How to Melt Aluminum

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27-10-2017, 14:00
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Aluminum is one of the most heavily used metals in modern manufacturing. Its durability and plasticity make it an ideal material for multiple functions. Because of this, aluminum is a great metal for DIY forging. With the right information and materials, forging aluminum can be a fun hobby or a source of extra income.

Melting Aluminum in a Small Foundry

  1. Position your foundry. Set your foundry in a metal stand or on an insulated surface (like gravel, sand, or bare earth; concrete could crack from spills). Make sure that the surface can withstand the more than 1220 degrees Fahrenheit (660 degrees Celsius) needed to melt the aluminum. Avoid any wooden or plastic surfaces because they will melt or burn. For the best results, set your foundry in a sturdy metal stand that will not easily tip over.
  2. Place the crucible in the foundry. Make sure that the crucible is in the center of the foundry. A steel crucible works the best for melting aluminum.
    • If you’re using a charcoal-fueled foundry (instead of propane), place a layer of charcoal in the bottom of the foundry and set your crucible on top of it. Then fill in the space between the insulation and the crucible with more charcoal. Placing a layer of charcoal under the crucible will help it heat up quicker and more evenly.
  3. Connect the propane torch (or blower tube). If you’re using a propane-fueled foundry, connect the included torch end (with attached fuel and air lines) to the opening in the side of the foundry. Follow the instructions provided with your foundry (charcoal-fueled foundries are a somewhat safer DIY project).
    • For a charcoal-fueled foundry, set up your bellows after placing the charcoal and crucible inside. Place the steel end of the blower tube into the foundry. You can blow into the plastic end to maintain air flow or attach an electric hair dryer, which will provide a more constant flow of air.
    • Because it is at an angle, place something (like one or a few bricks) under the propane/blower tube to prop it up. This will keep it from breaking or damaging the foundry.
  4. Light the foundry. For a propane-fueled foundry, turn on the gas and follow the lighting instructions provided with the unit. For a charcoal-fueled foundry, a propane blowtorch is the quickest lighting method, but even a match will do. As the coals heat, blow through the blow tube or turn the hair dryer on low. Place the lid on the foundry and let it warm up.
    • Let the foundry heat for about 10 minutes before placing aluminum inside of it.
    • The temperature in the foundry will need to be above 1220 degrees Fahrenheit (660 degrees Celsius).
    • Once the crucible is glowing orange, the foundry is hot enough to melt aluminum.
  5. Place aluminum in the crucible. Once the foundry is hot enough, you can begin melting aluminum. You can choose to either: remove the lid and place uncrushed cans in the crucible, or leave the lid on and place crushed cans in the crucible through the vent hole. Both methods work well, but if you leave the lid on, less of the metal will be oxidized. The cans will melt in a matter of seconds, so you need to quickly add more cans to the crucible.
    • It is important to quickly add new cans in order to create a pool of molten aluminum. This is necessary to prevent the cans from being overheated and turning into a gas, a process known as oxidization.
    • You can put the aluminum in the crucible while using just proper heat-resistant gloves, but using long metal tongs as well is safer.
  6. Remove the crucible after skimming off surface slag. Use a metal rod or tongs to skim slag (thick clumps of non-aluminum materials) off the top of the liquefied aluminum. Then, with a pair of metal tongs, slowly remove the crucible from the foundry. To prevent oxidization, be sure to remove the molten aluminum from the foundry at least three minutes after the last piece of aluminum melted.
  7. Separate the pure aluminum from any excess slag. Once you have melted enough aluminum to fill your crucible, you will want to remove any remaining impurities. Things like aluminum cans will have lots of other materials in them (plastics and other metals) that will create slag or dross. The slag will form a thick clumpy layer on top of your pure molten aluminum. The easiest way to remove the slag is to use your tongs to slowly pour out the molten aluminum into a steel mold, and then tap the slag out of the crucible onto a square concrete paver placed on sand or bare earth.
    • Keeping the crucible clean allows you to melt more aluminum quickly.
  8. Pour the molten aluminum into steel molds. You can let the aluminum ingots air cool and then dump them out of the molds, or use water to speed up the process. To water cool the aluminum, take your tongs and place the ingot and mold into water for about 10 seconds. After soaking in the water, the ingot should be cool enough to touch. However, you should use your tongs to avoid being burned.
    • The pure aluminum ingots can now be reused for later castings and will not produce as much slag as before.
  9. Empty out the foundry after it cools completely. When you’re done melting aluminum, turn off the torch and/or blower (according to the provided instructions) and allow the foundry to air cool in place for several hours. When the foundry has cooled completely, disconnect and store the torch/blower components, and scoop out any charcoal ash or other debris from the foundry’s interior.
    • Supervise the cooling process, especially early on, when the foundry is hot enough to ignite items like wood, paper, and fabric.

Making a DIY Aluminum Foundry

  1. Make the outer body. Purchase a 12” x 12” (30 x 30 cm), 10 quart (9.5 liter) steel bucket with an open top. This common steel bucket can be purchased at most home and garden stores.
    • Because of the heat you will generate, it is important that you use a steel bucket. Other materials may melt or become brittle under the intense heat generated by your foundry.
  2. Mix the materials for the lining. In a five quart (5 liter) or larger bucket, mix 21 scoops of plaster of Paris, 21 scoops of play sand, and 15 scoops of water (the scoop should hold roughly one cup or 250 ml). Quickly stir the ingredients together by hand. It is important to moisten all of the dry powder and work out any lumps. After a few minutes of stirring, the mixture should be runny and a uniform color.
    • Because the mixture will set in roughly 15 minutes, it is important that you do the step with some urgency.
  3. Pour the insulation into the bucket. Once you have worked out any lumps, slowly pour the insulation mixture into the steel bucket. The fluid should fill the bucket, leaving about three inches (8 cm) of space at the top.
    • To avoid creating a mess, pour slowly to limit splattering.
  4. Form the center of the foundry. Fill a 2.5 quart (2.5 liter) bucket with water or sand and place it in the center of the insulation mix. Slowly push the bucket into the mix. Move the bucket up and down a few times to help level the mixture before it sets. Finally, hold the bucket still for two to three minutes and let the mixture set around it.
    • Once the plaster has hardened, the small bucket should stay in place once you remove your hands.
    • Let the plaster mix sit for one hour to harden.
    • Clean off any splattered plaster from around the top edges of the steel bucket.
  5. Remove the inner bucket. After the plaster has hardened, use a pair of pliers or channel locks to remove the plastic bucket you used to create the opening. Grip the bucket with your pliers and twist it in on itself. With enough torque, the bucket should cleanly pop free from the plaster mix.
  6. Drill a hole for the air supply port. In order to promote air flow, you will need to drill a hole in your foundry for a blower tube. Use a 1-3/8” (3.5 cm) hole saw, attached to an electric drill, to cut a hole in the top line of the bucket (about three inches [7.5 cm] from the lid). Once you have cut through the bucket, position the blade at a roughly 30-degree angle and drill. This hole should be the perfect size to accommodate a one-inch (2.5 cm) steel tubing, which will act as your blower tube.
    • The hole saw can found at your local hardware store. Buy one that is specifically designed for cutting through metal. Ask a salesperson if you’re not sure.
    • Creating an angled air supply port will prevent molten aluminum from flowing out of the foundry if your crucible fails.
  7. Make a blower tube. Take a 1” x 12” (2.5 x 30 cm) steel pipe and screw on a 1” PVC coupling at one end. Once you have attached the coupling to the steel pipe, slide a 1” x 24” (2.5 x 60 cm) PVC pipe into the smooth end of the coupling. The coupling should have a threaded end for the steel pipe and a smooth end for the PVC pipe.
    • The blower pipe should fit smoothly into the air supply port, but not so snugly that it is difficult to slide it in and out of the hole.
  8. Create a lid. Fill a 5 quart (5 liter) bucket with 10 scoops of plaster of Paris, 10 scoops of sand, and 7 scoops of water (at roughly one cup or 250 ml per scoop). Stand up two 4” (10 cm) U-bolts in the plaster mixture, placing the ends with the nuts down in the mix. Let the plaster set for an hour. Once it has set, you can simply pop the lid out of the bucket. Finally, drill a hole in the top of the lid using an electric drill and a 3” (7.5 cm) hole cutting saw.
    • The vent hole will relieve pressure inside the foundry and allow you to add metal without taking off the lid.
    • Try to make the lid hole the same diameter as your crucible. This will help prevent heat loss when you melt your aluminum.

Preparing to Melt Your Aluminum

  1. Find proper pieces of aluminum. The best sources for scrap aluminum are old machine parts. Car cylinder heads, transmission cases, water pump housings and pistons are all great examples. More common sources are things like beer and pop cans, furniture frames, home siding, window frames, and turkey and pie pans. However, these sources tend to be weaker alloys that have lots of impurities, which means that they create more slag and oxidize quickly.
    • An easy way to melt aluminum cans and prevent oxidizing is to add them to a pool of already molten aluminum.
  2. Wear proper safety equipment. When you are working around extremely high temperatures, it is important to wear proper safety gear. When handling molten metal, you should wear a thick and long-sleeved shirt, pants, an apron, a face shield or glasses, and leather gloves. These things will prevent molten metal from burning your skin. Because molten aluminum can give off noxious gasses, you should also wear a respirator.
  3. Find an open or well-ventilated space. When working with molten aluminum, some alloys will give off noxious fumes. Because of this you will want to work in a well-ventilated space or outdoors. This will also help keep you cool while working around extreme heat and avoid dehydration or heat stroke.
    • If you begin feeling sick, have a headache, or are dizzy, turn down the foundry and take a break. Go to a cool place and drink some water.
  4. Use proper tools. Before you begin melting aluminum, make sure that you have the necessary tools for handling molten metal. You will need a pair of metal tongs, a metal strainer or stirring rod, a crucible, and a foundry. Things like the foundry and crucible can be made at home or bought at a store or online.
  5. Be safe. Because of the relatively low temperature necessary to melt aluminum, it can be melted in a variety of unsafe methods outside of a foundry. Avoid melting aluminum in large bonfires or on BBQ grills. These methods are less controlled and can lead to a fire or injury.
    • If you are new to working with molten metals, be sure to work with a more experienced person before attempting to melt aluminum.

Things You’ll Need

  • store-bought or DIY foundry
  • crucible
  • fuel source (charcoal or propane)
  • torch and/or air blower
  • metal tongs
  • metal stirring rod
  • insulated (e.g., sand or dirt) work surface
  • ventilated work area
  • thick, long-sleeved shirt and long pants
  • heavy-duty work boots
  • heat-resistant leather gloves and apron
  • face shield or glasses
  • respirator (optional if working outdoors)
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