Film thickness uniformity is a key indicator in the production of blown film. Vertical thickness uniformity can be controlled by extrusion and traction speed stability, while film transverse thickness uniformity is generally based on precision molding of the die. In order to improve the lateral thickness uniformity of the film, an automatic lateral thickness control system must be introduced. The common control methods include automatic die (thermal expansion screw control) and automatic air ring. Here, the automatic air ring is mainly introduced. Principles and applications.
The automatic air ring structure adopts a double air outlet method, wherein the air volume of the lower air outlet is kept constant, and the air outlet is divided into a plurality of air passages, each air passage is composed of a wind chamber, a valve, a motor, etc., and the motor drives the valve to adjust the air passage opening. Degree, control the air volume of each air duct.
During the control process, the film thickness signal is detected by the thickness measuring probe and transmitted to the computer. The computer compares the thickness signal with the current set average thickness, and calculates the thickness according to the thickness deviation and the curve change trend, and controls the motor to drive the valve to move when the film is biased. When thin, the motor moves forward and the air outlet is closed; on the contrary, the motor moves in the opposite direction and the air outlet increases. By changing the air volume at each point on the circumference of the air ring, the cooling speed of each point is adjusted, so that the lateral thickness deviation of the film is controlled within the target range. .
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