wenglor received a customer inquiry concerning the continuous thickness and layer thickness measurement of a coated film web. In the system, a carrier film – made of aluminum or fabric composite, depending on the product – is coated with bitumen. The overall thickness of the web is typically around 1 mm, whereby tolerances in the tenth of a millimeter range must be reliably detected. At the same time, the membrane extends over a width of around 1.2 meters, so that not only punctual but also area-wide statements on the layer thickness are required.
Directly after the rolling process, the film forms the so-called “0-line”. Bitumen is applied in the subsequent process, resulting in total thicknesses of between around 0.8 and 2 mm, depending on the product. The aim of the measurement is to monitor the applied layer across the entire width of the web and to detect deviations at an early stage. Different label materials, varying layer thicknesses and the process dynamics place high demands on the sensors.
A proven solution is to use two 2D/3D profile sensors above and below the web. Both sensors synchronously record the respective surface of the film. Software is used to calibrate the two profiles to each other and calculate the material thickness from the individual measurements.
A comparable principle is already being used successfully in the thickness measurement of polystyrene insulation boards. There too, the profile sensors enable precise inline measurement across large widths – even with vibrations or height offset. Transferred to the bitumen-coated foil, this means that The layer thickness can be continuously evaluated across the entire width of 1.2 meters, reliably detecting local deviations or edge problems.
Alternatively, the thickness measurement can be realized via several defined measuring points. In this case, nine measuring positions are distributed across the width of the web, at each of which two opposing laser distance sensors from the P3 series are used. A total of 18 sensors are used in this way.
Specifically, the combination of P3PC001 (red light) and P3PC041 (blue light), which are connected to each other via the patented ZC4V001 T-splitter, is suitable. As soon as two sensors are coupled in this way, they automatically switch to “thickness measurement” mode. The thickness is calculated directly in the sensor and can be output without a separate analysis module.
The P3 sensors work according to the triangulation principle and deliver highly precise, temperature-stable and material-independent measurement results thanks to the integrated TripleA technology. The combination of red and blue lasers offers additional safety, as different wavelength ranges do not influence each other – even on challenging surfaces such as bitumen.
A central advantage of this solution is the elimination of a separate analysis module. The patented T-splitter makes initial start-up particularly easy and reduces system costs at the same time. Measured values and sensor status can be conveniently monitored via tablet or smartphone using the integrated Bluetooth interface – ideal for continuous process control.
The multi-point measurement also allows local deviations in the layer thickness to be specifically recorded without the complexity of a full-surface profile system.
Two powerful solutions are available for measuring the thickness of bitumen-coated film webs over large widths: full-surface measurement with 2D/3D profile sensors or flexible multi-point thickness measurement with laser distance sensors from the P3 series. Which variant is better depends on the desired level of detail, the system design and the budget. In both cases, the quality of the coating can be reliably monitored and the process stabilized in the long term.
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