plating, anodizing, & finishing Q&As since 1989
Alternative Pre-Treatment Process Desired
Our company is plating furnace brazed automotive product with alkaline zinc followed by a clear trivalent chromate. The tubular components (with many bends) are made of low carbon steel, brazed together with copper rings and paste. They are oil/dirt free (relatively clean) as received.
We are having problems with air entrapment inside the part as racked. HCl fumes (after electrocleaning) activate the inner surface and start the corrosion process. Internal rust is not acceptable, and the parts can't be racked any other way. Solution bucketing is also a concern.
The current pretreatment process is
1)soak, 2)EC, 3)CWR, 4)CWR, 5)HCl, 6)CWR, 7)CWR, 8)plating tank
Can another de-scaler be used in place of the HCl? We don't think internal rust will be a problem if we can eliminate all acid from the process. Is there a pretreatment process for low carbon steel that consists of only alkaline materials that would also provide excellent adhesion?
Your suggestions would be greatly appreciated.Jeff Schnapp
A Cyanide or mon -cyanide p.r. electrolytic de-ruster may replace the HCl.Gabriel Schonwald
Bnei Berak, Israel
You need the HCl etch to give you good adhesion but there is nothing to stop you putting another Alkaline de-ruster step after the Acid, or simply installing an alkali wash prior to Electroplate.
A sequence such as HCl Acid, CWR, CWR, Alkaline Wash, Alkaline Zinc Electroplate. You could also install a rinse between the Alkaline Wash and electroplate if you were worried about Iron contamination.
If you opted for the Electrolytic Alkaline de-ruster I would recommend the use of a CWR prior to electroplate and it should be heavily agitated.
John Tenison - Woods
- Victoria Australia
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