Subject: propane forges/furnaces

From: [email-masked] (Geoffrey Keyes)
Date: Wed, 25 Aug 1993 23:07:25 GMT

I posted an article about propane forges earlier today and have gotten several
replies from people looking for more info.  It will take me a couple of days
to scrape up all of my sources, so expect a longish post Monday, or there
abouts.

Geoff Keyes

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From: [email-masked] (Geoffrey Keyes)
Date: Thu, 26 Aug 1993 16:50:25 GMT

Ok boys and girls, I'm going to attempt to put together what I know about 
propane forges/furnaces.  This may be somewhat rough since I am doing this 
extempore.  I'll be happy to answer any specific questions people may have.

A disclaimer up front.  I am not an expert on these beasts and I am not
responsible for any injuries, deaths, fires, unexplained explosions, or irate
neighbors.  The following is what I have tried or seen tried.

A little history.  I first saw one of these in operation at a North West
Blacksmith Association (NWBA) novice class about six years ago.  Since then
I have built three versions, Mk III is operating just fine today.  I hope to
be operating, part time at least, officialy as Ravens Forge by the first of
the year.

Gas furnaces are commonly called forges.  In fact, a forge is open topped and
a furnace is closed.  In my opinion an open topped version would lose to much
heat to be valuble.  The two basic types I've seen have been 1) The brick pile,
2) The pipe or box.

Basically, the furnace is a closed space, open at one or both ends, lined with
insulation, with an inlet for air and gas to enter.  

THE BRICK PILE
Just what the name suggests, is a pile bricks with a pipe stuffed in one side.
The bricks are stacked to provide an open space and the air inlet is inserted
into the space.  A fan is attatched to the end of the pipe and the gas line
enters between the fan and the box.  The opening is covered by a stack of 
bricks which can be moved around to provide an opening big enough for whatever
stock is being used.  Since I have'nt mentioned it until now, these bricks
are fire or refractory brick.  Normal red brick will explode under the 
thermal stress and even fire brick will break down over time.  

The first brick pile I saw is still in use.  The problems with them are they 
leak flame and unburned gas though all of the joints and they generaly lose
to much heat for welding.

THE PIPE
This is what I am using today.  Same basic form, a closed box, insulated, with
a pipe for the air and gas to enter.

My furnace is a piece of 1/4 steel pipe, 16 in long, with a 1/4 plate welded on the back.  About half way down one side a piece of 1 1/2 in pipe is welded to
the body.  There are two pieces of angle iron welded to the bottom of the case
to keep it from rolling over and a shelf welded to the opposite side of the casefrom the inlet pipe.  I use the shelf to preheat steel and to keep my tea cup
hot.

Attached to the end of the pipe is a fan, in this case an old hair dryer.  Aboutmidway between the fan and the case there is a hole drilled for the gas inlet.
I use two inches of insulation (on which more later) in the case and a pile
of fire brick to close up the open end, with just enough space for my stock to
enter.  The gas source is a 5lb propane bottle.  The whole thing sits on the 
end of 55 gal drum.

The air/gas inlet can be as simple as a piece of pipe or a complicated as you
like, basically you're going to have to experiment with the size of the outlet
end.  I put a twisted piece of steel in the end of mine to impart some swirl
to the gas as it enters the furnace.  This works, but not as well as I would
like.  Don't push the end of the tube to far into the furnace, since it will
just burn off.  This is a sort of self correcting problem since if it is too
far into the fire it will just disappear over time.

I've got a valve on mine, between the fan and the gas inlet.  However, my fan 
is too wimpy for me to use the valve much.  The fan is blowing its heart out
just keeping up.  My next modifcation will be a burlier fan.

INSULATION
The insulation used by most of the smiths I know is called KAOWOOL, which is
a Johns-Manville product.  There is also INSWOOL made by A.P. Green.  Both of
these are spun ceramic blankets.  WARNING The ceramic fibers are fairly friable
when the blanketis new and unheated.  I suspect that breathing them is a bad 
idea, so use a filter mask when building your furnace and during the first
firing.  After that the surface gets hard and crusty and the problem seems to
go away.

Some smiths I read about have used castable refractory cements to build furnace bodies, but I don't have any direct experience with them.  Fire brick, KAOWOOL,
and the like can be found under "Refractories" in the yellow pages or try
ceramic supply houses.  I bought my first KAOWOOL from a ceramic supply.

LIGHTING UP
This is an exciting process.  First insert a burning piece of paper into the 
fire box, turn on the fan, then turn on the gas.  There should be a whump and
then a burst of flame.  Now adjust the gas so that fire is not streaming out
of every crack.  Give it enough time for the box to heat up (2-5 min) and off
you go.

SAFETY
Propane is a flamable, heavier than air gas.  It will accumulate on the floor
until it gets a spark.  Then it burns very fast.  If enclosed at all it will
explode.  Check all of your valves and connections frequently.

A regulator AND a blowback valve are a good idea.

I got most of this info word of mouth and by trying it out myself.  However,
there are some publications that may be helpfull.

The summer 1991 Vol 5 Num 3 of Knives Illustrated has a pair of good articles
on gas forges.

ABANA
P.O. Box 1181
Nashville Indiana 47448

This is the largest blacksmiths association in the US and is a source for all 
kinds of good stuff.  In particular they sell plans for a furnace.

"A recuperative gas fired forge furnace"
Sandia National Labs.

I don't know what they charge for these plans anymore.

W.L. Goddard
473 Durham Ave.
Eugene OR 97404

Wayne writes a column for BLADE magazine and is an ABS Master Smith.  He also 
used to sell a pamphlet of basic bladesmthing info including a section on 
gas furnaces.  I don't know if these are still available.

As I said above, I am not an expert and am not responsible for any problems,
injuries, or unexplained fires that might result from any of the above info.
On the other hand, I have used a furnace decribed above to forge and heat 
treat approximately a dozen knives with good results and no injuries or other
accidents.  If there are questions or if things are not clear (almost a 
certanty) please feel free to contact me at 

		[email-masked]

Good forging

Geoff Keyes
Ravens Forge