Segmental Thin Plastic Refractory/Wool Furnace Build 14" Dia Bore

Discussion in 'Furnaces and their construction' started by Melterskelter, Jun 12, 2020.

  1. Melterskelter

    Melterskelter Gold Banner Member

    3/4 furnace hot face. Now comes decision time concerning the tuyere. Mark is looking at some of the same questions I am tossing around with respect to burner tube/nozzle location relative to the hot face interior.

    image.jpg 1C49A1C1-936C-4C47-AF8F-2C961F88CE7E.jpeg E4B1840E-0DC6-44DE-BB9F-FC14FFED7545.jpeg FA46221F-6084-4293-995E-532DCACE7531.jpeg

    Tobho Mott likes this.
  2. Tobho Mott

    Tobho Mott Gold Banner Member

    Aside from height and angle, I don't know if it matters. I personally favour a counter-clockwise tuyere, being located in the Northern hemisphere. :D

    If the section with the tuyere hole is much more complicated to build than the first 3, maybe put the hole fairly near one edge edge so the burner aims at am adjacent plain section, in case it gets cooked and needs to be replaced. Hopefully not an issue...

  3. Melterskelter

    Melterskelter Gold Banner Member

    I agree that location may not be that critical and it will probably work pretty well regardless. But, I also think that dwell time of the fuel/air mix in the furnace has some impact on optimizing performance. So, I think I may make a conical entry of refractory into the chamber and have the burner tube end a few inches from the chamber sort of imitating Mifco. That way I hope ignition of the mix will occur nearer the entry into the furnace and lower in the furnace. Will that make a practical difference? Hard to say but seems right.

    Tobho Mott likes this.
  4. Melterskelter

    Melterskelter Gold Banner Member

    I’ve decided how I am going to build the tuyere. I am going to use castolite since I have some and it held up well on my present furnace. Yes it cracked but it is still going what it needs to do. The burner tube will insert into the tuyere just outside the
    furnace and the tube will be supported by a piece of steel angle much as is my present setup. So the tuyere is not actually much mechanically impacted by the burner. The tuyere will externally be generally square with generously chamfered corners and the interior will be a maybe 6 degree included angle cone about 4 inches on its shortest side. The tuyere will be made pre-cracked in two parts with the seam being in a horizontal plane. The hot face will have a square cutout into which the tuyere will fit but will not be cemented into place. The tuyere will just be set into place resting on the hot face and the furnace skin. It will fit fairly close but can be easily removed and replaced independent of the hot face. The wool between the furnace skin and hot face will provide a draft-free gasket. (I’ll stuff some extra wool in as I insert the tuyere.) The cone will be arranged to cause the flame to tangentially impact the adjoining hot face segment and the plinth will be high enough so no flame hits the crucible. I may try one of the discs that (I think) Mark has innovated. That disc would be made from Bl-Ram and the plinth from dense castable or Blu-Ram.

    My hope is that the air/fuel mix will be igniting just about at the point where the tuyere enters the furnace cavity. My other hope is that the increased volume of my new furnace will allow a bit more fuel burn and bit more efficiency. Or will this be another “learning opportunity?”

    Mister ED likes this.
  5. Melterskelter

    Melterskelter Gold Banner Member

    Well, I imagine when I am all done the chamber will be somewhat eccentric and lobular and certainly not round. ;-) All I had time for today was drawing the entry of the tuyere into the chamber. Good to have that on paper finally after much deliberation. Tomorrow I will mold up the tuyere and probably the fourth, tuyere containing, furnace segment.

  6. Melterskelter

    Melterskelter Gold Banner Member

    Here is an installment of information on my segmental furnace build that shows some of the details of Blu-Ram sheet forming and transfer of the sheet to a metal form.

    I'll be putting up another video soon concerning completion of this segment.

  7. Melterskelter

    Melterskelter Gold Banner Member

    Making the opening for the tuyere:

    And here are a few stills of the panel as I cut out the hole for the tuyere and a photo of the pounce wheel and perforations in the surface it made and of the segment after I used a weed burner to heat it to 650 to 700F.

    Outlining the hole and reinforcing it with Blu-Ram IMG_6766[1].JPG

    Cut out two views IMG_6768[2].JPG IMG_6769[2].JPG

    Pounce wheel and perfs. The wheel did almost completely (one small blister) prevent blistering. IMG_6771[1].JPG IMG_6770[1].JPG

    Cooked. To my relief the corner did not crack. I was pretty careful when raising that area to 210 and then to 300 to not cause a steam explosion. IMG_6772[2].JPG

    Once it cools down I will lift it off the form. The wax paper does a good job of preventing adhesion to the steel form.

    OMM, Petee716, Tobho Mott and 2 others like this.
  8. Petee716

    Petee716 Gold Banner Member

    That pounce wheel was a neat idea. Information that I've gotten from a couple of different sources have indicated that not having a slick surface is important because it inhibits proper drying. The tool my friend uses is one of these
    Judicious use of water really helps a lot too.

    Nice work on your forms.

  9. Lou

    Lou Copper

    The molybdenum wire should be avoided if there is any chance that it can oxidize. I work with Mo and it will literally up and turn into a white sublimate of MoO3 with any oxygen at a dull red heat. In vacuum applications, Mo, Ta, Zr etc. are well and good, but in air, they oxidize. One of the reasons we have MoSi2 is because the Si component forms a Mo depleted SiO2 liquid surface scale that is self healing and protective of further oxidation (mostly anyway, the SiO2 does indeed somewhat volatilize)

    Unfortunately, your best bet for a wire retainer is going to be platinum (for long term use at high temperatures). Everything else oxidizes and scales.
  10. Melterskelter

    Melterskelter Gold Banner Member

    Sounds like the moly wire is going to be a bust , so to speak

    Lou, if you could send me a couple pounds of platinum wire, I’d much appreciate it! (And I will never be heard from again. ). :)

    Thanks for the information. I do truly appreciate it.

  11. Lou

    Lou Copper

    Hey, that's what we make it for...applications where it needs to get white hot, then cold, then white, then cold over and over and over.

    Platinum is beautiful stuff---what else can you TIG weld with no cover gas? Or oxyfuel weld with an oxidizing flame?

    In all seriousness, I'd just try 310 or 309 wire on the outside.
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I'm glad Lou posted that. My bud didn't say anything about using it in vacuum furnace service.....that's kind of an important detail!

    Sometimes the most obvious thing is sitting right in front of you (Me). I may have some 14 ga Kanthal A1 (FeCrAl) left over that is too short to make replacement heating coils but maybe enough fro a lap around your refractory. It's 063", pretty stiff and sure seems to resist oxidation pretty well at 2200F any way. I don't have any NiCr in heavier gage.

    Lou, would 309 or 310 survive 2200-2400F in air for any period of time and or have any strength at that temp?

  13. Melterskelter

    Melterskelter Gold Banner Member

    Thanks, Pete.

    Yes, I have added practically no water to the refractory. Only if remixing bits and pieces that had dried somewhat. The other time I use some water is when joining uncured refractory to cured refractory. Then I sparingly brush some water onto the surface.

    As far as drying the refractory, I have followed advice of the foreman at the foundry I(love to) visit. They just line their ladles with a couple inches, play a lazy weed burner or two flame on the refractory until it is no longer steaming much, and the hit it hard with the burner. Following that techniques has worked well with only hints of occasional blistering easily pressed down followed by strong stoneware-like partially cured refractory.

    Thanks, Kelly.

    It would have been nice to wrap my plinth and hot face in a 5000 degree wire, but sounds like the wire would rapidly burn away. Oh well. I toyed with burying moly wire in the plinth since it would be insulated from O2 there. But, then realized that any crack that would develop would channel oxygen to the wire and then the wire would fail precisely where it was needed.

    I will be wrapping wire around the wool. There I will use simple concrete-form tie wire. There will be about 3” of wool between the hot face and the wire. So, I think the wire should not get much over 450 to 500 degrees. That should pose no problems for plain steel wire. It will be protected from weather by the 55-gallon barrel shell. The shell will lift off intact leaving the refractory and wool standing there naked. I may eventually cut an access panel into the shell if I find I need easy access ti the wires to wind up any slack that may develop.

    I just finished testing tie wire to hold the refractory and I think it will do the job just fine. I considered using thin steel battens to spread the compressive force, but that would be a lot of extra work and more mass. If needed, they can be added later.

    Right now I am cooking pie-like floor Blu-Ram segments in my kiln. My temperature program is to ramp 300 F per hour to 220, hold for 30 mins and then cook to 800. That will be enough to partially cure the Blu-Ram to a quite hard state.

    I’ll be holding my breath when I fire this contraption up. So many untested features....

  14. Lou

    Lou Copper

    1150 C is max on 310. Not much of anything resisting the effects of air will have much strength at those temps but for PGMs. I know high iridium alloys are mechanically useful at those temps with plenty to spare.

    NiCr and aluminum modified versions will start to get stretchy. Creep will become a concern...
    Melterskelter likes this.
  15. Melterskelter

    Melterskelter Gold Banner Member

    Here are a couple pics of the segmental floor pieces and of the plinth.

    The floor has a step to index the vertical wall segments and the banding of the vertical segments will also keep the floor pieces together (I hope). I will fettle the edges of the pieces so they fit up better and I think there will be a thin sacrificial plate of Blu-Ram on the floor which could be broken out for cleaning the floor. I am thinking of putting a thin layer of play sand between the sacrificial plate and floor. That part of the furnace is unlikely to be hot enough to melt the sand. You can see the segments are each supported by blocks. That will allow placement of wool to fill the space between the floor of the chamber and the external floor shell of the furnace.

    The plinth is hand laid up just like a "primitive" pottery piece. It is hollow to reduce its mass and has a "daisy" of raised bars on top to allow circulation of flame under the crucible. That part of the plinth will be above the tuyere entry point. It is 5" tall and about 7" diameter. I am hoping it will have sufficient integrity to not fracture badly enough to cause collapse. I will be keeping an eye on it. The more traditional approach and safer approach would have been to go fully solid. I'll weigh it later when it comes out of the kiln. It is presently on its way to 1400F bisque firing.

    I regret to give up my current plinth which has over many firing and gradually melting crucibles become beautifully glazed with the same material used to glaze Super Salamander crucibles. That glaze is very hard, is gluing the pieces of the plinth together nicely and, lastly, looks good! ;-) It probably took over a hundred firings to get to this stage. It is too short and is so glued to the floor of the current furnace that I am pretty sure I will not be able to extract it intact when it comes time to decommission my present furnace.

    Floor Segment.JPG Floor Segment1.JPG Plinth.JPG Plinth1.JPG

    Last edited: Jun 23, 2020
  16. Melterskelter

    Melterskelter Gold Banner Member

    I finally got to put some fire in the furnace today. No metal, today was just a run to vitrify the refractory and to make sure nothing cracked, collapsed, exploded, or otherwise misbehaved. The burn went very well. For about a half hour I used a weed burner in the tuyere to slowly ramp the interior temperature up to 950 degrees F. Then I switched over to my siphon burner running diesel and just burned at .05L/m or about 3/4 gallon per hour. That was enough to bring the interior to a distinct red glow. Then I gradually ramped up the fuel and air until I got to about .2L/m. that seemed to be the sweet spot and was about 10% greater than the sweet spot for my old smaller furnace. That took the interior rapidly to a nice white heat.

    There were no surprises. No cracks. The panels stayed where they belonged. The maximum surface temp of the furnace body was 350F. With the old smaller furnace it would go 550 to 600. So the extra inch of insulation seems to be having a good effect on heat retention. I hope that translates to better performance. Most likely I will pour a 55 pound (65 pound melt) square late this week. That will be some indication of performance. However, I may need to fumble around a bit to find the optimal settings for the new furnace.

    On this furnace I did space the nozzle back in the tuyere about 2.5" and noticed that the fuel was igniting as it entered the furnace. I also noticed coking would occur if I ran my atomizing air below 10 PSI. That was no surprise. But since I did not use the chimney today, I could actually observe real-time what was going on inside the furnace.

    Here it is on wheels and blocks. When burning the wheels are off.
    Completed furnace.JPG

    I will use a rain cap over the tuyere when it is sitting between burns. This little lip will shield the upper edge of the cap. The cap will have a couple magnets to hold it wedged into place under the lip. The pop rivets were placed into a ridge on the barrel. That way they are out of the way and don't drag through the insulation as the barrel is slid off the insulation when servicing a panel or insulation is needed.
    Burner tube support and drip lip.JPG

    This is the support for the burner tube. Burner tube support.JPG

    Detail shjot of the rain cap lip.
    Drip cap detail.JPG
    Last edited: Jun 29, 2020
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    All sounds good Denis, let'er rip!

  18. Melterskelter

    Melterskelter Gold Banner Member

    Use of a curry comb to roughen the surface is specifically recommended in the Vesuvius instructions for installation of Blu-Ram. I uploaded those instructions in a separate thread.

    There is a lot of information in the instructions much of which does not apply to our uses, but there are some nuggets too.

  19. Petee716

    Petee716 Gold Banner Member

    I read the PDF you posted. Boy, getting that info was like pulling teeth! They're pretty in-depth about the installation instructions but I'll admit I skipped over some of it. Lol. Layered walls and roof structures just aren't anywhere in my future plans. But the drying schedule was interesting. It appears that in the larger scale the dryout and firing is every bit as stringent as castable. But I've been assured, and we've both found out for ourselves that our accelerated firing is just fine for our purposes. As long as the outside remains porous we're ok. One thing that I did take away from it is that heating should commence right away on thicker items like our plinths, etc to avoid locking moisture in. Thanks for your efforts in finding it and posting it.

  20. Melterskelter

    Melterskelter Gold Banner Member

    Today I did my first melt using my new furnace. It shave 25 minutes off my 2h 20 min 65 pound iron melt with a pour temp of 2550F. I burned fuel at a slightly greater rate but more than made up for it with a 10% overall fuel saving. My flow rate was kept at .195L per minute or 3.1 gallons per hour. The walls and lid appear to be no worse for wear. The lid now has 17.5 hours on it at iron temps.

    I'm happy and relieved. There were no guarantees...


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