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Arcing incident in hard chrome plating

Q. We have had an incident of arcing during a hard chrome process.
The arc occurred between the threaded fixture and the threads on the part which was a shaft drawing 600 amps at the time.
We are at a loss at this point to determine why this has happened as this fixture has been used many times in the past.
The fixture is a steel and copper mix with the steel making the contact with the part and the copper carrying the current from the cathode rail.

My questions are, What is the best material for attaching to such a part at this amperage, What might have caused the arcing and what exactly occurs at the point of arcing?

Frank Dunleavy
Plating Shop Supervisor - Dublin, Ireland.
February 17, 2012

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February 21, 2012

Somewhere in the system you probably had enough chrome salts build up so as to act like an insulator which caused the electricity to try to find an easier path.
You do not state the size of the conductor rod or the number of leads. 600 amps is a good size load for a smaller tank.

I would go to a copper all thread terminating in a small iron plug that contacts the load. Tape the rod with a stretchy pvc tape. I would use a vinyl maskant to cover any part that could move and not interfere with the motion.
Tape without glue, that is secured with a wire, is cheaper than regular platers tape and is easier to remove.

James Watts
- Navarre, Florida

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Contact was made through 4" flat copper bar folded into a hook which hung on the cathode rail. This plate was then attached to the threaded steel cap which was attached to the part. A second threaded cap was on the opposite end of the shaft and both caps connected by a steel draw bar.
The masking was wax and the bath is quite large at 6 x 6 x 10feet deep.

Frank Dunleavy
- Dublin, Ireland
February 23, 2012

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February 25, 2012

The second post helps but a picture of the connection would help.
For now, I will go with my original guess that most of your connector was not carrying current to the part. IE: it had become fouled or dirty or??

Aerospace would not let me connect to threads and critical flanges because of potential arcing.

James Watts
- Navarre, Florida