Apparatus and method of extruding tubing having a variable wall thickness

Abstract

An extruder apparatus and method for producing an extruded tubing having varying inner dimensions without changing the outer dimensions. The tubing is forced from the die face of an extrusion head having an extruder die and an internal mandrel determining the outer and inner dimensions, respectively, of the extruded tubing. The outer dimensions of the mandrel varied by the user to change the inner dimensions of the extruded tubing. A pressure is maintained in the extruded tubing to prevent its collapse and that pressure is changed based upon the change of the external dimensions of the mandrel and the wall thickness of the tubing. In one embodiment, the mandrel is comprised of a core and a plurality of telescoping sleeves. Each sleeve is movable between a retracted position where the sleeve is displaced away from the die face and an extended position where sleeve is at the die face. There may be multiple mandrels in the case of multi-lumen catheters.

1 - 20 . (canceled)  
   
   
       21 . A method of extruding a length of hollow plastic tubing-through an extrusion head having an inner mandrel and an outer die surrounding the mandrel and forming a space between the mandrel and the outer die, with the outer die and mandrel terminating at a die face, said method comprising the steps of: 
 providing a quantity of a material to be extruded,    introducing the material into the space between the mandrel and the outer die and forcing the material outwardly from the die face to form a hollow tubing having inner dimensions determined by the outer dimensions of the mandrel,    varying the outer dimensions of the mandrel while forcing the material outwardly from the extrusion head to selective vary the internal dimensions of a plastic tubing, and    providing and controlling the pressure within the plastic tubing as it is forced outwardly from the extrusion head to maintain the inner dimension of the tubing and to prevent the tubing from collapsing.    
   
   
       22 . A method of extruding a plastic tubing as defined in  claim 21  wherein said step of varying the outer dimensions of the mandrel comprise the steps of: 
 providing a mandrel comprised of a core and at least one sleeve coaxial with the core and adapted to slide over the exterior of the core,    moving the at least one sleeve between a retracted position where the at least one sleeve is displaced with respect to the die face and a extended position wherein the sleeve is located at the die face.    
   
   
       23 . (canceled)  
   
   
       24 . A method of extruding a plastic tubing as defined in  claim 22  wherein the step of providing and controlling the pressure comprises controlling the pressure based upon the outer dimensions of the mandrel.  
   
   
       25 . A method of extruding a plastic tubing as defined in  claim 24  wherein the step of providing and controlling the pressure comprises increasing the pressure when the outer dimensions of the mandrel are increased.  
   
   
       26 - 31 . (canceled)