Current density required for chrome plating

A. Hi. 60 Amps/dm2 is a very high current density for most plating, so can we assume you are doing hard chrome plating? I believe that proponents of the reversible rack system say it's okay even with a straight Sergeant's bath with the chrome tank running at a high temperature. Tell us the details of your plating installation for a proper answer. For conventional decorative chrome plating this would probably be too high to be feasible.

On the other hand, if this was a typo and you actually meant 60 Amps total for a surface area of 7.06 dm2, then no, that's unlikely to be enough current to get any chromium to deposit at all.

Please tell us who you are, what your job is, what the situation is that prompted you to ask this question.

Luck & Regards,

"Chrome Plating Simplified"
by Clarence H. Peger
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A. Hi again, cousin. Thank you for the excellent reply. I assume you realize that temperature is central to the answer though. The allowable current density at 143 °F is way higher than at 130 °F let alone lower temperatures.

The upper limitation on current density is the point at which "burning" occurs. If you are not experiencing burning, I think all is well. Although 60 A/dm2 is higher than most installations can achieve, it is not unprecedented -- Clarence Peger advocated his 'reversible rack' chrome plating system for decades, operating at higher than conventional temperatures, with conventional Sergeant plating bath but higher than usual concentrations, and current densities in this range.

If you can find some of Peger's writings it should help re-assure you that your results are feasible. His book, "Chrome Plating Simplified" is not currently available for sale anywhere in the world according to Worldcat, but there are 4 or 5 libraries claiming to have copies (https://www.worldcat.org/title/chrome-plating-simplified-reversible-rack-2-bus-bar-system/oclc/2399195?referer=di&ht=edition).

You can try contacting Hard Chrome Plating Consultants, Inc. in Cleveland, OH but I am not confident that they still exist because their website looks to not have been modified in the last 4 years. Continued good luck!

Regards,

A. Hi Francisco. It is always difficult to put limits on an answer like this, due to variations in temperature, agitation, anode-cathode spacing, etc.; guidebooks will tell you 0.25 to 6.0 amps per square inch. But I have personally never seen chromium plated either at 0.25 or at 6. If this is decorative rack plating, and nothing unusual, you should probably aim for more than 1 but less than 2 amps per square inch and you should be okay. Best of luck.

Regards,

A. The current density will vary with the conductivity of the solution and the distance of the anode from the cathode. The further they are apart, the more resistance there is and the more electricity is turned into heat versus conversion of the chrome ion to chrome metal. The max current that you can apply before "burning" is dependent on the temperature of the bath. Obviously, there is a minimum amount to have it plate, but a higher minimum to have "good" plate and a higher amount for a better plate rate. Ted's 1-2 ASI is a good middle of the road set of numbers for many applications.

"Hard Chromium plating"
by Robert K. Guffie

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A. Hi Ahemd. It's probably a bit of each. There is science available, like Faraday's Law and Ohm's Law which apply to plating. But there are also things that are beyond our present analytical capacity, so empirical knowledge is used.

For example, while Faraday's Law says that one gram equivalent weight will be reduced for each 96,485 coulombs, we know empirically that most of that current is wasted to the liberation of hydrogen and only 10 to 25 percent of it actually goes towards deposition of chrome -- but I don't think we fully understand the science of why.

Similarly, we know that higher temperatures mean greater ion mobility and allow faster plating, but I don't think we can yet really calculate exactly what will go on in the boundary layer. Rather, we determine the maximum rate at which we can plate without burning from experience rather than formulas. Good luck.

Regards,

A. Hi Bojan. 40 °C (104 °F) is a pretty low temperature. I'm not familiar with going lower than 110 °F (43 °C) even for decorative chrome. As James observes above, it depends on spacing, concentration, etc., but I'd guess that it could be 1-2 Amps per square inch unless you are using a reversible rack system.

Regards,

Q. Why it's too low? From decorative chromium the temperature it's around 45 I haven't seen that it's over 50. Here we keep temperature at 45 for chrome and 55 for nickel bath. Current density in nickel is 2.2 A/cm2^^dm2 [ed. note: 2044^^20.44 Amps/square foot] and in chrome is 9-10 A/cm2^^dm2 [ed. note: 8361-9290^^83.61-92.9 Amps/square foot].

A. Hi again Bojan; I think we may be having some language difficulties. I did not say that 45 °C was too low, I said I haven't seen less than 43 °C. Upon looking at your numbers a second time, I should probably have suggested that I think the temperature range seems too wide or loose, rather than saying that the low end sounds too low.

I think there is an error in your Amperage figures, as they seem impossibly high.

Regards,

A. Hi again. I am not a chrome plating expert, and we already have many threads on whitewash in chrome plating, so it might be productive if you put "whitewash chrome" into the google custom search engine to read some good discussions.

Typical current densities for decorative nickel-chrome plating are about 40 amps/sq. ft. for the bright nickel and 150 amps/sq.ft. for chrome. So now I think your current densities are on the low side. I don't know for sure what will work best in your specific case (your particular parts might have have sharp corners that will burn at higher current density), but if you run some Hull Cell panels, I think you'll possibly see that your current density can and should be increased by about 50% or a little more.

Regards,

A. Current Density required for chrome plating, 150 amps per sq.ft at 110 °F Temperature .

A. Yes

Regards,

Q. We operate at 9,5 A/dm2 and 45 °C. I know this is very low current density, but they are working like this for many years and I came to this company only a few months ago. Don't know why they chose so low current density.

A. Hi. That's 88 ASF, and sounds very low for chrome plating, but depending on the shape of the articles maybe it's not outrageous.

If it's working well, it's fine :-)

Regards,

A. For each makeup of a chrome plating solution there is an optimum parallelogram shaped box on a temperature vs amperage graph that gives the best plate.
At your temperature and amperage, you are probably getting smooth uniform bright plate. BUT, you are on the very edge of getting either soft or whitewash plate on portions or all of your part.
A slightly higher temperature would allow you to carry a bit more amperage and still get smooth plate.
For zero reason that I can understand, the cooler tank actually has a bit higher deposition rate for any given amperage.

A. Hi Bojan. Unfortunately, plating can be complicated and it is little more than guesswork to try to attribute a verbally described defect to a given cause. But, yes, no chrome deposition at all takes place below a threshold low current density, and the surface will be relatively "yellow" because chromium is significantly "bluer" in comparison to nickel plating.

Lots of things can cause a milky deposit, from passivated nickel to incorrect catalyst ratio, to excess brightener in the nickel tank, to burning being mislabeled as a dull or milky deposit.

I think what may be missing here is a "hanging Hull Cell" which would allow you to see the effect of varying current densities. And, of course, double-checking the numbers you are being given! -- as we see above for several months now, the numbers you've given have been wrong time and again :-)
Good luck.

Regards,

A. Hi all,

Ted says he's not a chrome plating expert...but his reply above shows otherwise.
Bojan, you are advised to go through those contents with a fine piece of comb....
Good Luck.

A. Hi Bojan. Everything you said sounds right, and you apparently do not have any burning.

Regards,

A. Hi.
For the benefit of Bojan, for decorative chromium plating, using a mixed catalyst bath, I have plated using 30 A/dm sq., 40 °C bath temperature, plating time 5~10 seconds (important) ... I was pleasantly floored it could be done that way. Good Luck.

A. Hi.
I know ... I have plated decorative chrome for many years using the standard 40~45 °C, 10~20 A/dm2, plating time 1~3 mins. What I'm saying is that, I've tested and run using above unusual current density and plating time, the decorative chrome looks similar to that of the standard parameters...
Of course, as Ted suggests, the chrome deposit may be thin (less than 0.1µ) and corrosion resistance may suffer.

Regards.

Thanks for the insight into this approach, Cheah. We all continue to learn from each other.

Regards,

A1. Hi cousin Sudhakar. If you can tell us whether you are using reversible rack system, and thieves in the high current density areas, and whether you are using Sergeant's, SRHS, or HEEF bath, people may have further comments in addition to the input offered above. But a hanging Hull cell in your own tank would probably be the best way to know the acceptable plating range. Good luck.

A2. Hello again, I got/saw your 2nd posting after answering your first one. So I appended it here. What current density are you applying and what deposit rate are you getting? Efficiency as low as 10-13% is possible for some baths some times, and up to 25% for HEEF. Posting abstract questions when you obviously have actual data available to post isn't an efficient way to proceed; please tell us what deposit rate you are getting that you consider too low, and the current density and time rather than just saying they are as they should be :-)

Regards,

A. Hi Jagdish. The surface area of that shaft is about 94 dm^2 (10 ft^2), so your rectifier is on the small side but probably just barely workable. But I would be very dubious about the chance of success with that anode or with horizontal plating without rotation. Very few things are actually impossible, but I think you will regret it if you accept this job unless the volume of the order justifies building a proper facility to do the job right :-)

Luck & Regards,