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Ghent (USA), March 09, 2021

Heat-to-coat: New line concept for pickling and galvanizing of strip

Nucor Steel Gallatin's line also produces galvannealed strip up to 6.35 millimeters thickness and 1,854 millimeters width

With a capacity of 500,000 t/year, an output of up to 180 t/hour and a vast range of galvanized strip (up to 6.35 millimeters in thickness and 1,854 millimeters in width), the new “heat-to-coat” line of Nucor Steel Gallatin in Ghent, Kentucky (USA) sets new standards in the field of hot strip galvanizing.

To Nucor Steel Gallatin, domiciled in Ghent, Kentucky, U.S.A., systems supplier SMS group delivered a new “heat-to-coat” pickling and galvanizing line, including engineering, process technology, furnace equipment, pickling and galvanizing technology as well as electrical and automation systems, all from one source. The line was put on stream in September 2019 and, since then, has continually increased  capacity. Meanwhile, the line produces even strips with socalled galvannealed surfaces. In a “heat-to-coat” line this is a worldwide unique achievement. Right behind the air knives, the liquid zinc is inductively reheated and allows a zinc-iron alloy layer to develop. Even strips of maximum possible dimensions, i.e. 6.35 millimeters thickness and 1,854 millimeters width, can be produced with galvannealed surfaces. This is another one of the line’s unique features.

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The latest generation of X-Pro® laser welding machine safely and quickly welds together the individual steel strips to produce endless strip. An efficient solid-state laser is used for this purpose.
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The turbulence technology in the shallow tanks achieves a maximum pickling effect with a minimum of acid and energy.
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FOEN® air knives continuously ensure a highly precise layer thickness. As soon as the galvanizing process is completed, another induction unit can be run into the line. This enables Nucor Gallatin to produce so-called galvannealed surfaces, which is a world first in a “heat-to-coat” line.
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In the control station, all processes and results are shown in a clear overview and consistently logged for certified quality grades. All electrical and automation systems were supplied by SMS group, just as the complete plant digitalization technology including X-Pact® automation and pertaining process models, the material tracking system with quality documentation, the advanced X-Pact® MES 4.0 (Manufacturing Execution System) plus the digital sensor system for the whole plant.

The “heat-to-coat” process based on SMS group's patented technology excels with its high profitability, as all processes take place in a single facility. The process permits the production of galvanized steel strip with durable corrosion protection, an appealing visual appearance, as well as an increased mechanical load-capacity while still maintaining low production and investment costs. Due to the integrated inductive galvannealing furnace the line is also able to produce galvannealed strips.

There is a broad area of applications for galvanized hot strip, especially in construction, transportation and automotive industry. Furthermore, it is possible to substitute galvanized cold strip with hot strip.

The “U-shape” design allows a quick and easy bypass of the coating section in order to use the line as a continuous pickling line and produce just pickled and oiled material. Since entry and exit are located side by side also fewer staff is required.

Furthermore, the “heat-to-coat” process stands for an environmentally-friendly production of galvanized material since the whole process takes place in one line and uses efficient technologies. Compared to the conventional process some process steps are even omitted. Another advantage is the inductive furnace which operates with electrical energy and therefore emission free. Furthermore, a special fume exhaust system will be integrated which ensures low emission rates for the whole process.

In my view, SMS group did a great job. Ben Williams, Electrical Engineer and Project Manager, Nucor Steel Gallatin