Foundry From Scrapped Oven for Cheap, Clean Castings

Home-built foundries are a popular project, and with good reason. Being able to melt and cast metal is a powerful tool, even if it’s “only” aluminum. But the standard fossil-fuel fired foundries that most people build are not without their problems, which is where this quick and clean single-use foundry comes into play.

The typical home foundry for aluminum is basically a refractory container of some kind that can take the heat of a forced-air charcoal or coal fire. But as [Turbo Conquering Mega Eagle] points out, such fuels can lead to carbon contamination of the molten aluminum and imperfections when the metal is cast. With a junked electric range, [Turbo Conquering Mega Eagle] fabricates a foundry that avoids the issue in an incredibly dangerous way. The oven’s heating element is wrapped around an old stainless saucepan, fiberglass bats from the stove insulate the ad hoc crucible, and the range’s power cord is attached directly to the heating element. The video below shows that it does indeed melt aluminum, which is used to sand cast a fairly intricate part.

We can’t see getting more than one use out of this setup, though, so it’s only as sustainable as the number of ranges you can round up. But it’s worth keeping in mind for one-off jobs. For a more permanent installation, check out this portable propane-powered foundry. And to see what you can make with one, check out this engine breather cast from beer cans.

[via r/Metalworking]

32 thoughts on “Foundry From Scrapped Oven for Cheap, Clean Castings

  1. For extra safety, he made his molds inside a plastic container… *facepalm*
    Anyone know what the final product(s) is/are? Look like they might be for a lathe, or possibly a filament extruder.
    I didn’t even know you could bend heating elements like that. I thought they were filled with some kind of brittle, ceramic material.
    Other than the fiberglass being torn to bits, what would make this method only last a few times? “The Art of Weapons” made an electric foundry from a kiln element and fire brick. If you used fire brick instead of the fiberglass and powered the oven element with a PID thermostat, it seems like it would be just as sturdy.

    1. Speaking of PID thermosats, does anybody know a good, cheap way of electrically measuring temperatures up to 1500 deg F? All the thermocouples I’ve seen top-out below 1200.

      1. Most thermocouple types are useable to higher than 1200F. K-couples (the most common off the shelf, included with many multimeters), for instance, top out at about 1350C (which is about 2400F)

        The real cheapies (often supplied with low end meters) aren’t insulated for high temp, and are often made using transmission wire, which is less expensive, but not as accurate when used to make the junction.

        Good couples are still pretty cheap, at less than US$7 for a 300mm, ceramic insulated K-type probe (air/gas use) from McMaster. Controllers are not expensive to make, but are a bit pricey to buy. To just measure temp, many multimeters have it built in, and dedicated units show up various sites regularly. I just picked up a backup unit for less than US$10.

        1. I’ve just hooked up an ebay bargain kiln using a $20 PID and $5 K-type, the ones which withstand 1200degC are harder to find (especially as long probe type) but they’re out there, and not noticeably more expensive.

          I did splurge on some non-ebay relays to switch the 240v @ 16A, because I like my workshop not on fire.

      2. Find a local ceramics shop, they’ll have k-types which will go up to kiln firing temperatures, which melt most common metals except steel. Locally, I think I got 2 for $15. I don’t tend to see them online for that price. Here’s basically what I got: http://www.bigceramicstore.com/thermocouple-type-k-6-in-8-ga-open-element-kiln-mount-skutt-pn-1515.html (at double the price)

        You can extend that with a more conventional thermocouple wire. You shouldn’t really use a different metal as it can throw the calculation off. You can get that if you don’t have other sources, by taking apart a lower temperature thermocouple, trim the end off and you’ve got the right type of wires.

        If you do use another metal, like copper, make sure it’s the same metal, and that the leads are the same length and temperature as where you record them. As you’d be actually creating 2 more thermocouples with those connections. At one point, I tested this. I measured things two comparatively, up to as close as I was willing to go to the limit of insulation of one thermocouple, and the temperature difference was been minimal (2C at up to 400C, or maybe 300C), if the copper wire connection is in the air where the sensor is, as opposed to in the heat, so there’s little to no temperature differential along the junction and copper wire (and thus no real induced voltage on that thermocouple junction. Here’s a video showing how it can be thrown off: https://www.youtube.com/watch?v=s4V-j-BZ75A .) I’m not saying you have to get thermocouple wire, or scrap a low temp thermocouple. However, as always, you need to be aware of the issues, if you don’t. In one use, If I’m at say 700C, the +/- a few degrees doesn’t matter too much for most applications, so I do use copper wire, as I didn’t have any other wire when I started the project, and as it works, I haven’t bothered to change it. (I’m using a dumb system on that, so far as opposed to a PID drive.)

  2. Not being capable of waiting for your casting to cool down seems like a negative indicator for this kind of work…

    The video says that there’s a limit to how much you can melt with an oven element wrapped around a bowl. This isn’t technically true. How much you can melt depends more on the insulation than on the heat source. If you have perfect insulation, the time it takes to melt metal is proportional to the weight, so it’s just a question of not losing more heat than you’re putting into it.

    In addition to not contaminating your metal with carbon, electric heat is a LOT more efficient. All charcoal- and propane-fired foundries need airflow to support combustion, and this means that there’s constant airflow REMOVING heat from the foundry. Electric foundries can be closed (like an electric kiln, and those can get VERY hot using household electric power), so they can keep getting hotter until something melts. Usually you want this something to be the metal you’re trying to cast rather than the components of the foundry, but for aluminum, zinc, and Al/Zn and ZAMAK alloys I think the components used in electric ovens are sufficient. The heating elements regularly get up to orange hot in everyday use, and will do this reliably for decades. This is well above the temperatures you need for these metals.

    For this reason, I’ve been toying with building an electric foundry. And by “toying”, I mean that I’ve bought a hotplate that has a solid cast iron heating surface, and a roll of ceramic wool insulation. My “other” objection to most of the DIY foundries I’ve seen is that they use massive chunks of some kind of refractory material as their main structure. When it comes to insulation, massive is not good. My plan is to use something like a paint can for the outer shell, mount the hotplate element inside that on ceramic risers, and rely on the ceramic wool to maintain the inside shape. Yes, plaster and sand and cement and the like are cheaper than ceramic wool, and they do provide some structure (up until they start to crack up), but they soak up a lot of heat, and unless you can whip them up into a foam (and have them set that way), they also conduct a lot of heat. So I agree with [Turbo Conquering Mega Eagle] in his use of lightweight glass wool over refractory mixes.

    I’m wondering what the purpose of the bowl is, though. If the oven element was wrapped around the crucible itself (the can, that is), then allowed to relax a little from there so that the crucible could be removed, you would have a cylindrical space slightly bigger than the crucible, leading to even quicker melt rates. Keeping the heated volume small minimizes the amount of outer area exposed to ambient-temperature air, and therefore the less insulating material you need for a given heat input and target temperature.

      1. Maybe. Seems like a commitment to me, and I don’t have a lot of time to spend on this particular project. If and when I move it to the “front burner” (pun fully intended, with no apologies), then maybe.

    1. Ceramic wool and refractory cement/bricks can have similar thermal mass and insulation properties, but they’re used for different physical situations. We turned a 20′ shipping container into a boiler using three layers of insulation – ceramic fiber batts, refractory brick, and refractory cement with stainless “needles” mixed in. There was a second type of brick used for wear-prone areas, which is maybe what you’re thinking of – it was heavy and less insulative than softer refractory insulation.

      1. I was talking about the DIY projects that cast the foundry out of a mortar-like mix, usually of plaster, sand, and sometimes portland cement. The low-density firebricks are much lighter, but I’ve just seen to many examples of them crumbling.

        And um, that sounds like a heck of a boiler.

        1. Aha. Yeah the light-density blocks are fragile. We were only burning wood for fuel and never had the output side of the boiler over 230 degrees C but it still took 4 days to cool down with all the doors open before we could go inside. Coincidentally, it was the same power as for a hospital incinerator…

    2. Electric is cleaner but you’re limited by your electric service. Typical US ovens are 220/240 60A, 14kW. A low pressure propane regulator can deliver 60k BTU/ 17kW, high pressure reg’s obviously give more BTUs. For the DIYer who doesn’t want to pay through the nose to upgrade their electric service (100 & 200A service are the norm) it’s easier to build a bigger furnace using propane/waste oil. You can also move the furnace away from buildings to keep the Fire Marshall happy.

      1. “Electric is cleaner but you’re limited by your electric service.” No, you’re not. As I said, lower-power heaters don’t limit the amount you can melt, just the time it takes to melt it, as long as your insulation is good. And sure, you can get tens of thousands of BTUs out of a propane burner, but most of that heat is lost out your vent outlet. The heat of fusion of aluminum is 398 KJ/Kg, which is about 110 W*Hr/Kg. This ignores the heat it takes to get the metal to its melting temperature, but that is much lower than the heat of fusion, so I’m being lazy.

        Based on that, an 1100W element can melt a kilogram of Al in six minutes, assuming perfect insulation. How hot you can get in reality depends on the equilibrium between your heat input and heat loss through the insulation. Since heat loss increases proportionally with the difference between inside and outside temperature, at some temperature the input and loss will be equal, so the foundry will never get hotter than that. How much metal you can melt in a specific amount of time depends on the heat input, but the temperature you can melt at depends as much on the insulation as the heat input.

    3. What I’d suggest (and what I’ve done) is go find a nice 110V kiln, and I’ve been adding things so I can use it both for burnout and melting. I’d like to get a second kiln one, as usually a simple ceramic hotplate has been used for burnout so far.

      It’s a little more expensive than DIY, but watching craigslist, I got a nice one that I can take places (like the local makerspace for example), and run pretty much anywhere in the US, for $150. (Also included some ceramic supplies.) Actually, just saw another 110V, when I just checked, for $100. Which I might look into getting, though it’s a bit of a drive.

      To get back on track, it will work basically as is, and it’s probably got better insulation than you’ll do on your own. (I have also built one based on charcoal, with cast refractory providing a lot of it. Moving that is one hell of a pain. It’s far smaller than my Kiln, but far heavier, and I don’t think it’s as well insulated.) You can, if you have the money buy the type of blankets they use in those kilns, but looking into it, it was far cheaper (and easier) to buy a finished kiln, and hack it.

      1. I almost bought a kiln at one point, and I still may end up doing that instead of hacking something together, especially after reading your comment. You mention using yours for burnout and melting, so I’m guessing you’re doing lost-wax, not just lost-styrofoam (most people just let the molten aluminum burn out the styrofoam), and probably other metals besides aluminum, where a kiln would be a big advantage over a merely-red-hot foundry. I’d need to find a pretty small one, though – I don’t have the space it takes for most of the kilns I’ve seen.

        It’s great to hear somebody verifying my claim that having only standard household electric service does NOT force you to resort to charcoal or propane to melt metal. It’s also good to be reminded that hey, there are some “hacks” that require only minimal hacking, and in the easy direction (e.g., adding a controller to get to specific temperatures BELOW its intended range). Yours sounds like an elegant solution.

  3. While this is a nice, clever hack, it is a bit dangerous. Oven heating elements contain a nichrome coil inside a metal tube, with a separator keeping the two apart. I’m not sure what the separator is made from (at the point where the electrodes enter the tube, it’s ceramic), but straightening and re-bending the tube can damage the separating material, so if you’re not lucky, the coil contacts the tube, the tube contacts the pot, the pot contacts the can, and if you pick up the can with pliers, that contacts YOU. Which even aside from the electrocution hazard can cause you to jump and spill or splash molten metals onto yourself.

    1. I thought exactly the same thing, and it is possible that [turbo conquering mega eagle] did too, because he made a point of throwing the electrical plug on the floor in view of us before picking the thing up.

  4. Please is anybody really want to get into metal casting for softer sake visit the website of Budget Casting Supply. Read the whole site. This is super dangerous stuff. What he is doing can kill you in so many ways. Start on the right foot and do it right. It is not very expensive but you need to know how things work for safer reasons. Generally aluminum melts at red heat. Funny thing is that aluminum does not glow red from heat. It stays silvery. ZAMAC was mentioned by a reader. This is an excellent material but being a aluminum and zinc alloy it suffers the zinc heating problem which is is you get zinc too hot and breathe the fumes, younpretty much are going to die, and that heat point can come on at any time. Such as zinc splashing out of the pot onto a heating coil and there you go. Toxic cloud. Also use tongs! A real crucible is dirt cheap or a welded steel one can be cobbled together from scrap. Stainless steel is ok but you. Never know what’s really in cookware. It will fracture eventually. HE appears to be using a lost wax kind of mold based on the amount of flame and smoke escaping. This is extremely dangerous without tongs because the escaping has can blow the molten metal right back at you! You want to be out of the way and with at the very least a leather body apron and face shield.

    This video is exactly the wrong way to do this! molten aluminum can hurt you fast! I will never forget the first burn I got through my extra thick casting gloves. And it was only the tiniest of dribble.

    1. While one can easily get zinc fever if not being careful it is far from a death sentence – the usual treatment is about the same as for a normal fever (rest and hydration). Zinc isn’t really toxic and the reaction are from metal fumes irritating the lung tissue, not from a specific toxic effect. Unless one really make an effort working with zinc is a minor danger and not a lethal one, AFAIK the deaths associated with zinc fever were people with previous lung problems inhaling massive amounts of fumes.

      That doesn’t mean one shouldn’t make sure to handle zinc (and other metals) correctly. Just the heat can kill directly or indirectly (don’t drop heated/melted metal on flammable objects).

  5. So much stupid in this one, how did he propose to leap backward from that position if the casting went feral on him? The end result does not justify all of the completely unnecessary risks he took. Keep that up mate and one day you are going to burn your balls off no matter how big you think they are.

  6. I’ve written about this on previous casting threads here, and people seem to appreciate it, so: I did a ton of casting in the late 1980s and early 1990s and like everyone else started with pop cans. When I got to needing more than about 7-10kg of material per week there was no way I could supply it with pop cans so I went to a local auto salvage yard and started buying pistons. It was revolutionary. Aluminum alloys optimized for casting are so nice — and the material is bulky so you don’t lose as much to oxidation as you do with high surface area pop cans. Nearly pure aluminum, used in pop cans, pours more like honey, where silicon-based casting alloys pour like water. Far better surface texture, better thin-section castings, stronger finished material. Most salvage places don’t have big bins full of pistons. I ended up buying whole trashed subaru engines, and breaking up the heads and aluminum block. I built something out of some old bricks with some fiberglass inside and three propane-powered torches firing into it, and would heat a big chunk of aluminum until it started to sweat lower melting point alloys out in fine beads on the surface. Then I’d pull it out and drop it on a big steel plate on top of concrete (no hot aluminum straight on concrete: concrete has enough water content that it’ll have a steam explosion and blow a combination of concrete chips and hot aluminum into your face: wear a face shield, not just safety glasses.) Aluminum is hot-short: it gets brittle (for lack of a better word) when it’s near melting so it crumbles like cottage cheese. Then I could take the small chunks, put them in a crucible, and batch-cast them into muffin tins, leaving me with perfect ingots for when I had a casting project.
    There are inductive casting setups for jewelry work that have the whole system: crucible, heating element (well, inductive coil) and insulation mounted as a group on a pivot so when the stuff is ready to pour you tip the whole works on the pivot and pour it into your mold. I think a build like that would work well for making this setup reusable.

  7. Did this a few years back. Those electric elements are a PITA to bend easily – it is possible, after all that’s how they were manufactured in the first place. However, the elements only survive a couple of melts, since they are running much hotter than they normally would in an electric stove application. I gave up on them and used a propane burner instead – much more reliable, quicker, and pretty clean.

    Yes, important point about choosing the right aluminum for casting. Extrusions are pretty poor, stuff that’s already been cast (engine blocks, heads, pistons….) is much much better. Degassing helps hugely as well.

    1. The more you know, the more some things look absolutely insane.

      Electricity is a great tool. So far, our makerspace has avoided any issues. Part of that has been because of people basically stamping out bad ideas before they happen, or should they be made, giving the people who make them no end of a hard time. (Yes… a 120 V source will directly cook a hot dog… no, it is *not* a good idea.)

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