Since kinetic impact force is a product of the pellet mass and velocity over time, our 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.
Even at these high impact velocities and direct head-on impact angles, the kinetic effect of solid CO2 pellets is minimal when compared to other media (grit, sand, PMB). This is due to the relative softness of a solid CO2 pellet, which is not as dense and hard, as other projectile media. Also, the pellet changes phase from a solid to a gas instantaneously upon impact, which effectively provides an almost nonexistent coefficient of restitution in the impact equation. Very little impact energy is transferred into the coating or substrate, so the process is considered non abrasive.
Thermal Shock Effect
Instantaneous sublimation (phase change from a solid into a gas) of the CO2 pellet upon impact absorbs maximum heat from the very thin top layer of surface coating or contaminant. Maximum heat is absorbed due to latent heat of sublimation.
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. The shear stresses produced are also dependent upon the coating thermal conductivity and the thermal coefficient of expansion and contraction, as well as the thermal mass of the underlying substrate. The high shear produced over a very short period of time causes rapid micro-crack propagation between the layers leading to contamination and/or coating final bond failure at the surface of the substrate.
Thermal-Kinetic Effect
The combined impact energy dissipation and extremely rapid heat transfer between the pellet and the surface cause instantaneous sublimation of the solid CO2pellet 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.
This "micro explosion", as the pellet changes from a solid to a gas, is further enhanced for lifting the 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 the 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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