| 摘要 |
PURPOSE:To increase the rust preventing effect produced by chromating, by treating a zinc coated steel plate with a chromic acid soln. after specifying the ratios among the concn. of Cr<+6> in the soln. the concn. of reduction products of Cr<+6>, the amount of a Cr<+6> reducing agent and the amount of an acid contg. oxyacid ion. CONSTITUTION:A zinc-coated steel material is chromated with a chromic acid soln. In the soln., the ratio between the concn. (mole/l) of Cr<+6> and the concn. (mole/l) of reduction products of Cr<+6> is regulated to (1-7):1, and when a strong acid is added to the soln. in an unreacted state, the ratio between the concns. in total and the amount (equiv./l) of a reducing agent capable of reducing Cr<+6> is regulated to 1:(0.01-0.2). The molar ratio of the total amount (mole/l) of >=1 kind of compound in the soln. selected from acids each contg. oxyacid ion such as sulfuric acid, phosphoric acid, nitric acid and chloric acid, hydrofluoric acid, fluorides, hydrochloric acid and silicofluorides to said concns. in total is also regulated to <=0.1. The steel material is coated with the soln. and dried without carrying out washing. |
