Why we use Ceramic Shell Casting

We use 2 primary casting methods for non-ferrous metals. Firstly lost wax vacuum investment casting and ceramic shell casting. Both of these methods lend themselves to different types of products, ceramic shell allowing us to make much larger cast products. This method is perfect for sculptural works.

 

In this section we would like to explain a little of what the ceramic shell process of casting metal is.

 

Ceramic shell casting is a type of investment casting that creates a hollow ceramic mold, or shell, from a disposable pattern. The pattern is typically made of wax, which is melted away after the shell is constructed, leaving a precise cavity for molten metal. This process is valued for producing high-quality, intricate castings with excellent surface finishes and close tolerances. 

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The ceramic shell casting process.

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The process involves several key steps to construct and prepare the mold for casting:

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1. Wax pattern assembly: A wax master pattern, which is a replica of the desired object, is created. This pattern is often a single component or is attached to a "tree" of sprues and risers that will guide the molten metal into the mold cavity.

2. Slurry dipping: The wax tree is dipped into a ceramic slurry, a liquid mixture of fine refractory particles and a binder.

3. Stuccoing: After the wax pattern is coated in the slurry, it is immediately covered with a coarser, dry ceramic material known as stucco.

4. Drying: The assembly is allowed to dry, and the dipping and stuccoing process is repeated to build up the desired shell thickness, which can involve 6 to 10 layers.

5. De-waxing: Once the shell is sufficiently thick and dry, it is heated in an autoclave or furnace to melt and remove the wax pattern. This is why the process is also known as "lost-wax" casting.

6. Firing: The empty ceramic shell is then fired at a high temperature (around 980 °C) to strengthen the mold and remove any remaining impurities.

7. Casting: The hot shell mold is filled with molten metal. Pouring a hot shell prevents thermal shock from cracking the ceramic and increases the fluidity of the metal, allowing it to fill intricate details.

8. Knockout: After the metal has cooled and solidified, the brittle ceramic shell is broken away using methods like hammering, sandblasting, or high-pressure water jets.

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Ceramic shell casting materials.

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High-quality casting results depend on the materials used to create the ceramic slurry and stucco. 

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• Binders: These liquid agents hold the ceramic particles together.

  • Colloidal silica: A common water-based binder that creates strong shells. Their are various varieties dependent on the manufacturer. Different products have minor differences relating to drying time and strength.

  • Ethyl silicate

    : An alcohol-based binder that is also used.

• Refractory materials (flour and sand): These are the high-temperature ceramic components that form the bulk of the shell.

  • Fused silica: Provides a strong shell with low thermal expansion, but can be more brittle than other options.

  • Aluminosilicates (e.g., Molochite): A popular, cost-effective alternative to fused silica that provides high strength and stability.

  • Zircon

    : Used for high-temperature applications like casting stainless steel.

  • Chromite

    : Another heavy sand alternative to zircon.

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Advantages and applications

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Ceramic shell casting is used to produce high-precision parts for many industries. 

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• High-quality finish: It produces castings with excellent surface finish, often requiring little to no post-processing.

• Complex geometries: The process can create intricate and complex shapes, including thin sections, that are difficult to produce with other casting methods.

• Variety of materials: It has no metallurgical limitations and can be used for a wide range of ferrous and non-ferrous alloys.

• Applications:

  • Aerospace (e.g., turbine blades, jet nozzles)

  • Medical and dental equipment

  • Tool and die making

  • General industrial parts

  • Art and sculpture (e.g., bronze sculpture)