The current annual capacity of the Severstal Columbus 6-stand hot strip mill is 1.5 million tons, with a design rating that is well in excess of 3.0 million tons.
The mill is designed to roll product 36 to 74 inches wide, 0.065 to 0.500 inch thick, with a PIW of 1,204 and a maximum coil weight of 44 tons. With a coil ID of 30 inches, coil OD can vary between 45.7 and 82.7 inches.
The principal components of the mill are a pendulum shear; descaler; the 6-stand, 4-high rolling mill; a laminar flow cooling runout table with edge masking; and coil handling units.
Overall mill length -- from the last roll in the tunnel furnace to the coiler -- is approximately 427 feet. Mill length from stand F1 to F6 is 107 feet with a 243-foot-long runout/cooling table. An entry side guide is located immediately after exit of the tunnel furnace. On the exit side of the guides an emergency pendulum-type crop shear can cut a slab section up to 2.75 inches (70 mm) thick at temperatures above 760°F. Between the crop shear and the first mill stand (F1) are hydraulic entry guides and a scalebreaker that consists of two top and two bottom header and spray units that operate at a pressure of 5,500 psi.
The mill is equipped with the following features:
- Hydraulic gauge control on all stands.
- Continuous variable crown and positive work roll bending on all stands.
- Hydraulic loopers between each stand through F5, with a differential tension looper between F5 and F6.
- Three inter-stand descaling headers at the first three stands.
- Inter-stand cooling.
- Work roll cooling to retard roll breakdown and to maintain a superior strip service for a longer period of time.
- Roll lubrication on stands F2, F3 and F4. Lubricant is injected into the roll bite to further enhance strip surface.
- Automatic roll changing facilities that permit all six stands to be changed within 10 minutes.
The run-out table consisting of 276 rolls of which the first 25 rolls are internally water cooled has a maximum run-out speed of 2950 fpm. Laminar cooling is applied to the strip through 10 banks of laminar flow nozzles to produce the desired steel structure for critical grades. Strip edge masking is provided to avoid overcooling the edges.
Exiting the cooling table, strip enters a downcoiler equipped with hydraulic sideguides and gap control on the pinch roll. Coils are then transferred to a stripper car, and a delivery line that includes a walking beam system, an in-line coil inspection/sampling station, weigh scale, an automatic bander and coil identification unit.
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