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topic 43365 p.3

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

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A discussion started in 2006 but continuing through 2019

July 11, 2012

Q. We have a continuous steel wire galvanizing line here in Kampala, Uganda.We are facing the following problems:
High dross formation and An acid flux bath.
We try to neutralize the flux bath by adding an ammonium solution but the rate of con termination is high.
Yes we have a rinse tank but still its not enough!
Sir, what is your advise on the above?

Collins Wasswa
- Kampala, Uganda


July 18, 2012

A. Collins:

Are you "wet" or "dry" kettle? What is too high of rate of dross? How long do your kettles last?

Regards,

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


September 23, 2012

Q. Dear Dr. Cook:
I have a serious problem with bare spot because of Chinese raw material. I produce steel tower angle and plate, our flux is double salt acn 0.8 and fe+2, 0.28%, so, my supervisor tries to solve the bare spot problem by brushing the angles with ammonium chloride solution for 45 minutes, then immersing in zinc kettle. The result became okay but as per my little experience the dross will increase too much. I read an article before that every additional gm of ammonium chloride causes 20 gm of dross, is it right or not? And what's the side effects of doing it my supervisor's way?
Thanks.
Regards,

Ahmed Hassan
technical manager - Yingkou Anshan China


simultaneous September 25, 2012

A. Sir:

Your English is excellent.

It is NOT true that 1 gram of ammonium chloride in the flux gives 20 grams of dross at the kettle.

Your question reminds me of my work 40 years ago and for this I feel badly for you. Properly formulated, tested, and used, quadraflux does an excellent and extremely effective job of galvanizing your types of steel (assuming the pickling is good). Unfortunately there are some extremely bad inhibitors in the market place that prevents proper pickling. I do have a good article in the journal titled Metal Finishing. The name of this article is something like: "Testing, Control, and Use of Hot Dip Galvanizing Flux." I looked for a copy here at home and was not able to find it to properly reference it, sorry. This website has a search engine and I have made many replies to questions like yours. So please search this website and the general web via Google.

Regards,

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


September 25, 2012

A. Dear Ahmed;

Is your kettle dry or wet? In dry applications, excess ammonium chloride will have no effect, just extra fumes.

Why don't you try using sandblasting -- would be quicker and cheaper.

Ozge SARACOGLU
- Ankara, TURKEY


September 26, 2012

Q. Hi Ozge,
Sorry, I forget to tell you that our kettle is dry and we have preflux double salt with temperature 50 °C and in our kettle we never use lead; we can use nickel and aluminum and bismuth alloys.
And I have good friends in Turkey, Mrs. Isik Spaci. They are good galvanizing consultant.
Thanks
Regards
Bye

Ahmed Hassan
- Liaoning, China


September 26, 2012

Q. Dear Dr. Cook /Mr. Ozge.
Thanks a lot for your kind support.
1st, I suggested the shot grit blasting since the sand blasting will increase the silica in the degreasing and pickling.
Regarding the ammonium chloride, does it really only cause white fumes, or increase the dross & ash also?
Also, I think that one mole or gram from iron gives you 25 mole or grams. Am I right?
Dr. Cook, you kindly suggested me to use quadraflux, can you give me the best specifications (composition ratios, pH, temperature, etc.] Please advise.

Thanx
Regards

Ahmed Hassan
- Liaoning, China


simultaneous September 27, 2012

A. Sir:

Quadraflux is 1.6 parts ammonium chloride and 1 part zinc chloride. Best baumé is 13. Best pH is 4.2. Best temperature of flux solution is 71 °C. Keep product in flux solution about 3 to 5 minutes to heat fully the steel. Take out steel and lay at an angle to promote drainage. Drying should be done within a few minutes. Fluxed steel should enter kettle with little spatter. Faster entry is best. Slower withdrawal is usually best.

Regards,

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


September 28, 2012

A. Dear Ahmed;

I will give Mrs. Sapci your compliments at our next meeting.

Ammonium chloride will cause increase in white fuming. Double salts are always "fumeless" but as triple (ZnCl2.3NH4Cl) or quadraflux (ZnCl2.4NH4Cl) would have higher fuming. You might also try to sprinkle ammonium chloride powder before you dip into zinc. This is very old application, causes heavy fuming but best option for poor pickled parts. It won't affect your dross and ash formation, but will cause drop in aluminum content (especially if your kettle is small).

Also you might try to agitate your acids strongly or heat them over 35 degrees. This would give better pickling.

One more option; dip your products by normal procedure, immerse, withdraw, dip into flux again without cooling, re-galvanize. I used to do it a lot with angles, I-U beams, which have very poor steel quality. But of course coating thickness will exceed 150 microns.

Dross is 96% zinc and 4% iron. Thus we can say 1 gram of iron will produce 25 gram of dross. But actually this doesn't mean that every 1 gram of excess iron will result in that much dross. Some will dissolve in zinc (if your nickel is high this solubility will be less) some will oxidize while immersing, (zinc ash may have 3% iron) etc. The rest will form dross.

Quadraflux is ZnCl2.4NH4Cl. Best ideal pH range is 4-4.5 (best will be 4.2) - use titration method, pH meters are rubbish -- and ideal Temperature would be 60-65 degrees.

Ozge SARACOGLU
- Ankara, TURKEY


September 29, 2012

A. Ozge:

35 °C (95 ° F) is too hot to heat 17% HCl. The fumes will destroy the roof and the building, which will happen anyway if a good inhibitor at the right concentration is not used.

Regards,

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


October 2, 2012

A. Dear Mr. Cook;

Of course I am assuming inhibitor, good ventilation system and moreover an enclosed pretreatment unit. Thanks for mentioning about all these.

Ozge SARACOGLU
galvanizer - Ankara, TURKEY


October 2, 2012

A. Sir:

HCl is a gas which is heavier than air. It fills a galvanizing plant from the floor upward. This gas along with water vapor is terribly corrosive. I have seen steel corrosion in warmer climates for areas around a galvanizing plant corrode to orange black dust over the years. The best HCl fume control that I saw exhausts the HCl gas down through the floor. Simply put the best HCl temperature range in my experiences is between 70 and 85 °F. Above 85 °F the workers and the cranes suffer.

From which country do you purchase your HCl inhibitor and at what concentration do you use it? Also do you test its effectiveness in the HCl pickle tank?

Regards,

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


simultaneous October 4, 2012

A. Dear Dr. Cook;

I know all these. Because of all things you mentioned, we have good ventilation system that is sucking and blowing air 10 cm below the acid bath top edge. Thus, all acid fumes are sucked and sent to treatment unit. I guess it is forbidden to give brand name but we use an Italian famous brand, which has 2 additives (inhibitor and anti vapor). Also our environmental advisors regularly measure the acidity in the air and reports that it is very low. And also you can notice little smell, even standing in front of a fresh acid.

Even I don't usually exceed 30 °C (guess it is like 85 °F) , but in extreme cases exceeding this value does not cause problems for us.

Ozge SARACOGLU
galvanizing - Ankara, TURKEY


October 4, 2012

A. There's a lot to be said about having a good inhibitor, as Tom has said.
There are some that prevent proper pickling.
There are some that do nothing useful.
There are only a few that do what you really want them to do - allow the dissolving of oxides of iron while preventing dissolving steel.

HCl fume is an issue, dependent of temp and concentration.
In "sunny" Scotland the temperature is not much of a problem. I remember one year breaking the ice on the surface of one pickle tank!

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



October 5, 2012

Q. Dear Geoff;

Do you mind if I ask about your average pickling time during "winter" (for fresh acid and for 30 baumé)?

Ozge SARACOGLU
galvanizer - Ankara, TURKEY


October 6, 2012

A. Ozge,

You answered my question of where you get your inhibitor EXACTLY AS I EXPECTED. Regarding this supplier I respond "NO COMMENT."

Incidentally 30 °baumé FRESH HCl is NOT available, the highest concentration is 20 ° baumé (e.g. about 35.5% HCl). After being fresh the dissolving of iron and zinc causes the baum é to rise to the 30 to 40 ° baum é range. Some iron is required for good pickling in HCl.

In my inhibitor testing of 38 years ago (now published in the magazine METAL FINISHING) I did all my testing at 3 parts inhibitor/10,000 parts mixed acid (e.g. 3 liters inhibitor/10,000 liters mixed acid). For sulfuric acid I used 10% acid, 2% iron, 1% zinc and 160 °F. Only one inhibitor (produced in the USA) did everything I wanted, including NOT slowing the pickling (in a separate test). For HCl I used 1:1 HCl/water 3/10,000 and the same iron and zinc and at 90 °F. Again only one (produced in the USA) did what I wanted.

About 10 years ago I was called into a new start-up plant using sulfuric acid, which previous to my arrival had 3 (55 gallon) barrels of fume suppressant plus inhibitor put into each of three 20,000 gallon pickle tanks. The fumes were so bad that I could NOT walk across the plant floor crosswise. Simply put, my lungs closed up and I could not take a breath. The workers were having nose bleeds and quitting. I drove to a nearby galvanizer and obtained two 5 gallon buckets of the good inhibitor and put one gallon into each acid tank. The next morning I came into the plant and the workers all came up to me and were thanking me for the clean air that they could take a breath. The supplier blamed the first product on a "bad batch." RIGHT!!! With the good inhibitor the air in the plant was the same as clean outdoor air.

A few months ago I went to the East Coast of the USA and noted that the HCl was not properly pickling. A test confirmed that the acids were over-inhibited (same supplier) as the case 10 years ago. This was quite unusual because the plant manager said they had not added any inhibitor for the last 5 months. To increase pickling they had heated up the HCl tanks and the guy was there getting ready to remove and replace the roof. All the acid tanks were then hauled away and new acid brought in and inhibited with the good inhibitor. It was a pleasure having acid that pickled very well and with almost NO fumes. Thus the combination of a good inhibitor and with proper testing, fast pickling, very low fumes, and very long acid tank lifetimes are easy to attain.
Geoff has very good experience.

Regards,

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


simultaneous October 9, 2012

A. Pickle time?
It's like asking how long is a piece of string.
There are so many variables.

But, structural steel, (beams and columns for buildings) in winter might take 2-4 hours.
We manage to use pickle tanks where heavy long pickle time material is at the bottom, while lighter quicker material sits near the top.
In another plant further south (warmer), winter pickle time can be 1-2 hours for light material.

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



October 9, 2012

thumbs up signDear Dr. Cook,

Sorry for my rubbish English, I have asked for 2 different values; new fresh acid and 30 baumé acid (after it is used and reached to 30 baumé).

After your good response I will consider about the inhibitor and temperature. Thanks for your help.

Ozge SARACOGLU
- Ankara, TURKEY


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