Slide 002: Abrasive Media Types and Selection

Slide Visual

Slide Overview

This slide covers the major categories of abrasive blasting media, their physical properties, appropriate applications, and selection criteria. Students learn to match media to substrate and desired finish profile.

Instruction Notes

Media Classification

Abrasive media are classified by material, hardness (Mohs scale), shape (angular vs. spherical), and mesh size. The three primary categories are:

1. Metallic Abrasives — Steel shot (spherical, Mohs 8), steel grit (angular, Mohs 8), cast iron grit. Used for aggressive cleaning, peening, and heavy scale removal. Recyclable 50–200 cycles.

2. Mineral Abrasives — Aluminum oxide (Mohs 9), garnet (Mohs 7–8), silicon carbide (Mohs 9.5). Angular particles ideal for cutting and profiling. Aluminum oxide is the makerspace standard for metals.

3. Soft/Organic Abrasives — Glass bead (Mohs 5.5), walnut shell (Mohs 3), corn cob (Mohs 2.5), baking soda (Mohs 2.5), plastic media (Mohs 3–4). Used for delicate cleaning, paint stripping without substrate damage, and cosmetic finishing.

Mesh Size and Profile Depth

Mesh Size	Particle Diameter	Typical Profile Depth
16–24 (coarse)	0.7–1.7 mm	3.0–5.0 mils (75–125 μm)
36–60 (medium)	0.25–0.7 mm	1.5–3.0 mils (38–75 μm)
80–120 (fine)	0.13–0.25 mm	0.5–1.5 mils (13–38 μm)
150–220 (very fine)	0.06–0.13 mm	0.25–0.5 mils (6–13 μm)

Selection Decision Matrix

Consider these factors when selecting media: - Substrate hardness: Media should not exceed substrate hardness for cleaning (match or exceed for aggressive profiling) - Desired finish: Angular media = matte/rough; spherical = satin/smooth - Recyclability: Steel shot can be reused 200+ times; garnet 3–5 times; soda is single-use - Environmental: Walnut shell and corn cob are biodegradable; steel and aluminum oxide are recyclable - Cost per cycle: Factor in reuse — steel shot at $0.50/lb reused 100x beats garnet at $0.30/lb reused 4x

Health and Safety Implications

Each media type generates different hazardous byproducts. Silica sand is banned in many areas because it produces respirable crystalline silica dust causing silicosis. Always verify the Safety Data Sheet (SDS) for any media before use.

Key Talking Points

• Never select media harder than necessary — over-aggressive media damages substrates
• Mesh size directly controls surface profile depth
• Total cost includes purchase price, reuse cycles, and disposal costs
• Always consult the SDS before using any new media

Learning Objectives (Concept Check)

• Compare metallic, mineral, and soft abrasive categories
• Use mesh size to predict surface profile depth
• Apply a selection decision matrix to choose appropriate media for a given application

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Last Updated: 2026-03-19