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topic 43365p6

Hot dip galvanizing flux Q & A's, Problems and Solutions

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A discussion started in 2006 but continuing through 2020

December 20, 2016

Q. Dr.Cook,
Thanks for your kind reply.
This is the result from the report; we use double salt flux.
What is your opinion in this analysis, and what precautions should I take?

Zinc(zn) total = wt% 8.5
chloride (Cl) = wt% 17.8
total iron (Fe) = wt% 1.67
Ammonium ion (NH4) = wt% 0.32


- Ammonium as Ammonium Chloride ( NH4Cl) = Vol% 0.95
- Zinc as Zinc Chloride (ZnCl2) = Vol% 17.71

Your guidance is always appreciated.

aly elsokkary [returning]
- Saudi arabia

March 17, 2017

Q. Dear sir,

My flux gravity is 1.18 and its temperature is 40 °C, and I'm also doing online flux filtration. Iron content in flux is 4.5 gm/lit.

Now I am struggling from more ash formation in zinc bath and also heavy ash marks on material.

I am using platinum flux.

Please advise me how can I solve the problem?


kiran gaikwad
- davangere, karnataka, india

June 13, 2017

Q. Hi,
I prepared the flux solution from the reaction of zinc chloride with ammonium chloride. When analyzing the solution, the ratio of zinc chloride was 21.66% while ammonium chloride was 15%. When the solution was left for a period of time, a precipitate was formed. I do not know what is the reason? It also gives little adhesion. I hope you will help me to give the exact proportions of the reactive materials.

ali amal
- baghdad, Iraq

June 15, 2017

Q. Dear Sir
I want to use only NH4CL for new fluxing tank. What will happen? Please answer me? We galvanize all kinds of structures and towers.

Thaw Kaung Maw
Myanmar Economic Corporation - Yangon, Myanmar

June 16, 2017

A. You will certainly get a lot of fume.
It might work, but it could also be that you don't get full wetting and fluxing and that results in bare patches.

You could try it in a small batch on some sample plates and see what happens, that way you don't waste a whole flux tank of materials.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland

June 23, 2017

Q. Thanks sir
I also want to know the ratio. How much NH4Cl to use in 1 liter?
Please advise me.

thaw kaung maw [returning]
myanmar economic corporation - yangon, myanmar

June 2017

thumbs up sign Hi cousin Thaw. I am not a galvanizer, but I try to listen and learn -- and I think in your eagerness to get started you have not slowed down to listen closely :-)

I think the answer was essentially: "It's a bad idea and liable to not work well for several reasons; but if you insist on trying it, then run some experiments on a few small parts". Demanding that people provide the details on exactly how to do what they've repeatedly suggested that you not do can be considered badgering, but good luck :-)


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

June 23, 2017

A. Sir:

45 years ago I did experiments using NH4Cl alone and ZnCl2 alone for hot dip galvanizing fluxes. NH4Cl dried very quickly on the steel but corroded the steel very badly. ZnCl2 never dried and the steel did not corrode. The NH4Cl flux gave much skimmings (ash) and smoke. The ZnCl2 spattered badly when going into the molten zinc. In the end both steel samples galvanized fairly well with about 3 mils of zinc (75 microns). Do not expect good results from ammonium chloride alone or zinc chloride alone.

Experiments with hot 160 °F (71 °C) triple or quadraflux dried quickly and did not corrode and gave an excellent result. The steel must be in the hot triple salt solution long enough to heat the steel completely so the heat of the steel dries the flux from the inside.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

December 11, 2017

Q. I'm a process engineer at a hot dip galvanizing plant in Morocco. We are facing a problem with the flux solution: the ACN is going up and we can't explain the ZnCl2 consumption.
We use a double salt flux with temperature 45 °C. Our ACN went from 0,8 to 1 in about 4 months.
I would be very thankful to you if you can help us out on this issue.

Soufiane esslaoui
- rabat, rabat, morocco

December 21, 2017

A. Sir:

If you are using ammonium hydroxide (aqua ammonia) to raise the pH of your flux then this is the same as adding ammonium chloride. Each U.S. gallon of ammonium hydroxide is the same as adding 11 pounds of ammonium chloride.

If this is not the "problem", then perhaps whoever is dong the testing may be doing it incorrectly.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota USA

December 22, 2017

Q. Thank you sir for your quick reply.
Actually we are using ammonium hydroxide 25%, and for each 1000 l of ammonium hydroxide we're adding 275 kg of zinc chloride to correct the ACN.

Soufiane esslaoui [returning]
- Rabat, Morocco

December 24, 2017

A. Sir:

By adding 1,000 liters of 25% aqua ammonia (expressed as percent NH3), and 275 Kg of zinc chloride, you are indeed increasing your ACN.

The Kg of ammonium chloride in 1,000 liters of 25% NH3 is:
0.25 * 1,000 L * 0.91 * (53.45/17) = 715 Kg ammonium chloride.

The resulting ACN of your additions are:

ACN = (715 Kg/275 Kg) ACN = 2.60

In the above calculation: 0.25 is the % NH3.
The 0.91 g/ml is the density of the NN3 solution.
The 53.45 is the molecular weight of ammonium chloride.
The 17 is the molecular weight of ammonia

The real question here is WHY would you need to add 1,000 liters of NH4OH to neutralize excess acid in your flux? This is enough ammonia to neutralize about 2,000 liters of 17% HCl. You must not have a rinse tank between your HCl tanks and your flux OR you have an old rinse solution that is stagnant for many years? Perhaps clean water is costly in your country.

I do not normally give any advise without knowing more about a plant, however skimmings or ash possibly could be added to your flux to both neutralize acid carry-over and to keep your ACN down.

What is the density (in Be' units or g/ml) of your flux.
Your operation is not in control.

And by the way I do not like double salt.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs South Dakota USA

July 21, 2018

Q. I want to know which type of flux used in tower galvanising unit, and tell me solution used in flux?

gopal dwivedi
- NEW DELHI, india

July 27, 2018

A. Sir:

The best results that I have found for flux is: 12 to 14 degrees baumé (measured at room temperature; 4.2 pH; temperature 160 °F (71 °C); below 1% sulfate; non-traditional non-volatiles below 7,000 (Ca, Mg, Mn, K, Na expressed as chlorides). The ACN which should be 1.6.

Unfortunately, many commercial fluxes sold in India, China, and Europe are made from recycled materials or poor starting materials and give poor results in galvanizing. Only by testing the actual process flux can suitability be determined. Fortunately in the USA there is one excellent flux manufacturer.

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota USA

September 22, 2018

Q. Sir galvanizing plant running in every type of material. purlin start the production 2 mm this material is red in 5 min flux ph 2 and specific gravity 1.17 g/ltr

yashwant ashok patil
- sangli maharashtra

September 2018

Hi Yashwant. Can you please post more words, so we can be clear exactly what the problem is before the waters get muddied by people misunderstanding your question? :-)

You're saying that after 5 min in the flux tank (why that long?), purlins (bare steel? what grade?) made of 2 mm thick material turn red (bright red or the color of rust?) for some unknown reason? Then they galvanize correctly anyway, or they galvanize unsatisfactorily, or you stop the process and don't even attempt to galvanize them? Thanks!


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

September 5, 2019

Q. Dear sir, I would like to ask that why the flux color is red and what's the chemical reaction in this process?

I would like to ask what's the correct chemical addition of flux.

Mohd Tariq
Galvanizer - Ghaziabad,uttar pradesh, india
  ^- Privately contact this inquirer -^

September 15, 2019

A. Sir: The red color is Fe(OH)3 and is likely from too high of pH. Check the on-line library on this website for a better understanding.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota

September 17, 2019

Q. Respected Dr. Cook: Sir I would like to know whether this is the correct chemical addition to preparing the new preflux if we are using ready made flux. Also with respect of this standard, i.e., pH is 4 to 5, specific gravity is 1.16 to 1.25 and addition is 1 litre water+ 275 grams ZnCl2 + 715 grams NH4Cl + 250 ml aqua NH3. Give your comment soon.

MOHD Tariq [returning]
Salasar techno engineering ltd - Ghaziabad india

September 19, 2019

A. Sir: You do not specify what the "ready made" flux is? Therefore there can be no answer to your question. Also the "standard" is wrong.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota

September 20, 2019

Q. Dr.cook sir if our ACN of flux is 1.17, then what's the correct composition of chemicals like as addition of ZnCl2, NH4Cl, aqua ammonia and hydrogen peroxide.

MOHD Tariq
Salasar techno engineering ltd - Ghaziabad india

September 16, 2019

Q. Hello sir,
I am process Engineer of Hot dip Plant. I have a question regarding Galvanizing process of flux dipping. After Flux dip parts got reddish.
Kindly suggest what to do to avoid this problem ?

amit Mondol
Employee - ballabhgarh, India

September 16, 2019

Q. Hello, I work for a galvanized steel pipe company in Korea. Our company uses dry flux and wet flux as the last step of pre-treatment. We're currently building dry fluxes with ACN 1.01, Baumé 2.58 (24.7% saline zinc, 25.0% ammonium chloride). As far as I know, both zinc chloride and ammonium chloride remove oxides. And I was wondering, if we had less ammonium chloride, it would affect the fluidity of zinc. The company that supplies us with flux says that zinc chloride only removes oxide, and ammonium chloride lowers the melting point of zinc when flux reacts with zinc. For this reason, it is said that lower levels of zinc chloride and higher levels of ammonium chloride should be increased in desiccation and higher fluidity of zinc, but no data has been found. If you know the exact role of zinc chloride and ammonium chloride, please advise. Have a good day.


September 22, 2019

A. Sirs: One point that you guys do not understand: As flux solution is used each day the parameters change. For example: If the flux is exposed to zinc (from stripping rejects or from using zinc coated racks in the flux), then within some months starting with triple salt with ACN of 1.17 can easily become ACN of 0.5. With an initial pH of 4.2 this can increase to 6.0 within a week. I am not able to give advice when I do not have credible analysis of each parameter. See my on-line library articles on this website to better understand flux.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota

October 24, 2019

A. Sirs:

ACN = NH4Cl/ZnCl2


Thus ACNV is the desired measure for hot dip galvanizing flux, because more ammonium chloride is needed to make-up for the non-volatile impurities. In order to measure ACNV see my methods in the on-line library.


Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota

February 11, 2020

Q. I have problems when I add salt type 2 to flux and measure zinc chloride in flux I found it decreased until pH became 2,5

Hany hossam
Chemist - Cairo, Egypt

March 4, 2020

? I don't understand the last post. Is it a question? What is "type 2"?

Geoff Crowley
- Glasgow Scotland

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