Refrigeration lubricating oil

First, the role of lubricating oil

Lubricating oil is commonly referred to as refrigeration oil in refrigeration engineering, and it plays an important role in the operation of refrigeration compressors. The main aspects are as follows:

1. Lubrication: reduce the friction and wear of the moving parts of the machine, and prolong the service life.

2. Reduce temperature: The refrigeration oil is continuously circulated in the refrigeration compressor, which can take away a lot of heat generated during the working process of the refrigeration compressor, so that the machine can keep the temperature low, so as to improve the efficiency and reliability of the refrigeration compressor.

3. Sealing: The refrigeration oil plays a sealing role between the shaft seal and the cylinder and the piston to prevent refrigerant leakage.

4. Provide the power of the unloading mechanism: In the refrigeration compressor with the unloading device, the oil pressure of the refrigeration oil is used as the power of the unloading mechanism.

Second, the performance index and selection of lubricating oil

(1) Performance indicators of lubricating oil

1. Viscosity: viscosity is a major performance index of lubricating oil, different refrigerants have different requirements for viscosity, such as R12 and lubricating oil can dissolve with each other, which will reduce the viscosity of lubricating oil, so lubricating oil with higher viscosity should be selected. It is not good to have too much viscosity or too little viscosity of the lubricating oil in the compressor. The excessive viscosity increases the frictional power and frictional heat of the compressor, increases the starting torque, and reduces the efficiency of the machine. If the viscosity is too small, the desired oil film cannot be established, and the wear of the bearing, etc., will be accelerated. Therefore, the viscosity must be moderate.

The viscosity of the lubricating oil varies greatly with the temperature (for example, when the temperature rises from 50°C to 100°C, the viscosity value of the mineral oil decreases to 1/3-1/6 of the original value). Therefore, lubricating oil with little influence on viscosity should be selected.

2. Cloud point The cloud point of lubricating oil is the temperature at which paraffin begins to precipitate (that is, the lubricating oil becomes cloudy) when the temperature drops to a certain value. The cloud point of the lubricating 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 lubricating oil is dissolved in the refrigerant and flows to the refrigeration system with the refrigerant, if there is paraffin precipitation in the oil, it will accumulate at the throttle valve to cause blockage, or accumulate on the heat transfer surface of the evaporator, weakening the heat transfer effect.

3. Freezing point Under the test conditions, the lubricating oil is cooled to the temperature at which the flow stops, which is called the freezing point. Lubricants used in refrigeration compressors should have as low a freezing point as possible. Generally, the freezing point should be lower than -40°C. When the lubricant and refrigerant dissolve each other, the freezing point decreases.

4. Flash point When the lubricating oil (inside the open oil container) is heated to the point where its steam comes into contact with the flame, the lowest temperature at which a flash fire occurs is called the flash point. The flash point of the lubricating oil used in the refrigeration compressor should be 25-35 °C higher than the exhaust temperature, so as not to cause the combustion and coking of the lubricating oil. Generally, the flash point of lubricating oil for ammonia, R12 and R22 should be above 160-170 °C.

5. Stability and oxidation resistance Lubricating oil should have good chemical stability and oxidation resistance, otherwise under the catalytic action of high temperature or metal, it will react with refrigerants and other harmful substances such as coke and acid.

6. Water content and mechanical impurities Lubricating oil should not contain water, because water will not only reduce the evaporation pressure and increase the evaporation temperature, but also aggravate the chemical change of the oil and the effect of corrosive metal. Moisture in freon compressors can also cause "steel plating", which causes copper parts to decompose into copper by interacting with freon, and accumulates on the steel surface of bearings, valves, and other parts. As a result, the thickness of these tables increased, the clearance of the bearings was destroyed, and the machine was not functioning well. This phenomenon is more common in hermetic and semi-hermetic compressors.

Generally, new oil does not contain water and mechanical impurities, because the lubricating oil used in refrigerators has undergone strict dehydration treatment during the production process.

However, dehydrated lubricating oil has strong hygroscopicity, so contact with air should be avoided as much as possible during storage, transportation and refueling.

The residue of the lubricating oil after it is dissolved and diluted with gasoline or benzene and filtered with filter paper is called the mechanical impurity of the lubricating oil. The mechanical impurities in the lubricating oil will accelerate the wear of the parts and the reduction of the insulation performance of the oil, and block the lubricating oil channel, so the less impurities the better, generally not more than 0.01%.

7. Breakdown voltage Breakdown voltage is an indicator of the insulation performance of lubricating oil, pure lubricating oil insulation performance is very good, but when it contains impurities such as moisture, fiber, dust, etc., the insulation performance will be reduced.

Semi-hermetic and fully hermetic compressors generally require the breakdown voltage of the lubricating oil to be above 25kV. This is because the lubricating oil is in direct contact with the motor windings.

(2) Specifications and selection of domestic refrigeration oil

Continental's current refrigeration oil specifications are produced in accordance with GB/T16630-2012 standards.

In practice, N32 (No. 18) is generally used for R12 compressors, N46 (No. 25) is used for R22 compressors, and N22 (No. 13) or N46 (No. 25) is used for ammonia compressors.

(3) Mineral oil and Wuleng lubricating oil

Mineral oils are refined from paraffin base oils with a high viscosity index and are dewaxed at a low temperature of around -30°C in order to remove substances that are insoluble with the working fluid (or to lower the flocculation point) and to improve the chemical stability with the refrigerant.

These petroleum-based lubricants are naphthenic hydrocarbons that are less refined, more complex in composition, and unstable in physical and chemical structure, which can affect performance in refrigeration applications.

Generally, the viscosity temperature is not good, the viscosity index is low, the lower the temperature, the greater the viscosity, the energy consumption of the system increases, and it is easy to deposit mineral oil in the evaporator, and it is very difficult and sometimes impossible to achieve optimal performance with refrigerant by matching the compressor and the system. Mineral oil is widely used in refrigeration systems due to its low price.

However, we recommend an evaporation temperature of around -30°C due to:

1. Once the suction temperature reaches about -30°C, a large amount of wax will be precipitated on the suction filter of the compressor, blocking the filter screen, reducing the suction capacity and greatly reducing the refrigeration capacity;

2. The long-term accumulation of mineral oil in the evaporator seriously affects the heat transfer, resulting in lower evaporation temperature and reduced refrigeration capacity;

3. In the ammonia system, the mineral oil forms sludge in the evaporator, which is toothpaste-like, and the oil cannot be discharged smoothly through the oil collector;

4. The oil temperature of the unit is high, and the viscosity of the fuel injection is low, which affects the lubrication and shortens the life of the bearing;

5. High carbon content, easy to precipitate and produce oil residue, clogging the filter screen;

6. High volatility, reducing oil effect;

7. Through measurement, the above items can reduce the refrigeration capacity by 10%~60%.

Introduction of Wuleng lubricating oil

-WL1 Refrigeration Oil (Semi-Synthetic)

Low volatility, low solubility with ammonia, good oil effect, can reduce 60% of refrigeration oil consumption, so that the oil separation accuracy is improved to more than 5ppm, operating temperature: 15~-40°C, good lubricity to compressor:

Reduce wear and extend bearing life;

Produces a cleaner system with no oil residue;

Allow the oil from the old system to be slowly replaced;

Compatible with all other oil and rubber materials commonly used in ammonia refrigeration systems;

The wax content is very low, the wax will not be precipitated at low temperature, and will not be adsorbed on the filter screen, giving full play to the performance of the compressor;

Low pour point, easy to drain oil from the evaporator;

Good oxidation stability, the oil change interval is 3~6 times longer than that of N46 refrigeration oil;

It has polarity and self-cleaning effect, which can bring back the dirt in the heat exchanger and improve the heat exchange efficiency.

-WL2 Refrigeration Oil (Semi-Synthetic Oil)

Specially developed for R717 applications, based on semi-synthetic oils, relatively inexpensive;

Special acid-free additives are used to prevent the formation of ammonium salts of fatty acids, and have excellent adaptability to ammonia refrigeration system;

Excellent thermal stability - prolongs the service life of the oil, prolongs the maintenance interval and reduces the number of oil changes, the oil change interval is 2~5 times longer than that of N46 refrigeration oil;

Eliminate the formation of varnish, gum and sludge – improving equipment reliability and efficiency;

The miscibility with ammonia is very small, the volatility is small, the oil content effect is increased by 50%, and the oil separation accuracy is increased to more than 5ppm;

High viscosity index and low temperature fluidity – improve evaporator efficiency;

High oil film thickness in the presence of refrigerant - improve the shear resistance of compressor oil, prolong compressor life, and have good sealing performance;

Operating temperature: 15~-40°C.

-WL4 冷冻机油（PAO 合成油）

It has all the characteristics of WL1 oil;

The operating temperature is lower and the range is wider: 15~-60°C.

- WL5 Refrigeration Oil (Alkylbenzene Refrigeration Oil) (Oil for Fluorine System)

Low volatility and good oil effect, which can reduce the consumption of refrigeration oil by 50% and improve the oil separation accuracy to more than 5ppm;

Operating temperature: 15~-45°C;

Good lubricity for compressors:

Reduce wear and extend bearing life;

Produces a cleaner system with no oil residue;

Allow the oil from the old system to be slowly replaced;

Compatible with all other oil and rubber materials commonly used in ammonia refrigeration systems.

-WL8 Refrigeration Oil (Synthetic Oil) (for propane/propylene refrigeration systems)

Low volatility and good oil effect;

Operating temperature: 15~-45°C;

Good lubricity for compressors:

Reduce wear and extend bearing life;

Produces a cleaner system with no oil residue;

Compatible with all other oil and rubber materials commonly used in ammonia refrigeration systems.

This oil is designed for propane/propylene refrigeration systems and has a 5-fold longer life than mineral oil.

Wuleng OEM lubricating oil parameter table
Wu Leng number	Type of lubricating oil	Applicable media	Applicable temperature (°C)
WL1	Semi-synthetic oils	R717	15～-40
WL2	Semi-synthetic oils	R717	15～-40
WL4	PAO	R717	15～-60
WL5	Alkylbenzene	R22	15～-45
WL6	POE alcohol ester oil	R22	15～-60
WL8	Synthetic Oils	R290/R1270	15～-35
WL9	PAG	R600/R600A	15～-45
WL10	Synthetic esters	R22/R23	15～-100

N46 VS WL1 & WL2 性能比较：

Wu Leng used 1 LG20IIIA to do several months of comparative tests on the test station, the test results are amazing, the following is only a common working condition of -15/+35 °C as an example:

Compare items	N46	WL1	WL2
Cooling capacity	100	110.1	109.7	%
Shaft power	100	95.2	95	%
COP	100	115.7	115.5	%

In other words, after using WL2, not only the cooling capacity is increased by 9.7%, but the power consumption is reduced by 5%! This does not include the strengthening effect of the heat exchanger.

1 LG20IIIA, calculated according to the annual operation of 8000h, the increase in refrigeration capacity is not counted, the annual power consumption is saved by 75,000 kWh, and the annual electricity cost is saved by 0.5 yuan/kWh, and the annual electricity cost is 37,500 yuan!