Air compressor lubricant replacement standard and market analysis

1. The selection criteria of air compressor oil

  1) Oil selection: mineral oil, semi-synthetic oil, synthetic oil (synthetic oil is mainly PAO series)

  2) Pour point: ≤-10℃

  3) Flash point: ≥180℃

  4) Acid value: 0.2

  5) Performance requirements: good oxidation resistance, anti-emulsification, and less residual carbon

6) Select the type of air compressor oil according to the design type of compressor oil, environmental conditions, and operating load. Generally, under long-term high temperature environment (>30℃), use synthetic oil, high-speed water cooling or low-pressure, small compression ratio The compressor can choose low-viscosity compressor oil.

   usually choose the label:

  1) Air-cooled piston shaft output power <20KW, select 32, 46, 100 (ambient temperature <-10 ℃ optional 32) DAA, DAB, DAC air compressor oil;

  2) Water-cooled piston type uses 68 or 100 oil;

  3) Rotary dripping oil selects 100, 150, 220 oil;

  4) No. 32 or 46 oil is selected for the rotary injection type.

  5) The lubricating oil used in centrifugal air compressors is similar to hydraulic oil or gear box oil. It is very different from the previous four air compressor oils. Because the above four air compressor oils are used for cooling, sealing, lubrication and noise reduction, and the lubricating oil on the centrifuge is only used to lubricate the bearings.

   2. What is the oil change index of the compressor?

  Answer: Under normal circumstances, the compressor oil in operation should be sampled regularly to observe the color and cleanliness of the oil, and periodically analyze the oil viscosity, acid value, and physical and chemical properties such as n-pentane insolubles. If one of the following situations occurs, consider changing the oil.

  The oil has turned green, and the color number has been deepened by 4 levels; ②The acid value exceeds 0.5mgKOH/g; ③The viscosity change exceeds ±15%; ④The n-pentane insoluble matter exceeds 0.5%. The special oil change index for light-load oil-injected rotary air compressors is SH/T0538-93

   3. Failure analysis of air compressor lubricant

  一) Lubricating oil composition analysis

  1) The mineral oil base oil has a complex composition, consisting of alkanes, cycloalkanes, and aromatics. Among them, alkanes and cycloalkanes are saturated hydrocarbons, and aromatics are unsaturated hydrocarbons. The molecular structure of alkanes is chain-like, the viscosity index is high, and the chemical properties are stable. They are the most ideal component of engine oil. The structure of cycloalkanes is a combination of ring and chain, and the viscosity index is very low, which will make the engine start at low temperature difficult, and the evaporation loss is also large, the chemical performance is not very stable, and it is not an ideal component of engine oil. Aromatic hydrocarbons are unsaturated hydrocarbons, which are the most undesirable components of engine oil, and are easily cracked and deteriorated at high temperatures.

   2) Fully synthetic motor oil and synthetic motor oil refer to that the base oil used in the motor oil is a fully synthetic or synthetic base oil. In addition to the base oil, there are about 10% to 25% additives in the motor oil.

   Base oil, the content of unsaturated hydrocarbons is generally less than 0.5%, the content of alkanes is more than 80%, and the viscosity index is above 120. It has good low-temperature startability, heat and oxidation stability. The general hydrogenated oil with a viscosity index below 120 and alkane content below 80% cannot be called a synthetic oil because of the shallow hydrogenation reaction.

  2) Analysis of lubricant operating environment

   also contains a small amount of nitrogen, sulfur and oxygen compounds. Alkanes at temperatures above 100°C, especially with metal contact, will reduce their oxidation resistance and easily produce oxides and fatty products, which are further condensed into gums and asphaltenes. These products are mixed with mechanical impurities in the suction air and metal wear debris in the compressor, deposited on the surface of the machine head, and further heated to produce carbon deposits. Due to the special circumstances of the screw air compressor, the special oil for the air compressor (mineral oil or synthetic oil) will inevitably appear oxidation and carbon deposition, and the oil will age too fast.

  1) High temperature: Temperature is the main factor causing oil oxidation. The temperature did not increase by 10°C, and the oxidation rate doubled. During the compression operation, the compressor not only needs to suck into the compression chamber until the separator is separated from the compressed gas, the lubricating oil basically exists in the form of mist, and its surface area is greatly increased. The compressed gas is fully mixed and the temperature rises rapidly.

   2) High oxygen partial pressure: The oxygen partial pressure is the product of the total pressure of the gas and the volume percentage of oxygen in the gas. The oxidation rate of lubricating oil is proportional to the oxygen partial pressure. Therefore, when the compressor is running, the lubricating oil is more likely to be oxidized than in the atmosphere.

  3) Oxidation catalysis of condensed water and metals: both water and metals are catalysts for the oxidation of lubricating oil, and the presence of both has a more significant acceleration effect on the oxidation of oil.

  4) Residual carbon: In the screw air compressor, the lubricating oil is repeatedly heated and cooled, which is prone to aging and deterioration. Finally, residual carbon is formed.

   In summary, the main reason for the above-mentioned air compressor oil is that oxidation occurs under the interaction of high temperature, moisture, impurities and carbon residue, and the internal structure changes and deteriorates.

After communicating with oil purification manufacturers and learning about oil filtration related materials, oil filtration equipment can filter out impurities, moisture and related particles in air compressor lubricating oil, delay the oxidation rate of oil products, and extend oil products But the use time is only extended and cannot be changed in essence.

   Fourth, the current status and existing problems of oil filter applications

   There are few applications of oil filtration in air compressor lubricants on the market. The main reasons are as follows:

1) Screw air compressor equipment uses relatively little oil, the oil composition is relatively complex, and the price is relatively low (generally, the price of semi-synthetic oil is about 30 yuan, accounting for about 80% of the market, and only high-end air compressors The processing cost of the machine using synthetic oil, such as Atlas or Ingersoll Rand, is relatively high.

  2) The reduction in oil procurement costs and the risk of damage to the air compressor equipment using filtered oil are not equal. As the air compressor equipment is relatively expensive, tens of thousands of small, even hundreds of thousands of large, the use of oil filtration equipment may save thousands of dollars, but in the face of the use of filtered oil there is a risk of tens of thousands or hundreds of thousands At the time, every customer will adopt a more cautious attitude.

  3) On-site oil product testing equipment cannot meet the needs of customers for understanding oil product indicators.

   The current on-site oil testing equipment can only detect whether the existing oil is replaced, and simply test the moisture and particle content in the oil. These are far from reaching the changes in oil composition and oil indicators that customers need to understand.