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

A. There are several answers to your question.
First pH. Yes about 4 is OK. Too low means acid is being moved across from pickling, likely by poor rinsing, or rinsing in acidic water.
Density. There are at least three systems of measuring density, and I've seen galvanizers using all of them. This is similar to different measures of distance (miles / kilometers), temperature (Fahrenheit, Celsius) etc. These density measures are SG (where water = 1.0) Baume: where water = 0, and Twaddle, used mainly for liquids with SG > 1.0. zero Tw = 1.0 SG.
Yu mentioned 20, so that';s likely Baume, (abbreviated "Be") and a good target for flux is 20-25 Be. In SG the target range is 1.19 to 1.22.
But which type of flux? Double salt, triple? quadra? Each has its place, and its different target density (or concentration).
And remember flux is a mixture, nt a pure substance. Its water, ammonium chloride and zinc chloride. The ratio of these last two is what determines the double, triple etc.
Double salt is two parts ammonium chloride to one zinc chloride.
Contamination and wrong concentration are the two most common issues I've found in galv plants. Usually the flux is too weak, and often too high in iron (Fe). Fe should be less than 1%, and preferably less than 0.5%.

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,

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

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,

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,

A. 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.

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,

! 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,

A. Sir,

If these are heavy angles (thick) then your results are average to good. If they are light (thin) angles then your results are very good to excellent.

I believe I have already responded on this website to your other questions.

Regards,

A. Hi, Nag.

Sorry, but in this context I can't quite understand the question. Please take a paragraph to try to phrase your question in terms of the answers that are on the page if possible. Thanks!

Regards,

A. S.R.

Perhaps you could e-mail a photo of a "passing" and a "rejected" "TUBE" with some scale indicator (ruler or tape measure or a human hand in the photo). I have had very good success in reducing ash on product over the years via flux composition. In the last 1.6 years I have had outstanding success, via other means of eliminating flux and ash sticking to the product. The work goes on.

Regards,

A. SR:
I am not able to determine your problems from your photos.

Crux Dee:
First I do not necessarily believe the flux test results. Secondly you are using mixed (both USA and European methods). You have high temperature 65 °C. (USA) but high baumé and low ACN (Europe) flux. My experience is that such mixing of methods does not work properly. I do not have a "manual for flux preparation."

M.Patel:
What is the chemical composition of the brass wire and why would you want to galvanize brass wire?

Regards,

A. Kevin:

Good question. A few years ago I gave a corporate workshop and I tested the 10 fluxes first. In one case, the ACNV was about 0.4 whereas the ACN was 1.2 (near triple salt). The reason for such deviation was obviously the high iron content, which by my limited memory was around 5%. The easy way to answer this question is to calculate both ACN and ACNV but ALWAYS use ACNV as your standard. It has taken many years just to get galvanizers knowledgeable to ACN. Now the task is to get them to understand and use ACNV.

As a side note, a few months ago I found an ACNV of 1.0 for a 10,000 gallon flux tank and advised that about 4,500 pounds of ammonium chloride was required to attain quadraflux with ACNV of 1.6. The galvanizer added about 3,000 pounds of ammonium chloride and then sent it to a flux company for testing. The result was 0.69 for ACN which was clearly NOT correct. This flux had a sulphate of 1.2% and iron (Fe+2) of 0.8%. I have never really decided where to include sulphate but I expect it should be included in the denominator. This has not been an issue for me because the way I test gives ACNV directly and I have used this ACNV very successfully for many years. 15 years ago I made up in lab a flux with ACN = 1.00 and sent it to 13 labs. ALL the labs got VERY WRONG RESULTS. The results are published in METAL FINISHING under a title like TESTING AND CONTROL OF HOT DIP GALVANIZING FLUX.

A. Sir,

I expect triple flux will allow you to galvanize brass wire. Over time, copper will enter the kettle zinc and likely cause the iron zinc kettle to have a short lifetime.

I have no experience in galvanizing brass.

Regards,