Exit die

Claim 1

In an annular exit die for an extrusion head having a tapered die core and an outer casing ring concentrically disposed around the die core and cooperating with said die core to define an annular die gap for fabricating a hollow extrudate, the die core being tapered radially outwardly as measured in a direction toward the die gap, and wherein the radial width of the die gap varies upon relative axial movement between the die core and casing ring, the improvement wherein the casing ring comprises: (a) a lower end; (b) an inner wall defining the outer boundary of the die gap, said wall having: (1) a first step adjacent to the lower end of the die casing ring and having an inner radially undulating circumferential profile and a radially undulating first step edge defining the boundary between the first step and the lower end of the casing ring, and (2) a second radially inwardly disposed step adjacent to the first step and having an inner radially symmetrical profile and a radially symmetrical second step edge defining the boundary between the first step and the second step; (c) the ring steps independently defining the outer boundary of the die gap as a function of relative axial positions of the casing ring and die core; (d) said die core and the casing ring, with the first and second steps thereof, being axially movable with respect to each other to selectively position the die core in cooperating lateral alignment with the first and second steps; and (e) means for axially moving the die core and casing ring, with the first step and second step thereof, with respect to each other to selectively position the die core in cooperating lateral alignment with the first and second steps.