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Why can China produce a good galvanization and Canada cannot?

I am a Quality Manager of a casting company. We often send out our iron castings for hot dip galvanization. (about 0.003" thick as reg. on the drawings) We have a lot of problems with poor quality. Clumps, dents uneven coatings. We have complained and changed suppliers with similar results. Sometimes good, sometimes very bad.

Presently we have sent parts to be done in China and Brazil. The quality is much better, with even coatings, and no clumps or dents. I understand that their process is different. Our galvanizing supplier says it is a mechanical galvanization and not hot dip. They said that this process is very costly and there are not many suppliers in Canada for this process. We are losing business because of the poor quality. Can you enlighten me on why China can produce a good galvanization and Canada cannot?

Gary G [last name deleted for privacy by Editor]
castings and machine shop - Coaticook, Quebec, Canada
2003

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2003

I think the first thing you need to do is determine whether your supplier is giving you the straight scoop, Gary_. Have a few parts mechanically galvanized in the USA or Canada, and see if this is the coating you are looking for. Try asking Plating Systems and Technologies [a finishing.com supporting advertiser] if they can give you the name of a shop where they have installed a system in your area.

You can't judge the quality of hot dip by how closely it resembles mechanical galvanizing. Good luck with the project.

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

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2003

Dear Gary,

Of course I cannot judge how the goods are treated in Brasil and China. I only can guess why quality in Canada is bad. In general steel casting can be galvanized without special care.

However, iron castings (i.e. gray- and tempering iron casting) need special care to get a quality almost comparable with normal galvanizing. To get a reaction between iron and zinc you need a perfectly clean steel surface before dipping into the zinc kettle.

Different from normal steel/iron, cast iron surface will be "polluted" with oxides, graphite, moulding sand, and have problem zones. Normal pre-treatment in pickling acid (sulfuric/ hydrochloric acid) will not be sufficient to remove all these pollutants and will cause irregular zinc coating, black spots rough surface etc.

To try out you could blast some parts carefully and ask a short dip in the pickling acid. Galvanizing plants especially equipped for treatment of cast iron use diluted fluoric acid for pickling to get a clean surface.

Dolf van den Berg
- Leusden, The Netherlands

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You are manufacturing Cast Iron items which needs a different way of Hot dip Galvanizing. 1. Shot Blast the item, 2. Pickling of Item for a very short time, 3. After rinsing and fluxing Dip in molten Zinc at 440 Deg. Cel., 4. Do not quench the item, take it back to Fluxing again, after Fluxing again Dip in molten Zinc at 440 Deg. Cel.,5. Now quench the Item.
By this way you will get a good finished cast Iron Items.

Umesh Dalela
hot dip galvanizer - Dubai, UAE
2007