Ceramic Foundry Sand for Vacuum Casting refers to a specialized, high-performance material used to create the rigid mold shells that house the flexible silicone molds in the vacuum casting process.
| Chemical Analysis[%] | |
| Al2O3 | 70-73 |
| SiO2 | 8-20 |
| Fe2O3 | ≤3 |
| TiO2 | ≤3.5 |
| CaO | ≤0.45 |
| MgO | ≤0.35 |
| K2O | ≤0.33 |
| Na2O | ≤0.08 |
| Physical Properties | |
| Grain shape | Spherical Ball |
| Roundness | 90% |
| Refractoriness: | ＞1790℃ |
| Shape Coefficient | ≤1.1 |
| Thermal Expansion Ratio | 0.13%（Heated up for 10 min at 1000℃） |
| Thermal expansion coefficient | 6×10-6 /℃(20-1000℃) |
| Thermal conductivity | 0.698W/M.K(1200℃) |
| Specific Gravity:: | 1.95-2.05g/cm3 |
| Bulk density(LPD): | 3.4 g/cm3 |
| Color: | Black |
| AVAILABLE SIZES | |
| AFS25-35,AFS35-45,AFS45-55,AFS55-65,AFS60-70,AFS70-80,AFS95-110Customized sizes are available upon request | |
1. The Role of Ceramic Foundry Sand in Vacuum Casting
In vacuum casting, the process flow involving ceramic sand is as follows:
Master Model: You start with a high-quality master model (often 3D printed and finished).
Silicone Mold Making: The master is placed in a casting box, and liquid silicone is poured around it to create a flexible mold. Once cured, the silicone mold is cut open, and the master model is removed. You now have a hollow, flexible negative of your part.
Creating the Shell Mold (Where Ceramic Sand Comes In):
The flexible silicone mold is too floppy to handle the pressure and vacuum of casting. It needs a rigid support.
The silicone mold is placed back in a casting box, and Ceramic Foundry Sand mixed with a binder is packed around it.
This mixture cures to form an incredibly rigid, durable, and thermally stable shell.
Casting: The entire assembly (ceramic shell + internal silicone mold) is placed under a vacuum chamber. Liquid polyurethane resin is injected. The vacuum removes air bubbles, ensuring a perfect cast.
Demolding: After the resin cures, the ceramic shell is broken away, the silicone mold is opened, and the final part is removed.
In essence: The Ceramic Sand creates a rigid “mother mold” or “support shell” for the delicate silicone “working mold.”
2. Key Advantages of Using Ceramic Foundry Sand
Why is it preferred over other materials like plaster or conventional sand?
| Feature | Advantage in Vacuum Casting |
|---|---|
| Extremely Low Thermal Expansion | This is its primary advantage. Unlike quartz sand, which expands significantly with heat (causing casting defects), ceramic sand is dimensionally stable. This is critical because the exothermic reaction of curing resin can generate heat, and a stable shell ensures part accuracy. |
| High Refractoriness | It can withstand very high temperatures without breaking down. This makes it suitable for casting high-temperature resins and allows the mold to be used for multiple production cycles without degradation. |
| Excellent Collapsibility | Despite being strong, the ceramic shell is brittle enough to be easily broken away from the silicone mold and the final part without damaging them. This is crucial for preserving the silicone mold for future casts. |
| High Strength | It creates a very rigid shell that completely eliminates any deformation of the silicone mold during resin injection, leading to highly dimensionally accurate parts. |
| Reusability | While not infinite, some ceramic sands can be reclaimed and reused for multiple shell-making cycles, offering better cost-efficiency for larger batches compared to one-time-use plasters. |
3. Typical Specification for Vacuum Casting
When selecting a ceramic foundry sand for vacuum casting, you would look for:
Type: Spherical or sub-angular ceramic sand (like Ceramiste™ or similar brands based on alumina silicate).
AFS Grain Fineness Number (GFN): A fine grade is typically used, often in the range of 80 to 130 GFN. This ensures a smooth shell surface and captures fine details from the master model.
Binder: It is typically used with a furan resin or phenolic resin cold-box binder system, which cures rapidly and provides high strength.