such as the compressor of R22, the refrigeration oil should be below -55°C), otherwise it will affect the flow of the refrigerant and increase the flow resistance, which will lead to poor heat transfer. consequence.

(2) the viscosity of frozen oil is an important parameter in the characteristics of the oil, the use of different refrigerants to choose different frozen oil. If the freezing oil viscosity is too large, the mechanical friction power, friction heat and starting torque will increase. On the contrary, if the viscosity is too small, the required oil film cannot be formed between the moving parts, so that the due lubrication and cooling effect cannot be achieved.

(3) Cloud point The cloud point of a frozen oil refers to the temperature at which paraffin begins to precipitate in the frozen oil when the temperature drops to a certain value, making the lubricating oil turbid. The cloud point of the refrigeration oil used in the refrigeration equipment should be lower than the evaporation temperature of the refrigerant, otherwise it will cause the throttle valve to block or affect the heat transfer performance.

(4) Others such as chemical stability and oxygen resistance, moisture and mechanical impurities, and insulation properties.

(5) Flash point The flash point of frozen oil refers to the lowest temperature at which the lubricating oil is heated to the point where the steam contacts the flame. The flash point of the refrigeration oil used in the refrigeration equipment must be 15~30 ℃ higher than the exhaust temperature, so as not to cause the combustion and coking of the lubricating oil.

(6) The oil temperature should generally be maintained between 45-60 ℃, and the maximum should not exceed 70 ℃, and it is stable. If the oil temperature has been unstable and slowly rising, it means there is a fault. Oil temperature is too low or too high will make the deterioration of lubricating oil, at the same time, often foreshadow the arrival of failure. The key to the freezing oil pressure is the oil pressure difference. Due to various reasons, the oil pump cannot be oiled, that is to say, the oil pressure difference cannot be established. The oil pressure depends on the structure of the compressor. The external gear oil pressure difference of the vertical compressor is 0.5~1.5MPa, and the oil pressure difference of the new series compressor is 0.5~1.5MPa. Newly purchased compressors often use high oil pressure differences in operation and debugging, so as to increase the amount of lubricating oil, better complete the running-in period of moving parts such as cylinders, and extend the service life of the machine.

5. performance:

1. Chemical stability: It will not chemically interact with refrigerants or other materials present in the system.

2. Thermal stability: does not accumulate excessive carbon deposits in high temperature areas such as discharge valves.

3. Low wax content: It can prevent the oil/refrigerant mixture from forming flocculent wax deposits in the low temperature part of the system.

4. Low pour point: It can prevent the precipitated oil from solidifying in the pipeline.

5. High dielectric strength: to ensure good insulation performance. In a sealed unit, the oil/refrigerant mixture acts as an insulator between the motor and the compressor.

6, the viscosity is moderate: although diluted by the refrigerant, it can still have a high strength oil film under extremely high temperature operating conditions. At the same time, it can still maintain good fluidity under extremely low temperature conditions.

7, no pollution: to prevent the surface of the bearing, blocking the pipeline and premature aging.

6. temperature and pressure:

1. Viscosity: Viscosity is a major performance index of refrigeration oil. Different refrigerants have different requirements for viscosity. For example, R12 and refrigeration oil can dissolve each other, which will reduce the viscosity of refrigeration oil. Therefore, refrigeration oil with higher viscosity should be selected. It is not good for the viscosity of the refrigerant oil in the compressor to be too high or too small. If the viscosity is too large, the friction power and friction calorific value of the compressor will increase, the starting torque will increase, and the efficiency of the machine will decrease; if the viscosity is too small, the wear of the bearing will be accelerated due to the inability to establish the required oil film. Therefore, the viscosity must be moderate. The viscosity of frozen oil varies greatly with temperature (for example, when the temperature increases from 50 ℃ to 100 ℃, the viscosity of mineral oil decreases to 1/3-1/6 of the original value). Therefore, refrigerant oil with little effect of temperature on viscosity should be selected.

2. cloud point: frozen oil cloud point is that when the temperature is reduced to a certain value, frozen oil began to precipitate paraffin (ie frozen oil becomes turbid) when the temperature. The cloud point of the refrigerant oil used in the refrigeration compressor should be lower than the evaporation temperature of the refrigerant. Especially in the fluorine system, a part of the refrigeration oil is dissolved in the refrigerant and flows with the refrigerant to all parts of the refrigeration system. If paraffin is precipitated in the oil, it will accumulate at the throttle valve to cause blockage, or accumulate on the evaporator The heat transfer surface weakens the heat transfer effect.

3. Freezing point Freezing oil is cooled to the temperature at which it stops flowing under the test conditions, which is called the freezing point. The freezing point of the refrigerating oil used in the refrigeration compressor should be as low as possible. General freezing point should be below -40 ℃. When the refrigerant oil and refrigerant dissolve with each other, the freezing point will be lowered.

4. flash point: frozen oil (in the open oil container) heated to its steam contact with the flame, the lowest temperature flash fire is called the flash point. The flash point of the refrigeration oil used in the refrigeration compressor should be 25-35 ℃ higher than the exhaust temperature, so as not to cause the combustion and coking of the refrigeration oil. Generally, the flash point of refrigeration oil used for ammonia, R12 and R22 should be above 160-170 ℃.

5. The stability and oxidation resistance of frozen oil should have good chemical stability and oxidation resistance, otherwise under the catalytic action of high temperature or metal, contact reaction with refrigerant, etc., will generate coke, acid and other harmful substances.

6. Water content and mechanical impurities: frozen oil should not contain water, because water will not only reduce the evaporation pressure, evaporation temperature, but also aggravate the chemical changes of the oil and the role of corrosive metals. Moisture in the Freon compressor will also cause "steel plating phenomenon", so that copper parts and Freon effect and decomposition of copper, and accumulated in the bearing, valve and other parts of the steel surface. As a result, the thickness of these watches increases, the clearance of the bearings is destroyed, and the machine runs poorly. This phenomenon occurs more often in hermetic and semi-hermetic compressors. Generally, the new oil does not contain moisture and mechanical impurities, because the refrigeration oil used in the refrigerator has undergone strict dehydration treatment in the production process. But the dehydration of frozen oil has a strong hygroscopicity, so in the storage, refueling, should try to avoid contact with the air. Dissolving and diluting the frozen oil with gasoline or benzene, and filtering with filter paper, the residual substance is called the mechanical impurity of the frozen oil. The mechanical impurities in the refrigeration oil will accelerate the wear of parts and the reduction of oil insulation performance, and block the refrigeration oil channel, so the fewer impurities, the better, and the general requirement is not more than 0.01%.

7. Breakdown voltage: Breakdown voltage is an indicator of the insulation performance of refrigeration oil. Pure refrigeration oil has good insulation performance, but when it contains moisture, fiber, dust and other impurities, the insulation performance will be reduced. Semi-hermetic and fully hermetic compressors generally require the breakdown voltage of the freezing oil to be above 25kV. Because the refrigeration oil is in direct contact with the motor windings.