Original Date: 08/26/1996
Revision Date: 01/18/2007
Information : Continuous Galvanized Line
WSC’s Sheet Mill produces hot-dipped, galvanized sheet steel on three main continuous process lines. These lines run at speeds up to 400 feet per minute and produce more than 600,000 tons of galvanized steel annually. The sheet lines produce galvanized steel in thickness ranges from 0.010-inch to 0.168-inch and in widths up to 48 inches. WSC offers galvanized sheet steel in commercial, lock forming, drawing, structural qualities, and all types of surface finishes.
The process of manufacturing galvanized sheet steel on #5 Continuous Galvanized Line begins with cold rolled, sheet steel for thicknesses less than 0.050-inch. Hot rolled steel is used for thicker material requirements on #3 Continuous Galvanized Line. Two steel coils are loaded at the start of the continuous process line with the first coil fed into a vertical accumulator. This accumulator keeps the continuous line running while a changeover is made from reel #1 to reel #2. The steel is run down the line to the various machines in the process line. When coil #1 is expended, the second coil is spliced onto the tail of the first by a continuous spot weld as the line continues to move. This is possible because of the additional length of steel in the accumulator. After passing through the accumulator, the steel is cleaned in a sodium hydroxide (NaOH) soap bath to remove oils and iron fines from the prior rolling processes. Following this operation, the steel is annealed in a large furnace, dipped in a bath of 99.4% zinc, and transversed through a specially-designed air knife to remove excess zinc from the sheet steel. Exiting the air knife, the steel may be reheated in a second furnace for galvanneal, then quenched and dried. Finally, an automated x-ray machine measures the zinc coating of the galvanized sheet steel, and the steel is cut and rewound.
To enhance the process capability, WSC changed the NaOH bath from a manual batch process to one that automatically adds soap and water, based on measured conductivity readings of the cleaning bath. As a result, the company disposes of 24,000 fewer pounds of NaOH per year for an annual savings of $80 thousand. The specially- designed air knife saves an additional $280 thousand per year by reducing spooled-edge rejects by 83%. Finally, by upgrading the coating weight gauge, WSC eliminated the test coupon step of each galvanized sheet roll and reduced overcoating from 16% to less than 10%.
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