Compressor rotor manufacturing process

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With the development of science and technology, the rotor materials of screw compressors and centrifugal compressors have made great progress and changes. The author has done some research and experiments on this, and this article will briefly talk about it. 1. Centrifugal compressor rotor material: Centrifugal compressor rotors are mostly made of stainless steel. However, some people use aluminum alloy to make rotors for centrifugal air compressors on hydrogen battery cars. However, similar automotive superchargers generally use stainless steel to make rotors. Since centrifugal air compressors on hydrogen battery vehicles require smaller volumes and higher rotational speeds, people feel that it is more appropriate to use high-strength aluminum alloys to make rotors. For this type of centrifugal compressor, it is very important to reduce rotor vibration. The maximum speed of this compressor is as high as 144,000 rpm or 160,000 rpm. For a rotor made of aluminum alloy, the centrifugal force generated due to unbalanced mass will be 2 times smaller than the centrifugal force generated by a rotor made of stainless steel of the same size. That is to say, the centrifugal force generated by a rotor made of aluminum alloy due to the same unbalanced mass is only one-third of the centrifugal force of a stainless steel rotor of the same size. The resulting vibration will * * alleviate. This is a rare advantage of aluminum alloy rotors over rotors made of other materials. For small centrifugal air compressors, this aluminum alloy rotor has the advantages of good elasticity, light weight, easy processing and low cost. 2. Twin-screw compressor rotor materials 1. Oil-injected twin-screw compressor rotor materials. In the early days of the development of twin-screw compressors, foreigners mainly used free-cutting steel to make oil-injected twin-screw compressor rotors. When the Chinese purchased a large number of British screw rotor-specific milling machines, they felt that China's ductile iron was superior to free-cutting steel rotors in terms of cutting performance and processing capacity, and the cost was lower. Therefore, domestic oil-injected screw rotors were mostly made of ductile iron. Because my country is rich in rare earth elements and has mature rare earth ductile iron technology, ductile iron rotors have become screw compressor rotors with Chinese characteristics. The oil-injected twin-screw compressor rotor works in a mixed state of oil and gas two phases. During operation, due to the combined action of pneumatic and hydraulic forces, oil and gas are evenly sprayed into each element volume of the compressor, and are also sprayed onto the surface of the rotor and body to form a protective layer, and the high-speed flowing air and lubricating oil wash away the tiny particles on the surface of the rotor. Although the surface of ductile iron is not as fine as that of steel rotors, it is still capable of performing the function of a rotor. The reliability of the operation of the screw compressor rotor is guaranteed by the accuracy of the bearing. It seems that there is almost no big difference between the steel rotor and the ductile iron rotor. For the rotors of large screw compressors, people still tend to use steel rotors because they think steel rotors are more reliable. 2 Dry screw compressor rotor materials Since people need more reliable and cleaner compressed gas, the oil-injected screw compressor plus precision filtration of compressed gas still cannot completely replace the dry compressor. Later, due to differences in reliability and maintenance periods, people never gave up to partially restored various types of dry compressors. The rotors of dry screw compressors are different from those of oil-injected compressors. Due to the high price, high speed and complex compression medium of dry screw compressors, stainless steel is generally used to make dry compressor rotors. In order to enhance the wear and corrosion resistance of the rotor, different dry compressor rotors have different anti-corrosion coatings or platings on their surfaces. In order to increase its wear resistance and anti-corrosion properties. With the continuous advancement of anti-corrosion coating technology, the performance of anti-corrosion coatings has been further strengthened, and different compressor manufacturers have adopted different coatings or platings. There are two types of coatings: chemical coating and sintered coating, and vacuum titanium plating is a more advanced coating process. Although the plating is thin, it still needs to be polished. Different manufacturers use different polishing processes. Most use manual-assisted mechanical polishing, machining center polishing, chemical and physical polishing for better performance, electrostatic polishing is also used, and large-volume parts use advanced heat treatment polishing technology. 3 Water-lubricated twin-screw compressor rotor materials Most of the rotor materials of the water-lubricated twin-screw compressors currently introduced are stainless steel, and no water-lubricated twin-screw compressor rotors of other materials have been found. Of course the body is also made of stainless steel. Three single-screw compressors have different rotor materials. Single-screw compressors have different rotor materials. 1 Oil-injected single-screw compressor rotor materials Domestic oil-injected single-screw compressor rotors are generally made of free-cutting steel and ductile iron, and the star wheel is made of carbon fiber-reinforced polyether ether. 2 Water-lubricated single-screw compressor rotor materials In recent years, water-lubricated single-screw compressors have been widely used in pharmaceutical, food, beverage, textile and other industries. Different manufacturers use stainless steel and copper alloys to make rotors for different considerations. Since water-lubricated single-screw compressors are more expensive, manufacturers will achieve good economic benefits regardless of which material the rotor uses. Of course, rotors made of different materials are suitable for certain formulas. The star wheel discs are mainly made of the same material as reinforced polyether ether. The material of the star wheel discs of water-lubricated single-screw compressors is different from that of oil-injected single-screw compressors. The body and rotor materials of the water-lubricated single-screw compressor are matched. The rotor material has higher hardness and the casting fluidity of the body material is better. Four high-strength aluminum alloys are suitable for making rotors. The analysis of the screw compressor rotor and body temperature is conducive to a more comprehensive understanding of the screw compressor rotor materials. As traditional rotor materials, free-cutting steel, ductile iron, stainless steel, copper alloy, etc. can be replaced by some other materials. The material strength of high-strength aluminum alloy oil and gas cylinders can be no less than that of high-quality carbon steel. The machined surface of the parts is smooth and the threaded holes are bright and smooth, which is much better than that of ductile iron. It is not difficult to see from the above analysis that high-strength aluminum alloys have certain advantages. No wonder high-end automobile engines have evolved into all-aluminum engines, and it is easy to understand the possibility of using aluminum alloy rotors for screw compressors. Since the force on the rotor is different from that of the body, and the temperature of each point is different, the aluminum alloy material used to make the rotor of the compressor should correctly match the aluminum alloy material used to make the body. The grade (composition) and heat treatment of the aluminum alloy are also different. ； The aluminum alloy of the rotor should have higher hardness and higher overall strength. 5. Tests and developments conducted by the author The author has developed aluminum alloy oil and gas cylinders for twin-screw air compressors. Before 2002, a company in Germany produced a 2m3/min screw air compressor for railway vehicle braking, and its oil and gas cylinder was made of aluminum alloy. However, a domestic company produces a 2.4-3m3/min screw air compressor for railway vehicle braking, which lacks the materials and processes of the aluminum alloy oil and gas cylinder, and the oil and gas cylinder is a steel welded part. Steel welded oil and gas cylinders are heavy and easy to rust, so they are not suitable for supporting railway vehicles. They are barely used when they are irreplaceable. After the author discovered this phenomenon in the company, he suggested that the leaders approve the development of aluminum alloy oil and gas cylinders to replace steel oil and gas cylinders. After approval by the research leader, the author selected a special high-strength aluminum alloy as the material of the oil and gas cylinder. In terms of design, in order to fully reflect the advantages of the aluminum alloy oil and gas cylinder, the author and other engineers used the finite element method to optimize the internal structure of the oil and gas cylinder to reduce stress concentration. After several iterations, after completing the drawing design, the sample was put into trial production with approval. On the basis of sample trial production, the aluminum alloy oil and gas cylinder sample was subjected to a pressure test. The author ensured that the oil and gas cylinder was intact and had no leakage under a hydrostatic test of 4 times the working pressure (pressure vessels are generally required to undergo a hydrostatic test of 2 times the working pressure). At that time, Mr. Wang Shizhang, the leader of the expert group for the introduction of electric locomotives of the Ministry of Railways (the old man participated in the earliest introduction of four Alstom electric locomotives in my country, which ran between Baoji and Fengzhou on the Baoji-Chengdu Railway to replace two or three steam locomotives). After seeing the pressure test situation, they were very pleased. After their research, they believed that it could be loaded and tested. After the loading test came to an end, it was confirmed that the pilot test was approved. On the basis of pilot testing, it will be transferred to formal supporting facilities. On this basis, the author developed an aluminum alloy oil and gas cylinder screw air compressor for the company for high-speed trains, light rails, and subways. The company has been using the products developed by the author to this day. 6. Screw compressor rotor running-in agent To make the screw compressor rotor more reliable and the new machine succeed the first time, the author recommends Dow Corning's mechanical rapid running-in agent. When assembling the screw compressor, applying a small amount of this running-in agent to the friction-prone parts of the rotor and body can prevent accidental strain during the initial start-up of the factory test, which is very reasonable and cost-effective. The anti-wear repair agent developed by the author has a unique effect in this regard.