When rotational molding engineer Dru Laws had questions about wall thickness, he found answers using a computer simulation software program, RotoSim.
You get to watch the rotomolding process from the comfort of your desktop, said Laws, who recently began his new job as operations manager of Rotonics Manufacturing Inc.'s plant in Bensenville, Ill. He moved to Commerce City, Colo.-based Rotonics from his job as rotational molding director at color maker Chroma Corp., which is part of ICO Polymers North America.
Laws presented his research April 13 at the Society of Plastics Engineers rotational molding conference in Cleveland.
Wall thickness is important for rotomolding, and not just because of impact strength. Wall thickness also affects things like cycle time, shrink, warpage and part price.
Laws gave a lesson in Rotomolding 101. Plastic sits at the bottom of a mold in what he called a powder pool. The heated mold revolves around, picking up a thin layer of melted plastic every time it moves through the pool.
Using RotoSim, a user can select specific parts of the mold and see how often each one visits the powder pool. The more visitation time, the thicker the wall in that section of the part, he said.
His conclusion: Rotation speed is the only way to manipulate powder pool behavior.
Using an offset arm, or an axial arm, does not affect wall thickness, Laws said.
He added that RotoSim also can show data on wall-thickness distribution throughout a part.
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