Oil-free water lubrication air compressor and dry screw air compressor

In recent decades, the research on oil-free screw compressors has become increasingly active, and many countries and enterprises have begun to explore the road of oil-free screw compressors on the basis of the original oil-injected screw compressor models. In the field of high gas quality requirements, such as textile, metallurgy, food, chemical, pharmaceutical, petroleum and air separation and other places that need pure oil-free compressed air, oil-free screw compressor can provide high-quality compressed gas to meet various needs, so the application prospect is broad.

Application areas

in the food manufacturing and packaging industry, when the oil-injected screw compressor is used to prepare compressed gas, the performance of the lubricating oil in the compressor has been greatly reduced and acidic after many times of high-temperature oxidation and condensation emulsification in the production process. Not only can it not lubricate the subsequent equipment, but it will destroy the normal lubrication. The use of oil-free screw compressor can avoid the negative impact of invalid lubricating oil on the equipment. In pharmaceutical and biological engineering, the pollution of bacteria and bacteriophage in compressed gas can not be ignored. The pure compressed gas provided by oil-free screw compressor can avoid the breeding of bacteria and bacteriophage in the gas.

In the electroplating industry, there are some problems in the production process, such as the surface of the coating, burning, pinhole, crack and so on. People use stirring to solve such problems, and the stirring needs the support of compressed air. The quality of compressed air has a great influence on the deposition rate and plating efficiency of bright nickel electroplating. The application of oil-free screw compressor can effectively avoid the occurrence of problems such as flower, scorch, pinhole and crack on the surface of the coating. Therefore, oil-free screw compressors have been used to prepare pure gas for electroplating.

In the automotive spray industry, impure gases often result in inferior coatings. If the compressed air contains oil, there are some scattered or concentrated small bumps on the surface of the coating. These blisters are generally produced in a coating under the topcoat, and the blisters are caused by water vapor or dirt under the coating. In addition, oily compressed air may also lead to the appearance of dot-like distribution of small potholes on the surface of the wet coating, forming crater-like silica pits, and sometimes visible substrates at the bottom of the pits, commonly known as fish eyes. Nowadays, the automobile spraying industry has begun to apply oil-free screw compressors to prepare pure gas for spraying, so that the spraying level of domestic automobiles has been improved.

In the textile industry, air-jet looms require dry and oil-free compressed air. In the production process, the fine nozzle will blow compressed air onto the wire harness to form a vortex, thereby giving the yarn shape, elasticity and elasticity. The pure compressed air provided by the oil-free screw compressor can ensure the quality of the finished cloth.

Rotor Material and Profile

rotor Material

in the dry screw compressor, because there is no lubrication of lubricating oil and takes away tiny particles, the gas will corrode the rotor, the inner wall of the casing and the air passage. Therefore, on the basis of the traditional oil-injected screw rotor material, anti-corrosion coating is usually sprayed, such as polytetrafluoroethylene, molybdenum disulfide, Teflon, etc., to ensure that the rotor is not deformed and not corroded.

In the water jet screw compressor, due to the injection of water into the compression cavity, not only the functions of cooling, sealing and maintaining the purity of the gas are obtained, the efficiency of the compressor is improved, but also the exhaust temperature is controlled. Moreover, the stainless steel rotor makes water have no adverse effect on the rotor and other components. At the same time, due to the difficulty in processing 304 stainless steel materials, it is expected to develop and develop updated technologies to solve the problem of long delivery period. In addition to the 304 stainless steel rotor, the choice of rotor material is generally as follows:

(1)NSB steel rotor

the rotor is made of NSB steel (nickel-phosphorus alloy plated, resistant to corrosion in torch gas, H2, H2S and SO2). This kind of coated rotor, coating shedding, failure, rotor exposed to the air, bear the influence of impurities in the air and temperature changes. Ultimately, it leads to a reduction in operating performance and even damage to the machine.

(2) polymer ceramic rotor

polymer ceramic rotors are also used. Its rotor can be precisely machined to an accuracy of a few hundredths of a millimeter. The results of long-term tests show that this material is wear-resistant and has good reliability and applicability. Not suitable for machine processing, so the use of precision casting, and casting process is one of the difficulties. In general, defects such as pores and cracks of ceramic products need to be detected by X-ray instrument with microscopic focus, and the consistency of density of ceramic blanks needs to be monitored by ultrasonic instruments.

(3) Engineering plastic rotor The use of engineering plastic rotor has opened up a new economic way of screw compressor rotor material and processing means, and has provided good conditions for the development of water jet screw compressor. Precision injection molding of engineering plastic rotor, stainless, low cost, while reducing the noise and vibration of the screw compressor. It creates very good conditions for the use of water spray seal cooling technology in the compression chamber.

Screw rotor profile

for screw compressors, the design of the profile is very important, and it is necessary to comprehensively consider the meshing requirements of the rotor profile, the continuous contact line, the processing performance and other factors.

The profile is characterized by bilateral asymmetry, and all the constituent tooth curves are circular or circular arc envelopes, which can reduce the lateral leakage through the contact line and improve the efficiency of the compressor. In addition, the processing performance of the rotor is improved, and it is convenient to use a variety of methods for processing.

Technical difficulties

technical difficulties of dry screw compressor

(1) Rotor deformation

the performance of a dry screw compressor depends to a large extent on the sealing gap when the rotor is meshed. There are many leakage channels between the rotor and between the rotor and the casing, and the leakage of fluid through the gap directly affects the volumetric efficiency and the total efficiency. In the actual operation process, the rotor undergoes thermal and force elastic deformation under the action of thermal and force boundary conditions, which makes the actual operating gap and the design gap difference. If the gap is too large, leakage will increase and volumetric efficiency will decrease; if the gap is too small, burn and death will occur.

Although the temperature difference of the whole rotor is not large, the radial deformation of the rotor is still different along the length direction. This is mainly because the entire rotor shape is complex, teeth, grooves are spiral, rather than strict axisymmetric structure. The analysis of the radial deformation of the male and female rotors along the contact line shows that although there is a difference in the deformation along the axial length direction, the total deformation of the two rotors is basically unchanged, and the total deformation changes linearly with temperature. Dry compressor exhaust temperature is often high, in order to prevent the occurrence of rotor seizure or even serious damage to the rotor teeth, should consider increasing the design gap or take appropriate cooling measures.

(2) Coating failure

the inferior rotor coating will fall off after a period of operation. The rotor is exposed to the air and bears the influence of impurities and temperature changes in the air. Ultimately, it leads to a reduction in operating performance and even damage to the machine. The process of spraying anti-corrosion coating is one of the difficulties. Molybdenum disulfide, polytetrafluoroethylene, and molybdenum-stone coatings are more commonly used today.

Technical difficulties of water jet screw compressor

(1) Manufacture of ceramic rotor

due to the wear resistance of ceramic materials, it is not suitable to use machine tools, so the use of precision casting, and casting process is one of the difficulties. In general, defects such as pores and cracks of ceramic products need to be detected by X-ray instrument with microscopic focus, and the consistency of density of ceramic blanks needs to be monitored by ultrasonic instruments.

(2) Water pollution cleaning due to the presence of water, it will inevitably cause certain corrosion effects on the screw compressor host and cooling water system, and will form a certain scale in the pipeline. After the scale is formed in the cooling system, it will reduce the cross-sectional area of the water flow channel, increase the resistance of the water circulation, and hinder the normal heat exchange. With the continuous thickening of the scale layer, it will cause serious poor cooling of the equipment and bring a series of adverse effects, such as increasing the power consumption of the compressor, reducing the intake volume, reducing the exhaust volume, etc. Therefore, the scale treatment method is also very important. Scale treatment methods generally have chemical reagent method, physical method, artificial method, etc.

(3) Water-lubricated bearings

water lubricated bearings need to change the material properties and lubrication structure of the traditional metal bearing system, and integrate the bearings with the dynamic sealing device and other components, using water as the lubricating medium. At present, there are relatively few manufacturers that can provide water-lubricated bearings, and SKF in Sweden is actively engaged in research and development in this area.

development trend

research on noise reduction

noise as a screw compressor is an obvious problem has been raised many times. In the oil-free screw compressor performance is particularly prominent. Therefore, the study of noise reduction will become a hot spot, along with the noise research of other models, noise research technology will continue to develop and progress, to provide sufficient theoretical basis and experience guidance for the study of oil-free screw noise.

Research on Water Lubrication Technology

with the oil-injected screw compressor in many areas of application limitations of the increasing exposure and dry screw compressor itself a series of problems, water-lubricated oil-free screw compressor has been put forward, there is a very promising prospect. With the development of coating process and bearing manufacturing industry, some companies such as water lubricated bearings have been adopted, and abandon the original synchronous gear need oil lubrication limitations. Moreover, under the general trend of continuous improvement of the rotor shape line, the meshing between the rotors can be realized to form a very water film seal. The rotor, bearing and the whole host are made of 304 stainless steel. The water-lubricated oil-free screw compressor will no longer be an unrealistic idea.

Improve compressor performance

improving the profile of the oil-free screw compressor rotor is the key to improve the compressor performance. The continuous improvement of the performance of screw compressors and the continuous expansion of their market share are inseparable from the development of rotor profiles. The design method of optimized line will become a research hotspot.

Summary

compressor as a kind of general machinery, in many fields have very application prospect. Oil-free screw compressor has unique advantages. With the deepening of its research and the continuous improvement of design technology, the performance of oil-free screw compressor will be further improved, and its application field will be more and more extensive. In some medical and other fields, such as the field of dentistry, the current use of oil-free piston and other models, the future may have a place for oil-free screw compressors. In addition, in the chemical industry, aerospace, aviation and many other aspects will also be more extensive and in-depth application.