Question on melting furnaces for wootz ingots and if atmospheric burners out there are suitable...

[Al Massey]

Subject pretty much says it. Although my forge is a beast ultimately I'm going to want a proper melting furnace. I don't see too many commercial ones available for the temp range I want, if anyone has a line on them let me know. I'm probably looking doing about 1 kilo ingots or a little better, tops.

Also, I've had great success with forging with Rex Price's T-Rex atmospheric burners. He also has a 1" dia. foundry burner, curious if it would suit my needs if I built one. Definitely will need to invest in hi-temp rated Innswool though if I build- I think I'm looking to get 2500-2600 and the regular stuff is out of the game at 2400.

Any advice for this guy catching the bug? (No, not THAT one- double vaxxed personally. 60 yo with pneumonia damage and older coworkers and relatives, ain't taking chances.)

Another question, anyone ever use metal powder as in cannister damascus as a wootz melt?

[Wayne Coe]

You can probably get much higher heat, more controllable atmosphere and use less fuel with a ribbon burner.

 

Check out the Build a Gas Forge and the Ribbon Burner attachments on the Forge Supplies page at

www.WayneCoeArtistBlacksmith.com.

Let me know if I can help you.

About $100.00 plus the hose, regulator and burner using a 20# Propane tank.

 

[Al Massey]

Would a ribbon burner work in a crucible melting furnace setup?

Cheers,

Al

[Alan Longmire]

Yep.  Any blown burner will do fine for  a crucible furnace.  You can use the 2400 degree wool if you line it with one of the 3000 degree castables.  I think the highest-rated wool is only 2600 degree anyway, isn't it?  I never saw Jeff Pringle melt any, anyway.  And he was running bare wool, no lining or coating at all.  But, he considered the entire furnace to be a consumable.  Get maybe five runs out of it and toss.  That's one reason he used to light them with a $20 bill...

[Sean Blum]

40 minutes ago, Alan Longmire said:

I think the highest-rated wool is only 2600 degree anyway, isn't it?

Inswool HTZ is rated for 2700

 

but mixing "insulation" types means the 2400 standard is good enough. The 2700 wool would be good for a more consumable furnace with just a containment coating.

[Tim Mitchell]

Hey Al, welcome to the world of making crucible steel! It can be a bug with sharp teeth!

 

As far as making a furnace, I have used ceramic wool by itself a few times but it doesn't last long especially if you don't coat it with some kind of furnace wash.  But that is a recipe for lung cancer down the road at furnace temps, disintegrating ceramic wool will go into your lungs and cause big problems if you get too much. 

 

You really need to make a furnace with a cast refractory cement lining.  I recommend using around 2 inches of cement backed with the ceramic wool.  That way you can use 1250°C rated blanket and not have any problems.. it is only for keeping the heat away from the shell and increase efficiency.  Don't make the furnace too large or it will not work properly.  Keep about 2 inches between your crucible wall and the crucible itself.  Make sure you have enough room to get tongs in there to lift the crucible out later on..  Also line it with a zircon refractory wash which will make the bore last longer and will reduce the heat reaching your wool.. You can use thicker cement in your wall (it should be 1700- 1800°C rated) if you want to but remember that it is all thermal mass to heat up and that will increase the burn time to reach temp, and reduce efficiency.

 

Take care to not make your vent hole too small, this is very important if you are using a venturi burner.  Too much back pressure will cause problems, it is better to make a 90mm opening and then choke it down a little with a brick if you need to increase efficiency. 

 

A venturi burner will get hot enough to do a melt, but I am not sure if the T-Rex 1 inch burner is large enough to do the job quickly enough.  The few smiths I know who use a venturi burner on their furnace for melting wootz say that it takes significantly longer to get to temperature than with a blown burner.  This suggests to me that either the size that they are using is just a bit too small, or perhaps that the extra furnace internal atmosphere pressure which you get from a blown burner helps with efficiency and speeds up the melting process.

 

I know of no smiths who have ever used ribbon burners for melting wootz and although if you have enough burners you may be able to get it to melt, I would be surprised to see it work without several burners in one furnace.  Using a blown burner, even a crude one is efficient and so long as you use a flare cast in the wall of the chamber to keep the flame anchored at the wall, you will have success after a bit of tweaking.

 

Raise the crucible up using a plinth to avoid the blast of the burner, and get a type S thermocouple ... or two.. they are cheap from Aliexpress, to monitor your temperature with it just peaking out of the chamber wall not quite at the level of the top of the crucible. Also set it up so you can put the thermocouple directly up from the bottom under the crucible, it will help you to make sure you don't get your melt too hot, a very common fault.  The burner must enter at a tangent and hit the wall not the crucible or plinth directly for the best result.

 

The two things to avoid when tuning your furnace are poor mixture and poor temperature control. You want it to be roughly neutral but not too oxidizing or carburising.  Too many melts are ruined from having a mixture which is too rich or two lean especially with an open top melt.  (usually a 3 to 4 inch flame visible above the vent is sufficient for a good mixture).  Poor temperature control is a major issue, if you are guessing what your temp is, then you are much more likely to fail that is why I suggest using a thermocouple.  One in the wall is very useful to help tune mixture if you know how, but it will show hotter than the crucible temp as you are measuring the air flow temp which is always hotter.  When you work out how much hotter for the position then you are good to go.  That is why one up the guts is a good idea at least for working out the difference and calibrating your furnace temp... there is no substitute for knowing your temp.  The old smiths didn't have thermocouples, they had set bellows sizes and songs which kept the correct airflow rate, so their temperature control would have been very precise.  There are other ways which require an open crucible but that has it's drawbacks too.. A thermocouple is easy, cheap and assures consistency from one melt to another, and they more than pay for themselves in the ruined materials they save you.

 

Good luck on your journey, it has only begun....

Edited November 20, 2021 by Tim Mitchell

[Tim Mitchell]

On 10/12/2021 at 3:08 AM, Alan Longmire said:

I never saw Jeff Pringle melt any, anyway.  And he was running bare wool, no lining or coating at all.  But, he considered the entire furnace to be a consumable.  Get maybe five runs out of it and toss.  That's one reason he used to light them with a $20 bill...

Kind of dangerous for the lungs there...

Edited November 21, 2021 by Tim Mitchell