Introduction: Aluminium Can Furnace

By Biji Biji Initiative
About: A social enterprise whose design core is open sourced and inclusive.

Equipment list:

2x Buckets. One for measuring, one for a weighted mold
1x Steel drum
1x Large mixing bucket
1x Bag of plaster
1x Bag of sand
2x Wooden planks
2x Bricks
1x 1” steel pipe at approx 2 foot in length
1x set of steel handles
1x crucible
1x circular mold for casting the lid
1x centre hole former, slightly bigger than an aluminium can

Toolkit:
Angle grinder- to remove lid from the steel drum Drill and 1 inch hole saw- to drill air hole in the side of furnace
Metal circular saw-for cutting pipe/ handles/ casting tools
Welding machine- making handles/casting tools/crucible

  1. Source all the equipment and prepare your tools
  2. Cut the lid from the steel drum and clean inside (this doesnt need to be thorough)
  3. Collect or weld a round steel container; roughly 3” diameter and 5” height- Big enough to fit a can inside. This will be the crucible to melt the aluminium inside.(Tip: the bottom of an old fire extinguisher is ideal!)
  4. Consider making some tools for casting the aluminum. A set of steel utensils that allow you to pick up the crucible and tilt it to pour

Step 1: Calculating Volume for Casting

  1. To measure the internal chamber volume: Use a small bucket of known volume
    (Tip: fill bucket using a water bottle and mark litre levels)
  2. To calculate volume of drum: Measure the
    Height (h) of drum (cm)
    Diameter (d) of drum (cm)

    V = π/4 d^2h

    Total volume of drum - volume of internal chamber = Volume needed to be cast
  3. Place two wooden planks on the rim of the steel drum to support the weighted bucket; weigh it down with water or sand, etc. Using the mixing bucket combine the sand and plaster first, and the water last.

    At a ratio of 7:7:5 plaster : sand : water

Step 2: Casting the Furnace

  1. Working quite quickly here you must create an even mix to pour into the steel drum before it sets too hard. You can mix with your hands or with a stick. Dont be alarmed; the chemical reaction here creates heat.
  2. Pour the mixture carefully into the drum until it reaches just under the rim. Agitate the surface to level the mixture and hold the weighted bucket down until it begins hardening.
  3. Using a wet cloth you can wipe the top of the plaster mix. (Tip: To clean the buckets leave the plaster mixture to dry in the bucket before cracking and removing.
  4. Before the mixture has fully hardened, use a 1” hole saw to drill an air pipe. At a 30 degree angle bore into the side of the furnace through to the chamber so the opening is around 2” from the base.
  5. Place a 1“ diameter pipe inside to avoid tunnel collapsing. Air source: hairdryer, compressor

Creating the lid:
The size of the lid should be the same diameter as the furnace and 2” thick. Calculate the volume of the lid and mix a fresh batch using the same ratio as previous. Prepare a pair of metal handles and place into a circular mold. Using a soup can ( or anything slightly bigger than an aluminium can) place in the centre and pour the mixture semi- submerging the handles and the can. Before the mixture properly sets remove the centre can so it leaves an access hole.

Step 3: Lighting the Furnace!

The furnace needs to be completely set and dry before lighting.
Preparing your workspace is so important for efficiency and safety;

  • Bricks can be used to raise the furnace and the casting tray from the ground to avoid scorch marks
  • Organise an area that you can place hot tools upon. This could be bricks or a steel table top
  • Attach a hairdryer or any other form of airflow, to the end of the steel pipe. This is vital in getting the furnace up to temperature.
  • Add some sand to a container and leave to one side. This is to dispose of the hot impurities before casting.

  1. Place the crucible inside the chamber and pack with wood or charcoal. If necessary pour a small amount of petrol onto the wood to help with lighting the fire.
  2. After lighting the fire turn on the airflow.
  3. Add the lid and wait for the furnace to heat for around 10 minutes.

Step 4: Casting

It is advised to crush the cans before dropping them into the furnace. This avoids excessive oxidation.

  1. Add the first can and wait for it to melt.
  2. When you have added a number of cans and the aluminium is molten.
  3. Scoop the slag/impurities from the surface of the liquid with a steel tool.
  4. It is then ready to cast into nuggets or into a pre-prepared sand mold.

Step 5: