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topic 38877p2

Some problems in alkaline zinc plating, p.2

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A discussion started in 2006 but continuing through 2019

September 18, 2013

Q. Dear Sir,

We have alkaline zinc plating tank, and we use the HNO3 for yellow dip 2-3 ml/ liter , and also we use the H2SO4 for color maintaining. Now it's improved.

We are facing a problem in cleaning now; we are doing pretreatment (cleaning) process in HCl , but component shine is not coming, so please give us the cheap and good suggestion so that we can get shining on component.


Sanjeev Yadav
- Delhi INDIA

September 27, 2013

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,

Daniel Montanes
- Canuelas, Buenos Aires, Argentina

December 29, 2013

Q. Dear sir,

1. Why the discolouration comes at the olive green zinc plating?

2. Why the white passivation comes at the metal bonded area at green zinc plating?

3. Salt spray requirement for green plating?

4. What is difference between alkaline plating and zinc plating?

rubber to metal bonded - Tamil nadu, Madurai

December 2013

A. Hi Kumar. Please ask as many questions as you like, but please provide details on each of them rather than presenting the readers with a flash-card quiz; it's considered best netiquette to use more words in your question than you want people to spend on their response :-)

1). You have given us no data about what you are doing, from which people might be able to tell you what you are doing wrong (or what you mean by discoloration).
2). I don't think you mean "white passivation" ... maybe you mean "white rust"? White rust is corrosion of the zinc plating.
3). The customer often specifies the required salt spray hours, but 96 to 192 hours to white rust could be pretty customary.
4). Zinc plating can be done from cyanide-based zinc baths, alkaline non-cyanide zinc baths, and acid zinc plating baths. Cyanide has the disadvantage of being highly toxic, and is rapidly falling out of favor around the world. Today's alkaline non-cyanide baths can replace the cyanide processes. Acid zinc baths give a brighter plate, but usually have poorer throwing power so are less capable of achieving relatively even plating thickness.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Iridescent passivation peels off of alkaline zinc plating

February 23, 2014

Q. I am facing problem of passivation at customer's end.
The process is as below:
Base : Fe
Plating : Non-Cyanide alkaline Zinc
Passivation : Iridescent hex-chrome.

Problem : Passivation Adhesion problem. The plated parts after passivation shows slip out of passivation meaning improper adhesion of passivation.
Could anybody explain the reason for this and remedy for it ?

Yogesh Kulkarni
- PUNE,Maharashtra,India

September 2, 2015

I have a component in diameter 8.
Material: Mild Steel
Total length of component is around 800 mm

My customer is asking plating thickness more than 15 Micron

My question is
1. Whether it is possible to give coating thickness 18 micron?
2. What will be effect of cost?

Pramod shah
United Pressings - Pune, Maharashtra, India

September 2015

A. Hi Pramod. Yes, even 25 microns is still a "standards-based" thickness for "very severe" exposure.

Nobody can quote you the cost of someone else's services, of course. But you should have little difficulty finding a plating shop willing to do 15-18 micron plating for twice the cost of 8 micron plating, It will take twice as long, and will half their production rate, but they will see materials savings in the other processes, and probably labor savings, if they half their production rate. Good luck.


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

Yellowish zinc deposit after alkaline zinc plating

February 10, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We use alkaline non-cyanide zinc plating with 800 liters. The bath is working good but lately the plated barrel shows yellowish or golden deposit after plating instead of bright silver color. Please tell me the problem.

Eskedar bekele
plating bath supervisor - Addis Ababa Ethiopia

February 23, 2016


popat patel
Popat Patel
    Beacon Park Finishing LLC - Roseville, Michigan

December 31, 2016

Q. If the temperature of the alkaline Zinc bath is increased up to 35 °C then what will be the effect on the plating and the reactions going on in the plating tank??

Veerendra kumar
- delhi, India

January 2017

A. Hi Veerendra. Alkaline zinc plating temperatures can range from room temperature up to about 48 °C. As a very general rule, plating speed increases at higher temperatures, but so does brightener consumption. What temperature does the process supplier suggest? Why do you want to exceed it? Thanks.


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

January 9, 2017

Hi Veerendra,

Alkaline zinc temperature range 25 °C to 35 °C , Optimum temp 26 °C. You can run with higher temperature but it burns brightener and other components and increases plating speed.

Howard Finishing LLC - Roseville, Michigan

January 18, 2017

Q. Hello sir, I face a problem that diameter of component becomes less after plating. What is the reason? Please help. Material is 16mncr5

Sidharth kamboj
- Karnal,Haryana,India

January 2017

A. Hi Sidharth. That strikes me as exceptionally unlikely. To begin solving the problem you would need to measure the diameter after each step in the plating process and determine in which tank it happens. If you discover a reduction in diameter after rechecking, please tell us the starting diameter, ending diameter, and which tank it happened in (soak cleaner, electrocleaner, acid activator, alkaline zinc plating tank, chromate conversion coating tank, etc.) Thanks.


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

Burning in Alkaline Non Cyanide Zinc plating

March 22, 2017

Q. We have been seeing problems where the edges of the parts end up with a serious amount of high current density burning. We have added low current formula and brightener to keep these concentrations up. I've sent samples of the plating bath to our chemical manufacturer and they come back in balance. We still see this issue and it's causing issues with powder coat paint applications after the plating process.

Paul King
QC for Manufacturing - Lynchburg, Virginia, USA

March 2017

A. Hi Paul. Obviously there is a current density beyond which burning in the high current density edges is unavoidable, and the only resolution is to plate at lower current density. I'm not sure how to say exactly where that point is except from vendor suggestions, reports of successful and unsuccessful current density, and previous experience.

It might vaguely be possible to increase the current density by shielding those edges, but only if it's a long run of identical parts.


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

March 24, 2017

"...sent samples of our plating bath to our chemical manufacturer and they come back in balance" ?!
Did he run a Hull Cell Panel? The solution might titrate "in balance" and be loaded with dragged in HCl which has converted to NaCl and will surely chew up the HCD edges.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

thumbs up signThank you for the responses. Yes, we did a hull cell. We did that first and it came up with the parts looking good. Of course the hull cell was a flat panel and didn't have any variance in the plating because of this. Thanks for the thought there though.

What we did and will continue to do is add a small daily quantity of a LCD booster. And change the concentration of our brightener feeder pump. Both of these additions have resulted in more uniform finish across the surface of all the parts and specifically in the HCD areas on the bigger parts. When the brightness gets too high, I'll cut both back and see how long it takes to plate out.

Thank you both for you contribution.

Paul King
plating - Lynchburg, Virginia, USA

March 25, 2017

A. Hi Paul, I would suggest a brightener feeder system based on your rectifier amp hours, especially on tanks larger than 500 gal. Adding a small amount, say every 500 to 1,000 amp hours, based on the Tech Data sheet would maintain an even level. Takes the human error out of it ... well, not completely.

jim conner
Jim Conner
Anoplex - Dallas, Texas USA

Shiny edges and dull centers on zinc plated parts

April 19, 2017

Q. Hello

I work in a metal finishing shop and we have been having issues with our zinc plating on some parts. The biggest issue is the finish is not uniform and we are getting shiny edges and dull centers, especially on larger parts. I have heard this referred to as "TV screen effect" but hours of googling have not given me any results.

38877-7a  38877-7b

Our technicians are reasonably certain that the problem lies in our zinc solution and not anywhere else. Our zinc phosphate and even our yellow zinc do not have these issues. We have been in business for over 20 years and never had an issue like this.

I believe our problem started because we have recently moved our shop across town. This meant pumping out our zinc solution into totes and and then back into our zinc tank. (3000 gallon tank). This is what leads me to believe there is some contaminant in our solution. (I assume organic contaminants, possibly oil). We never had issues like this at the old shop and the only change we have made is our location. This is the first year that we have not froze out the carbonates but I don't think that is our issue.

As per our chemical supplier, we have added 5 gallons of 7.4% sodium hypochlorite. Plating seems to be improving but we are still seeing the same issues.

One of our technicians thinks it could be a bad batch of carrier or brightener but the boss has ruled that out.

I imagine adding more sodium hypochlorite would help? 5 gallons into a 3000 gallon tank doesn't seem like enough to me. I've also heard EDTA or activated carbon or Rochelle salts but I have no experience with those.

Any ideas or suggestions would be very much appreciated! Thanks! I will try to attach some pictures of our problem.

Josh Ziemba
Plating shop employee - Ottawa, Ontario, Canada

April 2017

A. Hi Josh. I am not a zinc plater, so we will will have to wait for someone who is to offer their best guess at the problem. But what I do know is that you don't start by adding sodium hypochlorite or EDTA or Rochelle salts to a 3000 gallon tank ... you add stuff to your 267 ml Hull Cell and see what helps and hurts. Good luck.


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

April 20, 2017

A. What are your numbers? (Zn, NaOH) And, what's your Hull panel look like? Might be additives.

I don't think bleach will help, either.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

April 28, 2017

A. Hi !! Josh,
Add 0.5gm/ltr Potassium Permanganate (KMnO4). Mix well. Settle the solution for overnight. Impurities will settle at the bottom of tank. Next morning separate clear solution from sludge. Discard the sludge and use clear solution for plating. I think your problem will get solved with this process.

Amol Chitte
- Pune, India

August 18, 2018

Q. Dear sir: alkaline plating problem.
Alkaline plating in white spot part (okay metal and casting), but white spot problem, so please sir, help.

saurabh singh
tools - faridabad hariyada, India

August 2018

A. Hi Saurabh. Unfortunately, I don't think people can even visualize the defect you are experiencing, let alone guess what might cause it. Please send pictures of the defect to for posting here, and tell us what you see in your Hull Cell testing. Thanks!


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

March 28, 2019


from context, ncz would mean non-cyanide zinc

Q. Hi, sir I am using ncz tank bath. I have problems in a tractor pin like as bolt types pin when we hang with wire. After zinc plating and hexavalent gold chromate it shows wire marks. Please suggest me why this comes. What should be added.

Ram Gopal Verma
Bright and bright electroplating - Ludhiana, Punjab, India

April 2019

A. Hi Ram. Using wire for racking can be a problem, and is usually okay only for certain types of parts. These pins should probably be either barrel plated or use custom racks which do not leave rack marks in unacceptable areas. Good luck.


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

September 24, 2019

Q. I am having a rack system of alkaline zinc electroplating. Its contents are Caustic 130 g/L and zinc metal 1 2g/liter.
I face white rust on Mild steel CRCA component where spot welding is done.


After passivation is done and when the component is kept for natural drying the caustic water comes out from the welded area and the golden passivation gets removed. This leads to white patches on the component.
How do I neutralize the caustic between the welded parts before golden zinc passivation?

My post treatment process is
1. Water rinse
2. Nitric rinse
3. Golden passivation
4. Water rinse
5. Hot water rinse

Kartik Kanuga
- Ahmedabad, Gujarat, India

September 26, 2019

A. Hello Kartik,
My advice would be to employ any of the following types of agitation in your rinse(s).
1) Work bar agitation in the direction best suited to remove the entrapped solution.
2) Solution agitation
3) Air agitation
4) Work bar vibration.
If you don't use work bars in the rinses and it's manual dipping, you could employ #s 2 & 3. Good Luck!

Mark Baker
Electronic Plating - Winston Salem, North Carolina USA

September 29, 2019


ajay raina
Ajay Raina
Ludhiana, Punjab, India

Chemical flow in between wielding area

October 16, 2019

Q. Good evening,My self Arvind Soni from India we are facing problem in sector welding parts when after welding we are plating the same in between cavity sector and arm chemical flow after plating and giving proper curing time of 24 hrs.
This is in Zinc plating process. Kindly suggest -- it's urgent and generating heavy rejection.

Arvind Soni
employee - Bawal,Haryana-India

October 2019

? Hi Arvind. The picture seems to be of a stained part hanging on a plating rack but, sorry, I do not understand the shinier units I see in back of it, nor do I understand your text. Hopefully another reader familiar with this type of part will catch on better. Apologies :-(

This is just a public forum where questions sometimes remain unanswered for a long time; please don't rely on it for urgent answers. Good luck.


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

December 6, 2019

A. Dear Arvind,

Please improve the welding between the two plates.
Avoid the Gap. Your problem is not from plating but from a badly made assembly.

The uneven gap between the two plates entraps the solution and causes bleed out of plating solution later.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser 
Bengaluru, India
Saify Ind

November 18, 2019[ed. note: sorry for the delay in posting]

Q. Hello everyone,
My name is Bartek and I come from Poland. We run a small galvanic line (racks and barrels on the same line) with the alkaline zinc process. Most of our production is the black finish passivation (based on Cr III) with sealer. The part coating is made on the racks.
We are facing a problem with a white tarnish (white corrosion?) which always turns up after a few days. This problem concerns mostly parts which we have to correct (re-coating process). Parts are made of material and 11SMnPb30.





The process flow chart:
chemical degreasing -> electrochemical degreasing -> 3-step rinsing -> acid pickling -> 2-step rinsing -> alkaline activation -> zinc plating (alkaline) -> 2-step rinsing -> acid activation (HNO3) -> black passivation -> 2-step rinsing -> sealing -> drying
Do you have any ideas what we can do to avoid this problem?
Thank you in advance.

Bartek Haja
- Silesia, POLAND

December 2019

A. Hi Bartek. Looking at the graphics it looks like the parts are pitted. Perhaps the replated parts are more prone to white rust because they are pitted from their two trips through the acid pickling? But if you search the site for "11SMnPb30" you will find some suggestions regarding the pickling and plating of this leaded steel. Good luck.


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

December 8, 2019

A. Extending on Ted. Lead on the surface forms and insoluble salt in most "pickling solutions" like HCl, and sulfuric acid. Make up a bucket of 30%/vol fluoboric acid which does not form an insoluble salt, try it, come back, let us know.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

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