Pipe bending head

Abstract

A bending apparatus for forming a helical strip of material. The bending apparatus comprises at least one bending head and is arranged to deform a strip of material into a helical form by applying a stress to a ridge running longitudinally along the strip of material to provide a plastic deformation of the ridge. The helical form of the helical strip of material is a permanent distortion due to the deformation of the ridge applied by the at least one bending head.

1 . A bending apparatus for forming a helical strip of material, wherein
 the bending apparatus comprises at least two balanced bending heads;   a first bending head being arranged to deform a strip of material into a helical form to form a first helical strip of material by applying a stress to at least one ridge running longitudinally along the strip of material to provide a controlled plastic deformation of the ridge,
 wherein the helical form of the first helical strip of material is a permanent distortion due to the deformation of the at least one ridge applied by the at least one bending head; and 
   a second bending head being arranged to deform a second strip of material into a helical form to form a second helical strip of material by applying a stress to at least one ridge running longitudinally along the second strip of material to provide controlled plastic deformation of the at least one ridge,
 wherein the first helical strip of material comprises a first asymmetric interlock feature formed by the at least one ridge running longitudinally along the first helical strip of material and the second helical strip of material comprises a second asymmetric interlock feature arranged to engage with the first interlock feature when the second helical strip of material is wrapped around the first helical strip of material, and 
 wherein a non-ridge portion of each helical strip of material is deformed into a cylindrical shape by elastic deformation. 
   
     
     
         2 . The bending apparatus of  claim 1 , wherein the ridges are formed by at least two roll forming stations and the bending heads are arranged to receive the helical strip of material after it is formed by the rolling form stations. 
     
     
         3 . The bending apparatus of  claim 1 , wherein the at least one ridge running longitudinally along the strip of material is adjacent to the non-ridge portion of the strip of material. 
     
     
         4 . The bending apparatus of  claim 1 , wherein the non-ridge portion forms a cylindrical shape with a central axis coaxial with the central axis of helical strip of material. 
     
     
         5 . The bending apparatus of  claim 4 , wherein the at least one ridge is circumferential about the cylindrical shape. 
     
     
         6 . The bending apparatus of  claim 1 , wherein the at least one ridge of the first strip of material and the at least one ridge of the second strip of material are physically engaged by the bending apparatus. 
     
     
         7 . The bending apparatus of  claim 1 , wherein the helical strips of material are formed around a liner pipe. 
     
     
         8 . The bending apparatus of  claim 1 , wherein each bending head is a roller set comprising male and female roller shapes arranged to apply a stress to inner and outer surfaces of each ridge in order to deform the respective strip of material by plastically deforming the at least one ridge of the strip of material. 
     
     
         9 . The bending apparatus of  claim 1 , wherein a ratio of a maximum strain of the non-ridge portion to the at least one ridge of the helical strip material within the bending head is approximately 1:8, greater than or equal to approximately 1:2, less than or equal to approximately 1:20, or between approximately 1:2 and approximately 1:20. 
     
     
         10 . A method for forming a helical strip of material, the method comprising:
 at a first bending head of a bending apparatus, receiving a first length of strip material, wherein the first length of strip material comprises at least one ridge along its length and a non-ridge section adjacent to the at least one ridge along its length;   at the first bending head, plastically deforming the first length of strip material into a helical form by applying a stress to the at least one ridge along the length of the ridge;   at a second bending head of the bending apparatus, receiving a second length of strip material, wherein the second length of strip material comprises at least one ridge along its length and a non-ridge section adjacent to the at least one ridge along its length;   at the second bending head, plastically deforming the second length of strip material into a helical form by applying a stress to the at least one ridge along the length of the ridge;   wherein there is substantially no plastic deformation of the non-ridge sections by the bending head; and   wherein the first and second strips of material have a common central axis when formed into a helical form.   
     
     
         11 . The method of  claim 10 , wherein the bending head is a roller set comprising male and female roller shapes that apply a stress along the length of inner and outer surfaces of the ridge. 
     
     
         12 . The method of  claim 10  further comprising:
 at the bending head, receiving a liner pipe, wherein the helical form of strip material surrounds the liner pipe.