Summary for excessive aluminum in zinc Discussion
Excessive aluminum in zinc is discussed as a likely cause of bare spots after hot dip galvanizing. The original poster, Tan Kok Teong, suspected about 0.5% aluminum in the bath. Dr. Thomas H. Cook replied that for general galvanizing with zinc ammonium chloride flux, the maximum usable aluminum is only 0.007%, and said there are several ways to reduce or remove aluminum, but the right method depends on the type of operation, such as general galvanizing or continuous sheet. When the poster later clarified it was a structural galvanizing plant, the thread did not include a detailed follow-up solution. A later question from Margaret Hutcheson described a similar problem in a general galvanizing plant with low-fume flux and about 0.163 aluminum added as pure aluminum; she said part of the zinc had already been replaced, but the problem remained. The thread points to aluminum control as critical, but does not give a single universal fix.
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Q. I am a galvanizer in China. Recently, we experience a lot of bare spots after hot dip galvanizing. We have suspected the aluminum content in the zinc bath is too high, about 0.5%. Please advise how can ‘remove ‘ the excessive aluminum in the zinc.
Tan Kok Teong
galvanizing company – China
2005
A. For general galvanizing (using zinc ammonium chloride flux solution) the MAXIMUM usable aluminum in the zinc is 0.007%. There are a variety of ways to quickly and easily reduce the aluminum in the zinc. Which of these ways depends on the type of operation. That is: if this is general galvanizing, continuous sheet or whatever. Simply put, more information about your operation is needed to choose the proper method of aluminum reduction or removal.
Regards,
Dr. Thomas H. Cook
Galvanizing Consultant – Hot Springs, South Dakota, USA
Q. this is structural galvanizing plant.
s.k.rakshit
manager – Indian
August 12, 2024
Ed. note: Dr. Cook has been away from the site a long time, but you can review the other postings below while you await an expert to spend the time to offer you a personalized response. But minimal posting effort minimizes that likelihood.
Q. We have too much aluminum in our Zinc bath about .163 this was added as pure aluminum we have already taken out one third of the zinc and replaced it but we still have the same problem is there anything else we can try.
We are a general galvanizer and use a low fume flux.
Margaret Hutcheson
Galvanizing – Londonderry, Northern Ireland
2006
SUGGESTED GALVANIZING BOOKS
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“Hot Dip Galvanizing of Steel Structures” by Kuklik & Kudlacek (2016)
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“Handbook of Hot Dip Galvanization” by Maass & Peissker (2011)
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“Galvanized Steel Reinforcement in Concrete” by Stephen Yeomans (2004)
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“Hot Dip Galvanizing — A Guide to Process Selection & Galvanizing Practice” by M. J. Hornsby (1995)
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“Faults in Hot-Dip Galvanizing” by Dietrich Horstmann (in English, French & German)
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“User’s Guide to Hot Dip Galvanizing for Corrosion Protection in Atmospheric Service” by NACE (1997 only rarely avail.)
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A. As aluminium stays at the top of the kettle, by using your flux powder you can reduce your aluminium content to some extent, which you can throw on the kettle top and skim it off.
Regards,
S.R.Ameen
– Riyadh, Saudi Arabia
A. I HAVE THIS PROBLEM SOME TIME AGO. ¿YOUR PROCESS IS CONTINUOUS OR BATCH? ¿IS WIRE OR STRIP?¿HOW MUCH ZINC HAVE THE BATH?
MAYBE YOU CAN PUT AN AIR LANCE INTO THE BATH(THE ALUMINIUM IS MORE REACTIVE AND WILL FORM OXIDE)
THERE IS ANOTHER “UNCONVENTIONAL” PROCESS THAT YOU CAN TRY: FOUND A BIG PIECE OF GREEN WOOD, AND PUT THIS UNDER THE ZINC. MAKE THIS WITH EXTREME CAUTION, THE GAS THAT COME FROM THE WOOD WILL OXIDIZE THE ALUMINIUM.I HOPE THIS CAN HELP YOU.
VICTOR MENDOZA
CALUR – CANELONES, URUGUAY
A. Dilution is really your only choice here I think. Have seen a similar situation, and seen all manner of “old wives tales” tried, including coconut husks, potatoes, oxygen lancing, top skimming, etc.
Pump out and dilute with fresh zinc. (If you can find any of this increasingly rare commodity)
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
Dear Sir,
Dusting Ammonium Chloride powder will react with excess aluminium and convert into aluminium Chloride in vapor form.
Please be careful because AlCl is volatile and poisonous.
Rajesh Sardhara
– Vadodara
October 17, 2024
Closely related topics:
Thread 54105, “Aluminium Addition to Galvanising Kettle”
Thread 25997, “Prevention and Removal of White Rust on Galvanizing”
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