Process for molding sintered polytetrafluoroethylene articles

Claim 1

THE METHOD OF MOLDING POLYTETRAFLUOROETHYLENE TO PRODUCE SOUND ARTICLES FREE FROM POROSITY AND CRACKS AND FREE FROM HARD LEATHERY TEXTURE EVEN WHEN RECLAIMED MATERIAL IS USED, WHICH COMPRISES, COLD-PRESSING POWDERED RECLAIMED POLYTETRAFLUOROETHYLENE MATERIAL UNDER PRESSURE OF 500 TO 3000 P.S.I. TO MAKE A DENSE COHERENT PREFORM, CLOSED MOLD OF A SIZE TO ALLOW LIMITED EXPANSION OF 15% TO 35% AND THEREAFTER TO CREATE HIGH PRESSURE OF 400 TO 1800 P.S.I. IN THE MATERIAL UNDER COMPLETE CONFINEMENT WITHOUT ESCAPE OF MATERIAL, SINTERING THE PREFORM IN THE MOLD WITH CONCURRENT EXPANSION OF THE MATERIAL BUT WITHOUT ESCAPE OF MATERIAL UNTIL THE DESIRED PRESSURE IS CREATED, AND SUBSEQUENTLY COOLING THE SINTERED PREFORM IN A MOLD WITH A CONTINUOUSLY APPLIED FOLLOW-UP PRESSURE SUFFICIENT TO MATERIALLY REDUCE THE SIZE OF THE BODY OF MATERIAL IN THE MOLD UNTIL THE MATERIAL IS COOL AND DENSE.