Apparatus and method for producing and molding structural foam

A cylindrical plunger for rotation and reciprocation in a plasticate extruder barrel, said plunger including:

• (a) a longitudinal metering section for metering fluid foaming agent into said plasticate, the length of said metering section being at least equal to the intended length of reciprocation of said plunger, the surface of said metering section having a plurality of alternate metering-section grooves and lands extending substantially the length of said metering section;
• (b) a mixing section downstream of said metering section, the surface of said mixing section having a plurality of alternate grooves and lands, said mixing-section grooves having upstream ends severally communicating with the downstream ends of said metering-section grooves;
• (c) said mixing section further having an internal bore and a plurality of radial slots, said slots severally connecting the surface of said plunger in said mixing section with said bore;
• (d) first barriers in said grooves and in said radial slots in said mixing section, said first barriers at a uniform location longitudinally downstream of the upstream ends of said mixing-section grooves;
• and
• (e) second barriers in said internal bore and in said radial slots in said mixing section, said second barriers at a uniform location longitudinally downstream of said first barriers.

An plasticate extruder comprising:

• (a) a hollow barrel;
• (b) a foaming agent inlet fixed in said barrel;
• and
• (c) a cylindrical plunger mounted for rotation and reciprocation in said barrel, said plunger having:
• (1) a longitudinal metering section contiguous to said foaming agent inlet, the length of said metering section being at least equal to the intended length of reciprocation of said plunger, the surface of said metering section having a plurality of grooves and lands extending substantially the length of said metering section so that said foaming agent inlet is alternately covered and uncovered by said metering-section lands and grooves when said piston rotates and reciprocates;
• (2) a mixing section downstream of said metering section, the surface of said mixing section having a plurality of alternate mixing-section grooves and lands, said mixing-section grooves having upstream ends severally communicating with the downstream ends of said metering-section grooves,
• (3) said mixing section further having an internal bore and a plurality of radial slots severally connecting the surface of said mixing surface with said bore;
• (4) first barriers in said grooves and in said radial slots in said mixing section, said first barriers at a uniform location longitudinally downstream of the upstream ends of said mixing-section grooves;
• and
• (5) second barriers in said radial slots and in said bore in said mixing section, said second barriers at a uniform location longitudinally downstream of said first barriers.

An extruder comprising:

• (a) a hollow barrel
• (b) a foaming agent inlet fixed in said barrel;
• and
• (c) a cylindrical plunger mounted for rotation and reciprocation in said barrel;
• (1) said plunger having a screw section for advancing plasticate into a longitudinal metering section for metering fluid foaming agent into the plasticate, the length of said metering section being substantially equal to the intended length of reciprocation of said plunger;
• (2) the surface of said metering section having a plurality of alternate metering-section grooves and lands extending along the length of said metering section, said metering-section grooves terminating before each end of said metering section thereby forming a circumferential land at each end of said metering section, said circumferential lands having passages therein severally connecting said metering-section grooves with longitudinal sections of said plunger upstream and downstream of said metering section.