Kronoswiss has bought a fully automated production line with a short-cycle press – and some special features – from Wemhöner.

Menznau, in the canton of Lucerne, is the headquarters of the Swiss Krono Group. Here it manufactures particleboard, HDF, MDF, postforming elements, laminated furniture panels and laminate flooring and sells them worldwide under the Kronoswiss brand. Products include 450,000m3 of particleboard, 250,000m3 of MDF/HDF and 30 million m2 of laminate flooring per year.

The Swiss Kronospan plant consists of two parts separated by a main road. On one side of the road, raw wood is processed. It is then transported through two large pipes to be made into MDF, HDF or particleboard on the other side.

In addition to the production lines for wood based panels, there are seven decor paper impregnation lines, printing and lacquering lines and the distribution centre.

To be ahead in worldwide competition, Kronospan needs production technologies which deliver consistently high quality at high availability, economically. Therefore, the managers in Menznau are always seeking the ultimate for their production.

Their latest search ended at Wemhöner Surface Technologies GmbH & Co KG of Herford, Germany, manufacturer of short-cycle presses. It was the overall concept of the line and its specific features which secured the order to produce flooring and furniture panels with synchronous pores and in trendy colours, says Wemhöner.

After approximately a year of decision making for Kronospan, contracts were signed on January 9th, 2012.

Two lines were ordered: One for Menznau and one for the company’s factory in Heiligengrabe, both in Germany, but with different configurations.

Kronospan said it experienced "very good teamwork" and professional implementation of its requirements. The control system was developed jointly with the client, based on a Siemens S7 adapted by a Wemhöner- Kronospan team to meet the site’s needs. This constructive dialogue, as well as the cooperation by both sides, resulted in the production of the first board slightly less than a year after the contract was awarded – and that first board left the plant in A1 quality after only three reject boards.

In addition to the technical demands, the line also had to meet architectural requirements as the line’s components were distributed over two floors requiring connection of the main film storage, intermediate film storage and film lay-up stations, as well as the demanding execution of the magazines for the paper lay-up stations. Kronospan prepared the hall and laid the plant’s foundations.

Wemhöner created the overall design of the plant. Due to the restricted space at Menznau, the line could not have a great width, but an unconventional layout finally arose, particularly for intermediate film storage.

For this magazine, Wemhöner designed several buffer magazines directly connected to the lay-up stations. In the specifications, Kronospan demanded a highly flexible lay-up station, which in turn had to be fed from a highly flexible film storage magazine. Because primarily smaller lot sizes and specialities were to be made on the new line, this meant fast material changes at the stations upstream of the short-cycle press. So feeding from the main film storage magazine was not appropriate.

For this specific use the intermediate paper magazine was designed to feed the three layup stations without loss of time. One of the layup stations is equipped with three daylights, the two others have two. This ensures that the film composition, top and bottom, can be programmed quickly and easily and changes easily performed, says Wemhöner. The lay-up accuracy of the decor papers for embossed-in-register printing is +/-1.0mm. The correct position of the decorative films is checked and aligned with a special camera and alignment system before infeed into the short cycle press. The tolerances (in length and width) that will arise through the printing and impregnation of decorative films are also recorded by this system and automatically transmitted to the press.

The raw boards are fed into the line from their magazine, with six infeed and two residual board positions, via gantries with vacuum suction cups, following a brush cleaning station.

The lengths of the work pieces can be 2.5 to 3.25m, maximum width is 2,070mm, minimum thickness 4mm. Maximum thickness varies according to the substrate:

Particleboard 50mm, MDF 40mm and HDF 20mm. The special lay-up concept already mentioned makes it possible for the raw plates to be transferred next to each station so even products with different decors can be produced next to each other. Lot sizes of five boards were intended.

Wemhöner says the short-cycle press KT F 1E is one of its core competencies. The ’12 cylinder’ builds up a specific pressing pressure of 700N/cm2, with which deep structures are possible in the embossed-in-register mode. But that was only one side of the coin with Kronospan. Equally important to them was the homogeneous pressure distribution. It has a decisive influence on the result if solid colour papers are pressed in intensive colours – with uneven pressure build-up, slightly milkylooking areas would arise at the surfaces.

Wemhöner says this is not an issue with the uniform pressure of its short-cycle press. However, such surface defects may also arise if the press plates are not exactly straight and this happens if there are temperature differences within the press plates. These temperature differences lead to a curvature – even if only in the millimetre range. This can be seen even with a heating plate size of 3,450 x 2,200mm, as in this case. Wemhöner countered this problem with a heating technology that ensures the temperature is correct from the first plate. The upper and lower heating plate can be heated with two separate control circuits which provide for constant and uniform temperatures on the one hand with the main heating at the caul plate and, on the other hand, via the counterheating in the heating plate.

The intelligent control technology ensures that the temperature losses arising during transfer of heat to the substrate are compensated within seconds and we are talking about up to 240 press cycles per hour in standard mode, or 180 in the synchronous mode. To reach these values, even the pressure-less time must be short; if it is too long, optical defects in the surface can occur. So speed is also a topic here. Therefore, the drives of press infeed and outfeed play a crucial role. Here, and throughout the whole line where movement is generated, Wemhöner says it used highly dynamic servo drives.

Of course, the quick change of lay-up stations cannot be transferred to the same extent into exchanging caul plates; this requires a greater effort, but 10 minutes for a caul plate change is still quite impressive. The procedure is relatively simple as the press plate magazine is placed right next to the press and the change is performed automatically up to the last manual step at the heating plate itself. Forty daylights for the caul plates illustrates the variety of options that had to be mastered at Kronospan.

After the press outfeed, the narrow edges of the boards are trimmed by an edge trimming unit while the line is stopped for a short time; the longitudinal edges are processed in a throughfeed operation. After cleaning with rotating counter-moving brushes above and below, the workpieces are raised through a gantry which is timed to allow visual inspection.

Then there are two possibilities: Direct discharge to the six stacking positions at the end of the production line; or the workpieces run through the two board cooling devices, each with 44 compartments. Moreover, the boards can be discharged to an intensive control if a more detailed surface inspection is necessary; a board turning device allows inspection of top and bottom surfaces. The operator can choose the assignment of the stacking positions to A or B quality, or protection board, and this can also be controlled very flexibly, says the supplier. The first project between Kronospan Menznau and Wemhöner is a great success, says Wemhöner. "With this new line concept, the Swiss have advanced into a new dimension in terms of flexible manufacturing, with the highest quality standards for the final product."