Method of making expanded polytetrafluoroethylene products

A method for shaping expanded polytetrafluoroethylene tubes into a shaped three-dimensional article, comprising the steps of:

• extruding a mixture of polytetrafluorocthylene resin particles and lubricant to form a tubular extrudate;
• drying the tubular extrudate to remove at least a major fraction of the lubricant;
• longitudinally expanding the tubular extrudate to form an expanded polytetrafluoroethylene extridate having a microstructure of a plurality of nodes interconnected by fibrils;
• at least partially sintering the expanded polytetrafluoroethylene extrudate to form a sintered expanded extrudate having a dimensional stability greater than the expanded polytetrafluoroethylene extrudate;
• radially expanding the sintered expanded extrudate at a temperature greater than ambient but below the crystalline melt point of polytetrafluoroethylene forming a radially expanded sintered extrudate with a diameter greater than a diameter of the sintered expanded extrudate;
• engaging the radially expanded sintered extrudate circumferentially about a shaping mandrel, the shaping mandrel having a shaped three-dimensional conformation;
• heating the shaping mandrel and the radially expanded sintered extrudate to shrink the radially expanded sintered extrudate into intimate contact with the shaping mandrel so that said extrudate adopts the three-dimensional conformation of the shaping mandrel;
• and
• sintering the heat shrunken extrudate.

A method for shaping expanded polytetrafluoroethylene tubes into a shaped three-dimensional article, comprising the steps of:

• extruding an admixture of polytetrafluoroethylene resin and lubricant into a tubular extrudate;
• longitudinally expanding the tubular extrudate forming a longitudinally expanded tubular extrudate with a polytetrafluoroethylene microstructure having a plurality of nodes interconnected by fibrils;
• at least partially sintering the longitudinally expanded tubular extrudate forming an at least partially sintered longitudinally expanded tubular extrudate having a dimensional stability greater than the longitudinally expanded tubular extrudate;
• radially expanding the at least partially sintered longitudinally expanded tubular extrudate at a temperature greater than ambient but below the crystalline melt point of polytetrafluoroethylene forming a radially expanded at least partially sintered extrudate with a diameter that is 200%-400% greater than that of the at least partially sintered longitudinally expanded tubular extrudate;
• engaging the radially expanded at least partially sintered extrudate circumferentially about a shaping mandrel, the shaping mandrel having a shaped three-dimensional conformation;
• and
• heating the shaping mandrel and the radially expanded at least partially sintered extrudate, shrinking said extrudate into intimate contact with the shaping mandrel so that said extrudate adopts the three-dimensional conformation of shaping mandrel.

A method for shaping expanded polytetrafluoroethylene tubes into a shaped three-dimensional article, comprising the steps of:

• extruding a mixture of polytetrafluoroethylene resin particles and lubricant to form a tubular extrudate;
• drying the tubular extrudate to remove a major fraction of the lubricant;
• longitudinally expanding the tubular extrudate to form an expanded polytetrafluoroethylene extrudate having a microstructure of a plurality of nodes interconnected by fibrils;
• at least partially sintering the expanded polytctrafluoroethylene extrudate to form a sintered expanded extrudate having a dimensional stability greater than the expanded polytetrafluoroethylene extrudate;
• radially expanding the sintered expanded extrudate at a temperature greater than ambient but below the crystalline melt point of polytetrafluoroethylene within a constraining chamber to form a radially expanded sintered extrudate with a diameter greater than a diameter of the sintered expanded extrudate, shaped by and in intimate contact with an inner surface of the constraining chamber;
• engaging the radially expanded sintered extrudate circumferentially about a shaping mandrel, the shaping mandrel having a shaped three-dimensional conformation;
• heating the shaping mandrel and the radially expanded sintered extrudate, shrinking said extrudate so that said extrudate adopts the three-dimensional conformation of the shaping mandrel;
• and
• sintering the heat shrunken extrudate.

A method for shaping expanded polytetrafluoroethylene tubes into a shaped three-dimensional article, comprising the steps of:

• extruding an admixture of polytetrafluoroethylene resin and lubricant into a tubular extrudate;
• drying the tubular extrudate to remove at least a major fraction of the lubricant;
• longitudinally expanding the tubular extrudate to form an expanded polytetrafluoroethylene extrudate having a microstructure of a plurality of nodes interconnected by fibrils;
• at least partially sintering the expanded polytetrafluoroethylene extrudate to form a sintered expanded extrudate having a dimensional stability greater than the longitudinally expanded tubular extrudate;
• radially expanding the sintered expanded extrudate at a temperature greater than ambient but below the crystalline melt point of polytetrafluoroethylene to form a radially expanded sintered extrudate with a diameter greater than that of the sintered expanded extrudate;
• engaging the radially expanded sintered extrudate circumferentially about a shaping mandrel, the shaping mandrel having a shaped three-dimensional conformation;
• applying pressure to the radially expanded sintered extrudate, to bring said extrudate into intimate contact with the shaping mandrel;
• and
• heating the shaping mandrel and the radially expanded sintered extrudate, shrinking said extrudate so that said extrudate adopts the three-dimensional conformation of the shaping mandrel.