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Yellow rust formation before zinc phosphating of tubes [China] 

August 18, 2008

Dear All,

We are seeing yellow rust formation after we do the HCL Pickling & rinse 1 & 2. we have cascading facility for the rinse to maintain the pH of the bath, but still the tubes are turning yellow before the activation.

And aslo we are observing non-uniform coating of Phosphate in the Tubes.

I request your opinion on the above.

thanks for your valuable time

Kaarthic Natarajan
Product Designer - China

sir,
If you use Hcl you will get this problem of yellowing, use Phosphoric acid based derusting along with inhibitors and surfactants.
The rough coating of phosphating is due to 2 reasons.
1) you are not using a surface conditioner, use it.
2) The formulation problem of the mother liquor by the supplier, Check if your Total acid and Free acid are in correct ratio.

Shankar Khandelwal
- Coimbatore, Tamilnadu, INDIA