The VenPad film gauge measuring system developed by Octagon Process Technology GmbH, Würzburg/Germany, has stood the test of several months' application on blown film lines under the rough conditions of actual industrial practice. As the system works on the non-contact measuring principle, it is also able to measure films with tacky and/or sensitive surfaces without blemishing them. The capacitive sensor of the VenPad system measures single-layer and co-extruded films within a range of 6 to 500 μm with a resolution of 0.1 μm. The measured data and the thickness profile are displayed – via a field bus interface – on the VDU of the control unit of the blown film line. The manufacturer recommends installing the VenPad between the calibrating cage and the collapsing boards. VenPad is available in seven standard sizes for film bubble diameters of between 600 and 3,250 mm and/or for maximum layflat widths of 1,350 to 5,100 mm. Enquiries for special sizes are welcome.
The high precision and sturdiness of the VenPad system is achieved by means of a patented air shield in which the sensor is mounted. Air jets operating on the Venturi principle generate an active air cushion that ensures the maintenance of a settable attraction force between the film and the sensor ensuring a constant distance of 0.01 mm.
The film gauge measuring system moves round the film bubble automatically through a full 360 degrees on a rotating ring driven by a stepping motor coupled with an adjusting unit. For movements in a radial direction, the VenPad is virtually without load and can therefore be moved very easily, enabling the sensor to follow all radial movements of the film as the measuring system moves around the film bubble. Thus the system operates at a constant distance from the surface of the film – an important prerequisite for high measuring precision.
Even greater user benefit is afforded by an application-specific combination of the VenPad system with Octagon's SmartLip automatic thickness profile control system. This combination ensures the production of films of uniform thickness and hence improved downstream processability. It also achieves considerable savings in material consumption, this being as high as 20%, not least in the case of thin films.