PURPOSE: To prevent the thermal expansion of a rotor and the corrosion of a shaft part by forming the tooth part of a screw rotor out of a material whose main component is Ni of 32W46% by weight ratio and the rest is Fe and forming the shaft part out of corrosion resistant alloy.
CONSTITUTION: The tooth member 8 of a screw rotor is formed of Fe-Ni group alloy whose main component is Ni of 32W46% (by weight ratio) and the rest is Fe and unavoidable impurity and Fe-Ni-Co group alloy whose main component is Ni+Co of 32W46% and the rest is Fe and unavoidable impurity, etc., both of which are small in thermal expansion coefficient at less than 6×10-6. And the shaft member 9 is formed of austenitic alloy in excellent in corrosion resistance, especially of austenitic stainless consisting of Cr of 16% or more, Ni of 6% or more and Fe and unavoidable impurity for the rest. And it is connected to the tooth member 8 through a connecting layer 10 formed by internal chill, welding pressure welding, diffused junction and brazing, etc.
KURAGANO MITSURU
KONDO YASUO
