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topic 43365

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

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A discussion started in 2006 but continuing through 2019

2006

Q. Dear Dr. Cook,

I have read the valuable suggestions you give to various galvanisers and here I would like to take this opportunity to get your advice. We galvanize tubes. presently, we are facing problems in getting the right quality of flux. can you please advice us the process and the formulation so that we can prepare our own quality flux based on triple salt.

Regards,

Rajiv Shah
pipe manufacturer - Hyderabad, India


2006

A. Dear Rajiv,
Triple Salt is 54% Ammonium Chloride and 46% Zinc Chloride. This is an "ACN" (Ammonium Chloride Number of 1.17; which is the weight of ammonium chloride divided by the weight of zinc chloride; e.g. ACN of triple salt = 54/46). If you strongly heat the pipes after fluxing then the double salt is more thermally stable with an ACN of 0.8. If you only slightly heat the pipes after fluxing then quadraflux with an ACN of 1.6 is good. Quadraflux has the advantage of producing thinner and smoother zinc coatings on the inside of the pipes. A certain wetting agent produced only in the USA and Germany is the only one that I have found works well in galvanizing fluxes.
Thank you for asking me your question. You could get additional information from my journal articles in Metal Finishing.
Regards,

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


2007

A. Flux solutions should be kept on 50 degrees to perform well.

Sondergaard
- Denmark


2007

A. Dear Sondergaard,
It is true that many automatic pipes galvanizers use 50°C and high baumé(density)flux solution for galvanizing medium and small diameter pipes. If the flux solution is hotter, then the last pipes in the bundle will have corrosion lines on the outside and have "black" (bare) spots. (Higher flux temperature causes faster corrosion.) If however, large diameter pipes are galvanized or the "breaking table" is wide enough and slanted such that a single layer of pipes results (for the fluxed pipes), then low baumé and hot flux gives a better result. Better by having a thinner zinc layer on the inside of the pipes and having much less ash (skimmings) at the kettle.
For general galvanizing it is common practice in North America to use either triple salt flux (ACN=1.17) or quadraflux (ACN=1.60) at about 13 to 14 degrees baumé and 71 °C (160 °F). (ACN = weight of ammonium chloride/weight of zinc chloride.) This often gives a percent gross zinc usage between 4% and 5% (%GZU = zinc consumed/steel galvanized all times 100%) (no zinc credits for ash or dross). The correct pH and the proper wetting agent (surfactant) in the flux also help prevent corrosion of the fluxed steel.
Regards,

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



What is Quadraflux?

2007

Q. Sir,

I read the name quadraflux during the course of above discussion. I want to know what is quadraflux and what is triple salt flux. Currently I am using flux which is mixture of Ammonium chloride and zinc chloride. Is it called double salt flux. Do triple salt and quadraflux give better result in terms of surface finish and zinc consumption?

Regards

Atul Mishra
Pipes manufacturing - Anjar, Gujrat, INDIA


2007

A. Dear Atul,
Galvanizing Fluxes Are:

   Name       Formula     ACN   Uses
Monosalt ZnCl2.NH4Cl 0.4 Sheet
Double Salt ZnCl2.2NH4Cl 0.8 Preheater Gen. Pipes
Triple Salt ZnCl2.3NH4Cl 1.17 Dryer Gen. Pipes
Quadraflux ZnCl2.4NH4Cl 1.6 Gen. Pipes

Many pipe galvanizers use double salt with starting ACN=0.8. In doing rework zinc is stripped into the flux and the ACN goes down as the pH goes up. Over time these out-of-balance conditions interfere with fluxing action. Flux function can be restored with proper amounts of hydrochloric acid and ammonium chloride. This is true of all fluxes.

Pipe galvanizers often use high baumé double salt and get thick zinc coatings on the pipes, particularly on the inside diameters (as much as 200 to 1000 microns). With quadraflux the i.d. zinc coatings are much thinner (as little as 20 to 40 microns). To use low baumé quadraflux the proper equipment after fluxing which includes a broad, tilted "breaking table," walking beam transport, and suitable zinc immersion device (like progressive screws)are required.

For pipe galvanizing, quadraflux is highly successful in South Africa, Southern India, and the USA. It has not been successful in South America and Central India. Proper equipment is essential.

For general galvanizing, the double salt is widely used in Europe (along with preheaters), whereas in the USA triple salt and quadraflux are widely used (no preheaters) at 71 deg. C.
With proper equipment and flux maintenance, YES, quadraflux does give a higher quality product and much less zinc is consumed. I have published a comprehensive article in the journal Metal Finishing regarding quadraflux and you can get it off the internet.

Regards,

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


2007

Q. Thank you Dr. Cook for your comprehensive reply.

I think by "breaking table" you mean skid or stand before dryer where bundle is kept after fluxing and feeding in to the dryer. We do not have walking beam type conveyor but chain conveyor and pneumatic cylinder (Plunger Type) dipping flux. Should I adopt quadraflux since I cannot change the equipment?

Regards,

Atul Mishra [returning]
Pipes manufacturing - Anjar, Gujrat, INDIA


2007

A. Dear Atul,
The breaking table is indeed the stand for the fluxed pipes prior to the dryer. The real question here is if the flux is scratched off the pipes prior to entry into the zinc. If the equipment and the pipes do not rub too much then quadraflux at rather low baumé may work for you. Certainly I cannot advise without seeing how the equipment handles the pipes. For small diameter pipes a progressive screw zinc entry is by far the best way to put the pipes into the zinc. A push down device can allow the pipes to bob up causing black (bare) spots. A progressive screw is strictly one way and that is INTO the zinc. Bending of the pipes during entry is also a problem well known to you.
Regards,

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



2007

thumbs up signDr.T,
What we really NEED is a Seminar organised by you in India (a 3 Day Workshop?).

Regards,

Vipul Tewari
- Kolkata (Calcutta), West Bengal, India



"Handbook of Hot Dip Galvanization"
by Maass & Peissker
from Abe Books
or
info on Amazon

August 9, 2008

Q. Doctor cook
I want to ask is there any chemical which can be used before galvanization with flux or even alone so that
1. It will enhance & intensify surface chemistry
2. It will strengthen the contact bond of interfaces during the process as the iron and zinc combine to form an intermetallic compound at the surface
3. It will heighten the catalytic property of the flux by reducing the surface tension between interfaces.
4. It will let the metal to attain the highest Galvanic protection with zinc by reducing interfacial tension under basic chemical mechanism.

Rahul Sidher
- Hisar Haryana India



July 30, 2009

Q. Kind Attn: Dr. Thomas H. Cook

Dear Sir,

We got the good knowledge of your suggestion regarding Galvanizing Flux; but still we are facing some problem regarding fluxes.
We are manufacture of Galvanizing flux in India. We have hot dip galvanizer customers in India, they are manufacture of transmission tower & we are supplying galvanizing flux to them, but we are not able to satisfy their quality of flux.

As you suggest in above conversation regarding wetting agent(surfactant) in the flux. We want to try this also, for that we want to know the correct name of the wetting agent (surfactant) and the process. So we can satisfy our valuable customers.


Regards,

Vijay K, Limbachia
- Mumbai, Maharashtra, India


July 22, 2010

Q. Sir,
what is the function of BLANKET FLUX in hot dip galvanizing process?

Arpan Mallik Mallik
Trainee quality engg - Kolkata, West Bengal, India


"Hot Dip Galvanizing
A Guide to Process Selection & Galvanizing Practice"
by M. J. Hornsby
from Abe Books
or
info on Amazon

March 2, 2012

Q. Dr. Cook,
I have read your immensely helpful paper on galvanizing flux. I am currently puzzled by a few things, however. I would very much appreciate if you could give me an answer to these:
1. For quadraflux, the baumé range is quite small and as you have mentioned can go up with use. How do I control the rise of the density?
2. What would be the best indicator to tell me at what pH my bath is?
Much appreciated.

Tatyana M.
- Canada


March 7, 2012

A. Sir:

To your first question--- The baumé of the flux likely increases because rework or racking fixtures with zinc on them, or spin baskets (to be stripped) are put into the flux and some zinc dissolves causing the baumé to rise. If needed some flux should be taken out and water added. In this stripping process the baumé rises, the pH rises (counter balanced to some extent by acid carry through of the acid rinse), and the ACN drops. Thus the ability to correct for baumé changes, pH changes, and ACN changes are all three required.

To your second question--- The pH testing and control are consulting matters. This Sunday March 11, 2012 I go consulting to three plants and will install the required testing and control equipment, along with other things.

It would be interesting to know what part of Canada you are residing in.

I presume the article you are referring to is the one with the title like: "Testing and Control of Hot Dip Galvanizing Flux" in Metal Finishing?

Regards.

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


March 12, 2012

thumbs up signDr. Cook,

Thank you for the answers. Indeed that was the paper that I have studied. I am writing to you from Scarborough area in Toronto. Currently I am looking to see how I can make maintenance of the quadraflux bath easier (stretching the baumé range by adding wetting agents?).

Tatyana M. [returning]
- Canada, Toronto



Compensating for Fe Concentration When Analyzing Flux

March 15, 2012

Q. In considering flux, and analysis of it, what correction should be applied to measured density to compensate for Fe concentration.

If measuring flux density to ensure correct strength, in a solution with high [Fe], say 2-4% that some operate at, what correction gives a density that simulates 0% Fe?

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



March 18, 2012

A. Geoff:

2% to perhaps 4% iron (Fe+2) in the flux likely increases the baumé by about 2 units. I rarely consider this and have found the best baumé in most cases to be near 13 for quadraflux, and temp. of 71 C. Keep in mind that the original concept of ACN was ammonium chloride as numerator and zinc chloride as denominator. With higher dissolved iron a better concept (ACNV) is to have ammonium chloride as numerator and the zinc chloride plus iron (II) chloride as denominator.

I am now at a site where there are many things I do not like including dirt floors and dirt packed tight against the sides of heated caustic, sulfuric acid, and flux tanks. This causes the heat to go into the ground. This location will be a difficult one. They also use carbon-stick heaters which combust under the solution in the tank, without using suds (causes double the heat bill).

Regards,

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


March 2012

! I am on a trip in Eastern USA. The baumé of the flux here is now 14.5. I would rather have it 13.

Three days ago the ACN was 1.0, then 1.2 and today 1.4 (just now being tested here in the plant). I may raise it to 1.6 tonight. Going from 1.2 to 1.4 ACN gave much better zinc drainage at the kettle and the icicles are now thin like a foil gum wrapper, whereas yesterday they were still like a pencil point.

The flux required 10 gallons of conc. HCl to attain the proper pH of 4.2 the first day. Yesterday it required 4 gallons of HCl. The test today shows the pH is correct. Thus the flux side is good.

I am doing some other things with excellent results, giving absolutely NO BLACK SPOTS whatsoever and the product is very bright indeed.

Regards,

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


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