Importance

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Abstract

An annular exit die for an extrusion head of the type having a die casing ring and a tapered die core cooperating to form an annular die gap or orifice for fabricating a hollow extrudate of thermoplastic material. The tapered die core is adjustable in the axial direction and changes the radial cross-sectional dimension of the die gap as a function of its position. The casing ring has a lower end and an inner wall defining the outer boundary of the die gap. The wall has a step at the lower end of the ring. The step has an inner radially undulating circumferential profile and a radially undulating edge defining the boundary between the step and the lower end of the casing ring. The inner wall of the ring also has another step disposed radially inwardly of the first-mentioned step. This step has an inner radially symmetrical profile and a radially symmetrical edge defining the boundary between the two steps. The ring steps independently define the outer boundary of the die gap as a function of the relative axial positions of the casing ring and die core. Axial movement of the tapered die core varies the cross-sectional dimension of the die gap both uniformly about the circumference of the gap and at localized points therearound.

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First Claim