| 摘要 |
PURPOSE:To prevent the blackening of the surface of hot zinc dipped steel sheet, by heating the steel sheet having been machined by a prescribed way previously to the rust preventive chromate treatment thereof. CONSTITUTION:Machining such as levelling, skin pass, buffing of the surface of hot zinc dipped steel sheet breaks or removes locally the plated coating so as to expose active zinc or zinc alloy surface. Heating the steel sheet by a burner, a high frequency oscillator, or an electric heater etc. at a temp. not lower than 200 deg.C, and at a limited temp. for a limited time where no iron-zinc alloy layer grows on the surface of the plated layer restores the surface properties, thereby restraining the blackening of the surface. The following chromate treatment permits to keep the beautiful silver white color of the plated layer. |
