The continuous hot-dip galvanizing and galvannealing line at Severstal Columbus has an annual design capacity of 450,000 tons and a rated capacity of 60 tons/hour. It is designed to coat cold rolled strip, 0.014–0.060 inch thick, 36–72 inches wide, for exposed automotive and appliance applications. Product coating levels are: galvanized, G20 to G130; galvanneal, A20 to A65; as well as chromate surface treatment, cr 6 and cr 3. Delivery coil weights range from 11 to 44 tons with a coil OD of 39.4–86.6 inches and an ID of 20–24 inches.
The line, with an overall length of 950 feet, contains 3,500 feet in process capacity, divided into five sections: entry, furnace, coating, process and delivery. The entry section includes an electrolytic cleaning section, pairs of payoff reels, thickness gauges, flatteners and cross-cut shears, and a lap seam welder. There are also head-end and tail-end scrap removal systems.
The furnace section begins with scrubbers and an air drying system, as well as a vertical accumulator with a storage capacity of 984 feet. The radiant 120-tube heating furnace includes a hot bridle for optimum tension control through the zinc pot.
The coating section includes a 245-ton-capacity zinc pot that operates at 460°C; air/nitrogen gas knives for coating control. If galvanealing is required, an induction furnace is available on the line, along with an up-leg and down-leg cooling tower and a water quench tank.
If necessary, coil can move to the temper mill and a tension leveler for shape and surface enhancements. The process section also includes surface treatment units for phosphatizing and chromatizing. A tail-end vertical accumulator with a storage capacity of 1,377 feet provides 2.75 minutes of operation. The accumulator is followed by an inspection station for vertical and horizontal surface examination, a noncontact continuous inkjet printer for strip identification, and an electrostatic oiler.
The delivery section includes an x-ray thickness gauge, cross-cut shear, edge trimmer, a scrap removal system, and an electronic edge guide system that provides uniform winding on a delivery reel.
The operation of the line is supported by a laboratory equipped to monitor coating weights, zinc adherence, strip hardness, surface roughness and zinc spelter composition.
The galvanizing line has its own warehouse and shipping facilities that include two in-line stretch wrap machines for packaging both galvanized and temper mill products. With a storage capacity of 30,000 tons, the warehouse is served by five cranes and three 65,000-pound tractors.
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