Announcement

Collapse
No announcement yet.

Refractory Casting Oven

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    OK I found http://www.monolithic.org/calculators/dome-calculator and put in two calculations:

    Inside dome: diameter 30", height 16" stemwall 6" and got total volume of 12,040 (units unknown).
    Outside Dome: diameter 34", height 18", stemwall 6" and got 16,672.4.

    Leaving me a net of 4,631.72 ??? cubic inches?? cubic cm?

    Comment


    • #17
      Jeff at High Temp In in Portland, OR says it might be cubic inches. After conversion that's 2.68 cu ft. Seems about right for a dome alone. Factor in another 1 or 1.25 cu ft for the front opening. But what I can't find is the cu ft production from a bag of castable. 55 lb bags especially. Seems most people are using like 4-600 lbs of refractory for various sizes of 36 to 41" domes.

      Comment


      • #18
        Originally posted by mendozer View Post
        OK I found http://www.monolithic.org/calculators/dome-calculator and put in two calculations:

        Inside dome: diameter 30", height 16" stemwall 6" and got total volume of 12,040 (units unknown).
        Outside Dome: diameter 34", height 18", stemwall 6" and got 16,672.4.

        Leaving me a net of 4,631.72 ??? cubic inches?? cubic cm?
        Volume of a dome is 4/3 x pi x r3
        vol outer dome 20582 in3
        vol inner dome 14139 in3
        difference 6443
        div by 2 for hemisphere = 3222 in3 or 50 litres

        The amount you lose in the doorway of the oven is about equal to the door surround so just go on the calculation of the whole hemisphere.
        Dry castable comes in 25 Kg bags (55 lbs) but everyone I've measured is exactly 24 Kgs (within limits of approx.)
        There are 16.37 litres of dry loose castable per bag with the stuff I use. That makes it 1.466 Kgs/litre of dry mix
        The problem is that dry loose mix even when the extra volume of water is added to make up the wet mix only gives you 85% of the dry volume.
        This means that you need 50/0.85=59 litres of dry mix to make the 50 litres of wet mix
        or 59/16.37= 3.6 bags
        You always end up using more and you need extra to cast the entry so you should probably get 6 bags

        Hope my maths is correct.

        Kindled with zeal and fired with passion.

        Comment


        • #19
          Originally posted by mendozer View Post
          yeah those were for example of forms. There's no good form that I can find other than a foam 3d one that was much more like $2k. I'd much rather build one. A friend of mine used a physioball for his form. I like this concept, but also I don't know how thick I'd be able to make it. I've seen 2" walls are ideal for cast refractory. Then there's always the wooden frame with sand mound in the middle, but I don't know how exact or smooth I could make it. Then I saw this cool one, with interlocking panels mortared in. This would be good for expansion right?

          http://www.theclayhearth.com/finishe...d-final-paint/
          That's a ridiculous amount of mould work to make one oven. Casting over a physio ball is ok, but you have to dig a hole in the ground and build a flat bottom halfway up the ball to cast against, then lift the whole casting into position. It is far simpler to make a sand castle right over your oven floor. so you only have to dig out the sand when done, no moving required. Use around 10% water in the sand (a little powdered clay in the mix as well to help hold it together. Cover the thing in strips of wet newspaper and trowel over it with wet castable. if you get the mix just right it stands up vertically by itself ok. You get a few fine cracks in a one piece casting but nothing to worry about. Mine is 8 years old, gets plenty of use and is certainly not falling apart.
          Kindled with zeal and fired with passion.

          Comment


          • #20
            Thanks for the insight. I figured 5 or 6 based on seeing other people's 7 bags for larger ovens.

            Comment


            • #21
              This is a question for David:
              The above casted oven had a 30" ID, with a 4" thick casted dome. I was under the impression that 2" would be enough. Even for a 36" ID. Is there a practical limit to how large one can cast? Really I'm thinking between 30 and 36", over wet sand. Is that impractical? I was hoping to cast the dome and flue/entry all in one casting. Perhaps with a thermal break.

              Comment


              • #22
                2" thick for up to 36" oven diam is enough, but go thicker if you want more thermal mass. Stainless needles are not essential but will enhance strength. Not sure if FB add them to their manufactured ovens, probably not as they're expensive and make working the mix a bit more difficult. Casting the dome and flue gallery in one piece would be difficult. Better to cast the dome first then build another sand form in front of it to create the flue gallery casting. Cover your sand mould in strips of wet newspaper before casting over the mould.
                Kindled with zeal and fired with passion.

                Comment


                • #23
                  Excellent. What does more mass do for the oven? Assume it will super insulated all around. Just strength?
                  Last edited by cnegrelli; 02-26-2017, 01:13 AM.

                  Comment


                  • #24
                    More mass allows more storage of BTUs and will have more strength. It does not mean super insulated. Insulation is accomplished by how and what you use to insulate the dome with, ie ceramic fiber blanket, v or p crete etc.
                    Russell
                    Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

                    Comment


                    • #25
                      My insulation comment was not meant to relate to the mass. I will have plenty of ceramic blanket was my point. Tons acquired free a few years back.

                      So more BTUs means longer firing times, but more stored energy as well as strength it seems.

                      There's a trade-off there it seems, and that's where the insulation comes in. If 2" with SS needles is adequate for strength, and I have a ton of insulation on top, as well as the CaSi board at 4" underneath, does a thicker cast dome make sense? Or am I simply adding extra expense and weight? What does the extra BTUs buy, longer heat dissipation of heat, for longer baking times?

                      Comment


                      • #26
                        Originally posted by cnegrelli View Post
                        ... If 2" with SS needles is adequate for strength, and I have a ton of insulation on top, as well as the CaSi board at 4" underneath, does a thicker cast dome make sense? Or am I simply adding extra expense and weight? What does the extra BTUs buy, longer heat dissipation of heat, for longer baking times?
                        In order to answer the "Does a thicker cast dome make sense?", you need to figure out what and how much you want to bake with this oven. If you're looking at simply having a weekly pizza party on Saturday night and then baking half a dozen loaves of bread and/or a roast on Sunday, the 2" thickness is probably going to work just fine for you. If you are thinking of baking much larger quantities of bread daily or using it almost every day for fixing meals, you might find the thicker casting to be more useful. The more BTUs stored, the longer window for baking (at steadily reducing temps) you will have. It's not going to be like a lithium battery that works at pretty much full strength and then just quits...more BTU storage will simply give you a much longer, slower temperature loss profile. Ovens made with 4.5" thick dome and floor components will allow you to easily cook over several days (for quick example-- in daily meal sequence--pizza, bread, roasts, beans, drying fruit). You plan and use the lower temps available each day for the appropriate food. Make a very small, thin-wall cast pizza oven and you'll be able to have great pizza but the following day(s) baking options with residual heat (stored BTUs remaining) might be quite limited.

                        Long winded answer to the thicker cast dome being "worth it" question is again, highly dependent on what and how you plan to use the oven. I suspect that if the 2" thick cast isn't going to provide you enough BTU storage for your needs, you really should be looking at building a larger oven with firebricks instead of casting something larger and thicker (until you gain some experience with one of these ovens).

                        As a sidebar, it would be interesting to figure out how many BTUs are used for particular quantities and types of bakes. For example, how many BTUs does it take to bake a dozen baguettes...how many BTUs are needed to bring five pounds of pork tenderloin to medium rare? With that kind of information, you could much more easily determine the size and thickness of oven that would suit your needs or at least eliminate what won't work. Anybody seen anything like that?
                        Mike Stansbury - The Traveling Loafer
                        Roseburg, Oregon

                        FB Forum: The Dragonfly Den build thread
                        Available only if you're logged in = FB Photo Albums-Select media tab on profile
                        Blog: http://thetravelingloafer.blogspot.com/

                        Comment


                        • #27
                          Appreciate that explanation and it was in line with what I thought. I'd like to avoid the 3 hour prep time to pizza that is described in the other thread by n8huntsman.

                          Comment

                          Working...
                          X