Thread: Black Scale Removal

I have been looking for a better method of removing the hard black scale that hot rolled steel is covered in before machining it. I used to remove it with the Poly Disc- Clean and strip discs that Smith & Arrow supply, they do a good job but are messy and don't last that long. While reading up about various other methods, most of which I have tried, I found a post by John Stevenson outlining his preferred method, I always found his advise sound so I opted to try it out.
It is the simplest and most effective way I have found. You simply head down to your local hardware store in my case it is Bunnings as it is only 1 klm away and buy a container of Brick Tile & Paver cleaner. John's advice was to mix it 1:1 with water and leave the steel in overnight. I did this and put some a variety of sizes in the mix late in the afternoon and the next morning removed them and gave them a quick hose and all the scale just washed off- brilliant. I noticed that the mix of steels I had ended up slightly different shades but all were completely scale free. I could clearly see cracks in several pieces that were previously hidden.
RC will like this as the liquid is in his colour range.
A few pictures to show the results.
Bob

Very interesting Bob, do you reckon it would remove rust stains on a lathe bed?

Is this stuff expensive?

Ken

Originally Posted by neksmerj

Very interesting Bob, do you reckon it would remove rust stains on a lathe bed?

Is this stuff expensive?

Ken

Gday Ken,
lathe beds don't really like hydrochloric acid.
shed

Just be aware, the active ingredient in most of those Concrete / brick / tile cleaners is Hydrochloric Acid.

MSDS of same confirms it. http://www.chemtech.net.au/SDS%20Cle...Jan%202013.pdf

It makes things rust like there is no tomorrow. I wouldn't allow it into my shop. The fume's migrate, even from containers that are fully sealed. Case in point, 2 decades ago, when my kids where little. I set up a locked cupboard, paint, mower fuel, and a 4l plastic container of brick wash.

Cost me nothing, the bride was still with MLC Super at the time. Scored one of their old ones. One of those Brown Built storage cabinets. It rotted out the middle shelf 12 months in, just from vapours. Raw steel 8 feet away was rusting. The pivot hinges on the tilt-a-door.

I'd question why you think its necessary, to pull the scale off prior to machining? There's a gazillion tons of that done every day. Just cut deeper than the scale, and turn it into dusty swarf.

Its a real mystery to me, why any one would bother to pickle the scale off. Prior to machining it.
Regards Phil.

Originally Posted by Machtool

Its a real mystery to me, why any one would bother to pickle the scale off. Prior to turning

Regards Phil.

True....but try wire buffing 800 or more baluster rods, I can see a quite a bit of labor saving here.
In the right situation it could be a godsend

Originally Posted by shedhappens

True....but try wire buffing 800 or more baluster rods,

I don't see how that's relevant? The O.P specifically mentioned "machining" It was only the first sentence.

I have been looking for a better method of removing the hard black scale that hot rolled steel is covered in before machining it.

I'll have to google baluster rods. But wire buffing, pretty sure that's not conventional machining. By the sound of it, I hope you were wearing a dusk mask.

Phil

Simple things like 4140 /ANSI 8620. They only come in black / hot rolled.

Rule of thumb, you'd order 1/8" over size to ensure clean up.

Now days, don't ever ask for "black". It's hot rolled, or as milled, or you're a racist bigot. True story. I was after a chunk of 4140 recently.

Receptionist, gave me the rounds of the kitchen, because I'd enquired about Black Bar.

Regards Phil.

That nearly mirrors a (female) mate of mine asking for a "long black" in a coffeeshop in Johannesburg last year..... she got the rounds of the kitchen and was then asked to leave

Angle grinder with one of these makes quick work of removing scale
Abrasive Discs Sanding Belts Metal Grinding Industrial Abrasives: Cubitron II 3M_US

Even on a baby mill I don't even bother removing it beforehand tho, carbide inserted face mill, give it a skim cut before you start. I know the black scale gives HSS endmills hell tho.
I have one of these that I have turned the shaft down to 10mm and it will do 0.2mm depth of cut, full cut width on a 1/4hp machine easily enough, gets rid of the black scale and gives you a pretty decent surface finish to boot.
45 DEGREE INDEXABLE CHAMFER ENDMILL #H94 | CTC Tools

//metalworkforums.com/f65/t199727-citric-acid

Looks like when I next go to order some BMS, I will have to ask for mentally gifted mild steel.

All this racism is just a pigment of your imagination

Originally Posted by Machtool

Simple things like 4140 /ANSI 8620. They only come in black / hot rolled.

I was at Bohler Uddeholm just yesterday buying 4140 rod - bright finish.
20 mm $15/m and 16 mm was $9/m inc GST for 3m lengths.

Never seen 4140 with mill scale. Always comes T&G here.

Considering black iron oxide was an ingredient in the old-fashioned emery back when that was the principal abrasive I have never liked wasting HSS cutters on it or, even with carbide cutters, spraying the machine ways with it. Even when manually filing we were taught as apprentices to 'break the scale' with a piece of broken grinding wheel & save the file teeth. Working for an employer I used to bead blast any black steel before machining, post retirement & not having a bead blaster (yet) I went thro' the progression of disc or orbital sanding with 80 grit..very tedious & dirty, next hydrochloric acid in a bucket at the bottom of the backyard, now I simply soak it in the molasses & water a week in winter, couple of days in summer (looks just like Bob's samples), hose off & into it. I don't worry about the paint on my machines, the ways are another matter.