• Topic #41906 "Dummying" an electroplating bath?"

A. Hi Khozem.

Yes the zinc and copper displays on the low current areas. Plate the bath with a dummy sheets and use a low current for copper 0,1-0,3 amp per dm2 and for zinc 0,2-0,5 amp per dm2. You must also inspect the bath if the part dropped from the rack. About the chrome solution, following reasons will make burning on the HCD areas. High temperature, Low CrO3, High ratio between CrO3 and sulphate acid, the current being turned on too fast.

Regard
Anders

A. Hi Khozem. Anders is correct that the Cu and Zn will deposit in the low areas and cause them to be dull. Getting the parts out that fall in the tank is imperative. They dissolve fast. A regular schedule of low current dummying will keep those metals below the level they start to interfere. We also send samples to a lab to have the levels checked. It only takes a few ppm of either metal in the bath before it starts to show. They do have additives that will complex these metals temporarily but they are just harder to remove later.

A. Hi Khozem,

I too agree with both Andrea & Jim, but we plate these contaminants out by adding GW Additive 42; though the deposit is a little dull but its not black. Also try keeping pH on the higher side. You can avoid decanting by just placing a mesh tray coated with PP at the bottom of the tank, this way you'll just have to raise the basket and take out the parts if any fall in the tank.

A. Dear Khozem ...all the above suggestions are very good. We run the pH at 4.2-4.5 and check at least hourly. Makes for smaller additions to adjust the pH. The temperature we found of the nickel in this application was 138-142 °F. Decorative chrome should be 108-115 °F -- I try to keep it 108-110 °F.

A. Dear Khozem

We also experience the same chemical burning on our Mazak 3 die castings we have tried many different ways to plate this very difficult material but however thick we lay down the copper the acid nickel still gets through and attacks the Mazak leaving the black marks. Jig plating is a solution but the cost is prohibitive compared to barrel plating. We are investigating other finishes than nickel but so far have had no success but we will let you know if we find one

We also experience discolouration of the bright zinc , we believe that this is due to contamination of either zinc or magnesium in the nickel bath this can only be removed by electro cleaning the bath which then goes back to a bright nickel finish.

If we could find a reliable UK plater we would be over the moon.

But we haven't found one yet

We wish you good luck in you solution to the problem

Best Regards

Thanks everyone for the advice. Mr Stuart, despite all the common difficulties, we still consider ourselves as reliable platers! As labour is cheaper in India, we are yet Jigging and not Barrel plating. Ball pen tips made of Mazak are also being successfully Barrel plated only with one hour of heavy copper undercoat using a potassium cyanide based copper plating.

Regards,

A. Plating of Mazak will always end up with zinc and copper impurities in the nickel solution. It is true that there are commercial additives (usually named purifiers) that give a temporary relief as they create a complex with the zinc metal in the nickel solution. It turns the black low current density into dull nickel. But remember, these additives are temporary and help for a day or two only. Dummy plating is necessary every few days when plating Mazak. Try to add hydrogen peroxide prior to the dummy plating. Regarding the chrome solution, well, the copper and zinc can cause throwing power problems but NOT burning at high current densities. If you have burning problems, check the parameters mentioned by Anders like, chrome/sulphate ratio, temperature, current density, contacts, etc.

Q. Dear Sara M,

When we dummy the bath we generally reduce the pH to about 3 before dummying although we have never tried adding Hydrogen Peroxide. How much do you recommend ?

Thanks in advance,

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

A. Tom.

I hope you use pre-contact.You should use filtration with a cationic system like nickel purifier (Atotech). Best regards

A. Hi, Upali. You are not attempting to plate acid copper directly on zinc diecastings, are you? That won't work; you must start with cyanide copper plating (or copper pyrophosphate). Good luck.

Regards,

A. Hi, Upali.

You must achieve 100 percent pore-free copper layer in the cyanide copper. The process cannot work if any zinc is exposed in the acid copper tank. And then you probably should also enter the acid copper tank with a live lead so the copper (and zinc) does not dissolve in the acid copper tank. Good luck.

Regards,

A. Hi Kushal. We appended your inquiry to a thread which covers some of the issues of copper, nickel, chrome plating of Mazak. If you read between the lines, you should align yourself with a process supply house who will sell you those chemicals, and give you the operating parameters, and help you troubleshoot the issues. The principal advantage of automation is labor savings. Manually carrying racks of work from one tank to the next can be a drudge. Good luck.

Regards,

A. Hi Ashok. Barrel plating of zinc diecastings isn't easy, as you have read on this thread. Blisters can be due to a number of causes, but the first suspect when plating diecastings is parts with porosity or cold shuts.

I can't give you a typical reject rate from diecasting, especially since continuous improvement should be constantly reducing it. But I can tell you that you will not satisfactorily plate parts which have porosity or cold shuts, so there's your starting point on what portion of your diecastings are rejects.

Regards,

A. Hi Ashok. We have numerous threads on line here that answer each of your questions and I can refer you to them if you wish; or, if you'd like a more tutorial approach, we can point you to plating books that have good chapters on nickel plating. But before sending you off on possibly the wrong track: two comments.

1. Suggestions regarding nickel plating parameters should generally be under the direction of your nickel plating process supplier.

2. Copper and Zinc contamination, and minor variations in nickel plating pH and temperature, are unlikely (in my experience and opinion) to manifest themselves as a "peel-off problem". If you are sure that the acid copper is fully adherent, and the nickel will not adhere to it, I think I'd suspect something wrong with the copper plating additives. Other readers may be better informed about this than me, so I welcome additional comments.

Regards,

A. Good day Ashok.

There is some info at letter 51199 regarding peeling on acid copper. Remember to try an acid etch/electrocleaner after acid copper, to remove brightener films (organics) which can cause peeling of nickel. What is the condition of your nickel?
Is the bath overloaded with excess brightener? Are you ensuring there is no current interruption during nickel plating? This can also cause peeling.
Hope this helps.
Regards,
Eric Bogner.

A. Hi.
For zinc die-casting material, here's some important pointers.
1. Ensure the soak cleaner and anodic electrocleaner are proprietary chemicals specially for zinc die-casting.
2. 1% sulfuric acid ( 10~20 sec ) pickling before cyanide copper plating.
3. Ensure a minimum of 5 microns copper thickness. ( current density at 3 A/dm2 for 15~20 minutes ). I prefer a CuCN at 60 g/l, Free cyanide at 12 g/l.
4. Followed by nickel/chrome.
Be warned, blister free plating on zinc die-casting also dependent on the porosity of the die-casting itself. Check the condition of material during incoming. Good Luck.

A. What is your plating cycle?
Ted assumed you have a problem with acidic copper but I am not sure you even use acidic copper following the cyanide copper.
Anyhow, you have to make sure that the hot soak cleaner and the electrolytic cleaner have low hydroxide concentration.
Acidic activation - that is the key for the process - do you have fluorides there? Do you recharge this solution often?

Hi again, Ashok.

1. Five people previously offered their suggestions regarding your first problem. Maybe you missed those responses. Can you start by commenting on those suggestions please? Thanks!

2. If you do not see sufficient info earlier in this thread about zinc and copper contamination to satisfy your needs, please search the site with the term "zinc contamination nickel plating" and "copper contamination nickel plating" to find several discussions on each subject. I apologize for assigning you that extra work, and I don't wish to be evasive, but we are finding that these threads are more coherent and useful as a reference for other readers, and get much better search engine coverage when they stay narrowly focused. Apologies.

3. If your nickel bath is Watt's bright nickel, sulfuric acid pre-diluted with DI water is used to lower the pH; again we have several threads about pH control of nickel plating baths. Good luck.

Regards,

A. Hi Anand. It is uncommon to grind diecast parts before plating because only the skin of the casting is non-porous, and if you break through the skin and reveal porosity, the parts will not plate properly. An alternative, although not cheap, may be to vacuum impregnate the castings.

Personally, I would suggest one of two courses of action:
1. - send trial lots of parts to competent plating shops to see whether the parts are reliably plateable, or
2. - retain a good plating consultant to figure out what you are doing wrong.

If you have tried 5 different suppliers, you have already wasted far more money already than either of these alternatives would have cost you. Best of luck.

Regards,

A. Hi Anand.
I don't see a cyanide copper before the EN. ASTM B252 Standard guide for Preparation of Zinc Alloy Die Casting for Electroplating recommends a cyanide copper plating of at least 5 micron thickness before any other subsequent plating.

A. Hello Deepak,
Could you please elaborate on your complete plating process, such as what types of Cu plating you are using on the Zamac? On Zamac there is normally a Cn Cu strike and Cu plate. You don't mention this. Thanks.

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A. Hi Hans. I'm not familiar with those 3 layers of copper plating; I suspect there are some translation difficulties. Usually the copper plating is done in two layers: cyanide copper plating (just enough for coverage), then bright acid copper plating to a total of 5-8 µm. If the copper plating is done right, 20µm shouldn't hurt anything, but as noted in the MFSA Quality Metal Finishing Guide, "copper cannot be substituted for any part of the nickel thickness specified".

4-6 µm would never be correct for any exposure; 20 µm would be for moderate exposure. And 0.1-0.2 µm of chrome is probably too thin as well.

China is capable of some of the highest quality metal finishing in the world, as witness such processes as the anodizing on the iPhone. But almost all of the copper-nickel-chrome plating from China these days is a scandal of trash! If you don't want your company to be identified with that absolute garbage quality, you'll have to work very hard indeed to get things done right. Your website says your stuff is all made in the USA; you might want to consider having the plating done locally.

You can probably specify 16 hours of CASS testing per ASTM B368 or Corrodkote per ASTM B380 rather than having to specify salt concentrations and temperatures, etc. Good luck!

Regards,