Both have their up side.
The venturi or naturally aspirated are portable, and can be taken
anywhere you can carry a gas bottle.
Blown requires an extra air source, whether delivered by hand or by an
Some say that you can't get the temperature to forge weld with a
naturally aspirated burner... bollocks to that, it can be done.
The forced air burner in theory can get hotter than a venturi style, but
I find that propane without air is enough for me. I smelt bronze also
with a naturally aspirated burner. I don't think I could smelt wootz,
but I have an experiment in the pipeline (thanks to an earlier post :-) )
It really depends on the size of your firebox and if the flames from the
burner are forming a vortex.
Give me the details of the forge it's going into (if it's going into a
forge at all that is). Is it for a forge application?
The one I've heard is the force air type is easier to get up and
running the first day. ;)
I wonder if that's really true if the naturally asprirated type is
designed and ran at optimum? It's still just air and propane...
unless they are talking some sort of pressurized setup?
Rust, got a little blower? Brand new ones ain't exactly cheap and
the small ones I've found at the scrap yard lately were all 240v.
I missed that post somehow. :/
There's some sort of limit to propane's heat, especially diluted
with air. It'll be interesting what you can do with it. :)
Hmmm... if you're down-under my voltage problem may not effect you?
The scrap yard's always got lots of little blowers in old central
heat type furnaces, a good scrapyard will let you remove them and
sell them to you for scrap metal prices. :)
Alvin in AZ
Alvin, central heaters are in short supply here in subtropical
Queensland - Brisbane.
But we have plenty of airconditioners, so perhaps I can get one from
Please post all your 240v units to Chilla and I, we use 240v here, like
the British :-)
I have a nice new blower I got off the shelf while I was OS about 2
years ago, cost $20 pacific peso's. Wish I'd got a couple of them :-)
I have power to my smithy, and a handcranked blower if I need it.
Portability would be nice and thats a good selling point. Thanks for
the idea, its important, I'd not considered it. DOH!!!!! :-)
Mitre 10 has a Fathers day special a 1 hp dust extractor for $99 AUD,
just use it to blow instead of suck (I don't know about you guys, but
I've got a dirty mind and this somehow sounds filthy :-) ).
Way too much air and noise if you sak me.
(but you didn't ask me ;)
(used RR signal-case blower)
The holey screen was picked up off the ground at the scrapyard it's
some sort of automotive exhaust system guard for them newfangled
Cut round, edges-ground all around to form an "edge" like a cold
chisel, bent in one spot then screwed right into the pipe threads.
Nothing but a stack of insulated firebricks. The darker yellow
bricks are the "common, cheap and heavy" fireplace liners the
others "feel like" styrofoam. Inside where you can't see it are
2 more insulated fire bricks for the "floor".
None of that stuff is prob'ly what you're needing, but shows you
The first time I fired it up with the new insulated firebricks...
tried heat treating a small O1 knife blade I didn't see the steel go
through its "arrest point" so kept heating the knife blade. The O1
blade got so soft, it got all jiggly-n-wiggly. :)
I suppose that's hot enough for forge welding?
Search for- ron reil burner
...it's prob'ly the best way to go anyway?
Alvin in AZ
"bollocks to that" is exactly correct. I've done a lot of pattern welding
with a venturi burner, no problem. I don't know if forced air would have
been faster, I've never forged with a forced air burner. Preheating the air
would definitely be faster, but I've never tried that either.
Midland, Ontario, Canada
Charles, I've aquired some lengths of pipe, 10 & 12 inches in diameter,
I'm going to put 2 1 inch layers of Kaowool, and coat it with ITC
100HT. pipe is currently 18 inches long but I may cut that down. I
plan to build a smaller unit from the left over kaowool - its
7.2m*0.61m so there should be plenty left over from building 2 forges -
to use for small stuff. I plan to put a fire brick in the bottom. As I
have not constructed them yet, I'm still sorting details - like burner
type - I don't know the exact volume.
Yes I know thats a fairly large forge, but i wanted a large unit to
accomodate some larger work. I was thinking if i put 2 burners in, I
could just use a firebrick or 2 to cut the internal size, and only run
the front burner. Ok so perhaps I'm kidding myself or my thinking is
faulty, I don't know yet. Thats why I'm asking.
Is there some rule or guide as to the number of burners per area within
Hmmm that's a big firebox, potentially 8 - 10 inch diameter x 14 - 16
inches long, that's going to require a lot of propane to heat up.
Let's see 352 - 503 sq inches, if you want to make that into a forge as
is that will definitely require 2 burners to effectively heat it up.
I'm just thinking the only reason you'd want to heat up that amount of
metal at one time is for heat treating, or the item is bulky.
What do you want to make? We might be able to design something a little
more purpose built for your desired application, that wont cost a
fortune to run.
There may be some rule about burners per area, but I prefer common sense.
I made the mistake of telling the blacksmith class how easy it is to set
up a forge and now I have to make 5 portable modified propane tank
forges. These will be able to make swords, anneal sheet for raising
operations and be used as a melting furnace for non-ferrous metals.
I was tempted to buy a 7 metre roll of Kaowool, but thought I'd use up
what I've got first. I did buy 10 litres of "Kaowool Rigidizer", and
have found this to be an excellent product.
Anyway tell me what large item you want to make and we can design
ok I was basing my building on these plans for a start:
I've seen pics of forges made from old gas tanks, but i don't have one
to use, except one of the large size that are about 5 foot high. So
based on this guys ideas I asked a mate for pipe offcuts in the 10 to
12 inch diameter.
I mentioned I intended to build a smaller unit while I was at it :-)
but you are right it is a lot to heat. I've never used nor witnessed
the use of a gas forge, so I only have what I've read on the net to go
on. I have a coke forge that I've been using for years, and have found
that extra space in the forge never goes astray, but its true I don't
have to heat all of the space in the coke forge at once, which does not
apply to the gas forge.
Hmmm you could make 6...... ;-) If I were you I'd make one as a demo
and let them go for it, unless you are charging for each unit and
making a profit out of it.....
Your time is worth something.
Ok the guy at Thermal Ceramics told me it was a 7m role. He was only
new there, so I ahve as yet to speak to one of their experts. What is
this "Rigidizer" product? The Itc100 was recommended by a blacksmith i
did a course with. Heres a pic of his setup.
Thanks to everyone who has given me feedback, I appreciate all your
comments and ideas, keep them comming.
My time is worth something... well so people tell me. I'm going to ask
them to just pay for materials, as I'm using the forges to work out the
kinks in a commercial design I'm working on.
I bought the "Kaowool Rigidizer" from Thermal Ceramics, and Thermal
Ceramics "only" sell the Kaowool by the roll, however you can get
Kaowool at any kiln or potter supply place, this is where I bought my
first metre :-)
I did this test, get an oxy acetylene torch and point it at your
Kaowool... it disintegrates very quickly, apply "Kaowool Rigidizer" to
another piece of Kaowool, wait the 12 hours drying time (if you force
dry, the Kaowool shrinks a lot). Apply the torch and nothing happens to
the Kaowool, except it gets hot to touch. Apply some thixotic zirconium
paint and heat is reflected back :-)
I couldn't get ITC100, so I got the rigidizer instead. Is ITC100 a
reflector as well as a hardener or is it just a hardener. Kaowool
Rigidizer costs $23 for 5 litres from Thermal Ceramics.
I'm not sure if it's the same or not, but a common rigidizer is
colloidal silica. You can find it on the net. I got some in liquid
form, from what I hear there is a colloidal silica powder sold as an
additive for fiberglass resin.
I've been using the colloidal silica with good results. About the only
problem with it is that it's very brittle. A little pressure and it
I ended up buying a bag of fine-milled silica powder from a ceramics
supply place and made my own colloidal silica by mixing it with water.
Whatever didn't drop out of suspension in a week or so was decanted off
to another jug. It's cheap and seems to work just as well as the
I have a single burner forge that is 8" inside diameter and 14" long.
One burner is marginal, but it works. I haven't done any welding with
this particular forge.
I used to have a forge with 10" ID and 24" long. It had 3 burners. This
worked very nicely, worked well for pattern welded billets.
Both forges were atmospheric (Reil burners) and insulated with 2"
Durablanket. I used some Satanite as a rigidizer, no ITC.
Getting complete combustion -- involving all available fuel with
sufficient oxygen -- will get the highest theoretical temperature for
that fuel. That is, the peak temperature of the flame.
A naturally aspirated burner will have a small range of operation where
the fuel burns fully -- or is more 'finicky' to operate. This works
well. Any time you vary the amount of fuel -- the pressure -- you have
to adjust the draw of air. Pretty straight forward. You adjust the
air to get complete combustion, adjust the amount of fuel for total
amount of heat you want.
Similar with the blown air forge. The temp is pretty constant - just
keep the blower providing enough air for complete combustion. Too much
air will cool the resulting burn, but the adjustment is less critical
than getting the naturally aspirated burner to peak temp.
A blown forge is capable of more heat. Both have the same peak temp
with the same fuel. But the naturally aspirated burner has a limit to
the amount of air it can draw, which limits the amount of fuel that can
be burned effectively. A blown burner is also limited by the rate at
which air and fuel that can be burned, but the blower can typically
supply much more air than the naturally aspirated burner can draw, thus
allowing more fuel to be burned effectively. With the typical air
choke plate, a blown burner can easily be adjusted for very low
pressure/heat operation, too.
A naturally aspirated burner could theoretically be built to burn any
large amount of air -- at the cost of giving up operation at lower
pressures of fuel. The Reil style burner often uses a choke to limit
air draw, but stable operation at lower, choked-down air flow may be
more difficult to set on the larger burners.
Blown burners may also have an advantage in forges with an open side,
or open ends. They can create a larger peak heat region in the
firebox, even with one or more sides open as with a farrier's forge.
The naturally aspirated burner will be more susceptible, at lower fuel
pressure operation, to movement of air around the firebox.
Designing the volume and shape of the forge, capacity of the burner,
fuel selection, all work best when they are in the right range to suit
the other components. For many larger firebox uses, two or more
burners of either type can be much more flexible than a single, larger
burner. Sometimes. It depends.
That was cool, Brad, you ain't messing around. :)
All I really do is heat treat so my setup with the blower and rather
"open box" has worked out great. :)
But there has been a few times where I used the burner for "out of
the box" stuff like pre and post heating welds and bending heavy
steel parts... stuff like that. I have a bunch of different sized
"double-heads" and a "single head" too.
Like Brad said, mine sure as heck ain't finiky about full blast or
with the baffle all the way shut (for smaller heads than shown).
The side-outlet-elbow there is a 1" with 3/4" elbows holding the
screens. Since then I've screwed in a couple 1/2" reducer bushings
with their own screens, right on top of the screens shown. I've had
better luck heat treating my little pocket knife blades and springs
with the smaller flames. Easy as pie to run it too, I just "close"
the baffle and it leaks enough air to give me the flame I want. :)
To heat treat a butcher knife, all I have to do is take out the 1/2"
reducer bushing and run it with the baffle sitting a little more
closed than what's shown.
Not that what I'm doing is a direct use to anyone else... the whole
thing is done by the seat of your pants... that's just where I'm
"sitting" is all. ;)
Alvin in AZ
so the nice people at iforgeiron have put together a page "getting
started in blacksmithing" with links to their forge plans etc. It may
be of use for someone here.... ok thats me ;-)
Oh my head is now spinning after all the posts :-)
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