DIY Anti-Scale Compound

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So... I knew that eventually this uppity degree of mine would actually come in usefull for something other than actually working. This is what happens when an engineer tries to save money, and I may be a little late to the party on this but I at least felt accomplished when I figured it out.:D

I burnt out a set of coils in my heat treat oven the other day because I was burning charcoal in my oven to control the atmosphere. Apparently the coils do not like the hydrogen and free carbon that emanates from the charcoal at those high temperatures, which are the very things that give us the nice reducing atmosphere that prevents scaling and decarb.

There are several ways to overcome this problem, one being coating the coils with ITC213, which is expensive, or making them out of Kanthal AKM or Nikrothal 70, which are expensive and merely delay the inevitable. Obviously you can't have a true reducing atmosphere, but you could try for neutral. Some industrial ovens do this with nitrogen or argon purge, but you never really eliminate the problem(oxygen), just dilute it. You can always go the pouch route, but stainless foil is expensive, and it is really touch and go with shallow hardening steel trying to tear a pouch and get the blade quenched quickly. You could use a digitally controlled forge and control the atmosphere by richening the gas mixture, but alas I was fresh out of PID controllers, solenoid valves, fan speed controllers, or inconel sheathed thermocouples. The final way to control scaling and decarb that I considered was anti-scale coating such as PBC or the other Keepbrite stuff from Brownells. Now, I'm not too keen on paying $90 for 5 pounds of a consumable, especially when I could probably figure out what is in the stuff and cut the profit margin from the material cost.

So, that's exactly what I did. I started with our old friend borax, since it has almost the exact effect I am looking for, except that it is very hard to remove after it is cool, at least for me, and these commercial compounds apparently rinse away in hot water. I did a little searching around about borax, precursors, and products, and stumbled across boric acid. One of the industrial uses of boric acid was listed as "hardening steel". I thought "That's odd... I don't remember that being a step in my heat to cherry red, won't attract a magnet, quench in the backfat of a virgin slave on the harvest moon heat treat procedure." So, I did some more looking, and found that our friends in the jewelry and gunsmithing community use boric acid to prevent scaling when heating precious metals or heat treating precision firearms parts. It prevents oxidation and washes away in hot water. Eureka! But wait, I said... while this may work, is it the same stuff that, say, Keepbrite or PBC is made of? Well, that's where I ran into a wall. MSDSs were no help, and I am not going to just call them up and ask them what's in it, but I will say this... Keepbrite is not soluble in cold water, but it is in alcohol, and that is the one thing that boric acid is very soluble in at room temperature. Keepbrite is red, apparently. I don't know if that's a pigment or something like iron filings mixed in, because boric acid is a white powder. PBC is made by Rosemill, who traffic a lot in borate chemicals. I know... it's all empirical or downright circumstantial evidence, but there's a lot of it.

Anyway, once I was resonably sure that anti-scale compounds were by and large just boric acid, I had to actually find a source of the stuff. Oh sure, you could get it from somewhere like JumpinJackFlashPyroSupplies.com for $7.45/lb plus shipping, but there had to be a better way, a local way. Well, once again, the internet is our friend. Apparently boric acid is an excellent insecticide, and is peddled as a safe, natural way to decimate the local cockroach and silverfish populations. So, a trip to the local house of home improvement yielded this:

Roach_control.jpg


Ingredients:99% orthoboric acid, 1% other ingredients. Now, that worried me a little until I read the msds and it said that harmful decomposition products were not known. That means that it doesn't have anything really nasty in it, or it would be known. So, for a little more than $6/lb with no shipping, I effectively have the same stuff that costs 3 times as much. I bought a little denatured alcohol because I wanted to just dip and go.

Now, I don't think this is going to be the have all end all, as it probably starts to chemically attack steels at high temp. Judging from PBC's website, it's about 1600 degrees. That doesn't concern me too much as I use O-1 and 1095 a lot. At those temps, it might be best to use anhydrous borax and deal with the bark, or break down and use a commercial compound. I might have to try borax and try removing it with hot water with hot vinegar or cold muriatic acid. Borax is a base, so an acid might have better luck removing it than just hot water.

So, if I were going tomake an entry in the knifemaker's myth handbook, would it read: "Dust your blades with roach killer before you heat treat to prevent decarb and scaling."?

Taylor
 
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Taylor,

Sounds good so far. Of course, we're waiting on the lab work report, I mean, on the data and photos from the heat treat experiments.

All the best, Phil
 

JTknives

Blade Heat Treating www.jarodtodd.com
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I know that boric acid is sometimes mixed with borax to help with the fluxing. because boric acid has a lower melting point then borax. which means you start to prevent scale at a lower temp and once at welding temp the borax takes over and does its job. and that means no bad scale :D. but i had never thought about using it as an anti scale stuff for heat treating, but it makes since. you can also get pure boric acid from the drug store as it has medical uses. I am going to be doing some heat treating and will try this out as i was going to try using some borax but man its a pain to remove. here is a place on ebay that sells 5 pound bags of the pure stuff for real cheep and its free shipping.

http://cgi.ebay.com/5-lb-Boric-Acid-Tech-Grade-100%_W0QQitemZ250450255901QQcmdZViewItem
 
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Boric acid comes off in jewelers pickle (sodium bisulfate in water) which removes forge scale as well and makes a nice "discovery" to see what your damascus patterns will look like
it is available at pool and hottub suppliers as a product called "PHDown"
use in well ventilated area, the fumes when you put steel in WILL burn your throat and eyes!

-Page
 
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I've been using boric acid mixed in with my borax recently for exactly the reasons JT mentioned above. I hadn't thought of using it as an anti-scale since I wasn't sure what temps it burned off at. I'll definitely try this with my next HT since I have some on hand. Also, you may want to try your local Dollar General (if you have one). Around here they sell the 1lb bottles of 100% orthoboric acid roach powder for about $3.

-d
 

Stacy E. Apelt - Bladesmith

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Boric acid and alcohol is the standard cheap and easy anti-fire scale dip for our industry ( goldsmith). I have a 50 pound barrel of it.
It also works well as a fluxing agent when mixed with borax and a bit of powdered charcoal.
As to making HT anti-scale, mix it with alcohol and satanite. Shake up the bottle and apply a thin wash. It will dry and coat the metal, preventing scale.Let dry well before HT. Removal can usually be done with washing in hot water, or soaking in mild acid ( vinegar works fine).A post HT acid soak is usually desirable for several reasons anyway.

What I have been able to reverse engineer from using Turco, is that it is a borate with red/brown/yellow ocher mixed in. There is also some sort of colloidal carrier. Ocher is known as goethite, and is nothing but iron oxide clay ( basically ,red clay). I made a batch with boric acid, borax, satanite and ocher, with gum tragacanth as the binder, and it worked identical to Turco. I used a mixture of red and yellow ocher, since I have both on hand. Chemically, the ocher, which is an oxide of iron (mostly Fe/2-O/3), acts as a reducing agent. The various colors of ocher are just the amount of hydration, and are identical otherwise. Yellow is fully hydrated, brown is partially, and red is anhydrous.

Another cheap and very useful anti-scale is plain water and satanite mix. Make a thin slurry and put a wash coat on the blade. Dry it with a hair dryer, or let it air dry. Another thing to try would be a slurry of potters clay.


If you wanted to make a batch of anti scale try this (Quantities are in fluid oz.):
( This is off the top of my head, so feel free to tweak it as desired)

5oz boric acid (roach powder)
3oz borax ( 20 mule team is fine)
8oz denatured alcohol ( the cheap paint store variety, not the drug store stuff)
2oz satanite ( our old refractory friend)
3-4oz ocher (any color ocher - finely sifted dried red clay would probably work)
3-4oz gum tragacanth ( bottle of leather edge dressing)
water

Mix,adding additional alcohol until it becomes a well mixed thick paste.Add water until it becomes a slurry ( I think it needs some water to allow proper hydration and solution of some ingredients). Try it on a piece of steel to check results, and adjust the ingredients as needed. Keep in a tightly capped container,away from heat. Shake well each use, and paint it on with a small brush, or dip the blade and let the excess run back into the container. A batch should last for a long time.

Do not use above 1600F as the borates will become corrosive.

Stacy
 
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I wouldn't work with pesticides without knowing exactly what was in it !!
IIRC there is borax, boric acid and sodium octaborate [ ?] which is the one used for bugs.
 
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I wouldn't work with pesticides without knowing exactly what was in it !!
IIRC there is borax, boric acid and sodium octaborate [ ?] which is the one used for bugs.

the stuff I use is 100% pure orthoboric acid according to the label...at any rate, I'm not dead yet! :)

Stacy, thanks for the info. I have everything listed except the alcohol at the house. I only have yellow ochre, but I suppose that'll do. I'll have to give it a shot.

thanks!

-d
 

Bufford

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Toxic fumes are a concern here. Would the temperatures present in the HT oven be enough to neutralize the toxic compounds to prevent dangerous levels from building up in the air in a typical shop?
 
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Toxic fumes are a concern here. Would the temperatures present in the HT oven be enough to neutralize the toxic compounds to prevent dangerous levels from building up in the air in a typical shop?

The way I see it:
  • alcohol burns off rapidly and cleanly, no problem.
  • ochre won't burn off, no problem.
  • satanite for sure won't burn off, no problem.
  • borax has proven safe enough in blacksmith's shops over the centuries, no problem.
  • boric acid hasn't hurt all the jewelers over the years, I guess no problem.
  • Gum Tragacanth...no idea.

I'm willing to give it a shot.... :)

-d
 
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This thread is "VERY INTERESTING"

So lets see a WIP on this with pics showing the results of with and without!!;)
 
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Orthoboric acid = Boric acid manufactured by Ortho chemical
every bottle of roach killer I have gotten that claimed to have Orthoboric acid were manufactured by a division of Ortho Chemmical

-Page
 
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Toxic fumes are a concern here. Would the temperatures present in the HT oven be enough to neutralize the toxic compounds to prevent dangerous levels from building up in the air in a typical shop?

The boric acid IS the toxic chemical to the roaches, and to us in large enough quantities, but it is nonvolatile, so you don't have to worry about fumes. I wouldn't snort a line of it, though.

I plan a write-up of just the boric acid wash after I get my HT oven back in action, and if it leaves much to be desired I will switch to Stacy's formula, which obviously works well.
 

Bufford

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This is interesting, because of the drawbacks of using stainless foil, with getting a good quench. I like the idea of getting the knife out of the oven and straight into the oil.
 

jorasco312

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I read somewhere that Magic Markers/Sharpie's/etc., i.e., the stuff inside, was originally developed for the circuit board industry as a resist. I thought, if it will resist ferric chloride perhaps it will resist an oxidizing atmosphere in the forge. So, I paint my blades with a big ol' Sharpie, tweak the forge till I have a reducing atmosphere and HT. Seems to work fine at eliminating scale. You do have to scrub/sand the stuff off but it is a heck of a lot easier than removing scale.
 
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I read somewhere that Magic Markers/Sharpie's/etc., i.e., the stuff inside, was originally developed for the circuit board industry as a resist. I thought, if it will resist ferric chloride perhaps it will resist an oxidizing atmosphere in the forge. So, I paint my blades with a big ol' Sharpie, tweak the forge till I have a reducing atmosphere and HT. Seems to work fine at eliminating scale. You do have to scrub/sand the stuff off but it is a heck of a lot easier than removing scale.

Wow! That's a lot easier than working with a pesticide. Do you think that maybe the reducing atmosphere has a lot to do with it?
 
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Wow! That's a lot easier than working with a pesticide. Do you think that maybe the reducing atmosphere has a lot to do with it?

Yep. If you have a proper reducing atmosphere all of the anti-scale compund talk is a moot point. Your oven coils don't like that atmosphere, though. $50 later I know that...
 

Stacy E. Apelt - Bladesmith

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Yeah, Troop, I am thinking it is more the atmosphere than the ink. There is so little solids in marker ink that I doubt it would survive 1500F for long.( resisting FC is an entirely different thing). However, I have discovered that the white metal marker pens will stay on through 1900F HT. I mark the tangs of stainless blades with metal type and other info ( or you will never be able to tell one from another), and do stainless HT in batches. I have found that the white pigment just burns off to leave a titanium oxide stencil. It makes it easy to ID the blades after HT ,too.

Stacy
 
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