Alkaline Zinc Plating Q&A's, Problems & Solutions

A. Hello Yahya.
You didn't ask a question, but apparently you are showing us unsatisfactory plating.

I have never heard of continuous alkaline zinc plating of wire myself, although hopefully other readers have. Even so, the idea of doing satisfactory plating at all, let alone in continuous fashion, using just a zincate solution doesn't sound promising, let alone easy. If possible, I think you should try to get access to Geduld's "Zinc Plating" [on Amazon, AbeBooks affil links], perhaps through a university library, and meet with someone familiar with alkaline zinc plating and someone with wire plating experience. There is sometimes a tendency to believe that plating can be learned in 15 minutes, and solutions made up from raw commodity chemicals, but in truth it's probably roughly as complex and demanding as wire manufacturing and drawing :-) Luck & Regards,


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

A. Hi again. What about alkaline cleaning before the HCl? What about chromate conversion coating after the plating? Those 2 things are conventional.

8 minutes in HCl sounds excessive to me.

Luck & Regards,


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

A. Hi Shrey

Can we assume that there is no roughness in the Hull Cell panels that you run?

Can you pull a few parts after plating and before chromating to determine whether they come out of the plating tank rough or acquire the roughness in the chromating?

Luck & Regards,


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

A. Hi,

If the roughness appeared on Hull Cell panels at all current densities and before chromating, it sounds liker perhaps your filter is defective in some way. You should be able to filter 275 ml for a Hull Cell test through a Wattman filter in your laboratory to see if particles are causing the roughness and can be removed.

Luck & Regards,


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

A. Protolux solutions don't cope well with high concentrations of Sodium Carbonate. If the concentration is above 60 g/l you would expect quite a drop in solution efficiency.

A. Try to maintain 1:10 ratio Zinc:Sodium Hydroxide. Ideal composition for vat is 12:120 and for Barrel is 14:140 Needless to say that the additives you use should be from reputed and proven source. Presently This is not a problem T.K. Mohan plating process supplier - Mumbai, India A. It sounds to me that your having problems keeping your metal content up. 135 g/l sodium hydroxide is ok but 8.5 g/l sounds a little low. We help the dissolution of zinc by using zinc domes in mild steel cages. The rust from the mild steel helps lots. I run my non-cyanide zinc tanks with a metal content of about 10-11.5 g/l Chris Matthews - East Sussex, England

A. Dear Ms. Anggraeni,

Have you checked with "Hull cell" the performance of the solution whether is it okay or not?

Your problem can be the additive system or lack of control of the additive and has other contamination like water hardness, do you use Demineralized water for the plating solution and might be rinsing before entering plating bath?

You did not tell properly what kind of Chromating that you are using now, either Hex-Blue or Trivalent Blue.
In my opinion, Trivalent Blue is more sensitive to be yellowish blue and non uniform for Alkaline Non-cyanide Zinc (I presumed) that has Iron contamination inside the solution.

Try to treat the solution by using zinc dust ⇦ this on eBay or Amazon [affil links] treatment and consult with your local supplier.

Good luck.

Best regards,

A. Dear Anggraeni,
You have not given any details about your process and other details about what kind of items you plate.
Kindly give details:

Process used: Alkaline Zinc, Cyanide or non cyanide:
Vat or Barrel plating:
Bath capacity:
Work being plated:
Metallurgy of the product plated :
amperage per sq. ft. applied:
Plating time:
Details of addition of all additives:
Details/intervals of regular maintenance carried out:
Details of regular treatment carried out:
Do you analyse your bath:
From your letter I think your bath is not properly treated or maintained. The additives and the constituents are imbalanced. Please give clear details to get clear suggestions.
Regards,

A. Hi, Guna. What problems would come if you made coffee or soup with this water? :-)

Lots of people use raw water if it is not terrible. But the best path is to keep moving forward and to decide that you need RO or DI water because this junk doesn't belong in your plating tanks. It is difficult to say exactly what problems would result from use of water of unknown quality; excessive calcium, chlorides, iron, and the other things in raw water are contaminants that eventually spoil the plating solution. You would have to study what contaminants are in the water and in what concentration, and whether this is close to or far less than the technical data sheet suggests as troublesome.

Sorry that I don't have a "real" answer for you.

Regards,

A. Dear Gunashekaran,

Raw water if not really good say not of good quality will give a yellow tint to plating and this will continue to show if blue passivated. Generally supply houses will supply a conditioning agent to deal with such impurities from water.The best is as Ted said, invest in a DI/DM water generating equipment. But make sure you give a sample of water presently used to the equipment maker.
Good luck

A. Dear Friend,

Using DI/DM water is advisable. But if you hardness is moderate, in some cases you can use water softening chemicals in your bath.

Hope you are in Chennai and it is difficult as the hardness is more in your case.

Please opt for DM/DI water.

Thanks

A. Hexavalent olive green passivation is dark green with blackish shade, which is okay. If you still want green, then change pH to higher side this will work.

A. Hi Srinivasan. I certainly don't claim to have seen everything, and I cheerfully welcome a contrary opinion . . .
But having never seen a problem like that resulting from a plating operation, I tend to disbelieve the evidence that the mark was not there before plating. I suppose it's possible that parts were racked in such a fashion that an interrupted contact could cause a bipolar effect that dissolved the component along this line . . . but again I have to doubt it.
Can you tell us anything about frequency, whether the line runs the same direction each time, etc.?

A. Hello Peter and Jeremy,

Please give some information:

Passivation (Chromate conversion coating): Hex chrome or trivalent chrome?

Bath: Jeremy, you have the same problem with an alkaline or acid zinc bath?

Thickness: Is it uniform? Is it above 5 microns? Are there scratches or chipping of the surface?

Storage conditions: Is it humid? The parts could be exposed to fogs or sprays?

Well, this is all I recall as important now. If you can give some more information, we may be able to help you both! Regards and good luck!

A. Hi Jeremy,

Jeremy, the trivalent chromating bath generally works from 0 to 8-10 g/l zinc concentration. 15 g/l is very high, and the chromate must be very thin in this condition. I would suggest you to change, at least partially, the chromating bath.

Then, if this effect (discoloration) has always been there, I would see if the storage is done in humid conditions, if there could be some spray or fogs in the storage room or near the packaging, if the parts are exposed to light...

So, I hope we can help you too! Regards,

A. Hello Peter,

First, if the storage hasn't changed, it isn't the cause... But you should keep the parts away from the rain!

On the EDS result, if has some more oxygen and carbon I cannot say that it is different, they are elements present in dust and in sample preparation could be some variations that could increase the carbon and oxygen proportion. If you have iron content, then you should worry!

I didn't understand the water situation, with the flow and resin. Could you explain what you mean? pH in the chromate process is very important, you should maintain the pH value in ± 0.5 points from optimum pH value for a good corrosion resistance, and trivalent chromates need a good quality water for preparation. If you define your process with more detail we could help you more!

Good luck!

A. Hi Peter,

Do you control the pH in your chromate conversion bath? It is very important to maintain this value stabilized. The nominal value (in standard chromates, you should ask your vendor in this case) is 2,0. Please check this up! If the chromate has 2 steps, check both steps have controlled pH.

I haven't understood the resin situation yet, what did you mean with "flow out resin fragment randomly"? The chromate has a resin part?

Good luck!

A. Hello Peter!

Ca and Mg are a problem in some chromate formulations and are a problem in zinc electroplating bath always. For alkaline baths you have some conditioners that improve bath performance with the presence of Ca and Mg by getting them out the way, but you should try to avoid to replenish your bath volume with this "hard" water.

You should try preparing your chromate with another water (not hard, maybe demineralised) and see if you have some change in your process. If this improves your result of "discolored" parts, you have some problem there. If there is no change, then you have some problem elsewhere...

Hope you can solve this issue! Keep us informed and maybe we together can sort it out :)

Regards,

A. Hi Peter,

That the zinc plating solution is still and not working during maintenance is not a problem. Is this what you refer as "pending"?

If they always do maintenance on Sunday and you have problems with the parts plated on Monday, there must be a connection between the maintenance routine or the Monday startup and this. I can't tell what could be wrong in this, but if you know what is the routine for maintenance, startup and normal work, the differences between them are possible causes...

Hope you can solve this! If you do, please share what you found with the community :)

Regards,

A. Hello Sanjeev,

That your parts shine, or your parts brightness, could depend on how you clean your parts or how you plate your parts... If you have a cleaning problem, you should see if you are loading fully degreased parts, that your HCl is in correct concentration, if you use or not a wetting agent (if you don't, you should, I think it is very helpful, and cheap), if you use or not an electrolytic degreaser...

If you answer most of these questions with "yes", then you must tell us more about your process in order to help you. If not, you should see if you can make that happen.

We (at least I) can't say anything else to help you if you don't specify more what is the defect, what are you doing, and in which conditions.

Hope this helps! Best regards,