Geometric design and performance analysis of conical-rotor screw vacuum pump with adjustable flow field clearances

Structure rotor takes a great effect on the performance of screw vacuum pump. An optimized design for conical rotor profiles with adjustable flow field clearances is proposed. Mathematical models of cross-section profiles and helix of conical rotor are established. Meshing model can generate directly by the profiles with stable circumferential clearance, tooth clearance, tooth side clearance and radial clearance. Effects of offset distance involute, deflection angle of epicycloid, the radial offset distances of addendum and dedendum circles on the clearances are analyzed. Mathematical models for working chamber volume, tooth width, pumping speed and shaft power of the vacuum pump are established. Furthermore, the calculated pumping speed and shaft power are verified by comparing the experimental measured results. Effects of rotor structure parameters on the geometric characteristics and working performance of the vacuum pump are revealed as well as the comparisons with the fixed-pitch and variable-pitch cylindrical screw vacuum pumps. Results show that shaft power of the conical rotor pump are smaller than those of the two cylindrical pumps under similar actual pumping speeds, resulting in superior performances.