Automatic thickness control of slot dies for cast film and sheet began in the 1960s. Black Clawson developed a motorized mechanical wrench on a traversing rail for automatic die-bolt adjustment in 1962. The German Institute for Plastics Processing (IKV) in Aachen also devised a system with an electric motor along the die to adjust die bolts. But both could adjust only one bolt at a time, not much better than an operator could do by hand, and bolt rotation wasn’t very precise.
The need for finer automatic adjustment became critical with the advent of thin OPP sheet in the ’60s. As sheet got thinner, gauge errors were magnified in importance.
The earliest attempt at controlling die lips with heated bolts was in the mid ’60s, when Roy Lowey Jr. at Blaw-Knox patented heated bolts on a sliding-lip die. But sliding lips had inertia, so this did little to improve sheet uniformity.
Frank Nissel at Welex had the idea of heating and cooling die bolts on a flexible-lip die. The first system was installed on an OPP line at Rhone-Poulenc in France in ’72. Welex patented the concept in 1976. His technology uses a traversing thickness gauge to determine TD gauge and adjust the bolts as needed. That has been the basic approach to automatic gauge control for flat dies ever since.
Welex trademarked his Autoflex die and licensed Extrusion Dies Inc. (EDI) exclusively to build them.
Very few readers of this issue can remember, or even imagine, what it was like when an injection mol...