Corrosion-resistant screw vacuum pump

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Currently, for screw pumps, the rotors and casings, as well as the exhaust end components, are often made of QT500/HT250 materials with coatings applied to them to prevent corrosion. Therefore, the quality of the coating determines the corrosion level of the entire pump. When used in chemical production, the operating conditions may involve high suction temperatures, the presence of particles, and corrosive gases. All will accelerate the wear of the coating. Once the thick coating is worn away, the QT500/HT250 material will be exposed to high-temperature and corrosive environments, leading to corrosion of the rotor and casing in the screw pump, which in turn affects the vacuum level. The common repair method is to recoat the rotor and housing, but this approach does not effectively solve the problem, as the clearance between them has increased due to corrosion ； Or simply replace the rotor and housing. The fundamental way to address corrosion is to avoid using coatings and instead use corrosion-resistant stainless steel for the rotor and casing. Common 304/316L grades, being austenitic stainless steels, have a thermal expansion coefficient that is much higher than that of ductile iron, so they cannot be used. Some manufacturers use 2205 duplex steel as this material. Dual-phase steel also contains austenite components, and its thermal expansion coefficient is slightly higher. Therefore, for pumps made of 2205 material, the gap between the rotor and the casing must be increased in order to counteract the rotor sticking caused by thermal expansion. An increased gap between the rotor and the casing reduces the pump’s ultimate vacuum level, preventing it from achieving the performance levels expected when using QT500/HT250. There is now a vacuum pump factory in Yantai, Shandong, which uses a type of stainless steel different from 2205 for the vacuum pump rotors. The thermal expansion coefficient of this material is similar to that of QT500, and its corrosion resistance is comparable to that of 316L. Using this material, the rotor is entirely made of stainless steel forged bars, which solves the problem of corrosion that occurs after the coating peels off and also eliminates pores in castings. It ensures the long-term and stable operation of the equipment. The only drawback is that, due to the material used, its price is higher than that of vacuum screw pumps with QT500/HT250+ coatings; furthermore, stainless steel is difficult to machine, which results in a slightly longer processing time.