Stator for gas exhaust pump, method for manufacturing the same, pump having the stator, and manufacturing method and assembling method of the same

Abstract

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

1 . A stator for a screw pump, the pump comprising:
 a 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 stator containing the screw rotor therein,   wherein an inner wall surface of the stator has a film of PFA of the structural formula 1:   
       
         
           
           
               
               
           
         
         wherein Rf is a perfluoro alkyl group and m and n are both positive integers. 
       
     
     
         2 . The stator according to  claim 1 , wherein the PFA film is a film formed through a remelting process. 
     
     
         3 . The stator according to  claim 1 , wherein the PFA film is provided on an Al 2 O 3  film formed by non-porous anodic oxidization. 
     
     
         4 . The stator according to  claim 1 , wherein the PFA film is provided on a Ni or NiF 2  film. 
     
     
         5 . A manufacturing method of a stator for a gas exhaust screw pump, the method comprising:
 preparing a stator having a coating film of PFA of the structural formula 1 on an innermost surface of an inner wall thereof,   
       
         
           
           
               
               
           
         
         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. 
       
     
     
         6 . A manufacturing method of a gas exhaust pump, comprising the processes defined in the manufacturing method according to  claim 5 . 
     
     
         7 . An assembling method of a gas exhaust pump, comprising using the stator according to  claim 1  as an assembly part. 
     
     
         8 . A gas exhaust pump comprising the stator according to  claim 1 .