What Is Sandblasting?

Quick Answer

Sandblasting (also called abrasive blasting) is a surface treatment that accelerates hard particles in a high-velocity stream to clean, texture, or finish a substrate. The media—such as aluminum oxide, silicon carbide, garnet, glass beads, or steel grit—impacts the surface, removing contaminants (rust, paint, scale), creating an anchor profile for coatings, or delivering aesthetic finishes like matte or satin. Processes include pressure/suction air blasting, wheel blasting, and wet/vapor blasting. Media choice, particle size, velocity, and angle determine removal rate and surface roughness.

Table of Contents

• 1. Definition and Terminology
• 2. How Sandblasting Works (Mechanism & Core Variables)
• 3. Process Types: Air, Wheel, and Wet/Vapor Blasting
• 4. Abrasive Media: Properties and Selection
• 5. Media Comparison Table
• 6. Equipment & System Components
• 7. Process Parameters: Size, Velocity, Angle, and Coverage
• 8. Applications by Industry
• 9. Quality, Metrology, and Coating Readiness
• 10. Safety, Environmental & Compliance
• 11. Troubleshooting & Best Practices
• 12. FAQ

1. Definition and Terminology

Sandblasting historically referred to blasting with natural silica sand. Due to health risks from respirable crystalline silica, modern practice prefers the generic term abrasive blasting and uses safer substitutes (e.g., garnet, alumina, glass beads, steel media). The essential idea remains: propel abrasive particles at controlled speed and angle so that millions of micro-impacts remove material or modify the surface.

2. How Sandblasting Works (Mechanism & Core Variables)

At impact, each particle transfers momentum and energy to the surface. Angular media micro-cut and plow, rapidly removing coatings and raising roughness. Spherical media peen and clean, lowering roughness and producing uniform satin finishes.

• Impact energy: For a particle of mass m and velocity v, energy E = ½ mv². For spherical particles with diameter d and density ρ, m ≈ (π/6)ρd³, so E ≈ (π/12)ρd³v².
• Energy flux: If media mass flow is ṁ (kg/s), power delivered P ≈ ½ ṁv². Small increases in velocity strongly amplify removal rate.
• Particle shape and size: Angular → aggressive profile; spherical → gentle cleaning/peening. Coarse sizes remove faster but raise Ra; fine sizes refine the finish.

For a deeper dive into how hardness and density steer abrasive behavior, see your in-depth guide Abrasive Materials for Blasting and Polishing and the SiC-specific article Silicon Carbide Abrasives: Types, Properties, and Industrial Applications.

3. Process Types: Air, Wheel, and Wet/Vapor Blasting

• Air Blasting (pressure/suction): Uses compressed air to accelerate media through a nozzle. Flexible, precise for job shops and cabinets. Pressure systems deliver higher velocity than suction (venturi) systems.
• Wheel Blasting: A rotating wheel throws media at high speed (steel shot/grit commonly). Ideal for high-throughput, heavy descaling, and large components; media is continuously reclaimed.
• Wet/Vapor Blasting: Media suspended in water; minimizes dust, produces cleaner surfaces and smoother finishes. Useful for delicate substrates or contamination-sensitive environments.

4. Abrasive Media: Properties and Selection

Media choice governs cutting aggressiveness, finish, recyclability, and cleanliness.

• Silicon Carbide (SiC): Mohs ~9.2–9.4; very sharp and hard; rapid cutting on hard substrates; limited recyclability due to friability.
• Aluminum Oxide (Al₂O₃): Mohs ~9; versatile general-purpose blasting; multiple colors/grades (white = purer, brown = tougher).
• Garnet: Mohs ~7–7.5; natural mineral, sub-angular; clean blasting with relatively low dust; widely used for coating removal and field work.
• Glass Beads: Mohs ~6; spherical; gentle cleaning and cosmetic finishes; good for peening and reducing surface roughness.
• Steel Shot/Grit: High density, high recyclability; shot (spherical) for cleaning/peening; grit (angular) for profiling before coatings.
• Plastic/Organic Media: Soft; used on composites, aluminum skins, historical restoration where base-material damage must be avoided.

5. Media Comparison Table

For extended property comparisons and application matrices, consult Abrasive Materials for Blasting and Polishing.

6. Equipment & System Components

• Blast Cabinets / Booths: Enclosed environments for visibility, reclamation, and dust control. Cabinets for small parts; walk-in booths for large structures.
• Media Feed: Pressure pots (high velocity, efficient) or suction/venturi (simpler, lower rate). Wheel blast machines use impeller blades instead of compressed air.
• Nozzles: Boron carbide, tungsten carbide, or SiC-lined; internal geometry (venturi) influences velocity and pattern. Replace as they wear to keep performance stable.
• Reclaim & Separation: Cyclones, screens, and magnetic separators remove fines and contaminants, stabilizing finish and reducing consumption.
• Dust Collection: Cartridge or baghouse collectors; essential for visibility and worker safety.
• Air Quality & Dryers: Dry, oil-free compressed air prevents clumping and nozzle blockage.

7. Process Parameters: Size, Velocity, Angle, and Coverage

• Particle Size: Coarse (e.g., 16–36 mesh) for heavy removal and deep profiles; mid (60–120) for balanced cleaning/finish; fine (>180) for smooth finishes.
• Velocity/Pressure: Higher pressure and well-designed venturi nozzles raise particle speed; removal rate scales roughly with v² but so does wear.
• Stand-off & Angle: Close standoff intensifies impact. ~90° maximizes cut; shallow angles yield gentler cleaning and lower Ra.
• Coverage: Uniform traverse speed and pattern prevent streaks; for peening, verify coverage % and intensity using Almen strips.
• Substrate Sensitivity: Softer substrates (aluminum, composites) require softer or spherical media and lower pressures to avoid deformation and embedding.

8. Applications by Industry

• Protective Coatings & Corrosion Control: Removal of rust/mill scale and creation of anchor profiles for paints, primers, thermal spray, and powder coating.
• Automotive & Aerospace: Component cleaning, shot peening for fatigue resistance (steel shot), paint stripping with plastic media to protect skins and composites.
• Oil & Gas / Marine: Large-scale surface prep on tanks, pipelines, and ship hulls; garnet and steel media common for speed and economy.
• Manufacturing & MRO: Deburring, cosmetic finishing (glass bead satin), pre-bond prep for adhesives or coatings.
• Glass/Stone/Concrete: Etching, texturing, and decorative finishes; low-silica media preferred.

9. Quality, Metrology, and Coating Readiness

Quality control focuses on achieving the correct profile and cleanliness with minimal contamination.

• Surface Profile (Rugosity): Replica tape and stylus profilometry measure peak-to-valley. Coatings often specify a range (e.g., 50–100 μm).
• Roughness (Ra/Rz): Finer media and lower angles reduce Ra; spherical media move finish toward satin/low Ra.
• Cleanliness: Standards (e.g., visual blast standards) define rust/scale removal grades; salt contamination tests support coating performance.
• Adhesion Readiness: Proper profile + contaminant control → improved coating adhesion and lifespan.

10. Safety, Environmental & Compliance

• Silica Risk: Traditional sand is avoided due to silicosis hazards. Select low-silica media and ensure effective dust extraction.
• PPE: Blast helmets with airline supply, eye/ear protection, gloves, and protective suits.
• Ventilation & Filtration: Maintain negative pressure and efficient dust collection; dispose of spent media responsibly.
• Noise & Ergonomics: Wheel blast and high-pressure systems can be loud—use enclosures and hearing protection.
• Wet/Vapor Systems: Reduce airborne dust and static; improve visibility and cleanliness at the expense of equipment complexity.

11. Troubleshooting & Best Practices

• Inconsistent finish: Check media size distribution (remove fines), nozzle wear, pressure stability, and traverse uniformity.
• Low removal rate: Increase pressure/velocity, use more angular/coarser media, shorten standoff—balanced with finish requirements.
• Excessive roughness: Shift toward finer/spherical media or reduce pressure/angle; confirm substrate compatibility.
• Dust & visibility issues: Upgrade dust collection, reduce media breakdown (choose tougher media), dry and filter compressed air.
• Embedding/contamination: Use spherical/softer media for sensitive alloys; ensure media cleanliness and prevent oil/moisture in air lines.

12. FAQ

Q1: Is “sandblasting” the same as “abrasive blasting”?

In modern usage, yes—“abrasive blasting” is the preferred term since most facilities no longer use silica sand, opting for safer media like alumina, garnet, glass beads, or steel.

Q2: How do I choose the right abrasive?

Match media hardness/shape to your goal: angular and hard for rapid cut and profiles; spherical and softer for gentle cleaning or peening. Consider recyclability, dust, and contamination limits.

Q3: What pressure should I use?

Typical ranges are 60–120 psi for air blasting, but optimal pressure depends on media size, substrate sensitivity, and finish targets. Start lower, then tune upward while monitoring Ra and throughput.

Q4: What’s the difference between dry and wet blasting?

Wet/vapor blasting suspends media in water, greatly reducing dust and often improving surface cleanliness and finish. Dry blasting yields higher aggressiveness and is simpler to set up.

Q5: Can I reuse abrasive media?

Yes, many media are reusable (steel shot/grit very durable; glass beads moderate; SiC/alumina limited by friability). Reclaim systems and sieving extend life and stabilize finish.

Q6: How do I measure whether the surface is ready for coating?

Verify profile with replica tape or profilometer, check cleanliness visually and via salt testing if required, and ensure the specified anchor profile range has been achieved.

Further reading on media fundamentals: Abrasive Materials for Blasting and Polishing and Silicon Carbide Abrasives.