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Three colors on LSR press with one barrel and one injection unit

Using a 110-ton all-electric Toshiba injection molding machine, Fluid metering equipment, Gayson coloring, and a new Dow Corning liquid silicone rubber (LSR) material, a white 10g plaque, with overmolded Toshiba blue and red strips (84 cm3, each), was molded on one machine with one barrel thanks to a novel tool. The key was a new M.R. Mold tool technology, wherein colorants are introduced to clear LSR inside the mold via their own valve-gate runner nozzles, keeping the metering equipment, screw, and barrel free of the different colors. The two-cavity tool features a six-drop valve-gate cold-runner system. In the system, the red and blue stripes were overmolded simultaneously onto the white plaque via a slide mechanism in the tool. By mixing in the colorant in the cavity instead of the barrel, the need for time-consuming purges is eliminated, and multimaterial LSR parts without multiple injection systems are made possible, saving costs and setup times. M.R. Mold sells a line of proprietary silicone baking cups, provided in a variety of colors, which heretofore necessitated long changeover times to fully purge colorants prior to molding a new color cup. With the new system, each cavity could receive its own coloring on the same machine, with no changeover downtime. Those cupcake cups are molded in an eight-cavity tool, and M.R. felt it could apply this system in that tool, for potentially eight different color LSR parts in one machine cycle. Dow Corning Corp., Williams Township, MI; www.dowcorning.com; Fluid Automation Inc., Wixom, MI; www.fluidautomation.com; Gayson Silicone Dispersions Inc., Barberton, OH; www.gayson.com; M.R. Mold & Engineering Corp., Brea, CA; www.mrmold.com; Toshiba Machine Co. America; Anaheim, CA; www.toshiba-machine.com.

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