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Galvanizing Kettle melted -- why?

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An ongoing discussion from 2003 through 2014 . . .

Is it possible to electrolytically slow the corrosion of a galvanizing kettle?

(2003)

Q. Hi, we are Hot dip galvanizers of small articles in large numbers and use conventional and traditional methods not exactly perfect though. Just an idea ... we also have the problem of the steel pot slowly getting eaten away by the zinc due to dross formation. Is it possible to slow the reaction of dross formation by some electrostatic or electrolytic means? E.g., by applying a voltage across the zinc and the pot?

Dipesh Gupta
engineer - Chd, Uttar Pradesh, India


(2003)

A. How much life are you getting out of your current kettle and how much due you hope to get? Improving your burner system would probably be the best way to extend kettle life. I assume your kettle is made from steel with the proper steel chemistry (kettle steel). Impressing a current to the kettle may not be possible with the high temperatures.

Mike Stroia
galvanizer - Canton, Ohio


(2003)

A. Regular dross removal and agitation is essential (every 2 weeks minimum). Kettle must be ultra low Si content. Low iron level in flux solution (<1%) helps.

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




Locating cracks in galvanizing kettle

(2005)

Q. I am a material science student of university of Lagos, Nigeria. I am presently doing my industrial attachment with galvanizing industries limited. The galvanizing kettle has cracked and it takes a long process to determine the cracks (6days). Is there anything like a crack detector which can tell the exact places of the cracks immediately.

Bukky Lawal
student - Lagos, Nigeria


(2005)

A. X-Ray

Tom Gallant
- Long Beach, California, USA



Safely emptying the galvanizing kettle

December 6, 2011

Q. Hello Sir. Our zinc kettle is reported for leakage at several points. We now want to empty the kettle. What is the best and safe technique for this? Once we tried via buckets and then dipping those buckets in water and after that taking the solidified zinc out of the buckets, but it's taking so much time and blasts are also reported when dipped in water.

Khuzafa Rauf
- Dammam, Saudi Arabia


December 8, 2011

A. Buckets are NOT a safe way to empty a kettle. You need a pump and if you have holes it needs emptying quickly.

Its a specialist job, and several such specialists exist, some advertise on this site.

And don't cool molten zinc with water. You risk lives being lost!

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



December 26, 2011

Q. Thank you so much for the kind reply sir. Our kettle has been emptied and now we are planning to replace it with the new one. You told me not to solidify zinc with water, a part from the blasts and splashes, is there any other effect on the zinc quality by doing so? Can you kindly refer some book/literature about this very issue (regarding maintenance in HDP) I am a very new person in galvanizing industry and would really love to learn from you. Thanks a lot again for your kind help!

Khuzafa Rauf [returning]
galvanizing - Dammam, Saudi Arabia


December 26, 2011

Q. Sir:

How many years did your galvanizing kettle last?

Regards,

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


December 28, 2011

A. The reason to not solidify molten zinc with water is to avoid trapping water beneath zinc where it can explosively vapourise, forcing the zinc to violently splash.

Zinc so cooled by water is not damaged, and is reuseable, but there are much higher losses due to the higher surface area, and resultant oxidation on re-melting.

So the reason not to solidify with water is mostly a safety one not so much a metallurgical one.
After solidification, water could be used very carefully to speed up cooling, but not too cold or you risk water inclusion in the ingot, and on re-melting this could explode.

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



May 5, 2012

Q. Sir there is a leakage in our galvanizing kettle, we solidified the zinc in that kettle, now we are are going to repair it via weld, is it technically right? your suggestion please

Khizer Abbas
- Pakistan



Steel galvanizing kettle melted

June 10, 2013

Q. Dear sir,

Our galvanising kettle inside plate melted during the galvanizing process. For what reason the kettle melted we did not find out. Kettle is manufactured from dead soft quality steel plate. Thickness of plate 40 mm. Please advise me of reason.

Shehel Rezvi
- Dhaka, Bangladesh


June 23, 2013

A. There's not enough information in the question to give a meaningful answer.
What tonnage galvanized by this kettle?
What operating temperature?
How many times frozen? For how long?
What actual grade of steel was the kettle?
What material being galvanized? At what rate?
How long a life did the kettle give?
What drossing procedure? (how often, how much)
What flux type?
How heated?
What furnace design?

All this info is relevant, but even then an answer might not be obvious. Answering these "might" reveal a suggested cause.

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



January 12, 2015

Q. Hi,
A project has been assigned to me on "Fabrication of a Galvanizing Setup". Please can anyone give me suggestions about the materials used for galvanizing kettle?

SHAHZAD KHAN
Student - Karachi,Sindh,Pakistan



January 12, 2017

Q. Hello ! Our new zinc kettle manufactured by steel of CGL is is cracked during initial heating up. The temperature was raised up to 487 °C. What may be the reasons of cracking the new pot ? Please answer.

Saiful Islam
Making CI sheet - Dhaka, Bangladesh


January 30, 2017

Q. Sir,
our zinc kettle was detected leaking in December 2016. the zinc has been evacuated and the leakage points/area have been identified. we gouged (using gouging electrodes) the leaking points/area and fill up the area using super quality welding electrodes imported from india. My questions are:
1. what is an estimate quantity of LPG (Liquefied Petroleum Gas as source of heating the zinc kettle) required to melt the evacuated zinc and new zinc ingots that will be added?
2. how long (days) will it take to melt the zinc for production to start sine we are starting all over again?
3. what is the expected life span of this repaired zinc kettle if we galvanize 40tons of steel per day?
many thanks

Jinadu bola
- sagamu, ogun, nigeria


February 2, 2017

Your questions appear straightforward, but actually are quite difficult to answer.

1. what is an estimate quantity of LPG (Liquefied Petroleum Gas as source of heating the zinc kettle) required to melt the evacuated zinc and new zinc ingots that will be added?
Many factors can influence this. The efficiency of your burners; insulation effectiveness of furnace, insulation effectiveness during meltout of the surface of the zinc;


2. how long (days) will it take to melt the zinc for production to start sine we are starting all over again?

This is the wrong question, and that you are asking suggests a reason for the kettle leak.
You should be asking what rate of temperature increase should I maintain in a melt-out profile. The answer might be somewhere in the region of 5-17 °C per hour, but with some stopping (hold) points at the two main critical temperatures during this operation.

3. what is the expected life span of this repaired zinc kettle if we galvanize 40 tons of steel per day?

That's like asking "How long will my tyre now last with the puncture repaired? There are so many variables involved that the answer could be from weeks to years.
For example these factors: Residual kettle thickness; zinc chemistry; flux practice, hours of operation; temperature of normal operations; chemistry of typical steel; drossing practice; ashing practice; rate of immersion; rate of withdrawal; stability of temperature; shape of burner flame; existence of protection plates; layout of kettle insulation inside the furnace and so on...

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


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