Barrel chromium plating

A. If it were commercially feasible, the equipment and process would be sold by every company that could legally break a patent.

A. Chromium passivates nearly instantly, such that make-and-break contact causes laminar plate. Hexavalent chromium therefore cannot be robustly barrel plated in the conventional sense.

When I started my career way back in the 1960's the company I worked for already had an ongoing research project on the subject; so strong interest has been present for many decades. Our unsuccessful approach for mass plating of small parts was sort of a shaker conveyor.

On the other hand, there was a local plating shop barrel commercially chrome plating the clips for PaperMate pens in conventional polypropylene plating barrels. The "rub" was that their success rate, even after all their optimization efforts, was under 20%. This meant very careful 100% inspection and sending more than 80% of the parts back for chrome stripping and another try. So, yes, it was a commercial process, but one which probably would be scorned today. In the intervening years some special equipment has been offered and used for the process -- for example, barrels that rotate at very high speed to keep the parts pressed in place via centrifugal force). I'm not versed in their success and practicality but it seems that the approach never took the world by storm..

Some vendors have substituted trivalent chrome or tin-cobalt barrel plating and claimed some success. Unless you have years and millions for a major development effort, I don't think hexavalent chrome barrel plating will prove at all practical.

A. Dr.D.Sen,

You may consider the plating of bright tin-nickel alloy which has the same corrosion resistance as chromium, a hardness of 650 HV and can be very well plated in barrels.

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Ed. note: Dr. Sen and readers may want to give a listen to "The Lost Art of Tin-Nickel Plating"

A. Dear Mr Sen, You can try tin cobalt plating it is a barrel process and finish is very close to chromium plating.

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Ed. note: For further info on tin-cobalt plating, please see:
• Thread 47247, "Chrome Plating Alternative and Substitutes"
• Thread 47866, "Tin Cobalt plating problems Q&A"

A. Hi Cheah. It is not completely impossible to do hexavalent chromium plating in a barrel, but it's close enough to impossible that you should not consider it until you fully understand the issue of make-and-break contact in chrome plating: the instant the contact breaks, the chromium plating passivates -- so the chrome will deposit in poorly adherent laminar layers.

Some special machines were built for the purpose, and consisted of multiple barrels on a single frame, sort of like a ferris wheel (Fuji Platerite Ltd). The idea was that they could maintain the G's so the parts did not break contact; I can't tell you how successful they have been except to say that I haven't seen them advertised for decades.

I will tell you that it will probably be less expensive to rack plate the parts than to plate them in a conventional plating barrel, and that if you do barrel plate them you will need to process very small loads, include careful 100 percent inspection, and you must plan on an enormous reject rate even after are very good at it.

Fluosilicate is a catalyst used in SRHS (self-regulating high speed) chromium plating baths. As you may know, hexavalent chrome plating will not take place unless there is a precise ratio of chromic acid to catalyst; too much or too little catalyst and the plating stops. The idea here is that you can keep an excess of fluosilicate precipitated out in sludge at the bottom of the tank, and the dissolved portion of the fluosilicate will act as the required catalyst. As it is dragged out or consumed, additional amounts will go into the solution from the sludge to achieve automatic regulation of the catalyst ratio. You can go to most plating process suppliers for fluosilicate catalyzed hexavalent chrome plating solution.

Dubpernells's Electrodeposition of Chromium from Chromic Acid Solutions [affil link on Amazon] includes this rather cryptic note, early on:
"About the only exception is in barrel chromium plating where the current densities and temperatures are quite low in the complex fluoride catalyzed solutions used, and a ratio of about 110-115 appears optimum." -- but the volume later includes 3 pages of info about the formulations. Best of luck.

Readers: take a trip in the time machine: click on the graphic to read "Chemical Balance", a poem about SRHS chrome -- probably the plating industry's only well-known poem.

A. Dear Mr. Lee,

I have heard a self regulating mix catalyst bath containing Silicofluoride and sulphate gives somewhat higher current efficiencies as compared to a conventional chromium bath. There are proprietary chemicals out there and easily available in Singapore.

Regards,

A. Barrel plating chrome is virtually impossible, but if you search the archives you will find someone that swears it can be done with his special equipment. Consider switching to electroless nickel. It will be a lot cheaper and easier if it can be used as a substitute.

A. Hi. Decades ago I visited a shop in Newark, NJ which specialized in hexavalent barrel chrome plating of components for Papermate pens. They simply used very small loads in conventional plating barrels, but did not reveal what rotation speed or other tweaks they employed. They were by far the best in the area, yet the percentage of rejects after 100% inspection was something like 20%. It's not so much that the theory is impossible, but that employing it as a practical production process with a manageable percentage of rejects has proven virtually impossible :-)

There are shops today who do barrel chrome plating (Whitaker Finishing in Ohio, for example), but their sales information does not reveal whether it is hexavalent or trivalent chrome. Please, no comments pro or con about that shop or any other finishing shop; please keep the discussion technical and non-commercial ( huh? why?). Thanks.

Regards,

A. Hi Ishtiaq, Hi Gurmeet. Reliable chrome plating in a barrel has been sought for decades. Some specialized machinery like high centrifugal force barrels have been sold for the purpose. Equipment manufacturers have tried multiple approaches.

The state of the art 45 years ago when I started in this industry was to carefully develop a semi-workable procedure based on using standard plating barrels with very small loads, fully expecting a huge percentage of rejects, and then hand sorting to find the good ones. I believe the state of the art today is essentially the same :-)

A. Barrel Chrome plating has been accurately described by Mr Mooney. The system remains imperfect, with a great sensitivity to small factors which, as you know better, are all labor oriented aspects. If you wish to finish barrel Nickel Plated components with a Chrome finish there are three possible options

1) Wire the components which you are doing then Chrome.
2) Use a Barrel Centrifuge Chrome system as described by Mr Mooney.
3) The Third alternative is interesting:

This is an alloy of Tin and another metal. The Work after plating acquires a chrome look. It is plateable in the barrel. It has been done on a number of small articles where the hardness of chrome is not a major issue and where appearance plus ease of plating in a barrel is the major factor. Timings and operations are nearly similar to running Nickel Barrel operations. If Regards,

A. Hi Umer. Your question is somewhat abstract in that you haven't told us what you know about the main problem of current break. Nonetheless, barrel chrome plating is more a laboratory curiosity than a proven industrial process. I have known people who have spent their life at it and never achieved a remotely acceptable reject rate. The composition is probably not the central issue, it's how you are going to avoid breaking current. Still, as mentioned higher up in the thread, Dubpernell has some suggestions about solution composition. Further, Weiner & Walmsley's "Chromium Plating" .
discusses the possibility of cold chrome plating in a barrel, and also includes a 3-page section on "Articles in bulk; automatic plants". Good luck.

A. Hi Amjad. How did you come to know of it, and what did you learn about it? And what patents are extant -- people cannot help you violate patents if what you are speaking of is a patented machine. Although there have been many attempts at hexavalent chromium plating in a barrel, all have enjoyed only limited success.

If you will entertain proprietary trivalent chromium plating, then George Shahin's article "Barrel Chromium Plating from a Trivalent Chromium Electrolyte", published in the August 1992 issue of Plating & Surface Finishing, should answer most of your questions. And it also briefly describes seven early designs of barrels for hexavalent chromium plating. British patent 351,168 (1930) sounds something like what you are describing. Best of luck.

A. Hi Patrick. Although you've read some posts here about chroming in a barrel, we have recently consolidated many threads into the dialog you see, so you might give it another quick glance and check if anything here that you didn't see before helps.

Earlier on I mentioned seeing hexavalent chrome plating being done in a very conventional polypropylene horizontal barrel, with very small loads and atrocious reject rates, but it was so long ago that I can't swear the barrel had danglers as opposed to some sort of button contacts.

If you can't use a proprietary chrome substitute like tin-cobalt, I think trivalent chrome simply HAS to be more practical than hexavalent because it simply can't be less :-)

Regards,