[TheForge] Gun Burners (AKA fan blown)

[Jerry Frost]

I'd really be interested in what temp a 3/4" Rex will 
bring 500 cu/in to. A good regulator will help too, I 
tried a BBQ reg but it wouldn't work at all.

Taking it's temp will require a thermocouple but I 
believe that's been addressed already. I generally go 
by color and feel so can't give numbers. Things like 
Tempil(sp) sticks and kiln cones are okay but not so 
appropriate for a forge. Especially the kiln cones, 
they take temp and time to slump and you probably don't 
want to leave it going for hours to find out.

As to what the burning paper indicates, you're 
basically right. Opening up the forge makes it more 
transparent to air flow so the mixture will lean down; 
eventually becoming oxidizing. Conversely closing the 
forge down will richen the mixture up. A pretty common 
trick used in oxydizing propane forges is to toss in a 
lump of charcoal to absorb excess oxy. My little forge 
burns so rich a lump of charcoal will just glow bright 
yellow till I turn it off, then burn up. Mine burns 
richer than it should but I get no scale at all.

A property of propane is it doesn't mix well with air. 
So it's pretty normal to be introducing a reducing 
air:fuel ratio into your forge and still have an 
oxydizing atmosphere. This is one reason the Don Fogg 
vertical cylinder forge is so good for knife making, it 
gives the air:fuel lots of time to burn before coming 
in contact with the steel. Another method of dealing 
with this is to mount your burner nozzles tangenitally 
at the top of the chamber to give the flame additional 
time to consume the oxy.

Running the tube around corners, adding swirl strips, 
cavitation baffles(?), etc. are all more ways to induce 
complete mixing of the air:fuel but they require a 
naturally aspirated burner to be tuned for the extra 
back pressure. If you use a gun burner it's much easier 
to tune for it. You can also just introduce the propane 
into the blower intake and let the blades do the 
mixing.

Frosty
-------------------------------
If it ain't forged
it ain't real.
Wrought iron is.
The FrostWorks

Meadow Lakes, AK.

http://www.artmetalradio.com/

From: "Ben Barrett" <stircrazyben at gmail.com>


> Well I'm borrowing a 3/4" T-rex to fire my first 
> (home-built) forge.
> I'm not sure of the internal volume (but I 
> guesstimate ~500 in^3), and
> I'm running off a crappy BBQ regulator at present 
> (but have a better,
> higher-pressure one ready to be hosed up).  The forge 
> roof is a
> half-round with kaowool, coated with ITC-100 and also 
> the ITC
> finish-layer (296A topcoat), and the table (which I 
> welded to hold a
> dozen soft bricks) has one layer of softbrick holding 
> up the insulated
> half-round, between which the burner tip is injected, 
> sealed with some
> spare kaowool.  I usually kept one end closed off 
> with soft brick,
> read on below...
>
> It was a joy to see this intial setup get me to 
> forging temperatures,
> and within 20 minutes the whole inside is glowing 
> (IR3 helps for
> examination, I took some digital photos through the 
> lens too :) and I
> can heat up pieces really quickly right in front of 
> the burner.
>
> I have been reading about these [venturi] naturally 
> aspirated burners
> here on TheForge, even though I already have a 
> laundry list of tweaks
> to improve performance.... well this weekend (along 
> with selling my
> first couple smithed pieces, small hooks) I was 
> heating some pieces
> from both ends, and after reading about needing 
> *enough* ventilation
> in these things, and wadding up little bits of 
> starter paper which had
> nto burnt and tossing them into the forge, I had a 
> great AHAH:
> With both ends of the forge OPEN, the wadded-up bits 
> of paper burned
> really violently & quickly, and made a large yellow 
> flame, compared to
> when one side was clased-off -- the "ahah" is that 
> the forge is now
> getting enough air, right?  Or is my flame too 
> oxidizing if a wad of
> newspaper burns that quickly?  I am running about 
> 14psi, fwiw.
>
> Well I need to make more tongs and hardy tools, and 
> do the right
> regulator... I think I will take out one wall of 
> bricks, and
> experiment with spiraling my flame more... I get 
> dragons breath but it
> seems unavoidable... I like the idea of venting most 
> of the heat away
> from the ends of the pieces I'm heating up, it is a 
> pain to quench so
> often (relative to working coal or coke).
>
> I'd like to find a good high-temp thermometer, but a 
> friend suggested
> using some cheap disposable indicators to get started 
> (they melt at
> certain temps, I think)... feedback?  Really curious 
> about the correct
> amount of air/ventilation.  :)
>
> thanks y'all!
>
> ben
>
>
>