Method for making tubing

A method for making an elongated tube having an annular wall with an outer surface and an inner surface that defines a central passageway, the tube also having a first section comprised of a first resinous material, a second section comprised of a second resinous material, the first and second resinous materials being of different stiffness, and an intermediate section joining the first section and the second section, the intermediate section being a transition section in which the wall of the tube gradually changes from the first resinous material of the first section to the second resinous material of the second section to form a continuous unbroken tube of differential stiffness without abrupt joints, said method comprising the steps of:

• providing a first resinous stream of the first resinous material;
• providing a second resinous stream of the second resinous material;
• introducing the first and second resinous materials into separate flow channels in a co-extrusion head that defines a plurality of flow channels;
• controlling the flow of each of the first and second resinous streams into the co-extrusion head;
• causing the first resinous stream to join with the second resinous stream in the co-extrusion head to produce a contact volume of joint flow so as to form a wedge structure in the transition section in which the first resinous material extends into the second resinous material so that the second resinous material surrounds the wedge structure of the first material;
• controlling the flow of each resin stream within the co-extrusion head;
• and passing the resinous materials through an extrusion die to form a continuous unbroken tube of the desired length having the desired sections formed of the first and second resinous materials with the resinous materials naturally adhering to each other in the sections.