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Refactory Cast Oven New oven build with high density/thermal conductivity material

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  • #16
    Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

    My thoughts exactly, but unfortunately my schedule didn't allow me to breakdown the mould in time so we are crossing our fingers.

    When we applied the material, we did a first pass in each section just a centimetre or so thick and really pressed it against mould so hopefully the voids etc will be limited. Also we covered the cut/outside of the styrofoam edges with linoleum to provide a very smooth surface. This is a tip for everyone casting refractories. The linoleum along with a decent release agent, will provide for an extremely smooth surface, what we call a "baby bottom" finish. Overkill possibly for a pizza oven, but very desirable with liquid metals, plus it looks good!

    David s, is the internal diameter of your flue 4 or 5", 100/130mm? The price is basically the same here, but with the larger diameter then I can use a shorter piece, rather than the 1000mm length, or possible use the 1000mm length regardless. I am just trying to make everything as compact as possible, but on the other hand, if I am going to have a flue, then I don't want to make it to small and have black marks on the front of the oven like I see in so many pictures of ovens with flues.


    • #17
      Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

      I use a 5" flue, but my oven is smaller than yours. If I were making one your size I'd use a 6" flue. Mine is 900mm long. You can make the flue too short and too narrow, but with a front flue you can't really make it too long or too wide
      Keen to see your castings,
      Last edited by david s; 09-03-2013, 06:11 AM.
      Kindled with zeal and fired with passion.


      • #18
        Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater


        With a 130mm flue then my landing will need to be at least 200mm depending on the size of the console/anchor plate. Essentially the size of the flue will determine the size of the landing at this point and I need space to make the vent area up to the flue. I backed off the mouth out of the oven by about 25mm to gain some extra space for the flue. Will go on and order today. Thanks.



        • #19
          Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

          My flue pipe is 5" and my flue gallery depth is also only 5" because I like a shallow entry to make the oven easy to work. Here's how I achieved it. The flue gallery only weighs 11 Kgs by the way, so does not sap much heat from the oven.
          Kindled with zeal and fired with passion.


          • #20
            Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

            Just been looking at your specs again. Yours is 61 cm diam. (13% more than mine) but this translates to 44% more volume, although I see you have an internal dome height same as mine, so lets say you volume is about 20-25% more. You could probably get away with a 5" rather than a 6" flue, just make it reasonably tall will help.
            Kindled with zeal and fired with passion.


            • #21
              Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

              These are really helpful pictures and very similar to the route I have been thinking about, but my solution was not quite as elegant. I would like to make the flue as large as possible, but with such a low dome and opening I really need to minimize the entry otherwise it could quickly feel like performing keyhole surgery with a pizza peel! A 5" flue with 1 meter pipe can be my starting point. I can always add to it in 30cm segments if it is not enough.

              How do you attach the pipe to your casting? I was thinking about using an anchor plate similar to the attached which I could cast in, thus giving plenty of support for a 1 meter pipe. If I could get rid of the anchor plate that would make the job a lot easier and allow for a smaller build, but worry about getting a robust connection.

              Picked up firebricks yesterday, so now just have to figure out and build my stand in the next week before I can begin my pre-firing.



              • #22
                Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                Mouth and Chimney

                It?s been awhile since my last update but been working on the pizza oven in the meantime.

                After checking out many different types of chimneys, and trying to figure out an elegant way to attach it, just decided to just make a single section to include the mouth and chimney. The mold for the mouth was easy, simply shaped it out of Styrofoam, but for the chimney that was a bit of a challenge.

                Went through about 10 ideas that were either too expensive or impractical. In total frustration want back to the garage and kept hunting and eventually saw a large section of vinyl/linoleum in the rafters that was left over from the previous tenants, grabbed a 3 meter piece of 2x2 from the wood pile and started rolling. Set it on top of the mold and nailed the top end of the 2x2 to the rafter in the garage so it wouldn?t tip over. Worked like a charm. Had about 30kg of material so it only made it about 15-20cm from the planned top, but that has actually turned out well.


                • #23
                  Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                  Stand, Base, Floor of the Pizza Oven

                  10x10 impregnated lumber
                  Metal Europallet 1200x1200mm
                  Paving Stone
                  Hardie Cement Board
                  Calcium Silicate Block Insulation ZelieBlok? 2000S ? 6 sheets 1x12x36 inch

                  Again this phase turned out to be another big challenge as we need to have a portable pizza oven as we don?t want to leave this behind on the next move.
                  Made the stand from 10x10?s bought at the local diy store here in Scotland. The Metal Pallet took longer to find but was finally able to source it in England.

                  On top the metal pallet (1200x1200mm) laid 4 paving stones, a single layer of concrete board and then two 1? layers of Calcium Silicate Block Insulation ZelieBlok? 2000S that I was able to pick up in Toronto left over from an installation.

                  Tried to source the bricks while travelling, but just too much variation (size, weight etc) between the bricks I collected. Also, they quickly eat up your weight allowance on flights, and difficult to pack so they aren't cracked/broken on arrival. Security doesn't like them either.

                  Decided to see if I could get them locally and was able to source them from a local builder. After much searching he found them on the top shelf of the racking. Was able to scavenge just enough usable pieces, most were broken and chipped and of variable size. Cut them with a grinder, it works but it wouldn?t be my first choice if I had to do a lot of cuts.

                  Measured and weighed several of the bricks to check if they were the correct density, they seem to be, but density doesn?t always tell the whole story on refractory products but they should be OK. I don?t have a perfectly smooth floor, some small gaps < 1mm, but with the grinder was able to make it smooth and the small gaps will quickly fill with ash (I assume!).


                  • #24
                    Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                    Missing some photos here, will upload them once I find them.

                    Metal Drywall Studs
                    Hardie Board Sides
                    1200x1200mm Aluminum Roof
                    Thermal Ceramics Superwool? 607? HT? Blanket (96kg/m2)
                    Thermocouples ? generic from China

                    Had to build a ?litter? for the dome out of 2x4?s. At 90kg it?s pretty heavy and there was no way we could simply lift and then correctly position over the fire brick. Screwed it all together, moved the dome on top and strapped it down. Took 5 people to safely carry and place on the firebricks.

                    Put in a heat break between the dome and mouth with several layers of 1mm insulation we normally place between steel and cast refractory material to allow for expansion. Doesn't have the lowest thermal conductivity, but was easy to get my hands on. Positioned the mouth and sealed the mouth to the dome with fire cement . Also sealed all around the outside of the dome between the dome and the firebrick with the fire cement.

                    Next step was to frame with metal studs, ensuring there is no wood on the pallet except for 3 small strips on the two sides and the back. Am using Hardie board for the sides and will tile them over (as soon as it quits raining, possibly in a few months).

                    Was able to pick up a 7 meter roll of the Superwool? 607? HT? Blanket (96kg/m2)from Thermal Ceramics in Chicoutimi on another trip and stuffed it into my suitcase. Not much for anything else. Although the 96kg/m3 has slightly ?worse specs? than the 128kg/m3, I can?t imagine that with the tolerances in the rest of my build that I would even notice the difference in the insulation.

                    Thermal Conductivity
                    Superwool? 607? HT? Blanket
                    96kg/m3 128kg/m3
                    200?C W/m.K 0.05 0.04
                    400?C W/m.K 0.10 0.08

                    Was able to fit 3 layers around the sides and 4/5 layers on the top.
                    Finally time for the roof. First time I?ve ever cut Aluminium, but turns out to be no problem at all. Chimney has an 18cm outside diameter so made the cut out about 18.5cm. Used the jigsaw with the Bosch Aluminium blades. Took a total of 10 minutes max and made a very neat hole.

                    The decision for the Aluminum top wasn't for aesthetics, simply that it rains so much I didn't think that any stucco, Hardie board, tile combination would ever stand up to the constant rain here. Secondary benefit is that I can get inside whenever I want!


                    • #25
                      Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                      Break in / Dry out

                      6 days in total, 20 fires. The first 2 days I used coal, simply to control the temps through the 150C hold and then switched to wood. Wood is much easier above 175, but couldn?t manage with wood at the lower temperatures.

                      With this material I needed a 6 hour hold at 150C, 275C and 375C as it will explode and when that happens it?s not a crack, but can fly a couple of meters. The 150C isn?t so critical, but both the 275 and 375 are known to really cause problems. For these holds I tried to keep within the band for at least 6 hours before moving up to the next hold temp in 25C intervals.

                      I had 6 thermocouples installed: 1) 1cm inside from the top, 2) outside top, 3) outside right 4) outside back, 5) through the right side measuring air temp inside the oven and 6) on the top between the last two layers of insulation.

                      A Lesson learned. Don?t buy cheap thermocouples in China, particularly at the market in Pudong, or if you do, buy enough to replace the ones that break in service. The outside top, right and back worked for about an hour and then went silent. Was left with the top inside and air temp. As those were the two I was most interested it worked out OK.

                      During the firing I took a several different measurements, but have only plotted the temperature from 1cm inside the dome and the surface temperature inside the dome which I took with an infrared thermometer. You can see where after about 2-3 hours the temperature drops 25-50C and all of the measurements come together. Thermal soaked at that point. Time to fire again.

                      On Saturday, once through the 375C barrier, decided to take it as high as I could in hoping to hit 500C 1cm inside the dome. Made it to 460C, dome surface temperature was 546C / 1000F and was then told I had to run some errands. No discussion allowed as I had put it off since the morning.. Got back a couple of hours later fired it up again and cooked the first pizza. That's another story, great pizza, need to work on the dough, tasted like flour, and keep the fire going to the side, not as simple as I thought it would be, but my wife has those photos and will have to wait to get them.

                      Insulation seemed to be working fine. When the oven hit 460 measured the temperature between the last two insulating blankets and measured 40C and with the infrared thermometer had a reading of 5C on the outside. Air temperature was around 2C. Underneath the oven was warm but not hot. I definitely think I will lose most of my heat through the floor and door due to by build design, but as I will be building an new oven in the autumn or latest after the next move, not really too worried about that. This one is just a practice run.

                      Overall the thermocouples are extremely helpful in the break in / dry out, but not sure if they really offer any long term assistance. When the dome goes white, it really turns white and slowly expands. Can't really miss that at all.

                      Somehow I was expecting this to be very complicated, but it's really not once you get a feel for it.

                      Wood consumption over the week wasn't to much. Just a single "sack" measuring 80x80x180cm. I counted all the wood going and it was extremely consistent, approximate one piece of wood 25cm long, wrist thick per 8C needed. When I needed to go 100C, I know at the end I needed 12-15 pieces. I didn't once empty the ashes during the week. Sunday morning, found at most two small shovels of ash and coals. Everything during the week was completely incinerated or out the chimney.

                      Now just waiting for the rain to stop to finish off the outside. In the meantime the kids have all scheduled "small parties" for pizza, and for once we aren't being banished to the TV room!


                      • #26
                        Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                        Good job. The Superwool you chose is a good product and uses safe fibres, although it's more expensive than other ceramic fibre blankets that are classed as carcinogenic. Now you can enjoy the fruits of you labour. You wil find the small oven extremely economical with fuel. Did you incorporate your idea with the "pocket" and the thicker refractory over the top of the dome? and if so how do you think these ideas are working out now you're up to operating the beast.
                        Kindled with zeal and fired with passion.


                        • #27
                          Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                          Killie, Your semi-permanent build looks good. I am at the planning stages of my build and
                          recently ordered (also) 6 thermocouples from china, but I have been having a hard time finding a decently priced thermometer which captures the reading via graphs. Do you mind sharing the make and model of the one you purchased. I like the way yours displays the info. I assume you were able to download the info onto a flash drive and on-wards to a PC.

                          Any information shared would be appreciated,

                          Thank you,



                          • #28
                            Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                            Saovicente, funny you asked about the thermocouples. I am just getting ready to order some "real" thermocouples from a supplier here in the UK, but just can't really justify the 100GBP it will cost vs what I paid in China. I really don't know brand I bought but they look very similar to the ones you can find on Amazon.

                            As to the datalogger, I don't have one of those, I just took measurements every time I fired up the oven and then when I reached my target temperature. We use the data loggers extensively at work, but decided that doing it the old fashioned way was good enough for me. It's similar to that Omega OM-DAQPRO-5300. Cheaper ones exists i am sure but they can then usually do only 1 or 2 sensors at a time and then it's just as easy to take them manually.

                            My experience so far is that they are very helpful in the curing / pre-firing of the oven as I needed to make sure that I didn't overshoot on my temps and made my 6 hour hold at 150C, 275C and 375C levels. Moving forward I have the feeling that only two of them will really be of help, the one measuring the surface temperature on the outside of the refractory and the one measuring the air temperature inside the oven. The top of dome and floor temp I can get with my infrared gun shooting inside. The others I think I would check them out on a couple more fires and then never look at them again.

                            At this point I am struggling to upgrade the thermocouples (another GBP 100/160USD) and will most likely stick with the Chinese ones and replace as needed. With my design I can always remove the roof and get inside, but honestly I don't think that will happen as once I get to know the oven a bit more.


                            • #29
                              Re: Refactory Cast Oven ? New oven build with high density/thermal conductivity mater

                              David S

                              The insulation seems to be working well. Had the oven up to 500C/900 on the outside of the refractory and 568C/1054 on the dome and the temp on the outside of the insulation layer was less than 40C. I don't know how that compares to others but I wasn't complaining.

                              Total heat up time was 2 hours exactly.

                              Just for fun I think I will pick up some of the ThermalWrap Blankets made in Germany when I can get some excess. I will put that as the outer layer. At .015 vs 0.05 W/m.K at the 125C range its almost 3-4 times more insulating. Overkill I am sure, but why not?

                              As to fuel, I don't know what the "norm" is, but I used about 5 of standard heating logs used here in Scotland. Am guessing they are 25cm in lenth 25 cm in diameter and cut in two. So either 5 logs or 10 1/2 logs. Cut them down to wrist size so had 40 pieces in all. We I made it to 500C with 3/4 of them and then used the rest to burn on the side and recharge the oven.

                              Daughter had 10 friends over for an impromptu pizza party. cooked about 12 pizzas, first 5 or 6 excellent bottoms with the last 5 or 6 with great tops but the bottoms weren't that browned. Hearth was at 300C at that point. Threw in another 6 pieces of wood and the oven was back up to 475+ within 15 minutes. Did another 2 pizzas and called it a night around 20:00.

                              At noon the next day the temps were at 200C (16 hours later) and we threw in all the extra pizza dough in one big ball. Cooked for 45 minutes and had acceptable bread. I was fairly pleased that it was still at 200C after 16 hours.

                              The pocket works out really well, but I don't have any experience without it. Kinda of a pain in the *** when framing it, cutting the brick hearth, insulating it etc., but it does give me an extra 10cm for the pizza.

                              Couple of other things - Rice Flour really works, didn't loose any pizza this time sticking to the paddle. Wife picked up a nice paddle in the USA last week. Also picked up a couple of pizza screens, complete waste of time.

                              Now just got to decide on if I go with upgraded thermocouples or just let it go.

                              Still lots of rain so haven't been able to do any work on the outside of the oven, that will hopefully happen soon.

                              Have attached a couple of photos. My attempt at setting up a top down fire
                              our first bread, photo of the fire in the pocket with a pizza and a photo of a pizza that apparently someone at the party took with my phone without my knowledge, but including it anyway.