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topic 25523

Current density required for chrome plating



A discussion started in 2003 & continuing through 2017

(2003)

Q. What is the current density for chrome plating?

Thanks,

Francisco Hernán Ledesma
Facultad de Ingeniería - Buenos Aires, Argentina


(2003)

A. Hi Francisco. It is always difficult to put exact limits on an answer like this, and guidebooks will tell you 0.25 to 6.0 amps per square inch. But I have never seen chromium plated at 0.25 or at 6. Unless your situation is unusual, aim for 1 to 2 amps per square inch and you should be okay. Best of luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2003)

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.

James Watts
- Navarre, Florida



January 30, 2013

Q. I'm a student in production engineering department, and I have a question in how to get the optimum current density for chrome plating and the heating temperature of the solution. These are by calculation or is it by experience? Thanks in advance.

Ahemd Saad
- Egypt


January 30, 2013

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 96,487 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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



August 24, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. So can you tell us what a current density should be if the bath operates at 40-45 °C?

Bojan Koren
- Bovec, Slovenia


August 2014

A. Hi Bojan. That's 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 doubt that it could be much more than 1 Amp per square inch unless you are using a reversible rack system.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 27, 2014

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].

Bojan Koren [returning]
- Bovec, Slovenia


August 2014

A. Hi again Bojan. 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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 27, 2014

Q. Yes I made a mistake on current densities for nickel we have 2.2 A/ dm2 not cm2 and for chromium is 9-10 A/dm2

Is the temperature and current density ok for chromium? We sometimes get whitewash on plated parts, but I think its something wrong with with current, maybe its not always DC but also AC current? Only my opinion. Have to check the sulphate content next week when I get barium chloride.

Bojan Koren [returning]
- Bovec, Slovenia


August 2014

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 near the top of the page to read some good discussions.

Typical current densities for decorative nickel-chrome plating are about 40 amps/sq. ft. for 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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 2, 2014

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

popat patel
Popat Patel
    Howard Finishing
Roseville, Michigan



November 5, 2014

Q. For decorative chromium?

Bojan Koren [returning]
- Bovec, Slovenia


November 2014

A. Yes

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 6, 2014

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.

Bojan Koren [returning]
- Bovec, Slovenia


November 2014

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

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

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 6, 2014

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.

James Watts
- Navarre, Florida


November 10, 2014

Q. Now I checked the current density from last month and I realized that the men who was in charge he didn't use constant current density for chrome. He was changing current density for chrome.
The maximum was around 230 ASF to 75 ASF :)))
Now I know why the workpieces were yellow -- 75 ASF is way too low for chromium!
The temperature is constant, but he always changes current density; that's not good.
I have one question: few days ago the workpieces had dull and milky deposit. The temp was kept at 45 °C and the current density was 102 ASF. Reason for this is low current density, am I correct?

Bojan Koren
- Bovec, Slovenia


November 2014

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. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 10, 2014

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.

Cheah Sin Kooi
- Penang Malaysia


November 11, 2014

Q. Hello thanks for your opinion.
I don't have hanging hull cell, but I made a hull cell test of chromium bath and I can see at which current density the plating begins. Above 7 A/dm2 [65 ASF] the plating begins and in the range from 7 to 10 or 11 A/dm2 [65 ASF to 93 or 102 ASF] the deposit is white, cloudy. From 12 A/dm2 on [111 ASF] the bright deposit is plated. So from this hull cell test I think the reason for milky deposit of workpieces was too low current density.
What did you mean by this "burning being mislabeled as a dull or milky deposit"?
At current density 10 A/dm2 the deposit could not be burned. Or am I wrong?
Burned deposit should look like grey stain and rough when you touch it. This I read in one book.

Bojan Koren [returning]
- Bovec, Slovenia


November 2014

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

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 11, 2014

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.

Cheah Sin Kooi
- Penang Malaysia


November 12, 2014

Q. I never heard about this to plate only 5 to 10 seconds??
We use SRHS chrome bath and we plate always for 4 min at different current densities from 9 to 25 A/dm2

Bojan Koren
- Bovec, Slovenia


November 2014

Q. I've never heard of plating for 5 to 10 seconds either, Cheah, and I'm not confident that it offers much corrosion protective value.

Per the MFSA Quality Metal Finishing Guides, required chrome plating thickness ranges from 0.1µ for mild interior exposure to 0.3µ for severe service. But 4 minutes sounds long; I would have expected about 30-45 seconds for mild service and 2 minutes for severe service to be typical.

Even at a full 30 A/dm, I figure you'd need 15 seconds to get even 0.1µ at an estimated 18% efficiency. Can anyone quote a chrome plating time or thickness from a current automotive spec?

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 13, 2014

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.

Cheah Sin Kooi
- Penang Malaysia


November 2014

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

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Mixed catalyst chrome burns at low current density one day, and not another

November 14, 2014

Q. Hello again.

Im getting confused with this current density for decorative chrome.
Yesterday we plated workpieces at 13 A/dm2 [120 ASF] and became burned at so low current density? Confusing is this that last week my colleague was plating at 19 A/dm2 [175 ASF] and the workpieces were okay.
Can anybody help me with this strange situation? Why some workpieces get burned at very low current density and other are not burnet at even higher current density?

He use chromium bath with two catalysts, sulphur and fluoride, at temperature 43-45 °C, 320 g/L [43 oz/gal] of chromic acid.

Bojan Koren [returning]
- Bovec, Slovenia


simultaneous November 14, 2014

A. Because of the low efficiency of chrome plating it is extremely line of sight. simply change the position of your anodes relative to the edge that is burning.
Your friend is very probably using a bath with a higher efficiency and throwing power.

James Watts
- Navarre, Florida


November 15, 2014

A. Hi,
There is no mention about the concentration of your sulfate and fluoride catalyst content.

Cheah sin kooi
- Penang Malaysia


November 16, 2014

A. HI,BOJAN
CHROME BURNING PROBLEM: DO YOU HAVE NI ACTIVATOR AND CHROME PRE-DIP BEFORE CHROME PLATE? CHECK CHROME AND SULFATE RATIO BETWEN 200 TO 230. MAKE SURE OF TEMPERATURE KEEP 110 °F. TAKE THE MISSING PARTS OUT FROM CHROME AND MICROPOROUS NICKEL TANK.

popat patel
Popat Patel
    Howard Finishing
Roseville, Michigan




December 23, 2017

Q1. What is current density for hard chrome plating at 55 °C [131 °F] temperature?

Q2. We are not getting required deposit rate in hard chrome plating if we give current density and time as per technical data

sudhakar chavan
- pune maharashtra


December 2017

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 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. Posing vague questions when you have actual data available to post isn't an efficient way to proceed :-)

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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