[TheForge] hybrid burners, reducing atmospheres, and SAFETY

Wed May 9 13:00:56 EDT 2007

 Ben,
Sorry about the delayed reply; this is gardening weather.

You asked "what qualifies as a hybrid burner?" The first hybrid experiment was
made with copper fittings from two different pipe sizes connected by a reducer.
The air and gas entree chamber was larger than the mixing tube. So, I thought of
it as a hybrid version of two different burner sizes; the name stuck. These days
Hybrid Burner simply means this burner was sold by Rex Price. Ron Reil, who
desired to find someone willing to build a good burner design for sale,
introduced Price to me shortly after the original copper burner was posted on
Ron's site, and I told him what I knew of the subject. He changed the series of
burner holes to a slot and sent me his experimental design for evaluation. The
slot was a very important change, and the burner certainly did work fine, but
was 23" long. I cut it down to the present size & shape, and then sent the
burner back, followed by prototypes of other sizes over the following months; he
refined their designs until he was completely satisfied, and then began selling
them too. As far as I know he still does. 

It seemed obvious that, if the change from a series of holes to a slot could
improve performance, a further change from slot to a rectangle with beveled ends
would boost performance even further. The result was so dynamic that the new
burner design needed a completely different nozzle shape to handle the increased
flow speed, and oversized mixing chambers simply became irrelevant; also the
bias towards oxidizing flames is not present with a straight tube burner, so the
improved tube burner is the design featured in Gas Burners for Forges, Furnaces,
& Kilns. However, even an Aussi burner does fine with a gas accelerator. Also
gun burners and compressed air/fuel burners, and oil burners have their place.
The modified "T" burners designed by Larry Zoeller, not only work well but are
much less effected by cross drafts than either hybrid or high speed tube
burners. The key to doing well with any given burner design is a thorough
understanding of it; this is the real advantage to building burners--not saving
money.

To find the sweet spot on a hybrid burner, open the choke about 1/2". Next, open
the gas valve just enough to get a stable flame and ignite the burner. After
giving the burner nozzle a minuet to warm up, open the choke completely and
start increasing gas pressure; air entrainment increases automatically as a
function of gas pressure. Watch the flame as you increase pressure; at some
point the secondary flame will suddenly reduce. Look over at your pressure gage
reading and note it; this is the sweet spot on your particular burner. Continue
slowly raising gas pressure until you see that the flame is a hard well defined
blue with little secondary flame. With a hybrid burner, this should be a
slightly oxidizing flame EVERY TIME (you can run experiments trying to heat up
steel round or flat bar with the flame, and the heavy scaling experienced will
confirm this to be true). At this point choke the burner until you see a little
softening in the primary flame; you now have a neutral flame once more. When the
same steel bar is heated with a neutral flame there is much less scaling. There
will still be some scale formed by entrainment of oxygen bearing ambient air,
which is created by a venturi effect from the strong flame these burners make;
but the difference in your results with oxidizing and neutral flames will be
painfully obvious. So, we see that there really isn't a problem with the hybrid
burner, other than people forgetting to choke them a little. Burners function
differently in forges than they do outside of them. This means that you will
have to do a little more refining of your understanding with the burner in the
forge, or you can always resort to a lump of charcoal :-)

The instructions above should be correct, but may vary in some small detail
(after all, I haven't played around with hybrid burners for six years).
Mikey

-----Original Message-----
From: theforge-bounces at mailman.qth.net [mailto:theforge-bounces at mailman.qth.net]
On Behalf Of Ben Barrett
Sent: Monday, May 07, 2007 12:25 PM
To: Sponsored by ABANA
Subject: Re: [TheForge] hybrid burners, reducing atmospheres, and SAFETY

So I've been following these burner threads, and now try to call my venturi
"atmospheric", and to call my buddy's forced-air + propane setup a "gun
burner"... so what qualifies as a "hybrid"? :)

More importantly, what tips can you offer in finding the sweet spot?
I have trouble finding it on my 3/4" mini-rex... I just got one of Art's fine
Montanan burners at the Spring NWBA conference, and haven't hooked it up yet,
but am anxious to try out my 2nd burner and learn by comparison.
So far, I've been limited by a BBQ regulator, also, so I'm not surprised that
I'm having trouble tuning the rex.  I know it deserves/needs better.

Anywhoo, is there something I can do by observing the little wads of paper I
toss in there?  I'm pretty sure my current/old setup is too oxidizing, so it
makes sense to slowly (say, session by session) turn it back until the evidence
of oxidization disappears.... surely there are some good tricks out there from
all y'all old-timers ;)

regards,

ben

PS - some said this conf in Enumclaw, WA was smaller than usual, prolly due to
being only a week after the one in California.  I had a great time though, very
treasured time in my smithing memory.  Thanks to all who help make these
conferences happen, and especially to the extra attention to welcome new-bees
like me :)

On 5/4/07, Kathy <keporter at comcast.net> wrote:
> The hybrid style burner has a facet I've not seen discussed; it tends 
> to run with a slightly oxidizing flame. Each burner has a "sweet spot" 
> in its turndown range, which is neutral burning with the choke wide 
> open. However, throughout the rest of its range the choke must be used 
> to keep from ending up with an oxidizing flame. This is no big deal as 
> long as you're aware of the potential problem. However, all the 
> comments about oxidizing problems in forges with hybrid burners has convinced
me that it's time someone pointed out the obvious.
> Don't just open up the burner and adjust the gas pressure for flame 
> size, thinking that this is all the adjustment needed. You must also 
> choke the burner a little if you're outside the sweet spot.
>
> What Jerry said about the problem of free oxygen in a forge run on 
> propane is also quite correct. It is truer of propane and methane than 
> other fuels, but applies even to oxyacetylene. When you burn any fuel, 
> there will be some fuel molecules, and also some superheated metal 
> devouring scale causing oxygen molecules blasted out ahead of the wave 
> front of accelerated flames. Whether you choke your burner to make a 
> reducing (fuel rich) internal environment, or add a lump of charcoal 
> to make sure the oxygen is eliminated before it can touch your work, is up to
you.
>
> Whichever path you take, make darn sure that your working environment 
> is protected from the carbon monoxide rich exhaust you will then be 
> creating (powered exhaust hood and CO monitor).
> Mikey
>
>
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