Dry screw vacuum pump having spheroidal graphite cast iron rotors

摘要

A dry vacuum pump that includes a casting having an inner cylinder communicating with an inlet and an outlet of the pump, shafts supported by the casting, spiral toothed parts formed on the shaft a plurality of screw rotors each of which includes the shaft and the spiral toothed parts received in the inner cylinder intermeshing with each other. Timing gears each of which are attached to the respective shafts of the screw rotors that intermesh with each other. Locking mechanisms for fixing the timing gears to the shaft. Both of the shaft and the toothed part are made of spheroidal graphite cast iron containing 20 to 30 wt % of nickel are cast integrally.