To obtain an enameled Al-plated steel sheet excellent in resistance against stained streak by rain by coating SiO2-Na2O base enamel glaze having a specific value of softening point and a specific grain size on the Al-plated steel sheet and heating at a specific temp. for a specific time to make specific surface range roughness.
The upper limit in the softening point of a first for the enamel glaze is made to 490°C. The frit remained on a sieve having 325 mesh adjusts the grain size so as to become 0.1-0.5g per 100ml of the enamel glaze. This glaze is applied on the Al-plated steel sheet, and is heated at 400-480°C for 5-10min, then this steel sheet is heated at 550-660°C lower than the m.p. of the Al-plated layer for 5-10min. After burning the roughness of the enamel surface is made to be 0.5-1.5μm Ra the average roughness at the center line. The composition of SiO2-Na2O base enamel glaze is, by wt.%, 30-45 SiO2, 25-35 Na2O+K2O, 15-25 TiO2, 4-8 ZnO and 1-5 V2O3.
MAKINO TOMONORI
MAEDA YASUHARU
KOSHIISHI KENJI
