How to choose the suitable size of the ceramic sand for foundry

Choosing the right size of ceramic sand for foundry applications depends on several factors, including the type of casting process, metal being poured, mold design, and surface finish requirements. Here’s a step-by-step guide to selecting the appropriate size:

1. Understand Ceramic Sand Properties

Ceramic sand (such as fused ceramic or proppant sand) is spherical, high-refractoriness, and chemically stable. Common sizes range from AFS 30 to 100 (approx. 0.1 mm to 0.6 mm).

2. Consider the Casting Process

  • Sand Casting (Green Sand/Resin Sand):

    • Coarser sand (AFS 40-70, 0.2–0.4 mm) for better permeability in large castings.

    • Finer sand (AFS 70-100, 0.1–0.2 mm) for intricate details and smooth surfaces.

  • Investment Casting (Shell Molding):

    • Very fine sand (AFS 80-120) for precision casting.

3. Metal Type & Pouring Temperature

  • Steel/Iron (High Temp): Coarser grades (AFS 40-60) to withstand thermal stress.

  • Aluminum/Copper (Lower Temp): Finer grades (AFS 60-100) for better surface finish.

4. Mold & Core Requirements

  • Cores (Thin Sections): Finer sand (AFS 70-100) for strength and detail.

  • Large Molds: Coarser sand (AFS 30-50) for better gas escape.

5. Surface Finish Needs

  • Rough Castings (e.g., engine blocks): AFS 40-60.

  • Smooth Finish (e.g., jewelry, aerospace): AFS 80-100+.

6. Permeability vs. Strength Trade-off

  • Higher permeability (coarse sand) reduces gas defects but may weaken the mold.

  • Finer sand improves surface finish but may need higher binder content.

7. Test & Optimize

  • Conduct trial casts with different AFS grades.

  • Check for defects (veining, inclusions, poor finish) and adjust.

General Recommendations

ApplicationRecommended AFS Grain SizeApprox. Size (mm)
Large steel castings30-500.3–0.6
General iron castings40-700.2–0.4
Aluminum/brass60-1000.1–0.3
Precision investment80-1200.06–0.2
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