Types of zinc used for galvanizing

? Did you read ASTM A123 to see what it says about the grade of zinc?

First of two simultaneous responses -- February 13, 2009

A. Sir:
I presume you are thinking about:
1) leaded zinc (Prime Western) at about 1% lead,
2) Lead-free zinc at about max 0.05% lead, and
3) Nickel zinc at about 0.03% to 0.05% nickel for reactive silicon semi-killed steels.
There is also the use of tin, however above about 0.2% tin, the tin attacks the steel and causes the product to crack.
All types of galvanizing zinc normally have about 0.001% to 0.005% aluminum (daily additions) to have a brighter product. Above about 0.007% aluminum causes many problems on the product.
Another patented zinc uses bismuth rather than lead. Both reduce the surface tension of the molten zinc. Tin and probably bismuth lowers the free zinc point and provides better zinc drainage upon withdrawal of the product from the molten zinc. Tin, bismuth, and lead give "spangle" to the zinc coating.
There are ASTM specifications on the minimum zinc content in galvanizing zinc. Some impurities like copper cause very early kettle failure and must be avoided.
Regards,

Second of two simultaneous responses -- February 13, 2009

A. There is no one answer to this question. There are many factors to take into account.
Types of zinc commonly used include:
Remelt: (recovered from scrap zinc). Its lower priced but higher in impurities. Can be successfully used in blends with other types.
SHG: (Special High Grade). A purer zinc from refineries and smelters. More expensive, perhaps most pure form of commercial zinc. So pure that you might have to add some impurities like Pb, Ni for example
GOB: Cheaper but higher impurity levels, including Pb.
ZiNiGal: A Ni blended zinc having Ni added to reduce reactivity. Higher priced, but better recovery of the Ni into the melt than many other ways of adding Ni. Results in lower coating weights, and therefore a saving. Low in Pb though, so that might need to be added.

The answer to your question though, will depend on many things.
What is available?
What can you afford?
What is your product mix?
Are there special issues in your plant?
Are micro-alloys available locally (Ni, Pb, etc.)
What do you want to achieve?

A. Sir:
You would need to post the exact compositions of the various zinc sources, before anyone could even begin to suggest which (cheapest) zinc might work okay. Keep in mind that use, harmful effects (to the kettle or product), and health issues can all play a part. My general experience is that most zinc should be primary (new) zinc and some secondary zinc is usually okay. However in your a part of the world secondary zinc could be bad (e.g. copper, tin, cad., arsenic, nickel, iron, dirt, suspended impurities, whatever). Do you really want to risk your whole zinc bath, just to save a bit of money? Also consider that the folks from whom you might buy this cheap zinc may not disclose everything that is in it. Good luck.
Regards,

A. There's still the question of standards. If your customer (I assume you have one - could be doing this galvanizing for your own company), demands galvanizing to a standard then you'll need to buy some higher grade of zinc than scrap remelt.
But if not, then buy the cheapest you can. Temperature has more effect on kettle life than zinc purity, though if you were to have very high Sn and Cu you might find problems of accelerated wear.

A. Sir:

About 2001-2 North American galvanizers reported having their hanging wires breaking and stressed steel products cracking. This included tubular products that split like a banana peal, overhead sign structures cracking, and scaffolding cracking. Roof trusses in a soccer stadium in England cracked. Edison Welding Institute did a study and found that TIN in the zinc was the problem. Specifically TIN above 0.4% in the zinc was the cause.

A few months ago I sent out 40 sets of 12 steel samples each to galvanizers and the cast iron pipe fittings were severely attacked in short kettle times in a cool zinc bath when lead was at 1% or tin was at 0.2%. An 822 °F zinc bath with 0.2% tin gave a 12 mil (305 microns) in one minute. Further time caused the coating to slough-off the coating into the zinc kettle to form dross and fall to the bottom of the kettle. Results for leaded zinc were similar.

Regards,

A. Tin in galvanizing zinc is to be avoided.
Identified as a contributor to liquid metal assisted cracking (LMAC), and is limited by BS EN ISO 1461, the international galvanizing standard, used almost everywhere.


It has not been UK practice to add Sn, and have not heard of any UK galvanizers using it, but I believe that some German galvanizers have in the past.

A. Tom,
Apologies, My comment was unintentionally misleading.
I said that ISO1461 limited Tin (Sn). It doesn't directly, only indirectly.
Section 4.2 of the latest (2009) version of the standard refers to other standards ISO752, EN1179 and EN13283 for zinc melt composition.

Accepted practice in the UK is that the melt composition should not exceed Pb + Sn < 1.3%
and that Bi < 0.1%

I'm not sure what those other standards say, but intend to satisfy my own curiosity now.
For one of our plants, a recent analysis showed Sn = 0.04%, Pb = 0.75%, Bi <0.001% I'd guess this to be typical.

It is possible to buy zinc that is recycled. This typically has about 0.2% Sn. It's used a lot in Germany I understand, but rarely in the UK plants.

A. I can think of many ways to deliver zinc. They depend on the country, distance to be delivered, availability of delivery vehicles etc. A truck is a pretty common method.

Or did you mean something else by the word "deliver" ?

If a galvanizers wants to comply with some of the several standards for galvanizing (such as ISO1461, ASTM A123 etc, then they will be quite particular about the level of impurities. Getting the zinc out of dross doesn't leave "pure" zinc, rather it makes contaminated zinc. You should speak to your prospective market about this before getting your production system built.
While speaking to them, ask them what delivery mechanisms they can accept? Some might be close to rail, ports, airports, and could take zinc those ways?