View of my furnace running, with investment molds in the foreground:
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419 downloadsMe checking on or poking something:
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492 downloadsTaking the crucible out of the furnace:
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481 downloadsPouring:
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441 downloadsPoured:
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449 downloadsThis is what was inside (16 acorns + gating system):
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468 downloadsAcorn TIG welded to a steel stub (will be attached to a forged branch on a gate):
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462 downloadsA bunch of acorns, ready to be attached to the gate:
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416 downloadsSAFETY
Don’t do this unless you’ve done your due diligence. Ideally you would learn from someone in person, but if this isn’t possible you should read a few books (recommendations at the end of this post) and watch some videos of home metal pours on the internet. Molten metal in any quantity larger than a weld puddle is extremely dangerous, and not respecting it is for a serious accident. If you have questions, ask. Don’t blame me if you hurt yourself.
MOLTEN METAL
Once you have any quantity of molten metal, moisture becomes an extreme danger. A drop of molten metal on concrete (which holds moisture) will turn the water in the pores to steam, causing a small explosion which will propel liquid metal and chips of concrete into the air. Now think about what would happen if you spilled a whole crucible. ALWAYS CARRY AND POUR METAL OVER DRY SAND.
If you stick anything—a stirring rod, a skimmer, more pieces of metal to melt—into the crucible when there is molten metal in it, that object needs to be DRY. This is as simple as preheating metal on top of your furnace while it is running, and holding the end of any tools in the exhaust flame for a few seconds, but if you forget you will cause the molten metal to explode while you are standing there with your face over it. Likewise, your ingot molds (where you pour the leftover metal after filling your molds) need to be preheated on the furnace, or an explosion will occur. ASSUME THAT UNLESS SOMETHING IS TOO HOT TO TOUCH, THAT IT IS WET.
SAFETY EQUIPMENT
Goggles and a faceshield, not one or the other. Thick leather jacket, stick welding gloves, jeans, and heavy leather boots. That’s what I wear. Works fine to protect against the occasional bit of splatter, and at least won’t melt to your skin in a disaster scenario. Always keep a bucket of dry sand and a shovel on hand in case of a spill, and a chill bar (piece of heavy angle iron welded to the end of a three foot rod) to seize up the flow in case of a mold bursting or leaking.
HOMEMADE CRUCIBLES
Because of the serious dangers involved in working with molten metal, I strongly recommend NOT using a homemade crucible for anything hotter than aluminum (ie any copper alloys and cast iron). The proper crucibles will be discussed below with each individual metal, and a suitable homemade crucible for aluminum and other low-temp alloys will be explained.
Proper crucibles are essential, even if you make every other part of your setup:
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First I’ll give a quick overview of some different metals you might want cast, and then I’ll give some details about the general equipment you’ll need to make for a small foundry.
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METALS
STEEL
Alright, so first off, you are probably never going to cast steel at home, and you are definitely never going to make a steel casting the size of an anvil. That’s just reality. Getting a crucible furnace to the temperature needed to pour steel is possible, but it will turn your furnace into a consumable. I’ll address this first, since it seems like a lot of people are interested in casting steel.
Here are approximate melting points of some various metals (all temperatures in F):
Mild Steel: 2750
Cast Iron: 2100
Silicon Bronze: 1800
Aluminum: 1200
Lead: 680
Keep in mind that you need the metal to be superheated a few hundred degrees above these temperatures to successfully pour them, so for example iron will be poured around 2300-2500 (hotter for thinner castings). The temperature in your furnace will need to be even hotter than this, meaning that your internal furnace temperature will be close to 3000. The refractory I used for my furnace is rated at 3000, and as mild steel melts at around 2750, you can see why melting it will rapidly destroy your furnace. Here is a picture of the refractory lining on my furnace where a drop of molten iron landed on it:
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431 downloadsBronze and aluminum will just stick to the surface, but molten iron literally eats right into it. The furnace gets so hot that you need one of the green oxy-acetylene faceshields just to view it with the lid open. It just can't handle the temperatures needed to melt steel.
CAST IRON
That said, with a properly constructed furnace melting cast iron is not at all difficult, however you need to use sand molds, as investment molds of the type you make at home (discussed below) cannot handle the temperature of molten iron (I’ve tried). Sand molding is an art form in itself, and getting it right will take a good bit of practice. There are a number of good books on this recommended at the end of the post. Finally, for cast iron, you need to purchase a clay-bonded graphite crucible. DO NOT MELT IRON IN SOMETHING YOU MADE YOURSELF. A crucible will run you $50-100. It’s an extremely cheap insurance policy, and is well worth every penny. Seriously. Not kidding. Virtually every piece of foundry equipment I have is homemade, except my crucibles for bronze and iron.
BRONZE
Ok, on to the nonferrous stuff. I personally only use silicon bronze for my copper-alloy castings, for a number of reasons. The first is it’s composition: Roundabouts 96% copper, 3% silicon, and 1% manganese. Here’s why that is important: brasses and other bronzes generally contain considerable amounts of zinc, tin, and/or lead in addition to the copper. To melt these alloys, you need to heat them above the temperature at which the alloying elements vaporize. This means that some zinc, lead, tin, etc will escape from the surface as a gas, especially when you stir or skim the melt. This means that besides exposing yourself to seriously toxic fumes, you are changing the composition of the metal every time you melt it. Silicon bronze does not change composition even after melting it dozens of time (as long as you keep a crucible only for that alloy), making it perfect for home use where we can’t test the composition of our alloys and where we want to immediately reuse the metal that makes up the gating system. Additionally, you can buy silicon bronze rods from most welding suppliers, meaning that you can weld it with an oxy-acetylene torch or a TIG welder and get a perfect color match (especially great for fixing small pits in castings, and welding two casting together and blending the weld in). For these reasons, I consider it worth the money to buy silicon bronze instead of using scrap bits of unknown composition.
For bronze, you really really really want to buy a crucible rather than making one. In particular, buy a silicon carbide crucible—again, around $50-100, and again, totally worth it. I’ve used a homemade crucible of the type described below for melting pure copper, since I didn’t want to contaminate my crucible for silicon bronze and I didn’t want to spend $100 on a one-time experiment. All was going well, the copper melted, I skimmed it, and then closed the lid of the furnace to heat it for another minute as the casting was going to be pretty thin and I wanted it really hot. When I reopened the lid to remove the crucible, it had failed and the bottom of the furnace was a lake of molten copper. If I hadn’t opted to put another minute of heat into it, it would have failed right as I was lifting it out of the furnace. That would have been about half a gallon of molten metal all over my legs and boots.
ALUMINUM
Aluminum works fine with scrap material, but for best results use cast (not extruded) aluminum. This means car wheels, bicycle parts, etc. are perfect, but tubing, sheet, beer cans, etc. not so much. Because aluminum melts at such a low temperature, you can safely use a PROPERLY CONSTRUCTED steel crucible, or better yet, a cast iron pot. To make the steel crucible, you can just weld a piece of thick-walled pipe to a thicker plate. I've used with much success a 1/4” wall, 4” pipe that was about 10” tall welded to a piece of 3/8” plate. I welded lugs on the side for tongs to grab. If you aren’t a competent welder please have someone else weld it for you, this isn’t the weld you want to fail. Also, as with any crucible, you need to purpose-make tongs that fit very well with no play.
LEAD
Lead melts at such a low temperature that you don’t even need a furnace, just a suitable steel or cast iron container and some torches. My neighbor recently cast an 1100 pound lead keel for a boat he’s building by putting the lead in a modified cast iron bathtub, melting it with a few roofing torches, and tapping it out of the bottom in to a sand-backed wooden mold. I don’t recommend wooden molds—the surface finish is not the best because of moisture in the mold, and the fire department was called because of the excessive smoking. Even without a furnace, all above safety precautions apply, and remember that lead is extremely toxic.
EQUIPMENT
Aside from your crucibles for bronze and/or iron, as well as a blower, you can easily make everything you need yourself. My entire foundry cost was easily under $1000, which includes a some good books (bought new, listed below), two crucibles, my furnace (cost about $300 in materials), a pottery kiln ($60 on craigslist, and only needed for lost wax casting), an electric blower ($25 on craigslist) and a slew of homemade equipment, mostly made from scrap steel. My furnace is overbuilt, and probably larger than many people on here would even need. You could spend much less on a simple setup. Here’s my entire foundry, packed away in a corner of my shop (it only comes out from time to time):
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409 downloadsFURNACE
The central piece of equipment in a foundry is the furnace. For the scale we’re talking about, a crucible furnace is by far the most reasonable thing to build, so it’s all I’ll discuss. You can build a relatively furnace that run on propane or natural gas, which is basically just a vertical gas forge with a lid. However, these furnaces will have a hard time melting iron, if they can do it at all. I strongly recommend buying the manual from Colin Peck (in England) called “The Artful Bodger’s Iron Casting Waste Oil Furnace”. This is what I did, and would never build a different style of furnace. The design of the furnace body is simple and easily modified to use the scrap you have on hand, and he has perfected a burner design that uses a gravity feed to burn waste oil (used vegetable oil, used motor oil, and diesel all work well). There is no nozzle on the burner, so the fuel isn’t atomized, meaning you can use waste oil (free but contaminated with particulates) without clogging the burner. Also, since it is gravity fed there is no need for a pump, and oil at atmospheric pressure is MUCH safer than pressurized gas when you’re working with molten metal. Plus, it puts out much, much more heat than propane or natural gas—I can melt 30 pounds of bronze from a cold start in less than 45 minutes. Properly built, it burns very cleanly (zero smoking) and can easily melt cast iron. It could definitely melt steel if you wanted, but it will rapidly deteriorate the furnace lining. Using mostly scrap materials, I spent around $300 on my furnace. The cost is primarily the 3000 degree castable refractory (very highly recommended), which I believe cost $65 for a 50 pound bag (I used 3) about 5 years ago. I won’t give much detail about the furnace design since Colin is trying to sell his book, so you’ll have to buy it from him if you want the plans (please note, I in no way profit from this, nor do I even know Colin. It’s just such a good design that it’s all I care to recommend).
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283 downloadsHAND TOOLS
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229 downloadsThere are various, simple tools that you need, all of which you can easily make yourself. Pictured here are the pouring shank (long thing that holds the crucible while pouring), crucible tongs (to lift the crucible in and out of the furnace), skimmer (angle iron welded to a rod, curved on the end to fit my crucible, used for skimming slag prior to pouring), and an ingot mold (angle iron with the ends capped and a handle, for pouring off leftover metal after the molds are filled). Other tools not pictured include a 1/2” steel rod for stirring, a chill bar (described above in safety equipment), a pair of tongs for loading preheated metal into the crucible. Really simple stuff. Also note that you don’t need a pyrometer to measure the temperature. Just take your 1/2” rod that you use for stirring and stick it into the melt for a second and then pull it out. If the molten metal slides right off the end, you’re ready to pour. If it clumps up on it, it’s not hot enough. That method has never failed me, for aluminum, bronze, and iron.
MOLDING TOOLS
This varies depending on whether you are doing sand casting or lost wax casting. I haven’t done sand molds in a few years and no longer have my tools for that, so I won’t try to catalog what you need, but it’s just simple hand tools, and a muller if you're lucky enough to cross paths with one. I would recommend going with Petrobond (oil-bonded sand) over water-bonded sand for a beginner, as it’s easier to deal with and maintain.
I won’t go into much detail here on the actual investment casting process, but if you are interested you should buy the last book listed at the end of this post. I will say though that “microcrystalline wax” is what you want to buy if you are making sculptural pieces. It gets very soft when heated from your hands, and can then take any amount of twisting or bending without cracking, and it blends into itself very smoothly. Like silicon bronze, it is a product so superior that it is well worth the money. Investment molds can easily be made from 1 part water, 1 part pottery plaster, and 2 parts coarse sand.
For this process, you will need to burn the molds out in a kiln to melt out, burn off, and finally vaporize the wax, as well as calcining the molds. You need to run it for a few days and slowly ramp up the temperature, eventually keeping the molds at 1200 for a day and filling them with molten metal when they cool to around 800. A standard pottery kiln works fine, but be prepared to wake up once or twice each night to check on the temperature unless you have a digital controller. Also, you can burn out other organic objects (vegetables, sticks, etc.) instead of sculpting something with wax.
SUPPLIERS/MATERIAL RESOURCES
Budget Casting Supply is your best bet for online shopping, but if you live in or near a big city you should really look for local suppliers. If you don't know of one, try searching on ThomasNet. If you're not familiar, that website is a searchable database of manufacturers and suppliers for industry—extremely useful. Often, places that supply foundry equipment or refractory never have walk-in customers, and if you explain what you are doing they are often very intrigued and go out of there way to help you. I still have yet to pay for any ceramic fiber insulation, though I've gotten plenty of it between various forges and my furnace—a large refractory supplier can generally give you a "sample" that is more than enough for whatever you're working on.
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That’s about all I’ve got for you without writing a book on this. Hopefully this will be helpful to some of you who are interested in adding casting to your metalworking skills. I’m more than happy to answer any questions you have, and if anyone is in the Philadelphia area and wants to see a pour just let me know and I’ll invite you to the next one.
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RECOMMENDED READING
-“The Artful Bodger’s Iron Casting Waste Oil Furnace” by Colin Peck
...available from the author at http://www.artfulbod...alcasting.com/. This manual is what I used to build my furnace described above. I don't think I would ever build a crucible furnace that was not based on this design. Terribly written, never even proofread, but invaluable nonetheless.
-“The Metalcaster’s Bible” by C.W. Ammen
-“The Complete Handbook of Sand Casting” also by C.W. Ammen
...Ammen’s books are very readable and straightforward. Get these regardless of whether you are making sand or investment molds.
-“U.S. Navy Foundry Manual” reprinted by Lindsay Publications
...invaluable resource, but not the kind of book you read straight through (ie, boring technical manual). Again, though it is written for sand casting in particular, much of the information is very pertinent to investment casting as well.
-“Charcoal Foundry” by Dave Gingery
...great for starting out, it’s sand casting in its most pared-down form. Perfect for a super-low-cost setup to pour some aluminum to see if you like it.
-“Metal Casting: A Sand Casting Manual for the Small Foundry” by Steve Chastain
...there are two volumes. Good books, but not necessary if you are only interested in investment casting.
-“Studio Bronze Casting: Lost Wax Method” by John Mills & Michael Gillespie
...for investment casting.
Also check Lindsay Publications for other books on casting, including some of those listed above.
