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Products and solutions, 2004-03-03, 01:00 AM

ThyssenKrupp Stahl: New inline thin-film coating line goes into production

ThyssenKrupp Stahl AG has become the world`s first steel manufacturer to combine electrolytic galvanizing and organic steel new inline thin-film coating line has a maximum speed of 120 m per minute. This reduces the production time for the complete coating of a coil to less than one hour compared to the several days needed for conventional production on separate lines. Around 15 million euros were invested in the line.

The inline thin-film coating line produces steel strip in widths of 950 to 1,900 millimeters and thicknesses of 0.5 to 1.75 millimeters. In the strip coating section, a thin film is applied either on one or both sides of the strip. Thin-film coated material is used by the automotive industry in body construction. The coating ensures long-lasting rust protection, even in areas not protected by the normal painting process at the plant, e.g. in cavities or panel overlaps. This means that auto manufacturers have to take fewer secondary corrosion protection measures. The coating consists of an epoxy resin lacquer which provides the rust protection and zinc dust which ensures that the material can still be welded. Depending on customer requirements, this coating is 2.5 to 4.5 micrometers thick. A new generation of thin films with thicknesses of 4 to 8 micrometers is currently being developed for even higher corrosion resistance. This product can also be made on the line at Beeckerwerth.

New to the steel industry: NIR technology

In extending EBA 2 it was important to design the coating section to ensure that the electrolytic coating process was not slowed down. It also had to fit into the existing shop space due to rail tracks directly behind the building which cannot be moved. The ThyssenKrupp Stahl AG plant builders solved these two problems by choosing an innovative dryer technology: an NIR dryer in the coating section ensures that the lacquer hardens far more rapidly than in the convection ovens previously used for the organic coating of steel strip. The dimensions of the dryer are correspondingly shorter - at around twelve meters in length it takes up only just over a quarter of the space needed by conventional convection ovens. NIR stands for Near Infrared, which is electromagnetic radiation with a wavelength slightly higher than that of visible light. The radiation heats the coated steel strip to approx. 270 degrees Celsius within a few seconds. ThyssenKrupp Stahl is the first steel manufacturer to implement this technology on a commercial scale.

Chromium-free pre-treatment

It was mainly due to the compact dimensions of the NIR dryer that it was possible to fit the entire coating section vertically in a multistory steel structure 28 meters high covering a floor area of only 25 meters by 25 meters. The height of the shop was increased from 21 meters to 43 meters in the thin-film coating area. In addition to the NIR dryer, the coating section consists of a so-called chemcoater, where the galvanized strip receives a chromium-free, water-based pre-treatment. It is then dried in a convection oven and runs through a cooling section. A paint coater applies the thin-film coating. Like the chemcoater, the paint coater consists essentially of two pairs of counter-rotating rolls which continuously apply the coating to the steel strip as it moves through them. The thickness of the coating is automatically measured both after the chemcoater and the paint coater. The solvent vapors which escape during drying are extracted from the NIR dryer and burned in an environmentally sound way, producing carbon dioxide and water. The last element in the coating section is a further cooling zone before a coiler rolls the steel strip into a coil.

Construction during ongoing production

The ThyssenKrupp Stahl AG plant builders and the partner companies involved erected most of the coating section while EBA 2 continued to run normally. For example, 20 meter deep holes had to be drilled in the shop without interrupting production to strengthen the foundations. A further logistical challenge was to raise the height of the shop roof without exposing EBA 2 to the damaging effects of the weather. The first step was to fully assemble the elevated roof, and only once this was complete was the existing roof removed from the inside. The steel structure which weighed around 800 metric tons was also erected and the individual parts of the line assembled and installed while production on EBA 2 continued as normal. The line was only stopped for around two weeks in total in order to integrate the individual units of the thin-film coating section into the production line.

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ThyssenKrupp Steel
Dietmar Stamm
Tel.: +49 203 / 52 - 2 62 67
Fax: +49 203 / 52 - 2 57 07

Bernd Overmaat
Tel.: +49 203 / 52 - 4 51 85
Fax: +49 203 / 52 - 2 57 07

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