- Joined
- Aug 16, 2008
- Messages
- 222
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.
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:
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
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:
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
