Hot-Dip Galvanizing Kettles: how to build or where to buy

A. It is indeed an interesting idea. But a kettle is a wearing item, it slowly dissolves in the zinc. Putting a thinner lining on the inside would require that the lining itself does not also dissolve, otherwise after the lining is dissolved, the lower grade steel behind it would rapidly deplete.

So the question really is what rate does some other alloy such as "stainless" dissolve. You mentioned a family of steels with widely variable chemistry. The more common forms of Stainless, 316, 304 etc would not be suitable, their rate of dissolving is slightly slower than low Si carbon steel, but not that much. Someone might know about special grades such as duplex, where the Fe content is low or nil. That might be the area to look at.

Cost is always a consideration too. I could imagine a duplex steel kettle being very expensive.

Zac,
I wonder if your customer has asked the same question of 2 suppliers and you both posted your question here...

Your customer clearly understands that the correct steel for making kettles is very important. The most important elements are Si and P. Si should be as low as possible, also P. C is less important, but 0.1 might be OK. In China the grade that is commonly used is XG08.
The effect of higher Si% is rapid dissolving of the kettle in the zinc, and so very short life of the kettle. That means more frequent changing of the kettle and all the very high costs associated with that.

Geoff, I went back and checked to better understand the duplication. Both postings are from the same IP address, which is neither in Shanghai nor Tianjin :-( Gentle Readers, please -- We established this Q&A forum years before the internet ... It was an instant success because, unlike the countless other 'Shop Problems' columns in nearly every technical magazine of the time, we opted for the camaraderie and human interest of people posting with their real names, real locations, and real situations. We ask that if you are not willing to post with your real name & location, that you retain a consultant for confidential discussions, or read anonymously, or post on a different site rather than corrupting a mission that I and so many posters have been on for 36 years :-) Luck & Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey

A. In the United States it called Flange and Firebox quality steel. It basically is a very low carbon, very low silicon steel plate. Rods for welding it should also be low in C and Si.

A. Sir,
Cast iron is NOT a suitable material to make a galvanizing kettle. In the "old days" the common material was fire box steel. Some years ago "Max Ten" was specified which means the alloying agents in the steel would add up to no more than 0.10%. Today modern kettle makers know what can and cannot be used to make a galvanizing kettle. Certainly silicon, aluminum, and phosphorus contents in the steel must be VERY LOW. Also one MUST use the correct welding rod or else the welds will be "eaten up" by the zinc. In addition only the side walls can be heated (NEVER THE BOTTOM). Also a horizontal stripe 6 inches high at the top of the walls and a horizontal stripe 12 inches at the bottom of the kettle are insulated and (NEVER HEATED). The maximum heat throughput through the walls is 10,000 BTU/sq.ft. on the heat zone of the side walls. My article about a year ago in Metal Finishing (the magazine) would help you. A proper kettle with a proper furnace can have a lifetime of 10 years or more even with high production. A kettle depth to width ratio (e.g. d/w) should be 2 or greater.
Regards,

A. Use a special alloy or a ceramic bath.

A. Dear Sir:
About 35 years ago kettle makers used "max ten" which means that the kettle "steel" was nearly pure iron with the combined alloying agents adding up to less than 0.10%. Armco made "steel" (iron) of this type. Today I do not think this type steel is available. Another term that I have heard is "boiler plate steel."
Today there are two kettle makers that likely make most of the galvanizing kettles. One is in the USA and the other is in Germany. These kettles now usually have 2 inch thick walls (years ago they were 1 inch thick). The weld rod and welding methods are quite specialized. I recommend that you purchase rather than make a kettle. With a proper kettle and proper furnace, the kettle can last 10 or more years. A poor kettle and poor furnace can give a kettle life of only a few months.
In the journal Metal Finishing you can get my article on kettle furnace design though interlibrary loan (xerox copy) from most large libraries. This article details the most efficient system which is end-firing with high velocity burners. Galvanizing kettles and galvanizing kettle furnaces are NOT do-it-yourself projects.
Regards,

A. The most critical element in the steel for kettles is Silicon.
This needs to be at or close to zero.
Silicon is used extensively in steelmaking to de-oxidize the steel while molten and in casting processes. (The slabs cast in continuous casting plants are later rolled to plate.)

Alternative de-oxidants are available for this special grade of plate.
S and P are also important.

A. Sir:

Obtain and read the two books: Hot Dip Galvanizing by Heinz Bablik and Handbook of Hot-Dip Galvanization ⇨
by Peter Maas.

Visit galvanizing plants including San Diego Galvanizing and LA Galvanizing.

California is an environmentally tough state to have a galvanizing plant. Check the California Proposition 65 list to better understand the regulations, especially with regard to lead, nickel, and hex chrome.

Regards,

A. Hi Asit. Welcome! We appended your inquiry to a thread which answers some of your questions, but it's a tall order to ask for complete instructions for safely designing and fabricating a galvanizing tank. I don't think it's going to happen for free in a public forum.

Good luck, but if you don't have all the info you need quickly enough, please see the ads for galvanizing consultants at the bottom of the page.

Regards,

A. You should not attempt to make a galvanizing tank yourself if you cannot answer these questions.

Your depth of 0.5 m seems far too small. What could you use such a tank for?

At length 5.5 m, more typical dimensions would be 1.2 m wide and 2-4 m deep. Material will be very low Si steel, a special steel not readily available, and made especially for this purpose of galvanizing tanks. Typically its 50 mm thick. Special welding electrodes are required, and special techniques for welding.
There are 3-4 suppliers worldwide who supply long lasting kettles, but the furnace is equally important for long life.
You might expect 10 years or more from a well made kettle of the right material.
You might expect a few months from a homemade one.

A. Hi, Asit.

Its better to define first size of your materials which are going to be galvanize and required production per day or per shift.

Based on same you have to select the size of your Galvanizing kettle.

A. Dear Friend
The Welding Electrode must be of same material as Plates. I recommend 45 S, D&H electrodes for DSQ steel.

A. Dear Ruphert Connok.

It's better to hire a consultant and supplier who can guide you how to start Galvanizing plant. It will be more advisable then doing it yourself.

Thanks.

A. Not a good idea to build your own kettle for galvanizing if you have to ask how to do it.

If you want it to last any time, then buy one from a reputable supplier. There are several, even one not so far from you.

Homemade might last 6 months. Bought one 10-14 years.

Hi cousin Rama. That question was already answered in quite deep detail. Please try to request clarification rather than starting over. Thanks!

Regards,

A. Dear MR. Rama Rao Ch.

for Galvanizing Bath , in India, people use DSQ Plate (dead soft Quality).

? Hi Teslime. We appended your inquiry to one of several threads here on galvanizing tank construction. I'm reading between the lines that you are talking about a tiny kettle for a short-term experiment, but if you can give us a feel for its size it might be helpful.

Regards,

A. Several steel manufacturers make a special steel for this application. It's a low carbon mild steel, but with ultra low Si - almost zero. I'm not sure if there's a grade name.
To make a kettle out of plain grades of steel would be to ensure a very short life for the kettle.

A. Dear Sir.

It's better to purchase Kettle from Reputed manufacturer as they have experience in manufacturing kettles.

Steel generally used to manufacture Kettle should be low carbon, low silicon, with same property for welding electrodes.

A. Dear Juan De Lira

As per specification of A 36 grade steel, Silicon content is much more higher then allowable to fabricate Galvanizing Kettle.

Galvanizers prefer to have silicon content Trace or maximum 0.03 % for better life of kettle.

A. Dear Aleksandro Bardhi,

Selection of Metallic or Ceramic bath mostly based on what kind of materials you would like to Galvanize.

Generally for Fasteners, threaded items peoples are going with Ceramic bath with higher temperature otherwise for structure and bigger job, better to go with Metallic bath.

A. Dear Sai.

Basic reason of deterioration in Galvanizing pot are

1 ) uneven heating
2 ) furnace design.
3 ) Deposition of Hard zinc (Dross) inside zinc kettle.
4 ) Quality of Pot materials.

A. The best material for kettles is "CLASS A DSQ (Dead Soft Quality)" and "GP2"

Warm Regards,

Hi Bob. Apologies but we've learned from 25+ years of this forum that suggesting brands & sourcing questions on a no-registration-required website is a huge mistake (why?)

We hope you'll start by contacting Western Technologies [a finishing.com supporting advertiser] and Gunatit Builders [a finishing.com supporting advertiser] who are making this forum possible for you, before using google for other possibilities.

Regards,

A. Dear Marcin.

According to your subject, it looks like you would like to start small Hot dip Galvanizing plant.
first of all we need to know what kind of materials that you are going to be Galvanize, what would be size of materials and what amount of quantity you would like to produce per day in 8 hrs. shift.

Based on all above , we would suggest you more on size of Kettle and its feasibilities.

? Dear Sir.

You mean to say , you would like to galvanize 12" dia pipe and length of pipe would be 6'-0" long and you would like to dip it vertically.

At a time how many pipes you would like to dip or per day how many pipes you would like to Galvanize.

Based on your answer we will revert back with suitable size for your product.

adv.
You may contact us directly on sales@gunatit.com

A. Hi Ilesh. No, I think Marcin is proposing that his galvanizing kettle will be a 12" diameter pipe standing about 6' tall, with a bottom plate welded onto it, and the weld protected from the zinc by powdered ceramic insulator material.

I think, however, that 12" diameter pipe is seam-welded rather than cast or extruded. So if the zinc preferentially attacks weld lines, this would still be an issue.

If you get a chance, look at Marcin's fascinating "TED Talk". His interest is in deploying small, simple, inexpensive machines around the world as the building blocks of civilization.

Luck & Regards,

A. Ted,
At a substantial cost increase you can get tube that has no welds. They are extruded with a mandrel piercing through the billet/ingot.

Q. I would be interested to know if the zinc attacks the welds due to the slightly different chemistry or if the microstructure changes due to the heat of fusion.
Most pipe/tube is made by induction welding which is a forge welding process so there should be minimal if any change to the chemistry of the weld.
If it is due to the different microstructure then normalizing the tube should mitigate the issue at the weld (and if I understand Marcin's intent, it is a relatively easy operation, at least for someone who in going to galvanize things).

A. Hi James. Although I don't have galvanizing plant design experience, I have 50 years of electroplating plant design experience, and the shop environment and the acids used, and their effects on the structure, are very similar. Although zinc coatings like electroplating and galvanizing are excellent at corrosion prevention in many outdoor environments, they work only because their corrosion products are stable, tight, and relatively non-porous in most atmospheres.

You may remember from science class that zinc is a very active metal, with lab demos like zinc ribbon dissolving almost instantly in hydrochloric acid. Zinc electroplating and even zinc galvanizing are therefore very very poor finishes in acid-laden environments. I suspect that zinc-rich dip-spin or aluminized coatings would be just about as bad. I think that painted steel, or alloy bolts (and stainless steel for any very small fasteners) is the way to go.

Luck & Regards,

A. Hi Basel. Yes there is a risk. Please see Dr. Thomas Cook's comment on this subject on thread 57908

Luck & Regards,

A. Yes there's some risk.
A kettle should not be overheated locally, but requires the temperature of the steel to be as even as possible. If it reaches about 500 °C, then serious erosion of the kettle wall occurs. This is the kettle dissolving in the zinc. Its fastest rate is somewhere around 530 °C, but anything over about 480 °C is too fast. This thinning of the kettle wall keeps going wherever zinc is touching the wall on the inside.
If the zinc level is low, then the top layer of zinc is touching, however low that might be. A furnace is designed to have an unheated area at the top, perhaps about 20 cm from the lip downwards, and it's for this reason. Heat is then only applied to the area that is internally submerged in zinc, so the heat flows into the zinc and doesn't cause the steel to overheat. If you let the level fall too low, below the insulated unheated area, then the steel of the kettle will overheat.