What Is The Difference Between Shot Blasting And Sandblasting?

What Is Shot Blasting?

Put simply, shot blasting entails propelling small rounded beads, nuts or pellets towards a workpiece surface within an enclosed chamber using compressed air. Typical shot sizes range from 0.1mm upwards. Media materials vary widely but steel, glass and ceramic balls are most common.

Due to their weight and inertia, shot particles impact with substantial kinetic energy – enough to aggressively cut, peel or abrade non-ferrous metals, composites, and hardened materials. The spherical shape produces consistent results devoid of sharp points that could gouge.

Common applications include rust and scale removal prior to painting, wear surface preparation, and peening for induced compressive stresses. Heavier shot types are even used to embed particles into soft materials like plastics and resins through micro-blasting. Across industries, shot blasting improves surface traction, integrity, and corrosion resistance.

So in simplified terms – shot blasting propels spheres to physically etch and condition hard, durable surfaces. The energy produced by its hardened media produces strong effects through brittle fracture and plastic deformation mechanisms.

What is Sandblasting?

By contrast, sandblasting utilizes an angular abrasive like silica sand, crushed glass, baking soda or walnut shells that are less dense than shot media. Propelled via compressed air within an enclosure, these granular particles bounce and roll across materials removing contamination.

Due to the sharp edges of particles and their lower mass, sandblasting creates a scouring action rather than cutting deeply like shot media. It contours and polishes softer substrates rather gently through controlled surface abrasion instead of stock removal.

Common uses include preparation of timber, composites, and architectural elements prior to finishing. The low-energy impacts smooth without damaging substrate integrity as with stronger shot blasting. Artists also preference grainier media to texture surfaces for certain applications.

In essence – sandblasting is a lighter-duty deburring or texturing process utilizing softer, granular abrasives to gently contour materials unlike harsher shot blasting. Its lower kinetic energy impacts scour lightly rather than cut.

Comparing the Variables – Shotblasting vs Sandblasting

Beyond media type, several other factors further separate shot and sandblasting in terms of capabilities and effect:

Material Used

The abrasive media is a key distinguishing factor. Sandblasting traditionally employs silica sand or substitutes like glass beads due to silica’s health issues. Shot blasting uses small sphere-shaped beads, generally constructed of dense metals like steel, aluminum oxide, or carbon.

Compared to sand, the metallic shot media is more durable due to its density and rounded shape. This durability makes shot blasting effective for robust cleaning of tough surfaces versus sandblasting. However, silica and angular sand enable gentler texturing of delicate materials.

Media Propulsion

How the media is accelerated also differs. Sandblasting propels abrasives pneumatically via compressed air through simple nozzle-based systems. This is an economical approach but provides less control over velocities.

Shot blasting employs more sophisticated centrifugal or turbine-wheel driven mechanisms to mechanically catapult shot spheres. This imparts higher kinetic energies that potently remove contaminants from sturdy substrates. Pneumatic propulsion through nozzles suffices for less demanding de-rusting or finishing applications.

Surface Effects

Distinct surface topographies result. Sandblasting often creates a smoothed profile suitable for some coatings but risks inadequate keying of paint if too polished.

Shot blasting, conversely, controllably textures the workpiece through its bombardment. This enhances adhesion of subsequent protective treatments through a profiled yet not excessively harshly abraded stratum – prolonging their effective lifespan through mechanical interlocking.

Health and Safety

Silica sandblasting poses acute lung hazards as dust from this angular media endangers workers. Modern substitutes reduce such risks which led many jurisdictions to curtail silica.

When using standardized safety equipment, shot blasting does not liberate respirable or toxic particulate that can cause respiratory illness. Its shot media types are increasingly selected to minimize environmental and occupational dangers compared to sandblasting.

Application-Specific Considerations

Choosing between shot blasting and sandblasting depends heavily on the substrate material and end purpose. Some common usage scenarios illustrate where each technique uniquely excels:

Metal Components: Shot is preferred for deep rust/scale removal on castings while sandblasting risks embedment and rounding edges.
Historic Masonry: Soft aggregate media like baking soda maintain historic facade integrity compared to more aggressive shot types.
Timber Refinishing: Sand gently reveals grain without damaging tissue like potential shot embedment into softwoods.
Fiberglass Reinforcements: Loose sand embedment causes issues versus consistent rounding from shot for textured surface bonding.
Coating Applications: Shot produces a more chemically-receptive anchor profile for durable paint adhesion vs smoother sandblasting.

Clearly no single technique prevails universally. Careful consideration of variable factors ensures selecting the right preparation method aligned with the specific material and performance objectives. Let’s explore this topic through some real world examples.

Comparing Results in Practice

To better illustrate the tangible effects of each process, examining side-by-side case studies provides valuable insight beyond theoretical discussions:

Cast Iron Components

Shot blasted sections revealed deeper scaling/contamination removal with a uniformly scratched texture ideal for epoxy primer bonding compared to inconsistently scoured sandblasted pieces.

Fiberglass Wind Turbine Blades

Loose silica sand embedment caused lamination issues versus consistent dimpling from glass bead shot blasting, which enhanced subsequent bonding for added service life.

Reclaimed Architectural Timber

Walnut shell sandblasting gently revealed grain character, while consistent shot bead rounding would have compromised antique wood appearance valued by builders.

Steel Road Sign Posts

Aluminum oxide shot provided the deep profile specification required for traffic paint adhesion, surpassing baking soda sandblasting unable to fully remove rust on these durable beams.

In all cases, evaluating the substrate, required surface properties, and each technique’s technical outcomes proved shot blasting better served functional preparation needs on some items versus sandblasting. Real installations showcase where theories align with practical outcomes.

Effects on Different Material Types

The behavior and results of shot blasting and sandblasting vary significantly depending on the substrate composition. Let’s evaluate their performance when used on some common industrial materials.

Metal Surfaces

Ferrous Metals: Both methods effectively clean rust and scale from steel alloys. However, shot blasting is better-suited for robust de-rusting applications through its more forceful media acceleration. Sandblasting risks rounding sharp edges on intricate components.
Aluminum: The low density of this metal means sandblasting poses embedment risks versus shot blasting, which polishes without penetrating the surface. Shot blasting is preferred for aircraft-grade aluminum alloys.
Copper & Brass: These soft metals are easily abraded. Sandblasting gently contours them while maintaining dimensional tolerances, outperforming shot blasting’s potential for over-blasting.
Titanium: The hardness of titanium calls for aggressive descaling through high-velocity shot propagation over weaker sandblasting impacts. Media selection also avoids contamination from softer abrasives.

Composite Materials

Fiberglass: Loose silica sand can lodge between fibers and corrode reinforcing strands from the inside. Well-rounded shot creates a more forgiving dimpling that enhances bonding via mechanical interlocks.
Carbon Fiber: Both processes can abrade these strong, brittle composites if misapplied. Careful sandblasting at low pressures achieves cleaner surfaces than potentially damaging shot impingement.

Concrete & Masonry

Concrete: Coarser shot may crack and damage concrete. Finer abrasives like baking soda or walnut shells sandblasted at reduced working distances gentler clean and texture concrete surfaces.
Brick & Stone: Delicate masonry demands the most subtle media like crushed eggshells or apricot pits to sandblast away surface contaminants and algae growths without compromising integrity.

Wood Substrates

Most Hardwoods: Sandblasting exposes timber grain through a softened contours. Shot blasting risks compromising integrity through deeper scoring depending on application variables.
Softwoods: These porous woods are too fragile for embedded shot yet benefit from enhanced coloring following careful sanding. Walnut shell media add organic texture.
Engineered Panels: MDF, chipboard and other engineered boards can delaminate under high-pressure shot blasting. Gentle silica sand treatment cleans without damaging board structures.

Conclusion

Shot blasting and sandblasting denote more than synonymous terms – each defines a specialized industrial process leveraging distinct physics that warrant tailored application based on consideration of variables from the media up through the final surface requirements.

Armed with knowledge of their technical capabilities and limitations, fabricators and preparers can appropriately match shot or sandblasting techniques to a wider range of materials, conditions and performance specifications – whether removing corrosion before painting or imparting non-skid textures. With careful technique, either serves industry well for surface finishing applications aligned with their unique strengths.