Copper Nickel Chrome Plated Parts Fail CASS Test

A. Hi George. While it's true that ions in a plating bath prefer to take the path of least resistance, such that the plating thickness is greater at corners than in recesses, I don't think the term 'Faraday Cage' is applicable to this phenomenon.

I'm not sure what you mean by '3/4 inch rule' -- maybe you're referring to the fact that thickness specifications often require a minimum thickness for any spot on the part that can be touched with a 3/4" dia. ball? Similarly I don't know your '1-1/2 diameter throw rule', but perhaps it relates to an expectation of plating coverage in holes to a depth of 1-1/2 times their diameter. This may be possible for some types of plating, but I think it is unrealistically optimistic for chrome plating.

I would start with the chrome coverage problem and figure out what you need to do. A Hull Cell test will reveal whether your plating solution is deficient or whether you need an auxiliary anode to get chrome coverage in the recesses. It should not be too hard to gauge progress because you will be able to see from the yellowish color of the nickel where you are failing to get chrome coverage.

Once you have good chrome coverage, if you still are failing the CASS test, you need to get better nickel thickness distribution. Again a Hull Cell will warn you if the solution is deficient. If it isn't, your experience with auxiliary anodes will guide you toward one way to solve the current distribution problem, and the use of simple polypropylene shields to block the high current density areas is another.

Can you expound on these 'lot of cracks'? I don't know quite what you are talking about there, but if the nickel plating is cracked, it may be further indication of something amiss with the solutions. While you can get improved thickness distribution by electroless nickel plating in place of your nickel chrome plating or prior to it, you probably shouldn't discard this ideal solution, copper-nickel-chrome plating, just because it has to be done well. Although it's an expensive solution, you could electroless nickel plate before the nickel-chrome plating. Good luck :-)

A. Hello sir,

You need Good Pretreatment. No rust , No dirt. Clean plateable surfaces. You need Semi-bright sulfur free Ni 18 microns. You need a second layer of 12.5 to 15 microns of bright Nickel. Followed by 0.25 minimum Bright decorative chrome.

Regards

A. Dear Mr Gopinath,

96 hours CASS is a tall order. Tri- Nickel followed by microcracked chrome will probably get you past 48 hours.

Regards,

A. Dear Gopi,
Nothing like experimenting with different processes of cleaning, bath filtration and thickness.

A. DEAR SIR,

96 HOUR SALT SPRAY CAN BE EXPECTED BY 20 MIC HARD CR OR ELECTROLESS NICKEL. I RECOMMEND YOU ELECTROLESS NICKEL.

A. Thank you for giving me the opportunity to run my opinion up the flag pole and see what people have to say, Xiaolin: which is that there is no correct thickness because single layer nickel plating should not be used if 96-hour CASS test is required :-)

A. Dear Xiaolin,

40 microns is much too thick for a single deposit, the stress will make the deposit crack. You should use a semi-bright Ni and then a bright Ni layer. Contact a plating chemical supplier and they will be able to help you.

Regards,

A. CASS test is a function of additive chemistry for duplex nickel layer. You have not mentioned what type of plating you are carrying out.

You can try periodic reversal cleaning in alkaline+cyanide type cleaner for good results.

A. Mr Bhatia

Ask your principal to give you a spec sheet of thicknesses to follow for SB nickel, Tri Nickel and then Bright Nickel followed by Chrome plating.

Here is a rough guide for that 48 Hour CASS dream..
SB Ni. 15 - 17 Microns
Tri Nickel. 2 microns
bright Nickel 7 to 12 microns
Chrome 0.3 - 0.35 microns

Hope you get the CASS results with this direction.

Regards

A. Mr. Bhatia,
Improve the filtration in all the SB/Tri/Bright nickel baths.
Also check that no traces of bright nickel solution is allowed to enter into semi bright nickel.
Thanks,

A. Try 35 microns of Nickel.

A. I agree with Ms. Sara: by increasing nickel you will get good results if the basic raw material is ok; check the surface roughness before going for plating, and also increase the layer of chrome up to 0.7 µm to 0.9 µm.

A. I would not advise a higher chrome deposit. Over 0.5 microns you will get cracks instead of micropores.

A. As I know to get higher CASS result is not only the thickness of the nickel, on other hand thickness in Asia for Triple Nickel layer is maximum 20 microns, beside that to plate up to 35 microns I think a bit costly especially now where the nickel anode price is very high.

In modern nickel plating bath system for multiple layer I think we need to consider the STEP value, this value should be above 100 mV between semi-bright and bright nickel to get good corrosion resistance, beside other parameter like roughness due to poor filtration and bad housekeeping and don't forget the surface of the parts.

Good luck,

A. Hi, Carsten. 48 hours is a "very severe" CASS (ASTM B368) test. So your plating needs to be very good to withstand it. You should have duplex nickel plating (semi-bright nickel followed by bright nickel), rather than single nickel plating, and microporous chrome.

Remember that the CASS test, and all accelerated corrosion tests, are Quality Assurance methods to make sure something hasn't gone wrong. Obviously something has gone wrong, but it's hard (maybe impractical) to troubleshoot a process from thousands of miles away. My own experience has been, however, that when copper-nickel-chrome plated diecastings start going bad, it's usually because the quality of the diecastings has gone down. You're not going to properly plate a diecasting that has porosity or a cold shut.

Regards,

A. The corrosion test reveals porosity. Check the surface to be plated for pores. If none are found, the pores may be caused in your preparation procedure. Avoid etching. Be sure that the filtration is adequate in the nickel plating tank and that there is no airborne particles that can get into the plating solutions. Thicker nickel plating layer would be helpful, and the dual nickel - porous chromium is the best process for corrosion protection.

A. Hi Dinesh. Usually the buyer/designer will specify the CASS test hours based on how he perceives the exposure conditions to be. The National Association for Surface Finishing (www.nasf.org) has (or had) a series of "Quality Metal Finishing Guides" for various finishes. The chart below comes from page 18 of the "Decorative Copper-Nickel-Chromium" guide. Good luck.



Regards,

A. Hi Stanley. As you see, we added your letter to a thread on the same subject, which should at least partially answer it for you. I'd consider that exposure "very severe". But it may be best to not use ASTM B117, and use CASS testing per the discussion. Good luck!

Regards,

A. Hi Yuva. A quality nickel-chrome finish is a wonderful and beloved finish. But a low-quality nickel-chrome finish accelerates rather than retards corrosion because nickel is a "barrier layer" coating which is cathodic to steel. If there is porosity or pinholes, the steel becomes a sacrificial anode and protects the nickel by rapidly rusting away.

You are calling for 20 microns of nickel, which is appropriate for "moderate" exposure (indoors in kitchens and bathrooms), but are getting 8-9, which is short of the minimum 10 microns for even mild exposure. The first step in improving the process is very simple: do not accept less than 20 microns. At some later date you might cut back to 15 microns if the chrome plating is top notch. Good luck.

P.S. 1: what are these "stay rods" used for?
P.S. 2: I'd be very suspicious about a claim that an 8-9 micron plating which rusts in 48 hours in the atmosphere survived 42 hours of CASS testing.

Regards,

A. Hi Vishal. We've jump-started an answer for you by appending your inquiry to a similar thread. To pass 50 hour CASS test, while keeping the nickel thin enough to not peel from a spring surely requires duplex nickel plating or tri-nickel. Please tell us your plating spec. Thanks.

Regards,

A. Hi Avinash. I doubt it. On this and other threads, Triplex nickel is suggested. It's possible with duplex nickel, but would probably require almost twice your thickness of both nickel and chrome. Good luck.

Regards,

  Thanks Ted for your immediate response. I am also doubtful about this specification and hence asked the question.
Thanks again for your response.