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Hard Chrome plating with Nickel undercoat

Q. I am attempting to assist a customer with an intermittent hard chrome plating issue and would appreciate any additional input from other chrome platers who may have experienced similar problems. This customer plates a high volume of steel rods approximately 7 ft. long in a fully automated line. Recently, perhaps 5% of the time, an entire rack of rods comes out with bad adhesion of the chrome to the underlying nickel sulfamate plate only at the bottom 12" or so at the end of the rod (see pics).

When the defect occurs, it affects all parts on a particular rack, with other racks running simultaneously in other plating cells within the same chrome tank being perfectly fine. Their racks are numbered, so I was able to verify that there were no particular racks that had a problem. I was also able to verify that no particular plating cell was a problem. Similarly, each plating cell has its own rectifier, so there was no particular rectifier that had a problem. It appears to be entirely random- not related to chemistry, rectifier, plating cell, or rack. Since the underlying sulfamate plate has no adhesion issue, I seem to be able to eliminate any issue with the plating pretreatment- electroclean and acid etch. The only tanks the parts see between the sulfamate tank and the chrome plate tank is a rinse and then a chromic acid pre-plating dip (chemistry is the same as the chrome plate tank, but there is no current). The timing is part of the automation, so there is not a significant difference in dwell times between loads. The tanks have been emptied to ensure that there is nothing unusual down at the bottom of the tank that could cause a stray current or other malfunction. I also verified that the tool the air tool that they use to attach parts to the rack fixture (by bolt) results in a consistent torque that should not be a source of variation between racks. After all of this, I am at a loss for what else to consider. Any thoughts?

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri

April 19, 2022

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A. Hi Jon I'm not sure if it may be a reason in this case, but once I have seen somehow similar Chrome peeling appearance and it was related to dirty and passive Lead anodes. Good luck, Leon Gusak - Winnipeg, Canada April 20, 2022 A. It couldn't be an SRHS chrome plating bath where the limited solubility fluoride sludge settles in the bottom of the tank and requires hoeing up before running, and the bottom of the rods is submerged in it? Luck & Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey April 2022 A. With more than rectifier in one solution you have varying voltages all over the tank and either a high voltage or a low voltage is passivating the nickel. Try making contact, with battery jumper cables, before entering the solution (but do not burn up your jumper cables).. Robert Probert - Garner, NC 27529-4772 April 21, 2022

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Answering Ted's comments, it is a standard bath without fluorides. The tank solution has been emptied to confirm that we did not have excessive sludge. They remove the sludge every 6 months as part of a maintenance plan which seemed to be effective. The adhesion was tested and it was very good once we are above that bottom foot or so.

Answering Robert's comment. Going in live is a good thing to try. It will be tricky with the automated hoist movement, but we will figure something out. Thanks.

Answering Leon's comment- the anodes have been inspected. They are the correct color and I do not see any problem there, but perhaps there is more that we can do. The seemingly random nature of the defect seems to rule it out.

Continuing to think about this, I think that there must be something related to the timing of the rinses between sulfamate and chrome. Perhaps delays in the automated hoist movement cause some some bars to dwell in those tanks long enough for the nickel to become passive. It could explain at least why the defect would be only occasional, but would effect entire racks. I'm not sure if it would explain the defect only being at the bottom.

Jon Barrows, MSF, EHSSC
GOAD Company

Independence, Missouri

April 22, 2022

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