HT1's Insane overpowered new furnace build

Discussion in 'Furnaces and their construction' started by HT1, Sep 18, 2021.

  1. HT1

    HT1 Silver

    well the furnace ate the interior of the lid this morning, sections of the rigidized kaowool started to flake off, then the wool began to melt and was spun all around the furnace, the interior of the furnace is pure hell just slag everywhere, I guess I'll have to patch everything up and give the whole thing a coat of satanite


    V/r HT1


    IMG_5598.jpg
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Lid's have tough duty for high energy furnaces. Especially in the vicinity of the vent hole. You may want to look into BluRam for your lid. It's a plastic refractory like a very firm clay, but it can be pounded/rolled in sheets and hand placed on a form like your domed lid. It's Mullite based and performs like very high alumina content materials and phos-bonded refractory which puts it into a higher class of service temp. Melterskelter has had good success with it in his iron furnace. Even a relatively thin hot face made from it should drop the temp enough for other insulations like high temp fiber.

    BLU_RAM_HS.jpg

    Best,
    Kelly
     
    HT1 likes this.
  3. Melterskelter

    Melterskelter Gold Banner Member

    Last edited: Nov 15, 2021
    HT1 likes this.
  4. HT1

    HT1 Silver

    I'm really getting frustrated with the new furnace, when I have to fix the lid for a second time I will have done more repairs on this 2 month old furnace then I did on my previous furnaces 7 year life span, I developed a hot spot near one of the Burner Tuyere , pulled the burner, I'm missing about half an inch, I patched the tuyere with kaowool satanite and a layer of Mizzou .

    Big story I'm rally mad at myself for not taking little steps , so I cannot really determine what is working and what is not,
    the issues:
    1) 2 burner design,
    2) Insulated Fire Brick
    3) the insanely overpowered blower
    b. burner size
    I really wish I had paid more attention to Kelly back when I was planning (SEE Below)

    Dropping the Burners down to 1.5 inch, but upping the blower to 166CFM is definitely part of my issue of the furnace eating itself, in the new year I may have to go with a new furnace, probably in steps, smaller blower being first, if that doesn't work I will go to a castable furnace, guys the IFB looks like SHEEEITT and I have been hitting it with satanite constantly



    IMG_5640.jpg

     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The facts of life are, there's a limit to how much fuel/air you can efficiently burn and push through a furnace of a given size/volume. As you approach that limit, the furnace is usually quite pressurized, and wants to leak combustion gas. Obviously, one solution, when you approach that point, back off a bit. Besides patching/sealing leaks, the other thing that may provide some modest gain is a larger vent hole, say 5 or 6". That's probably too large for where you'll end up but you can cast a refractory insert to neck it down, and hopefully the insert will take the thermal beating, and you can just replace that if/when need. Here's my reducing insert:

    50 Vent Insert.jpg

    You just need to decide how much aggravation a few minutes improvement in melt time is worth to you.

    Best,
    Kelly
     
    HT1 and Mark's castings like this.
  6. HT1

    HT1 Silver

    the furnace continues to burn in one of the burner pipes, after several attempts to repair it pull it out, adjust the air and fuel , it just kept eating the same burner pictured above!!! so I pulled it out completely cut the fuel to it, and plugged one of the Tuyeres with Kaowool and satanite and ran a heat with only one burner! the unused burner I simply cut the fuel to and let it sit aside so I had an Air relief, I added 10 Minutes to my 30 Minute Melt time (brass) I suspect I could have pushed the single burner harder , but I got a good heat with a good time with no additional damage to the furnace , I will be making this a permanent change , By slightly adjusting the air pipes , and completely removing the unused burner, but leaving the gate valve to help control the air, hopefully getting rid if the VFD going to the blower

    yes I was warned about the use of dual burners causing issues I suspect Mifco's mixing the Air/fuel and sending that to both burners makes that issue go away , I really have to wonder how Devil forge makes it work with a pair of Reil burners, seems like it would require an insane amount of tuning to get right

    https://www.ebay.com/itm/265134645821?hash=item3dbb41a23d:g:4ggAAOSwX1VggWfK


    V/r HT1
     
  7. Ironsides

    Ironsides Silver

    Wow! you need deep pockets to buy that furnace, $2000 and I would assume that is in U.S. dollars.
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    HT1,

    Per your post over at MS' thread, I have a couple questions.
    1. Do you use the same crucible for every met? Or most often used?
    2. What is the Top and Bottom OD and height of the crucible. Is it Bilge or A style?
    3. What are the internal bore and height dimensions of your furnace?
    4. Is the lid still dome or flat? If domed, how high of a dome?
    5. What is the OD and height of your plinth?
    6. How far off the furnace floor is the center of Tueyer(s)?
    Best,
    Kelly
     
  9. HT1

    HT1 Silver

    1 Super salamander A-16 or A-20 https://www.morganmms.com/media/7322/salamander.pdf
    2. A-20 H 10.24 TOD 7.75 BOD 5.7 A-16 H 9.13 TOD 7.25 BOD 5.1
    3 13 inch Diameter 18 inch tall
    4. domed about 1.5 inch (as designed, with use its getiing lower)
    5 6 inch od 3.25 inch tall
    6. 1.75 inch to center

    V/r HT1
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    One more, do the Tueyere(s) enter tangent to the furnace wall so the OD of the Tueyer is at/on the edge of the furnace wall or is it further inward?

    Best,
    Kelly
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    HT1,

    Without getting into a bunch of theoretical dribble, let’s try the simplest things first. Have you tried a taller plinth? The reason I ask is this:

    I took the dimensions you provided and calculated the internal furnace volume, then subtracted the volume of the crucible and plinth. I call this free furnace volume. This indicates at least 31% of your free furnace volume is above the crucible. I say at least because this did not include the volume in the domed lid so with that, it would be >31%. This is with an A20.

    I don’t recall the diameter of your lid vent, but even if it was 5” in diameter, if the A20 was raised to within 1 ½” of the dome, it would still allow twice the area around the top of the crucible compared to a 5” vent. So if you had a flat lid, you could add another 3” to your plinth height, more with the dome. For experimentation, how about stacking another plinth on top of the existing one?…..or maybe make two 1.5” tall and stack them.

    The reason I suggest such, is to test the principle/assumption that there is a limit of energy for a given furnace volume, that being, free furnace volume will limit the dwell time of air/fuel for any given fuel/air flow rate…..give the fuel enough time to combust within the furnace, but better yet, in the best location. If you take it to the extreme, and say you had 50% or 75% of free volume above the crucible, and you were pushing the max fuel/air flow rate possible to be burnt in this furnace volume, a very large percentage of the burn would need to occur somewhere other than in the immediate vicinity of the crucible.

    So in simple terms, we’re just trying to give the fuel/air more time to combust and release energy when it is near the crucible.

    As far as the back burn into your second burner tube, that can be caused by having too large of a Tuyere or too little blower flow causing the flame propagation speed to be greater than the gas velocity in the Tuyere. However, if you are anywhere near the 130+CFM blower volume, with two 2” Tuyeres, I don’t think you have back burn due to this because a quick calc shows you'd be way above the FPS.

    Along with the other previous discussion about lid and burner tube sealing, I think it's more likely your furnace is pressurized and you have a slight imbalance in your blower plumbing causing one burner to be overcome by the other. One simple thing you might try to help remedy this is place a small obstruction on furnace floor between the plinth and furnace wall before each Tuyere to obstruct/deflect the flow from the opposing burner. It could be a cut piece of fire brick and I’d make the height so it was at least to the center of the Tuyere and perhaps to the top of the Tuyere. It could be a ramp too, depends upon how fancy you want to get.

    The other thing you could do to promote more uniform air flow, is plumb the blower into one end of a larger can (a plenum, say at least a 5 gal bucket), and then connect the two hoses/pipes that feed your burners to the other end of the can/plenum. The plenum will act as a buffer/damper to supply more uniform pressure to each burner.

    Increasing the plinth height may aggravate the level of pressurization in your furnace, but I sort of doubt it, especially if you only have a 4” vent.

    Then tune as you normally would to achieve the desired vent flame characteristic.

    Best,
    Kelly
     
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  12. HT1

    HT1 Silver

    yes it is tangent
     
  13. HT1

    HT1 Silver


    great info!
    alot of it I have tried, I can defiantly confirm Plith Height effects the melt times ,

    the burn back in the second burner is a done issue, I removed the second burner with little effect on melt times
    And yes this furnace is DEFINATLY pressurized ,

    I hate to Say it I'm probably going to build another cast monolithic furnace, the IFB is becoming a maintenance issue, I have to satanite and patch it after every use, and the Lid is very sketchy, I maybe in a different category then most people, "bordering on Professional" when I cast its at least 2 often 3 heats pouring 10-14 molds , often pouring twice a week OR more, my furnace is getting an insane amount of HARD use,
    not all the blame can be placed on the IFB, if I had gotten a better fit, it might be holding up better ,

    Im really thinking an insulated castable (Kastolite) and using crushed IFB as a Grog, might produce a better performing furnace, balancing melt time, and durability better

    Thank you
    V/r HT1
     
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Despite all of the above,you still need the right air fuel ratio and optimal flow rate.

    How big is the vent? A fuel fired furnace is always going to be a little pressurized, but highly pressurized can make your burner less stable and more finicky.

    Then the double burner is an unnecessary complication for no gain.

    Why mess with the composition of a commercial refractory? Select the right one and use it. The Phos-bonded plastic refractories are very tough and durable. You might look at those for the lid.

    It's really more of a tweener. Build a more thermally massive furnace with high refractory materials and it will be durable but cost you more fuel and time on the first heat, but not so on subsequent heats.

    Best,
    Kelly
     
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