In the process of blown film production, the uniformity of film thickness is a very key indicator. The uniformity of the longitudinal thickness can be controlled by the stability of the extrusion and traction speed, while the uniformity of the transverse thickness of the film generally depends on the precision manufacturing of the die., And change with the change of production process parameters. In order to improve the film thickness uniformity in the transverse direction, an automatic transverse thickness control system must be introduced. Common control methods include automatic die head (thermal expansion screw control) and automatic air ring. Here we mainly introduce automatic air ring. Principle and application.

Basic principle of blow molding machine

The structure of the automatic air ring adopts a double air outlet method, in which the air volume of the lower air outlet is kept constant, and the circumference of the upper air outlet is divided into several air ducts. Each air duct is composed of air chambers, valves, motors, etc., and the motor drives the valve to adjust the opening of the air duct. Control the air volume of each air duct.

During the control process, the film thickness signal detected by the thickness measuring probe is sent to the computer. The computer compares the thickness signal with the current set average thickness, performs calculations based on the thickness deviation and the curve change trend, and controls the motor to drive the valve to move. When it is thin, the motor moves forward and the tuyere is closed; on the contrary, the motor moves in the reverse direction and the tuyere increases. By changing the air volume at each point on the circumference of the wind ring, adjust the cooling speed of each point to control the lateral thickness deviation of the film within the target range.

Blow molding machine control scheme

The automatic wind ring is an online real-time control system. The controlled objects of the system are several motors