Removing mill scale from Mild Steel Sheeting

[Polished]

Hi folks just a tip that worked for me that might help others. I'm in the process of making steel doors for my 'Man Cave' :-). all door frames made and I've begun sheet with 2mm 8x4 steel sheet which of course is covered in mill scale. Cleaned off edges whilst welding with flap disks but way too expensive to go over the entire sheet to remove the scale before priming and painting. The answer when looking around the interweb was Muratic acid more comminly know as hydrochloric acid.
Quick trip to my local builders providers and looked around came across 'Boss Cement and Grout Cleaner' 20% Hydrochloic acid - perfect ! :-)



As with any acid of any concentration , safety is a must, full face visor, Long Rubber gaunlet gloves, plastic apron if available but certainly no uncovered skin.
Never add water to acid to dilute , add acid to water - read instructions !

Painted it on with brush, had a few rough bits so used a pot scourer and left for 5-10 mins, ran the pot scourer over a few more times and flushed (from a distance) with lots of water from the garden hose
heres the result, had to run the wire brush over one or 2 spots but it fell off.
Anyone who has tackled with this in the past will know what a PITA it is.



Hope this helps.

 

[pedrobedro]

It's called brick acid in the trade, used by motorbike shops all over the country to clean up exhausts and other awkward items. It will clean the drains up nicely as well, not sure of the legality of flushing it down them though.

 

[Welderpaul]

Save a lot of bother by buying pickled and oiled sheet - not that much more than bog standard hot rolled plate.

 

[Hitch]

Just buy cold rolled sheet.....

Or just sand back the loose, and paint

 

[chunkolini]

I just discoverd that buying 1.6mm sheet that a bright finish adds another three quid to the cost per sheet. if I remember to ask for it.
But a useful technique to file away for future use.
Could be good for removing mill scale from hot rolled strip.

 

[stew]

my question is why?

paint will stick fine to 2500x1250x2mm sheet, quick clean with petrol rag, primer and then top coat. overkill in my opinion.

although to be fair it does look like it has cleaned it up good.

 

[outofthefire]

I cant remember if its the same stuff as battery acid, but one of them also eats galv. A problem to be aware with brick acid is it makes steel rust really bad if its not neutralised properly.

 

[chunkolini]

Brick acid is Hydrochloric acid (HCl)as said earlier.
I use Ammonium Chloride (NH4Cl) as a rust promoting agent.
The Nh4Cl gives off Ammonia NH3 to leave behind a weak salt of HCl which rusts the steel beautifully in a very short time.
Be very careful about cleaning it off after removing the black oxide layer.

 

[Chipper]

Citric dissolves millscale too, v.fast with hot water solution. And dissolves galv too.
Or strip & clean discs work well for mill scale, though just painted some chop parts with the millscale from hell on it. Very hard to shift, flap discs & strip discs just seemed to polish it and of course didn't want to chew too deep since it was in to be painted. Deox Gel helped (seems to be citric).

 

[chunkolini]

Have just bought some Citric acid from Fleabay to have a play with.
Will report back.
Much cheaper then the DoxyC stuff.
Will report back when I have had time to test drive it.

 

[Chipper]

It's great, v.fast with hot water (thanks to someone on here for that tip). Usually done in a hour. Overnight in cold has always de-rusted things so far too. Millscale becomes a wipe-off slime.

 

[chunkolini]

Thats what I am after, I have used the deoxyC stuff, make up a batch and keep it a drainpipe, sealed at the bottom and pop hot rolled strip in at the end of the day and remove in the morning.

 

[MattF]

Have just bought some Citric acid from Fleabay to have a play with.

Same here. Ordered some one kilo containers of it a while ago. Just need to get chance to try it out now. Space constraints and digging out a suitable container have been my main reasons for not trying it out yet.