How can we minimize/control galvanize coating thickness

A. Si is indeed one of the factors that affect galvanizing thickness, but if you knew what it was prior to processing, what would you do differently?

The only time I think this becomes relevant is in a manufacturing plant where in-house galvanizing is done. Then there is control on the purchase of the steel, and a specification for the steel can consider the impact on the galvanizing cost.

In our case the many hundreds of customers (we're very much a jobbing plant) make their own decisions, and I doubt they ever consider the impact of their steel chemistry on galvanizing. They do not buy steel to suit galv.

So, even in jobbing, if you were to measure Si content (and that's not the exclusive impacting element), then you find Si % that suggests it will be a heavy (thick) coating, what to do next?

A. Hi

According to your discussion, I think that an important thing in coating size in galvanization is to factor:
1. flux
2. pick up speed

We in our project with a little change in flux composition and daily control of its several material %, such as Fe, and its gravity, reduce coating size about 20 micron off, but coating size depending on ST of steel and its pick up speed is variable. However, I think don't use Ni in flux, please control its Fe and its temperature about 40-60 °C. In addition you should pick up your staff entirely.

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Ed. note: Sorry, we couldn't figure out the last 5 words of this reply.

? Sir:

I have some questions relating to your response:

What do you mean "...a little change in flux composition..."
What change(s) did you make?

What is "...ST of steel..."
I do not know this term.

"...don't use Ni in flux..." I agree, did you try this?

What is: "...Pick up your staff entirely..."

Regards,

A. Sir:

By "pick up your staff entirely" Do you mean get the workers out of the kettle area during the time the steel is entering the kettle? If "yes" then the usual way to protect the workers (from molten zinc splashes) is to have a vertical moveable "wall" with a safety glass window. The glass usually has wire reinforcement.

Regards,

A. Hi Sunil. Further up the page Geoff has already said 1 meter per minute, so please try to phrase your question as part of the ongoing dialog. Or you may wish to continue the discussion on letter 47904, "Speed of crane for hot dip galvanizing", where Thomas Cook seems to say that it can depend upon what flux is being used (I have no galvanizing experience, so I'm not sure that I am correctly interpreting his posting).

Regards,

A. Hi Sunil. That's true. Mr. Geoff informed earlier for withdrawal speed of materials from zinc bath should be 1 mtr / min ... you can reduce up to 0.8 mtr / min.. Generally for Galvanizing plant we prefer two speed EOT Crane. Dipping should be fast and lifting should be slow.

Hi Jinadu. As you see, we've appended your inquiry to a thread where the subject has been discussed at great length. But if there is something you don't understand or need clarification on, please get back to us. Good luck.

Regards,

A. In order to determine the zinc usage per ton of galvanized work you need two pieces of information: (1) the surface area, and (2) the thickness of the zinc coating. You don't need any more information than this and you cannot determine the usage without both of these pieces of information. The math is pretty simple.

A. Sir:
Average zinc usage 40 years ago in North America was about 10% (200 kilograms zinc for every 2,000 kg of galvanized product), Now the average zinc usage is about 5% (100 kg zinc for every 2,000 kg of galvanized product).

Regards,

A. While knowing the thickness of the coating and the surface area will allow the calculation of zinc consumed and reporting to the coating, this isn't the whole story. You do need more information.

If you do a zinc mass balance on zinc in a galvanizing plant, it becomes apparent that Zn is reporting, in significant quantities to a variety of other places that the coating.
These include: jigs, acid, dross, ash, rinse water, fume particulates. The quantity reporting to all these undesired places is what can differentiate a profitable plant from another, and can amount to 20-40% of the weight of Zn in the coating. It's highly variable and influenced by many factors.

The numbers Dr Cook has quoted are the total consumption including these sidestreams.

A. Galvanising is a quite complex topic, as the zinc forms a complex intermetallic structure with the base steel. the amount of zinc on a steel product also varies with the time it is in the galvanising tank, but as a rule of thumb, hot dipped galvanised steel has a zinc thickness of between 40 and 100 microns (1.5-4 mils). This compares with general electroplated zinc coatings of approximately 0 to 25 microns (0 to 1 mils).

Hi Faisal. We try our best to offer help to students when they need it, without doing their homework for them. Your question is the topic of most of the 30+ postings on this page, so please slowly carefully review the page and
1. Offer detailed followup questions about the parameters you didn't understand, or (even better)
2. Offer a hypothesis about calculating zinc consumption, based on what you read here, and ask for the readers' comments and suggestions on your hypothesis. That would really be taking advantage of the opportunity offered to you. Thanks and good luck!

Regards,

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Ed. note Mar. 2018: It's okay, folks. Although 9 out of 10 students blow off our suggestions when we don't immediately supply the answers to their homework questions, 1 out of 10 does appreciate them, and that's a pretty heartening thing :-)

A. Some photos of the black patches would help diagnose this. It could be one of several issues and pictures might help.
Are the "black" patches bare steel (ungalvanized)? If so this might be under pickling. Are the patches on top of the zinc? Might be excessive aluminium.

When you say "too much" zinc, what thickness are you getting, and what dipping speed, angle, zinc temp? flux type, temp of flux? strength of flux, chemistry of flux? additions in the zinc. All of these have an influence, and without these parameters only wild guesses can be made.

A. Hi Venkata. We appreciate that you have identified your product as 2 mm metal sheet; nonetheless, the question remains vague :-(

Is this a coil reel-to-reel line where some sort of wipers might be applicable, or is this post-galvanizing of discrete components? How thick are the present coatings, and how thick would you like them to be? Is there any chance that electrolytic zinc plating could get you the thickness you desire?

Regards,

A. Sir: Looks like you are a sheet galvanizer. Are you sheet to sheet or continuous coil to coil? Does the sheet go cross-wise through the kettle or length-wise? Is your zinc kettle iron or ceramic? What is the temperature of the zinc? What is the time the steel is in the zinc? Most modern sheet galvanizers use gaseous flux 5% H2 and 95% N2. Have you heard about "Galfan?" I wonder if it may work better for you. From what country to you buy flux? I have only moderate information on sheet galvanzing.

Regards,

Dear Mr. Sunil.

As mentioned by you, it seems that you are having sheet metal galvanizing job.

Please let us know if it's continuous process or batch-wise process. If it's continuous then coating seems too high; however, if you have batch-wise process, your coating should be around 75 to 90 microns.

Tell us your immersion of materials speed as well lifting speed and also tell us your working temp.

We will help you to solve the problem.

A. You need to know the surface area per unit weight. With that, it is simple arithmetic. Without that it is just guesswork.

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Ed. note: Tom is the author of "Surface Area Formulas and Tables -- A Resource for Surface Finishers"

  Ok thank so much TOM. I will calculate surface area per unit weight of Plates, C Channels, Angles, H and I Beams, Tubes, Bars, of some sample dimensions and then take a average of it.