What Is Compressor Oil?

Compressor oil refers to a class of petroleum products. Used to lubricate the cylinders, valves and piston rod seals of compressors. Requires high oxidation stability and high flash point. Generally, the flash point should be 40 ° C higher than the maximum temperature when the compressor is compressed. Its viscosity should be suitable for the type of compressor and operating conditions. ^[1]

Under normal circumstances, compressor oil can be divided into two types according to the type of base oil: mineral oil compressor oil and synthetic compressor oil; according to the structure of the compressor, it can be divided into reciprocating air compressor oil and rotary oil. There are two types of air compressor oils; air compressor oils and gas compressor oils are classified according to the nature of the compressed gas; light, medium and heavy-duty compressor oils are based on the air compressor.

China equivalently adopted the international standard ISO 6743 / 3A-1987 and formulated the compressor oil classification standard GB / T 7631.9-1997. Reciprocating air compressor oil is divided into three types: light load L-DAA, medium load L-DAB, and heavy load L-DAC. Among them, DAA and DAB are mineral oil type, and DAC is synthetic oil type. Rotary air compressor oil is also divided into three types according to light, medium and heavy load, namely light load L-DAG, medium load L-DAH, and heavy load L-DAJ. DAG and DAH are mineral oil types. DAJ is synthetic. Gas compressor oil is divided into five types according to composition and characteristics, namely DGA (mineral oil type), DGB (specific mineral oil), KGC (common synthetic fluid), DGB (non-hydrocarbon synthetic fluid), DGE (common synthetic fluid). ^[2]

I. Foreign compressor oil product standards

Foreign air compressor oil specifications include German DIN 51506 and ISO / DP 6521.3, and the most representative compressor oil standard is the German industrial standard DIN 51506. The standard was proposed in the 1970s because of concerns about the safety of air compressors. The standard includes three types of oils, VB (VBL), VC (VCL) and VDL, which are suitable for the lubrication of air compressors with different loads. VB and VC are pure mineral oils without additives and belong to light-load air compressor oils; VBL and VCL contain additives with anti-aging properties and belong to medium-load air compressor oils: VDL belongs to high-pressure and heavy-load air compression Motor oil.

2. Domestic compressor oil product standards

China has adopted the German Standard DIN 51506-1985 "Classification and Requirements for VB and VC and VDL of Lubricants with and without Additives for Lubricants with Lubricants and Lubricants," and formulated the national standard GB 12691-1990 for DAA and DAB air compressor oils. For rotary air compressor oil, the national standard GB5904-1986 for light-load oil-injected rotary air compressor oil has been formulated. DAH rotary (screw) air compressor oil is the only enterprise standard. ^[2]

First, base oil

The base oil of compressor oil generally accounts for more than 95% of the refined oil, so the quality of the base oil is directly related to the quality level of the refined oil of the compressor oil, and the quality of the base oil is directly related to its refining depth. With the development of compressors toward miniaturization, air cooling, high pressure, and purification, the amount of oil used will inevitably decrease, the oil load will increase significantly, and the oil temperature will rise. This requires the oil to have better oxidation stability.

Additives

(1) Antioxidants

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Compressor oil is used to lubricate compressor parts (automobiles, valves) and is used as the sealing medium for the compression chamber. For most compressors, the temperature of air or gas after each stage of compression usually exceeds 170-180 ° C, but there are also piston compressors with higher thermal strength at an outlet temperature of more than 220 ° C. In order to ensure the safe operation of the compressor, extend the oil change period, keep the air pressure system clean, reduce friction and transmission energy consumption, the compressor oil should have good thermal stability, prevent the formation of carbon deposits, and have good corrosion resistance and anti-emulsification. And anti-foam properties.

1.Viscosity

Appropriate viscosity can make the compressor perform good lubrication, cooling and sealing under the working temperature and pressure, and ensure the normal operation of the compressor. Under the condition of dynamic lubrication, the oil film thickness increases with the increase of oil viscosity, but the friction force also increases with the increase of oil viscosity. Lubricants with too low viscosity do not easily form a sufficiently strong oil film, which will accelerate wear and shorten the service life of the parts. Conversely, if the viscosity of the lubricating oil is too high, it will increase the internal friction and increase the specific power of the compressor, which will increase the power consumption and fuel consumption. It will also be in the piston ring groove, on the valve, in the exhaust passage, etc. Formation of deposits. Under the premise of ensuring lubrication, proper viscosity has a very important impact on energy saving and reliable operation of the compressor.

2.Viscosity

The oil-injected internal-cooled rotary air compressor is repeatedly heated and cooled during the working process. Therefore, it is required that the viscosity of the oil should not change too much due to temperature changes, and it should have good viscosity-temperature properties.

3.Flash point

The flash point indicates the temperature at which the vapor pressure of an oil product under atmospheric pressure reaches the lower limit concentration ignited by an open flame. If the flash point is too high, the oil fraction will be heavy, the viscosity will be large, and the asphaltene content will be high. If one-sided pursuit of high flash point compressor oil, it will become an unsafe factor. Therefore, the flash point requirement of the compressor oil is suitable.

4, carbon deposition tendency

How the compressor oil resists carbon deposition is crucial to the reliable operation of the compressor oil. In actual industrial use, fire and explosion accidents of large and medium-sized compressors due to carbon deposition have been common. The accumulation of carbon deposits in the exhaust system will make the exhaust valve close tightly, and at the same time, the cooling effect is poor, the exhaust temperature will rise, the compressor will malfunction, and even the fire or explosion will occur. .

5. Oxidative stability

Because the discharge temperature of the compressor is usually 120-200 ° C, it may reach 300 ° C. The compressor oil is susceptible to oxidation at high temperatures and deteriorates to form sludge.

6, anti-corrosion and rust resistance

The material of the compressor's oil cooling and other components is copper or copper metal, which is easy to be corroded, which will cause early oxidation and deterioration of the oil and generate sludge. This requires that the oil should have good corrosion resistance. The moisture in the air is easy to cool in the compressor cylinder that is operated intermittently, which is not good for lubrication and can cause wear and rust. It is required that the compressor oil should have a good anti-rust effect.

7, oil-water separation

During operation, the compressor continuously meets the condensed water in the air and is vigorously stirred, which is prone to emulsification, resulting in unclear separation of oil and gas and increased fuel consumption. Because the oil is emulsified, the oil film is destroyed, causing wear. Emulsified oil promotes the dispersion of dust, grit, and sludge, affects valve function, and increases friction, wear, and oxidation. Therefore, high-quality compressor oils have good anti-emulsification properties and oil-water separation properties.

8, defoaming

Rotary compressor oil has a fast circulation speed during the cycle use, which makes the oil in a vigorously agitated state and easily generates foam. When the compressor oil is started or depressurized, the oil in the oil pool is also easy to foam. A large amount of oil foam is poured into the oil and gas separator, which increases the resistance and the fuel consumption, which will cause serious abnormalities such as overload and overtemperature. Therefore, excellent rotary compressor oils are added with anti-foam additives to ensure that the oil has a low tendency to foam (ie, foaming) and good foam stability.

9.Other

It also requires low oil volatility, suitable pour point, and no mechanical impurities and moisture to ensure the compressor can run safely for a long time. ^[2]