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Lead (Pb) in Hot Dip Galvanizing



What is the purpose of lead?

+++

Q. In hot dip galvanising, why do we use a low level of lead along with Zinc with other metal composition in metal pot, and what is the basic function of lead in hot dip galvanising?

vipin jain
Vipin Jain
galvanised steel manufacturing - Biratnagar, Morang, Nepal


+++

A. Hot-dip Galvanizing is based on alloying Iron with zinc. Traces of iron introduced into the zinc kettle(carry-over with the material to be galvanized from wet pre-treatment, from the steel zinc-kettle-wall and the material to be galvanized will alloy with the zinc too, thus forming zinc-iron alloy particles called dross. This dross is some heavier than the zinc and will slightly sink to bottom of the kettle. Lead has two functions: 1. dissolved lead in the zinc-melt has influence on the fluidity of the zinc and will help dross particles sink to the bottom - floating dross particles will cause roughness on the material to be galvanized(bad quality) 2. The lead layer on the bottom of the kettle will prevent dross will be stuck to the iron kettle-bottom and makes it possible to remove the dross from the bottom of the kettle, because lead is heavier than the dross and will not alloy with the dross and zinc - so dross floats on the lead-layer.


Dolf van den Berg
- Leusden, The Netherlands



September 13, 2009

A. DEAR SIR,

IN HOT DIP GALVANIZING, PURE LEAD CHARGES IN POT SAVE THE LIFE OF POT, LEAD BEHAVES AS A CUSHION EFFECT.

rajkumar singh
- bombay, India



What can be substituted for lead?

+++

Q. In my previous question, I asked, why we use low level of lead in zinc kettle, and I got a satisfactory answer. Now will anyone please tell me, can we use another metal in place of lead in zinc kettle for such functionality in the galvanising process.

Regards,

vipin jain
Vipin Jain
galvanised steel manufacturing - Biratnagar, Morang, Nepal


+++

A. Coming back on your second question I don't know the reason why you'd like to change lead for something else, but in Scandinavia lead will be forbidden for environmental reasons.

Bismuth or Tin could be elements to replace the function of dissolved lead. These elements cause a high fluidity of the zinc and a good wetting of the steel. De-drossing of the kettle is hardly a problem. Cominco Canada made investigations adding Bismuth to Zinc for hot-dip galvanizing.

Regards,


Dolf van den Berg
- Leusden, The Netherlands



++++++

Q. SIR-
I WANT TO KNOW - HOW TO REFINE THE LEAD FROM THE BOTTOM LAYER OF LEAD USED IN HOT DIP GALVANISING TANK? I.E., ZINC BASED LEAD, CONTAINS DROSS ALSO? AND WHAT WILL BE THE RECOVERY EFFICIENCY?

GULSHAN RAM
- HYDERABAD, INDIA



What is ideal lead percentage?

October 19, 2010

Q. So what would be the ideal amount of Lead to charge in a Zinc bath (lead layer thickness or % zinc)?

Jaydip Atodaria
- Harare, Zimbabwe


October 19, 2010

A. Hi, Jaydip. Environmentalists think the ideal amount is zero :-)

You can search the site for "lead-free" galvanizing. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

October 26, 2010

Q. Dear Sir,

Thanks for your reply. Our problem is we have a zinc tank 10x1.0x1.5m deep which leaked and we are in the process of changing the kettle. From the pot wear it seems it wore out due to dross. Will adding a layer of lead increase the effectiveness of drossing? Then in that case we need to know when charging the new bath how much lead should be added?
Thanking you.

Jaydip Atodaria
- Harare, Zimbabwe

October 26, 2010

A. Sorry Jaydip, I can't answer that. But if you patiently search the site, similar subjects have been discussed at length by true experts several times. Good luck!

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

May 3, 2012

A. Lead ideal amount is 1.3%.

Khizer Abbas
- Pakistan


How to lower the Lead content in the zinc kettle

June 18, 2013

Q. Hi,
We have a content of 0.11% Pb in our zinc kettle.
Due to new restrictions, we have to lower our Pb content to 0.05% Pb
Are there any other ways to lower the Pb content, then pump out zinc and replace it with new SHG zinc?

Ulf Larsson
- Sweden
  ^- Privately contact this inquirer -^


July 2, 2013

A. Its interesting that someone is forcing you to reduce Pb content. Can you say why they want that?

I think you could perhaps pump the Pb rich Zn off the floor of the tank and so reduce it that way. If you get the free Pb out, and then only replace with Zn without Pb, then it must come down. At about 1% Pb in solution, you probably have some free Pb on the bottom. Getting that out first would help.

Is there a time limit by which you must do this? If not, I think you could get it down in 6 months or so without a complete pumpout. But I'm guessing this, I don't know of anyone trying it.

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

July 5, 2013

A. Sirs:

Lead solubility in zinc depends on temperature:

800F 1.0%Lead (Pb)
820F 1.2%Lead
840F 1.4%Lead
860F 1.6%Lead

Calculation to determine lead content in zinc as it is used and replaced by SHG zinc:

(Fraction Changed/Day)Raised to Power,Days Times Orig. Pb%

Example:

500,000 pounds zinc in kettle.
5,000 pounds zinc consumed each work day.
0.11% Lead Original Lead percent.

(500,000-5,000)/500,000 = 0.9900

(0.99)Raised to power 20 days times 0.11% equals 0.090% Pb
(0.99)Raised to power 60 days times 0.11% equals 0.060% Pb
(0.99)Raised to power 80 days times 0.11% equals 0.049% Pb

Notes: "days" are work days. Use "x raised to power y" on scientific calculator. Thus put in 0.99 hit enter and then put in 20 (days) then hit "=" Then multiply by 0.11. At 0.11% lead there would be no benefit to pump from the kettle bottom. Be sure to use "brightener bar (10% Al 90% Zn) that DOES NOT CONTAIN LEAD.

The real issue here is that zinc with no additives does not work as well as zinc with lead. I am working on this issue just now with excellent success and no need for lead.

Regards,

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

July 8, 2013

A. On our last kettle pump out, which started with a dissolved Pb content at 1.0%, the Pb content of the bottom zinc was about 80% and we got 2 ingots out like that.
So while the theory might say its not worthwhile, the practical experience suggests that a significant reduction might be possible way to hasten the dilution process.
We have not used the technique to take Pb out, but have taken Pb out as an unintended consequence.

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

July 10, 2013

A. Geoff,

In your case with 1% lead, you obviously had liquid lead under the dross. In the other case with only 0.11% lead it is obvious that there is no liquid lead under the dross.

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

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

July 16, 2013

A. Apologies: I mis-read the Pb level in the original post.

Yes, reducing from 0.11 to under 0.05% is another matter entirely.

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


December 20, 2013

Dear sir ,
I want to know can I ingot lead at continue my production? And your answer is no, so when I can use lead ingot at kettle?
Different colour created in my kettle this type problem created. I think that this type problem created after ingot lead during continue production. What you say about this sir?

Kadva Muinulhaq i.
- Vadodara, Gujarat, India
  ^- Privately contact this inquirer -^


December 20, 2013

A. Hi Kadva. Sorry but I don't understand your question. Hopefully someone who is more familiar with this may understand what you are trying to ask.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

December 20, 2013

Q. Dear sir,
Thank you for your reply.
Sir, I mean can I add lead into the pot while continuing my galvanizing production?

Kadva Muinulhaq i.
- Vadodara, Gujarat, India

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