Welcome to another episode of Forge Diaries.
Today, I will show you how to rebuild a propane forge - an activity I have to engage in about
once a year.
When I create swords, I often forge weld different types of steel to create visually interesting
patterns.
If you have watched some of my videos, you know exactly what I mean.
The flux for forge welding is very aggressive and over time slowly destroys any forge.
What you see here is a forced-air propane forge.
At the bottom, the blower supplies pressurized air.
The propane and air combine in a mixing chamber and a tapered nozzle shoots the mixture into
the forge chamber it combusts and generates heat.
This is probably the 5th or 6th time that I am rebuilding this forge.
The main chamber was a propane bottle originally.
The forge is 12 inches long and has a diameter of 12 inches, too.
Since forge welding is so hard on the forge, it's important to have a setup that can be
repaired easily.
What you see here is the system that has worked the best for me.
The shiny black material on the floor is borax slag but as you can see the constant heat
itself is another factor for internal breakdown.
Let's go back to the anatomy of my forced-air propange forge.
The burner enters the forge chamber at the top and causes the flame to circulate.
To maintain forge welding temperatures, heat efficiency and
thus insulation become very important.
I am using two inches of ceramic fibre blanket and a thin layer of high-temperature refractory
mortar on top to protect the fibre blanket.
My favorite refractory mortar used to be Satanite and ceramic fibre blanket that was rated at
2600F (1023C).
These are difficult to get, so this time we are trying something different.
Tony and I visited a local pottery supply store (Clay Planet - they were super helpful)
and bought all materials there.
I will describe all of them as we start using them.
As we are doing the rest of the clean up, let's take a closer look at the burner.
It's heavily influenced by Tim Zowada's forced air manifold (check it out at tzknives.com).
The main difference is that I prefer to use a ball valve over a gate valve regulate propane
flow.
The ceramic fibre blanket we found was 2 feet wide and roughly 1in thick.
To figure out the length, we do some very simple math; 2Pir for the circumference of
a circle accounting for the thickness of the material.
A word of warning, ceramic fibre blanket contains a lot of sharp little fibres.
You don't want them on your skin and you don't want to breathe them in.
We are not wearing appropriate protection and are trying to make do with
a fan to keep the fibres out of the air around us.
Since the blanket is two feet wide (that's 24 inches) and the forge chamber is 12 in
long, we can cut it in the middle to get two layers of heat insulation.
This fibre blanket is rated at only 2400F (roughly 950C) and would quickly break down
at the temperatures I am running my forge at.
The hope is that the refratory mortar will provide a little bit of protection.
Cutting the material is challenging and much slower than the time lapse makes it appear.
Another way to prevent the fibres from going air borne is to wet down the ceramic fibre
blanket.
In this case, we also bought some regidizer which increases surface hardness and supposedly
also protects against erosion.
As time always tends to be limited, I usually try to put off fixing the forge as long as
possible.
In this case, Tony was visiting again and we decided the time had arrived on the spur
of the moment.
That is also the reason why we did not have masks or long sleeved shirts.
Once the rigidizer has been applied we need to get the blanket through the opening of
the forge chamber and then slowly spread it out so that it hugs the inside surface and
does not have any overlapping areas.
This operation would be somewhat more difficult if the blanket had not been wetted down.
With the rigidizer applied, it stays in place where I press it.
The next challenge is to create a hole for the burner.
I am using the outside tube to guide a screw driver through the blanket.
Where it comes out, I can cut an opening with scissors.
Now that the first layer of insulation is complete.
It's time to start on the second one.
The process is very similar.
The main difference is that the inside radius is smaller and we need less length.
When I first started forge welding about 8 years ago, I was using a commercial propane
forge.
I remember the day when the first drop of liquid borax ate straight through the forge
shell.
Since then I have always made my own forges.
Especially when forge welding, there is not really any way around that.
Also, building a forge yourself makes the notion of slowly destroying it much less scary.
It's just part of the business.
Spreading out the second layer of insulation is a little bit more challenging since we
cut it somewhat too long.
As with the first layer, I need to cut a hole at the right location for the burner nozzle
to fit through.
Since there is less room for navigation now, getting in the scissors takes some time.
Now that the insulation is in place, we need to coat it with a layer of high temperature
refractory mortar.
This mortar is usually meant to hold fire bricks together and is not really made to
coat a forge.
My refractory mortar of choice is Satanite which is rated to 3000F (1180C).
However, it's difficult to find and the clay store had a different product called Smoothset
which is rated to 2900F.
I have never used this product and it's going to be interesting to see how it's going to
hold up in the forge.
In the meantime, the mixture ratio of mortar to water is pretty similar to Satanite.
Roughly 3:1.
The application of the mortar is pretty straight forward.
The goal is to coat all of the ceramic fibre blanket and that's really all there is to
it.
The mortar is also very dusty and easily airborne.
The fan also helps somewhat with keeping it out of our lungs.
The round form of the chamber helps with coating even the ceiling without the wet mortar dropping
down.
It also somewhat sticks to the fiber blanket which also helps.
Although all of this is pretty straight forward, it still takes a fair bit of time.
Including getting the supplies we probably spent about 4 hours on this whole procedure.
As I mentioned before the liquid borax is quite aggressive and quickly eats its way
through any material.
For that reason, I also like to put a scarificial floor into the forge.
It would be best if it actually fit the whole length but in this case we did
not have enough half thick fire brick and had to do with the material at hand.
Alright, this took quite a while.
The only thing remaining is to get fire bricks in blace to create openings on both sides
of the forge.
The fire bricks are another experiment.
The shop had high temperature insulating fire bricks left over from a previous job.
They are rated at 3000F and so should not melt even when forge welding.
On top of that, they look really prestine and pretty.
As you may hear the blower is running already to help out with drying the mortar.
The whole procedure for curing it requires slowly cycling up the temperature and the
air is the first step in that.
I will usually run the burner for an increasing amount of time; starting with just a few seconds
till I work my way up to a couple of minutes.
At that point, the forge is ready to use.
Alright, that's it for now.
I hope you enjoyed watching us take a destroyed forge and transforming it into to prestine
condition.
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