FW: [TheForge] Burner angle

Wed Jul 18 18:39:32 EDT 2007

Pete,
If you wish to use a ceramic material to protect fiber blanket from an upward
directed flame, than I would suggest looking into ceramic saggers, which are
pretty inexpensive, replaceable, and are an easy way to obtain a curved surface.
I have long been considering building a furnace this way.
Mikey

-----Original Message-----
From: theforge-bounces at mailman.qth.net [mailto:theforge-bounces at mailman.qth.net]
On Behalf Of Jerry Frost
Sent: Wednesday, July 18, 2007 11:10 AM
To: artgawk at thegrid.net; Sponsored by ABANA
Subject: Re: FW: [TheForge] Burner angle

From: "Peter Fels And Phoebe Palmer" 
<artgawk at thegrid.net>

>  aww Mikey; Guess i'll cancel my plans to picket in 
> front of your shop then.
>

Geeze Pete. Does that mean you're not picking me up on 
the way? I had my sign made and everything. Oh well I 
guess I'll drink the beer I had packed. <sigh>

> The reason i brought it up is that, prior to your 
> excellent book, many naturally aspirated forges have 
> had difficulty making a high welding heat. Many 
> smiths have gone for blown forges for that reason.
> I've read recommendations that owners of cool forges 
> ( hey, cool forge dude) carefully polish the inside 
> of their burners, fool with venturi placement and so 
> on, all to gain some bit more flow.
> So it always seemed to me that facing up from below 
> would be a bit more efficient...one can always choke 
> it down if it's too much.
> In a related consideration, many forges pull the 
> exhaust off the top, where the hottest gases hang 
> out, spewing extra  BTUs
>

I don't know how many decades commercial forge builders 
used really poor linear inducers for their burners. 
Most wouldn't reach welding heat at all unless you used 
a really agressive flux. The result being the myth that 
a naturally aspirated burner couldn't reach welding 
heat. I wouldn't go so far as to say it lead to selling 
more expensive gun burner forges but . . .

Anyway, the truth is a burner is nothing more than a 
system for introducing a flamable material and air in a 
metered ratio, mixing them and delivering them to the 
desired location. Both gun (blown) and naturally 
aspirated burners deliver air under pressure, that 
result is the same either way. A gun has the advantage 
of delivering it in a more robust manner and is less 
sensitive to outside conditions like open or closed 
forge doors, etc. A naturally aspirated burner will 
usually need to be adjusted for changing conditions of 
smaller degree.

In either case the effects of natural convection are so 
slight as to be a zero effect variable. This isn't 
necessarily true with the commercially produced forge 
burners as most are made to barely do the job. They 
simply do not have any reserve to overcome any level of 
adverse conditions. In this case convection may indeed 
effect performance to a noticeable extent.

>
>
> The test, while very interesting, isn't all that 
> relevant because you don't have 2000* of hot gas 
> pushing up from below.
>

Actually that test illustrates the only effect 
convection has in a forge. The burner is introducing 
air and fuel into the forge chamber under pressure, 
combustion causes them to expand but they're already 
moving in one direction; towards the exhaust port 
whether that is a dedicated port as in a melting 
furnace or an open door like most forges. Force seeks 
the route of least resistance; Always.

>> 2. "The greater heat of the top of the forge would 
>> cook the burner faster."
>>
>> The minuet the burner is shut down, interior gases 
>> can enter the burner through
>> buoyancy; this is called the "chimney effect," and 
>> is prevented by closing the
>> burner's choke completely during shutdown. While 
>> running, the burner prevents
>> the forge gases from entering. Refrigeration effect 
>> from the expanding fuel gas
>> is sufficient to keep the burner from overheating do 
>> to conduction and
>> convection gain from the forge body and nearby 
>> exhaust gas. These rules apply
>> equally to top mounted burners (the overwhelmingly 
>> dominant mounting choice),
>> whether they are placed at vertical down (90°) for 
>> spot heating, or 3” down from
>> top dead center (on a 14" diameter forge) to create 
>> a swirl.
>>

As Mike says so well, the only time convection is a 
problem for a downward aiming burner is on shut down 
when gasses super heated in the forge will rise through 
the burner. This can burn up your gas hose but is 
unlikely to actually damage the burner itself. Shutting 
the choke completely or just stuffing a piece of 
Kaowool (or whatever) into the intake eliminates this 
potential problem.

>>
>> Finally, why is vertical down the dominate choice 
>> even for swirl effect? Because
>> portable  forges use ceramic fiber for most of the 
>> interior insulation, and
>> placing a burner at the forge's top allows it to be 
>> aimed directly at the
>> firebrick or kiln shelf slab on the forge's bottom. 
>> Should you decide to use
>> Kastolite 3000 insulating refractory for the forge's 
>> interior, instead of
>> insulating fiber and a kiln shelf floor, than the 
>> burner placement can be
>> changed to whatever you find most convenient. Also, 
>> solid refractory is a much
>> better choice for multiple use forge/furnaces, or 
>> for a forge employed in billet
>> heating. A typical five gallon cylinder with a two 
>> inch thick Kastolite 3000
>> refractory lining will still be portable 
>> (approximately 65 lb.) On the other
>> hand the same forge built with ceramic fiber and a 
>> kiln shelf floor can be
>> lifted comfortably with two fingers; it's all a 
>> question of what features you
>> find most convenient.
>>

> Perhaps a burner target  area of kastolite ( thanks 
> for the reference) or kiln shelf would solve that.
> Speaking of that, i got an old carbide kiln shelf i 
> cut up for a floor, very durable.
> Thanks Mikey...your answers are informed, considered 
> and help a bunch!....pf

>
> Mikey
>

Careful consideration of the target material is 
important and a small argument in favor of tangential 
burner placement. A flame hitting something on a 
tangent spreads the heat over a greater area so the 
target material stays at a lower absolute temperature.

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

Meadow Lakes, AK.

http://www.artmetalradio.com/

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