Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Hard Chrome Plating Bath Contamination
Q. We have a hard chrome plating bath where we monitor the surface tension, and lately we have noticed that the surface tension is on the rise, more so than usual.
We are wondering what effect on the solution would there be when a current is applied when either there is no cathode in the tank (i.e., out-of-tank plating) or the anode-cathode ratio is greater than 4:1?
Aerospace - Winnipeg, Manitoba, Canada
2006
A. Unless you have a cooling coil in your tank, the temperature will rise. Temperature will have the greatest effect on surface tension. Chemistry of the solution will be next. Drag in is another possibility.
James Watts- Navarre, Florida
2006
Q. Our tanks are temperature controlled, and the tanks are checked prior to taking a sample to ensure that they are at the correct operating temperature.
We believe that there is a contamination issue, but we are unsure where it would be coming from.
- Winnipeg, Manitoba, Canada
2006
A. Ok, I confuse easily. Why are you checking surface tension? If it is for controlling emissions so you can get by with less exhaust, then that is controlled by an additive which is subject to drag out and possibly consumption or evaporation.In that case, you need to add more additive.
I have never heard of anyone being concerned with surface tension in a hard chrome tank (for aviation) as a QC item.
- Navarre, Florida
2006
A. The possible reasons for rising surface tension generally are: depletion of surface tension additive by the introduction of oil/grease, failing to add surface tension additive as specified, increase of chrome metal in bath, operation at very high current density where solutions is "vaporized" and surface tension additive is lost.
The above assumes that you are using one of the fluorocarbon type permanent additives and not a surfactant type "foam blanket".
process supplier - Great Neck, New York
2006
Q. We are only checking surface tension to ensure we are not violating our environmental license, and not using it as a QC check.
We have noticed lately while performing the analysis, that the color of the hard chrome solution has changed dramatically, and at the same time our surface tension values have also changed dramatically. We believe this to be a symptom, not the actual "disease" so to speak. We are looking into sources of contamination in a hard chrome bath, which was the original intent of my question. I apologize if that was not overly clear
- Winnipeg, Manitoba, Canada
2006
A. Jennifer,
Consider the fact that you are looking for a source of contamination, how can anyone help if we have virtually zero knowledge of your operation. You know, little things like what size and shape are you plating, what base metal, what temp, what concentrations, what additives, what preprocess tanks (especially what rinses) just to mention a few.
Tank color changing to darker could be trivalent going up or a metal contamination or an organic contamination.
If you are not using a fluoride catalyst or additive, I would recommend using porous pot technology for control of the tramp metals. I used Hard Chrome Technologies out of Cleveland, OH as the cheapest adequate source.
- Navarre, Florida
2006
A. I see you have indicated that the solution color has changed. How so? If it has darkened, I would bet that there is a leak in a cooling coil. If your cooling system is running a glycol mixture as the medium, the glycol will reduce hexavalent chrome to trivalent quite readily.
Best Regards,
Kansas City, Missouri
2006
Q. I have experienced a small leak in a heat exchanger in my chromium tank. At the same time this occurred building maintenance was treating the boiler and pipes with a corrosion inhibitor. ChemCal 46130P Sodium Metaborate 7-10% and Sodium Nitrite 65-80%.
I pumped out the tank to change out the exchanger, and clean the tank. I plan to pump the solution back in, and try to plate. Any feedback on how to handle this?
- Fort Worth, Texas
January 25, 2013
Hard chrome bath contaminated with anti-freeze
November 26, 2018Q. Hi, I'm looking for some advice regarding one of my hard chrome baths.
Unfortunately the cooling coil sprung a leak and has ruined the solution (Cr110).
Has anyone had this happen, and did you manage to salvage the solution, or is it a new solution? (I have no idea how much antifreeze solution has gone in).
We have our supplier testing it, and they seem to think it is salvageable, but it could take up to 60 days to plate it out. I'm not so optimistic as it currently looks like tar! We are getting a large build up of "something" (looks like black mud, with green film on the underside of it when it is removed - tri) on the cathodes each morning so something is happening. We were told to plate it at 12 v with low cathode area -- there is no gassing at the anodes.
Any advice would be appreciated -- I'd rather replace the solution , but I'm not the one paying for it! Also we are limited to the amount of chemicals we can buy from the U.S yearly, so I can understand the need to try and save it.
Thanks for any help.
malcolm
employee - essex uk
A. Hi Malcolm. CR110 is a SRHS bath which relies on partially soluble fluoride sludges settling out in the bottom of the tank, so it seems to introduce even more problems. And I'm not sure the purification attempt is even safe; ethylene glycol degenerates to all sorts of stuff when reacted with strong acids and oxidizers. Google.com talks a bit about the reactions.
Any experimentation should usually be done in a Hull Cell or a lab flask, not in an actual multi-gallon production tank, even if there is no possibility of dangerous reactions. My feeling is that purification is not going to be practical, but that you should run experiments on small volumes rather than making a large volume of witches' brew. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2018
Thanks for your reply Ted; we are doing tests using Hull Cell, and so is our supplier . We received an email earlier stating they are not confident about saving it now!
I'm not allowing the plating out test on the tank to be done during working hours as I don't want to work near it!
I'm hoping that the powers that be will renew the solution as I feel it's a waste of time. Fingers crossed!
Thanks again
Malcolm
- Essex uk
November 26, 2018
A. Hi Malcolm
I wonder why a cooling solution should contain anti-freeze.
But if it does and it contains ethylene glycol (which will almost certainly have reacted with unknown results) it is an organic chemical and cannot be plated out. Carbon treatment is a possibility but unlikely to be successful. I am surprised that your supplier has not said this.
You will save a lot of time and frustration by replacing the solution.
Another question is why you are sourcing chemicals from US.
There are plenty of local suppliers.
Geoff Smith
Hampshire, England
November 28, 2018
Q. Hi Geoff; sorry I meant it's the catalyst we have to get from the U.S.
I'm not sure I'm allowed to name our supplier on here , but the name begins with A ;)
If you can let me know how we can get it more locally, that would be fantastic! - I'm the plater so I don't get involved with suppliers, etc., so I can pass on any info you have that can help to my relevant people
Thanks,
Malcolm
- Essex uk
December 8, 2018
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Ed. note: We don't wish to interfere with communication, and have no issue with people mentioning a supplier in a way that does not bring them commercial benefit or commercial harm, Malcolm. We just don't want any recommendations or testimonials (why?)
Hi Malcolm
Searching the web will mostly give you links to sellers of plating kit to amateurs.
I suggest that you contact the Institute of Materials Finishing who will happily advise on the major industrial suppliers. I believe there is a link on this website or go straight to ...
http://www.materialsfinishing.org
Geoff Smith
Hampshire, England
December 9, 2018
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