Armco Inc.

Armco Steel Corporation

Fred Byrd

Thomas A Compton

James A Fisher

Marvin B Pierson

Frank C Dunbar

Improved means and method are provided for the guidance of metallic strip in a horizontal continuous furnace having hearth rolls and wherein the strip temperature and furnace atmosphere are such as to promote the transfer of metal, oxides, dirt and the like from the metallic strip to some at least of the hearth rolls. At least one lifting hearth roll is provided in an elevated position wherein it lifts the metallic strip from those critical hearth rolls subject to contamination transfer. The elevated position of the lifting roll and its diameter are so chosen to assure a wrap-around contact between the metallic strip and the lifting roll in its elevated position. In practice the metallic strip is fed through the furnace and continuous operation is begun. The lifting roll, in its elevated position, maintains the metallic strip out of contact with the critical hearth rolls.

Lift-off means and method for use with a horizontal continuous hearth

In a line for coating a ferrous base metal strip with a molten coating metal, the line being of the type having a preparation furnace for the strip comprising a direct fired furnace, a controlled atmosphere heating furnace, one or more cooling chambers and a snout leading beneath the surface of the molten coating metal bath, all in sealed relationship to each other, the improvement comprising a method and means for maintaining a non-oxidizing atmosphere at positive pressure within the entire preparation furnace during line stops. To this end, a retractable, refractory lined door means is provided in the conduit between the direct fired furnace and its exhaust fan to seal off the direct fired furnace from its exhaust fan and an air dilution opening in that conduit. Additionally, means are provided to add excess nitrogen flow to the preparation furnace to maintain a positive pressure therein. Thus, during a line stop, the refractory lined door will be shifted from its normal retracted position to its position sealing off the direct fired furnace and the means for adding excess nitrogen will be actuated to maintain a positive pressure within the entire strip preparation furnace of the metallic coating line.

Means for maintaining a non-oxidizing atmosphere at positive pressure

In a line for coating a ferrous base metal strip with a molten coating metal, the line being of the type having a preparation furnace for the strip comprising a direct fired furnace, a controlled atmosphere heating furnace, one or more cooling chambers and a snout leading beneath the surface of the molten coating metal bath, all in sealed relationship to each other, the improvement comprising a method and means for maintaining a non-oxidizing atmosphere at positive pressure within the entire preparation furnace during line stop. To this end, a retractable, refractory lined door means is provided in the conduit between the direct fired furnace and its exhaust fan to seal off the direct fired furnace from its exhaust fan and an air dilution opening in that conduit. Additionally, means are provided to add excess nitrogen flow to the preparation furnace to maintain a positive pressure therein. Thus, during a line stop, the refractory lined door will be shifted from its normal retracted position to its position sealing off the direct fired furnace and the means for adding excess nitrogen will be actuated to maintain a positive pressure within the entire strip preparation furnace of the metallic coating line.

Method for maintaining a non-oxidizing atmosphere at positive pressure

A method of preparing carbon steel strip and sheet for hot dip metallic coating in a Selas-type direct-fired furnace, wherein the atmosphere in the furnace is controlled to contain from about 3% oxygen to about 2% excess combustibles by volume, thereby forming a thin iron oxide film on the carbon steel surfaces. The strip and sheet is then heated in a subsequent furnace containing at least 5% hydrogen by volume at a temperature sufficient to reduce the oxide film, viz., at least about 675.degree.C. The direct-fired furnace is preferably operated at stoichiometrically equivalent fuel:air ratios.

Growing community of inventors

Lebanon, OH, United States of America

Fred Byrd