To provide a manufacturing method for a porcelain enamel steel sheet capable of preventing lowering of a yield, by detecting and judging a defect brought to a blister defect and by removing it.
This manufacturing method for the porcelain enamel steel sheet has a steel sheet manufacturing process, and an inspection process for inspecting the defect in the midway of the steel sheet manufacturing process or before the enamelling. In the inspection process, leakage magnetic flux flaw detection is carried out in a plurality of different magnetization conditions, as to the same portion, an obtained flaw detection result is computation-processed, and the defect is determined using a computed result thereof, in the manufacturing method for the porcelain enamel steel sheet. A detection signal level in the strong magnetization condition and a detection signal level in the weak magnetization condition are measured in the leaked magnetic flux flaw detection, and a ratio of the detection signal levels is calculated to determine the defect, or a harmful defect is determined when the detection signal level in the strong magnetization condition exceeds a prescribed level, and further a depth-directional position and a size of the defect is calculated based on detection signals in the magnetization conditions to determine the defect, in the computation-processing of the flaw detection result.
KATO HIROHARU
NAGAMUNE AKIO
