Experimental Study on Noise Reduction of Multistage Dry Roots Vacuum Pump Varying the Amount of Dynamic Unbalance

Multistage dry Roots vacuum pumps (MDRVPs) are vacuum equipments widely used in IC industry. This paper analyzes the influence mechanism of dynamic unbalance to vibration and noise of rotor axis in MDRVPs, and calculates the vibration deformation of the rotor axis caused by dynamic unbalance through the finite element method. Moreover, a series of experiments on noise source identification are carried on a MDRVP sample machine varying the amount of dynamic unbalance. Through the experimental results, conclusions are drawn that the periodic incentives generated by the unbalance of rotor axis are the main attribution of vibration and noise. Therefore the noise reduces when the amount of unbalance of rotor axis deceases. However, when the allowable unbalance of the rotor axis decreases to a certain degree, aerodynamic noise generated at the outlet becomes the main noise with dominant frequency. It is true that noise of MDRVPs should be no more than 72dB, so the allowable amount of dynamic unbalance should be chosen at a moderate lever as 1.0 g•mm/kg. In that way, this conclusion offers a rule for MDRVPs design and dynamic balance operation because this lever would not only meet the demand of noise reduction but also save working hours and cost for dynamic balancing.