Rotation mechanism for gas exhaust pump, manufacturing method of the same, gas exhaust pump having rotation mechanism, and manufacturing method of the same

Abstract

In a gas exhaust pump, there is provided a rotation mechanism that can ensure safe rotation and can greatly reduce the usage of a seal gas. A rotation mechanism of the present invention is formed of a rotating shaft and a seal housing. Between the rotating shaft and the seal housing, there is provided a predetermined gap. On at least one of an outer surface of the rotating shaft and an inner surface of the seal housing, there is provided a PFA film. As to a PFA film on a surface of at least one of the rotating shaft and the seal housing, after coating with PFA the wall surface of the rotation mechanism member defining at least the gap, followed by melting and remelting processes, the PFA film is formed to have a high smoothness on its free surface.

1 . (canceled) 
     
     
         2 . The rotation mechanism for a gas exhaust pump, the pump comprising:
 a rotating shaft fixed to a screw rotor or formed integrally with the screw rotor and rotatably engaging with a rotation driving means so as to rotate the screw rotor; and   a seal housing having a structure of rotatably holding the rotating shaft to allow high-speed rotation of the rotating shaft, wherein   at least one of an outermost surface of an outer wall surface of the rotating shaft and an innermost surface of an inner wall surface of the seal housing is provided with a film of PFA of formula 1, and the PFA film is formed through a remelting process,   
       
         
           
           
               
               
           
         
         in which Rf is a perfluoro alkyl group and m and n are both positive integers. 
       
     
     
         3 . A manufacturing method of a rotation mechanism for a gas exhaust pump having a rotating shaft of a screw rotor and a seal housing containing the rotating shaft rotatably mounted therein, the method comprising:
 preparing at least one of a rotating shaft having a PFA coating film of formula 1 provided on an outer wall surface thereof and a seal housing having said PFA coating film provided on an inner wall surface thereof;   exposing the prepared member 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 prepared member 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 prepared member 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   
       
         
           
           
               
               
           
         
         in which Rf is a perfluoro alkyl group and m and n are both positive integers. 
       
     
     
         4 . (canceled) 
     
     
         5 . A manufacturing method of a gas exhaust pump, comprising the processes defined in the manufacturing method of the rotation mechanism according to  claim 3 . 
     
     
         6 . (canceled)