Modernisation instead of a new production line

The trend for eco-friendly products that are non-hazardous to health can cause manufacturers to use materials with difficult production-related properties. As a result precisely tailored production facilities are required. An example is textured wallpaper. Conventional textured wallpapers use PVC colours and foams for printing and texturing the surface. These are easy to process and can be exposed to air for periods of time without degradation. Their eco-friendly equivalents use water-based colour systems which are PVC-free and low in solvents. They not only dry quickly when exposed to air, but also result in the printable width being smaller than with conventional colour systems because the wallpaper web absorbs water, curls, and expands slightly.

In spite of these restrictions, Ralf Taubert, Plant Manager at Hohenberger, sees the future of his company and the industry closely linked to PVC-free textured wallpapers. He says: "So far, water-based mineral foam wallpapers are only purchased by consumers who are particularly quality and health-conscious because they are considerably more expensive than conventional vinyl wall-papers. However, the continuing trend for materials which are healthy for living will shake up the market. Time is clearly on our side." Some markets are already taking legislative steps; for example, since 2012 emission labelling has been required in France.

In these circumstances the management team at Hohenberger decided on replacing an existing production line with a new line for the production of mineral foam wallpaper suited to water-based colour systems. Ralf Taubert explains: "The purchase of a completely new plant offered by printing machine manufacturers was out of the question for us due to the high investment and the financial risk involved. Almost more important is the aspect that it would have been difficult to tailor a plant bought "off-the-peg' to our individual requirements at a reasonable cost."

Therefore, the management decided to combine tried and tested modules of the previous plant with bought-in used machinery such as print units, turret winders and new mechanical components. To that Hohenberger added the latest drive and control technology to provide a tailor-made system.

Complete automation system including engineering support

Hohenberger chose Lenze as their technology partner for the automation of the plant. Taubert points out: "Other companies that we know recommended Lenze to us. Lenze also have successfully managed similar projects. It was also decisive that Lenze were able to provide us with the complete automation system including engineering support from one single source."

Lenze Engineers carried out the planning and implementation of the automation system to Hohenberger's specifications - from the selection and dimensioning of the drives, the programming of the control and visualisation to the construction of the control cabinet. After a project time of only 4 months, the plant was commissioned within only 14 man-days work due to Lenze's optimal project planning and complete responsibility for the automation system.

At the heart of the plant are three silk screen printing units and an embossing station. The web is unwound from a turret winder developed by Hohenberger. After a print unit has detected a reference mark and the web has passed through an accumulator for incoming material, the wallpaper reaches the first of the three silk screen printing units. A web edge guide control and a dryer are assigned to every printing unit. After passing through the third printing unit, the material is pre-dried in an oven and then foamed which adds thickness to the web. The material then reaches an embossing station which serves to further texture the wallpaper. After the seaming of the edges, the finished wallpaper passes through an accumulator for outgoing material before it is wound onto rolls.

Two HMIs of the Lenze EL100 series and a p500 panel PLC are used for plant visualisation. Ralf Taubert adds: "That way, we were able to replace the previ-ous pushbuttons by touchscreen control. This is the optimum solution, and in addition, we could design the screen layout precisely according to our specifications in a way that is absolutely easy to use. Among other benefits, this gives us flexibility with our operator allocation."

The HMIs are linked to a Lenze 3200 C motion controller via Ethernet TCP/IP. Thirteen Lenze servo motors with resolvers in combination Lenze 9400 servo drives provide the required dynamics and precision for the printing process. They are responsible for the reliable & smooth transport of the paper web through the machine and driving the print units (tension, web guide, chill roll) and the embossing station. The register sensors link to the integrated digital I/Os of the 9400 sevo drives giving very fast response for the web edge guide control.

Dynamics and accuracy

Due to the high number of axes and the required dynamics and accuracy, the Lenze engineers decided on EtherCAT as motion bus. In addition, four inverters of the Inverter Drives 8400 series are connected to the control system via Ethernet. They supply the motors for the central inlet and exhaust fans of the dryers as well as the motors of the seaming system and the accumulator for outgoing material. At field level, the modules of the Lenze I/O System 1000 gather the sensor signals and route them to the control system via EtherCAT.

Ralf Taubert summarises: "The consistency achieved by the Lenze servo technology, the high precision and the excellent synchronous running properties working at a maximum print width of 640mm have enabled us to eliminate the problems associated with water-based colours."

To compensate for the reduced print width, the output of the machine had to be increased considerably. This target was achieved by means of several measures. Due to the higher dynamics and response of the drive system, the line speed was increased from 50 m/min to 70 m/min. Accurate "electrical shaft' gearlocking meant that individual colours are registered rapidly after a product change and process fluctuations are compensated for more quickly leading to less wastage. The new line has a total length of only 40m, considerably shorter than conventional silk screen printing lines, so that there is less paper in the machine and less waste. Ralf Taubert observes: "That way, we were able to reduce the scrap rate by 80 per cent." The production costs are also reduced by the fact that the ventilation system is now demand-based with variable speed drives. This is eco-friendly and cost-effective.

Ralf Taubert concludes: "In close co-operation with Lenze as our partner in automation, we were able to modernise our production line. Our new plant now compensates for the disadvantages of a water-based colour system and provides a higher output. At the same time it reduces waste considerably and cuts the energy consumption to a minimum. Hence, the economical production of quantities from 300 rolls up to large batches can be achieved. We are very satisfied with the result and we are already planning the next project together with Lenze."

Please visit www.lenze.com for further information about automation technology from Lenze.