Operating Principle Of Blow Molding Machine

Simple Overview
In the production process of blown film, the thickness uniformity of the film is a crucial indicator. The longitudinal thickness uniformity can be controlled through the stability of extrusion and traction speed, while the transverse thickness uniformity of the film generally depends on the precision manufacturing of the mold head and changes with the production process parameters. In order to improve the transverse thickness uniformity of the film, an automatic transverse thickness control system must be introduced, Common control methods include automatic die head (thermal expansion screw control) and automatic air ring. This article mainly introduces the principle and application of automatic air ring.
Basic Principles
The automatic air ring structure adopts a dual air outlet method, where the air volume of the lower air outlet remains constant, and the circumference of the upper air outlet is divided into several air ducts. Each air duct is composed of an air chamber, a valve, a motor, etc. The motor drives the valve to adjust the opening of the air duct and control the air volume of each air duct.
During the control process, the thickness sensor detects a thin film thickness signal and transmits it to the computer. The computer compares the thickness signal with the current set average thickness, calculates based on the thickness deviation and curve change trend, and controls the motor to drive the valve to move. When the thin film is thin, the motor moves forward and the air outlet is turned down; 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 and adjusting the cooling speed at each point, the lateral thickness deviation of the film is controlled within the target range.
Control plan
Automatic wind ring is an online real-time control system, where the controlled objects are several motors distributed on the wind ring. The cooling airflow sent by the fan is distributed to each air duct through the constant pressure of the air ring air chamber. The motor drives the valve to adjust the size of the air outlet and air volume, change the cooling effect of the film blank at the mold head discharge, and control the film thickness. From the control process, there is no clear relationship between the change in film thickness and the motor control quantity, The nonlinear and irregular variation between the thickness changes of different thin films and different positions of valves, as well as the control variables, has a significant impact on adjacent points every time a valve is adjusted. Moreover, the adjustment has hysteresis, making the different moments interrelated. For this highly nonlinear, strongly coupled, time-varying, and control uncertainty system, its precise mathematical model is almost impossible to establish, and even if a mathematical model can be established, it is very complex, It is difficult to solve and therefore has no practical value, while traditional control has better control effects on relatively certain control models, while for highly nonlinear, uncertain, and complex feedback information, the control effect is very poor or even powerless. Given this, we have chosen the fuzzy control algorithm. Simultaneously, changing the fuzzy quantification factor can better adapt to changes in system parameters.