Aluminium addition to Galvanising Kettle

A. When the workpiece is immersed in the galvanizing bath, the greater the tension on the surface of the galvanizing bath, the less likely the galvanizing bath is to adhere to the surface of the workpiece, and the more likely it is to cause defects such as missing plating. More Al will cause more galvanizing bath tension to prevent plating occurs. For your reference.

A2. To galvanize bolts and nuts, without having to 'brush' the threads, you need a centrifuge or 'spinner' This industrial centrifuge spins the bolts inside a basket, at high rpms to remove zinc from threading. In addition, if the bolts are too long to fit into the centrifuge you can do what is called 'rolling'. This is done by rolling bolts (hot out of the kettle) along a 45 degree decline, essentially 'spinning' the excess zinc off as it completes its roll to the ground.

A. Problem is that adding Al to steel is easy (MP steel about 1490 °C, and casting temp typically 1630 °C or so).
But galvanizing temperature is about 450 °C, below melting point of Al.

It will dissolve, but slowly.

A. Steven:

From our e-mails and phone conversations you know that I have advanced technologies, a small part of which allows you to never purchase Al/Zn brightener. With the main features of this advanced technology and with proper formulation, control, and use of quadraflux, I expect to eliminate your use of nickel (which according to the CDC causes lung and nasal cancer). In addition, if you follow historic results, the ash reduction and thinner zinc on the product could be substantial additional savings. (World-wide about 150 galvanizers use this advanced technology to advantage beginning in 1992.

[Ed. note: Dr. Cook quantified these potential savings but we have deleted the numbers from the above discussion because Steven may not wish his sizes and production figures which were discussed in private conversation to be publicly posted.]

I have already recommended that at your next kettle change to increase your kettle furnace to 100% firing (10,000 Btu/sq.ft./hour through the side wall heating zone; with proper air/zinc protective insulation to prevent wash-line erosion, and zinc/dross protective insulation to prevent deep kettle burn-through) so as to provide production of about 20 MT/hour. An end-fired kettle gives more production and uses 25% less natural gas. Kettle lifetimes are expected to be 10+ years. By doing this you can galvanize at a reduced temperature and reduce the reaction of the reactive steels.

Also as you know I recommended the acid rinse water treatment system (uses no chemicals; but requires 3KW of electricity to operate) to keep the non-volatile iron (+2) chloride low in your flux to allow short kettle cook-out times. For reactive steels each minute in the zinc gives 25 additional microns of zinc thickness.

The spec. for Al/Zn brightener bar is ASTM 860. Brightener bars can contain ANYTHING, including iron, copper, tin, cadmium, lead, silicon, magnesium, etc. Thus these brightener bars (from unreliable sources) could burn out a kettle, cause thicker zinc on the product, cause more dross, more ash, be toxic, cause white rust, etc.

Ash and dross can contain nickel.

Regards,

A. If you are not facing any problem in process of Galvanizing, then let it be at 0.01%. As such, apart from specifications, Galvanizers are using up to 55% Al in Zinc Kettle (Galvalume).

I once knew of a plant that added pure aluminium in error. Ended up with excess %Al (about 3% if I remember), and the whole kettle contents was unusable and had to be pumped out.
In theory there's nothing to stop adding pure Al, but the solubility is lower than in the 5%Al 95%Zn alloy. It won't melt (Al MP = 660 °C, versus Zn 419 °C, and kettle temp probably 450C), but will slowly dissolve. So this is more like adding rock salt to hot water - doesn't melt, but slowly dissolves.
It's less controllable in end result, and slower, so why choose the hard route that gives unpredictable results?