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36" Mobile Cast Neapolitan

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  • 36" Mobile Cast Neapolitan

    Hi All.
    Ive begun the form for the mold of this oven and have some questions I'm hoping for some input on. I have chosen to use Iron Pony's mold design (post link tab doesnt seem to respond for me)
    because its brilliant and I like the fact that I can reuse it if need be. I have done some modifications to the mold sub frame Im hoping they will work for me.

    I seem to be having an issue with the Vent and Throat transition and have some mix questions.

    Throat transition:
    You may be able to tell from the pic I have created an assembly for the opening with a door "revel". After looking at it I am wondering if I'm correct in thinking I should cut that web and slide it back to the 10" mark where if I were doing brick it should sit? I'm pretty sure that's where it needs to be for a good transition. I have built a couple barrel ovens out of brick and the area I'm talking about is where a the steel lentil (angle iron) would go. Why Im having trouble visualizing this for a cast oven is beyond me.
    QUESTION: Should cut that web and slide the throat assembly back to the 10" mark? (where blue line meets curve of web) Click image for larger version

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    Vent & Landing opening:
    I made it too big (front to back) for this size oven, a 6" or even 4" vent should be more than sufficient. This oven is going to be mounted on a trailer and although I love the look of a clay flue liner its just not practical. I will be using a Steel or S Steel anchor plate for the vent pipe eventually. There is a lot of moisture in the process of these ovens and galvanized doesn't hold up to the heat and moisture cycles in my experience.
    QUESTION: What size flue works best for this size oven?

    Refractory Material Consistency:

    I have a lot masonry experience but NONE with this product (is an AP Green product for this application, cant recall right now specifically what mix it is prob K4 or KS?
    QUESTION: In others experience what is a good working consistency for this material?

    Addition of Stainless Steel Needles:
    The guys that use this material to line steam generators in my area say they dont generally use them and the product holds up well at temps well above my application.I have some maybe about a pound or 2 but just not sure they are necessary. I was thinking to add them certainly wouldn't hurt and I'm sure they would help in the mobile aspect.
    QUESTION: To add or not to add needles and if so at what rate?
    Attached Files
    Last edited by mefornaio; 09-30-2015, 06:50 PM.

  • #2
    You don't say what mix you are using, but if it is a proprietary castable because it is rated to a much higher temperature e.g. 1400 C that does not mean it is not going to be subject to damage through firing. Castable refractories are actually designed to be fired to a high temperature creating a different chemical bond like you get when clay is fired in a kiln. You never get to these temperatures firing a WFO so it only relies on the calcium aluminate cement bond. The result is that the material remains in the "unfired" state and is subject to the damaging temperature range of 500-600 C. However it still works pretty well in the unfired state and that's what counts.

    Apart from driving out the water extremely slowly to prevent steam spalling, the very rapid rise in temperature e.g. 300 C/hr is really way too quick to prevent uneven expansion rate which leads to damage. The stainless needles in this case do provide a degree of strengthening, but are not essential. I think you need to make the flue gallery as shallow as possible because when cooking you have to work past this all the time. I made mine only 5" deep and with the outer decorative arch in front of it adds another two and a half inches for a total of only 7 1/2" This makes the oven a joy to work. My oven is small with only a 5" flue, but you can set the flue exit back slightly over the top of the oven mouth.

    Regarding consistency you should follow the manufacturers recommendations on water addition, but making it fairly fluid reduces strength while making it less fluid leads to a greater propensity of creating voids.
    Last edited by david s; 09-30-2015, 04:52 PM. Reason: avoiding post timing out
    Kindled with zeal and fired with passion.


    • #3
      Thanks David

      It is a proprietary mix from AP Green. I have some Vesuvius product as well its a light weight mix that i purchased by mistake.

      In the oil field these materials are used in the fabrication of steam generators. My previous employer did NDT inspection at one of the fab yards that make some of the largest ones so I was there pretty frequently. The contractor that installed the insulation would literally have a small dumpster every Friday FULL of the high temp blanket and board insulation that was just throw away..crazy when you think of what the going price is for home oven builders.

      Here are some progress pics. This is just the rough base for the plaster mold. Its fairly crude but its the topcoat that will matter. I cut down the entrance but I still feel like it needs to be shorter. I suppose if I just put a stop at the length I want before the final cast It will be fine. I have been in the mind set of a bread oven, that's what I'm used to operating. Load and maybe check on it once then pull product. Pizza is different.

      Click image for larger version

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      Roughing in base mold.

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      Filling gaps with quick set 20
      (green spray paint was intended to serve as a visual aid for next step)

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      Door stop

      Clearly too late now for this but I was wondering?
      QUESTION: What are some opinoins on dome on top of floor or floor inside dome?
      Attached Files
      Last edited by mefornaio; 10-02-2015, 08:43 AM.


      • #4
        mfornaio, I am in the process of building a 40" cast oven. My vent area is 10" deep for an 8" chimney pipe. The vent area was originally 12" but I had some space restrictions with the base and reduced it to 10". I did this by extending the vent area over the mouth of the oven like david s suggested. Here are two pics.

        I'm no expert but I would not use less than a 6" chimney pipe on a 36" oven.

        I used stainless needles in my homebrew castable mix for some added strength. They are not that expensive around $2.00 and change a pound.

        Using the homebrew castable I made it too thick, closer to the consistency of peanut butter. I should have added a bit more water because I ended up with a few voids that had to be patched.
        My oven build in progress:


        • #5
          Thanks Purplehaze.

          I came across your thread a few days ago looks like its coming alone well. I also noticed on your orig mold you had a long throat as well that it looks like you cut down. The cast looks great. The plan is to get this mold completely covered today and perhaps cast this weekend. The only variable left I think? lol is how many sections to make it.

          I'm going with a 6" flue it should be plenty. Also I'm going to head down and pick up some needles there so cheap its a "you might as well thing"

          I have some thoughts but I would like to hear your (as well as others that want to chime in) approach to getting the material to stand up during the casting without slumping into a pile?


          • #6
            I used an exterior vertical mold made from some Masonite, similar to what I did for the insulating perlite layer. I cut it 2.5" taller than the vertical edge of the mold which is the thickness of my oven. I made right triangle shaped braces to keep the vertical wall straight. I did mix my refractory cement fairly stiff and the only time it slumped a tiny bit is when I used the orbital sander on the exterior mold for vibration.
            If you go this route I would recommend that you support the exterior mold more that you think is necessary mine bulged a bit at the back of the oven. This is due to my over zealous packing of the refractory.
            My oven build in progress:


            • #7
              Thanks again.
              That is what I was going to do I just was not sure it was necessary. I guess I keep thinking this mix is going to act drastically different than concrete mix. I mean years and years ago working with my father we had made cast pieces for masonry fire places or furnaces but this was old school home brew.

              Im going to put a double layer of Masonite and surround that with 2x6s hard to describe I will post pics.

              Here are some progress pics:

              Click image for larger version

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              Cut the opening down


              • #8
                It works better if you cast the oven first, then when it has set, cast the flue gallery against it, so that it overlaps the dome casting.
                Kindled with zeal and fired with passion.


                • #9
                  Thanks David.
                  I was playing with that idea. My only reservation is one more area subject to movement being this will be mobile. I like the idea of Ironpony's design in that its minimal pieces. I have been thinking about adding another section to the dome casting for ease of lifting.
                  Making it 5 sections instead of 4, then again that's yet another point of movement ..
                  Last edited by mefornaio; 10-03-2015, 12:37 PM.


                  • #10
                    Yes, it's a catch 22. I made my mobile oven dome in one casting (but a separate flue gallery section) for that reason too. It has held up pretty well with one vertical crack in the back about 6" long. The larger your cast sections are the more likely you are to get cracks. The more separate sections you have the more likely you are to have problems with the thing shaking to bits.
                    Kindled with zeal and fired with passion.


                    • #11
                      Thanks again David.

                      I started out thinking 2-3/4" wall thickness but now Im leaning towards 2-1/2". I'm thinking of these sizes for oven management not so much for strength. Im wondering if the mobile users wish their ovens were a different thickness either for management or durability. Opinions of this would be appreciated.

                      QUESTION: What is a good wall thickness for a mobile oven?

                      This first oven although mobile, will only see a 6 mile radius on a tandem axle trailer. I have had some thoughts of air bags or possibly a spring system but I'm not sure its even necessary.

                      I had some distractions this weekend then my OCD kicked in. Im determined to make that mold perfect. Why I dont know. Right now its pretty darn close to completed. Its going to be way more clean (lines and curves) than if it made from brick so I dont know why I insist on toying with it. Heck I could have built 2 out of brick by now lol. Oh well its reusable (it better be) and that was the goal.

                      It looks like a Giant Cake..Buddy Valastro would be proud. Hey darn it I should have just made the base out of cereal treats and plastered over it. Then again with the price of cereal it prob would have been twice the cost of what i have in it..

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                      Still slightly out of round in some areas.
                      Going this AM to get Masonite for outer wall pour.


                      • #12
                        I purchase a trailer this weekend and just picked it up. After a few months of looking at outrageous prices of used trailers I was just going to build one but the price for this was much lower than I could build one for.
                        It has what looks like 5200lb axles which is over kill but again for the price it was a steal.
                        Its an odd deck width of 4'8" I'm thinking nobody wanted it because of the width but it will work for me right now. It has 16s on it right now and I may go 15s with a lower profile tire to get the deck height down a bit but not sure. I have entertained the though of making the oven able to rotate 180* but I may be too restricted by time i need to get this venture off the ground.

                        Searching on this site seems to be pointless so I will ask if anyone can point me to others that have gone mobile on this site,
                        Also is it just me or does spell check work only sometimes? For me it identifies a misspelled word by underlining but when right clicking it only gives me past or add table choices.. but only sometimes.

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                        • #13
                          This is Google Search of the Forno Bravo site for "Mobile pizza oven".

                          Edit: Here is a link to a temporary work around for site search engine. You may do better with different key words.

                          Edit: There are several threads under Commercial Ovens.
                          Last edited by Gulf; 10-05-2015, 06:17 PM.
                          Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


                          • #14
                            Thanks Joe appreciate it.

                            I always get slightly annoyed when people ask questions like mine. I chuckle at the classic "google is you friend" reply most give.

                            But In my defense I asked only after much frustration of trying on my own. This site is almost painful to navigate. I realize they are working on it and its greatly appreciated but none the less frustrating.


                            • #15
                              Ready to cast first section. If anyone sees an issue please let me know. Other than the paint color of course .lol I've had that in the garage for years.
                              I'm kind of concerned about working time (KS4V PLUS) and the water content.
                              Can anyone tell me if the manufacture suggested mix ration works well or should I use that as a guide. Not more water but possibly use less water.?
                              Thanks for any input.

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                              Last edited by mefornaio; 10-08-2015, 05:33 PM.