The Thickness Control and Auto Air Ring Technology of the Blown Film

The Reasons of the Thickness Deviation:

 The thickness deviation is caused by many factors. They can be concluded into two kinds according to its direction: machine (longitudinal deviation) and cross-section (thickness deviation).

• The short-time oscillation. Because of the different viscosity of the pitch, the fused-liquid of the conglomerate at the die discharge hole, in form of 5~10mm irregular oscillation. This deviation lasts for less than one second when in high-speed extrusion, which accounts for 1~15% in longitudinal deviation.

• The long-time oscillation. It is mainly caused by the imprecise processing and control leading to an unsteady extrusion capacity, the instable paul-off speed and the untimely regulation of changing the pitch.

The main factors affecting the thickness deviation of the cross-section: The structure and processing precision of the die head; the oscillation of conglomerate liquid; the instable air flow of air ring; the effect of the circumstance and so on. We can add the auto controlling system equipped with an installation of radial regulation to improve the precision of the thickness control.

The Way of Controlling the Longitudinal Deviation of the Film

The best way to solve this problem in current is to adopt the loss-in-weight” gravimetric dosing feeding-back control system. It will control the speed of screw rotation and Paul-off automatically through the online measuring to match the target value. This technology can decrease 2/3 deviation of this kind.

The Way of Controlling the Deviation of Thickness of the Cross-section

There are two ways to control the deviation of the thickness of the cross-section in general:

• The auto die head control system has an internally-set bolts which will inflate if be heated. It can control the film s radial thickness through the timely measuring and position calibration and the way of segmented heating to change the viscosity of the conglomerate liquid. For example, increasing the temperature of one section to control the speed of the conglomerate liquid, we can make the film thinner and decreasing to make it thicker. Therefore, we can overcome the disadvantage of thermal inertia and the delayed time to reply.

• Auto air ring” control system.

Picture 1: The Cross-section of the Double-airholes Air Ring” 

We always take the10～15 ℃air as the cooling medium . It will blow from the upper and the lower air holes. The air volume of the lower hole makes up the 15% of the total air. It is designed to form an air cushion for preventing the outside air flow to affect the bubble. The cooling of film depends on the air flow from the upper hole, which is the key of controlling. The body of air ring is segmented into some independent sections according to its different diameters. Each section has an air valve regulator driven by stepper motor. The online thickness gauging system will measure it in time and send the information to computer for processing it after the molding of the film. Then the control actuator will regulate to provide an optimal cooling air volume for the fine control of the film thickness. For instance, when the film in a certain section of the circumference is a little thick, the air valve will be turn down decreasing the cooling air to make the film thinner; meanwhile, when the film in a certain section of the circumference is a little thin, the air valve will be turn up increasing the cooling air to make the film thicker.

There are two outstanding advantages for auto air ring control system:

• A high control precision. It can control the radial thickness deviation of the blown film in 2%- 5%, which has approached the level of tape-casting precision.

• The time reply for control. It gets rid of the effect of the thermal inertia. This technology leading to a new direction for the whole world has a fast spread and extensive application.

Syncro Auto Air Ring

SYproAuto applies the double-air holes air ring. The materials of air ring is aluminum alloy die casting which takes on the quality of a good intensity, high surface finish and low wind resistance. What s more, it is designed with a stepper motor to regulate the cooling air. According to the different diameters of air rings ranging from 100mm~ 900mm, they are divided into 24~ 80 sections. We allocate responding research units with the films in different kinds, through which the cross-section thickness deviation of the film can be controlled in 2%~ 5%. This deviation control is ahead of the techniques in this area.

Picture 2: SYproAuto auto double –air holes air ring Picture 3: Parts of the blowing room

Picture 4: eaSYroto thickness gauging system