Study On The Dynamic Balancing Of Screw Rotor In Dry Screw Vacuum Pump

As the development of modern science and technology, the requirement about vacuum environment is more and more strict, and then the vacuum pumping equipment is required with a higher performance. The dry screw vacuum pump is a type of pump product which has a broad prospect in application and a huge market potential in commerce, so it is broadly used in the fields such as semiconductor, medicine, chemical industry and gain drying and so on. Along with the development tendency of miniaturization and high speed about the screw pump, the screw rotor is put forward higher requirement of dynamic balance performance. Therefore, it’s necessary for the rotors to be calculated the dynamic balance to reduce the amount of unbalance in the design stage to ensure smooth running.Aiming at the screw rotors with single-threaded and fixed pitch and that with varying pitch used in dry screw vacuum pump, some research about dynamic balance design and calculation method is carried out in this paper. The mass removing method is adopted to realize the static and dynamic balance compensation about rotors. According to the mass radius product principle, with the mass center position and mass radius product both equal to zero as the target, the complete and feasible dynamic balance universal design method and calculation formulas about the screw rotors are respectively obtained.In order to meet the practical needs of engineering design and simplify the calculation procedure, with the deduced universal dynamic balance optimal design method as the theoretical basis, three kinds of specific structure rotors with single threaded and fixed pitch are researched specially. The three kinds of specific structure are that the length of the screw rotor equals to integral and semi-integral multiply of lead and that with random length. The simple and feasible conclusions are got directly, and the calculation formulas about the parameters of removed solids are given directly. With the above parameters, the screw rotor can realize dynamic balance completely.In order to ensure the completeness of the tooth surface about rotors and decrease the residual harmful space to make all surface smooth and fulfill higher work requirements, a kind of hollow structure screw rotor with single threaded and fixed pitch which is removed mass inside the rotor is researched specially in this paper. And a kind of dynamic balance design method which is fit for the hollow screw rotor with single threaded and fixed pitch of integral and semi-integral multiply of lead is provided. In this assembly structure, the rotor shaft can adopt higher strength material which is different from the screw rotor. Thus this kind of structure is with higher stiffness and strength which can work steady at higher rotating speed.It is complicated to use the above universal optimal calculation method to conduct dynamic balance design about screw rotor, because the boundary conditions are difficult to control. Aiming at this problem, the dynamic balance optimal design of the rotor is realized by the Behavioral Modeling Extension in Pro/ENGINEER. Therefore, a kind of fast and effective method is provided for dynamic balance of the rotor in screw pump. At the same time, the above research conclusions can be realized commodiously and quickly with this method. For machine work conveniently, basing on this method, a kind of dynamic balance way in which the compensation mass is removed mainly on the end face and adjusted on addendum surface is put forward. The feasibility and value about the research conclusions in this paper have been verified in specific production technics. And the product samples are with better dynamic balance performance.In the deducing process of the formulas, the form of end face profile isn’t involved, thus, the methods provided in this paper are fit for screw rotor with single threaded and fixed or varying pitch of any type of end face profile. This method can be used to solve the dynamic balance problem of screw rotor in dry vacuum pump thoroughly and has been applied to practice in engineering successfully. And the rotors after balance with this method have a better dynamic balance performance. In addition, the research contents in this paper have successfully applied for two Chinese patents:A kind of dynamic balance design method of screw rotor with single threaded and fixed pitch (No:20110300961.0); A kind of dynamic balance design method of hollow screw rotor with single threaded and fixed pitch (No:201210068599.3). Some of the work in this research serves for the National Natural Science Foundation of China (Grant No.51176027).