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

A. Hi Albert. As you see we added your inquiry to one of several treads about similar problems in alkaline zinc plating. Pictures sent to mooney@finishing.com for posting here would help, but even still here can be several causes for any given plating problem. My first guess would be that you are drying at too high a temperature. The high current density areas (corners, edges) are also the area that will overheat first in a hot dryer. If the parts are not overheated during drying, my next guess would be 'burning' which just wasn't noticed earlier.

Luck & Regards,

A. Hi again. The pics are too small and from too far away to see any detail in high current density areas. But the unsatisfactory plating seems to be in random areas, which is hard to explain other than poor cleaning or poor plating bath composition/operation.

As always, Hull Cell panels can reveal whether the problem is on the plating tank. Good luck.
Regards,


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

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 about 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? 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 Anand.
In addition to the problem of lack of plating on the shank, the plating on the head is chipped off badly, and we can see from the cracks and lack of adhesion that it will soon be even worse. My first suspicion is that the problem isn't your plating bath but the fact that the bolts are not prepared suitably for plating -- possibly not truly clean, possibly still with scale on them.

Can you blast a few and tell/show us what result you get when you plate them?

Luck & Regards,

A. Dear sir,
Please increase the concentration of HCl pickling from 20 % to 40 %. This cause occurs due to cleaning of parts not properly done. The bonding of metal and zinc not in proper way -- that was this defect occurring. I think these parts look like tempered, and high carbon scaling on parts. That's why I recommend to increase the HCl concentration in tank.

A. Hi Jenny. Most chemical reactions occur faster at higher temperatures due to the greater mobility of the ions, but for this case the experimental results are what they are. Hopefully someone else can explain them.

Luck & Regards,

A. At the higher temp, particularly at 43 °C, you were making carbonate faster and carbonate slows down the plating rate.

A. Keep in mind that the operating characteristics of the brightener additives changes significantly once above 35 °C, e.g.,coverage issues arise in LCD areas first. Perhaps this may be playing a part of the decrease in efficiency.

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. 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,