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Defect Reduction in Sheet Extrusion

A manufacturer suffered low process yields due to the presence of "spots" or "gels" in a plastic sheet product made from a blend of polyethylene with a ethylene-propylene copolymer. Gel permeation chromatography of these defects revealed that they consisted of a poorly dispersed high molecular weight fraction of the copolymer.

A novel laboratory process simulator was designed and built to reproduce the material stress and temperature history as it advanced through the extrusion operation from the hopper to the sheet die. The primary dispersion mechanism in the process was identified and a screw profile modification dramatically reduced the frequency of "gels" in the final product.

engineering drawing of equipment

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