Summary for uneven plating thickness Discussion
Uneven plating thickness in acid zinc is usually a current-distribution problem, according to the reply from Ted Mooney. He explains that, by Faraday’s Law, thickness follows current flow, so one side of the rack likely has much lower current and the other much higher. He suggests checking whether the rack is centered between the anodes and whether the parts are the same distance from each anode on both sides. He also warns that an anode rod on one side may be effectively “dead” because of a poor connection. Ted recommends using a voltmeter to compare the anode-to-parts voltage on each side of the rack and notes that some variation may be normal, so the shop should gather numerical data before assuming the problem is abnormal.
Q. We have acid zinc plating line in house. The issue is the plating thickness is very low for one side of the rack and other side has very high for the same rack. What factor causes it and how to fix it?
Elaine Shen
– Menominee, Michigan, USA
October 3, 2018
A. Hi Elaine. According to Faraday’s Law the thickness of the plating is directly proportional to to the current flow to that surface. Thus you apparently have very low current flow to one side and very high to the other side.
Is the rack centered between anodes so the back of the parts are roughly the same distance from the anode as the front of the parts?
Is it possible that the anode rod on the one side is “dead” due to a poor connection somewhere? Have you tried a voltmeter from an anode on one side of the rack to the parts, and from the anode on the other side of the rack to the parts?
Another possibility is that you are expecting too much. Fairly wide variation is not unusual.
Try to get us some numerical facts. Thanks.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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October 2018
