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Chrome plating tank contamination

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Q. Hello sir. I have a problem in chromium plating where there is rubber mixed in my chromium solution. What's the solution for this?

Ahmed Munir
- Lahore Pakistan
August 4, 2022

A. Hi Ahmed. These days 'rubber' rarely means the product of a rubber tree, but usually means one of many varieties of artificial rubber. But yes, I believe that chromic acid is able to dissolve most of them, and will result in dissolved organic molecules that can mess up a chrome plating bath.

If you are sure that significant contamination with rubber is the problem, I doubt that anything practical can be done to fix it, and the solution will have to be dumped. But what problems are you experiencing, and what is the contamination level or evidence that rubber contamination is the problem?

Luck & Regards,

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

⇩ Closely related postings, oldest first ⇩

Q. I have iron and copper in my Hex chrome bath. What is the remedy? Who supplies equipment for such removal of impurities? Can dummying at low current density help to remove iron?

Kaushik Magiawala
plating shop employee - Gandhinagar, India

A. Iron contamination will cause hazy/cloudy deposit and lower the plating rate. Dummy at low CD can help to remove iron. However, bath dilution is recommended should iron content be too high.

David Shiu
David Shiu
- Singapore

A. Use porous pot technology. It also reduces the trivalent.

James Watts
- Navarre, Florida

A. There is a chrome purification system called a porous pot you should research.

Todd Osmolski
- Charlotte, North Carolina, USA


A. Mr Magiawala

It is practical to sell off the bath to a manufacturer of Chromating chemicals in your city.

Make up a new bath. Mask areas where no plating occurs and prevent further build up due to etching out of the offending metallics again.

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016

A. A porous pot is the key to reducing trivalent-copper and iron.
This product is excellent I have used them for years and works better than dummying.
Be sure to keep them running and fresh clean solution in them at least twice a week or more couldn't hurt just produces more waste. Be sure to block off before doing a reverse if using the same rectifier to plate with. The costs is around $1,100 U.S and are for tanks around 1,000 gallons. They make larger ones but are harder to get in and out of the tanks to check and clean. Just use a hand pump to change solution and take out once a month to clean and check plastisol coating. This is a very good investment.

William Berdet
- Atlanta, Georgia

A. Dear sir, there is an instrument called AAS [on eBay or Amazon]. Analyse your bath for trivalent, copper, zinc, iron, etc. remaining in the bath in ppm. If they exceed some limit then there is a problem, otherwise no worry.

ajay raina
Ajay Raina
Ludhiana, Punjab, India

thumbs up sign Thanks to all. I unfortunately saw answers very late. I never got indications of answers and was wondering why no response.

Kaushik Magiawala [returning]
- Ahmedabad
August 14, 2021

Ed. note: We always notify readers when their posting is published and of every reply. Such notices include a link so you can find the posting, but unfortunately some people's filters are set up to redirect anything with a link to their spam folder.
If you would please 'whitelist' <> it will solve the problem.

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

Chrome Plating Pitting and Metals Contamination

Q. I am a chemical engineer, just started working in a chrome plating shop. We are having some pitting problems, and I am slightly confused about what I have read about chrome pitting and metals contamination. Some people say metals contamination will only cause rough chrome, bad conductivity, but not pitting. Others say metals can cause pitting. (when I say metals, copper and iron seem to be the ones that matter)

Can anyone help set this straight?
If metals do cause pitting, what levels of contamination do I need to stay under?

Mark Robison
Engineer - Ogden, Utah, US
February 18, 2010

simultaneous replies

? Are you plating decorative or hard chrome? What is your thickness? Do you use a mist suppressant?

Jon Barrows
Jon Barrows, MSF, EHSSC
GOAD Company
supporting advertiser
Independence, Missouri
February 2010

A. Mark,

Pitting can come in many forms and have many causes. High levels of metal contamination can cause pitting under the right conditions, but I would look at two other possibilities first.

Firstly check that your pre-cleaning prior to plating is doing the job. If the surface is contaminated in any way after cleaning then pitting is very likely.

Secondly if the balance between the chromium (VI) oxide and sulfuric acid is out this causes pitting (usually a characteristic "teardrop" shape).

If neither of these things prove to be the problem then you will need to dummy out the solution. This is plating a large surface area with a low current density. This will help with the copper contamination. I don't think iron will be that much of a problem, unless it is particularly high.

Finally, get yourself one or two textbooks on the subject. My favorite is the Canning Handbook, but the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] is also an excellent reference book. Also check out the How to section on this website, very useful.

Brian Terry
Aerospace - Yeovil, Somerset, UK
February 2010

Q. We plate hard chrome, anywhere from flash chrome to 30 mils build, and we have no mist suppressant.

Mark Robison
- Ogden, Utah, US
February 22, 2010

Q. Our iron and copper levels are all under 2 gm/L, mostly under 1 gm/L. From what I have read, these levels should be too low to cause problems, do you agree?

Mark Robison [returning]
- Ogden, Utah, US
February 24, 2010

A. Mark,

I certainly wouldn't expect the iron at that level to be a concern. I would be rather more worried about a copper level measurable in g/l, I would normally expect that in the ppm range.

I would consider a dummy plate to reduce the copper levels if I was you.

Saying that, your problem still sounds like a surface cleaning problem or a sulphate:chromic acid imbalance.

Brian Terry
Aerospace - Yeovil, Somerset, UK
February 25, 2010

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

Allowable Trivalent Chrome in Hard Chrome Solutions

Q. What is the maximum amount (expressed as g/L or % of Chromic Acid concentration) of Trivalent Chrome that can be tolerated in a Hexavalent Hard Chrome plating bath?

Thomas Kemp
Supplier - Cleveland, Ohio
November 22, 2011

simultaneous replies

A. A large part of that depends on the amount of grief you can tolerate and the level of other impurities. Many people say that a tiny amount is necessary and that may be true.

I used a porous pot on a regular basis and it took the tramp metal ions out and converted the tri to hex, which took care of two problems.

It can be converted to hex by using a single rod cathode with a large amount of anodes and treating it at a very high amperage.

James Watts
- Navarre, Florida
November 22, 2011

A. In some cases, it depends upon the customers specifications. Some specify <2.5 g/L, but I've seen baths with over 7 g/L of trivalent chromium.

High concentrations of trivalent chromium and iron will decrease plating efficiency, the bath conductivity and throwing power. So if the contamination is high, longer plating time, higher voltages, and more careful use of auxiliary anodes will be required.

Lyle Kirman
consultant - Cleveland Heights, Ohio
November 23, 2011

A. An acquaintance of mine had done a good amount of research on metal contamination in the hard chrome bath. He was able to show that it was the total concentration of cationic metals (iron, trivalent chrome, copper, etc.) that was more important than having unique limits for the different metals individually. According to his study, you want the total contamination not exceed 7.5 g/L. In my own tests which extended his work, I found that limiting the total contamination to no more than 5.0 g/L was a better limit for quality assurance.

Jon Barrows
Jon Barrows, MSF, EHSSC
GOAD Company
supporting advertiser
Independence, Missouri
November 28, 2011

Q. Dear sir, I'm new in hard chrome plating.
Can you please tell me that how the impurity zinc enters the chrome bath when our cathode is of mild steel and the anode is of lead?

Rupesh yadav
gurgaon, India
February 10, 2013

A. Hi Rupesh. When you say that the cathode is steel, may be assume that this tank is only used for hard chrome plating of steel components? (I've seen some small job shops use the same chrome plating tank for hard chrome on steel, and decorative copper-nickel-chrome plating of zinc diecastings).

If you can make your posting a bit less abstract you'll probably get more helpful answers. For example, how much zinc contamination? A one-time event or constantly? What tool or evidence are you using to determine that you have a zinc contamination problem? Thanks!


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
February 10, 2013

July 3, 2013

Q. Hello, I'm working on the Chrome Plating process in a PVC processing company. The bath has high levels of contamination; this is the last analysis that was made:
Chromic Acid: 31,8 %m/v (42,3 oz/gal)
Trivalent Chrome: 1,32 %m/v (1,76 oz/gal)
Hexavalent Chrome: 1,3 %m/v (1,73 oz/gal)
Total Chrome (as Cr): 15,3 %m/v (20,4 oz/gal)
Chloride (Cl-): 4700 mg/L
Cadmium (Cd): 7,1 mg/L
Mercury (Hg): 0,031 mg/L
Arsenic (As): 0,12 mg/L
Lead (Pb): 31 mg/L

We are looking into the purification of this bath and was looking for recommendations.

Thank you for your help.

Andrea Mangel
PVC Company - Coyol, Alajuela, Costa Rica

A. I thought that hexavalent plus trivalent chrome had to equal total chrome in solution.

I think that your chloride is very high. Chloride is about 10 times stronger than sulphate as a catalyst. Unfortunately, it does not remain constant, so is bad.

If you can find one, a porous pot will do a wonderful job of removing trash ions and converting trivalent to hexavalent.

I used Hard Chrome Consultants in Cleveland, OH for mine. I think they went out of business a couple years after Clarence Sr. died.

There a few companies that sell this equipment as an outside of the tank set up, but they were extremely expensive.

James Watts
- Navarre, Florida
July 5, 2013

October 10, 2019

Q. Hello,
I have 5000 Litres of chromic acid which is contaminated with copper (4.51 g/l). When this chemical is used we face coverage issues so it's right now stored idly. I do not wish to discard all this chemical so I'd like to know of a way to reduce this contamination. How do I go about it?

Full test report:
Chromic acid: 253.8 g/l
Trivalent chrome: 98.49 g/l
Sulphate: 2.71 g/l
Copper: 4.51 g/l
Iron: 1.46

If anyone detects any other problem in the constituents I'd love to know.

Ashutosh Harish
Hard chrome plating - Bangalore, Karnataka, India

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