Patent ID: 7588704

Claim:
In a method of making lost foam casting patterns from polymer beads having a first density and a first blowing agent content comprising: (a) first heating said beads to pre-expand them into a batch of pre-expanded beads having a second density lower than said first density, and a second blowing agent content less than said first blowing agent content, but to too high for molding into dimensionally stable patterns; (b) second heating the pre-expanded beads in a stream of a hot gas for a time sufficient to reduce the blowing agent content of the pre-expanded beads to within a prescribed range of blowing agent contents suitable for molding the beads into dimensionally stable patterns, said gas being selected from the group consisting of gases that are unreactive with said polymer and said blowing agent, and do not interfere with the quantitative spectroscopic analysis of said blowing agent in the presence of said polymer beads; (c) charging a pattern-mold with beads having a blowing agent content within said prescribed range; and (d) heating the beads in said pattern-mold to further expand, shape and bond them together to form a casting pattern, the improvement comprising controlling the operation of said method by the regular, on-line, real-time NIR-spectroscopic measurement of the blowing agent content of the beads, and in response thereto automatically initiating such adjustments to the operating conditions of said second heating as may be needed to produce beads within said prescribed range.