Extrusion process of polytetrafluoroethylene tubing materials and apparatus therefor

A method of extruding a tubing material from a mixture of polytetrafluoroethylene and a lubricant using a ram type extruding apparatus having a smooth central mandrel having a portion tapering from a large diameter above a die to a relatively smaller diameter approximately equal to the inside diameter of the extruded tubing material, said die connected to a cylinder along and within which a ram is slidable to force the mixture into the die, comprising the steps of employing said die having a die insert terminating into a die-land, with the opening diameter of said die-land being smaller than the opening diameter of said die insert terminating into said die-land, rotating at least an end portion of the die in one direction during the extrusion of the mixture into a tubing material and thermally expanding said tubing material in the die by heating at least a portion of the die to a temperature higher than the temperature of the mixture in the cylinder, whereby fibrous-state formation in the direction perpendicular to the extrusion direction is accelerated.

A method of extruding a tubing material from a mixture of polytetrafluoroethylene and a lubricant using a ram type extruding apparatus having a smooth central mandrel and a die connected to a cylinder along and within which the ram is slidable to force the mixture into the die, comprising the steps of employing said die having a die insert terminating into a die-land, rotating at least the smooth central mandrel in one direction during the extrusion of the mixture into a tubing material and thermally expanding said tubing material in the die by heating at least a portion of the die to a temperature higher than the temperature of the mixture in the cylinder, whereby fibrous-state formation in the direction perpendicular to the extrusion direction is accelerated.