Melting Furnace
Contents
Disclaimer
General
Current Status
Assembly
Running It
Waste Oil Burner
Links
Disclaimer
This project involves handling explosive gasses and liquid materials that are heated to white hot. I am providing this information as help for others working on similar projects, but that does not mean that I accept the obligation to actually help anyone. I will help if I have the time and the inclination.
Also, I intend that the plans and methods outlined here are to be safe, but that does not mean that anything talked about here is actually is safe. This is the first time I have ever tried anything like this and I make absolutely no guarantee that anything in these pages is correct, accurate, or intended for any particular use. Doing these things wrong can lead to someone's death. It is the responsibility of the person doing the project to thoroughly research what they are doing and act in a safe and responsible way. I do not accept any liability under any circumstances from anyone in connection with this web page or anything else. By accessing this page, you accept that even if you follow these steps precisely, you could still be hurt or even killed. You accept responsibility for all of your actions, even if I direct you to do it.
General
This page gives the details of my latest project. It is a propane powered furnace that can be used to melt aluminum or copper based alloys so I can make castings. I am outlining the project with the intention of helping others to do a similar one. I plan to make simple things such as chess pieces and yard ornaments. I have always been interested in casting metal.
This is the beginning of a journey. 
Apparently.
I am doing my best to source everything that I need from local sources. Lowes has all of the hardware and the sand and portland cement. I tried Home Despot but they have a poor selection of pipe fittings and other materials. I honesty don't know how they stay in business. I have a links section below with sources for everything.
Current Status
I have a working burner, but that's all. I have basically run out of money until I can sell some more whistles. I am abandoning the idea that I will make my crucible. I think I will buy a graphite crucible instead. The steel that I was planning to make would cost about $30 in materials, (plus labor to get it welded up) and a graphite crucible of the same size will cost about $75. A clay crucible would be $40 and a silicon carbide (top of the line) would be about $150. Molten copper will dissolve steel. Or, as they say, it is a "strong solvent". It would be like trying to melt ice in a cup made of salt. It will work a couple of times, but the water will be salty. I want to do really good castings, so I do not think that will be acceptable. So, I am going to buy a crucible that is made for the job instead of trying to cheap it together.
Also, I am abandoning the idea that I will make my own refractory lining for the furnace. I can get pourable refractory for about $130, shipped. That is not much more than it costs for me to try and cheap it together and the result will be much better. So why should I build an inferior tool?
I have also decided to look into making a sheet metal exterior for my furnace. It should be fine. The shell is just there to protect the refractory. It has nothing to do with the actual function of the furnace. I am sure I can make it well enough to be useful.
Assembly
Burner
The burner body is a piece of 1" black pipe. Do not use galvanized. The zinc that it is coated with will burn and give off poisonous gas. I bought a 48" nipple that is threaded on both ends. The burner body is 10" long. 1" sch 40 pipe has an outside diameter of 1.32" and an inside diameter of 1.05". On the threaded end, I will have a inside threaded union and a plug that closes the end of the pipe. I drilled 8 3/8" airholes in the body of the burner and a hole for the jet in the end cap. The jet is held in place with a set screw. The jet is made from a 1/8" sch40 nipple 4" long with an ID threaded union and a plug. The jet orifice a #60 hole (really small) in the end of the plug. The jet is located just at the flame end of the air inlet holes. Adjusting the exact location of the jet is critical to control the fuel/air mixture. I had to play with it a bit to figure that out. Once it's adjusted, it does not need to move. If there is any interest, I will post a detailed construction article. Anyone can make one of these burners if they have a drill press.
I still need to buy some high pressure LP gas hose.
Layout overview
Valve closeup
Looking into the flame end. Notice the step-cut flare.
Tank and regulator.
Flame at 5 PSI. (ho hum)
Flame at 55 PSI! Now that's what I'm talking about!
LETS MELT SOMETHING! YAY-YA-BABY-YA! It was so hot that it raised the temperature in the garage by 10 degrees in less than a minute. Just needed some small adjustments. It really roars. Nice neutral flame, too. Not too lean not too rich. Just right. I think this is more than enough power to melt copper or bronze. Aluminum melts at a much lower temperature. It's probably not hot enough to melt iron. I added a different spreader on the end. The spreader is required for it to work in open air. It slows down the fuel/air mixture (FAM) so that it can burn. The FAM has to be moving slower than the flame front. But the FAM has to be moving fast enough so that it does not burn inside the tube. The spreader makes that work. It also will burn low, too. Seems like it will burn down to about 1 or 2 lbs, but the gage does not go that low. That means I could use this burner on a blacksmith forge. A good one will have a lever of a foot pedal to you can press to make it burn high and when you let off it burns at idle, just to keep the forge warm and not waste fuel. All totaled, I spent about $60 on the burner and about $110 on the tank and regulator. I bought everything new except the air nipples and set screws, which I had from another project.
Furnace Body
I am going to make the shell out of sheet metal. There is no point in destroying a perfectly good tank to make the shell. I am probably going to buy some of this stuff: http://www.budgetcastingsupply.com/Castable_Refractory_Kast-0-Lite-26-LI.php It can withstand temperatures higher than I can make and should last for years.
How much refractory do I need?
The volume of a cylinder can be calculated as (Π x (d/2)2 x h). If there is a hole in the cylinder (the body of the furnace, for example), then you just subtract the volume of the hole from the volume of the outside dimension and that gives the volume of the furnace wall. There are 3 cylinders in my furnace design. The lid, the body and the bottom. I have written a small python script (you can get it here) to play with the numbers to get it as close to an even number of bags. Any furnace that is a usable size will need 3 bags of refractory. A made up bag is 55lbs and makes about 1105 cubic inches, according to the seller's web page here. The script is set up for an A8 sized crucible. You can mess around with the numbers until you get something that suits your needs. You can see a table of crucible sizes here.
| Outside diameter | 9 1/2" |
| Total height | 17 1/2" |
| Lid and bottom thickness | 4" |
| Lid vent size | 4" |
| Inside height | 8 1/2" |
| Inside diameter | 9 1/2" |
This leaves a deficit of 1 cubic inch of material. That will be more than made up by the burner port.
Crucibles
I think I am going to buy a crucible from a reputable dealer. There is so much risk when dealing with molten metal, that it just does not make sense to fart around with trying to do it on the cheap. Here is a link to the dealer I am thinking of using: http://www.budgetcastingsupply.com/Crucibles.php
See here for my home made crucible. They work just fine.
Fuel
My fuel (propane) seems to be lasting pretty well. I have run it for about 30 minutes. It didn't just run out all at once. Seems like I have a couple of hours in a 5 gallon tank at 30lbs pressure.
Running it
Lighting the burner is easy. I just hold a bic lighter to the airholes and crack the valve. It just works, which is exactly what I want.
Waste Oil Burner
I made a waste oil burner. The reason I did that is that I really want to melt iron and make cast iron stuff. You can do that with propane, but it takes a lot of fuel and waste oil is (mostly) free. The burner that I made is a BEAST. It will literally atomize a gallon of fuel in about 5 minutes. I have no idea how to test it safely. To get an idea of how much fuel it uses, I put water through it. It makes a nice atomized cloud, but it's so much that I am uneasy about putting somethind that will burn through it. Here are a couple of pictures
The hose connects to the fuel. You can see the air fitting on the other end. The blunt end with nothing connected to it is where the fuel/air comes out.
This is a picture of it disassembled. The whole thing draws a surprising amount of vacuum on the fuel side. It is on the order of 6 inches of water. That means that the liquid can be 6 inches lower than the nozzle with no noticable loss of flow. I am sure it will make a flame about 7 feel long if I were to use diesel for fuel. I think I need to find a way to tone it down a little bit before I think about testing it with fuel.
Construction
The body is made from a 3/8" Tee. The internal nozzle is a 1/8" nipple with a union and a plug. The fitting that holds it in the body is soldered on. Right now, the only way to adjust it is to heat it up and move the fitting. I turned down the plug and nipple so that they fit nicely into the body and tapered the end. Also the plug where the fuel/air leave had quite a bit of turning done on the inside to make room. If there is any interest, I will post more pictures and details. Mostly, I am just trying to give a sense of the size of it. It's about 10" long assembled. The 1/8" nipple is 4" long.
Updates
12/8/2012
I have made over 20 melts now. I have cast both aluminum and copper. The furnace running propane works just fine. I do not have a working oil burner. I really have no way to test it without making more of a mess than I am prepared to clean up. No worries. I will get it working when I need to. For now, melting pure copper does not take very long. Propane works just fine for what I need.
Links
Here is a good link to a site that has a bunch of forges and burners:
http://ronreil.abana.org/sitemap.html
Another good resource for burner and forge designs:
http://zoellerforge.com/index.html
This is THE backyard foundry page:
http://www.backyardmetalcasting.com/
Link to how to make insulating refractory brick
http://www.bioenergylists.org/stovesdoc/Ogle/Clay/MAKING%20LIGHT%20WEIGHT%20REFRACTORY%20CERAMIC.pdf
Where to get yard bags of perlite in Austin
http://www.naturalgardeneraustin.com/
Link to a local place that sells steel here in Austin
https://www.speedymetals.com/
Good local source for fire clay and refractory brick here in Austin
http://www.armadilloclay.com/
I got my tank and regulator here
http://www.austinpages.com/YP/259/1196/
Jewelry tools store, including melting supplies
http://stores.ebay.com/Favorite-USA-18
Casting supplies. I am buying the furnace refractory from here
http://www.budgetcastingsupply.com/
This is an awesome place to go to ask questions about anything related to metal working
http://www.chaski.org/homemachinist/
Other miscellaneous links