• Make wax model
• Sprue wax model
• Weigh wax model with sprues
• Attach wax model to rubber sprue base
• A flask is fitted to the sprue base and surrounds the wax model
• seal flask to sprue base with clay
• Mix investment and vibrate to remove air bubble
• Invest wax model
• Burn out wax in kiln
• Weigh up metal to be cast
• Cast your model in metal
• Remove casting from mold
• Remove sprues
• Surface finish of casting

Wax model or pattern: Model made from wax to be replicated or cast in metal.

Sprue: Wax wires attached to your model their for the purpose of

• mounting of your model to the sprue base
• Providing a way out for the wax during burnout
• Providing a way in for the molten metal during the casting process

Weighing wax model: This is for the purpose of determining the amount of metal needed to complete the casting successfully. The wax model with sprues attached, is weighed and then multiplied by the specific gravity of the metal being used to cast with. Different metals have different specific gravities, compared to wax which has a specific gravity of 1.

Specific Gravity is the ratio of the weight of a given volume of a substance to an equal volume of water whose specific gravity is 1.

For example: Wax has specific gravity of 1

Sprue Base: Is a round rubber base with a cone at its centre. The wax model is attached to this cone via the sprues and the flask is placed over your model and sealed with this base

Flask: A stainless steel tube or pipe that is place over and around your mount wax model into which the investment is poured to make a mold. Allow 12mm of investment above your model to the top of the flask, and 6mm from your model to the sides of the flask. Seal the flask against the sprue base with clay.

Investment: A plaster like powder that is mixed with water to a slurry, this is done in a rubber bowl. The mixed investment is placed on a vibrating pad to help remove air bubbles from the investment. Air bubbles attached to your wax model will become an undesirable part of the casting. The investment is then poured into the flask filling from the bottom being careful not to knock over your model. Your wax model should be at least 12mm from the top of the flask and 6mm from the sides (see photo 1). If there is not enough investment covering the top of your model the investment may crack during burnout or the molten metal may break through the top during casting. The flask is filled to the top and the investment allowed to set. When the investment has set inscribe your initials and the wax weight into to top the investment.

Burnout: When the investment has set the rubber base is removed and the flask. The flask is placed in a kiln and over a period of up to 8 hours the temperature of the kin is gradually increased to 700 deg. C. This causes the wax to melt and burn out of the flask, it also cures the investment ready for casting. At the end of the burnout cycle there is a hollow space where the wax used to be, and the mold is now ready for casting.

Casting: Pouring or Forcing molten metal into the cavity left behind after the burn out cycle, thus creating a metal replica of your wax model. We use a centrifugal casting method, using the force created by a rotating arm to throw the metal into the mold. See photo.2. The casting is then broken out of the mold and cut free from the sprues using bolt cutters or a jewellers saw. The casting is then finished using files, abrasives paper, polishing, and colouring methods.

PHOTO 1

PHOTO 2

Centrifugal Casting Machine