The Science Behind Dry Ice Blasting
CO2 blasting works because of three primary factors: pellet kinetic energy, thermal shock effect, and thermal-kinetic effect. Dry ice blasting machines optimize blast performance for each application by combining these forces.
Pellet Kinetic Energy
The process incorporates high velocity (supersonic) nozzles for surface preparation and coating removal applications. Since kinetic impact force is a product of the pellet mass and velocity over time, the delivery system achieves the greatest impact force possible from a solid CO2 pellet by propelling the pellets to the highest velocities attainable in the blasting industry.
Thermal Shock Effect
Instantaneous sublimation (phase change from solid to gas) of CO2 pellet upon impact absorbs maximum heat from the very thin top layer of surface coating or contaminant. The very rapid transfer of heat into the pellet from the coating top layer creates an extremely large temperature differential between successive micro-layers within the coating.
This sharp thermal gradient produces localized high shear stresses between the micro-layers, which in turn causes rapid micro-crack propagation between the layers leading to contamination and/or coating final bond failure at the surface of the substrate, meaning that, for lack of a better term, the sudden, intense temperature change causes the surface coating to crack and peel away.
The combined impact energy dissipation and extremely rapid heat transfer between the pellet and the surface cause instantaneous sublimation of the solid CO2 into gas. The gas expands to nearly 800 times the volume of the pellet in a few milliseconds in what is effectively a "Micro-explosion" at the point of impact.
The "micro-explosion," as the pellet changes to gas, is further enhanced for lifting thermally-fractured coating particles from the substrate. This is because of the pellet's lack of rebound energy, which tends to distribute its mass along the surface during the impact. The CO2 gas expands outward along the surface and its resulting "explosion shock front" effectively provides an area of high pressure focused between the surface and the thermally fractured coating particles. This results in a very efficient lifting force to carry the particles away from the surface.
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