Aluminum Oxide Blast Media Grit Size Guide: Selection, Surface Finish, and Engineering Control

Selecting the correct grit size for aluminum oxide blast media is one of the most critical decisions in any blasting process. Grit size directly determines cutting aggressiveness, surface roughness, coating adhesion performance, substrate damage risk, blasting efficiency, and even long-term operating cost.

This guide is written as an engineering-level reference, not a simplified overview. It is intended for professionals who need to understand not only which grit to choose, but why that choice affects blasting outcomes, surface integrity, and downstream processes such as coating, bonding, or thermal spraying.

Rather than treating grit selection as a rule-of-thumb decision, this article breaks aluminum oxide grit sizing down into measurable variables including particle size distribution, surface roughness (Ra), anchor profile formation, equipment compatibility, and failure modes caused by incorrect grit selection.

1. The Role of Grit Size in Aluminum Oxide Blasting

Grit size defines the average particle size of aluminum oxide blast media. Because aluminum oxide is an angular, high-hardness abrasive, even small changes in grit size can produce significant differences in surface condition and material removal behavior.

At a fundamental level, grit size controls:

Impact energy concentration per particle
Cutting edge penetration depth
Surface profile height and sharpness
Rate of material removal
Risk of substrate deformation or erosion

In aluminum oxide blasting, grit size often has a greater influence on surface outcome than blasting pressure alone. Increasing pressure without changing grit typically increases cutting rate, while changing grit size fundamentally alters the surface morphology.

2. Grit Size Standards and Classification Systems

Aluminum oxide grit sizes are classified according to international standards. The most commonly encountered systems include:

ANSI (American National Standards Institute)
FEPA (Federation of European Producers of Abrasives)
JIS (Japanese Industrial Standards)

Although grit numbers may appear similar across systems, particle size ranges are not always identical. For industrial blasting applications, FEPA and ANSI standards are most commonly referenced.

It is important to note that grit size represents a range, not a single particle size. High-quality aluminum oxide blast media is tightly screened to ensure a narrow distribution within that range.

3. Grit Size to Micron and Particle Distribution

Understanding the relationship between grit size and actual particle size (microns) is essential for predicting blasting results.

Grit Size	Approx. Particle Size (Microns)	Typical Use Case
16	1000-1400	Heavy scale and coating removal
24	600-850	Aggressive cleaning of steel
46	300-425	General industrial surface prep
60	250-300	Balanced cutting and control
80	180–212	Coating adhesion preparation
120	90-125	Fine surface finishing
220	50–65	Precision blasting

Particle size distribution affects not only surface finish but also dust generation. As aluminum oxide is reused, fracture events gradually shift the effective particle size downward.

4. Grit Size and Surface Roughness (Ra) Control

Surface roughness (Ra) is a critical performance parameter for many blasting applications, especially when blasting is used as a surface preparation step prior to coating or bonding.

Aluminum oxide grit size is directly correlated with achievable Ra values:

Grit Size	Typical Ra Range (µm)	Surface Character
24	8–12	Very rough, deep anchor profile
46	5–8	Aggressive industrial profile
80	3–5	Optimal for many coatings
120	1.5–3	Smooth but still mechanically active
220+	<1.5	Cosmetic or precision surfaces

Excessive roughness can lead to coating defects, while insufficient roughness may reduce adhesion strength. Selecting grit size must therefore align with coating manufacturer specifications.

5. Coarse Grit Aluminum Oxide (16–36 Grit)

Coarse grit aluminum oxide is used for maximum material removal. The large particle size and high impact energy create deep penetration and rapid cleaning.

Typical Applications

Heavy rust and mill scale removal
Thick coating stripping
Structural steel surface preparation

Engineering Considerations

While coarse grit delivers high productivity, it also carries significant risk:

Substrate deformation on thin sections
Excessive anchor profiles incompatible with fine coatings
High media consumption

6. Medium Grit Aluminum Oxide (46–80 Grit)

Medium grit aluminum oxide represents the most widely used range in industrial blasting. It offers a balance between cutting power and surface control.