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Flash rusting problem when stripping chrome

At present we remove hard chrome from large 20 ton + castings with a sulfamic acid [on eBay or Amazon] salt solution(not possible to use sodium hydroxide electrolytically) after rinsing the castings we immediately get flash rusting, we have tried rinsing in a sodium hydroxide solution immediately after the sulphamic acid solution (limited success) does anyone have any ideas on how to prevent the rusting ?

Regards,

Norman Evans
Plating - Springfield, Ohio, U.S.A.
2004

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2004

Norman

Try this.

1) Raise component.
2) Slip a tray underneath which will carry away copious quantitys of dripping solution while transferring the component...
3) - IMM shift manually via overhead crane to a continuously flowing rinse bath. Immerse in RINSE bath.. Run air agitation vigorously.. The rinse shld be just large enough, not oversized. This is a key point..
4) Run water thru Rinse bath. Do not remove component. -Watch the ph. once it crosses 5 and rises towards 6... and hits 7 ....
5) Introduce a 7 to 10 % concentrated solution of caustic soda [affil links] into the rinse. A wetter at 0.1 % helps...

The air agitation can be stepped up to scrub the component till all the surfaces are totally neutralised. Maintain the pH around 8-10 . Thereafter remove and allow to drip into Rinse .

Air dry.
There is an obvious element of skill involved here. Try this with a small set of beakers [beakers on eBay or Amazon]s first on a table top to get the idea into work sequencing.

Good Luck.. Regards,

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016