| 摘要 |
A chromate rinse solution used to treat a succession of chemically-coated metal surfaces is replenished by adding water and either phosphoric acid to supply at least part of the free acidity or a dichromate to supply at least part of the hexavalent chromium, or both of these, any remaining free acidity and hexavalent chromium needed for replenishment being added as chromic acid. The solution preferably contains 0,01-0,1% hexavalent chromium (measured as CrO3) and has a free acidity of 0,05-1,0 points and a total acidity of 0,5-10,0 points and is replenished so as to maintain it within these ranges. The initial hexavalent chromium content of the solution may be provided by chromic acid or by a dichromate of e.g. sodium, ammonium, calcium, zinc, aluminium or cobalt. A suitable replenishing material for restoring the hexavalent chromium concentration contains 10-25% CrO3 and 90-75% of a dichromate, preferably calcium dichromate. The solutions may be used to rinse phosphate, oxalate or sulphide coatings. |
