Clearance distribution design and thermal deformation analysis of variable-pitch screw rotors for twin-screw vacuum pumps

Clearance distributions between a pair of intermeshing screw rotors greatly affect the gas leakage and pump performance of twin-screw vacuum pumps. Screw rotors generated by the traditional clearance design method have unreasonable clearance distributions and then affect the vacuum degree, especially for variable-pitch screw rotors. Aiming at solving the above problem, this paper presented a novel clearance design method, and designed a pair of intermeshing variable-pitch screw rotors with reasonable clearance distributions at each meshing surface. In addition, thermal deformations of intermeshing screw rotors were simulated, and variations of each clearance were analyzed. Two kinds of screw rotors, the novel and traditional screw rotors, respectively designed by the novel and traditional clearance design methods were manufactured, and their ultimate vacuum degrees of two corresponding twin-screw vacuum pumps were tested. It is found that clearance distributions of the novel screw rotor are superior to the traditional screw rotor designed by the traditional method; the novel screw rotor reduces the value of the reserved circumferential clearance by 41.67%, and the corresponding twin-screw vacuum pump with this screw rotor achieves a higher ultimate vacuum degree as 0.1Pa, while the pump with the traditional screw rotor just achieves the value of 8.4Pa.