Automatic Gauge Control for Blown Film Dies

Macro's ACCUPRO automatic gauge control system for blown film dies is the solution for processors wanting to produce high quality films that will be subsequently printed, laminated or converted in another process. The system consists of a Gamma Backscatter Sensor, an Auto Profile Control System, an Oscillating Scanner Ring and an ACCUPRO die lip that contains closely spaced cartridge heaters around its perimeter.

Film samples produced at Macro's pilot line using an 8-inch (200 mm) die retrofitted with an ACCUPRO system had gauge variations between ±2.5% to ±3.0% within 3s (three sigma) or ±2.0% within 2s (two sigma).

The ACCUPRO system is not only supplied with new dies but can be retrofitted on existing dies. The ACCUPRO system will improve the gauge variation on retrofitted dies by 50%.

prev next The operating principle of the Accupro system is based on influencing the degree of down-gauging the melt after exiting the die gap by controlling the melt temperature at the die lip. The gamma backscatter sensor detects deviations in film thickness. The temperature of the melt at distinct points around the perimeter of the die is adjusted to compensate for these film thickness deviations. 1. Slide 1 The operating principle of the Accupro system is based on influencing the degree of down-gauging the melt after exiting the die gap by controlling the melt temperature at the die lip. The gamma backscatter sensor detects deviations in film thickness. The temperature of the melt at distinct points around the perimeter of the die is adjusted to compensate for these film thickness deviations. 2. Slide 2 The gamma backscatter sensor ensures accurate film thickness measurement. Unlike other measurement techniques the gamma gauge is reliable, highly accurate, simple to calibrate and, insensitive to film composition, opacity, colour, temperature or the presence of masterbatches. Gamma backscatter sensors accurately measure resins such as PA, EVOH or EVA, which are not read well by capacitive sensors. 3. Slide 3 The gamma backscatter sensor is mounted on an oscillator ring to facilitate taking thickness measurements 360 degrees around the perimeter of the bubble. The speed of oscillation is adjustable, and the sensor is mounted in proximity to the die. This setup assures a quick response from the system when compared to other systems that are dependent on slow oscillation of the hauloff or the die before making complete thickness readings on the layflat at a downstream location. 4. Slide 4 The perimeter of the outer die lip is segmented into various temperature zones, which are individually heated by cartridges (red). When the system reads a deviation from a preset thickness value at a particular zone it will automatically make small temperature adjustments to correct for the deviation. For example, if a thick spot is detected, the cartridge heater will increase the temperature of the associated die lip temperature zone in order to reduce the thickness. In the case where the film is too thin, the system will stop applying heat to inhibit downgauging of the film. 5. Slide 5 The interface for the ACCUPRO Automatic Gauge Control System is a high-resolution touchscreen colour monitor, which continuously displays real time thickness. The operator friendly interface provides access to a variety of functions, including target settings, recipes, alarms, reports, auto control setups, and profile selections. This screen shows the Die Bolt Profile. 6. Slide 6 Flat Profile 7. Slide 7 Polar Profile.