Patent ID: 7632447

Claim:
A method of injection molding a thermoplastic leaching chamber having an arch shape cross section, a top, a hollow arch shape interior surface, a base defining an open bottom, and two opposing sidewalls which slope inwardly as they run upwardly from the base to the top, the sidewalls having a multiplicity of inward flaring perforations spaced apart along the length of the chamber, which comprises: (a) providing a multi-piece mold core part and a mating mold cavity part, which when mated together form a space, which when filled with thermoplastic forms said chamber; wherein said core part defines the hollow interior surface of the chamber and wherein said cavity part defines the exterior surface of the chamber; said core part having opposing side pieces with projections which define said perforations in the sidewalls of the arch shape cross section; (b) injecting thermoplastic into the space between said core and cavity parts, to thereby form the chamber; (c) moving said opposing side pieces of said mold core part which have projections inwardly relative to portions of the cavity part which define the exterior surface of the chamber sidewalls, so the projections withdraw from the molded sidewalls thereof; and, (d) moving the core part and cavity part away from each other, to thereby expose the chamber within the cavity part of the mold, so the chamber may then be removed from the mold.