Building a forge

C

carlosj116

Joined
May 13, 2012
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Ive decided to try my hand at bladesmithing and am building a forge to do so, I was wondering would a paint can lined with fire cement using a propane torch as the heat source be sufficient to provide a good forge for small to medium knives?
Also, if this will work would Everbuild KOS Black Fire Cement be good to use?
Thanks,
Carl
 
Hi Carlos,
Are you wanting to forge blades or just heat treat them? Your forge can be a little less efficient if you're just heat treating the occasional blade.
The fire cement won't be a good insulator. 2 feet of Inswool or Kaowool instead and some satanite to coat over it from www.hightemptools.com/
will get you going.
Also, keep the volume as small as is practical. That would allow you HT a medium size carbon steel blade with your torch.
Google "coffee can forge" and "two brick forge" for more info.
Good luck,
David
 
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Your reference to "Everbuild KOS fire cement" suggests to me that you are in the UK, if only because I recognize the brand name.

It's always worth filling out your forum profile with any information that might help anyone responding to your posts to give information that helps you specifically.

The fire cement is probably not ideal: it is pretty dense, so takes a lot of heat input to get it to temperature, and is not a great insulator. As David says, you are much better off with some ceramic fibre blanket. The googling "coffee can forge" and "2 brick forge" advice is good too.

Propane torches certainly can work well, but there's usually a bit of a learning curve and a total novice may not have enough of a grasp of what is happening to be able to make the sort of progress that keeps their interest up.

It's important to understand that the air:fuel ratio is what controls the flame temperature (degC or degF) of a burner. The gas flow (which varies with the square root of the gas pressure, if using a fixed gas jet) controls the heat input (BTU/hr or kW).

Most Propane torches don't give any easy way to adjust the air:fuel ratio, so adjustment ends up as having to tweak the amount of air that can get in between the inside of the burner port and the outside of the burner. An even-slightly-experienced smith can usually tell by the colour whether it needs to be hotter or cooler. A complete novice probably can't. I use a thermocouple and handheld readout.

I did some messing about with a cheap MachineMart burner set a couple of years ago. By fitting the jet from the smallest burner into the biggest burner, opening up the air holes and cutting additional air slots with a grinder, I managed to get a nice forging temperature in a coffee-can-type forge with the burner fitting tightly.

http://www.machinemart.co.uk/shop/product/details/fc108-gas-torch-with-nozzles

I'd strongly recommend a "proper" Venturi burner design, if you can stretch to it. This gives easy air:fuel ratio adjustment at the Venturi and will save a lot of hassle.
 
As has been said, the ceramic fibre blanket is the way to go. I built a two-burner forge from a 20# propane tank using Ron Reil's burner design. Great set of directions here: http://metalcast.boorman.us/reil_1.html I put just under $100 into materials. If you're just looking to play around, the two-brick forge is a good start.
 
benjamin2515101 said:
Is more insulation better? Anybody ever tried wool AND cement?
Click to expand...

I think most of us use both. Generally you have to use something to stabilize the ceramic fiber blanket(wool), a minimum of a rigidizer, but most use a castable or atleast spreadable refractory cement, like Satanite, Mizzuo, Kast-o-lite, Econocast, or any of the hundreds of other high temp refractory morters.

If you're forge welding with flux, it's pretty much mandatory.
 
I agree that you have to use the stabilizer, I was just wondering if a thicker layer would be better or just overkill.
 
Well I use 2" thick of cerachem blanket in my blown forges, bubble alumina in the bottom and about half inch thick kast-o-lite 30 smeared over the ceramic fiber.

These are mostly used for forge welding, and as such take aa lot of abuse from liquid flux, bang the end of billets into the walls, etc. My main one is in serious need of relining, and I'm going to use Mizzuo instead. The last forge I built with a buddy we used that and it held up better than the kast-o-lite is imho.

I'm going to build a bigger one soon, same blown vertical style, with the same 2" thick ceramic fiber, but I'm going to cast a solid inch of refractory on top of the wool.

I've heard some people discouraging people from using too much refractory morter claiming it takes too long to heat up but that hasn't been my experience, and especially if you're using an insulating castable, they seem to be a lot more efficient, and resilient.

For me my main concerns are a) keeping my fuel consumption down for long damascus making sessions, and b) not having to re-line often.

I am doing a lot more dry welds and can welds, and experimenting with kerosene instead of flux, but I still really get best results from doing my initial stack wet. So for now, I'm still dealing with flux damage.
 
benjamin2515101 said:
Is more insulation better? Anybody ever tried wool AND cement?
Click to expand...

If you make a cast liner sleeve from a castable refractory like Mizzou, you will still have to wrap that is a couple inches of wool. The whole cast shell gets heated up, and the wool keeps the heat in it.

The way to make a cast liner forge is:
Cast the forge shell between 3/4" and 1' thick, and cure it for at least a week. Make any holes needed for burner and TC entry.
Wrap in 2" High-Z wool.
Wrap that in a sheet metal jacket. The ends of the wool can be sealed with satanite.
Set assembly on a welded metal cradle or frame.
Install the burners and such, sealing with satanite.
Fire at low and fully cure liner. This is best done in short burns and allowing the heat to soak in. Increase burn time slowly until it gets to full red.
Patch up any cracks with Satanite, and re-fire.
Coat inside with ITC-100. Fire again to cure ITC.
 
Great post bladsmth, exactly what I was hoping to hear. It just makes sense to me to combine the properties of each for the best result.
 
What happens in a refractory lined forge is the liner heats up by the flames. It is a thermal mass, so it does not heat or cool fast. Once up to temp ( takes longer) it will stay at that temp easily. If the forge is PID controlled, it will hold an exact temp with ease. The wool jacket keeps the liner from cooling unevenly and cracking, as well as keeps the heat in. Without the jacket the forge outside would be really hot. Wrapping a sheetmetal shell around the wool makes assembly easier than trying to slide it all down a pipe.
 
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