Low coefficient of expansion rotors for blowers

A blower assembly comprising:

• a blower housing defining a blower chamber, the blower housing formed to include a gas inlet for allowing gas to enter the blower chamber and a gas outlet to allow gas to exit the blower chamber;
• a first screw rotor positioned within the blower chamber and adapted for rotation therein, the first screw rotor including a first shaft and a first helical flight around the first shaft, the first helical flight having an outer surface that defines a first screw profile;
• a second screw rotor positioned within the blower chamber and adapted for rotation therein, the second screw rotor including a second shaft and a second helical flight around the second shaft, the second helical flight having an outer surface that defines a second screw profile;
• and
• a coating positioned on at least one of an inner surface of the blower chamber or the outer surface of each of the first screw rotor and the second screw rotor, the coating including at least one of an abradable coating or a formable coating,
• wherein the first screw rotor and the second screw rotor are formed from metal having a coefficient of thermal expansion from 1 (10−6 in/in*K) to 13 (10−6 in/in*K), and wherein the first and second rotors are formed from a metal including at least 50% iron, 20% to 35% nickel, and 10% to 25% cobalt.

A method for forming a blower assembly comprising:

• forming a blower housing from a metal via investment casting, the blower housing formed to include an interior chamber, a gas inlet for allowing gas to enter the blower chamber, and a gas outlet to allow gas to exit the blower chamber;
• forming a first rotor from a metal having a coefficient of thermal expansion from 1 (10−6 in/in*K) to 13 (10−6 in/in*K) via investment casting, the first rotor having an outer surface;
• machining a portion of the outer surface of the first rotor to remove a portion of the metal to define a first rotor profile;
• forming a second rotor from a metal having a coefficient of thermal expansion from 1 (10−6 in/in*K) to 13 (10−6 in/in*K) via investment casting, the second rotor having an outer surface, wherein the first and second rotors are formed from a metal including at least 50% iron, 20% to 35% nickel, and 10% to 25% cobalt;
• machining a portion of the outer surface of the second rotor to remove a portion of the metal to define a second rotor profile;
• applying a coating including at least one of an abradable coating or a formable coating to one or more of the outer surface of the first rotor, the outer surface of the second rotor, or a surface of the interior chamber of the blower housing;
• and
• positioning the first rotor and the second rotor within the interior chamber for rotation therein.