Removing mill scale from hot rolled mild steel

[Charlie Boy]

As the title suggests. So what is the easiest way on half a square metre of 6mm?
I’m not happy using hydrochloric acid BTW!

PS I should say that the current plan is to form a barrier around the edge with some old bathroom sealant I want rid of, the pour on warm citric acid. However, I’m open to suggestions.

 

[Graham_Wright]

Flap disc.

 

[rogerthebodger]

Grit blast

 

[Zing]

Send to an electro plater. They will have the materials and equipment to do it. I agree about hydrochloric acid, which is the best stuff for the job. I had 20 lt of concentrate in my garage for a while. Scary as hell to use too. It felt like living with an atom bomb in the house.

 

[anoccasionalyachtsman]

Got time to let it rust off?!

 

[Adios]

This is the best place to ask MIG Welding Forum

 

[Clancy Moped]

Shot blast it.

 

[Lee Shaw]

Assuming it is going to be painted or coated after removing mill scale, make sure you get a primer coat on PDQ. Rounding sharp edges before painting is a good idea too.

 

[rogerthebodger]

Send to an electro plater. They will have the materials and equipment to do it. I agree about hydrochloric acid, which is the best stuff for the job. I had 20 lt of concentrate in my garage for a while. Scary as hell to use too. It felt like living with an atom bomb in the house.

We use hydrochloric acid all the time to correct the PH balance of out swimming pool

I also use it to clean off any rust on my steel boat.

With the correct PPE its should be OK. It like anything knowing the risks that the first part of using any dangerous materials

 

[NormanS]

Many varieties of "Brick cleaner" are dilute hydrochloric acid. That's what I would use.

 

[Rappey]

I had 5l of hydrochloric in its plastic container that it was shipped in.
Was put in the cupboard under the sink in utility room.
After a fair while I discovered all the hinges and metals in that cupboard had seriously oxidised and rusted.
Would assume it works the same way as petrol in a plastic fuel tank, as in it leaches through it.
Now kept secured outside.

 

[Caraway]

Like Graham Wright says a flap disc on a grinder.
Pop into any metal fabrication wokshop and see what they use.

 

[Charlie Boy]

Thing is about hydrochloric, its the disposal after whereas citric isn’t a problem, just takes longer.
Anyone tried oxalic?

 

[Neeves]

I'm assuming you want to do this by yourself - so grit blasting is out. I'd use a flap wheel or one of the discs to remove paint or a stainless steel brush wheel and finish with acid. Go and find a big plastic basin, the sort you might use to wash a big dog and finish off with acid. There is nothing wrong with dilute Hal, the usual problem is that many use the acid too concentrated because they lack patience.

If this is for marine use - galvanising will out live paint, factorially, and if you grind off the worst they will remove the rest (with acid - its part of their process). As mentioned if you are painting then paint as soon as you have washed and dried the plate as it will start to oxidise as soon as you have it clean, so paint before lunch! Round the edges as they will chip and will be the sourced of rust. If you need to drill any holes etc - do that before you acid wash.

Its a messy job.

Jonathan

 

[2Tizwoz]

Depends what you plan to use it for.

Galvanising is best for corrosion resistance but if you plan to have a shiny decorative finish that would need sweep blasting and painting. For cheapness a belt sander will remove the scale reasonably quickly without leaving swirl marks. Smith and Allan at Darlington sell a competitively priced zinc rich paint which can be overcoated with a decorative finish or left as is.

Zinc rich paint

 

[GHA]

Thing is about hydrochloric, its the disposal after whereas citric isn’t a problem, just takes longer.
Anyone tried oxalic?

I use phosphoric acid. Make a sort of coffer dam and leave it in there watered down a bit for a few days. Grinder won't get it completely clean even if it looks shiny.

 

[Charlie Boy]

Ah, I should have described the purpose. It’s for a welding work plate so it’ll be earthed when tigging. Hence getting rid of the mill scale. The intention is to get rid of that outside, then move the plate indoors to scour any flash rust. Some light oil perhaps and drill and tap a network of holes for clamps.

 

[rogerthebodger]

Ah, I should have described the purpose. It’s for a welding work plate so it’ll be earthed when tigging. Hence getting rid of the mill scale. The intention is to get rid of that outside, then move the plate indoors to scour any flash rust. Some light oil perhaps and drill and tap a network of holes for clamps.

I have a big steel plate that I use for welding ,Tig, Mig and stick IMHO no need to remove mill scale at the arc will soon make contact through the mill scale.

 

[NormanS]

My work plate gets weld spatter on it, which is taken off with an angle grinder. Mill scale is not a problem.