The main function of compressor lubricating oil is to lubricate and seal the male and female rotors and bearings. In addition to lubricating, cooling and sealing the parts, it also plays the role of cooling compressed air. Therefore, understanding the performance of compressor oil has guiding significance for the long-term operation of compressor.

Performance Requirements of Compressor Oil

1. সান্দ্রতা
Appropriate viscosity can make the compressor play a good role in lubrication, cooling and sealing under 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 also increases with the increase of oil viscosity. Lubricating oil with low viscosity is not easy to form a strong enough oil film, which will accelerate wear and shorten the service life of parts. On the contrary, if the viscosity of lubricating oil is too high, it will increase the internal friction, increase the specific power of the compressor, increase the power consumption and oil consumption, and form deposits in the exhaust channel. On the premise of ensuring lubrication, appropriate viscosity has a very important impact on energy saving and reliable operation of compressor.

2. Viscosity temperature characteristic
Oil injected screw air compressor is heated and cooled repeatedly in the working process. Therefore, it is required that the oil viscosity should not change too much due to temperature change, and should have good viscosity temperature characteristics.

3. Flash point
Flash point refers to the vapor pressure formed by heating the oil under atmospheric pressure and the temperature when it reaches the lower limit concentration ignited by open fire. If the flash point is too high, the oil fraction will be heavy, the viscosity will be large, the content of asphaltene will be high, and it is easy to accumulate carbon during use. If one-sided pursuit of high flash point compressor oil, it will become an unsafe factor. Therefore, the compressor oil requires an appropriate flash point.

4. The causes of carbon deposition
In the compressor with carbon deposition tendency are relatively complex. In terms of lubricating oil, the main reason is that the oil used in the internal lubricating system of the air compressor is often in contact with the air and metal catalyst with high temperature, high pressure and high oxygen partial pressure in the form of mist, which makes the lubricating oil oxidize and deteriorate rapidly. On the other hand, the continuous evaporation of oil makes the more heavy oil remain in the compression chamber, exhaust valve chamber and exhaust pipe, which is continuously heated, decomposed and dehydrogenated. The product is mixed with mechanical impurities in the inhaled gas and metal wear debris in the compressor, deposited on the body surface and further heated, which becomes carbon deposition. When the compressor produces more carbon deposits at the exhaust valve and exhaust pipe, the exhaust valve will act flexibly and close loosely, resulting in the exhaust gas flowing back to the cylinder and repeated compression (i.e. secondary compression), so that the gas temperature rises rapidly. The high gas temperature intensifies the oxidation reaction of lubricating oil, and the reaction heat cannot be released in time, so that the gas temperature in the exhaust pipe continues to rise. When the temperature reaches the spontaneous combustion point of the lubricating oil, the lubricating oil accumulated in the carbon deposit begins to burn.

Compressor Lubricating Oil Change Procedure

In order to ensure the expected use effect of compressor oil, the oil shall be changed in strict accordance with the oil change procedure.

1. Preparation before oil change
1.1. Record relevant parameters, brand, model, oil filling amount and current exhaust temperature of the machine.
1.2. Take the oil sample in use for testing, analyze and record the brand, model and service time of the oil in use, and analyze the state of the oil in use, so as to give the oil change and cleaning plan in the later stage.
1.3. Record the working environment information of the compressor to collect whether there is a large amount of dust in the air and whether there is acid / alkaline gas or substance in the air (such as power plant, chemical plant, electronic plant, galvanizing plant, etc.) Air humidity (such as underground mine), etc.

2. In case of oil conversion of other brands of compressors,we should follow the following principles: clean the system once when the physical and chemical indexes of oil are normal. That is, after cleaning the system according to the lubrication oil change procedure for at least 2 hours, replace it with new lubricating oil, and take the working oil after 30 minutes of operation as the reference sample for filing. When changing the same type or compatible compressor oil, when changing different types or incompatible compressor oil, use new oil for cleaning.

3. If there is coking and deterioration in the oil,it indicates that the oil has been seriously aged (abnormal increase in viscosity and acid value), and it is necessary to replace the same type or compatible compressor oil as soon as possible. Operation method: drain the old oil in the hot engine state, add carbon deposition cleaning agent, and drain the cleaning agent in the hot engine state after 48 hours of operation. Clean the system for one or more times. After the above operations, clean the compressor system with new oil for one or more times (the cleaning times should be based on the difference between the acid value of the newly added oil and the new oil is no more than 0.1mgkoh / g). Then add new lubricating oil, and take the working oil after 30 minutes of operation as the reference sample for filing.