Summary for barrel marks on plated parts Discussion
barrel marks on plated parts in acid zinc plating are discussed as either a bath contamination issue or a barrel loading issue. Senthil asked how to avoid the marks, and Ajay Raina said that if the dark spots echo the barrel perforations, they are usually caused by iron contamination. Paul Ellingson added that barrel overloading can also produce the same pattern because parts do not roll properly in the barrel. Sara Michaeli gave the most specific process advice: in acidic zinc, divalent iron should be oxidized with hydrogen peroxide or air, creating brown trivalent-iron sludge that must then be filtered out; she said this is a normal weekly maintenance step because divalent iron is continually generated. A later questioner described a small domino-like part picking up the barrel hole pattern on its faces, reinforcing the same symptom.
Q. In barrel acid zinc plating how to avoid barrel mark.
Senthil [surname deleted for privacy by Editor]
plating shop – Chennai, Tamilnadu, India
2004
A. I am not confident what you mean by ‘barrel mark’, Senthil, but if you mean dark spots on the work that seem to echo the pattern of the perforations in the barrel, this is usually due to iron contamination. Please see the article “Improving your Chloride Zinc Plating Operation”, by Stephen Schneider in our on-line library.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
2004
A. PRINT OF BARREL HOLES
1. C.D TOO HIGH
2. BARREL SPEED, i.e., r.p.m low
3. HIGH IRON CONCENTRATION
Ajay Raina
Ludhiana, Punjab, India
2004
A. Iron in the plating bath is a problem we have addressed at our plant. But the latest is barrel overloading — this will show the same spots due to parts not rolling in the barrel. Hope this helps.
Paul Ellingson
plating shop – Wahpeton, North Dakota
2004
A. Barrel marks in acidic zinc are a result of divalent iron. You have to oxidize it with hydrogen peroxide or air. Then the solution will develop a brown sludge which is trivalent iron that has to be filtered. This procedure is a normal procedure which you have to perform approx. once per week. The divalent iron is produced in this solution all the time and you have to get rid of it.
Sara Michaeli
Tel-Aviv-Yafo, Israel
2004
Q. Hello. I’m having problems with a piece. It’s a small part like a domino; the thing is that the piece is taking the circles (or holes) from the barrel in the faces of the piece. What do I have to do to avoid this issue? Please: your help.
Thanks.
Cesar Garcia
– Saltillo Coahuila Mexico
August 22, 2013