How can we minimize/control galvanize coating thickness

A. When you say 8% what do you mean? How do you define this?
Different people use different measures in this, some including residues (ash, dross) some excluding. Some measure against the black steel weight, some against white steel work. Depending on this, your 8% could be good, could be poor! What is your definition?

A. You want to reduce the Zinc Coating or pickup. Please try my way:
1. Keep flux Sp. gravity 1.20 and add 2% Glycerine. Add a Nickel base compound made by Soprine, Italy which reduces the alloy layer (follow their instruction).
2. Keep Zinc Bath Temperature 445 to 448 °C.
3. Get your steel to be galvanized tested.
4. In case you are not getting Soprine, then try nickel addition technique marketed by Rada Chemicals, Dubai (follow their instruction).

Hopefully your overall Zinc consumption will come down to 4-5%.

----
Ed. note: please try to keep the public discussion of these nickel addition techniques generic rather than recommending specific suppliers. Thanks.

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A. Sabir,

I assume you work for PECO. Under UNIDO I worked for your company three times (about a month each time) and we were able to reduce zinc usage about 25% (lowering total product cost by about 9%). The last time I was in Lahore was about 15 years ago during the first Gulf war. Over time you have obviously lost this technology. Now there may be a safety issue for Westerners in Pakistan.

I caution the use of nickel compounds in the flux because of safety issues because nickel compounds are known to cause lung cancer. There is a delay time from nickel exposure to the onset of lung cancer of 5 to 50 years (according to one printing of the CDC handbook).

A flux density of 1.20 g/mL is a baumé of 24.2 which is clearly the European way to galvanize not the North American way. I much prefer the North American way.

You say your zinc consumption is 8% which IS high for your operation. Be aware that a zinc consumption of 4 to 5% may or may not be good depending on the thickness of the steel (e.g. the thicker the steel the lower the surface area to galvanize). I have clients that have nearly 3% GZU.

I assume Mr. Dalela is recommending glycerine at 2% as a wetting agent. There are MUCH more effective wetting agents that are effective at about 0.03%. I am not sure if pyrolized glycerine products would be healthy or not.

Regards,

A. Dear Sir.

To minimize zinc coating on steel there are many aspects to see such as:
1 ) Pre Treatment process of materials.
2 ) zinc bath temperature.
3 ) silicon contents in your raw materials.

First check the silicon content in your materials.

Check specific gravity of your Flux, and Quality of your Acid.

Keep zinc temperature in between 450 °C and 455 °C.

Hope this will help you to get your result.

A. Hello,
1. Get the iron content checked for your flux.
2. Add inhibitors to your acid it can be that steel is getting over pickled. Zinc is directly proportional to the surface area.
3. What is the withdrawal rate for your steel
4. Frankly speaking I don't think 40 percent dross and ash in composite is bad.
Pickup is high but you need to mention what tonnage you are doing for material with thickness 3 mm and below.

A. You don't really give enough info to be definitive suggestions to help.
But your temperature seems a bit high to me. 450 °C seems better, but that might depend on the things you haven't told about.
What flux? What drying? What steel? Ni or not? Flux type? Steel/material types? Jobbing or manufacturing? Vertical dipping or mixed? Steel thickness? Withdrawal speed?

A. Only thing I can add is that your withdrawal speed (by crane) should be about 1 meter per minute vertical speed.

A. Sirs:

ACN is now replaced by a much better term which is ACNV. ACN is ammonium chloride divided by zinc chloride. ACNV is the volatiles (ammonium chloride) divided by the sum of the low volatiles (zinc chloride plus iron (II) chloride plus sulphate, if present). By using ACNV (especially in the presence of high iron (II) or high sulphate a much better result is attained.

While in Lahore I taught a fellow to do a distillation test for ammonium chloride, which frankly is too complex. I now use the "bake and shake" method which is based on heat of solution and density attained by dissolving a dried/weighed sample of flux in a specific volume of distilled water. These methods are easy and give excellent ACNV results directly.

Regards,

When you find the way to improve your zinc pickup, please publish it here.

A. Zinc pickup is so dependent on material type (as well as all the process parameters) that comparison is difficult.
I think 3.5% might be possible in a plant coating the same material all the time, and heavy sections.
We do jobbing work where no two days material is the same, so our consumption varies greatly.
I know of plants doing 10% and others doing 4%.
But each plant will have its own target based on experience with that material type they can sell.

A. Dear Raghul,

Zinc pick up rate (%) is very dependent on your steel thickness. Let just say you have 2 items, same size & design, only difference is that A is 1 mm thick and B is 2 mm thick. Their surface area is the same, but weight of A is only half of B. Therefore, even though they have the same zinc coating thickness, zinc pick up rate (%) for A is double of B's.

If your plant is only galvanizing items of above 8mm thickness, you can easily get a zinc pick up rate of below 3%. The thicker the item, the lower the zinc pick up rate.

Also, iron in pickling bath can help speed up your pickling process. You can refer to Kleingarn graph.

Regards,

A. The zinc consumption (pick up) is dependent on the thickness of the item galvanized. for a 6 mm thick angle and a coating of 610 gm , the pick up is 2.6%, and for an 8 mm item it is 1.9%. In actual practice to have a minimum average coating of 610 gm , the actual coating will be 630-650 gm i.e., 2.8% for 6 mm thick item. we galvanize items from 2 mm to 20 mm thick and every month, the theoretical pick up based on the surface area galvanized depending on the thickness is calculated and the actual pick up is compared. The ash being 16% of gross Zinc and dross as 5%. it is possible to achieve a gross zinc consumption of 4% with a pick up of 2.75% and balance 1.25% as Dross and ash. dipping time and temperature of the bath is to be controlled.