Extrusion die control system

Apparatus for controlling the thickness of plastic film from an extrusion die comprising:

• a die body having opposing jaw surfaces forming an opening therebetween, one of said jaw surfaces being adjustable with respect to the other to control the width of said opening;
• a plurality of thermal die adjusting bolts disposed along said one jaw surface, said bolts including electrical heating means for causing said bolts to expand and reduce the width of said opening upon application of increasing electrical power and to contract and widen said opening upon a reduction of said electrical power;
• thickness measurement and scanning means for measuring the thickness of plastic film passing through said opening and at different transverse locations along said film, said measurement means providing a signal proportional to the thickness of said film;
• temperature sensing means positioned at each said bolt for sensing the temperature of said bolts and providing a signal proportional to said bolt temperature;
• means for converting said thickness measurement signal into a temperature reference signal;
• means for comparing said temperature reference signal with said bolt temperature signal and providing a difference signal;
• and
• means for actuating said electrical heating means in accordance with said difference signal to control the temperature of said bolt and cause said bolt temperature signal to reach said reference signal whereby the thickness of said film is maintained at a predetermined uniform dimension.