Stripping Cadmium plating and choosing a method

? Hi Jan. Thanks, but isn't phosphoric acid the mojo in naval jelly, rust converter [on eBay or Amazon] s, and iron phosphating? Does it leave a bare steel surface or does it leave a black rust surface? Sounds to me like if you're going to paint the item after stripping the cad, this might be doable. But if it leaves a black rust or phosphated surface it might not be suitable for plating?

Luck & Regards,

A. Hi Jan. If it works, it works. But I would not expect good adhesion of plating onto a black rust or phosphate surface. I'd suggest trying some adhesion tests like the strongest adhesive tape you have, bending components that can be bent (like perhaps flat washers), or chisel tests.

Luck & Regards,

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.

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.

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.

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] :-)

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.

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

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.

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.

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.

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.

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.

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.

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 AMS2759/9.

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,

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.

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,

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

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,

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

Luck & Regards,

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

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.

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.

? 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.