| 摘要 |
PURPOSE:To prevent the discoloration of a steel sheet by adding hydrazine to washing water at the time of rinsing a steel sheet to which chemical cleaning, etc., are applied in the above washing water. CONSTITUTION:At the time of rinsing the surface of a steel sheet, after subjected to chemical cleaning and electrolytic cleaning, with washing water, hydrazine or hydrazine and 2-14C hydroxy carboxylic acid or water-soluble salt thereof are added to the above washing water. At this time, N2H4, N2H4.H2O, N2H4.H2SO4, etc., can be used as hydrazine and malic acid, tartaric acid, etc., are cited as hydroxy carboxylic acid and blended by about 1-50wt.% based on N2H4, and further, the amounts of the above hydrazine and hydroxy carboxylic acid to be added to the above washing water are regulated to about 50-1000mg/l. By this method, the occurrence of discoloration to the steel sheet whose surface is activated by means of chemical cleaning, etc., can be prevented. |
