Furnace Designs

Sitting here pondering and wondering if a design where somebody placed the burner around the middle to upper-ish section of a furnace with it pointing downward at an angle which would provide an adequate swirl of fire and keep more heat within the furnace during operation.

I quess the second question is,
If this were done would such a design create an inner chamber pressure which would be determental to the proper operation of the burner / furnace?

Any other cons to such a design???

Would it even work????

Thoughts anybody??????

 

I tried a dual oil burner configuration with the burner tubes at 180 degrees, and that provided a very smooth and even flame inside the furnace, but no other measurable advantages over a single-burner arrangement.

I have gone back to a single-burner design, and even though it tends to push the flame up the back wall (unlike the dual burner design), it does not seem to affect burner or furnace performance.

So my guess is angling the burner tube downward may counteract the tendency of the flame to ride up the back wall a bit, otherwise there will be no advantage.

The single biggest factor that affects burner/furnace performance appears (in my opinion) to be furnace mass, and the lower the furnace mass, the faster the melt, and the lower the fuel usage.

I also suspect that using a tight sheet metal jacket that contacts the refractory may act as a heat sink and cool the furnace to some extent, thus extending melt times and increasing fuel usage.
This factor depends on how insulating your refractory is, and the more insulating your refractory is, the less heat sink effect you will get.

I have gone with a very dense low insulation value refractory and kept it 1" thick (with stainless needles for strength, like re-bar in concrete), and am avoiding contact between the refractory and any metal parts of the furnace shell.

The fastest furnace I am aware of with the lowest fuel usage seems to be ironsides, and he uses a zircon-coated ceramic blanket, and thus extremely low mass.

None of this is critical for melting aluminum since it melts at such a low temperature that the furnace refractory does not need to reach a high temperature for a successful aluminum melt.
For an iron melt, the interior of the furnace (the refractory hot face) needs to reach an almost white hot temperature so that it reflects heat into the crucible and allows the iron to reach a usable pouring temperature.
So while a low mass furnace is not essential for melting iron, I think it does speed up the melting process considerably, and would use less fuel, especially for one-off melts.

For back-to-back iron melts, the furnace mass is not very critical since the furnace mass only has to reach the critical temperature on the first melt.

 

I dont think you can force heat to stay in the furnace, and a fuel fired furnace must vent, and heat will rise so pointing a burner down is just likely to cause all kinds of turbulence as the heat has to rise back through the flame,
insulation and efficient burner is the most tried and tested way to get more efficient, keep in mind the best insulation are not very resilient , you are working with molten metal and flux, other chemicals, so you are going to be hard on your furnace, I have replaced one, and really probably need to replace my current one... an area that there is some research to be done is size, some of us seem to have much better results with very large furnaces,


V/r HT1

 

My Keg furnace has 2” of Kast-O-Lite 30 Plus in addition to an outer layer of CFB.
Additionally, it has 2 heavy coats of ITC 100 mopped onto the inner face of the refractory.

It has NO problem reaching temps.

My thinking was that by placing the burner(s) in the above mentioned places and pointing downward into the furnace that by doing so it would retain more heat with the furnace.

 

Just seen you reply HT1.

Turbulence was the main concern when I was pondering my half witted idea.

Never know unless you ask.

 

I agree, but for me and probably for many backyard folks, we only seem to have time for 0ne-off melts, and so the initial furnace heat is always a factor.
I know my high mass furnace does absolutely nothing for 30 minutes when I start an iron pour from cold; no melting, just a bunch of fuel used; but my high mass furnace is very heavy, perhaps 500 lbs. (ludicrously heavy, but I did not know any better when I built it).