Removing galvanising from steel

[Bodgy]

This may be teaching youse all to suck eggs, but I did this for the first time and it worked like a charm.

I bought some 12mm steel rod from Bunies, couldn't be bothered to drive across town for a real steel supplier. Unfortunately it was galvanised. I notice that the lathe doesn't like turning off the zinc. Broke a parting tool last time I tried.

I googled the methods of removing gal, and for rod, grinding wasn't the best choice. I went the acid route.

I'd saved some old sulphuric acid from a dead battery. I simply dropped the rod in this and stood back. Lots of bubbles and presumably noxious gases, but I was in the open so no probs.

Five minutes later - clean bare steel.

Not often something I do works first time, so had to tell someone. Apparently Hydrochloric (from the pool shop) works justs as well

[echnidna]

even vinegar works but much slower

[Riley]

When you need to use a grinder , use an aluminium grinding disc , they don't load up like the metal grinding discs do.

Will have to remember that acid trick though, thanks for posting that.

[BobL]

The main reaction is

Zn + H2SO4 => H2(gas) + Zn++ + SO4--

Grade 9 chemistry - you obviously weren't paying attention!!!

BTW if anyone else tries this, no naked flames, that H2 stuff is hydrogen and is highly flammable.

And I presume you washed the acid off with lots of water before sticking it on the lathe.

BTW, if you want to keep the galvanizing on one part of the piece and remove it for another, then smearing a thin layer of grease or wax over the part you want to keep and not on the part you want to cut / treat works really well.

[gordonwindeyer]

As an extension of this thread, can you clean dulled galvanised steel to bring it back to its original shine?

Gordon

[joe greiner]

As an extension of this thread, can you clean dulled galvanised steel to bring it back to its original shine?

Gordon

Yes. You can polish the zinc coating with emery cloth and/or crocus cloth, followed by Brasso if you like. But the zinc coating is intended to be a sacrificial anode which oxidizes to prevent the steel from rusting. Over time, the zinc continues to corrode. The polishing helps to retard this process, but expect only about five years before the process must be repeated. Environmental effects can increase or decrease the longevity.

Joe

[gordonwindeyer]

Joe
Thanks for that input (albeit delayed)...the comment that the galvanising is effectively a sacrificial anode helps my understanding.
Does Crocus cloth also abrade the zinc?

Gordon

[joe greiner]

Joe
Thanks for that input (albeit delayed)...the comment that the galvanising is effectively a sacrificial anode helps my understanding.
Does Crocus cloth also abrade the zinc?

Gordon

Hi, Gordon.

Most polishing processes are combinations of abrasion and infilling, but as far as I know, the debate is yet unsettled. If repeated enough times, the coating will eventually vanish.

Joe

[soundman]

There is a bonus too

If you do quite a bit of removing zinc with acid.

Use hydrocloric acid and keep disolving zink till it wont desolve no more.

Whala......... bakers soldering fluid..... or close too


seriously i've been using acid to remove zinc from screws and the like before I paint them for years.


cheers

[BobL]

At work we make and purify (distill multiple times) an "interesting" array of acids starting with reagent grade acids or gases. Some of the pure acid with a certificate sells for over $1000/L. To make 1L of clean acid results in losses or waste of around 1L of the acid which ends up back in the 20L carboys the stuff arrives in. Some of this is sold back to the chemical companies for repurification. About a year ago someone puts some concentrated nitric waste in with some concentrated HCl waste. The combination makes Aqua Regia - so called because it dissolves gold and platinum - at the same time it also makes nitrous oxide and chlorine gas (very nasty). Obviously the chemical companies were not interested in recycling this so after a while I volunteered to dispose of it to "clean my newly laid recycled brick driveway".

Well it sure cleaned the driveway well but it also stunk to high heaven so after cleaning a couple of sq m I stopped and used plain spirits of salts. Meanwhile I have about 10 L of this still in a black poly container behind the shed so I decide to see how well it cleans Zn off a 100 mm of 2" galvanized pipe. I put enough in a plastic bucket to cover the pipe and in about 3 seconds there were lotsa lovely bubbles and about 10 seconds later a grey foam that overflowed the bucket . Luckily I had wrapped a piece of wire around the pipe so I was able to pull it out, and luckily I did it then because this stuff had just about eaten the wire. Anyway I diluted it by half with some water and the repeated - still vigorous but not overflowing the bucket. Same as Groggy - it took about 5 minutes to clean the Zn off.