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Problem of white spots after Zinc Plating

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Q. After plating there is a visible cloudy like on the surface and occasionally a rainbow one. We are using non-cyanide alkaline zinc. Plating parameters are 9-14 Zn 80-120 NaOH. What should be done to fix the problem?

15007-2b   15007-2c   15007-2a  

F A Pabalan
Engineer - Calamba, Philippines
April 2, 2022



simultaneous replies

A. Hello, Pabalan,

I've never worked with a non-cyanide zinc, but I've had similar problems with my cyanide zinc bath (36 g/L CN-).

Usually when this happens my first thoughts are that there is a problem with the deposition of zinc or low concentration of brightener.

I'd check for zinc concentration, cleaning of the parts and the integrity of the cables inside the barrel, as well as trying to add more brightener.

Regards,

Pedro Franco
Chemical Engineer - Nova Friburgo, Rio de Janeiro, Brazil
April 7, 2022


A. The NaOH will not rinse off, causes the chromate to "rainbow", so kill it with a 1/4 % nitric acid ahead of the chromate.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
April 7, 2022



? Can you confirm if this happens after the plating tank, or when you mention "after plating", is it after the complete process, e.g after chromate and drying?

A. I can offer two thoughts based on researching similar issues

If issue happens after chromating, check that PH, solution concentration and immersion time is as per your spec on the chromate tank. Having my process off recommended spec somewhat did appear to cause some iridescence.

Plating thickness across the whole part - the way in which the chromate interacts with different areas of plating thickness may cause some iridescence to show?

It has been mentioned before on this website that contaminants inside the chromate tank from drag in can cause this issue. Simple way is to prepare a small new solution inside a beaker [adv: beakers on eBay or Amazon] and do a test run there to isolate this.

Boris Siljanoski
- Perth, Western Australia
April 19, 2022




⇩ Closely related postings, oldest first ⇩



Q. Dear Sir,

We are observing a problem of white spots after zinc plating. Can you please tell a solution for this problem? Thanking You, Yours Truly,

C.D.Agashe
Pune , Maharashtra , India
2002



Q. We are also facing similar problems occasionally. Answer to this question will help us also.

Regards,

Sonu S Andrews
- Chennai, TN, India
2002



"Zinc Plating"
by Herb Geduld

on AbeBooks

or Amazon

(affil links)

A. I am guessing that the white spots you are referring to is actually white rust, which means that the zinc layer has been corroded. If this happens right after plating, maybe the problem lies in the drying process (not completely dried up), leaving droplets of water on the surface of the plated parts. Other possibilities might be from poor final rinsing and poor chromate dip.

Hartarto Ciputra
- Surabaya, Indonesia
2002


A. This is the common problem in White zinc. The most possible problems are in water rinses after plating & yellow passivation. First these things should be controlled. Secondly drying of the components is very important factor. Please look into that also. Very rarely there can be the problem of contaminations in the plating tank, which can be sorted out by various treatment you must be doing in your normal cleaning times. Please try & let me know.

SANTOSH ZOPE
DUBAI WIRE - DUBAI, U.A.E.
2002



? Dear sir,

Before we attempt to answer your query, it is very important to know what base metal are you plating? What is the pretreatment sequence? What type of zinc plating are you doing? Lastly where does the white spot occur i.e., HCD, lcd or random? Above will give better insight into the problem.

G.S. Sharma
- India
2002




Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)



Non-Cyanide Zinc Plating Problem

Q. White patches seen after trivalent blue / yellow passivation in non-cyanide/alkaline zinc plating process. Please tell me that what will be root causes starting from degreasing to passivation.

Nitin Kapare
Plating Chemical Supplier - Pune, Maharashtra & India
January 9, 2009


A. Hi Nitin,

Do you observe the white patches after the passivations, cos many a times when the passivations parameters, like the ph, time, are not set it gives such appearance, secondly if you have a electrocleaner in the line for non cyanide zinc is preferable , cos the cleaning of components I quite important in case of non cyanide zinc, did you check the hull cell for the working bath , do you observe any white patches and at last it have the zinc dissolution tank and are you maintaining the zinc content very well in the bath.
Thanks

praveen kumar
Praveen Kumar
plating process supplier
Mumbai, India

January 14, 2009


A. Is usually due to the hardness of the water and remove additives patent provider additives.

Oscar Villaobos
chemical supplier - Guadalajara, Jalisco, Mexico
January 29, 2009


A. Check the Nitric Dip (activation prior to passivation).

With alkaline zinc you may need a strong (minimum 1% by volume) Nitric Acid Dip prior to passivation.

There can be many causes for patches, etc... but this seems to be the most common cause.

Thomas E. Kidd
- Budapest, Hungary
February 24, 2009




Q. Our components after alkaline zinc plating are having white patches after 20 days even though the components are not exposed to environmental conditions in our plating shop, i.e., each component was packed with plastic cover separately and stored for 20 days. Now that we are observing white patches on the component, can any one explain the reason?

Raghavendra BN
- Bangalore, Karnataka, India
September 26, 2012



A. Dear Mr. Raghavendra,

I think you are experiencing this because of a bad or absent chromating of the zinc plated parts. The white patches are zinc oxidation/corrosion. Zinc corrodes in air, so you must apply a chromate (hexavalent or trivalent, according to spec) conversion coating so it does not corrode a few days later.

Hope this can solve your issue, best regards!

Daniel Montañés
fasteners manufacturer - Cañuelas, Buenos Aires, Argentina
October 1, 2012


A. The area of post water swill (even pre and post chromating) and a final hot water swill may be helpful. Packing inside plastic bag should be after proper drying.

t k mohan
T.K. Mohan
plating process supplier - Mumbai, India
October 10, 2012




Q. Hello sir,

We are observing white patches right after zinc plating.

Bhaktesh Naik
- Bangalore peenya, India
July 29, 2020




White Patches observed 4-5 days after Alkaline Zinc Plating (Cr6 Free)

Q. Our components after alkaline zinc plating (Cr6 Free + Top Coat) are having white patches after 4-5 days even though the components are not exposed to environmental conditions in our plating shop, i.e., each component was packed with plastic cover separately and stored. Now that we are observing white patches on the component. Can anyone explain the reason?

Digvijay Bhosale
- Kolhapur, Maharashtra.
October 21, 2020


A. You are probably not neutralizing off the strong alkali from the alkaline zinc. Use a 1/4%/vol Nitric Acid between the plating and the chromate.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
October 22, 2020


A. Please make sure that you can store your finished product at humidity [not] more than 90.
Do not pack you material immediately as after spin dry; there will be a chance of retaining moisture which may act as a SST chamber when you pack your finished product immediately in PP bags

Rahul VP
- Pune Maharashtra
September 8, 2021




Q. Our components after alkaline zinc plating and black coating are having white patches after 4-5 days even though the components are not exposed to environmental conditions in our plating shop, i.e., each component was packed with plastic cover separately and stored. Now that we are observing white patches on the component. Can anyone explain the reason?

ANKIT SRIVASTAVA
MANAGER - GURGAON
August 2, 2021


A. Hi Ankit. You copied & pasted Digvijay Bhosale's question, but then offered no comment to Robert Probert's answer to it. That seems kind of silly :-)

Please do us a favor and comment on Mr. Probert's proposed solution. Thanks!

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 2021




⇦ (tip: readers rarely show much interest in abstract questions, but people's actual situations usually prompt responses)   smiley face

Q. How to solve zinc white patches? Have any permanent solution?

15007-1

Lokesh Naik
- Kotture [India]
October 21, 2021


A. Hello,

We need more information about your process firstly to understand what the problem is. Is it NC alkaline zinc or acid zinc? What kind of passivation do you use? Do you have topcoat on it ?
But, by the looks of it, I would say it looks like alkaline zinc, and these spots can be easily solved by doing hull cell. Might be lack of an additive, probably the Carrier. If these white streaks appears on hull cell around MCD, then there's problem with hardness in your water you using for refill the level or you used to do the make-up. If so, you may want to use softened water in the future. Or just speak with your chemical supplier and explain the situation, they have additive for removing spots caused by hard water.
Keep in mind these things apply to alkaline zinc only.

S. Daniel, Romania
Chemical Engineer - Bucharest
November 1, 2021


A. Ahead of the chromate, try a 1/2% Nitric Acid Dip to remove the alkali, then maybe the chromate will "take"

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
November 4, 2021




Q. I am from India. Working in a nut manufacturing company. Doing Non-cyanide alkaline Zinc barrel Plating. Last one year we are frequently facing white spray like spots in our nuts after Plating. We are doing Trivalent Passivation and then top coat also. We have tried many trials in the same line and offline but problem remains same. After Plating and finishing process within two days this problem is observed. Initially starts with two hex sides. After Plating and before Passivation this problem found in the nut. We have three rinses after Plating. 2% Nitric dip also given.

Siva.k sivakumar kandasamy
- Pondicherry, India
November 27, 2021


A. Hi Siva. 2% nitric sounds excessive; as Robert Probert notes on this page 1/4% to 1/2% would be usual, but I'm not sure whether it has anything to do with the problem.

I don't understand how you can say the problem takes two days to turn up, but you can see it before passivating. But little white dots which take a couple of days to appear are probably the beginning of white rust, so for some reason the chromating isn't right -- could still be the rinses before it, the chromate itself, or the drying & packaging.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2021


A. SIVA,

AFTER ALKALINE ZINC PLATE, NEED 0.5% NITRIC DIP -- MAKEUP NITRIC DIP EVERYDAY.

popat patel
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan
January 17, 2022




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