Propane tank/fueled furnace build

Discussion in 'Furnaces and their construction' started by Shawno, Dec 27, 2020.

  1. Billy Elmore

    Billy Elmore Silver

    None taken. Having been in the business so long I am sure I have a much higher tolerance for things that might make others nervous.LOL I would rather you build it so you feel comfortable and use it even if it takes much longer to build and cost a little more.
     
  2. Billy Elmore

    Billy Elmore Silver

    Mine is 3/4" at 8" long with a .043" mig tip in the center and open around the tip...no restrictions...only mounting T for the tip and a smooth 1 1/4" flare on the end going into the furnace. Got 1/8" pipe tapped to accept the mig tip. Runs best at around 10 to 12 psi. Here is a crude drawing of how I connect the tip to the pipe inside a T. The T is tapped for the pipe and the inside of the pipe is tapped for the mig tip. All of this is connected to the 2 1/4 adapter with four bolts in the back. Very simple and works great!
     

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  3. Shawno

    Shawno Copper

    That sounds similar to what I ended up with. I kind of over complicated with it to save myself another trip to town but ended up with basically the same thing.

    If the inside of the furnace is flared where the burner pipe enters, do you still need a flare on the burner pipe itself? I am wondering about the size of the tuyere. Say my 3/4" burner pipe has an od of 1 inch, can't the tuyere be big enough to just accomodate it and then a flare shaped into the casting? Is air entrained through the tuyere? I realize the flare is to complete the venturi but wondering why just opening into the furnace does not suffice?

    Here is a link to today's version...I like it. ..runs way better than the last one with 1/2" pipe. I think the tee could be replaced with just a reducer (1" to 1.5" ) since I almost had one half the tee fully occluded with my thumb and the burner still ran fine. I just did not have one handy.

     
  4. Billy Elmore

    Billy Elmore Silver

    I have ran mine with the flare on and off the end and could tell no difference..but I did flare the inside of my tank using an old funnel that I cut the end off of which is almost identical in size to the flare. I was going to just take my flare off my burner and use the flare inside the tank just so I could get more angle on the entry and get the flame off of the crucible a little bit more, but decided to raise the crucible two inches instead (partly because after several heats the flare is stuck on there pretty good and I am not sure I can even get it off) and I think it heats up quicker now. I have tried using compressed air and a blower an honestly I cant use them effectively. Im not sure if it has to do with the volume inside the furnace but I seem to do better without them.
     
  5. FishbonzWV

    FishbonzWV Silver Banner Member

    The flare is only used outside the furnace for test burns.
    When I placed the 1" nipple for the tuyere, I left it back about 1" from the hotface and created a flare with the wool and Satanite.
    Also, your 2.5" vent is a little small, 3.5" would be better for feeding the crucible. You can always choke it off with preheating ingots.
     
  6. Tobho Mott

    Tobho Mott Gold Banner Member

    You could even go with a 4" vent. My 1st furnace had a 3" vent (still does) and my little muffin ingots were forever just a little too wide to drop through when topping up the crucible, but with 4" I can use bigger ingots and they always fit, with enough room to lower them in gently gripped in my ingot tongs.

    Jeff
     
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  7. Shawno

    Shawno Copper

    Thanks Jeff but already had the 3.5" hole done.

    I made some progress on Tuesday again. I mixed the refractory I had with the perlite and experimented. I only did the floor and the lid. I used a paint stirrer initially, but I think that pummeled the perlite into the refractory. Kelly suggested this might happen in post #57...oops... I did the floor first and the ratio was about 3:1 p to r. Then when I went to do the lid, I was a little short. I mixed up more but then added too much water. (I can't find the icon for head banging on the wall..) I figure the lid is redoable easy enough if things fall apart (and this is a bit of a learning thing) so finished it up. I only manually stirred this last batch too so the perlite held up. We will see what happens.

    Yesterday, I phoned around some more and found insulation at a woodstove shop. Now I am torn. Should I form a 1" wall (or what thickness that will stand up?) and put an inch of insulation behind it? Or just plunge ahead with a gently stirred perlite/refractory mix as we have been discussing? If I go the insulation route, how do I finish the top of it? I would think I would need to build a support around the top of the wall to support the top pour? I will try to do a drawing . I guess I am wondering how durable a 1/2 or 1" wall and top would be?
     

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  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Did you try mixing the refractory first and then add and mix the perlite by hand?
    Out of curiosity, did the addition of perlite seem to dry out the mix? It's very porous stuff and I'd imagine it can wick away a lot of water, so soaking it first might reduce any adverse affect it had on the refractory curing.
    If you went with refractory and fiber insulation I'm assuming you'd just plan to make a mold cast the hot face, let it cure, demold, install in you furnace with the outer insulation layer, and then cap the insulation with a thin layer of refractory. A 1" thick refractory wall should be plenty strong if you do a good job of casting it. It's very common. 1/2" wall becomes a little more difficult to cast without the aid of vibration.

    There's pro's and cons to insulated vs non-insulated, but either way you decide to go, it doesn't seem like the amount of work to cast two layers is much different than that needed to mold a 1" hot face wall. We tend to make a lot out of furnace construction but unless you intend extreme duty, they're just holes we dump a lot of heat into, to melt metal.

    Best,
    Kelly
     
  9. Billy Elmore

    Billy Elmore Silver

    Yes..durability is why I decided not to use wool in my furnace. I have access to two inch and one inch wool but everyone in industry told me the wool would not last as long as the castable...especially in cast iron. Why I went with solid castable lining. I poured mine too wet as well and it will be probably be ok...just takes lot longer to dry out. Use a light bulb right over it for a week or so. But I am not an expert on refractory by any means ...I merely go by what the industry usually does and guys with the most experience tell me.
     
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  10. Shawno

    Shawno Copper

    I made some progress. I think I will have to adjust the burner angle though. I had refractory mixed for the outer wall (with Perlite) then realized I did not even have the hole cut in the tank for the burner... Doh! So got drilling quick !

    I did the inner liner (hotface, straight refractory) yesterday and took the form off this morning. I don't want to mess with it too much to it gets a bit harder. I think it will be just a bit of grinding on the metal to get the flame more on the wall. I might have enough movement in the tuyere to correct the burner angle too.
    And yes, my form shifted a bit and I did not notice.... o_O
     

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  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Looks pretty good from the top view Shawno. Did that Tuyere hole turn out ok?

    Best,
    Kelly
     
  12. Shawno

    Shawno Copper

    Kelly, I think so. Not sure where the burner ends though....in the chamber or before the refractory, leaving the refractory to be the flare at the end? I am thinking I need to put the burner into place and then add refractory around it to close up the hole?
     

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  13. Billy Elmore

    Billy Elmore Silver

    Use refractory to make the flare and don't make it tight fit around burner...you will want some play and extra air will not hurt
     
  14. Shawno

    Shawno Copper

    Thanks Billy. I put the burner in tonight with refractory around it. I will take it out in the morning and grind it a bit while it is soft to make some wiggle room. I tried grinding some that has been set for a while. I think it was Jason that commented somewhere that it is not fun to grind and I found out why. Pretty hard when set. I guess I did something right....;-)
     
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  15. Billy Elmore

    Billy Elmore Silver

    I typed hard is good but I just didnt feel comfortable with that statement. Hard refractory is good.LOL Did you put a light bulb inside it to help it dry? I poured mine way too wet and let it set for a week with a bulb in it.
     
  16. Wool is extremely durable behind a hard refractory.:D

    If you do the heat transfer calculations you'll find just a little wool behind some castable really slows the heat loss, lowers the mass to be heated, protects the outside steel, and doesn't break down so long as the temperature at the castable/wool interface doesn't exceed the wool service temperature. Regardless of hot spots inside the firebox the layer of castable (or brick) dramatically spreads out the heat by the time it gets to the wool. I'm no insulation expert but I have designed lots of industrial furnace refractory systems, installed them, and repaired them in the petrochemical industry.

    A reminder to the poster that Satanite or equivalent is painted on in thin layers and is just a surface protector, but an excellent one.
     
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  17. Billy Elmore

    Billy Elmore Silver

    I would have had around an inch of refractory and a one inch layer of wool behind it. I do not think the one inch layer of refractory would be nearly as durable as a two inch layer of refractory as its more about the loss of the durability of the refractory not the wool. Hence the layer of satanite. Im sure for normal duty aluminum it will be fine but I like the flexibility to do other materials at higher temps...possibly even cast iron. I would rather have a thicker tougher liner, but that is just me...I am not saying you are wrong just looking at it from a different perspective....I know how destructive I can be. I also know that I would have had to buy more stuff and wait to build it and I am not that patient when I have the materials to do it another and possibly better way already in hand.
     
  18. Tobho Mott

    Tobho Mott Gold Banner Member

    Some of us here are hobbyists who only light our furnaces on the occasional weekend for a single melt and pour, starting from cold every time. A less durable 1" hot face might only last, say, half as long as a 2" hot face that takes twice as long to heat up, but at that rate 1" will likely still hold up for years and years (mine's 5+ years old and still almost like new). And those are years of faster melt times and fuel savings...

    But for someone who casts metal all day every day the wear and tear would be accelerated, plus back to back heats being more common instead of starting from cold every time would speed up average melt times of the thicker hot face drmatically.

    It's certainly a matter of perspective, as you say.

    I have no experience with cast iron though. Perhaps that would take a much greater toll on a 1" hot face faster than I am imagining.

    Jeff
     
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  19. Billy Elmore

    Billy Elmore Silver

    That is my thought..the higher temps would be more detrimental. Im no expert though....I just know that the guys who do this for us here at work told me they would go with the solid refractory if I was ever going to melt cast iron because it would last a lot longer. I do like faster heat up times occasionally though. I found this video of a guy melting cast iron with propane in a similar type setup with wool and refractory (not solid like mine)and it made me think the durability part may have been over considered. He was pouring in 40 minutes. I poured brass in 40 with a naturally aspirated burner and his has a vacuum cleaner setup blower. Looks like he runs his much higher than I do mine. Making me think I have not yet reached the full potential of mine and may go back to playing with compressed air. I didnt see who the poster was and he may be a member so sorry if that is the case for not giving credit.
     
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  20. Shawno

    Shawno Copper

    I got it assembled today. I have not even done the light bulb thing yet so was very hesitant to light it up for long, but at the same time, I know the refractory is grindable now, probably not so much later so I fired it, shot a fast video and shut it down. It looks like it swirls nice (from my vast experience...o_O) I had the small machined flare on it, which I think looks cooler....;-) but the flame seemed to fluctuate, sputtering like an engine with the choke on. I did not want to play too much so shut it down but will alter the pressure and see what happens in the future. I did then switch to the tee fitting on the inlet and I think the flame was better so maybe more air coming in? Once I feel comfortable with running the flame longer, obviously, I can play more with pressures and maybe even the orifice size.

     

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