I posted an electric foundry build here about a month ago (http://forums.thehomefoundry.org/index.php?threads/homemade-electric-furnace-build.1077/). It was really enjoyable to build and I've been melting a heap of scrap out of it. Now I'm thinking of building a larger burnout oven to accompany it for lost wax casting. I wanted to know the maximum interior volume I could make the oven out of with grade 23 insulating fire bricks, given I have a max of 2400 watts (240V at 10 amps) from my home outlets and need a max temp of around 800C. I also have 18 awg kanthal wire if that's useful to know. I wont actually use the maximum volume, but somewhere in between. I read somewhere in a knifemaking forum that you go by a certain amount of watts per unit of surface area for the interior walls of the oven, but I think this application will need a lower temp. Hopefully it's not too complicated of a question. thanks
How often will you use the kiln and how thick of a wall of K23 are you contemplating? The larger volume will always make for slower heating and there will be a limit when the heat loss through the wall equals 2400w. Whatever that limit turns out to be I can guarantee the terminal volume/temperature would be larger if you used ceramic wool instead of IFB, and the build would be much less expensive and lighter, like a top hat lift off style furnace. The issue with a wool is safely hanging the coils to protect them from damage and you from electrical shock. The allure of IFB for a resistance furnace is the ease of carving shelve for housing the heating elements. Why not have a hybrid with a shallow stationary IFB base that houses the coil and then a can or wire caged lined with wool to provide the additional furnace volume? http://forums.thehomefoundry.org/index.php?threads/the-furnace-thread.276/#post-4960 It could be a circular base with a wool lined garbage can for a deep lift off lid, or the base could be rectangular (or whatever) and have a wire mesh armature/structure lined with wool. The top could be removed by hand or you could have an overhead truss to hand it on. Best, Kelly
Probably wont use it very often as it's a small hobby. Twice a month at most, but I'm not too concerned about the practicality. the k23's would be 75mm thick. Quite a good idea you have actually. having the elements on the base firebrick would also lessen the chance of the coil coming out too, and I could raise the investment mold off the base coils with dense firebricks. Bit hesitant about using ceramic fiber due to its carcinogenic properties, but I can always use bio-soluble blanket, which isn't much more expensive, and still much cheaper than the bricks. Cheers for the idea, I'll definitely consider it.
The important dimension is wall thickness from inside furnace to outside. Most IFBs at 9" x 4.5" x 2-3". Might be better to position the IFB so the wall is 4.5" rather than 3". IMO opinion the health risk is exaggerated if you just take sensible precaution. I can tell you with certainty that industrial walk in ovens are either IFB or folded/pleated exposed wool hung on metallic hangers. The wool surface is lightly sprayed with colloidal silica to stabilize the exposed fibers and operators wear simple particulate masks when entering or leaving the oven, and these are compliant with regulatory guidelines. -That's it. The alumina silicates in IFB dust are every bit as friable and carcinogenic as wool but people don't hesitate to handle them. They create a lot of dust when they are cut or machined. Wear gloves, particulate mask, eye protection, and wash your hands and clothes after working with them. If you machine them with power equipment, do so outside. Inside will deposit dust all over your shop which becomes easily air borne. Clean the bulk of IFB dust with light brooming and only vacuum the minimum amount......that makes particles become airborne. Like everything these risks tend to be related to exposure time. If you work with them daily, greater care is required. If it concerns you the so called safe wool should be just fine for the modest refractory demands of a resistive electric burn out kiln. It's too economical and wonderful of a refractory material to unnecessarily discount it's use. Best, Kelly
Yeah I considered that option of laying the bricks to get the biggest wall thickness for my original furnace, but it just would've taken a crapload more of the expensive bricks and they don't seem to do it that way for the store bought kilns. I took a lot of care with those bricks as well. not letting some expensive hobby that makes me no money be the death of me haha, but thanks for the extra safety tips. yeah definitely much more economical and easy to lay out. Any idea how long the wool will last me compared to IFB's? Anyway I searched for some burnout ovens operating at 2400W (240V @10A) and the biggest capacity Paragon sells is 25 Litres https://www.paragonweb.com/TNFJ142.cfm, so to be safe I won't exceed 25L internal volume in my final design. thanks mate
Indefinitely at your duty and temps......as long as you avoid contacting the wool with tools and such. A lid with interior volume of a 25l bucket with 2-3" of wool and some modest steel structure would weigh just a few pounds. Best, Kelly
As another thought, unless you need a dedicated burn out oven, you might be able to remove the lid from your existing furnace, make a small platform for that insulated "top hat" to sit on and use your existing furnace and controller as the heat source. Might have to get a little creative about the platform the burn out investment sits on, especially if it has to collect wax, but for what it's worth, I have used my electric that way before and just repositioned the thermocouple for the PiD in the upper region. Sort of like I did to cure these pieces at the bottom of this post. http://forums.thehomefoundry.org/in...w-mass-electric-furnace.607/page-4#post-14126 Best, Kelly
Meet my 25dollar Cat piss kiln. It reeeked of cat when I first got it. Cleaned up some wiring and made it mobile. Still only running on 3 of the 4 elements, but she hits 1700 for my ceramic shells. The electric cord for it cost 3times what I paid for the kiln. With ANY electric kiln with exposed elements, SHUT IT OFF before you stick anything in there. It only takes 2 seconds to flip the switch.
Interesting idea too, but yeah I'd prefer to have it dedicated one for convenience and accuracy. thanks. Damn that moldable ceramic fiber you use is cool, never heard of it until today. Epic find Jason, I have seen a few steals on the classifieds.
