Sucker rod

Abstract

A sucker rod has end fittings secured to a fiberglass rod by threading a portion of the fiberglass rod into an insert assembled in the rod cavity of the end fitting.

I (we) claim: 
     
         1 . A sucker rod comprising:
 (a) an elongate end fitting including a portion defining a cavity extending longitudinally from an end portion of said fitting and having a substantially circular first cross-section of a first diameter proximate said end portion and a substantially circular second cross-section of a second diameter more remote from said end portion than said first cross-section, said second diameter being greater than said first diameter;   (b) an insert comprising an assemblage of plural insert segments, said assemblage having:
 (i) a first end; and 
 (ii) an annular cross-section defining an outer surface including a first portion proximate said first end having a diameter substantially the same as said first diameter of said cavity and a second portion more remote from said first end having a diameter substantially the same as said second diameter of said cavity and an inner surface defining a screw thread; and 
   (c) an elongate rod having a portion of an outer surface defining a screw thread, said rod secured to said end fitting when said insert is assembled in said cavity of said end fitting and said screw thread of said rod is engaged with said screw thread of said insert.   
     
     
         2 . The sucker rod of  claim 1  wherein said rod comprises fiberglass. 
     
     
         3 . The sucker rod of  claim 1  wherein said portion of said outer surface defining said screw thread extends from a first end of said rod to a second end of said rod. 
     
     
         4 . The sucker rod of  claim 1  wherein said assembly of insert segments comprises:
 (a) a first annular segment comprising a first portion of said outer surface of said insert and a first portion of said inner surface of said insert and defined by a plane extending longitudinally from said first end of said insert to a second end of said insert and spaced apart from a longitudinal axis of said insert; 
 (b) a second annular segment comprising a second portion of said outer surface of said insert and a second portion of said inner surface of said insert and defined by a second plane parallel to said first plane and spaced apart from said first plane a distance greater than said first plane is spaced from said longitudinal axis of said insert, said second plane extending from said first end of said insert to said second end of said insert; 
 (c) a first key segment comprising a third portion of said outer surface of said insert and a third portion of said inner surface of said insert extending between a first surface of said first annular segment defined by said first plane and a first surface of said second annular segment defined by said second plane; and 
 (d) a second key segment comprising a fourth portion of said outer surface of said insert and a fourth portion of said inner surface of said insert extending between a second surface of said first annular segment defined by said first plane and a second surface of said second annular segment defined by said second plane. 
 
     
     
         5 . The sucker rod of  claim 1  wherein a chord length defined by an intersection of said first plane with said outer surface of said first annular segment is shorter said first diameter of said cavity. 
     
     
         6 . The sucker rod of  claim 1  further comprising:
 (a) an end surface of said end fitting defining a radial groove; and 
 (b) a tab extending from said outer surface of said insert and engageable with said groove. 
 
     
     
         7 . The sucker rod of  claim 1  wherein said plural insert segments comprise a thermoplastic. 
     
     
         8 . The sucker rod of  claim 7  wherein said thermoplastic is reinforced. 
     
     
         9 . The sucker rod of  claim 7  wherein said thermoplastic comprises one of polyphenylene sulfide, polyether ether ketone, polyetherimide and polyphthalamide. 
     
     
         10 . The sucker rod of  claim 1  further comprising a sheath encircling a portion of said fiberglass rod. 
     
     
         11 . A sucker rod comprising:
 (a) an elongate end fitting including:
 (i) an outer surface portion proximate a first end defining a screw thread; 
 (ii) a second end surface defining an aperture and a radially extending groove; 
 (iii) a rod cavity extending longitudinally toward said first end from said aperture in said second surface and having a cavity surface defining plural frustoconical portions each having a smaller diameter base proximate said second surface and a larger diameter base distal of said second surface; and 
   (b) an insert comprising:
 (i) a first annular segment having an outer surface substantially conforming to a portion of said cavity surface and an inner surface defining a first portion of a screw thread on a circular arc, said first annular segment having a chord length shorter than a lesser diameter of said aperture and said smaller base; 
 (ii) a second annular segment having an outer surface substantially conforming to a portion of said cavity surface and an inner surface defining a second portion of said screw thread on a circular arc, said second annular segment having a chord length shorter than a lesser diameter of said aperture and said smaller base; 
 (iii) a first key segment having an outer surface substantially conforming to a portion of said cavity surface and an inner surface defining a third portion of said screw thread on a circular arc, said third portion of said screw thread continuous with screw threads defined on said inner surfaces of said first and said second annular segments; and 
 (iv) a second key segment having an outer surface substantially conforming to a portion of said cavity surface and an inner surface defining a fourth portion of said screw thread on a circular arc, said fourth portion of said screw thread continuous with screw threads defined on said inner surfaces of said first and said second annular segments; and 
   (c) an elongate fiberglass rod having a portion of an outer surface defining a screw thread corresponding to said screw thread defined on said inner surfaces of said segments of said insert, said end fitting secured to said fiberglass rod when said segments of said insert are arranged against said cavity surface and said screw thread of said rod is in threaded engagement with said screw thread on said inner surfaces of said first and second annular segments and said first and second key segments of said insert.   
     
     
         12 . The sucker rod of  claim 11  wherein said portion of said outer surface defining said screw thread extends from a first end of said rod to a second end of said rod. 
     
     
         13 . The sucker rod of  claim 11  wherein said first annular segment, said second annular segment, said first key segment and said second key segment comprise a thermoplastic. 
     
     
         14 . The sucker rod of  claim 13  wherein said thermoplastic is reinforced. 
     
     
         15 . The sucker rod of  claim 13  wherein said thermoplastic comprises one of polyphenylene sulfide, polyether ether ketone, polyetherimide and polyphthalamide. 
     
     
         16 . The sucker rod of  claim 11  further comprising a sheath encircling a portion of said fiberglass rod. 
     
     
         17 . The sucker rod of  claim 11  wherein at least one of said first annular segment, said second annular segment, said first key segment and said second key segment comprises a tab extending from said outer surface and engageable with said groove in said second surface of said end fitting.