Home > MacroLetter > 13.1 - Autumn 2009 > Blown Film Gauge Correction

Blown Film Gauge Correction

Continued from MacroLetter - Autumn 2009.

Methods of Correction

No matter what method of sensing is applied, the ability to correct the gauge will only be as good as the last part of the system; the method of correction.  In general, the thickness data retrieved by the sensor/scanner is examined by the gauge control software, which in turn makes adjustments to the process to make the necessary corrections.  

Commonly used methods of correction in commercial applications are to use either an automatic die or an automatic air ring.

Automatic Die Approach

The automatic die approach is based on precise temperature control at segmented portions of the die lip.  Small heaters are distributed along the perimeter of the die lip that can be turned on or off by the gauge control system software to make precise adjustments to the die lip temperature at specific points.  

With a greater number of heaters a greater resolution of temperature control is possible.

 
This configuration allows for fine control of film thickness as it leaves the die:

If a thick spot is read, the cartridge heater will increase the die lip temperature to raise the melt temperature at the zone.  This will lower the melt viscosity and increase downgauging at the zone, effectively reducing the thickness.

If a thin spot is read, the system will stop applying heat at the particular zone causing the melt to cool and downgauge less.

The advantage of the die-based approach is its mechanical simplicity; it does not contain moving components.  The downfalls are the system is not as effective with low blow-up ratios, and there is a small lag time (minutes) in response while the die zone heats or cools.  

The die-based approach can be implemented in retrofit projects; however, the die lips may have to be completely replaced to incorporate
the special heaters.

Automatic Air Ring Approach

The automatic air ring approach is based on making small adjustments to the cooling air supplied by the air ring to correct the gauge.  By adjusting the amount of cooling air at specific areas where thickness disparity occurs the polymer is cooled faster or slower to make the appropriate corrections:

When a thick spot is detected, the air flow on the corresponding segment is restricted to locally reduce the cooling of the melt. This permits the melt to be drawn out further towards the deflector lip to stretch the film and thin the gauge.

When a thin spot is detected, the air flow on the corresponding segment is increased to locally intensify the cooling of the melt. This restricts the melt from being drawn out towards the deflector lip, which reduces downgauging to leave the film thicker.

The air ring system's main advantage over the die-based approach is that it reacts must faster; there is no lag time for small temperature changes.  The auto air ring approach also works better for low blowup ratios, and is much easier and less costly to retrofit to older systems.  The disadvantage of the auto air ring is that it's a more complex system that requires more maintenance than automatic die systems.

Macro provides highly advanced gauge control systems for both die and air ring systems.  All configurations are available for testing/viewing in our lab facilities.

ACCUPRO Die Based Gauge Control System

Macro's die-based system of blown film gauge control, the ACCUPRO system, uses a series of die lip temperature zones to make fine-tuned heating adjustments at the die exit.  The system provides reliable and consistent response to improve gauge with minimal mainten-ance.  The ACCUPRO works in conjunction with a rotating scanner.  Macro also offers its ACCUPROflat system, which provides die-based gauge control with the use of a flat scanning system. 

D10 PRO Dual Lip Automatic Air Ring

For either flat or rotating scanning systems using the air ring, Macro offers its D10 PRO Automatic Air Ring.  The D10 PRO uses patented valve technology that redistributes the cooling air supplied to the air ring to make appropriate film gauge corrections.  This makes the D10 PRO highly efficient compared to other automatic air rings as no additional air is needed, or wasted.  Since it is based on the company's D10 Air Ring design, the D10 PRO is easy to use and provides excellent bubble stability and reliable gauge improvements.  


Advanced gauge control is an effective tool to improve product quality and performance and to minimize excess use of costly resins and additives.  The configuration and type of gauge control system that a processor should use depends on the gauge tolerances; the required sophistication, such as measuring individual layers; and the amount of capital investment that is feasible.  This article served to introduce the reader to a common variety of sensing devices and control systems and identified the basic advantages and limitations of each.  Before purchasing a gauge control system it is vital that a comprehensive understanding of these systems is achieved to ensure a successful solution is delivered.