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Tin Plated Copper parts black smear/residue

April 7, 2021

Q. Greetings to everyone in this great forum. I have made searches to find the same subject post but with no success.
Except the Coffee makers problem with their tin plated(?) copper barrels and the peeling off .
I am Miltos Gardikas and working on a icemaker manufacturing Company. We do make TIN PLATING ON COPPER in some parts of the icemakers we produce as the European Community dictates.
We have the following procedure:
TANK 1: 20% H2SO4 and 80% water.
TANK 2: WATER
TANK 3: WATER
TANK 4: ELECTROLYTIC DE-GREASING IN ALKALINE SOLUTION (NaOH)
TANK 5: WATER
TANK 6: WATER
TANK 7: 20% H2SO4 and 80% water
TANK 8: WATER
TANK 9: TIN PLATING (ACID SOLUTION H2SO4)
TANK 10: WATER
My question is --
After process finishes THE PROBLEM is that when we use a towel or a kitchen paper and rub the surface, we get black smears on the towel or paper.

61231-1a 61231-1b

Can someone share his knowledge on this? Is this correct?
Is the process wrong?
Does Tin smear? Or leave residue?
If so, Is there a process like food grade lacquering to prevent this?
Where can I find more information?
Thank you very much for your effort in answering this.

MILTOS GARDIKAS
- LAMIA GREECE

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