| 摘要 |
PURPOSE:To form a phosphate film having excellent properties on the surface of a galvanized steel sheet with good workability by repeating alternately a stage in which a phosphating liquid is brought into contact with said surface for short time of several seconds and a stage in which said liquid is not brought into contact therewith. CONSTITUTION:A stage consisting of bringing a phosphating liquid into contact with the surface of a galvanized steel sheet for several seconds and of prohibiting forcibly said contact for several seconds in succession to said contact is repeated at least twice to treat said steel sheet, by which the amt. of the sludge to be generated is decreased and the phosphate film having excellent properties is formed with good workability as a pretreatment for a painting surface. In the above-described method, the contact time is preferably 1-3sec, more preferably 1-2sec, particularly 1sec and the time when no contact is made is 1-3sec and 1-2sec are particularly preferable. The above-mentioned method is effective for the galvanized steel sheet having good resistance to corrosion. Said method has the effect of suppressing the elution and accumulation of Al in the galvanized layer contg. >=3wt% Al and permitting easy control of the bath. |
