Hi everyone, This is my first post and my first foundry build, certainly looking forward to it! I'm trying to use what I have laying around, one thing is a old standup 26 gallon air compressor tank with wheels. I'm planning on using ceramic fiber insulation 2-3" and a layer of castable refractory. I'm concerned that the rubber tires my be affected by the heat, I suppose I could fabricate some metal wheels if I had to. How much heat can I expect on the outside of the foundry?
I put a set of plastic training wheels from one of my kids' old bikes on mine, which is lined with 2" of ceramic fiber coated with about 1/4" of satanite. So far, no problems at all. But they do stick out to the side a bit, the way training wheels do... Welcome to the forum. Good luck and post pictures! Jeff
My furnace is fairly small, but it's got about 2" of inswool and a layer of satanite. I can run it for a couple of hours and even then it doesn't radiate enough heat to melt nearby plastic. That's at aluminum temps.
I used rubber wheels on mine for quite a while. They did fine unless you opened the lid so that the hot side of the lid was "looking at" the tire. Radiant heat from the lid will quickly overheat it with a resounding and attention-getting kaboom. To prevent that I just laid a piece of aluminum on the tire and it effectively blocked and reflected heat. Direct heat radiating from the furnace body warmed the tires a little, but not much. There was about 5 inches space between the walls of the furnace and the wheel and tire. Currently, I remove my wheels while the furnace is in use mostly to get the whole works lower by 5 inches since I use 10-inch wheels. I just make sure it is easy to pull the pins and slide the wheels off the axle. Turning the axle down a bit so that the wheels slide on and off with a somewhat sloppy fit is a plus. No need for a close fit on the axle for the little bit of rolling around you will be doing. I use the removable handle on the furnace (think lawn mower handle) to lever up the furnace and block it to slip off the wheels. Then the furnace rests on its frame on the ground. It is good to be sure the frame is broad enough to support the lid when it is in its raised and off position. Welcome. And good melting. Denis
Man thinking I should be better off than i thought. I might build the platform inside a little higher than the wheels, and yes keep the lid away from the tires and I will surely cover them. Thanks guys! So my next concern is the size of the air tank, it looks about 16" o.d. I've read that you typically build to your crucible. I want to start slow and small but I really dont want to build two back to back. Whats the max and minimum clearance crucible to foundry wall I need to consider? I imagine a small crucible in a large foundry doesn't do well. Is there a good reference I can use to find these recommendations?
Welcome Smokey, What you're building is a furnace which will be used at a foundry. My primary furnace is a beer keg about the same OD as your vessel. 2" of wool and a hot face of satanite will give you about 11+" bore. See the link in tobho's signature above for a proven build. I burn oil and max out at #18 crucible (Legend Mining budget graphite crucible). My hotface is 1" dense castable so it holds up better against tool abuse than satanite probably would, so any crucible less than 8" OD would probably be fine. Smaller only means a decrease in efficiency but your wool furnace would still be plenty efficient even with propane. If your going to do alot of A6 size stuff you might be better off building a smaller one too just for that purpose but you can cross that bridge when you get to it. Your tuyere (air/fuel pipe pronounced tweer) will be around 2.5" diameter and should come in about 1/2" off the floor (my opinion). Your crucible will sit on a plinth that keeps the base of the crucible just a bit above the tuyere so it's not getting direct blast from the burner. So whatever your max crucible diameter is, take that crucible's height, plus the plinth (3-4" or so), plus about 2" between crucible rim and furnace lid. That should determine your bore height. Add the thickness of the floor and that will give you the shell height. Pete
I use something similar to this trolley to move the keg based furnace around, the trolley has four air filled tyres to spread the load and the frame is made from 1" square hollow steel tube. I made the trolley quite tall so it had leverage for lifting fridges and it has a wedge shaped sheet metal nose to slide under things easily. It wasn't made specifically for the furnace but it does work well.
My A6 furnace is a propane tank, 12" shell with 2" of wool and 1/4" Satanite hot face. My A10 furnace is a 14" diameter by 15" tall body with 2" wool and Satanite hot face plus a 4" lid. Both of these furnaces weigh less than thirty pounds so no wheels needed, I just carry them around.
My smaller and most often used furnace is in a 15" OD container with 2" (nominal) of fiber and a thin layer of satanite. I ususally use a #6 crucible but when I built it I made sure I could use my #12 in it if I was running propane. There's enough breathing room to burn oil if I use a smaller one, but I rarely bother setting up the oil tank to do so. (My burners run both; drip-fed waste oil or diesel is optional but propane to at least preheat the furnace isn't). I can (and have) tossed that furnace in the back of my van easily if I need to take it on the road. The big furnace can take a much bigger crucible than my #12; it has a 12" bore that is honestly way too tall for that crucible, but one day maybe I will have one big enough to take advantage of all that space - I built it to last, therefore also to leave me room to grow into. It is pretty slow to heat up on the first melt, with its 1" thick layer of dense castable refractory in front of the fiber blanket and all that empty space in it. But it also holds its heat well if I am doing back to back melts. It can take a lot more abuse than the little one, but it is definitely way too heavy to call portable. General wisdom around here is that for melting with propane you really dont need much more "breathing room" around the crucible than is required to fit your crucible tongs in and out to place or pull the crucible, while a waste oil burner wants more like at least a 2" gap between the crucible and the furnace bore. More gap is ok, but a lot more gap wastes fuel in heating up all that extra space. Jeff
