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VEGA Pressure Measurement Technology for the Production of Decor Paper

The Felix Schoeller Group develops, produces and markets specialty papers for photographic applications and digital printing systems, as well as for the furniture and wallpaper industries, among others. From humble beginnings as a pioneer, the company has become the world market leader in photographic and decorative papers. The group’s corporate philosophy, "Best Performing Papers Worldwide", implies the highest standards of quality and flexibility in paper production. And this applies to all plant components – including the deployed measurement and automation technology.
Decor papers are special papers for the surface finishing of wood-based materials for furniture, floors or wall panels. Since the optical quality of the end product is decisive here, very high demands are placed on them. In the production of decor paper, sensors are particularly vulnerable to wear and tear due to abrasive fillers such as titanium dioxide as well as to in-line, high-pressure cleaning of the pipelines. In the case of pressure transmitters, this often results in high failure rates and a service life of only a few weeks. Every sensor exchange also involves a costly pre-calibration of the instrument in the installation position in the workshop as well as frequent recalibration after installation. That’s why maintenance planners decided very early on to use pressure transmitters with ceramic measuring cells from VEGA.
Since then, VEGA’s precise, overload resistant pressure transmitters have been ensuring the integrity of all decisive production steps on PM 15 – from the dye mixing system to the headbox, and from the dryer section to the calendar.

Unique features of VEGA pressure transmitters with ceramic measuring cells

Calendar section with reel winding on PM 15.

Colour hue is one of the most important parameters in decor paper production. On PM15 it is adjusted via 4 dye metering stations integrated in the online colouring process. Due to inaccurate level measurement, it was previously only possible to dose the required amount of water for one dye batch at a time via a common flow measuring system. Since the installation of high-precision VEGABAR 82 pressure transmitters, water is added via level control through simple on/off valves at all 4 stations simultaneously.
Having exact information on the quantity remaining in the pigment batch container now makes it possible to prepare the next batch with a changed concentration and avoid discarding the residual liquid. This has resulted in a substantial savings of raw materials. In the past, the pressure transmitters with metallic diaphragms were often damaged when the process vessels were being cleaned. Sensors with ceramic measuring cells have a clear advantage here, since they are far more robust. All in all, the conversion to VEGABAR 82 sensors has resulted in the reduction of travel times, an increase in capacity, colour pigment savings and thus quality and process continuity.
At the headbox, a fibre suspension is sprayed onto the wire screen. The jet velocity of this suspension is decisive for the strength of the paper in both the lengthwise and crosswise direction. It should be identical to the wire speed, but via small intentional variations it can set the longitudinal/transverse ratio. The VEGABAR 82 flush-mounted pressure transmitters installed at the headbox on the operator side and drive side allow the dynamic pressure to be precisely measured. Possible pressure differences between the two sides are detected and can be compensated by the return flow of the cross-flow distributor.
This is where the special features of this pressure transmitter come into play: very high measurement accuracy (measuring error < 0.05% !), absolutely flush installation in the side wall of the headbox, and space-saving design in protection class IP 68 (25 bar).

Drive-side pressure measuring point on the drying cylinder.

To further increase the dry content, the paper is fed through the drying section with steam-heated drying cylinders. The resulting condensate must be removed from the drying cylinder by means of differential pressure. Previously, the pressure and differential pressure measuring systems were connected to the process via condensate-filled tubes. Excessive condensate deposits led repeatedly to incorrect measurements.
If the differential pressure is too high, the wall of the drying cylinder may be washed out, and if the differential pressure is too low, drying cylinders may "drown". The consequences are speed fluctuations, sudden speed drops, breakage of the paper web and even production downtime. Since the installation of VEGABAR 82 sensors, only the pressure on the inlet and outlet side of the dryer groups is measured. The high accuracy of the transmitters enables calculation of the differential pressure in the mbar range (with measuring ranges up to 15 bar) and thus continuous, uninterrupted production.


Pressure transmitter VEGABAR 82.

The maintenance team were impressed by the unique features of VEGA pressure transmitters with ceramic measuring cell: simple installation and setup, self-explanatory operation and high resistance to abrasion. They quickly noticed that the front-flush mounting of the measuring cell protects against deposits and allows for easy cleaning, as the sensors can remain in the pipeline during in-line cleaning. The positive experiences they had with the sensors in the important production stages finally resulted in VEGA instruments being included in the device reference list at the Osnabrück site.

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