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topic 10261

Rusting problems due to humidity


We are the manufacturers of steel furniture made out of CRCA sheets. We are facing a rusting problems because of a very humid environment while the material is in fabrication process i.e. before painting.

We have a pre treatment process of 3 stages which is meant for only degreasing and phosphating, then rinsing in plain water & then rinsing with DM water. This does not help us from getting rid from rust.

Hence we tried dilutaed HCl to remove rust before pretreatment. This is removing the rust successfully, but the component after going through the pretreatment process after drying, within 15-20 minutes, it gets rusted again.

We seek a solution to this problem.

Thanks in advance to those of you willing to share your expertise.

SF Company India - India


If you are pickling in hydrochloric acid to remove rust, you must be very careful to fully neutralize. Is it practical to blast the rust before phosphating instead?

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey



HCl acid is effective but the fumes will only make rusting more likely in the area of use.

1. For derusting use 10% phosphoric or even citric acid [linked by editor to product info at Amazon], slower but less problems.

2. Paint without delay between dry-off and paint station

3. Use a rust inhibiting additive in stage 3 to afford some measure of protection.

4. Ideally after derusting, water rinse thoroughly and then use a dewatering fluid to remove the water and to prevent rust staining before retreatment.

Roger Bridger
- Croydon, UK

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