finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
Live! From beautiful Pine Beach New Jersey: Welcome to the world's most popular metal finishing website

topic 24568

Lead (Pb) in Hot Dip Galvanizing


A discussion started in 2003 but continuing through 2019

What is the purpose of lead in hot dip galvanizing?

2003

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


"Handbook of Hot Dip Galvanization"
by Maass & Peissker
from Abe Books
or
info on Amazon

2003

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
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?

2003

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 [returning]
galvanised steel manufacturing - Biratnagar, Morang, Nepal


2003

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
Dolf van den Berg
- Leusden, The Netherlands



2006

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,

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


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 [returning]
- 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,

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


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


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:

800 °F 1.0% Lead (Pb)
820 °F 1.2% Lead
840 °F 1.4% Lead
860 °F 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
Galvanizing Consultant - Hot Springs, South Dakota 57747


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
Galvanizing Consultant - 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

Q. 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


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,

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


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



March 28, 2016

Q. Dear experts,
How to reduce the lead percentage in bath, from 0.2%

Khaleel Ahmed
- Jeddah KSA


April 11, 2016

Q. How and what % to use Lead in new zinc kettle for long life of kettle?

SUPRABHAT BANERJEE
- Jaipur,India


August 12, 2016

A. Dear Mr. Suprabhat,

It is advisable to add lead after 10 days of complete melt out of ZINC in new kettle. Do not operate with more than 50 mm of lead in bottom of kettle.

Rajesh Patel
- Vadodara, India


User's Guide to Hot Dip Galvanizing for Corrosion Protection in Atmospheric Service
by NACE
from Abe Books
or
info on Amazon

April 15, 2016

Q. In our Hot Dip Continuous Galvanizing line, we are using Tin/Antimony for Spangles apart from Lead, we want to stop adding the Tin in the Zinc bath, what would be effect whether brightness would be affected or spangle formation. As per my knowledge, Lead & Antimony are main elements which forms the spangles on the Galvanized surface. If not what is the actual role of Tin in Zinc bath composition.

Kantilal P. Trivedi
Quality Head-Cold rolling & Galvanizing of Steel - Baroda, Gujarat, India


August 18, 2016

A. DEAR KANTILAL
TIN AFFECTS GLOSSINESS OF THE SURFACE. THERE IS NO SPANGLE CREATION BY ADDING THE TIN. YOU CAN USE LEAD AND ANTIMONY FOR SPANGLE.

REGARDS,

AJEET GUPTA
- ANGUL, ODISHA, INDIA



January 7, 2019

Q. Dear sir,
We are adding 2 kg (0.1%) of lead to our 2MT hot dip galvanizing pot. Our regular coating production is 6-7 MT per day of SGI casting. Our coating quality also okay and castings also passed after 6 dip test in copper sulphate solution. I want to know whether 0.1% lead addition daily is correct or not.

Sundararajan.M
- Abu road, Rajasthan, India


January 8, 2019

A. Sirs: Tin in the zinc is known to cause the galvanized steel to crack. In the USA a stressed steel bridge was destroyed by tin. In the UK a stadium had its roof support structures crack due to tin in the zinc. Too much bismuth causes white rust.

Lead in the zinc increases the reactivity of malleable cast iron and produces coating that side off the castings. In Ireland only one galvanizer is lead-free and it is known for good galvanizing of castings.

Lead in the zinc does not protect the kettle.

Regards,

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


January 9, 2019

A. Concerning lead in the kettle.
Pb has maximum solubility in Zn at about 1.2% at 450 °C. Further additions than this just accumulates on the kettle bottom as it is the most dense among Zn, dross and Pb.

Zeta dross crystals are not very dense compared to Zn, and the addition of Pb causes them to sink as they combine with Pb in solution, become heavier and sink. More floating dross is found in Pb-free kettles than those with 0.6% Pb or more.
Pb-free is rare (as in 0%) as much Zn supplied has some Pb in it; the ores are found together in nature, so they end up being processed together, and only by active separation is "pure" Zn made.
Pilling (perhaps worlds premier kettle maker) in their book "Galvanizing Kettles - recommendations for the user" recommend having minimum 0.6% Pb.

Sn in the melt is another matter. Rather than actually CAUSE cracking, it aggravates an existing problem. The most recent extensive research on this shows that the galvanizing isn't the cause of the cracking, even in Sn containing melts, but it reveals and exaggerates cracks that are there in the first place but undetected.

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


simultaneous
January 10, 2019

A. Geoff, In the USA the only prime Western producer (e.g. 1% lead) tried to switch to electrolytic zinc (e.g., near 0% lead) but technology did not work properly. In the old days, I liked lead in the zinc and there are certainly some advantages, but now I like lead-free better. I believe the top half-inch of zinc in the kettle is "special." In the old days floating dross was common on Monday mornings. We have found ways around this and floating dross for my clients is virtually zero. Does Pilling give any reason for recommending above 0.6% lead?

The use of tin in the zinc is risky. I certainly do not recommend tin in the zinc. The stressed steel bridge maker had to replace the bridge at considerable expense. Once tin was eliminated in the zinc the problem went away. One center pivot mfg. had irrigation pipe split down like a peeled banana due to tin. A galvanizer doing large diameter pilings had them split end-to-end along the weld due to tin. The entire tin problem has been studied by Edison Welding Institute and tin in high concentration has been found at the crack propagation points. It really does not matter if tin causes the cracks or widens them. Galvanizers with the tin problem have had to use ultrasound to identify the cracks. Tin in galvanizers zinc has resulted in some major lawsuits.

Regards,

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


January 11, 2019

Q. Sir, Thanks for the reply, Some things are clarified, however still my doubt of 0.1% Lead addition in molten zinc is correct or not?
Does this lead addition add any bad effect on the coating or to the kettle.

SUNDARARAJAN MUTHUKRISHNAN
- Aburoad, Rajasthan, India



If you have a question in mind which seems off topic, please Search the Site

ADD a Q, A, or Comment on THIS topic START an UNRELATED topicView CURRENT HOT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.