Nickel plating / striking on stainless steel

A. My initial thoughts are that the nickel plating is not thick enough and the sodium chloride testing "mist" is getting thru to the stainless steel,.

A. Hi Kse
In addition to Robert's comment, I have two additional thoughts.
• Is there any chance that some of these parts are occasionally vapor degreased? A vapor degreaser with old solvent can be a very aggressive chloride based acid.
• Have you considered having the testing done by a backup lab? Salt spray test results sometimes vary very widely from one testing lab to another, perhaps because one of them is doing something wrong.

Luck & Regards,


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

A. For plating Nickel on Stainless steel - almost for sure "Woods" Ni strike is used (mix of Ni Chloride with Hydrochloric acid).
Maybe the whole Ni layer is plated from the Chloride bath. However Chlorides should not stay on the part, unless it was no/bad rinsing and no neutralization after the plating.

A. Hi Nanaso.
Your question is very broad, and I don't think anyone can fully answer it in the few paragraphs appropriate to a public forum ... but the overall thrust of the subject is that stainless steel very quickly grows an oxidized surface, and plating cannot properly be done on top of that oxide, or the adhesion will be very poor.

So it is usual to do a nickel strike, usually a "Wood's Nickel Strike" as the first plating layer. This operation is very similar to regular nickel plating, but it uses a plating solution with a lot of strong acid and a low concentration of nickel at about double the usual amperage of nickel plating, that simultaneously dissolves that oxide on the stainless steel while depositing a very thin layer of nickel plating in its place. Other plating can then be done on this nickel layer.

You can search the site for countless threads on the subject of nickel striking, and Jack Dini's Electrodeposition [affil link on Amazon or on AbeBooks] has a good chapter titled "Adhesion" which explains this subject a bit further, while Crotty & Probert's "The Sulfamate Nickel How-To Guide" ⇨
offers some practical advice on both the Wood's Nickel Strike (they call it the 'all-chloride' strike, but I knew Donald Wood and will continue to honor his contribution to the subject), and an alternative sulphamate nickel strike.
Luck & Regards,


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

A. Hi E.J. Yes, stainless steel definitely requires a preplate sequence which includes a nickel strike. The very best treatment of that subject is in Jack Dini's book, "Electrodeposition ..." ⇨

Yes, 30% is a ludicrously high reject rate; but it is believable, because when a plating process is done wrong, there is no upper limit on the percentage of rejects.

I don't know how you can afford your parts being a learning experience for a plating shop 12,000 miles away which makes excuses for their incompetence when there are surely shops right in the Kansas City area who can deliver a 99.9%+ pass rate on those parts tomorrow morning :-)


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

A. You need a high chloride bath Nickel Wood's Nickel
                  Range          Optimal
Contents: Nickel 80- 96 gr/lt,  88 gr/lt
Nickel Chloride 420-467 gr/lt, 434 gr/lt
Chlorhidric Acid 70- 82 gr/lt,  75 gr/lt

3 to 5 volts

I hope this can help you.

Regards,

A. Wood's nickel is the most popular. It consists of a highly acidic, low efficiency, all chloride nickel solution prepared with 250 g/L nickel chloride, 250 mL/L conc. HCl, rest DI water. Operated at room temp, 20-100 a/sq-dm, anodes pure nickel.

A. If you have to ask this question, you really need a good reference book on plating.
A nickel strike is a very thin coat of a nickel that will stick to stainless that has been properly cleaned and activated. Typically a Wood's Strike is used. It is a very high chloride bath at a very low pH that plates very slowly and is extremely highly compressive stressed, so you only want enough of a coat to barely give a "color".

A. Are you rack plating or barrel plating? If you are barrel plating be sure to have good pump agitation as well as a slightly higher HCl concentration. Stainless Steel is not as tricky as some would make it seem. Also try to remember that a Ni strike normally requires a higher current to strike parts. Consider covering surface of your bath with plastic balls, available from plating supply companies, to reduce surface fumes. Good luck!

Regards,

A. Hello, Paulina. It's not clear to me if you are following up on E.J.'s question. In general, nickel can be stripped from steel relatively easily, but not as easily from stainless steel because they are somewhat similar. In this case, unless it lacks adhesion, it is more common to try to reactivate the nickel than to strip it.

Good luck.


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

A. Hi, B. In electroplating, the adhesion is molecular, not based on mechanical "keying" as in painting. So either sand blasting or vibro-finishing can be used, depending on what you want the surface to look like.

If sandblasting is practical and convenient for your parts, it's ideal, but you still need the Wood's Nickel Strike before the nickel plating and cadmium plating.

The allowable time lapse depends on your handling and your intentions. For example, if you are going to immediately plate, sandblasting is the only prep you may need before the nickel strike. But if the parts are going to hang around for a couple of days, you will need to alkaline clean them and acid activate them immediately before the nickel strike. The best approach is surely to plate immediately after blasting. Good luck.

Regards,

A. Hi, Mannu. When you say nickel on stainless, it isn't clear that you are applying a Wood's Nickel Strike as explained above. Please give full composition and plating conditions of the nickel strike you are trying to apply. Thanks! Jack Dini's "Electrodeposition" has an excellent chapter labeled 'Adhesion' which gives adhesion values for various approaches to nickel striking stainless steel. Please check it out. Good luck.

Regards,

A. Hi again.
If it's the gold plating peeling off of the nickel plating, rather than all of the plating peeling off, then probably you are either waiting too long to begin the gold plating (you should quickly rinse the nickel, then immediately go into the gold plating bath) or there is an excess of brighteners in the bright nickel plating. Good luck.
Regards,


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

A. Hi Jurek. We appended your inquiry to a thread which implies the answer: Electroplating must be done on bare metal (not tarnish or oxides) for proper adhesion, but stainless steel instantly forms a passive oxide on its surface which prevents that proper adhesion. The most popular way of addressing that problem is to start with a Wood's nickel strike or other nickel strike. Being highly acidic, it dissolves the oxide, while simultaneously applying a thin layer of nickel plating to the bare stainless steel. The book by Jack Dini that you referenced.
is excellent once you understand that the chapter in question is titled "Adhesion", and it's all about the best procedures for getting good adhesion onto stainless steel with a nickel strike.

Regards,

A. Hi Jurek. The short answer is, of course, that stainless steel is nickel plated when the surface properties of nickel are better suited for the application in question. If you search this site for "nickel plating stainless", you will see a number of applications discussed. For example, nickel will have much better surface conductivity and will be a much better electrical contact than stainless steel; also, as you suggest, it will be more readily solderable; it may be more corrosion resistant in certain environments. Also, the nickel plating may be necessary before other types of plating like gold plating can be done on the stainless steel. But it's not possible to list or predict every possible application where the surface properties of nickel would be more desirable than those of stainless steel. Good luck.

Regards,

A. Hi Asa,

You can find formulations for nickel strike in any decent text book on plating, such as the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] , the Canning Handbook [on eBay, Amazon, AbeBooks] and the Metal Finishing Guidebook. These include formulations, temperatures, voltages, etc.

It sounds like you have to go back a bit further than the nickel strike to start your investigation.

Firstly look at your degreasing and cleaning process, are you getting a water-break free surface? Yes - good, No - time to investigate your cleaning process.

Secondly look at your etching process prior to nickel strike. Are you using one? For stainless steels I would highly recommend it as the steel will have a naturally passive layer on it that needs removing before plating.

Next it is important that you do not delay from nickel strike to the plating tank. From nickel strike you need to rinse and be in the Zn/Ni tank within 2 minutes. Any longer and you'll end up with a passive nickel strike.

That should get you started down the right road to a robust process.

A. Hi Asa,

A couple more questions:

Do you know if the plating is failing between the base materials and the nickel strike, or is it failing between the nickel strike and the Zn/Ni plating?

If you find that it is failing between the base material and the nickel strike it indicates either a problem with the nickel strike or the pre-cleaning.

If it is failing between the nickel strike and the plating then it may be the nickel layer going passive or you may have a problem with the Zn/Ni plating process.

The nickel strike is designed to give a very thin, adhesion promoting coating on the surface of the base material. I must admit I have never checked the thickness of the nickel strike, but it would certainly be less than a micron, so I would guess the thickness is probably in the right ballpark.

If the nickel strike is acting unpredictably it could be due to a build up of tramp metals in the tank (usually copper and/or iron). You can do one of two things about that, either dummy out the metals (large surface area cathode, low current density) or dump and re-make the tank.

? You left out a lot of importance. What is your strike chemistry. Have you checked for tramp metals in solution. What are your anodes. Are the bags clean. What is the parent metal, not just SS. What is your agitation. What is your anode to cathode ratio? Tank temp. Exact pre-plate cycle (all of it)

A. Hi Jurek. The nickel plating deposits in proportion to the current flowing to the particular area (see Faraday's Law of Electrolysis). And the current flows in accordance with Ohm's Law (the greater the resistance, the lower the current flow). And the resistance between the anodes and points inside that 2 mm channel is very high compared to the resistance to points on the exterior. So little if any current will flow and little if any nickel will deposit.

Within reasonable limits of thickness the adhesion will not be determined by the thickness. Good luck.

Regards,