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"Stripping Cadmium plating and choosing a method"

adv.
Metalx nickel stripper

Current question and answers:

February 25, 2021

Q. Hi,
We are working on replacing cadmium plating with nickel on a bunch of old steel parts. We are stripping cadmium in HCl which works great and some parts come out of the batch nice and clean and ready to be replated. But some parts end up covered in some black residue after cadmium had been stripped. Literally two identically looking parts would be sitting in the same HCl tank and one will come out clean and the other covered in a layer of black residue. Probably those parts come from different manufacturers using different processes or what not. We can wipe that residue off the part and then plate it, but that's time consuming.

So I was wondering does anyone have any ideas what that black residue could be and whether there's a relatively easy way to dissolve it too.

Walt Tuchi
- Chicago Illinois
^

none
adv.
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February 2021

A. Hi Walt. HCl does not dissolve carbon, and smuts like this are a commonplace headache for platers even working on fresh parts. If you want to continue with HCl stripping, some possibilities for improvement include reducing the immersion time or concentration, or employing an 'inhibitor' in your acid to limit attack on the steel.

Nickel is an unusual replacement for cadmium because it is so very different in all of its characteristics. If you're still at the initial stages of planning the project, please think it through carefully.

Luck & Regards,

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


February 25, 2021

Q. Thank you for the response! Just to make sure I understand: are you saying that the black residue comes from carbon in the steel? I.e., that HCl attacks the steel but leaves behind the carbon embedded in the steel because HCl cannot dissolve it? But I am not sure that's the case because once we strip the cadmium and wipe off the black residue we can put the part back into the same HCl bath and it won't develop black residue again. Could there be another explanation?

I'll think about your comment regarding Cd vs Ni, thanks

Walt Tuchi
- Chicago Illinois
^


February 2021

A. Hi again. Yes, that's my belief. We'll see if anyone else offers an alternate explanation for the smut.

Luck & Regards,

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


February 26, 2021

A. Hi Walt,
We use ammonium nitrate to strip cadmium from steel parts. It is made up at 200 g/l, good mixing is required during the dissolution as it is endothermic.
When it slows down we add further ammonium nitrate to about a third of the original addition. Then dump it.
The solution goes blue in colour, eventually to brown as the solution gets old. You will need a good disposal site to send the spent and cadmium rich solution to.
Also we air agitated it when in use as well as LEV.
Best regards
Mark

Mark Lees
- A rock, in the Irish sea.
^


April 15, 2021

A. As was stated earlier, Ammonium Nitrate works well, but has a short bath life. At 1 lb per gallon, the bath works very quickly, with agitation in the bath of course (I use a pump). As to what the smut on the carbon steel parts is, I'd say some sort of amorphous iron oxide product. I find that weak pickle of oxalic and sulfuric acid can be used to desmut steel, by means of short immersion at 100-150 °F. The oxalic really does the desmutting, the sulfuric is there just for acidity.

Waltteri Vakki
- San Diego, California
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April 17, 2021

Steel is iron to which has been added other elements - mainly carbon. The black smut is carbon, which doesn't dissolve in anything. Platers used to talk about stripping plated surfaces and 'bringing the carbon to the surface" - which wasn't what really happened. What really happens is the a stripper dissolves the iron leaving carbon as smut on the surface.

tom_rochester
Tom Rochester Plating Systems & Technologies, Inc.  


supporting advertiser
CTO - Jackson, Michigan, USA

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^


June 18, 2021

? Good Morning!

What alloy do you tend to have issues with? I'm not very familiar with stripping coatings like this but am very familiar with passivation. We often see this on free-machining alloys during pickling/passivation, and it's the same story: same part, same rack, same tank. One part looks great and the other turns black.

In our case, this is attributed the free sulfur on the surface from insufficiently cleaned/polished parts. I'm unsure how you would clean the surface between the stripping and replating the part. However, we find a hot, high pH cleaner gets most of the residue off. Extended alkaline clean times prior to treatment tend to prevent some of this, but we can never control what is sent to us.

adv.
Again, I am not too familiar with Cd stripping or your operation, but CitriSurf/Stellar Solutions may be able to help you. Their technical team is brilliant, and they might have more experience with broader uses.

M Kim
Chemist - Williamsburg [NY Kim? --almost every state has a Williamsburg :-) ]
^

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Ed. note: We can't suggest brands & sources in this public forum (why?), so when someone suggests one of our supporting advertisers -- as in the case here -- we label it an advertisement.




Previous closely related Q&A's, oldest first:

1999

Q. I am wondering why someone would choose to abrasively blast off cadmium plating rather than use ammonium nitrate. What sort of test can you do to make sure the tank is charged at the right strength? Also, if you MUST blast the cadmium plate, what sort of media would you use? Are there alternative chemical strippers for cd plate? Thank you!

Carrie L. [last name deleted for privacy by Editor]
- Seattle, Washington
^


1999

A. Abrasive blasting of cadmium is a bad idea unless all the contaminated air is trapped in a sealed container and filtered before releasing to atmosphere. For released air, OSHA emission limit is <2.5 ug/cu.m. Ammonium nitrate should be inexpensive and adequate in most cases.

Mandar Sunthankar
- Fort Collins, Colorado
^


1999

A. Wow, someone is blasting cadmium! Not a good idea (see above) but isn't it, like zinc powder, explosive? Nitric acid @ 50% vol/vol can also be used to strip cad but you have to watch out for the nitric attacking the substrate.

Megan Pellenz
Megan Pellenz
- Syracuse, New York
^


1999

Q. Thanks for the thoughts. I think some places require at least a light blast prior to replating - doesn't it make the new cad plate "stick" better? Also, I guess cadmium plated parts with Be-Cu or Al-Ni-Br substrates could be damaged by ammonium nitrate (anyone know if this is true?).

Carrie L. [returning]
- Seattle, Washington
^


2001

A. Anytime you blast a substrate prior to plating it enhances the bond strength. This strip will not affect copper or aluminum as a direct substrate, however, alloyed materials are always a difficult call. The best way is to run a test sample part to determine the outcome.

Q. I am searching for the contents of MIL-8-175, it is the mil-spec for the stripping process, can anyone help me get or know where to get a copy?

Thanks.

Paul Arato
- Toronto, Canada
^


2001

A. Hi, Paul. I am not finding such a spec. I think perhaps your reference may have gradually become corrupted, by typos, transpositions, or smudges and maybe you're looking for MIL-STD-871 [link is to spec at dla.mil / Defense Logistics Agency] :-)

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


March 20, 2009

A. STRIPPING USING ABRASIVE METHODS IS THE BEST IDEA WHEN THE MATERIAL IS HIGH STRENGTH STEEL.
This takes away any chances of the process damaging or chemically altering the material.
Many Aerospace OEM's require baking after chemical stripping. This just to ensure that hydrogen pick up is bled out.

Terry Martin
- Toronto, Ontario, Canada
^


July 9, 2013

A. A simple chromate solution, with 13-15% nitric acid, will strip cadmium off of 4340 type steels without any damage to base material.

Larry Wasowski CEF
- Queen Creek, Arizona, United States
^



Pitting of Forged 4340 when stripping Cadmium Plate in Ammonium Nitrate

2005

Q. We have a cyanide-cadmium plating bath, and our cadmium strip solution is 5 years old and currently at 16 oz/gal Ammonium Nitrate. Recently, it has caused pitting problems on 4340 Forged Steel parts, we would like to know:
1. What are possible contributing factors for the pitting?
2. What are limiting factors as far as metal contaminants are concerned in the Ammonium Nitrate solution?

Thanks.

Jim Cummings
aerospace chemical processor - Wichita, Kansas, USA
^


2005

A. For a strip tank to be 5 years old, it is either a huge tank, or you have darn few parts stripped or your strip is so slow that the parts are selectively rusting in the strip. Test some parts in the lab with a new strip and if they are fine, do not waste your time trying to save a tank--dump it.

James Watts
- Navarre, Florida
^


2005

A. As a rule we dump our Cadmium Strip every six months and make up a new solution.
Ammonium Nitrate is relatively inexpensive and easily made up.
I think five years is far too long to be using this strip.

Frank Dunleavy
aerospace plater - Dublin, Ireland
^



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 :-)



2004

Q. Hello everyone...

I'm in a desperate situation. I have received an order of $10,000 USD. in MS5015 MIL connectors that are 316SS finished with black cadmium. Now, I have known that our requirements from the UK Navy states that no cadmium is allowed on their vessels, but I goofed and ordered the wrong part number. I have searched for answers here regarding stripping the CAD off, but I am an electrical designer with NO experience in finishing/plating etc. So, I turn to you. Am I going to have to eat the cost of these connectors, or is there a feasible way that I can send these off to be stripped? ANY suggestions would be greatly appreciated.

Thanks

Ron

Ron S [last name deleted for privacy by Editor]
Manufacturer - Peterborough, Ontario, Canada
^


2004

A. Stripping cadmium is not a big deal, Ron, but shops that don't plate cad don't want to strip it because it leaves them with a hazardous waste they don't want. So you'll probably need to find a shop that does cadmium plating. The parts will have to be replated with something, perhaps zinc or tin or nickel. Find a shop that offers cad plating and they can easily strip them and plate them with something else.

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


2004

A. There are quite a few plating shops in Toronto and Ontario that still do CAD plating. Most likely they can strip them for you.

Pablo Flores
- Toronto, ON, Canada
^


2004

A. You can strip the cadmium in 30% HCl very quickly. Again, as others have stated, the acid and rinsewaters will be contaminated with cadmium so it may actually be more expensive for you to dispose of the waste as opposed to the cost of the parts. You really should find a job shop who is willing to perform this task for you.

Daryl Spindler
Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
^



Stripping of Cadmium per BAC5771

May 25, 2010

Q. After stripping of cadmium titanium alloy plate, BAC5771 requires the parts to be dipped in 3 to 6 percent hydrochloric acid for 30 seconds. Followed by hydrogen embrittlement relief bake. This step is not required for parts which will be subsequently cadmium titanium plated.

This step is not required for stripping cadmium plating. Is it possible to identify if a part has been cadmium plated or cadmium-titanium plated?

Wayne Samsonoff
Plating Shop QA - Kelowna B.C. Canada
^


May 27, 2010

A. I've seen that requirement before and I found it pretty strange as well to have a ti-cad specific requirement since ti-cad plate is 99.5% cadmium. Oh well. For all practical purposes, I think that you will need to assume that your part plated with an unknown cadmium coating is ti-cad and follow that post-strip HCl dip and then bake if required. When you think about it, it is most like going to be Ti-Cad simply because, unless I am mistaken, there are far more platers performing BAC 5804 plating compared to BAC 5718 plating. If you really want to know if it is Cad or Ti-Cad, then I do believe that a good XRF will show the presence or absence of the Ti peak. Depending on the size of the part, that could be an option. If you decide by XRF that it is not ti-cad, you will probably need to save the evidence of your validated determination as part of your quality record for the part. Good luck.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
^



April 10, 2012

Q. Does glass bead blasting to remove Cadmium Plating from an aerospace rivet remove all of the Cadmium necessarily and will a Hydrogen embrittlement bake be required after the glass beading of the rivets?

Don Kelley
- Mesa, Arizona, USA
^


April 13, 2012

Hi Don,

A. I would not recommend blasting to remove cadmium, it will have two undesirable effects, potential for dimensional change and the fact you will contaminate your blasting cabinet with cadmium, so you will have to discard the blast media as hazardous waste and clean the cabinet.

I would recommend using ammonium nitrate solution, 10-30%. This will not cause dimensional change, but do not leave the parts in the solution too long or you may have a surface corrosion issue. De-embrittle in accordance with AMS 2759/9.

Brian Terry
Aerospace - Yeovil, Somerset, UK
^



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 4, 2014

Q. A supplier of ours stripped cadmium plate from a lot of NAS [National Aerospace Standards] bolts, and re-coated with Black Oxide. When chemically stripped do the parts require embrittlement baking prior to recoat?

Bob Newkirk
- Valencia, California USA
^


June 2014

A. Terry Martin is certainly correct that acid stripping of high strength steel can cause hydrogen embrittlement and these bolts may now be defective. Considering that these are supposed to meet an NAS specification, I think it is worthwhile to acquire the particular spec covering the bolts in question and see what it has to say on the subject of hydrogen embrittlement. Good luck.

Regards,

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


June 10, 2014

A. We use plastic bead blasting when type 2 cad is applied and needs stripping. This to ensure the chromate is removed prior to cad strip in ammonium nitrate according to Mil-Std-871. Use breathing protection anytime when blasting whatever material with whatever media - any dust is bad for your health! Never use abrasive blasting to remove cadmium. You can't tell when all cadmium has been removed and you'll probably damage the base material.

Ammonium nitrate works perfectly. However, make sure you have thorough air agitation on your tank. Embrittlement relief baking per Mil-Std-871 is not required with this method. However, quite some CMM's (in the MRO business) require you to bake anyway. Make sure you use an alkaline soak then prior to baking to prevent bad corrosion.

By the way, one of the posts above states that blasting will always improve adhesion; that is not true. Al2O3 grit blasting will cause embedded grit in the base material, even in ultra high strength steels, which will cause adhesion failures in hard chrome or nickel plating without rigorous pretreatment (HF pickling) after blasting prior to plating.

Jeroen Visser
landing gear - Geldrop, The Netherlands
^



December 2, 2020

Q. We are having lots of issues with our Ammonium Nitrate cadmium strip.
Any troubleshooting ideas?

David G [last name deleted for privacy by Editor]
- N.Andover Massachusetts
^


December 2020

A. Hi David. Jeroen notes that you need "thorough air agitation" -- have you addressed that? Please try to offer examples or specifics regarding "lots of issues". Thanks!

Luck & Regards,

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


December 2, 2020

thumbs up sign Great suggestion thank you. I tried to suggest it but was shot down. Maybe it will happen when I get a heater for our sulfamate Ni strike ... which is never

David G. [returning]
- N. Andover Massachusetts
^

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