Patent ID: 8491295

Claim:
An extrusion apparatus comprising: an extrusion die having an upstream side and a downstream side disposed longitudinally opposite from the upstream side, the die comprising a plurality of spaced apart pins defining an interconnected matrix of longitudinal slots opening to the downstream side, the pins having respective generally co-planar tops forming, at the downstream side, a discharge surface and a recessed skin former surface disposed radially outwardly of the discharge surface, the pins being comprised of boundary pins having tops terminating at the discharge surface and being disposed at the outer periphery of the discharge surface, and interior pins being disposed radially inward of the boundary pins; and an annular mask comprising an upstream transverse wall and an inward facing longitudinal wall; wherein the upstream transverse wall of the annular mask is spaced away from the recessed skin former surface in a longitudinal direction, thereby longitudinally masking the longitudinal slots terminating in the recessed skin former surface, to provide a skin former reservoir between the mask and the die; wherein the inward facing longitudinal wall of the mask is radially spaced away from the tops of the pins to form a face gap F that provides a terminal opening for the skin former reservoir proximate the tops of the pins; and wherein the mask longitudinally masks the slots terminating at the skin former surface at a location immediately adjacent the die where at least one of the longitudinal slots formed by one or more boundary pins and the corresponding one or more immediately adjacent interior pins is disposed substantially perpendicularly to the inward facing longitudinal wall; and wherein all slots in the recessed skin former surface at the 90's and immediately adjacent to a corresponding boundary pin is located at a distance equivalent to one half the thickness of the boundary pin, or more, away from the plane of the inward facing longitudinal wall of the mask.