PTFE tube

Abstract

The present invention relates to a polytetrafluoroethylene (PTFE) tube, and more particularly to a PTFE tube for a flexible hose. In particular the invention relates to a PTFE tube having a smooth bore for use in the production of a lined hose assembly farther comprising hose braids, external hose protection and end fittings. The PTFE tube comprises external roots and peaks, which tube is obtainable from a non-convoluted tube having an original wall thickness W 0 and an internal diameter ID by a process in which a region of the tube is thinned to provide external convolutions with a root wall thickness W 1 characterised in that the convoluted PFTE tube has an improved resistance, of greater than 7.6%, to permeation by comparison with the non-convoluted tube, the comparison being made between tubes of (i) equal nominal bore ID; and (ii) equal weight of PTFE per unit length.

What is claimed is:  
     
       1. A PTFE tube comprising external roots and peaks, which tube is obtainable from a non-convoluted tube having an original wall thickness W 0  and an internal diameter ID by a process in which a region of the tube is thinned to provide external convolutions with a root wall thickness W 1 , characterised in that the convoluted PTFE tube has an improved resistance to permeation of greater than 7.6% by comparison with the nonconvoluted tube, the comparison being made between tubes of (i) equal internal diameter ID; and (ii) equal weight of PTFE per unit length. 
     
     
       2. A PTFE tube as claimed in  claim 1  wherein the improved resistance to permeation by comparison with the non-convoluted tube is greater than 10%. 
     
     
       3. A PTFE tube as claimed in  claim 1  wherein the improved resistance to permeation by comparison with the non-convoluted tube is greater than 20%. 
     
     
       4. A PTFE tube as claimed in  claim 1  wherein the improved resistance to permeation by comparison with the non-convoluted tube is greater than 30%. 
     
     
       5. A PTFE tube as claimed in  claim 1  wherein the improved resistance to permeation by comparison with the non-convoluted tube is greater than 60%. 
     
     
       6. A PTFE tube as claimed in  claim 1  having a smooth internal bore. 
     
     
       7. A PTFE tube as claimed in  claim 1 , which tube is obtained from a non-convoluted tube having an original wall thickness W 0  and an internal diameter ID by a process comprising:
 1. subjecting the PTFE tube to a deformation force at a temperature at or above the gel transition temperature of PTFE to produce constrained convolutions having a thinned wall W 1 ; and  
 2. cooling the PTFE tube to below the gel transition temperature whilst continuing to constrain the deformations having the thinned wall W 1  until the convolutions having the thinned wall W 1  have become stable.  
 
     
     
       8. A PTFE tube as claimed in  claim 1 , which on heating to above its gel transition temperature without a restraining force in place returns to within 20% of the tubes original wall thickness W 0  but will not do so below the gel transition temperature. 
     
     
       9. A method of producing a PTFE tube comprising external roots and peaks from a non-convoluted tube having an original wall thickness W 0  comprising:
 1. subjecting the PTFE tube to a deformation force at a temperature at or above the gel tension temperature of PTFE to produce constrained convolutions having a thinned wall W 1 ; and  
 2. cooling the PTFE tube to below the gel transition temperature whilst continuing to constrain the deformations having the thinned wall W 1  until the convolutions having the thinned wall W 1  have become stable.  
 
     
     
       10. A method of producing a PTFE tube as claimed in  claim 9 , wherein the tube is placed on a mandrel and a helical tool comprising a leading end and a following end is rotated relative to the mandrel at a speed such that the leading end applies a deformation force at above the gel transition temperature and the following end applies a restraining force until the temperature has dropped below the gel transition temperature and the convolutions have become stable. 
     
     
       11. A method as claimed in  claim 10  wherein the mandrel is a plane cylindrical mandrel. 
     
     
       12. A method as claimed in  claim 10  wherein the following end of the helical tool is maintained at a temperature below the gel transition temperature. 
     
     
       13. A method as claimed in  claim 9  wherein W 1  is less than 25% of W 0 . 
     
     
       14. A method as claimed in  claim 13  wherein W 1  is about 20% of W 0 . 
     
     
       15. A hose assembly comprising a PTFE tube as claimed in  claim 1 , a braid and one or more end fittings. 
     
     
       16. Use of a PTFE tube as claimed in  claim 1  in a hose assembly for the purpose of improving the resistance to permeation of said hose assembly. 
     
     
       17. Use of a PTFE tube as claimed in  claim 1  for the manufacture of a hose assembly intended to have improved resistance to permeation. 
     
     
       18. A method comprising passing a fluid through a PTFE tube or hose assembly under a pressure greater than atmospheric pressure characterized in that the fluid is passed through a PTFE tube as claimed in  claim 1  or the hose assembly as claimed in  claim 15 . 
     
     
       19. A PTFE tube comprising external roots and peaks which tube os obtainable from a non-convoluted tube having an original wall thickness W 0  by a process in which a region of the tube is thinned to provide external convolutions with a root wall thickness W 1  characterized in that W 1  is less than 25% of W 0 . 
     
     
       20. A PTFE tube as claimed in  claim 19  wherein W 1  is about 20% of W 0 .