How do I recognize hot rolled steel?

[PekkaNF]

Hi

I need to build something using hot rolled steel. I have heard that hot rolled steel is more stable and does nor warp too badly when skin is milled away. Planning to make top slide for a lathe.

I need flat bar, something like 20-30 * 80-100 mm section.

Q1: How I can tell difference between hot rolled and cold rolled steel at scrap yard? Specially if it is rusty? I know hot rolled should have mill scale, but how does it look? I tried to google and founf a lot of articles about removing it with an angle grinder.

Q2: How do I remove mill scale? Piece is about 20*80*300 mm and I have time, but don't want to couge it with angle grinder

Q3: Does it works if I make a dovetail rail of hot rolled steel and slide cast iron? What kind of finish I need here? Does milled (dove tail cutter) produce good enough finnish for sliding contact or do I need to grind or build a lap for it?

Pekka

[Lew_Merrick_PE]

Q1: How I can tell difference between hot rolled and cold rolled steel at scrap yard? Specially if it is rusty? I know hot rolled should have mill scale, but how does it look? I tried to google and founf a lot of articles about removing it with an angle grinder.

Q2: How do I remove mill scale? Piece is about 20*80*300 mm and I have time, but don't want to couge it with angle grinder

Q3: Does it works if I make a dovetail rail of hot rolled steel and slide cast iron? What kind of finish I need here? Does milled (dove tail cutter) produce good enough finnish for sliding contact or do I need to grind or build a lap for it?

1) Mill scale is a ranges from a dark brown to an almost black coating to the HRS material.  CRS material will range from fairly bright silver-gray to all rusty.

2) Your choices for scale removal are: cut/grind or etch to remove it.  Many people here will use a vinegar & salt soak.  This is slow & steady.  I almost never have the schedule time for such slow methods and typically use muriatic acid to remove scale.  For a piece of the size you are quoting, my approach will take about 10-15 minutes.  Be very careful of the fumes from muriatic acid -- do it outdoors.  After you have etched off the scale, coat the part with a base.  I use baking soda as it is inexpensive and readily available.  Rinse thoroughly with water & dry it completely.  Newly etched steel will rust in a heartbeat.  I coat such parts with (wooden floor) wax to prevent that.

3) Unless you have an amazingly rigid spindle with very good bearings, you will almost certainly need to st/one out the resulting dovetail face to take it to a fine (but longitudinally scratched) finish.  The alternative to this is to stone it to a mirror finish (the reflection will tell you how flat you got it) and flake a pattern of "oil catches" along the face with a scraper.  Almost any decent book on scraping will give you a handle on the technique.

[Meldonmech]

Hi Pekka
               When using your angle cutter, try out cut depths, and feed rates, preferably on an off cut of the actual material you will be using for your cast iron and hot rolled slides.  You will the be able to assess the finishes you can obtain.  The final cut should be very light several thou. using a very fine feed.  Hard cast iron may need a deeper finishing cut. This should give you the best finish possible, and minimize final finishing.  Lapping is a possibility, lapping the sliding part to the rail, and the gib strip to the rail.  Again using scrap material to get a feel for the process.  Lapping compound obtainable in varying grades can quickly ruin the surface.  Try fine first to see if that will suffice. The final finish should be smooth and matt all over.  Use plenty of oil, and make sure the mating surfaces are perfectly cleaned before assembly.  The surfaces can then be scraped to provide oil retention as suggested by Lee.

                  I believe that if things work on scrap, they will work on the job, and save a lot off heart ache.

                                              Good luck with your project it sounds interesting.
                                                                                                                             Cheers  David

[Fergus OMore]

Ignoring the advice and whatever on steel, preferred top slide metal should be cast iron.

The latter is so much more stable, easy to machine and then scrape.

OK, I HAVE a set of slides on my little Stent tool and cutter grinder which are bright mild steel welded sections. Dead wrong as others will rush to comment but if you are prepared to normalise to get rid of the inbuilt stresses and scrape and whatever with way oil, you can do it.

Me, I got the thing for a song as I bought it for the motor as the maker had died.
Probably, the enormity of the task was too much. Again, as others will rush to point out, cast iron will move as well.  I was making a Westbury mill head - not a Dore and it moved on splitting. Rude Anglo Saxon mutterings again.

So think it out- carefully

Norman

[vtsteam]

Any blue-gray scale anywhere on it, even if mostly rust covered elsewhere is a giveaway.

Scale tends to resist rust for quite awhile, and there is often a protected patch somewhere on a rusted piece.

Also hot rolled tends to have rounded edges instead of neat clean square edges like cold rolled.

Like a typical piece of angle iron -- the edge is often rounded/tapered, not perfect.

[PekkaNF]

Thank you for description of the mill scale. I have seen it, just haven't recognized it. I think that now I know what kind of texture and corner I'm looking for.

I found a piece of "rail" very nice machined steel that is well aged and machined all over. It is pretty damn hard and nothing less than carbide cuts it. Pitty. it would be very close to right size. only to cut length and mill 10 mm out from top (L=300m) before cutting dovetails, grove and holes in it.

I would use cast iron if I could source right size piece anytime soon without paying premium. I'll see one local scrap yard today and see what they have.

My biggest consern is that is cast iron and HRS sufficiently different material to work as a top slide (bearing). Cast iron is one of those few materials that works pretty with itself as a bearing material. But I have no experience as cast iro - HRS pair.

I'm not planning to try scraping or flaking on this project, therefore sliding surface finishing must me done different manner.

I probably will make a plug/test and a lap before trying the "final cut".

What portions of salt and vinegar is used on traditional scale removal? How long it takes?

Can I use battery acid (sulphuric acid) as "muriatic accid"? I have plenty of citric accid too but access to other strong chemicals here is pretty limited.

Pekka

[philf]

What portions of salt and vinegar is used on traditional scale removal? How long it takes?

Can I use battery acid (sulphuric acid) as "muriatic accid"? I have plenty of citric accid too but access to other strong chemicals here is pretty limited.

Pekka,

Muriatic acid is Hydrochloric Acid which is readily available in the UK as Brick or Masonry Cleaner from hardware and DIY stores. I have used the Brick Cleaner further diluted 2:1. It shifts mill scale in around 15 minutes.

Phil.

[12345678910]

What portions of salt and vinegar is used on traditional scale removal? How long it takes?

Can I use battery acid (sulphuric acid) as "muriatic accid"? I have plenty of citric accid too but access to other strong chemicals here is pretty limited.

Pekka,

Muriatic acid is Hydrochloric Acid which is readily available in the UK as Brick or Masonry Cleaner from hardware and DIY stores. I have used the Brick Cleaner further diluted 2:1. It shifts mill scale in around 15 minutes.

Phil.

Toilet bowl cleaner is often pure acid too, not those coloured thicker ones, but the cheapest ones.
Read the labels.

[vtsteam]

I use diluted muriatic acid for scale, and the sodium carbonate electrolysis method for rust. But I have used white (distilled) vinegar and salt before for scale and it just takes longer -- usually overnight for newly purchased material wth thick scale. I do not dilute the vinegar, and just dump in some salt -- no problem if it doesn't all dissolve, you just have a saturated solution -- but I'm sure less will work fine, too. Not critical proportions, I believe.

Andrew likes citric acid. They all work.

Dilute sulfuric probably does too, but personally I feel more comfortable with dilute hardware store muriatic (hydrochloric) for some reason.

re. muriatic: I pour a little from the masonry cleaner bottle into about ten times as much water. I save the dilute stuff in a wide mouth sealed covered plastic container suitably decorated with skull and crossbones and warnings, and use it over and over again until exhausted. I keep it away from machinery and out of reach in  the shop, and I only use it outdoors. It will also strip hot dip galvanizing off in a matter of minutes, if you need clean metal for welding or brazing. Does that quit vigorously.

Pekka, re. your rail material that is hard. I also had a piece of what looked like rail from a junkyard, but it actually turned out to be cast iron -- easily shattered with a sledge hammer, and though I'd intended it for a homemade anvil, I decided it wasn't suitable for that, and have found that it is fine material for melting when doing iron casting (last summer).

So. not all rail is steel, though this stuff might not have been "real" rail.

[PekkaNF]

Thank you all for great info.

Tried to hit scrap yard in time....ended there five minutes before closing and they did not want to cut 1m out off 6 m bar of 40*100 HRS. I'll have that on monday.

But I'll entertain myself trying to descale some hot rolled square steel and trying to cut some 60 degree angle to it.

Put about 2 pints of vinegar and 1/2 lbs of salt. Less see.

I think I can recognize mill scale now.

Pekka

[sparky961]

I found a piece of "rail" very nice machined steel that is well aged and machined all over. It is pretty damn hard and nothing less than carbide cuts it. Pitty. it would be very close to right size. only to cut length and mill 10 mm out from top (L=300m) before cutting dovetails, grove and holes in it.
Pekka

Just kinda jumping in on this one, but depending on the size of this "rail" and the availability of a large heat source you could try annealing it.  I've done this with some "hard-as-diamond" parts and they machined like aluminum when I was done.  Then you can heat treat as you like, or not at all.

[PekkaNF]

About the "rail". They are machined all sides. I know that some of them were cast iron/steel something and the hardness was really funny, the machined "skin" was softer and under it it was a lot harder material. This is somewhat smaller item over metre long machined all over, some countersunk holes for bolts and stuff. I should saw off a little piece and give it a try. Maybe I should take a sample to the work and ask someone to measure hardness of it. It should tell a lot.

I pickled some steel and what do you know? One piece is machined! I can see machining marks and corners are sharp too.

The other piece seems genuine item. "Flakes" have fell off and it has rounded edges as VT pointed out before. Pretty evident when you think of rolling process.

So here is the picture. Is it picked enough?

Pekka

[PekkaNF]

Breckfast condiments seem to work wonders! I'm genuinely surprised. One day and mill scale & rust all gone, just a little brushing with nylon brush, wash with pine oil soap, drying and light oiling. I filtered and bottled back the vinegar. Not sure how fast it is spent, but hard to believe that it would do any damage on the plastic drain or on effluent treatment plant.

Some easy to separate solids were left. I like this. Some mild chemicals that you can buy from the shop, little time on the tub and done. No sparks, no noise, no obnoxious chemicals or waste to deal with.

I trawled selves of two stores for Muriatic acid discuised as toilet bowl cleaner....no luck. All were perfumed detergents. Hardware store had some branded Masonry Cleaner, but a less than 1/2 litre bottle cost way over 20€!

But I found some other drain opener PH13 and used it strip paint from cast iron parts.

Pekka
* Forgot the compulsory piccy!

[vtsteam]

I imagine the vinegar will work well for a lot more metal than that -- so saving it is a good idea.

Try it on some galvanized -- I imagine it will strip that off quickly, too.

Also if you can keep it warm it will strip scale faster.

[PekkaNF]

Went to scrapy and he cut (torch) me pretty close 1m long piece of 80*30 mm HRS. Cost about 23€.

Today I found that the "rail" is ductile iron GRP700, stress relived, annealed , hardness 260-320 HB , specified. Pretty good. Problem is that it's peppered with holes leaving maximum of 160mm of usable continous length.

So, this is what I need to work with.

Pekka