Progressive cavity pump/motor stator, and apparatus and method to manufacture same by electrochemical machining

Abstract

Electrochemical machining is used to generate the helical lobe profiles of the stator of a progressive cavity pump or motor. A thin, elastomeric liner, of uniform thickness is bonded either to the interior of the stator, or to the exterior of the rotor. Where the elastomeric liner is to be bonded to the interior of the stator, bonding is improved by electrically etching the interior of the stator during the electrochemical machining process to produce a roughened surface.

1 . A progressive cavity fluid mechanism, adapted for use as a pump or motor, comprising a stator housing and a rotor, said rotor having an exterior surface formed with helical lobes, and said stator housing comprising a unitary, tubular, rigid element having a circular, cylindrical exterior, and an interior surface also having helical lobes, said mechanism also comprising a flexible layer having a uniform thickness on one of said interior and exterior surfaces.  
   
   
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       16 . An apparatus for use in machining a tubular workpiece or the like, comprising: 
 a cathodic electrode shaped to machine helical lobes in the tubular workpiece;    a drive bar arranged to move said cathodic electrode along a linear path, while simultaneously rotating the cathode about an axis parallel to said linear path, wherein the drive bar is connected to the cathodic electrode by a machine taper, said taper having a frusto-conical exterior surface mating with a frusto-conical interior surface in one of said drive bar and said cathodic electrode;    a electrical power supply connected to the cathodic electrode, and connectible to a tubular workpiece disposed along said linear path and arranged so that said cathodic electrode can pass axially along the interior of said tubular workpiece, whereby said power supply can establish an electric current through said cathodic electrode and said workpiece, as the cathodic electrode passes along the interior of the workpiece; and    a flow path for directing electrolyte past the cathodic electrode, between the cathodic electrode and the workpiece;    wherein said flow path includes a space defined between a portion of the drive bar and the workpiece, behind the cathodic electrode as the cathodic electrode moves along said linear path; and    including an electrical conductor, connected to said electrical power supply and exposed to said space, whereby an electric current is established, through electrolyte within said space, between said conductor and said workpiece.    
   
   
       17 . An apparatus according to  claim 16 , in which said space is further defined by a seal on said drive bar, spaced rearward from said cathodic electrode, and sealingly engageable with the workpiece.  
   
   
       18 . An apparatus according to  claim 16 , in which a part of said drive bar is covered by an insulating sleeve, and in which said electrical conductor exposed to said space defined between a portion of the drive bar and the workpiece is a part of said drive bar not covered by said insulating sleeve.  
   
   
       19 . An apparatus according to  claim 16 , including a rear guide on said drive bar, located behind the cathodic electrode as the electrode moves along said linear path, said rear guide engageable with, and slidable on, the finished interior of the workpiece, for supporting the weight of the cathodic electrode as it moves through the workpiece, said rear guide being forward of said space defined between a portion of the drive bar and the workpiece, and at least one passage allowing flow of electrolyte past said guide, from said space toward the cathodic electrode.  
   
   
       20 . An apparatus according to  claim 19 , in which said at least one passage allowing flow of electrolyte past said guide is formed on the exterior of the rear guide, between the rear guide and the workpiece.  
   
   
       21 . An apparatus according to  claim 19 , in which said rear guide is formed to provide space allowing electrolyte to pass between the rear guide and the drive bar in order to transfer heat away from the cathode to drive bar interface.  
   
   
       22 . An apparatus according to  claim 19 , in which said rear guide is formed with a plurality of passages allowing electrolyte to pass between the rear guide and the drive bar in order to transfer heat away from the cathode to drive bar interface.  
   
   
       23 . An apparatus for use in machining a tubular workpiece or the like, comprising: 
 a cathodic electrode shaped to machine helical lobes in the tubular workpiece;    a drive bar arranged to move said cathodic electrode along a linear path, while simultaneously rotating the cathode about an axis parallel to said linear path;    a electrical power supply connected to the cathodic electrode, and connectible to a tubular workpiece disposed along said linear path and arranged so that said cathodic electrode can pass axially along the interior of said tubular workpiece, whereby said power supply can establish an electric current through said cathodic electrode and said workpiece, as the cathodic electrode passes along the interior of the workpiece; and    a flow path for directing electrolyte past the cathodic electrode, between the cathodic electrode and the workpiece;    wherein said flow path includes a space defined between a portion of the drive bar and the workpiece, behind the cathodic electrode as the cathodic electrode moves along said linear path;    a rear guide on said drive bar, located behind the cathodic electrode as the electrode moves along said linear path, said rear guide engageable with, and slidable on, the finished interior of the workpiece, for supporting the weight of the cathodic electrode as it moves through the workpiece, said rear guide being forward of said space defined between a portion of the drive bar and the workpiece, and at least one passage allowing flow of electrolyte past said guide, from said space toward the cathodic electrode; and    an electrical conductor, connected to said electrical power supply and exposed to said space, whereby an electric current is established, through electrolyte within said space, between said conductor and said workpiece; said space being sufficiently long, in the direction of said linear path, that the electric current established in said space can etch, and thereby roughen the finished interior surface of the workpiece after machining thereof by said cathodic electrode.    
   
   
       24 . An apparatus according to  claim 23 , in which the drive bar is connected to the cathodic electrode by a machine taper, said taper having a frusto-conical exterior surface mating with a frusto-conical interior surface in one of said drive bar and said cathodic electrode.  
   
   
       25 . An apparatus according to  claim 23 , in which said space is further defined by a seal on said drive bar, spaced rearward from said cathodic electrode, and sealingly engageable with the workpiece.  
   
   
       26 . An apparatus according to  claim 23 , in which a part of said drive bar is covered by an insulating sleeve, and in which said electrical conductor exposed to said space defined between a portion of the drive bar and the workpiece is a part of said drive bar not covered by said insulating sleeve.  
   
   
       27 . An apparatus according to  claim 23 , in which said rear guide is formed to provide space allowing electrolyte to pass between the rear guide and the drive bar in order to transfer heat away from the cathode to drive bar interface.  
   
   
       28 . An apparatus according to  claim 23 , in which said rear guide is formed with a plurality of passages allowing electrolyte to pass between the rear guide and the drive bar in order to transfer heat away from the cathode to drive bar interface.  
   
   
       29 . An apparatus for use in machining a tubular workpiece or the like, comprising: 
 a cathodic electrode shaped to machine helical lobes in a tubular workpiece;    a drive bar arranged to move said cathodic electrode along a linear path, while simultaneously rotating the cathode about an axis parallel to said linear path;    a electrical power supply connected to the cathodic electrode, and connectible to a tubular workpiece disposed along said linear path and arranged so that said cathodic electrode can pass axially along the interior of said tubular workpiece, whereby said power supply can establish an electric current through said cathodic electrode and said workpiece, as the cathodic electrode passes along the interior of the workpiece; and    a flow path for directing electrolyte past the cathodic electrode, between the cathodic electrode and the workpiece;    wherein said flow path includes a space defined between a portion of the drive bar and the workpiece, behind the cathodic electrode as the cathodic electrode moves along said linear path;    a rear guide on said drive bar, located behind the cathodic electrode as the electrode moves along said linear path, said rear guide engageable with, and slidable on, the finished interior of the workpiece, for supporting the weight of the cathodic electrode as it moves through the workpiece, said rear guide being forward of said space defined between a portion of the drive bar and the workpiece, and at least one passage allowing flow of electrolyte past said guide, from said space toward the cathodic electrode, wherein said rear guide is formed to provide space allowing electrolyte to pass between the rear guide and the drive bar in order to transfer heat away from the cathode to drive bar interface; and    an electrical conductor, connected to said electrical power supply and exposed to said space, whereby an electric current is established, through electrolyte within said space, between said conductor and said workpiece.    
   
   
       30 . An apparatus according to  claim 29 , in which the drive bar is connected to the cathodic electrode by a machine taper, said taper having a frusto-conical exterior surface mating with a frusto-conical interior surface in one of said drive bar and said cathodic electrode.  
   
   
       31 . An apparatus according to  claim 29 , in which said space is further defined by a seal on said drive bar, spaced rearward from said cathodic electrode, and sealingly engageable with the workpiece.  
   
   
       32 . An apparatus according to  claim 29 , in which a part of said drive bar is covered by an insulating sleeve, and in which said electrical conductor exposed to said space defined between a portion of the drive bar and the workpiece is a part of said drive bar not covered by said insulating sleeve.  
   
   
       33 . An apparatus according to  claim 29 , in which said at least one passage allowing flow of electrolyte past said guide is formed on the exterior of the rear guide, between the rear guide and the workpiece.  
   
   
       34 . An apparatus according to  claim 29 , in which said rear guide is formed with a plurality of passages allowing electrolyte to pass between the rear guide and the drive bar in order to transfer heat away from the cathode to drive bar interface.