method for the manufacture of black plated steel sheet, apparatus for the manufacture of black galvanized steel sheet, and system for the manufacture of black galvanized steel sheet

摘要

The present invention provides a method for the manufacture of a black galvanized steel sheet which enables more uniform browning of the galvanized steel sheet. The method produces a black galvanized steel sheet by placing a hot dip galvanized steel sheet containing Al and mg in contact with water vapor within a sealed vessel. This method performs in the following order: heating a galvanized steel sheet disposed within a sealed vessel in the presence of a gas, the dew point of which is always lower than the temperature of the galvanized steel sheet; exhausting the heated ambient gas within the sealed vessel to render the gas pressure within the sealed vessel of 70 kpa or less; and introducing water vapor into the sealed vessel in which the gas pressure has been reduced to 70 kpa or less to make the galvanized layer black.