An electric arc furnace is a type of furnace that heats up materials using a very high current. The rods (which are made of graphite for its semi-conductive properties) heat up and create a plasma that can be directed to melt metals. Although electrical arc furnaces (EAFs) are reliant on large amounts of electricity, it is fairly cheap and in certain circumstances, cheaper than using carbon fuels. In this instructable, I'll be showing you how to make a DIY EAF (acronyms galore) with materials you can find at home or at the very least, a local hardware store. Be aware that this is very dangerous and should be dealt with extreme caution and awareness of said dangers, which are very likely to be life-threatening.
This idea was based off a multitude of things and sources:
1) My innate (but unfortunate) tendency to end up electrocuting myself
2) Having knowledge about resistivity and all that is included
3) This video:
4) And most importantly, these videos
Quite a few pictures were taken directly from Mr. Thompson's videos, as his videos are very clear and concise, and we opted to use them over our own pictures. However, the procedure is practically the same and any differences are noted.
Step 1: Gather the Necessary Materials
As always, you'll want to gather up the materials and tools for the job. You will need everything listed below. Some of the materials can be subject to change depending on how you want to build your furnace, but I specifically used the following. This project deals with high voltage and current, as well as extremely bright electrical arcs, please take caution when building and using this. Basic tools like a handsaw and power tools will be used, which will require safety precautions. So first and foremost, grab a pair of safety glasses, some insulated gloves, a weldingmask and get to the workshop.
What You Need:
The Arc Welder
- 10-14 ft of 8 gauge stranded copper wiring (coated)
- 1x Microwave transformer (scrapped from a microwave that was thrown out)
- At least 2x 6V heavy duty lantern batteries
- 2x Vice grips
- A foot of copper tubing (half-inch diameter )
- 2x Half inch hose clamps
- A roll of electrical tape
- Miscellaneous pieces of wood (2x4's work fine)
- A Variable AC/DC Power Supply or source of power (2300 watts of power is about the minimum amount of energy required to sustain an arc, and about 100A if you plan to just use current to make a metal melter)
- 1x Aluminum silicate or fireclay refractory brick (note that it should be a soft material in order to allow for easy cutting)
- Machinery and power tools to cut the brick
- Power drill
- Drill press
- Round file
- Filter mask and safety goggles (you DO NOT want to inhale or get the dust in your eyes)
Approximate Cost of Project:
The fun thing about DIY projects is that you can scavenge most of the parts from other things or find them laying around your home. For this project, the only thing we actually bought was a pair of vice grips and 14ft of copper wire. However, if you don't have any of this we have included the approximate price of it all.
$7 of 8 gauge (AWG) stranded copper wire (usually runs for $0.49 a foot)
$8 for a two-pack of 6V lantern batteries
$10 for a pair of small vice grips
$2 for a pair of hose clamps for the vice grips
$1 for about a foot of copper pipe
$10 a roll of electrical tape
$14 for a 9"x4.5"x2.5" refractory (firebrick) aluminum silicate brick
The microwave transformer can be salvaged from a broken microwave (assuming it's not the transformer that is broken of course) for free. There really isn't another way to get these without making a special parts order or buying a new microwave to tear it out (which is a waste, please don't do that). As for the miscellaneous wood, we haven't counted it, as anything will work as a base plate and the jig can be made with anything you want as long as it fits the dimensions. The variable power supply can range anywhere from $30 to a couple hundred dollars depending on the quality and size. We fortunately already had a few in our workshops (either built-in or stand-alone) so we did not need to buy them. Please note that you will need this to safely (at least comparatively) operate this arc welder/EAF.
Total: ~$52, excluding electricity, labor, time, and tools to build.
Step 2: Transformer Cannibalization and Jig
The first and hardest part of the project is the actual arc welder component of the EAF. Be prepared to fully use clamps, vice clamps, and a bit of brute strength.
The first step is to take your microwave transformer and remove the top part of the contraption. Pry out the two copper coils and magnetic shunts (the metal pieces that separate the primary coil from the secondary coil). The primary coil is the one with the thicker wiring and the two tabs on it. This is the piece that we will need, so take great care when handling it. And make sure that the insulating pieces of paper do not get stripped off. Then, clean out the iron core/shell of the transformer. Replace the primary coil, but place the tabs/terminals facing down.
Build a wooden “I” shape with the center having the same width (where the core drops into the hole) as the center of the transformer shell. The length of the "I" block should overhang the core by ⅛” on each side. and the height should be less than ⅛” below the height between the primary coil and the top of the iron core. The top and bottom plates of the jig can be screwed on, but we advise using glue as the jig is so small that splitting of the wood is very common (we tried twice before resorting to glue). Place a rectangular piece of paper on each side of the center.
Step 3: Winding a New Secondary Coil
This part is what gives the transformer a bit more "oomf" to it. Also, it allows us to hook it up to our leads to create an arc.
After cleaning out the transformer is done with, and creating an "I" block, place this block into a bench vice and wind your 8 gauge wire around your contraption how many wires high as you can and then repeat for however many layers outward (easier said than done, trust us). Fold the paper over the wiring and tape the sides shut (please do this, it's an integral part of keeping it all together.) Remove the top of the “I” and pull out your wiring in one piece. Tape your wiring so it retains its shape for extra measure.
Place your new secondary coil back into the shell with the wire ends facing out in the opposite direction of the first coil. Replace the lid of your shell that you cut off and glue on with epoxy* or a very strong adhesive.
*Beware, as certain two part epoxies may react with metal and cause possible problems. Make sure the epoxy is safe for metal.
Step 4: Building the Leads
Now we'll start to build the leads that will strike the high current arc used to melt metal. In our case, we can also use our battery parts as the metal to melt.
First, open up your 6V battery, most likely with some pliers, wire cutters or whatever may be at your disposal. After that, cut the wires connecting them and pull out the centers of 4 cells to get 4 carbon rods. Clean out the zinc casings and use a bench vice to crush them. We'll be able to melt the zinc casings with it. Save this for later.
Strip about 2” from the wiring of your new transformer. Cut 4 pieces of 1” copper piping and place the transformer's wires into them and crimp the pieces together to create a makeshift lug by sticking the unsqueezed side of the copper pipe and squeeze them shut. Cut 2x 2ft pieces of wire from the leftover 8 gauge copper wire, and strip 2" (from each end) off them as well. Repeat the crimping of the copper piping. Attach the other stripped end to the vice grips using hose clamps. Use electrical tape to secure and insulate the handle areas for extra measure.
Safety: For safety reasons, try to work with only one hand because current can travel through your hands and across your heart with the potential to kill you. You can make a separate rig that holds one of the leads in place in order to accomplish this.
Step 5: Building the Furnace
This is easily the ... well, the easiest part of the project. Just make sure to wear safety goggles and a mask for this, to prevent inhalation of the dust.
Cut brick widthwise into three equal 3” pieces (or 3" from each side and then the 4” mark if you have a 9x4.5x3" block). This should make two furnaces either way. Take the utmost care with the bricks, as they are extremely brittle. For our furnace, we used the middle 3" piece and split it heightwise to provide lids for each furnace brick. If you split the brick into 4 pieces, then the smallest pieces should serve as the lids for the pieces.
Use a 2” forstner bit or a regular circular bit to drill roughly two inches deep into the center of the larger bricks. Empty out the chamber and either file or drill holes on the top of the walls for the electrode leads.
On a side you haven’t drilled a hole into, drill another one at an angle to meet with the bottom of the chamber. On the lids, drill two ⅜” holes into the side one inch from each of the ends. This is a place to put the electrodes into, especially when they're extremely hot.
Finally, connect a power supply (on AC) to the terminals/tabs on the primary coil. With that, you're ready to start operating the EAF. Just make sure to put on a welding mask and wearing insulated gloves. Electrical arcs also emit very intense UV rays, so wearing long sleeved clothing is beneficial to your health. Always include proper safety equipment in case anything goes wrong. Otherwise, happy metal melting!
Step 6: Time & Effort Analysis
The total time required to build the EAF was a little time consuming, based on how we built it and the materials we used. Transformers vary in size and constitution, although not by much. We built it over two months working on it a couple hours every day on average. If we were to fully commit our time, it would take less than 48 hours to complete, taking into account the gathering of materials, time spent constructing, winding the coil, cutting, gluing etc.
Following step-by-step instructions like this will definitely make it easier, as we took our information from a video. Specific materials are not always immediately available if at all, so you have to think of and ponder a myriad of factors into how you need to construct your own DIY project.
Most of the energy and effort spent went into winding the secondary coil and attempting to pack it into the transformer.
Step 7: Improvements
To improve this project, we should have realized that the dimensions of transformers and the amount of wire needed also varies. Our secondary coil could only fit 5 wires high and 3 wires out, while another transformer may fit 6 wires high. The videos make winding the wire seem a lot more simple than how it really went (with blood, sweat and tears). More safety precautions and some sort of case or cover for the EAF could be implemented. Another important factor is that the EAF can only run for about 2-4 minutes tops, whereas any longer would result in the electrical tape and rubber insulation completely melting from the intense heat. Furthermore, the carbon rods end up deteriorating after continued use.
Footnote: Our project failed to work, as we made our tolerances on the "I" block too small, and upon replacing the new secondary coil, we scraped off the insulated coating and exposed the copper wire to the laminated iron shell of the transformer (which is a huge problem for obvious reasons). Another possible issue is due to the sharp corners of the iron core, which also cut into the coating. We will be attempting to redo and replace the secondary coil, and possibly try to file/round the sharp edges. However, the procedure has been fixed for this instructable and should work as intended. We are submitting this for a school project, and plan to complete this and make it functional within the next week or two. We'll be posting an update of the testing soon (with a video).
The electrodes (Carbon/Graphite rods) had a resistance of about 3Ω, and our "failed" transformer had a voltage input of about 5V and an output of 0.1V. However, we found some cuts on the insulation of the secondary coil and opted not to test further due to the definite chance of a short circuit from the coils to the iron shell.
If you have any suggestions, criticism, or concerns, please let us know in the comments. Enjoy!