AFS 45-55 for chromite does not directly equal 50-100 mesh, but they represent highly overlapping particle size ranges and are often approximated in industrial applications (especially in foundry and abrasive fields). The key distinction lies in their particle size characterization systems—here’s a detailed breakdown:
1. Core Differences in Definition & Measurement
| Aspect | AFS 45-55 | 50-100 Mesh (Tyler Standard) |
|---|---|---|
| Nature | AFS Fineness Number (from the American Foundry Society) | Screen size range (based on sieve aperture) |
| Calculation Logic | A comprehensive average particle size index derived from cumulative residue rates across multiple sieve layers (e.g., 40, 50, 70, 100, 120 mesh). It reflects the overall fineness of the particle distribution. | A range of sieve aperture sizes: Particles pass through a 50-mesh sieve (≈297μm aperture) but are retained on a 100-mesh sieve (≈149μm aperture). It only defines upper/lower size limits, not the internal distribution. |
| Accuracy | Quantifies average fineness (requires full sieve analysis for calculation). | Qualifies size boundaries (no information on particle proportion within the range). |
2. Correlation in Practical Applications
For conventional chromite sand:
- Chromite sand with a 50-100 mesh size range typically has an AFS fineness number between 40-55.
- If the particle distribution leans toward finer grains (e.g., 70-100 mesh dominates), the AFS number will be closer to 45-55.
- If coarser grains predominate (e.g., 50-70 mesh), the AFS number will be closer to 40-45.
- Conversely, chromite sand with an AFS 45-55 rating usually has a core particle size range of 50-100 mesh, but may include small amounts of finer (120 mesh+) or coarser (40 mesh-) particles—provided the overall fineness index meets the requirement.
Thus, in industries like foundry (where strict precision is not always critical), 50-100 mesh and AFS 45-55 are often used interchangeably as approximations.
3. Key Notes for Usage
- General Scenarios (e.g., general foundry molding sand, sandblasting): The approximation is acceptable, and no strict distinction is needed.
- High-Precision Scenarios (e.g., precision casting, high-end refractory materials): Require a formal test report from the supplier, including both:
- Sieve analysis data (residue rates on 50, 70, 100, 120 mesh sieves),
- AFS fineness number.
This avoids performance issues caused by inconsistent particle distribution (e.g., excessive coarse/fine particles within the 50-100 mesh range).
4. Reference Table: Chromite Mesh vs. Typical AFS Number
| Tyler Mesh Range | Typical AFS Fineness Number | Common Applications |
|---|---|---|
| 30-60 mesh | 30-40 | Coarse molding sand, large castings |
| 50-100 mesh | 40-55 | Standard molding/core sand |
| 70-140 mesh | 55-70 | Precision casting, fine sand molds |