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topic 52366

Hard chrome plating: Volts, Amps, Anode-to-Cathode Distance

Current question and answers:

March 24, 2021

Q. How to calculate amperage and voltage for hard chrome plating?
I want to run a small shop of hard chrome plating in guns barrels and other part of guns.

52366-1b   52366-1a  

Anyone there who can help me I will be very appreciative.

aziz ullah
- peshawar pakistan
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March 2021

A. Hi Aziz. Chrome will not deposit at all at low current densities and will burn at too high a current density. You will probably want to size things for around 250 to 500 Amps per square foot (25-50 Amps per square decimeter), although these are not firm limits.

Voltage is not an independent variable. It is whatever value is required to deliver that amperage under the actual conditions of anode-to-cathode distance and solution conductivity. Relatively small parts usually means relatively close anode-to-cathode spacing and relatively low voltage. A 9-volt rectifier is probably safe if parts remain small and anode-to-cathode distance remains short. But it is better to find someone who is doing a similar job and doing it in a similar way, and find out from them what voltage they have found necessary than to try to guess :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey


March 27, 2021

Q. Hello sir again
How to hard chrome plate inner surface of guns barrels? I am using lead antimonial rod coated with oxide in inner side of guns barrels -- is this okay or not?
How many ampere and volt rectifier will be used if the distance of anode and cathode is 0.5 inch and cathode surface area is 18 square inch to 40 square inch?

52366-2a   52366-2b   52366-2c  

For small guns barrel (9 sq inch) is working but not for large (28.8 sq inch).

aziz ullah [returning]
- peshawar pakistan
^- Reply to this post -^


March 2021

A. Hi again, Aziz. I have no personal experience in chrome plating of gun barrels and can only report 'book knowledge'. Guffie says 2-4 Amps per square inch, which would mean 18-36 Amps for the small gun barrel and 57-115 Amps for the large. He also suggests that while 9 volts is usually enough, 12 volts is rarely not worth it.

But what he also makes a big point of is that the anode area should be as large as possible or the anodes will passivate and simply stop plating. That sounds like maybe that's a problem for you on the larger barrels.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey




Previous closely related Q&A's starting in:

1998

Q. Please tell me more about hard chrome plating, for example the ideal current density, voltage, temperature, solution percentages, etc.

I'm starting a hard chrome plant for rollers and plastic molds.

Thanks for any suggestions.

Remberto Brito
Reproqui S.A. de C.V.
^- Reply to this post -^


affil. link
"Hard Chromium Plating"
by Guffie
from Abe Books
or

or
see our review

1998

A. Hi, Remberto. We're always delighted to answer questions here, but you should probably start your investment in your chrome plating operation with the purchase of some books on the subject because a few paragraphs will prove a poor substitute for the broad knowledge you will need to bring to the enterprise.

"Hard Chromium Plating" [affil. link to book on Amazon] by Robert K Guffie is certainly the indispensable premier resource on this subject, but "Chromium Plating" [affil. link to book on Amazon] by Weiner & Walmsley is very valuable too. For general historical background "Electrodeposition of Chromium from Chromic Acid Solutions" [affil. link to book on Amazon] by George Dubpernell is interesting reading although I personally feel it tends to overstate the importance of M&T Chemicals folks and understate the contributions of everyone else :-)

1). There are at least three very different general types of plating baths based on their catalysts (1. sulfuric acid - the traditional 'Sergeant' bath; 2. fluoride - such as the 'Self Regulating High Speed' bath; 3. proprietary catalysts - such as the High Efficiency Etch-Free bath). Please see letter 35184, ./351/84.shtml">"Hard chrome plating catalysts" for an introduction to that topic.

2). A large range of chromic acid concentrations are employed from about 28 oz./gal to 54 oz.gal.

3). A number of different general approaches are used, for example, tank plating with stick anodes vs. Peger's reversible rack system.

4). Rollers are sometimes plated vertically, and sometimes plated horizontally, while slowly rotating, with the bottom half submerged and the top half above solution level.

For these reasons,
- the ideal current density may range from a low of about 1-1/2 amp/in^2 to at least twice that and more.
- the voltage is closely proportional to the anode-cathode spacing and solution conductivity, so it might actually be only 3-4 volts with a clean solution and close spacing or it might be 12 volts (maybe even more) in some cases.
- the temperature is usually between 130 and 140 °F, but again it can depend on the other factors.
- the concentration of chromic acid is usually, as previously mentioned 28-54 oz./gal. with 32 oz./gal. probably being most typical. But there will always be catalysts in the general range of 1% of the chromic acid concentration.

You might get hold of old issues of Metal Finishing magazine and read what Clarence Peger -- a strong proponent of reversible rack plating -- has to say. Best of luck!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


1998

A. In addition to looking at past issues of Metal Finishing magazine for Clarence Peger's articles about chrome plating, get a copy of Clarence Peger's books about chrome plating.

Hard Chrome Plating Simplified (CPSR) - a manual that consists of basic, simplified, hard chrome plating information to help you make greater profits; with over 200 illustrations and photographs; also includes 32 blue prints. 382 pages.

Hard Chrome Fixtures II (BLFT) a manual consisting of 80 full-color photographs of chrome shops, racked work, and other related images, 15 black-and-white photographs, 8 line-drawings, 5 papers, back issues of Hard Chrome Plating news letters, and other informative articles. Each photo has a commentary. 300 pages.

All of the information in these two manuals is based on a proven high-speed chrome plating method that produces even deposits at 0.006 + per hour plating rates. These manuals have been called the Hard Chrome Plater's Bible and the Cook Book of Chrome. If you hard chrome plate, you must have these manuals!

The manuals are available from:

Hard Chrome Plating Consultants , Inc., Cleveland Ohio

Mary Peger
Cleveland, Ohio

----
Ed. note: We're quite delighted to see you carrying on your father's legacy, Mary! With great respect for his contributions we've posted your reply. But in general we can't post advertisements in these forum responses (why?). Please become a supporting advertiser so you can advertise on this site; thanks :-)



(2008)

Q. Hi guys, Can anybody give me some hints of the operation costs of running a chrome plant?

Rolando Riley
- Panama
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A. Hi, Rolando.

As with many businesses, labor cost is surely the biggest single item. It takes several hours (occasionally several days) in the plating tank, and hard chrome plating jobs often require careful masking, building of specialized auxiliary anodes and thieves, etc.

Electricity costs can be substantial: look into Faraday's Law to estimate electrical usage based on the amount of chrome you will deposit, remembering that the chrome is in hexavalent form, and deposition efficiency is probably only about 12 percent. The air exhaust system also uses substantial energy.

The chromic acid itself is a fairly minor cost, but it can be expensive to manage the handling of chromic acid (hexavalent chromium) to avoid worker exposure and pollution of the environment.

Although it might not be easy, or even possible, it would be best if you very clearly understand chrome plating from visits to several chrome plating shops. Before you try to estimate the operational cost, it's useful to know what operations are actually involved and in what proportion. There are many plating shops which make good money ... but there are no plating shops which produce substantial rejects and make money. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



June 7, 2009

Q. We plan to install 10000 amps RECTIFIER for HARD CHROME PLATING
I am confused whether to select 0-8V or 0-12V output voltage
Please advicse

MIKKI MAYAKANI
PLATING SHOP EMPLOYEE - KOLHAPUR, MAHARASTRA, INDIA
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June 11, 2009

A. Hi, Mikki. If you have experience in this and you never use more than 8 volts, you should get an 8-volt rectifier. Simply, there is no value at all in oversizing a rectifier :-)

If this is a new installation and you are asking how much voltage an unspecified part will require, no one can answer exactly. But essentially the required voltage is proportional to the anode-cathode distance. If you use only very closely spaced conforming anodes, 8 volts is probably enough; if you do 'tank plating' with the anodes the better part of a foot from the part you are plating, it is probable that you will need 12 volts (maybe even more). The referenced book by Guffie suggests thinking very carefully before considering 9-volt rectifier because real-world contaminated plating solutions will require more voltage than new solutions. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



Anode cathode distance in hard chrome plating

December 16, 2010

Q. I find that the closer the distance between the anode & cathode (the work piece), the lesser is the required current (Amps/dm 2) to plate a particular thickness for a given surface area.
Could you help me to understand the theory behind this.

Srivarma Shetty
Electro Plater - Bangalore, Karnataka, India.
^- Reply to this post -^


simultaneous December 16, 2010

A. Other than you have to add 6 electrons for every chrome atom deposited, you have a very inefficient bath. Since the voltage is above both the hydrogen and oxygen overvoltage potential, you will use a good bit of electricity to have that happen. Next, the solution will generate a lot of heat, which is more lost electricity. When you move the part closer to the anode, you will generate less heat. If you turn down the voltage to lower the amperage, you will generate less hydrogen and oxygen. Result--You use less amps to plate the same thickness.
When you use conforming anodes, you can reasonably go to 1/2" spacing. This requires that you use a "mesh" type anode. This increases the solution flow over the part. Drilling holes in sheet lead will work, but not as well. Also, the mesh type anode is easier to remove a bit here and there to even out the plating thickness as in lessening the dog bone look at the end of a cylinder. It also makes it a bit easier to add lead wire to get more throw in a recessed area.
I takes luck or a lot of trial and error to get it right, but excellent and fast plate is the result. Heavy build at over a thou an hour per side of hard bright chrome. Over 2 thou per side on some parts.

James Watts
- Navarre, Florida


December 18, 2010

A. RESISTANCE OF HARD CHROME PLATING SOLUTION IS VERY HIGH.

Muhammad Umair Kahan
- Lahore Pakistan


April 18, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I have a Cylindrical part OD 38.50 mm & Length 205 mm. I have problem in chrome plating. I have No Idea For JIG & FIXTURE Design for this part.

When I try to do plating to this part/job down side is thickness variation. Suggest me how to do plating on this Part.

Gopal Jograna
- Gujrat, India
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April 23, 2013

A. Hi Gopal. Are you racking this part vertically or horizontally? If vertical, it's possible to arrange anodes in a ring around the part and get reasonable consistency of thickness. Anodes shorter than the part may help avoid dog-bone effect.

When you say you have "no idea" I'm not sure how literally to take that. If you are an experienced hard chrome plater looking for a tip based on this one particular shape of this part, hopefully someone can help you. If you literally mean that you have no knowledge at all of jigging & fixturing for hard chrome plating, you'll need to read some books or attend some classes as that would be way beyond what anyone can tell you via a public forum posting. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


April 24, 2013

Q. Dear sir

I set job in Vertical & I have already 1 plant.; this is my second plant. I purchased this plant for this job: it's automotive part used in heavy truck; it's called KING PIN.
I need thickness 75 micron per side total 150 micron ovality & taper maximum 30 to 40 micron.
When I try this job for chrome plating and after checking this part, Ovality & taper 80 to 190 microns.
Thanks & Regards

^- Reply to this post -^


May 11, 2013

A. Hi Gopal: It is kind of difficult to help you without seeing a diagram or something about the part, but I am going to give you a few hints based on my experience. Hard chrome plating is a very tricky business, it is very complex and the bath is very poor in throwing, for every 100 amps you are "really" using 12 to 14 amps, with your bath in top shape. You should use 2 to 4 amps per square inch of surface to plate well.
Put your part vertical in the tank ; jig it up with heavy copper bar or hook; hopefully you have threaded holes on both ends of your part; use a stack of steel washers or nuts (to thieve the high current density of both ends, so you can get better distribution of the layer of chrome); Like Mr. Mooney said, set your anodes in a circular way around the part (use a heavy copper ring for your cell) and keep your part in the center about 3" from the anodes. Make sure your cleaning and activation process is good, good rinsing and give it a shot. This the best I can do for you. Good luck.

Nick Cordero
- New York, New York



Chrome plating draws too little amperage

November 1, 2013

Q. Hello, I have a question concerning hard chrome plating. Over the past summer I have experienced a gradual loss of amperage on large parts. Example, if my part called for 10500 amps at 15 volts , I have slowly lost amps and am now around 7000 amps at 15 volts. My chemistry checks out good and temperature is good too.
Now here is what puzzles me. Through the summer I had slightly strengthened my chrome from 23-24 oz per gal to 26-27 oz per gal, disassembled mostly all copper contacts to clean mating surfaces and put in new anodes.
Now I thought this would give me an increase in amps but the decrease occurred. Does this mean that it now takes less amps to achieve the same end result? Or should I be looking into a problem in the rectifier?
Any info would be greatly appreciated.

Pete Salazar
chrome plating dept. - Chesterton, Indiana, USA
^- Reply to this post -^


affil. link
"Hard Chromium Plating"
by Guffie
from Abe Books
or

or
see our review

November 6, 2013

A. It's highly unlikely that anything you did reduced the required amperage because that is dictated by Faraday's Law. With half the current, you'd put on only half the chrome, and I think you'd have noticed that thinness ... so I suspect the rectifier readings. The first and easiest guess about the problem is the ammeter and shunt leads.
The ammeter on your rectifier doesn't really measure amperage :-)
What actually happens is that there is a precisely sized block of copper alloy in your bussing called the shunt. When current flows through the bussing there is a voltage drop across the shunt just like any of the other bussing -- except that the shunt was sized to have a fixed voltage drop, usually 50 mV, when the rectifier's maximum current is flowing. At half current the voltage drop will be 25 mV, etc. So your ammeter is actually a 50 mV voltmeter. If that voltmeter is defective or the shunt is the wrong size for the rectifier rating or the meter, or even if the shunt wiring is loose or the connections dirty, the ammeter can read wrong.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


November 8, 2013

A. Hi Pete,
I agree with Ted on his suggestion.
However you did not comment on the condition of your part.
Is the result same in same time or do you observe a difference? To my guess check your rectifier for a broken carbon leading to less current. Moreover in case you have a broken carbon it means that you are working on 2 phases which could harm the rectifier and the deposit too.

ALL THE BEST.

vikram dogra
Vikram Dogra
Irusha India - Chandigarh, India



July 14, 2017

Q. Hi

We have water-cooled IGBT based rectifiers for our automatic hard chrome plating line -- 12 V and 18000 A.

ACRONYMS:

IGBT = Insulated Gate Bipolar Transistor

Over the past six months, whenever the demand of parts current exceeds 70 - 75% of the rectifier current capacity, fluctuation of current happens and also the actual current observed at that 70 - 75% limit is 500 - 2000 A less than the set current.

The rectifier manufacturer says that constant current output should be obtained @ 85 - 90% of the rectifier capacity but is unable to diagnose the problem.

Our chrome plating bath uses HEEF-based chemistry, with chrome concentration of 250 gpl and trivalent chrome - 7 gpl, Fe - 9 gpl. Operating temperature is 60 °C and current density is 50 ASD. We use 2.5 meter length lead-tin anodes. We have checked the busbar connections from rectifier to tank and is ok.

If rectifier is the problem, what are all the variables to be checked, to confirm problem with the rectifier.

Thanks for your assistance.

Ezhil Thangapandi
- Bengaluru, Tamilnadu, India
^- Reply to this post -^


A. Hi Ezhil. If this problem developed as the plating solution aged, please consult Guffie for detailed comments on why this may happen with plating solutions as they accumulate impurities. An oscilloscope will show the actual voltage being delivered, and when sync'ed to your 50 or 60 Hz power, it can be very helpful towards revealing whether the rectifier is malfunctioning (these days some high-end digital multimeters can simulate an oscilloscope, plotting the waveform of the output voltage on an LCD display).

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

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