Ghent, Kentucky, July 13, 2018

Bright annealed steel strip for the U.S. market

SMS group has supplied a 20-high cold rolling mill and a stainless steel bright-annealing line to North American Stainless (NAS). The facilities have an annual capacity of 95,000 tons each of cold rolled and bright-annealed steel strip. So, NAS, a subsidiary of the Spanish Acerinox Group, has the most powerful plants in the U.S.A. producing such material.

20-high cold rolling mill

The 20-high cold rolling mill is a MonoBlock mill, type MB 22B-54“, and processes hot strip thicknesses of up to 6.2 millimeters. The compact and robust plant comes with high mill stand rigidity. Featuring a maximum rolling speed of 800 meters per minute and a maximum rolling force of 8,000 kilonewtons, it can achieve thickness reductions of up to 90 percent. Auxiliary and ancillary equipment is also included in the scope of supplies. A regenerative SUPAFINE® filter system makes sure the rolling oil is ecofriendly purified and cooled. Ecological plant operation is further supported by a fume exhaust system meeting most stringent environmental provisions of the local authorities. To reduce non-productive times, an uncoiling station, including flattener and crop shear, is integrated in addition to two reversing reels.

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The hydraulic valve stands arranged on the mill stand platform are easily accessible and greatly simplify maintenance work.
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The mill stand is equipped with hydraulic roll gap control and crown adjustment for backup shafts B/C and F/G as well as with inner intermediate roll shifting.
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A four-high skin-pass mill stand is integrated in the exit section of the facilities to improve surface and flatness as well as the metallurgical material properties. Strip flatness is then perfected by a downstream tension leveler. Thereafter, both strip edges may be straightened by a side trimmer.
Bright-annealing line

In the bright-annealing line the strip first runs through the cleaning section. This step is followed by recrystallization annealing in an oxygen-free inert gas atmosphere with high hydrogen content, in an all-electric vertical furnace from Drever International, a company of SMS group. The annealing process is performed at a temperature of up to 1,250 degrees Celsius in an inert gas atmosphere (up to 90 percent hydrogen) under overpressure to thus generate a perfect glossy surface. The exit section of the facility is equipped with a four-high skin-pass stand and a tension leveler for strip post-treatment. A side trimmer serves for strip edge straightening and cuts the strip to the desired width.

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In a two-stage cleaning section, the cold rolled strip is efficiently freed from rolling oil and other dirt particles.
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In the entry and exit sections, maximum strip speed reaches 75 meters per minute, whereas in the process section the material goes through at maximum 50 meters per minute.
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The technological highlight of the bright-annealing line is the all-electric vertical furnace from Drever International. Due to its high efficiency, the energy consumption of about 220 kilowatt hours per ton is 60 percent lower than that of a conventional line concept with muffle furnace.