The Science of Grit Size in Sand Blasting: Precision Surface Engineering

June 30, 2025
Posted by 黄朝灿
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How to Select Grit Size: A Data-Backed Framework

1. Grit Size Classification & Applications

Grit Type	Size Range (µm)	Ideal Use Cases	Avoid When
Extra Coarse	1,000–2,000	Heavy weld removal, rapid deburring	Thin-walled parts (±0.1mm tolerances)
Coarse (#36–#60)	420–250	Casting cleanup, oxide scale removal	Mirror-polished substrates
Medium (#80–#120)	180–125	General matte finish, prep for painting	Critical sealing surfaces
Fine (#180–#220)	80–53	Medical implants, aerospace interfaces	High-wear components
Extra Fine (#320+)	<45	Optical components, semiconductor tooling	Corrosion-prone environments

2. The Process Optimization Formula

Pressure Adjustment:
- Coarse grit: 60–80 PSI (ensures kinetic energy for material removal)
- Fine grit: 25–40 PSI (prevents surface deformation)1
Nozzle Distance:
- Short distance (15–20cm): Aggressive cutting with coarse grit
- Long distance (30–40cm): Diffused pattern for fine-grit uniformity
Angle of Impact:
90° for maximal material removal (coarse), 30–45° for peening effect (fine)

3. Advanced Techniques

Grit Mixing: Blend 70% #120 + 30% #220 for balanced roughness (Ra 1.5–2.0µm) and edge retention
Sequential Blasting: Start with #80 for defect removal → finish with #220 for Ra 0.4µm
Media Recycling: Reuse ceramic grits ≤3× to maintain consistency (saves 20% costs)

Results and Benefits: Quantified Performance Gains

Surface Integrity Metrics

Table: Grit Size vs. Critical Surface Properties (AISI 304 Stainless Steel Data)

Grit Size	Ra (µm)	Rz (µm)	Fatigue Strength Increase	Coating Adhesion (ASTM D3359)
#36	3.5–5.0	25–40	8%	2B (Moderate)
#120	1.2–1.8	8–12	15%	4B (Good)
#220	0.3–0.6	2–4	22%	5B (Excellent)

Operational Advantages

Reduced Secondary Processing: Fine-grit blasting (Ra ≤0.8µm) eliminates manual polishing, cutting labor by 40%
Extended Component Life: Aerospace studies show #220-blasted turbine mounts withstand 100,000+ cycles vs. #80’s 65,000
Contamination Control: Angular ceramic grits (Al₂O₃) leave no embedded residues vs. silica sand.

The Cost-Quality Tradeoff: Strategic Implementation

When to Go Fine:
- Functional surfaces (hydraulic seals, bearing seats)
- Biomedical devices (Ra <0.4µm inhibits bacterial adhesion)
- Adhesion-critical coatings (anodizing, PVD)
When Coarse Wins:
- High-volume deburring (automotive castings)
- Rust/coating removal (structural steel)
- Texturing for grip (hand tools, ladder rungs)
"Grit size selection is a multiplier—it either amplifies or undermines your entire finishing budget." — Surface Engineering Handbook, ASM International

Pro Tips for Engineers
1. Test First: Blast coupons at 3 grit sizes to correlate Ra vs. fatigue performance
2. Monitor Wear: Replace grit when 15% particles fracture (prevents Ra drift)
3. Layer Media: Use glass beads over #220 Al₂O₃ for compressive stress without Ra change
4. Automate: Robotic blasting with force-feedback maintains 0.02µm Ra consistency
Optimized blasting isn’t guesswork—it’s particle physics meets precision manufacturing. By mastering grit size variables, manufacturers achieve 30% faster finishing cycles and 18% longer component lifetimes. For Ra certification protocols or media lifecycle data, request our validation datasets.