IMM 9/97

My customer bought a mold from "the other guys," and we now are having trouble with gas entrapment. The part is a rectangular bucket, approximately 5 inches deep, with a 3-by-4-inch opening, .25-inch corner radii, .075-inch wall, and a brim three thicknesses square in section. It is currently gated at two adjacent corners on the parting line. Material burns before packout is achieved. The gas pocket is, of course, opposite the gates, at about 75 percent depth of the bucket. I'd love to hear some input.

In this situation where the mold is already built, find someone with C-Mold and have him do a quick mold filling analysis with different gate locations. Don't waste time and money by having different runners and gates cut into the mold without trying analysis. The part design sounds easy enough for someone competent to model quickly. A different material with different viscosity will fill differently also.
-A. Stinman, Hamilton Beach, Glen Allen, VA, (804) 527-7296.

Flow analysis will show that the part needs to be gated on the top, which is impractical in an existing conventional runner mold-forget it. I have solved this problem cheaply and effectively in the past with vent pins. Locate the vent pins so they vent at the site(s) of the burn(s) on the existing parts. If water lines can't be avoided, sleeve the pin or divert the water.
-F. French, Clayton Corp., St. Louis, MO, (314) 249-5333.