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topic 39907 p2

Steps for hot dip galvanizing, p.2

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A discussion started in 2006 but continuing through 2019

July 26, 2012

Q. Hi there.
I would like to have information on how to test the degreaser, acid, flux and passivation baths. I more or less know how, but would like to know the right way of testing these baths, etc. I could go for training if I knew where to go, any help on this would be very much appreciated.
Thank you.
Denzil

Denzil Clifford
galvanizing - Bellville, Cape Town, South Africa


July 31, 2012

A. Denzil,

I visited a galvanizer in Cape Town thirty years ago. The galvanizer that I worked for in JBRG wanted me to collect a flux sample from this galvanizer. The flux was very orange with much precipitate of iron (Fe+3) hydroxide (likely too high of pH). The guy running the place would not let me take a sample and I thought he would throw us out.

Acid degrease has many problems. If reject product or galvanized racking fixtures are put into acid degrease then zinc will dissolve and make the acid degrease not work properly. Also the iron (+2) builds, while the phosphoric acid concentration goes down. Almost no galvanizer takes proper care of acid degrease. For testing-- The phosphoric acid is determined via standard base with proper indicator. The dissolved zinc via EDTA with proper indicator and buffer with sodium oxalate to mask the calcium and magnesium in "hard" water. The density of the acid degrease needs also to be be measured about every month. The fate of the phosphate (into the acid and then the flux) could present problems.

For HCl the acid is tested by standard base and proper indicator. Under about 2% to 5% acid slows pickling too much. Iron (+2) is tested via hex chrome with proper indicator and buffer. Higher iron (Fe+2) speeds pickling. Zinc in acid is tested via EDTA with proper indicator, buffer, and oxalate to mask calcium and magnesium. Zinc in the acid very much slows pickling. It is extremely important to have an effective inhibitor at the right concentration in the pickling acid. Inhibitor testing is available for all acid inhibitors and it is simple and quick. With a good inhibitor at the correct concentration, pickling is fast, the acid lasts a long time, and there are few fumes in the plant. Of all the acid inhibitors that I have tested, very, very few are good.

Flux testing includes wetting agent, ACNV (bake and shake in plant), baumé,' temperature, iron (+2), spectrum of all non-volatile impurities (e.g. sodium, potassium, lead, nickel, manganese, aluminum, etc.), pH, sulfate (when pickling with sulfuric acid),etc.

For chromate quench, the hex chrome concentration is tested via color comparison the known concentrations. The pH is tested via proper color indicators. Total dissolved solids is determined via a conductivity meter. Sodium dichromate works best for hex chrome quenches, whereas chromium trioxide (chromic acid) badly stains the product. Chromate quench is dangerous because hex chrome is volatile and gets into the air. In some parts of the world chromate quench is not allowed, in other parts of the world it is required on specific products (e.g. rebar or guardrail, etc.). At a distance of 3 feet from a chromate tank I measured 1,700% the allowable hex chrome when the product was at 200C.

For many years, I put on 4 1/2 day workshops here on the ranch. With my new inventions and contracted clients, I no longer have time to do so. If I start up workshops again it will be for contracted clients only. Also I only sell dropper bottle test kits to contracted clients.

I enjoyed my work in South Africa and I learned much.

Regards, Dr. Thomas H. Cook, Hot Springs, South Dakota, USA

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747


August 8, 2012

Q. We are expanding our present operation of manufacturing steel boxes for Japan electricity company by setting up an in-house hot dip galvanizing facility. We would like to avoid pre heating the work before dipping in zinc by the use of an oven.
In what way can we avoid the hot oven yet get the work heated before dipping in zinc?

Chrsity Perera
- Colombo, Sri Lanka


August 9, 2012

A. Sir:

Just properly use quadraflux at 71 °C.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747


sidebar2 August 29, 2012

Q. I would like to start a galvanizing small scale plant in Gujarat, India. Would like to know technical steps for galvanizing.

Manish Patel
- Gandhinagar, Gujarat, India


September 2, 2012

Hi cousin Manish. Please do me a favor ...

I run this website and am constantly working to improve it. I can't see it through your eyes and am trying to understand why you would take a question which has been answered, explained, debated, clarified, and resolved ... and then simply copy and paste the opening question again? Maybe you are trying to ask salespeople to contact you? Please clarify. Thanks!

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



September 26, 2012

Q. Dear Sir,

Good Morning, I am RVK Patnaik from India, we have a galvanizing plant. We are facing a problem; can you please advise us how to short out the same.

PROBLEM: WHILE PREHEATING THE MATERIAL (20 FEET ANGLES), WE ARE DOING IN BUNCH (20 NOS.) WHILE PREHEATING BOTTOM MATERIAL IS DRYING BUT TOP MATERIAL IS NOT DRYING. DUE TO THIS LITTLE BIT OF WETNESS, WHILE DIPPING IN GALVANIZING TANK ZINC IS CONSUMING MORE. HENCE WASTE % IS GOING UP.

RVK Patnaik
- Hyderabad, AP, India


September 29, 2012

A. Dear Patnaik;

Can you tell us what temperature is your flux? What type of drying unit do you have? And what temperature? How many minutes do you do drying?

Does your flux have any contaminant like magnesia? Do you use wetting agent in your flux?
And what kind of "bunch" is it? Can you take a photo and upload? [Ed. note: e-mail it to ]

If you answer these questions I can help you better.

Ozge SARACOGLU
- Ankara, TURKEY


October 3, 2012

Q. Dear Sir
Thanks for your response.
Q. Please note that this is transmission tower parts (angles, channels, etc.) galvanizing unit. The tower parts are stacked,bundled for preheating before dipping in hot zinc bath. The jobs are first cleaned by dipping in HCl acid and then further processing is done, like bleaching, etching, etc. Finally the parts are cleaned by hot water and kept for drying, then we are required to heat before dipping in zinc bath. The heat of Zinc bath fumes is also used to heat the jobs, but not that effectively, hence seek your help.
Regards
RVK Patnaik

RVK PATNAIK [returning]
- HYDERABAD, AP, INDIA


October 4, 2012

A. Sir;

I don't really understand what do you refer by bleaching and etching and hot water cleaning. And why they bundle in drying. Don't they do jigging at the beginning?

Normally HDG pretreatment steps are; degreasing, pickling with acid, rinsing, fluxing and drying.

60 °C of flux will give good drying results even with poor drying unit.

Ozge SARACOGLU
galvanizing - Ankara, TURKEY


October 6, 2012

Dear Sir,

Thank you very much for your reply.

Q. Temperature in flux is 60° to 90°. Drying unit it is open MS platform; heat will be provided from bottom. One bundle of MS Angle / Channel will be 2MT. It will take for drying 30 to 45 minutes.

Degreasing, pickling with acid (HCl 30% diluted), and Fluxing is Gallonflux (Zinc Chloride 75% + Ammonium Chloride 25%).

Our problem is while drying the material on MS open platform, bottom material is drying but top material is not drying.

RVK PATNAIK
- HYDERABAD, AP, INDIA


simultaneous October 8, 2012

A. Sir:

What is meant by "Gallon Flux?"

Your flux as described would have an ACN of 0.333 (25/75).

Any flux with an ACN less than 1 does not dry well at all.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747


October 9, 2012

A. Sir;

Open drying systems can be both ineffective and energy inefficient. You might try to cover the top. If you cannot, try some air blades on the top edge in order to trap the heat below.

You should also use some flux wetting agent. This agent will reduce the surface tension of flux, thus preventing excessive liquid to be carried.

Ozge SARACOGLU
galvanizing - Ankara, TURKEY


Readers: although this particular thread wanders all over the place, we have hundreds of threads about specific galvanizing issues. We suggest that you search the site for topics closely related to your questions because potential responders may not find your questions in this gordian thicket :-)


December 17, 2012

Q. Kindly suggest a way so that during HDG no spurting* takes place (other than drying, as we are using drying oven at temperature 60 °C).

* -- Spurting indicates that if moisture is on surface of part to be galvanized, and it is dipped in hot dip bath, there occurs a vigorous reaction with a lot of noise and molten zinc comes out of that bath and makes working condition unsafe.

SURESH KUMAR
- Jaipur, Rajasthan, India


December 19, 2012

A. This "spurting" is a reaction of water on the steel turning very quickly to steam, and in so doing increasing its volume a lot.
While you have the two components of this reaction, water and heat, you can't avoid it, its a physics thing!

And of the two, the only one to be removed is water. You can't galvanize cold, so only drying the steel is left.

There are things you can do to assist drying.
Get your flux chemistry right (getting it wrong can put a hygroscopic mixture on the steel which will absorb moisture from the atmosphere, making the problem worse).

Allow enough time, between flux and zinc immersion.
A good system is that work sits drying, between flux and dip for two dipping cycles. If your dip cycle is say 15 minutes, then each dip would get 30 minutes drying time.

Have some temperature.
Heated dryers are a luxury. If you have one, that's a benefit, but not everyone has them, and successful dipping can be done easily without. Get flux temp high (70 °C is ideal). Leave steel in the flux for >2 minutes. This heats it enough to dry when it comes out.

Manage the splash.
The splash is only dangerous to those exposed to it, so if you can't stop the splash, then protect the people. A fume/splash canopy, inside of which the dipping takes place, means that the splash is contained.

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


December 20, 2012

Q. Dear sir, can I get the design of the canopy as suggested by you so that I can implement in my galvanizing plant?

SURESH KUMAR [returning]
- Jaipur, Rajasthan, India


December 20, 2012

A. There's no one single design for such a canopy. If you intend retro-fitting a dipping canopy it should be specifically designed to fit.

In a cross shop plant, they can be fitted to overhead cranes, or mounted on the ground next the bath.
In long shop plants, more commonly mounted on the ground.
Most have extraction of fume to a bag filter system. They can have armoured glass fitted so that the operator can see in.

The advertisers of plant and equipment on this site can help you. I'm not a plant builder, rather a plant operator.

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


January 2, 2013

Q. Hello,
What a great page for newcomers to the world of galvanising!
I am in the plastic fabrication industry and am considering a small setup for parts that we make to complement our plastic products. The max size I need will only be 500 mm wide x 3000 mm long and 1000 mm deep. Being in the plastics game we can manufacture the tanks easily from PP. Appearance of the finished galvanised parts is not a concern whatsoever, corrosion resistance is the sole purpose. We do not need quick turn around times for the process, drying times, cooling times, etc., can be long. My very simple questions are: can you put a figure on this type of setup? And can you recommend anybody in Australia that I could meet with to help further?
Thank you

Paul Williams
- Victoria, Australia


January 2, 2013

A. Hi Paul. Galvanizing plant designers, suppliers, and installers tend to work internationally. Please consider contacting the supporting advertisers listed in the banner at the top of the page, as only when people like them are willing to pay the bills are these pages which you are complimenting possible.

As robust a corrosion-fighting process as galvanizing is, there may be more practical corrosion-proofing approaches, like electroplating, for limited numbers of small parts.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



February 1, 2013

Q. Hello sir, I am starting a Hot dip galvanizing, hard chrome and blackodize shop in Surat city. But I have no more knowledge in this area. So give me some good ideas.

Gosai Jaydip
- Surat, Gujarat, India


ASM Metal Handbook
9th Edition, Vol. 5

"Surface Cleaning, Finishing & Coating"

from Abe Books
or
info on Amazon

December 2017

Hi Gosai. If you have no knowledge of these technologies, I would suggest that you start with the ASM Metals Handbook Vol. 5, "Surface Cleaning, Finishing, and Coating" which will introduce all of those topics.

Regards,

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



December 20, 2017

Q. Please give the ratio of Molten Zinc, NaOH, HCl, Flux Solution For Hot Dip Galvanizing.

Kush Patel
- Ankleshwar, Bharuch, India


December 2017

thumbs up sign Hello Kush. Apologies but that's an awfully broad question which can't be quickly dispatched on this thread. We have multiple threads, each one with thousands of words, on the suggested ratios for the Molten Zinc tank, the NaOH cleaner, the HCl strength, and the Flux composition. Please search the site and add follow-up questions to those topics if you have continuing questions. This is something that is going to take at least a couple of days of your time. Good luck.

Regards,

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



March 15, 2019

Q. We are going to start a hot dip galvanizing plant for street light fixtures (12.5 m length and 30 cm diameter) in Arab Republic of Egypt and we need you to provide us with the technical steps for galvanizing.

Regards

Abdelhamid Abdelwahab
- Cairo, Egypt


March 2019

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

A. Hi Abdelhamid. That was the starting question of this long thread, and was asked & answered 13 years ago and several times since :-)

At this point, please pose a specific followup question about the answers that were offered, and you'll hopefully get a response. But please recognize that if your company has no people experienced in galvanizing, you will have to retain a consultant or purchase turn-key from a supplier. I don't think you will be able to design a galvanizing installation based on internet information. Good luck!

Regards,

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



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