In commercial blast furnaces (these are coke based) air is preheated which differs several hundred degrees in furnace temperature, I don't know how that works in commercial gas fired furnaces. Anyway, I use forced air with my propane furnace and I guess I can raise temperature by injecting preheated air. But then I need a kind of spiral shaped copper tube above the exhaust hole to be preheated there which is connected with a stainless steel hose to the air entry of the burner. Are there any forummers who have experience with hot blast ?
I seem to recall a thread, on either AlloyAvenue or Backyardmetalcasting, where somebody was using heat exchangers made of castable refractory to preheat the incoming air. Somebody with a better memory than me might remember who that was. If I remember correctly he tried several different heat exchanger designs. Don
I dont remember that, alot of people tried preheating fuel, someone had great success with it V/r HT1 P.S. W2 probably had the most advanced DIY furnace , he used an adjustable pump to control fuel, and regulated air, so he could actually hold his furnace at a certain temperature , and pour all day long
I made a video of a friends propane furnace with a air preheater, it worked great but over heated his furnace refractory. Air preheaters do work but the added work in making it and finding a refractory to survive the higher temperatures put me of building one. Also my furnace will melt cast iron very quickly so why do I need to make a more complex furnace to do that. My friend also told me he could not melt cast iron without the preheater on his furnace. Have a look at 1:31 to see the steel air preheater.
HT1: He used a side exhaust on the furnace and made the heat exchangers modular so he could experiment with different designs without having to build a new furnace. I don't remember if he was using a gas burner or an oil burner. He tried several different heat exchanger designs to get better airflow through the preheater and less back pressure in the furnace. I think the only reason I remember the thread was that I was truly amazed at what he was creating using the castable refractory. The tubes in the heat exchanger had a remarkably thin cross section. I think he said that it took forever to heat up so it wasn't really of any benefit for a onesy-twosy caster, but it might help somebody that wanted to cast all day long. I don't remember any videos, it was a LOONNGG time ago, so Photof*ckup probably made the thread useless, even if it still existed. There are times when Mr. Peabody's Way Back Machine would be really handy. Don
I remember that thread, It was a work of art. The chap kind of dissapeared shortly after finishing it if memory serves.
W2 started his own Forum, which weathered away, I believe he had a health issue, that took him at least away from casting V/r HT1
I think I remember a discussion about the pros and cons of the hot air, something about the density. I tried to preheat fuel in a copper spiral attached to the furnace and discovered what backpressure means It worked for a few minutes then it splattered then it didn't work anymore until the furnace cooled down. My oil burner was very crude and the "fuel system" relied on gravity. I tried different set up then switched to an electric kettle, it was a bit messy but it worked.
from what I have read hot blast only makes sense on furnaces that run for long periods of time uninterrupted (multiple days). most cupola melting furnaces do not even use hot blast because they do not run long or consistently enough.
