How to Cast Aluminium With Plaster Molds

By James Black
A custom door knocker is a simple project when casting aluminum with plaster molds.

Aluminum can be cast into nearly any shape resulting in castings of sculptures, art pieces or even tools. Although casting aluminum involves very high heat and molten metal, it can be done at home with relatively little equipment.

Many people around the world cast aluminum, and many useful items have been produced by home casting. With experience and practice, you could build sculptures such as full-scale busts, or large machine tools such as a lathe or a mill.

Carve or sculpt the wax into the shape you want to cast in aluminum. The process used for casting aluminum with plaster molds is called lost wax casting. In this process, a model of the desired object is made of wax and coated in plaster. After the plaster has dried, the wax is melted out of the mold and replaced with aluminum.

Add sprues and vents to the wax model with leftover wax. Sprues and vents are how the molten metal passes through the plaster to fill the mold cavity. Cut or carve several small rods from casting wax and melt them onto the wax model. Be sure to add two or three vents. Vents allow air inside the mold to escape. Without vents, molten aluminum could splash back up during pouring.

Mix the plaster of Paris with water in the 5-gallon bucket. Be sure to mix enough plaster so that the model will be covered by at least 2 inches of plaster when placed in the bucket.

Tie a length of string to the end of each sprue and vent. Tie the other end of each length of string to a dowel rod. Submerge the wax model in the bucket of plaster. Be sure not to submerge the sprues and vents -- you will pour metal into these. Allow the plaster to dry overnight.

Fill one flower pot half full with charcoal and light the charcoal. Remove the plaster mold from the 5-gallon bucket and place your plaster mold into the fire. The wax in the plaster mold will melt and can be poured out after some time. Pick up the plaster mold out of the fire with tongs and pour the wax out into the bucket. This wax can be remelted and reused for additional models.

Add more charcoal to the flower pot and place the crucible in the fire. Use tongs to keep the crucible level in the fire. After the crucible has warmed, add scrap aluminum to the crucible. Blow on the fire with the bellows. Aluminum has a melting point of over 1,200 degrees Fahrenheit, so the fire needs to be at least that temperature.

Remove the crucible from the fire with tongs after you have melted enough aluminum. Pour the melted aluminum into the mold quickly. Fill the mold as completely as possible. When casting aluminum, it's better to have too much molten metal than not enough.

Wait at least one hour before attempting to release the casting from the mold. Even though small droplets of aluminum may have cooled, the large aluminum casting may still be hot.

Break the plaster mold with a hammer. Remove all pieces of plaster from the aluminum casting. Remove the metal left from the sprues and vents with a disc grinder. Use the rasp to smooth any imperfections in the casting.

Tip

Don't worry about any leftover wax in the mold. As the mold fills with aluminum, the wax will melt and flow out.

Warning

Molten metal is very hot. Be sure to wear a long-sleeve shirt and long pants when casting aluminum.

Plaster of Paris gives off heat as it dries and can become very hot.

About the Author

James Black has been writing about computers and the computer industry since 2001. His work has appeared in "2600" and several academic journals. James holds a Bachelor of Arts degree in journalism from the Shippensburg University.