Minimize/maximize spangle in hot dip galvanizing

A. If memory serves me, I believe "lead free" zinc means 0.05% or less in lead. To check look at the ASTM specs. or contact the American Galvanizers Association.
Regards,

"Hot Dip Galvanizing of Steel Structures"
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A. Lead free kettles are becoming increasingly more popular in the States. A big part of the reason is probably because of the new additions to the zinc bath in the last decade or so, most of which are supposed to help drainage of excess zinc as well as the appearance of the finished product (spangle, etc.). As far as what percentage is needed to be called "lead free", the first step is to add special high grade only to your bath.

You can look up nsf.org to see what it takes in the U.S. to get a certification for galvanizing food grade items. Their specs will give you a good idea of where you need to be. You will then need to get an analysis of your bath and decide what you need to do to get your existing inventory in your kettle right.

A. I'm working about 6 years in galvanizing line as a shift foreman and what I know is lead is better to be between .025-.035%. More than 0.04 will reduce adhesion or sticking of coating, but even we have worked with .01% Pb and minimum spangle. But if you need spangle you have to charge 20 kg antimony (Sb) for 10 - 15 shifts keep Pb%+Sb%<.03

A. We do many Land Rover chassis for people who are refurbishing them. Here's the important points:
* All paint needs to be removed and blasting is the best way. Chemical dipping might work, but few galvanizers do this and most are uninterested in the process.
* Old galvanizing will come off in the pretreatment process. Some galvanizers will charge a little extra for that, as it consumes a lot of their acid, and adds zinc to it making it less easy to recycle. It's not possible to galvanize over existing galvanizing, as this is an alloying process between zinc and Iron. If the Zinc can't "see" the iron (because there's something in the way such as paint or old galv) it doesn't happen.
* Small parts can be done. Best done by "spinning", so ask if your galvanizer has a spinner, otherwise tie these bits on loosely (with mig welder wire or similar) to the bigger bits and they are less likely to go missing.
* It's rare for these parts to distort in my experience.
* Chassis not previously galvanized sometimes require vert/drain holes. The hollow sections will float, or retain zinc, or trap air - all leading to quality problems. So they need a hole to let air out then back in, let zinc in and out. But you get the same protection on the inside of the box section as the outside.
* Beware greasy buildup inside parts. It's got to be removed.

Good luck

A. You probably won't get much spangle from a jobbing galvanizer, the zinc analysis isn't best for that. But spangle is only decorative and only lasts a short while, it has no influence on the corrosion protection - the real reason for using galvanizing. (If the spangle lasts a long time, then you didn't need to galvanize as its not corroding fast enough!)

Wonder what you mean by "poor" galvanizing. It's either there or it's not. It's not like some coatings where the coating is poorly adhered, etc. It's not so much a coating as an alloying reaction. If the steel isn't cleaned properly, then no reaction > no galvanizing.

Unless you mean drips, runs, ashy deposits, etc.
Even if you get these, they're easily rectified by filing (don't use an angle grinder).

A. Dear Sir
According to my knowledge and my experience Addition of Lead is really helpful after melt-out stage for increasing the life of kettle, also decreasing the viscosity. Only Tin is for formation of spangle due to intergranular structure.

A. Sir:
Lead, bismuth, and tin all produce spangle (zinc crystals) on hot dip galvanized steel. Lead is being used less due to environmental (toxic) reasons. One client that I have says that bismuth caused terrific "white" rust (They are a boat trailer manufacturer.). Tin causes a much smaller spangle and at levels higher than about 0.3% in the zinc causes stressed steel structures to crack. Also the steel wires used to hang the steel crack and break if the tin is too high. Usual additions of these metals to the zinc melt are: Lead about 1%; Bismuth about 0.1%; and Tin about 0.1% to about 0.2%. Excessive tin (about about 0.3%) has, in my opinion, been very, very bad for the galvanizing industry and for the safety of the public.
Regards,

A. Sir:

For general after-fab galvanizing minimize zinc additions of lead, tin, and bismuth.

Regards,

A. I found a reference that notes a .01% maximum for a coating to be considered lead free. Such coatings typically do not have a spangle finish unless antimony is added although antimony is not much better than lead. Non-spangle zinc coatings are widely used today. The reference can be found with search criteria: "lead-free" and galvanize.

A. Hi Nikolay. I know very little about galvanizing so I don't know if he's right, but if I understood correctly. for maximum spangle Jamal suggested adding 20 kg for 10-15 shifts, but ending up with <0.3% combined lead and antimony.

Regards,

A. Hi mohamed. I'm not familiar with the term "flower" as related to galvanizing, but from context I'm guessing you refer to what I call 'spangle'?

Regards,

A. Spangle (or "flower" as you call it, is a crystalline pattern formed during solidification of the zinc during alloying/galvanizing. It is more dependent on the steel thickness and chemistry than it is on the chemistry of your zinc. The Pb you add, won't make much difference, it has low solubility in Zn, and any excess sinks to the bottom of the kettle. Al can make for brighter galvanizing and larger spangle, but excess Al causes other problems, and levels around 0.001 to 0.003% are about the limits of normal operation.
Thin steel spangles easier, with a thinner galvanized coating. Thick steel rarely spangles.
Spangle can be present at the start, bu8t not visible and over many tears of weathering becomes visible.
Spangle is no indication of quality, longevity or any other desirable aspect other than perhaps some people like its aesthetic. It doe not indicate any functional quality.