Castable pour questions

Discussion in 'Furnaces and their construction' started by KC M@, Jan 3, 2021.

  1. KC M@

    KC M@ Copper

    How did you do your main body pours? In order to use wool I count 3 pours. 1-bottom 2-barrel and tuyere, then stuff wool and 3-top ring.

    The only way I see to do it in 1-2 pours is if you cast the refractory directly against the wool.
    If done this way I’m still concerned with the refractory weight basically pancaking the wool at the lower section when it’s vibrated in place. I’ve seen so many concrete forms blowout from the weight when vibrated.
    I’m forming up my build to pour and not seeing a clear path.

    Side note: is there a downside to pouring solid with no wool? It would make the pour so much easier with less steps. Just want to hear pros and cons from users that have experience.

    I already have a box of wool for this and another project. I also have 3 bags of refractory and a local supplier if I need more.
     
    Last edited: Jan 3, 2021
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It can be poured in one cast. Just cast it inverted with the top ring on the bottom and the bottom of the furnace completely exposed at the top of the mold. There is a case to be made for just casting three separate pieces with a cylinder that sits in a step in the base and top ring, assuming by "top ring" you mean the disc attached to the furnace body and not the lid.

    Yes, besides using more material which means it will be heavier and cost more, it will make the furnace more massive and take longer to heat up (the first heat of each session). Solid refractory inevitably means much higher surface temperatures on metal exterior surfaces.

    Best,
    Kelly
     
  3. Tobho Mott

    Tobho Mott Gold Banner Member

    That's how I did mine. Plus another pour for the lid, which I placed on top of the just-poured top ring (with a sheet of plastic between them) to squish it flat and smooth for a decent seal.
    I think you are right to worry about that if you pour the castable against the wool, you should probably use an outer form to cast your hot face. It's twice as much formwork (ie. another sono tube that's 2" wider) as just having an inner form, but it sort of is what it is. The really easy way would have been to paint a few layers of Satanite onto your wool instead of using castable... But you already have the castable, which should be able to take a ton of punishment.

    Jeff
     
  4. KC M@

    KC M@ Copper

    Tobho how long did you wait between pours. Also how big a pain in the ass was it to get the outer form off with only inches in between the can?
     
  5. Zapins

    Zapins Gold

    I've got both kinds of furnace an insulated wall furnace and a solid cast furnace. The insulated one does heat up a little faster but they aren't extremely far off. Maybe 10 to 15 mins more in the solid furnace.

    The benefits of a solid furnace (3" of wall thickness) are that there is no risk of tipping over or bumping it and having the crucible tilt due to the extra weight. It also doesn't require bulky out riggers for stabilization that you can trip over and it lasts forever being much more durable than the insulated kind.

    When you are pouring 300,000 BTUs of energy into an object it doesn't really make a huge difference in how efficient it is from what I've seen. Maybe it would if you were melting iron I'm unsure. But I suspect it's like worrying about casting in summertime 90 f vs winter time 33 f in terms of the metal cooling faster. Its a 60 f temperature difference compared with the flame temperature of 3500f. Makes very little difference in reality.
     
  6. Tobho Mott

    Tobho Mott Gold Banner Member

    I don't recall how long I waited, but IMO the waiting to let it cure and dry out before firing it is more crucial. It might have been a couple weeks between casting the floor and lid and hot face wall. But it probably could have been done without such a wait.

    I used a ring of aluminum flashing for the outer form. Just had to cut the top of the aluminum tape holding it together and the rest of the tape was easy to rip free so the flashing peeled off and came out easy. Sliding the wool into the 2" gap was the tricky part, not removing that outer form. It was 5 years ago so I don't recall if I slid in the insulation first or peeled off the outer form first. The flashi g isbslipperiwr than the castable so I think I might have removed itbafter to make the wool easier to slide in.

    The pipe I used to form the tuyere did want to stay glued inside the hole, so I suggest you either give yours a quarter turn or so a few times while the refractory is setting up to keep it from getting stuck, or wrap your tuyere forming pipe in something that can peel or burn out of the hole once the piece of pipe has been slid out.

    Jeff
     
  7. KC M@

    KC M@ Copper

    Great info. The sono tubes are easy but I think removing it would be a nightmare. Here’s a thought: what if I just left the cardboard outer form in there? I know it’s normally pulled but hear me out. The refractory is good to 3000 and the wool is good to 2300. Wouldn’t it just turn to ash? It’s locked between 2 faces that it can’t hurt? Has anyone tried this? The worst I foresee is it smoking a bit but in the minutes takes it to turn to powder it should stop. I think....
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's actually the inner tube of the mod that needs attention to release it. The ID of the Sono tubes are waxed, so they are water proof and release fairly easily. The OD of your inner sona tube is what needs to be wrapped and/coated. It is also easily burned out. What's the problem with pulling cardboard off of castable?

    Best,
    Kelly
     
  9. Fasted58

    Fasted58 Silver

    Last edited: Jan 5, 2021
  10. KC M@

    KC M@ Copper

    Kelly I do understand that. I’m just asking about leaving it in. Mechanically Im try to understand the reason to pull it other than it’s always been done that way. As cardboard It will disintegrate in the initial burning and then I think it will be like it was never there...with no additional removal work. Don’t get me wrong, I can get it out. If that’s what it requires I will find a way. I’m just making the observation that trying to slit or peel a potentially heat consumable form in a space 2” wide and 14” deep could be difficult for some. If the possibility that the removal is irrelevant to the integrity and functionality of the furnace then I think it should at least be questioned. Traditional methods from long ago have been the standard and have worked, and still work to this day but..they didn’t have or use cardboard forms. Why not try to improve designs and techniques as technology improves. Isn’t that what the inventor of the metal melting furnace did way back in the day? Even if that improvement is as simple as time saved it moves us all forward.
     
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    If you are making a mold that uses sono tube to form the ID and OD of your refractory hot face, why would you be limited to only a 2" space on the outer diameter to remove it? It's freestanding mold right?

    In principle, there is no reason you'd have to remove any part of the mold if it's all cardboard, wood, and plastic.....just incinerate everything. It makes a bit of a mess and hard to see how it can be viewed as an improvement, but up to you on that. Most people remove the mold so they can inspect the refractory casting and aid initial drying and curing before firing.......and occasionally folks burn out the inner hot face mold surface or Tuyere.

    Best,
    Kelly
     
  12. KC M@

    KC M@ Copper

    For the record I promise I’m not trying to be difficult.:)

    I initially planned to pour as you suggested outside the can inverted and that would make for easy removal of the forms. It also creates a few problems that a pour in place would resolve. The main issues being a tight fit of the tuyere and the top ring to the steel can as well as getting the insulation stuffed in as you try to slide the whole contraption in place. If I pour in place I am 100% confident of getting a spectacular fit of all three. If I form and remove it, then pour there is the potential for an ill fit requiring additional work to make it fit back in the can or worst case starting over losing everything invested.

    I’m sure everything will work out regardless. I’m going to pour it in place, leave the outer form in and incinerate it where it is. I plan to pour this weekend. I will post some pics of the pour and a follow up on whether it’s a disaster or not. I’ll even gladly accept a “I tried to tell you” if it goes that way. One way or another melted metal is in the forecast.
    Great book by the way. I read it for an hour and a half last night. Kept me up way past my bedtime.
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's not my work. It's a post by an former Admin at the Alloy Avenue site. I need to update the preface of the thread here with the history of the content. Today I attached a pdf version at the bottom of the first post. Download that and read it. It's indexed and has all the illustrations but is otherwise the same content.

    Best,
    Kelly
     
    dennis likes this.
  14. KC M@

    KC M@ Copper

    Will do.
     
  15. In industrial furnaces it is common to leave formwork in place and let it burn out or stay. I agree starting with wool, then putting in cardboard, or putting them in together, then casting and letting the cardboard go to cardboard heaven or hell (depending on it's religion) has merits. You know you have the wool all the way to the bottom since you can work it as you put the cardboard in. The ash hole left by the form may close with wool or it may be an insulating air gap.
     

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