[TheForge] Gun Burners (AKA fan blown)

[Ben Barrett]

The 500 cu in. is a half-round... I think the multiple coats of ITC100
plus a few thinner layers of the topcoat definately help it get
hotter.  I am maxed out on the bbq regulator, and just finished off my
first 10gal propane tank... so I am feeling more motivated to tweak
the burner setup now :)
Also, I'll be meeting some great folks up in Enumclaw, WA, this
weekend, and managed to sell a few small wall hooks at my local craft
market last weekend, so this is all going dandy, really.

Thanks for the confirmation on the oxidizing nature of my
arrangement... I have been getting a lot more scale lately, with the
far end open a crack... if it is open too much, it cools down.  I will
be curious to remount the burner, pointing up and diagonally along the
roof, to try to increase circulation.  I'm not really clear about the
downward-pointing burner setups, but I'm grokking the tangential.  ;)
I can't keep up, forging, with the amount of heat it produces, so I'm
hoping to put an nice ball-and-needle-valve-in-parallel throttle or
idle circuit in place here too; I am not working on it all day but
maybe 2-4 hours at a time.

As for the color/heat, my rods and cones are funky like many guys',
but I'm pretty sure it is getting into bright yellow.  It doesn't seem
like forge-welding temps (am a bit familiar with coke forge welding),
but two pieces' scale did stick together pretty well.  Anywhoo, that
seemed like the oxidation/scale growing together, not a weld.

Thanks Jerry, hope you're hangin in there!

ben


On 5/3/07, Jerry Frost <frosty at customcpu.com> wrote:
> 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
> >
> >
> >
>
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