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"Remove slag/dross of zinc from hot dip galvanizing"

Current question:

July 16, 2021

Q. Sir please guide us about ash box. What do we mean by "ash box manual or motorised". Any photo and description of the same would help. Where can we get this ash box? In plant I am facing excessive ash issue.

Vikash goel
President - Kolkata india

July 2021

A. Hi Vikash. We have several threads about ash boxes and ash reduction. Please see:

• thread 57810, "Methods of Ash Removal from Galvanizing Bath" where Geoff Crowley and Dr. Cook discuss ash removal equipment,
• thread 41571, "Converting from Wet Galvanizing to Dry Galvanizing" where Dr. Cook offers estimates of reasonable ash production and how to keep it under control, and
• thread 47534, "Galvanising - Reduce & Recover Zinc Ash and Dross" where both aspects are discussed at good length.
• or search the site for what you are looking for.

But, sorry, we don't publicly suggest vendors or sources for ash boxes or other products on this site (huh? why?). If you want a commercial suggestion, check the "RFQ" checkbox on the posting submittal form allowing us to release your contact info to vendors or others who request it. Thanks.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

August 10, 2021

A. An ash box is a device suspended in the zinc kettle and is an open top, open bottom rectangle of steel. It's shape can be to suit the kettle and the product being galvanized. If for example you could sacrifice 300mm of length on your kettle, it could be a box of the kettle's whole width, 300mm long along the kettle from one end, and 300mm deep from just above the surface to perhaps 250mm below..
Ash that is skimmed off the surface is skimmed into the box where it is "worked". This means raked about with a tool to agitate it. The ash will stay confined in the box, but zinc will melt out of the ash and join the zinc below. The primary function is to separate out the metallic zinc from the dry oxide of ash.
But if you have excessive ash, just gathering it up is not the best solution. Far better to prevent its formation, as ash production is at the expense of zinc loss, and while not possible to be eliminated entirely, it is possible to be reduced to minimise this cost.

Geoff Crowley
Crithwood Ltd.
supporting advertiser
Bathgate, Scotland, UK
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Closely related historical postings, oldest first:



I want to prepare a mixture to remove slag of zinc from hot dip galvanizing in lab.

Suah Saeed Naoom
- Baghdad, Iraq


What do you mean by "SLAG OF ZINC." If you mean DROSS then you need a dross scoop. If you mean DRY ASH then you skim it off and put it into a barrel. If you mean WET SKIMS then you skim it off and put it into a barrel. There are some agents when help reduce dry ash and there are manual ash boxes and motorized ash boxes. They reduce dry ash down to 1/2 and 1/4 respectively.


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

August 4, 2008

Q. I mean to prepare a mixture which can remove the slag in molten zinc to get a pure zinc.

suha saeed naoom [returning]
- baghdad -iraq

July 2021

A. "Remove the slag" to where, Suha? It seems that Dr. Cook is telling you that the dross & ash are already separate from the molten zinc and you need to physically remove them. I think we are not understanding where you think a chemical can put them aside from floating to the top or sinking to the bottom.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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