Screw rotor for exhaust pump, method for manufacturing the same, gas exhaust pump having screw rotor, and manufacturing method and assembly method of the same

Abstract

There is provided a screw rotor that can ensure safe rotation and can greatly increase a pumping performance of a pump. The screw rotor is placed with a gap between a top end surface of a tooth of a screw portion and an inner wall surface of a stator. A PFA film is provided on the top end surface. If the PFA film of the present invention is provided in a predetermined manner, the width of a gap between a free surface of the PFA film and the inner wall surface of the stator can be made significantly smaller than that of a conventional one, so that the pumping performance is greatly improved. After coating at least the top end surface of the screw rotor with PFA, followed by melting and remelting processes, the PFA film is formed to have a high smoothness on its free surface.

1 . A screw rotor for a gas exhaust pump, the pump comprising:
 the screw rotor;   a rotating shaft fixed to the screw rotor or formed integrally with the screw rotor and rotatably engaging with a rotation driving unit so as to rotate the screw rotor; and   a holding mechanism configured to have a structure of rotatably holding the rotating shaft to allow high-speed rotation of the rotating shaft,   wherein the screw rotor has a screw portion, and at least a top end surface of the screw portion facing an inner wall surface of a stator has a film of PFA of the structural formula 1, the PFA film being formed through a remelting process,   
       
         
           
           
               
               
           
         
         wherein Rf is a perfluoro alkyl group and m and n are both positive integers. 
       
     
     
         2 . The screw rotor according to  claim 1 , wherein the PFA film is provided on an Al 2 O 3  film formed by non-porous anodic oxidization. 
     
     
         3 . The screw rotor according to  claim 1 , wherein the PFA film is provided on a Ni or NiF 2  film. 
     
     
         4 . A manufacturing method of a screw rotor for a gas exhaust screw pump, the method comprising:
 preparing a screw rotor having a coating film of PFA of the structural formula 1 on a top end surface of a tooth of a screw portion of the screw rotor,   
       
         
           
           
               
               
           
         
         wherein Rf is a perfluoro alkyl group and m and n are both positive integers; 
         exposing the coating film to an atmosphere with a temperature higher than a melting temperature of PFA so as to melt at least a free surface area of the coating film; 
         then exposing the coating film to an atmosphere with a temperature lower than the melting temperature of PFA so as to solidify at least a portion to be a free surface area; 
         then exposing the coating film to an atmosphere with a temperature equal to the melting temperature of PFA or higher than the melting temperature of PFA so as to remelt at least the portion to be a free surface area; and 
         then lowering the temperature of the atmosphere to a temperature sufficiently lower than the melting temperature of PFA so as to increase smoothness of the free surface of a solid film consisting of PFA. 
       
     
     
         5 . A manufacturing method of a gas exhaust pump, comprising the processes defined in the manufacturing method according to  claim 4 . 
     
     
         6 . An assembling method of a gas exhaust pump, comprising using the screw rotor according to  claim 1  as an assembly part. 
     
     
         7 . A gas exhaust pump comprising the screw rotor according to  claim 1 .