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FLASH RUST ON ONE SIDED ZINC COATED STRIP

1998

We are producing electroplated zinc steel sheet in a continuous electroplating line from a sulphate bath (pH 1.5). Single and double sided zinc coated sheet is manufactured. An acid rinse(1.5 pH length of rinse section-approx 50 meter) is applied after coating in order to remove losely adherent particles and to prevent the formation of flash rust on the non-coated side(steel side) of single sided material. A water rinse (pH 6-7) is finally performed before the strip is dried and oiled with a rust preventive oil.

We would like to change to a total water rinse system. What is the best way to prevent the formation of flash rust on the steel side in a total water rinse system(safe pH range, addition of an inhibitor,etc.)?

Your help is deeply appreciated.

Koos Greyling

Koos Greyling
Scientist: Process and surface Science - Iscor

Addition of inhibitors to rinse water is the best way (cheap, convenient, efficient, no by-effect to the subsequent treatments, etc.) to prevent flash rust on steels. There are numerous commercial inhibitors available for your needs. You may try to add 1-5% sodium benzoate or sodium dichromate to the rinse water. Do a few experiments in your lab first to determine the optimum concentration. I believe both are able to provide prevention of steels from flash rust. However, sodium benzoate application is limited in the chloride-containing water, while sodium chromate is restricted for environmental protection.

Ling Hao
- Grand Rapids, Michigan
1997