Hi all, Greetings from Montana! Hoping to get some advice from folks here so I can stop going down so many rabbit holes. I've been slowly pulling together the pieces to make a home foundry to cast my bronze sculptures. I've done some apprentice work at a local foundry where I have cast some of my pieces in the past. I currently have a small setup to do small jewelry stuff but want to do bigger pieces. I'm stuck right now on the burnout kiln. I picked up a used Dunan EA-1029-2 ceramic kiln that needed some work but I was hoping to use it as my burnout kiln. It's 240 volts, 45amps, and 10,800 watts. Its diameter is 28" (10 sides, each around 8") and its interior height is 28". There are 12 elements split into 3 parallel sections, two of the elements are broken and need to be replaced. The others are intact but are reading a higher resistance than 3.68 Ohms than what the old manual says they're supposed to be at (they're around 4.2 Ohms). So guessing they should be replaced but I prefer not to if I can help it. While I can buy replacement ones from Paragon, they're $60 per element and I'm hoping I can do it myself for cheaper than that. I bought a ramp/soak pid controller, 2x 40amp SSRs, and a K-type thermocouple to upgrade the electronics. For doing the wax burnouts, I'm putting a vent hole in the lid along with vent holes already in the sides to help vent out the wax. I feel pretty confident doing the electronics upgrade as I did a similar one on my small burnout furnace. But I feel like I'm running myself in circles researching how to make my own heating elements using Kanthal or Nickel-Chromium. While I've read through many posts here (and spreadsheet calculators), I feel like I keep hitting a wall trying to figure it out. I'm hoping someone here might have some advice on helping me get this thing working for what I need and hopefully not break the bank getting it what I need! Many thanks for any help anyone might have! Kiln Manual https://corp.paragonweb.com/wp-content/uploads/W-EA-DA-1029-24-Body-Parts.pdf https://corp.paragonweb.com/wp-content/uploads/W-EA-DA-1029-24-Control-Panel.pdf
Hi Scotty, Welcome. I use a resistive electric foundry furnace of my own design, buy resistive wire by the lb, and wind my own coils. The easiest thing to do, is measure the wire (gauge) and coil diameter of you existing resistive coils, then see what length of wire will give you the approximate resistance you need, then see how that fit's with your existing coil shelf. I buy mine here but many pottery and kiln shops have similar offerings. https://euclids.com/collections/element-wire If you click on the links on that page, it will take you to the wire properties, namely resistance/ft and lbs/ft for a given gauge. You can use the spreadsheet calculators but if you measure wire diameter, it will most likely either be NiCr 80/20 or AlFeCr (aka Kanthal A1). You calculate the total length of wire to get your desired resistance and then calculate the close wound length of the coil. You should be able to fit it in the coil shelf of your kiln (shelf diameter x Pi) with a stretch between 3:1 & 5:1 beyond the close wound length. At the moment, KA1 is about $50/lb regardless of gage. The links will tell you how many ft/lb for a given gage so you can estimate cost per coil. My coil winder is simple as can be..... a piece of steel tube, a wooden guide block, and a cordless drill. See here. http://forums.thehomefoundry.org/in...w-resistive-electric-furnace.2874/#post-53537 and ..... Also see attach "Kanthal handbook" Best, Kelly
Hi Scotty, nice find with the old kiln. you may want to look into a way to catch and remove the first run of liquid wax before ramping up to burnout temps. I have seen the literature for side-loading kilns where there is a tray to catch wax that is removed before burnout temps are reached. https://forums.thehomefoundry.org/index.php?threads/burnout-in-a-ceramic-kiln.2909
Kelly, Thanks so much for your reply, I've read a number of your posts and was already planning on making your jig! Appreciate the links and the PDF! I measured my existing element and the coil was about 6ft long. The inner diameter of the coil was .264", the outer diameter was .409", and the length of one complete revolution of the coil was .404". From a rough calculation of the straight length of the 6ft coil, that comes to about 18.5ft of straight wire. According to the Euclid site table that shows resistance/ft for Kanthal 14 ga, it comes out to 3.94ohms for 18.5 ft which is close to the 3.7ohms listed in the manual. Does it matter that it's a little over what is recommended? Or should I just cut the correct length to match it exactly to 3.7 (which would be 17.3ft of wire)? I'm guessing there is a little wiggle room with that number. I ordered a couple of rolls of wire, so I'll start making the jig and patiently wait for the wire to arrive. I've got some wax chasing and adding sprues to finish before I fire it up so I guess I have time. Tops, thank you as well for the advice. I have a deep baking pan with a steel grate over it that I attached wire to so I can pull it out once a majority of the wax melts out before I ramp up the temps. I think that will work, but I guess I'll find out once I try it. Appreciate the help and encouragement, I'll keep you updated on the progress.
I'll think out loud with you a bit here........ I'm assuming this means you have 4 elements in series, and each of those four are then connected in parallel......and this is 240vac single phase. Is that correct? As long as the variation in stack up of the 4 elements in series doesn't exceed your electrical control capabilities, I'd say it's not too critical, maybe be within 5-10% of target. As elements age they tend to get consumed which makes the resistance go up and power go down. You mention several already measure 10% higher.....they're probably on their way out. It can be a little tricky to measure with a cheap ohm meter because the surface of the wire oxidizes. You'll get a more accurate reading if you polish the contact point. Also, keep in mind resistance will go up 3-5% with high temp operation. If you have four 3.7 ohm resistors in series, that's 14.8 ohms and at 240vac 1ph will be ~3.9kw per, x3 = 11.7kw, probably about 96% of that at temp as resistance goes up so about 11.2kw....... a little more than the 10.6kw but in the ballpark. Practically speaking, you'll probably use a 1/4" rod for a winding mandrel. 14ga is about .062D so the OD would be .375" but that's a pretty tight diameter for 14ga and you may get a little spring back and land pretty close to the .409 you measured. If you wind 17.3ft (207.6") on a 1/4" mandrel, that will be about 161 wraps (207.6/.409Pi) and since each wrap is .062 wide that means the close wound length will be about 10.0" (161*.062). So if the kiln ID is 28"D, 28*Pi = 88" that means an 8.8:1 stretch of the coil. ........or 10 sides at 8" = 80" means 8:1 stretch. That's quite a bit of stretch. Probably too much. The Kanthal handbook says it should be between 3:1-5:1. Are you sure the wire in your kiln isn't 12ga (.081"D and .13ohm/ft) instead of 14ga (.062"D .21ohm/ft)? That would get you closer to <5:1. Or, it could be just NiCr instead of Kanthal A1 it would be lower resistance and do almost the same at 14ga. You should be < $10/coil if you wind your own. Best, Kelly
Thanks for the additional thoughts, Kelly. I feel like Elmer Fudd from going down so many rabbit holes. This is correct. I canceled my Euclid order since you are correct in that 14ga is going to need too much stretch if I'm following the Kanthal handbook (3:1 - 5:1). I triple-checked the measurements of the wire already in there, and it is 14ga, so guessing it might be NiCr. I also did more specific measurements of the kiln dimensions, and where the wire sits in the kiln is a diameter of 24.625" (77.3" circumference). I also took into account the length of wire that is not coiled but exits the kiln to where it's wired up (3.25" on each end, 6.5" total). So to hit my 3.7ohm and get within the 3:1 - 5:1 range, I'm looking at either 12ga (3.8:1) or 13ga (5.2:1). I think I'll end up going 13ga as it fits the budget a little better. I'll update how the progress goes!
Owing to the fact you will have a mix of old and new coils, I don't think it matters if some are NiCr and others are AlFeCr as long as the resistance is on target. If you were to replace them all. I'd go with the latter. As far as the length that exits the kiln, I'd recommend you twist double or triple leads on that portion. The big reason for doing so is reducing the resistance by 3x will also greatly reduce the temperature at the junction with the electrical conductor which will keep it from failing by alloying with the resistance wire at high temp. Check it out here: http://forums.thehomefoundry.org/in...w-resistive-electric-furnace.2874/#post-53537 Best, Kelly
I had to replace my elements a few years ago and this thread discussion may be useful for you to scroll through for calculations and how to pick wire. https://forums.thehomefoundry.org/index.php?threads/clay-melted-into-my-kiln.487/page-6#post-24426
Current = Voltage divided by Resistance So for the listed resistance of 3.7 ohms Assuming 110V (one half of the 220V input voltage) That's 29.73 Amps You new coil of 3.94ohms with a voltage of 110 comes to 27.92Amps So you should be good. The higher the resistance the less current that flows. In theory that would mean the lower the max temp would be. but in practice a few tenths of an ohm isn't going to change it that much. It's always safer to go higher on the coil resistance than lower. At least from the electric controller's point of view.
Thanks for all the replies! I finally finished upgrading the kiln last night after waiting for all the various parts to come in. I ended up going with 13 ga Kanthal which I ordered from https://resistancewire.com/. Their prices were reasonable, they had various length rolls I could buy so I could get close to what I needed and had very little excess waste left after cutting the lengths I needed. They were friendly and easy to deal with too. I ended up replacing all 12 of the coils, as most seemed like they were quite brittle. I coiled these using a simple wood jig thanks to Kelly's helpful video. When all was said and done, each coil measured 3.8 ohms, close enough to what I needed! I built a new control box using an Auber PID (SLY-2352), 2 40amp SSRs, 3 rocker switches for each section, a redundant breaker, a power button, and a few fuses for each section. The 20-minute initial test run ran great and all seemed to work as it should. Tomorrow I'm going to attempt my first burnout, an eagle sculpture I completed recently and just finished the last dip in my slurry. I've got a few vent holes and a tray to catch the wax, all seems ready. Fingers crossed it goes well! Thanks again for all the advice, it was much appreciated!
