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Abstract

A method and apparatus for continuously treating a strip of hot dip-galvanized steel. The method comprises the steps of rapidly reheating the strip to a predetermined temperature between 460.degree. C. and 600.degree. C., with a heating flux greater than 180 kWatts per meter squared based for each face of the strip; maintaining the strip at a substantially constant temperature for a predetermined period of time lasting between 10 and 30 seconds; and subsequently cooling the strip rapidly to a temperature below 420.degree. C., using a cooling flux of a magnitude greater than 100 kWatts per meter squared for each face of the strip. The step of rapidly reheating is performed following a drying operation conducted on the strip as it exits from a zinc bath. The apparatus comprises various elements for performing the method, as well as a vessel containing the zinc bath, redirecting rolls which define an upward and substantially vertical trajectory for the strip and a drying mechanism disposed along the trajectory downstream of the vessel's exit. Preferably, the rapidly heating of the strip is accomplished using an induction furnace operating at a frequency between 100 and 500 kHz, and the rapid cooling is provided by nozzles which, in turn, deliver a mist or fine spray of water and air.

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First Claim