Method for continuously quenching electrolytic tin-plated steel strip while preventing quench stains

In a method for continuously quenching a moving, continuously electrolytic tin-plated steel strip while preventing quench stains, which comprises spraying streams of quenching liquid uniformly onto both surfaces of a continuously electrolytic tin-plated steel strip, having a tin-plated layer fused by heating in a heating furnace, and moving substantially vertically downward from said heating furnace, said streams of quenching liquid being sprayed on substantially the same horizontal level over the entire width of said strip, in the air below said heating furnace and above the surface of a quenching liquid in a quenching tank located below said heating furnace, thereby quenching said strip to solidify said fused tin-plated layer;

• and then, immediately, directing said strip further substantially vertically downward and passing said strip through the quenching liquid in said quenching tank, thereby further quenching said strip;
• the improvement which comprises:
• spraying the streams of quenching liquid uniformly onto both surfaces of said strip from two spray nozzles under the following conditions:
• 1. Spraying angle of the quenching liquid from said spray nozzles:
• from 45.degree. to 75.degree. downward against said strip,
• 2. Pressure of the quenching liquid sprayed from said spray nozzles:
• from 0.05 kg/cm.sup.2 to 4.0 kg/cm.sup.2, and
• 3. Position where the quenching liquid sprayed from said spray nozzles first comes in contact with said strip:
• in the air below said heating furnace and at least 25 mm above the surface of quenching liquid in said quenching tank;
• said spray nozzles being of double-tube construction based on the concentric combination of an inner tube and an outer tube, said spray nozzles having a longitudinal slit of a length substantially equal to the width of said strip through which the streams of quenching liquid are sprayed onto said strip, and said spray nozzles being located one opposite the other symmetrically on both sides of said strip moving substantially vertically downward, in parallel therewith and on substantially the same horizontal level, in the air below said heating furnace and above the surface of quenching liquid in said quenching tank.