Patent ID: 7740781

Claim:
A process for forming an insulator around a conductor comprising: paste extruding lubricated PTFE fine powder in an extrusion device comprising a die, mandrel, and at least one channel-forming member, said die and mandrel forming a converging chamber leading to an extrusion orifice with said channel-forming member positioned in said orifice, said mandrel having a central bore for supplying said conductor, said paste extruding comprising forcing lubricated PTFE fine powder through said chamber and out of the exit of said orifice as a lubricated green extrudate around said conductor forming an insulator with at least one closed longitudinal air channel spaced apart from said conductor, wherein said lubricated PTFE fine powder is forced around said channel-forming member and into a space between said conductor and said channel-forming member pressure coalescing said lubricated PTFE fine powder into said green extrudate around said conductor, said extrusion device having a high shear region which causes substantial fibrillation of said lubricated PTFE, and said pressure coalescing being performed upstream of said high shear region.