Pickling For Plating
The Primary Function of Pickling for Plating is to remove Rust and Oxides.
If parts have been Heat Treated (for Hardening or other purposes), the Pickle is also used to remove Heat Treat Scale.
The Pickle will react with and remove Oxides and Scales. Another problem that must be solved by the Pickle Process is
Welding Scale is very similar to Heat Treat Scale.
Lastly, there are also Inhibitors that prevent hydrogen from diffusing into the Steel Base Material... which help reduce the Risk of Hydrogen Embrittlement.
Typical Pickling Process Parameters...
Unfortunately, the best Chemistry for Pickling is Hydrochloric Acid (HCl). It IS absolutely the BEST!
However, when making additions of HCl... the smell is very strong. Also the HCl Pickle is unfortunately excellent at destroying any Zinc Plating Line Structures of Components that are made from Steel.
Regardless... our recommendation is for Zinc and Zinc Nickel Plating Companies to use a Hydrochloric Acid Pickle. We have seen Plating Companies using Sulfuric Acid at very high temperatures... but our opinion is that..
1) this is a dangerous situation (HOT SULFURIC ACID!!!), and
2) the Sulfuric Acid... even at high temperatures... just doesn't adequately remove Oxide Scale (Heat Treat and Welding Scale) and doesn't adequately "Activate" the Parts / Components for Plating!
So... we strongly recommend that your Plating Company uses a 1 to 1 (by volume) ratio of Water to Hydrochloric Acid.
If you have Parts / Components with either Welding or Heat Treat Scale... you are probably going to need a Temperature of 30 C (86 F)... and an Immersion Time of 10 minutes. Otherwise... 20 C (68 F) and 10 minutes is are typical Standard Parameters for the Pickling Process.
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