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radkins
01-11-2016, 10:08 AM
I started to ask this on the Heat Treat oven thread (excellent thread BTW!) when scaling control was discussed a bit but I didn't want to pollute the topic with an almost unrelated question.

Scaling is a problem and I have been somewhat successful using gas (C25 MIG welding gas) by flooding a small stainless steel box I built to place the parts in while heating. This has worked ok for really small parts but what I have has been a PITA to use at best and is worthless for all but really small stuff. I know little about stainless foil having only seen it mentioned and while I just recently bought some anti-scaling compound I have yet to use it so I know little about it too, the stainless foil appears to be the simplest to use but what is involved in properly doing so? Can the anti-scaling compound be used just as effectively? The gas seems to work ok but with my set-up it sure got spendy when I tried flooding the entire oven for a larger part but then maybe I could better control that? I am a complete novice with this oven so I am just learning these things.

rklopp
01-11-2016, 10:13 AM
One data point to consider is that the anti-scaling compounds off-gas nasty fumes that corrode electric heating elements and steel furnace casings. DAMHIKT.

Black_Moons
01-11-2016, 11:23 AM
AFAIK, the stainless steel foil is to be used *with* some kind of anti-scaling compound.. Or at the very least, something that will burn and consume all the oxygen (Wood chips, charcoal, whatever)

Idea is the foil keeps in whatever fumes where created by the anti-scaling compound.

sarge41
01-11-2016, 11:29 AM
Radkins: I haven't done a lot of heat treating, but some people will put a small piece of paper in the foil pack to burn up the oxygen.

Sarge

DR
01-11-2016, 11:34 AM
Foil should be sealed carefully around the part with a small wood match stick or such inside to consume any oxygen.

The anti-scaling compound (Staybright) I used worked okay as long as there aren't threaded holes it has to be dug out of. Don't know about off-gassing that might corrode heating elements, don't recall any mention of that on the can.

When my parts have significant value they're sent to the heat treater (minimum charge around $150).

radkins
01-11-2016, 12:00 PM
I didn't know about the corrosion problem with the anti-scaling compound, that would be a concern, but then as the old saying goes I could probably write a book about what I don't know yet! I will soon have some small gun parts I need to HT and this time I REALLY would like to avoid the scale which in the past has been enough of a problem to cause me to trash the parts and start over!

So simply wrapping in foil by itself is not sufficient? I suppose adding an oxygen consumer of some type would be simple enough but how about quenching when using foil?

lakeside53
01-11-2016, 12:15 PM
Radkins: I haven't done a lot of heat treating, but some people will put a small piece of paper in the foil pack to burn up the oxygen.

Sarge

Yes, this works perfectly. I had zero scale and minimal discoloration on O6. There's two (or more) grades of stainless foil - which one you can get away with depends on your temperatures etc.


You keep the foil "loose" but with crimped over (couple of folds) edges to seal. To get the parts out hold the PACKAGE end by tongs and snip the bottom of the package over your quench. Practice this a couple of times before trying it HOT. If your foil is too tight (especially if the parts have sharp corners) they will not fall out!

MichaelP
01-11-2016, 01:27 PM
Very good point. The stainless steel envelopes work perfectly, but the trickiest part is to get the content out and into the quenching solution VERY QUICKLY. Otherwise, the heat treatment result will be impaired.

In this respect, stainless steel wrapping is especially full-proof for air hardening steels like A2.

RWO
01-11-2016, 01:33 PM
This stuff is supposed to work well, but I have not tried it. http://www.brownells.com/gunsmith-tools-supplies/metal-prep-coloring/heat-treating-accessories/anti-scale-coating-prod23076.aspx

It is rated for temps above 1500F which is helpful for some tool steels. PBC doesn't take such high temps very well.

RWO

10KPete
01-11-2016, 01:39 PM
If you put a bit of steel wool in the packet and seal it tight you'll eliminate the scale. If you don't have sstl foil then the
anti-scale materials work well. One in particular, taught to me by a clock maker, is to loosely wind the part with soft
iron wire and then gloop it all over with a boric acid paste made by adding just enough denatured alcohol to boric acid
powder to get a 'just wet' paste. Parts come out just about as clean as when they started. You need to boil the part
in water to get the last of the residue off (kinda like silver brazing flux) but it comes off in the boiling water quickly with
no scrubbing.

Pete

Tim The Grim
01-11-2016, 06:56 PM
We used the stainless foil and added a 2 inch square piece of a heavy duty brown paper grocery bag. We put a few drops of water on the paper to just barely dampen it and then folded it over a couple times to a 1/2 inch square and placed it in the SS envelope with the workpiece. All seams on the envelope were double folded and sinched in a BP mill vice.
As the oven heats up, the water flashes off as steam and adds some positive pressure to the envelope.
The heavy brown paper then burns and removes any oxygen from the enclosure. You now have a pretty much inert atmosphere to prevent formation of scale.

For air type steels we just let it cool as required. For oil hard we had a set of long snips to quickly slit the bag twice before dipping. Believe me, the oil gets in there just fine.

Air hard comes out super clean and oil just need a little Scotch Brite to take of the residue.

This was the method my mentor, Oscar Wilde Lyons, taught me back in '76 when I was just an apprentice and it has always worked for me.

Enco sells the foil for about $95. With a good % off sale code and free shipping it's worth having a roll in the shop.

Bob Ford
01-11-2016, 07:37 PM
Radkins,

Some of my oil hardening parts I do not want to just drop in and hope they come out straight with a even hardness On these I use anti scale. They come out clean and the anti scale washes off with hot water.

As it has been said S S foil is double folded and squashed so the folds are air tight. I use a strip of brown paper bag to use up any oxygen in the bag.

Some of the knifes I have made require hardening at 2150 deg. These I have cooled by placing them between Two 1 inch thick aluminum plates and applying pressure. These are then tempered at 1000 deg. And I use anti scale to keep them clean. Results in a blade of Rockwell 62 and they do hold a edge. CPM 3V http://www.crucible.com/Products.aspx?c=DoList

Bob

radkins
01-12-2016, 01:19 PM
The Brownells compound is the one I have but as of yet I have not tried it, considering the simplicity and economy of use even if it does create fumes that attack the heating elements ad temperature probe it may still be a good choice because these are not expensive nor difficult to replace so I suppose the anti-scale compound is what I will try.

Bob Ford
01-12-2016, 04:04 PM
I have used both the casehardening compound and the anti scale. The case hardening compound does have fumes, but have not noticed any with the anti scale. I use a Evenheat furnace for most of my heat treating and have not seen damage. I did buy a spare heating element, so if it fails I can fix imeadiately.

Link to both. http://www.use-enco.com/CGI/INPDFF?PMPAGE=853&PARTPG=INLMK3&PMITEM=328-1122

Bob

Mcgyver
01-12-2016, 04:48 PM
Some of my oil hardening parts I do not want to just drop in and hope they come out straight with a even hardness On these I use anti scale. They come out clean and the anti scale washes off with hot water.

i'm not getting it....how does the anti-scale change the need for hoping and finger crossing that they come out straight?

Other that quickly straight in for even cooling and swishing about....I don't have a lot of techniques to avoid trouble. Oh, another is a long cycle stress relieve before heat treating.

ironmonger
01-12-2016, 05:56 PM
It's more trouble to build the equipment, but molten salt baths (https://en.wikipedia.org/wiki/Molten_salt) for hardening and tempering are a great alternative for elimination of scale. The entire part is submerged in a high temp salt bath, at 1400 to 1800 or what ever you require. The molten salt conducts the heat very evenly to the part being hardened, and when it is withdrawn to quench in the molten salt tempering bath it is protected by a film of salt, which keeps the metal scale free.

Typically various chloride salts are used for high temps and nitrates for tempering. Molten salt tempering baths, the ones using the nitrates, should never come into contact with combustibles... bad juju.

Some high quality knife makes use this technology. No reason it wouldnt work for gun parts.

Mark Rand
01-12-2016, 06:04 PM
I have had very clean results by heating the parts in molten table salt. Salt melts at 802C/1476F which is just below the 850C/1560F that's needed for most steels. Because you are dunking the part into the molten salt, the air can't get at it, the only chance for scaling is the couple of seconds during the journey to the quench medium.

Two downsides:-
1) Dropping a complicated part directly into the molten salt wil give it far more of a thermal shock than gently heating and pausing at 750C/1380F
2) Although the heat treated part will come out clean, if you melt a crucible of salt in your workshop, everything else will grow a layer of rust.:mad:

This link (http://www.test-net.com/hardening-final/) shows the procedure when I was hardening parts for the rebuild of my Hardinge HLV apron gearbox. Note that the salt has about the consistency of water, apart from the evil red glow. Also the music on the video clips wasn't deliberate, it's just what I had on at the time.:p

radkins
01-12-2016, 06:50 PM
Well as usual I am getting more than I bargained for! You guys have taught me a LOT and this topic has been no exception, VERY interesting indeed!

ironmonger
01-12-2016, 09:25 PM
<<snip>>
This link (http://www.test-net.com/hardening-final/) shows the procedure when I was hardening parts for the rebuild of my Hardinge HLV apron gearbox. Note that the salt has about the consistency of water, apart from the evil red glow. Also the music on the video clips wasn't deliberate, it's just what I had on at the time.:p

How many watts is your heating element element rated at?

Never got to hear the music, the files would not place on my linux system... I'll try later on a Winbox

Bob Ford
01-12-2016, 10:33 PM
Mcgyver

By coating a part with anti scale you are able to grab the part at the right temperature and have control of how the part is plunged into the oil. You also have control to move it sideways or up and down. This allows you to cool one side slightly quicker to help stop warp.

With S S wrap you ether dump it out of the bag into the oil risking warp or by the time you grab it out it is ether too cold or has formed scale.

Bob

KIMFAB
01-12-2016, 10:35 PM
Mark you should never have to apologize for Pink Floyd. Anyway here's a shot of some A2 used for a die I'm making.
I wrapped it in SS with the edges folded and some plain paper inside to suck the O2 out

I left it cool in the wrapper till I could barely touch it then back in the oven and up to 450 and let cool naturally

http://www.kimfab.com/pictures/forum/diea048.jpg

Mark Rand
01-12-2016, 11:28 PM
How many watts is your heating element element rated at?

Never got to hear the music, the files would not place on my linux system... I'll try later on a Winbox

That was about a kilowatt. Made by winding nichrome wire around the crucible and insulating it with a clay wash. Unfortunately it only lasted about five melts and then got a short between two turns that melted it when I was pushing a bit too hard with the Variac...

Files re MOV direct from an old camera. I need to try to convert them to avi or mpg.

Jim2
01-13-2016, 10:19 AM
I hardened a drive pawl for the table feed on my shaper this weekend. Now, I have practically no experience heat treating anything. I moved to where I'm at 8 years ago, and I've only run my forge once, maybe twice? But, I had done some blacksmithing in the past and was paranoid about scaling on the part which I'd just machined to the thousandths of an inch. . . . I used borax. I think somebody else referenced that as washing salts? My understanding is it's the same thing that's used to coat welding rods. I started the forge, heated the part a bit, dipped it straight into the borax (20 mule team brand, LOL), heated a bit more, dipped again--probably 3-4 times in all until the magnet wouldn't stick and quenched in water (was using W1 drill rod).

Results were overall good. The part was covered with a gritty substance that I took off with fine-grit sandpaper. I didn't see anything that would qualify as scaling. The original milling marks were still visible on the part. This certainly isn't a sophisticated process, but it was cheap and readily available to anyone.

Jim

Fonzy4140
01-18-2016, 09:25 PM
Yes indeed, borax, is a long time anti-scale/welding flux. I use it for my HT items. What I find works best is a fine powdered 100% borax anti roach powder that is [was] sold in my area Dollar stores. If you can get by the scary buggy poison labels on it, you will find it is a fully safe 100% borax[not safe for bugs tho...smothers them] Much cheaper and easier to use than 20 mule granules. Mixes into a paste with a little cold water. Brush it on. I find it is best to pre heat it to about 250 deg. to form a baked on tough layer first, then take it up to desired temperature.

ironmonger
01-18-2016, 09:39 PM
Yes indeed, borax, is a long time anti-scale/welding flux. I use it for my HT items. What I find works best is a fine powdered 100% borax anti roach powder that is [was] sold in my area Dollar stores. If you can get by the scary buggy poison labels on it, you will find it is a fully safe 100% borax[not safe for bugs tho...smothers them] Much cheaper and easier to use than 20 mule granules. Mixes into a paste with a little cold water. Brush it on. I find it is best to pre heat it to about 250 deg. to form a baked on tough layer first, then take it up to desired temperature.

Borax, technically sodium tetraborate decahydrate Na2B4O7 10H2O, is not the same as roach powder, which is boric acid.
They both make good welding flux for forge welds. the borax is less troublesome if it is anhydrous, ie has the water cooked off. It is also hygroscopic, so even if it's dried out it will suck up moisture for the air. It is the hydrate (chemically bonded water) which causes it to 'foam' when applied to hot metal. Once it stops foaming it works just fine.