[TheForge] blown forge

[Paul Sperbeck]

On blown burners the addition of a mixing stage will greatly help to
achieve complete combustion. This prevents stratification of the gas
will help get every BTU out that you stick in. Mine uses a couple of
fixed fan blades in the air stream that stir up the air to promote
mixing. One has a right hand twist the other a right hand twist. The gas
is injected into the air stream between he blades. Before I did this
part of the gas didn't burn inside the furnace cause the mixture was
stratified. Talk about dragon breath...

Johnson mixed the gas into the inlet of the air blower on some models.
This works great but you need to make sure you rig a safety to turn off
the gas if the fan fails.

The orifice size is unimportant as long as you can get enough gas
through it to achieve the BTU output you want. You need about 15 to 16
times the amount of air relative to the propane. Its all about cubic
feet with blowers. The propane injection pressure matters not.

You could certainly add oxygen, but I think you should get the
air/propane burner functioning first and experiment with oxygen

Propane is about 2550 BTU per cubic foot. To get about 100000 BTUH input
you need to burn about 40 CFH or .67 CFM of propane which requires a
little over 10 CFM of air. You may need more fan than that to be able to
force the 10 CFM into the furnace due to the back pressure of the furnace...

have fun

paul

On 09/04/2013 06:30 PM, Ben Barrett wrote:
> >From my little experience, blown is easier to rig up, due to lower
> pressures & great variety of what-will-work :)  Venturi's require more
> tuning, but a well-made unit can be easy—you may want to polish the inside
> of the venturi since any interruption to flow there makes a difference.
>  Common blown fan is a hair dryer, usually with the heater coil removed
> (leaving part of the heater coil will give the air a nice preheat & dry
> though!).
>
> >From what I've read, it can be difficult to get a complete burn with air
> and propane, I'm glad I was able to get one of Art Anderson's burners at a
> NWBA conference.
>
> Have you considered adding a little bit of oxygen when you want forging
> temps?
>
> On a related note, I am curious if anyone's used an oxygen concentrator
> with propane or even natural gas?
> I have access to some used models, which the local glassblowers are not
> happy with since they use a huge amount of oxygen.
> I was thinking that even a trickle of oxy, along with a well-tuned venturi
> design, might be very efficient.
>
> Ben
>
>
>
> On Wed, Sep 4, 2013 at 4:14 PM, Dan Scheid <damales at pollybutte.net> wrote:
>
<snip>