PURPOSE: To form an enamel coated layer free from surface defect and having high surface smoothness on the surface of an Al plated steel sheet.
CONSTITUTION: The surface of Al plated steel sheet is coated with a slip consisting essentially of a frit having lower m.p. than that of the Al plated layer and smaller coefficient of linear expansion than that of the Al plated steel sheet and, after that, previously heated at a temp. near the softening temp. at which the gap between particles communicated with outside air can be kept in the frit. Next, the temp. is raised to a lower temp. than the m.p. of the Al plated layer and fired. The previous heating can be executed by raising the temp. at the rate of 30-40°C/min from room temp. to 520°C or keeping for 5-15min at a fixed temp. in the range of 450-520°C. As a result, a volatile component is sufficiently removed, so the enamel coated layer free from surface defect and improved in quality is obtained.
MAEDA YASUHARU
KOSHIISHI KENJI
MASUHARA KENICHI
SUN WAVE IND