Recyclable plastic structural articles and method of manufacture

A method of manufacturing a plastic structural article comprising:

• blow-molding a plastic preform in a mold cavity into a shape of an elongated member using compress gas to at least partially form an elongated tubular plastic shell wall having opposed end sections, and a middle section there between forming a hollow interior cavity;
• extending a plurality if hollow pins through the shell wall;
• introducing a pressurized gas into the hollow interior cavity through the hollow pins;
• once the tubular plastic shell is fully conforming the elongated tubular plastic shell wall to the mold cavity while venting the mold to control cavity pressure;
• forming at least one fill port when the mold pressure reaches a predetermined pressure which is significantly above atmospheric pressure;
• filling the shell interior cavity with expandable polymer beads maintained in a bead reservoir in a pressurized state by opening a bead fill valve coupling the mold cavity to the bead reservoir while controlling the cavity pressure by regulating the flow of gas exiting the cavity;
• injecting a hot, at least partially vaporized heating medium, into a first group of the hollow pins while removing the heating medium from a second group of the hollow pins for a period of time then injecting the hot, at least partially vaporized heating medium, into a second group of the hollow pins while removing the heating medium from a first group of the hollow pins for a period of time to partially melt and expand the expandable polymer beads so as to substantially fill the interior cavity of the shell bonding to one another and the shell wall;
• injecting air into one of the groups of the hollow pins while evacuating the air and condensate formed by the heating medium from the other group of the hollow pins for a period of time, then injecting air into the other group of the hollow pins while evacuating the air and condensate from the one of the groups of the hollow pins for a period of time until the assembly is cooled sufficiently to limit substantial further expansion of the bead;
• and
• releasing the plastic structural article from the mold cavity.

A foam core system for use with an extrusion blow molding machine which forms an elongated plastic parison which can be blow molded into a hollow shell the shape of a mold cavity, the system comprising:

• a mold formed by a pair of mold halves defining an internal cavity with at least one of the mold halves provided with at least two groups of hollow pins which can be removably inserted into the mold cavity with each of the at least two groups connected to separate manifolds;
• a pressure sensor in communication with hollow shell;
• a source of expanded plastic bead;
• a reservoir for pressurized expanded plastic bead with an inlet coupled to the source of expanded plastic bead by a reservoir inlet valve and an outlet connected to a fill gun supply valve;
• at least one bead fill gun attached to a mold half to cut a hole in a hollow shell formed within the mold cavity and to selectively coupling the mold cavity to the source of pressurized expanded plastic bead via the fill gun supply valve;
• a pressure sensor in communication with hollow shell;
• each of separate manifolds the for at least two groups connected hollow pins, is also coupled to at least three valves connected to a source pressurized gas, an at least partially vaporized heating medium and a vent;
• and
• a system controller in communication blow molding machine to sequentially operate and control recited valves and the fill gun to insert the hollow pins, blow the shell, cut an opening in the shell, control the mold pressure while filing the mold with bead, to heat the bead sequentially in a plurality of zones, to cool the bead sequentially in a plurality of zones, to signal the blow molding machine to expel the completed article and to refill the a reservoir for pressurized expanded plastic bead.