DEVICE FOR CONTROLLING THICKNESS OF INFLATION FILM

PURPOSE:To control the thickness of an inflation film with a high precision. CONSTITUTION:An inflation film F extruded from a rotary mold 1 is drawn up by a receiving roll 2 via a converging guide 3, guided by a plurality of guide rolls 4 and rolled up by a roll-up machine 5 lastly. A thickness detector 7 is provided on an extension of the inflation film F. The thickness detector 7 can be moved back and forth with respect to the inflation film F by an air cylinder. A position detector 12 is made to face the lateral side of the rotary mold 1 rotating at a specific speed and detects a plurality of specified points coming at specific periods in the course of one rotation of the mold. The main body 13 of the controlling device calculates the average value of the thickness detected periodically from position data on the rotary mold 1 and thickness data on the inflation film F and controls the speed of rotation of the receiving roll 2 so that the average value be made a set value, while making the thickness detector 7 withdraw from the inflation film F till the start of the detection of the thickness.