Screw compressor and method of manufacturing rotor for the same

Abstract

A screw compressor of which a female rotor is driven by a motor, and of which a male rotor is driven by the female rotor. The male or female rotor is composed of a member which is made of cast iron and is subjected to surface hardening treatment or heat treatment including quenching. The surface hardening treatment may include sulphonitriding or nitiriding treatment. In the case of subjecting the cast iron to the heat treatment, austemper treatment is applied.

1 . An oil-cooled screw compressor comprising: 
 a male rotor having a shaft and a portion having a plurality of teeth;    a female rotor having a shaft and a portion having a plurality of teeth engaging with the teeth of the male rotor, the number of the teeth of the female rotor being larger than that of the male rotor;    a bearing member supporting the male and female rotors;    a motor for driving the shaft of the female rotor; and    a casing member accommodating the male and female rotors, the bearing member and the motor, wherein    the motor drives the female rotor, so that the male rotor is driven by the female rotor, and    at least the female rotor is composed of a member which is made of cast iron and is subjected to an austempering treatment.    
   
   
       2 . The oil-cooled screw compressor according to  claim 1 , wherein the male rotor is composed of a member which is made of cast iron and is subjected to an austempering treatment.  
   
   
       3 . The oil-cooled screw compressor according to  claim 2 , wherein the austempering treatment of the male rotor and the female rotor includes quenching in a liquid of a temperature of 200 to 450° C.  
   
   
       4 . The oil-cooled screw compressor according to  claim 1 , wherein the austempering treatment includes quenching in a liquid of a temperature of 200 to 450° C.  
   
   
       5 . The oil-cooled screw compressor according to  claim 1 , further comprising an oil reservoir within the casing member, and an oil supply passage between the oil reservoir and the bearing member.  
   
   
       6 . A method of manufacturing a rotor of a screw compressor in which a female rotor having a larger number of teeth than a male rotor is driven by a motor and the male rotor is driven by the female rotor, the method including the steps of: 
 making the rotor of ductile iron;    heating the rotor;    subjecting the rotor to quenching treatment in a salt bath of a temperature of 200 to 450° C.; and    then holding the rotor in the salt bath at a temperature of 200 to 450° C. for 5 to 240 minutes.    
   
   
       7 . The method of manufacturing a rotor for a screw compressor according to  claim 6 , including the steps of: 
 heating said rotor made of ductile iron to a temperature of 800 to 900° C. in an no-oxidation atmosphere,    after said quenching treatment, keeping the rotor at a temperature of 200 to 270° C. for 5 to 30 minutes, and    then flushing the rotor.