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How to prepare Hot Rolled Steel for marking/machining

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SamJo18/02/2010 20:08:47
9 forum posts
I'd like to know of a good method for removing the scale off HRS. So far I've made some experiments using an end mill but this seems to be rather time and tool consuming. What methods are more experienced engineers using to prepare this material for marking and machining operations?
mgj18/02/2010 20:45:18
1017 forum posts
14 photos
Using blue and a scriber. Is there more?
John Haine18/02/2010 21:02:56
5563 forum posts
322 photos
It's black.  And rough.  You just have to mill off the scale.
 
Ramon Wilson18/02/2010 22:04:14
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Hi,
 
Assuming you are refering to the mill scale as rolled and not the scale on any edges created by cutting processes I don't know if the following will be of any use to you but for what its worth -
 
There used to be  a product available from 'Jenolite' called Aldecon C.
This was used for 'etching' the surface of hardened and ground parts before using their 'Cold Black'solution. It is a very powerful agent and will remove the scale back to bright steel.
 
I did a set of frames from black rolled steel and with this plus a bit of elbow grease and some coarse emery had them looking like BMS in a day. I did them on a hot sunny day (bit of a problem at the moment!) - laid them on some thick polythene liberally coated with the (neat) stuff - wrapped them up and left them in the sun. Don't know if that improved the process - just the way I did it.. It certainly removed the scale without affecting the steel in any visually apparent manner.
 
Two things - if you do decide to try some. It contains hydrochloric acid - obviously take the usual precautions - and don't, definitely don't, leave this stuff open or use it (even if well diluted)  in the workshop as it will cover absolutely everything that is bright steel with a brown rust(?) like patina in very short order indeed.
 
Diluted it makes an extremely good pickle for silver soldered steel items taking all that black gunge off right back to the bright (though a little 'grey') steel leaving just the solder to clean up. A thorough washing in fresh water is required. A much fainter brown patina will still form though very slight and is easily removed with a bit of fine emery
 
I don't know if it's still available - I bought mine through my works along with Cold Black about ten years or so ago.
 
I don't know of any mechanical means that will remove scale (which, as you've probably already found out, can be glass hard) as well as this stuff.
 
Hope this helps to answer your question.
 
regards - Ramon
 
 
mgj18/02/2010 22:19:34
1017 forum posts
14 photos
Well good luck to all of you - I have just machined it without  any treatment with perfectly good success and without doing  damage to a tool/drill bit etc.I don't use much of it - milling clamps, and brackets that need bending on the TE because it is normalised and soft.
 
Clamping in vices I use packing to ensure an even hold . I don't turn it, and if I did, I'd hold it in a 4jaw and not a 3 jaw - obviously, but I have milled/drilled it reasonably regularly.
 
If I did hit a hard bit, just like cast, its an easy job to sharpen up again, but I don't remember doing so.
 
Perhaps I have just been lucky - but I'll wait till my luck changes before I start descaling.
 
Never troubled me at all. Razor sharp tools?
John Stevenson18/02/2010 22:21:21
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5068 forum posts
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You want some stuff called Phosphoric Acid, it's sold at B&Q as brick and cement cleaner, look at the labels and try to get one that 90or 95% acid.
 
Plastic tub, mix it 3 or 4 :1 with water and put the steel in overnight and the scale flakes off.
 
It's not a nasty acid, best to wear rubber gloves but it doesn't sting or burn, when used up it can go down the drain or wash the slabs with it.
 
Unlike some of the other acids it doesn't make nasty fumes, I have a tub on the floor next to a big dividing head and it been there for 2 months now and no rust or anything.
I descale about 100 disks per month using this method, they come out with a grey sheradised finish and if you lightly oil it that's all that needed.
 
I dropped a scrap tap I found in the base of a lathe, been there 40 odd years, all rusted up and grungy, Stuck it in overnight just to see and it came out next day grey all over and like new, it even felt sharp !!
 
John S.
mgj18/02/2010 22:55:58
1017 forum posts
14 photos
If time is not on your side and it is actually necessary to descale, (like you want to weld), you could always try the tool that is purpose designed for the job.
 
Its called a pin descaler. Most of them use air, but you might find an electric one. Come in various sizes.
Ramon Wilson18/02/2010 23:28:21
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1655 forum posts
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John
That is a interesting comparitive and, something tells me, probably a hell of a lot cheaper too!
 
The bonus of course is the ability to use in it in the workshop without the dreaded 'plague' covering everything - and the disposal!
 
Milling 'through' scale into the metal below is not a problem but it will dull the cutter at the point of the scale - the thickness of the scale will score the cutter edges - use the cutter after to face off the end of some part and you will see it - not very big but it is there. But to remove the scale using an endmill without affecting the metal beneath - which is how it reads to me - is definitely a no no, well, not unless you have lots of cutters or conversely a deep pocket.
 
Forget about the Aldecon SJ and get off down to B&Q
 
Best of luck with your project
 
Regards - Ramon
DMB19/02/2010 08:56:58
1585 forum posts
1 photos
In the past, I have used a coarse grade emery disc in pistol grip elec. drill - brings steel up nice `n` bright. Dont forget the ear - defenders or youll `pay` for it with life-long tinitus, like me but in my case, I`ve done a number of things to cause it.
Probably a cheaper source of Hydrochloric Acid  is sold as acid in builders merchants. Used by antique restorers for cleaning filthy brass antiques. I tried it neat from the bottle outdoors and boy! did it fume!! Did the job, though. Take care - VERY nasty stuff.
DMB19/02/2010 09:07:00
1585 forum posts
1 photos
In the past I have used a coarse grade emery disc in a pistol grip elec. drill. Cleans  up steel nice `n` bright but you need to be careful about very deep scratches which could be difficult to remove/hide with filler. Also, use ear - defenders or suffer tinitus later!
A cheaper source of Hydrochloric Acid which I used is a bottle of it from builders merchants who sell it to antique restorers for removing filth from brass antiques.
Only use outdoors as boy! does it fume!! Keep upwind of fumes and use it as drain - cleaner (outside), to dispose. Bet water authority wouldnt approve!
 
DMB19/02/2010 09:08:10
1585 forum posts
1 photos
Sorry, I typed 2nd version as my `puter seemed to have lost 1st version. 
Ian S C19/02/2010 09:11:36
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7468 forum posts
230 photos
If you must remove the scale, I'v used a number of methods. (1) sand blasting. (2) the electrolitic rust removal method. (3) Citric acid. Unless the piece needs machining, I usually leave well alone. Ian S C
Gordon W19/02/2010 09:48:09
2011 forum posts
I use a lot of black bar (hot rolled) mainly because I have lots of short ends, and can't get anything better. Beware of vastly different samples, some m/c well, sometimes can't even drill a hole, also beware the very ends of bars that have been cropped. I always use an angle grinder to take of the outside scale on bigger sections, smaller rounds 1/2" or so usually m/c ok, not as good as leaded en1. Treat it like a casting, get under the skin. Polish with flap disc or sander. Steel left outside usually looses a lot of the scale, just before it goes rusty. Just realise that some of it, and even more so nowadays, is rubbish
SamJo16/03/2010 18:17:19
9 forum posts
First of all, a belated Thank-You for the comments to my question. The original reasons for my inquiry were availablity problems with some square BDMS bar dimensions in small quantities plus the obvious cost advantage that the black stuff has. Good thing is I don't have to use it very often.
 
In the meantime I've mostly been shovelling snow and heating frozen drain pipes but was finally able to visit the local DIY / hardware store and bring back some Phosphoric Acid based rust remover. Unfortunately no straight acid was available. After an overnight trial with some scrap black bar I can confirm the stuff really works (thanks, John!). It's definitely going to be part of my shop inventory even if it means another liquid container on the shelf plus some disposal problems with the used brew.
Ian S C17/03/2010 10:14:38
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7468 forum posts
230 photos
Either trhe electrolitic method with washing soda, or citric acid would overcome most of the disposal problems. The liquid is OK down the drain, and the small amount of solids can go out in the house hold rubbish. Ian S C
SamJo17/03/2010 10:29:42
9 forum posts
Washing soda or citric acid?.......well, both seem to be available almost everywhere. Will definitely try them. This is getting interesting.
Axel17/03/2010 11:23:30
126 forum posts
1 photos
phosphous acid is nasty and strong, it can disolve more than one thinks! Dilute to a far weaker solution than poster above suggests!
Terryd17/03/2010 12:45:04
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1946 forum posts
179 photos

 
Posted by John Stevenson on 18/02/2010 22:21:21:
You want some stuff called Phosphoric Acid, it's sold at B&Q as brick and cement cleaner, look at the labels and try to get one that 90or 95% acid.
 
 

 

Hi there,
 
Phosphoric acid isn't quite so bad, it is actually an ingredient in Cola.  Just check the ingredients next time you have a Coca Cola - it is pretty dilute though but it will clean a copper coin beautifully!!
 
Terryd
Ian S C17/03/2010 13:57:59
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7468 forum posts
230 photos
We'r trying Coca Cola here today, my mate a hot-rod builder and shop owner found he had a crate of out of date Coca Cola and when I arrived at his workshop he had emptied half of them in a bucket,it was bubbling vigorously so I suggested he try its rust removal abilities. I'v got some machine work to do for him so I should find out tomorrow what happened. Ian S C
Nigel McBurney 117/03/2010 20:06:44
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1101 forum posts
3 photos
hi    Black iron is essentially the cheapest form of mild steel and suitable for welding and fabrication,avoid machining other than drilling holes,use bright mild for machining.If it must be machined try cleaning it up with an angle grinder and various grades of sanding discs. to mark out in the black scaly condition,chalk rubbed on the surface was a traditional way,it shows up scribed lines,a more modern way is to use grey matt primer from an aerosol.white wash was a very old  method to mark out black iron and castings but took time to dry.If I HAD to clean up and then machine say a 25 by 50 mm black bar section I would use a HSS or carbide tipped fly cutter on the mill,  NMCB

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