AUTOMATIC SYSTEM FOR CONTROLLING COOLING AND DETAILS OF MEANS FOR VARYING AMOUNT AND POSITION OF COOLING AIR DIRECTED AT FILM

摘要

Automatic thickness profiling for use in blown film and other extrusion lines. The automatic system is integrated into an air cooling ring device either external and/or internal to the bubble or extrusion. It comprises one or more high resolution circumferentially variable annular air outlets which act to cool the molten resin in a circumferentially variable way. Thin slide plates remain fixed in place except when adjusted to open or close the local annular air outlet by the action of at least one scanning actuator. The actuator is positioned by control signals generated by a control computer which calculates the appropriate local dimension of the variable air outlet in response to circumferential position correlated with thickness variations detected by a film thickness sensor. The film thickness above the frost line is mechanically scanned around the extrusion. In the case of making blown products with internal cooling, counteracting adjustments are made as local flow areas of the internal cooling device are changed to maintain constant the entrapped air volume. The novel actuation system is also shown to be useful in locally adjusting a finely segmented air lip. A method of correlating thickness changes with respective cooling zones is also disclosed.