THERMOFORMING VARIABLES
A study by Bayer Corporation's Polymers Division and Researchers from the Massachusetts Institute of Technology (MIT) sheds new light - and some of the first-ever hard data - on why sheet temperature, bubble height and mold temperature most significantly impact the quality of thermoformed parts. Researchers in this study used an experimental design to quantify the importance of these variables. Among the conclusions the researchers formed were the following: * Pre-stretch height has a large effect on part thickness variation and must be carefully controlled. The paper recommends use of a photoelectric eye to control height independent of sheet temperature variation. * Overall sheet temperature has only moderate effects on part thickness, which provides an opportunity to profile the temperature as needed to control localized part defects. * Mold temperature must be near the glass transition of the material to eliminate ripples in the corners; higher mold temperatures also minimize webs. Other areas of the mold should be kept lower in temperature to maximize part uniformity. In this study, part quality was evaluated using three criteria: thickness variation, incidence of webbing and minimum part thickness.

For more information, contact Bayer Corporation, Polymers Division, Marketing Communications Group, 100 Bayer Road, Pittsburgh, PA 15205-9741, 800-622-6604.