Adjustable extruder die assembly, die lip adjustment apparatus, and method

A thermoplastic foam extrusion die assembly, comprising:

• an annular die having a die body, a first die lip, and a second die lip, the second die lip spaced from the first die lip to provide an annular die gap there between, the die body including an undercut, sloped back wall and the first die lip having a circumferential groove opposing the back wall;
• a plurality of die lip wedges, each wedge having a tip and a heel, the tip configured to be received for pivotal movement in the groove of the first die lip and the heel configured to engage with the back wall of the die body;
• a collar encompassing the die body and having a plurality of guide slots spaced circumferentially about the die body each supporting one of the wedges;
• and
• a lifting mechanism for raising and lowering individual ones of the wedges as the heel is raised into engagement with the back wall to drive the first die lip toward the second die lip to adjust a local portion of the annular die gap formed therebetween.

A method for adjusting an annular die gap between inner and outer die lips of an annular thermoplastic foam extrusion die assembly, comprising:

• providing an annular die with a die body, an outer die lip, an inner die lip, a plurality of wedges provided between the die body and the outer die lip, and an actuator for individually driving each of the wedges against the outer die lip to locally deform the outer die lip and locally adjust the die gap;
• arranging the wedges circumferentially about the die body and against the outer die lip;
• moving individual ones of the wedges with the actuator to local portions of the outer die lip;
• observing uniformity of the annular die gap;
• and
• in response to observing, further moving individual ones of the wedges to adjust the annular die gap at selected locations.