15 elements of the quality of screw air compressor lubricating oil

Correct selection of compressor oil for reasonable lubrication is an important measure to ensure the safe and stable operation of the compressor. Therefore, when selecting special lubricants for screw air compressors, not only the working load, movement speed, working temperature, lubrication method, and operation Environment, but also from the quality of screw air compressor lubricating oil.

1. Air compressor lubricating oil base oil quality

The base oil of compressor oil generally accounts for more than 95% of the finished oil, so the quality of base oil is directly related to the quality level of compressor oil, and the quality of base oil is directly related to its refining depth. Highly refined base oil has less heavy aromatics and colloid content, low carbon residue, and good antioxidant susceptibility. It has a small tendency to deposit carbon in the compressor system and has good oil-water separation. The base oil has a great influence on the performance of the rotary compressor oil, so the screw air compressor oil generally uses high-quality hydrogenated mineral oil or synthetic oil as the base oil.

2. Oxidation stability of lubricating oil for screw air compressors

During recycling, oil products are constantly in contact with high-temperature and high-pressure oxygen in compressed air, and are easily oxidized and deteriorated to produce various acids, colloids, asphaltene and other substances, which make the color of the oil darker, the acid value increase, and the viscosity Increases and deposits occur, thereby reducing the amount of oil injected, increasing the temperature of the oil and the machine, resulting in excessive wear. Therefore, the screw air compressor oil must have excellent oxidation stability in order to ensure that the oil can be used safely for a long time.

3. Carbon deposition tendency of screw air compressor lubricating oil

Compressor oil resistance to carbon deposition is critical to the reliable operation of compressor oils. The main substances that are easy to form carbon residues in oil products are asphaltenes, colloids and composites of polycyclic aromatic hydrocarbons. Lubricating oil can remove most of the above substances after deep refining. Generally, low-viscosity and highly refined lubricating oils have low residual carbon value and are not easy to deposit carbon during use. The carbon deposition tendency of oil products is a comprehensive performance of various indicators, and there are many influencing factors. Among them, the additives should also choose ash-free additives as much as possible.

4. Oil-water separation of screw air compressor lubricating oil

During operation, the compressor continuously encounters 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. As the oil is emulsified, the oil film is destroyed, causing wear. Emulsified oil can disperse dirt, grit and sludge, affect valve function, increase friction, wear and oxidation. Therefore, high-quality compressor oil has good anti-emulsification performance and oil-water separation performance.

5. Defoaming property of screw air compressor lubricating oil

During the circulation of screw compressor oil, the circulation speed is fast, and the oil product is in a state of vigorous stirring, which is easy to generate foam. When the compressor oil is started or depressurized, the oil in the oil pool is also prone to foaming, and a large amount of oil foam is poured into the oil-gas separator, which increases the resistance and increases the oil consumption, which will cause serious overload, over-temperature and other abnormal phenomena. Therefore, an excellent rotary compressor oil must have excellent defoaming properties to ensure that the oil has a small foam tendency (ie, foaming property) and good foam stability (ie, defoaming property).

6. Rust and corrosion resistance of lubricating oil for screw air compressors

The components such as the oil cooling of the compressor are made of copper or copper metal, which is easily corroded, which will cause early oxidation of the oil and deteriorate it to form sludge. This requires that the oil should have good corrosion resistance. Moisture in the air is easy to cool in the intermittently operated compressor, which is not good for lubrication and can cause corrosion, so the compressor oil should have good anti-corrosion effect.

7. Base oil fraction of lubricating oil for screw air compressor

The composition of base oil is the key factor to judge the quality of air compressor oil. After the compressor oil composed of light and heavy components is injected into the compressor cylinder, the light component will leave the working part in advance due to its strong volatility, which will affect the lubrication effect, while the heavy component will have poor volatility. It still stays in the working part, and it is easy to generate carbon deposits under the action of heat and oxygen over time, which will affect the performance of the air compressor. Therefore, lubricating oil should use narrow fraction component oil, and should not choose component oil mixed with multiple fractions.

8. Viscosity of screw air compressor lubricating oil

Under the condition of dynamic lubrication, the oil film thickness increases with the viscosity of the base oil, but the friction force also increases with the viscosity of the base oil. Lubricating oil with too low viscosity is not easy to form a strong enough oil film, which will accelerate the wear of the air compressor, resulting in shortened service life of the short moving parts of the air compressor. On the contrary, the air compressor lubricating oil with too high viscosity will increase the internal friction, increase the power loss of the compressor, and increase the oil consumption (energy consumption) of the air compressor. Deposits form in channels, etc. Therefore, choosing an air compressor oil with a suitable viscosity is also a matter of serious consideration. It has been scientifically verified that: using the same test conditions on the same type of compressor, the use of oil with lower viscosity can reduce the power loss of the compressor by about 10% compared with oil with high viscosity, and there is no significant difference in the amount of wear of components . Therefore, under the premise of ensuring lubrication, choosing an oil product with a suitable viscosity grade has a very important impact on the energy saving of the air compressor and the reliable operation of the air compressor.

9. Flash point of screw air compressor lubricating oil

The flash point refers to the temperature at which the vapor pressure formed by heating an oil product under atmospheric pressure reaches the lower limit concentration when it is ignited with an open flame. The air compressor oil with too high flash point has heavy oil fraction, high viscosity, high content of asphalt and other impurities, and it is easy to form carbon deposits during use. If you only pursue the high flash point of compressor oil, it will become an unsafe factor for air compressors. Therefore, the flash point of compressor oil should be moderate, generally controlled above 200 °C.

10. Anti-corrosion and anti-rust properties of lubricating oil for screw air compressors

The oil cooling and other parts of the compressor are made of copper or copper metal, which is easily corroded, which will cause early oxidation and deterioration of the oil, and generate sludge. This requires that the oil should have good corrosion resistance. Moisture in the air is easy to cool in the intermittently operated compressor cylinder, which is unfavorable to lubrication and can cause wear and corrosion. It is required that the compressor oil should have a good anti-corrosion effect.

11. Consider the working load of the screw air compressor

The working load is the static load and dynamic load directly borne by the bearing (or friction pair), which should be fully considered when selecting lubricating oil. Under the condition of liquid lubrication, the greater the viscosity of the lubricating oil, the greater its carrying capacity; in the case of boundary lubrication, the viscosity has little effect on improving lubrication, and its oiliness and extreme pressure resistance are indispensable. At this time, anti-extreme pressure should be selected Lubricating oil products with good pressure performance; for shock loads, reciprocating motion or occasions where oil film formation is difficult, grease or solid lubricants should be used. Centrifugal compressor bearings are generally radial load bearings.

12. Consider the movement speed of the screw air compressor

The relative motion speed is an important parameter for the structural design of the bearing (or friction pair), and it is also a consideration factor for the selection of lubricating oil products. Generally, bearings with low relative motion speed are suitable for lubricating oil with high viscosity to facilitate the formation and maintenance of the oil film; Type compressors generally have a relatively high speed, some reaching 10,000r/min or more, so lubricating oil with a lower viscosity should be selected.

13. Consider the operating temperature of the screw air compressor

Working temperature refers to the ambient temperature where the bearing is working and the temperature that affects it. If the ambient temperature is low, lubricating oil with low viscosity and low freezing point should be selected; when the ambient temperature is high, then Lubricating oil products with high viscosity and high flash point should be selected; when the temperature of the working environment where the bearing is located changes greatly, lubricating oil products with good viscosity-temperature performance and high viscosity index should also be selected. In short, when selecting lubricating oil products, it is necessary to make them match reasonably and work reliably according to the temperature of the working environment of the bearing.

14. Consider the lubrication method of the screw air compressor

For intermittent lubricating lubrication or parts where lubricating oil is easy to lose, lubricating oil products with good adhesion and high viscosity should be selected; centrifugal compressors generally use continuous and forced lubrication, so they should choose lubricating oil products with low relative viscosity, good oxidation resistance and anti-oxidation stability. Anti-rust, anti-foaming and lubricating oil with good lubricating properties.

15. Consider the operating environment of the screw air compressor

If the compression medium of the compressor has special requirements for lubricating oil, the corresponding air compressor lubricating oil with resistance to the medium should also be selected, such as ammonia-resistant lubricating oil for ammonia compressors. In addition, when selecting oil, you should also refer to the lubricating oil recommended by the equipment manufacturer. To sum up, when selecting lubricating oil products, one is to consider the working and environmental conditions of the equipment to meet the needs of equipment operation; the other is to minimize the variety of lubricating oil products to facilitate the management of lubricating oil products.

Based on the above analysis: when choosing a screw engine oil, you should not look at one or more indicators one-sidedly, and then deny or affirm the quality of a certain oil. You must combine the above 15 elements to choose a suitable lubricating oil.

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