Extrusion International 5-2024

56 Extrusion International 5/2024 MEASUREMENT TECHNOLOGY, BLOWN FILM Market Launch of the KNC-401 Online Thickness Sensor for Blown Film Lines How do you manage to fly over a wobbling bubble of film with a capacitive thickness sensor at a distance of a few tenths of a millimeter, measure its thickness with micrometer precision and leave no traces behind? KÜNDIG CONTROL SYSTEMS (KCS), a specialist division of Hch. HCH. KÜNDIG & CIE.AG (HKC), has been tackling this challenge for over 20 years and is about to launch its latest film thickness sensor, the KNC-401. H igh-precision, fast online thick - ness measurement on the cylindrical film bubble is the cor - nerstone of film production with optimum thickness tolerances. Ca- pacitive thickness measurement is currently still the favored mea- surement method for films based on polyolefins and those with low proportions of polyamide, EVOH or similar. This is due to the measure- ment accuracy, the suitability for measuring colored films and the fact that the measurement process does not require a permit. For micrometer-precise, largely non-contact, capacitive thickness measurement, the distance be - tween the sensor surface and the film bubble must only be a few tenths of a millimeter. To achieve this, an air cushion is often created in the area of the measuring elec - trode by means of fine holes and the thickness sensor is pressed into the film. Especially when measuring the thickness of sticky or surface- sensitive outer layers, this method leads to bubbles or marks on the film surface. In addition, with such materials, the bubble is poorly sta - bilized by a non-contact calibration cage and the thickness sensor often loses contact with the film surface, resulting in zero measurements at these affected positions. As a unique selling point, KCS of - fers a type of thickness gauge in which the sensor head follows the fluctuating film surface by means of a linear motor. This guarantees high-precision thickness measure - ment, minimizes the volume of compressed air needed to generate the air cushion and allows the con- trol of the air cushion temperature. This temperature control of the air cushion reduces haze marks on high-gloss films, for example, in the best possible way. KNC-401 Rotomat KT 3G (Source: Coopbox Group S.p.A., Ferrandina, Italy)