Blow molding machines can be divided into three categories: extrusion blow molding machines, injection blow molding machines, and special structure blow molding machines. Stretch blow molding machines can be divided into each of the above categories. Extrusion blow molding machine is a combination of extruder, blow molding machine, and clamping mechanism. It consists of an extruder, a blank die head, a blow molding device, a clamping mechanism, a blank thickness control system, and a transmission mechanism. The blank die head is one of the important components that determine the quality of blow molded products, usually consisting of a side feed die head and a center feed die head. The storage cylinder blank die head is usually used for blow molding of large products. The minimum capacity of the gas storage bottle is 1 kilogram and the maximum capacity is 240 kilograms. The parison thickness control device is used to control the parison wall thickness. The maximum control points are 128, usually 20-30. The extrusion blow molding machine can produce hollow products with a volume range of 2.5ml to 104l.

Injection blow molding machine is a combination of injection molding machine and blow molding mechanism, including plasticizing mechanism, hydraulic system, control electrical appliances, and other mechanical components. Common types include three station injection blow molding machines and four station injection blow molding machines. The three station machine has three pre forming, bulging, and demolding stations, each with an interval of 120 °. The four station machine also has a pre forming station, with each station spaced 90 ° apart. In addition, there is a dual station injection blow molding machine with a 180 ° interval between stations. The plastic containers produced by injection blow molding machines have precise dimensions and do not require secondary processing, but the mold cost is high.

A special structure blow molding machine is a type of blow molding machine that uses sheet metal, molten materials, and cold billets as preforms to blow mold hollow bodies with special shapes and applications. Due to the different shapes and requirements of the products produced, the structure of the blow molding machine also varies.

Simple Overview

In the production process of blown film, the thickness uniformity of the film is a crucial indicator, where the longitudinal thickness uniformity can be controlled by the stability of extrusion and traction speed, while the transverse thickness uniformity of the film is usually influenced by the precision manufacturing of the mold head and changes with the production process parameters. In order to improve the uniformity of film transverse thickness, an automatic transverse thickness control system must be introduced. Common control methods include automatic die head (thermal expansion screw control) and automatic gas ring. This article mainly introduces the principle and application of automatic gas ring.

Basic Principles

The air ring structure adopts a dual air outlet mode, with the lower air outlet maintaining a constant air volume, and the upper air outlet divided into multiple air ducts on the circumference. Each air duct is composed of an air chamber, valve, 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 signal detected by the thickness measurement probe is transmitted to the computer. The computer compares the thickness signal with the current set average thickness, calculates the thickness deviation and curve change trend, and controls the motor to drive the valve movement. When the film thins, the motor moves forward and the air outlet closes; 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 loop is an online real-time control system. The control object of this system is multiple motors distributed on the wind ring. The cooling air flow from the fan is distributed to each air duct after a constant pressure in the air ring chamber. The motor drives the valve to open and close to adjust the size and airflow of the air outlet, change the cooling effect of the film blank at the die outlet, and thus control the film thickness. From the perspective of the control process, there is no clear relationship between the change in film thickness and the motor control quantity. The thickness changes of films with different thicknesses, valves, and control variables at different positions exhibit nonlinear and irregular changes. Every time the valve is adjusted, it will have a significant impact on adjacent points, and the adjustment has hysteresis, which makes different times interrelated. For systems with high nonlinearity, strong coupling, time-varying, and control uncertainty, it is difficult to establish an accurate mathematical model. Even if it can establish a mathematical model, it is very complex and difficult to solve, so it has no practical value. Although traditional control models have better control effects than deterministic control models, control effects with high nonlinearity, uncertainty, and complex feedback information are poor or even powerless. Given this, we have chosen the fuzzy control algorithm. At the same time, the method of changing the fuzzy quantification factor is adopted to better adapt to changes in system parameters.