Patent ID: 6371744
Filing Date: 2002-04-16
Classification: F04C,F05C

Abstract:
A dry vacuum pump comprising:a casing having an inner cylinder communicating with an inlet and an outlet of the pump; a plurality of screw rotors, each of which comprises a shaft and spiral toothlike parts, received in the inner cylinder with the toothlike parts intermeshing with each other, said shaft is supported by the casing and said spiral toothlike part, a cross section of which is formed by a Quimby curve, a circular arc and a quasi-Archimedean spiral curve, is formed integrally on the shaft; timing gears, each of which is attached to the respective shafts of the screw rotors, intermeshing with each other; and locking mechanisms, each of which is for fixing the timing gear to the shaft, wherein the screw rotor is made of spheroidal graphite cast iron containing nickel of 20 to 30% in weight and has substantially the same coefficient of thermal expansion with that of the locking mechanism made of mild steel.