DRY ICE BLASTING PROCESS
Dry ice production process
In practice, dry ice is produced by expanding liquefied CO2 from a suitable tank from a pressure of approx. 17 bar to atmospheric pressure. Liquefied CO2 is injected into the mold or antechamber.
Dry ice snow produced in this way is then hydraulically pressed with a dry ice press to produce dry ice in the form of pellets or blocks of various sizes.
Dry ice is solid carbon dioxide (CO2) that evaporates under normal conditions at temperature above -78.48 °C, which means that it goes directly to the gaseous state without first melting.
Dry ice is a white, odorless, ice-like solid that evaporates at atmospheric pressure. During evaporation, its volume increases up to 760 times.
If necessary, the CO2 exhaust gases produced during dry ice production can be re-liquefied by the CO2 recovery system and returned to production.
Principle of operation
THERMAL EFFECT
Selective hypothermia
Dry ice pellets are accelerated to approximately 1000 km/h (approximate speed of sound) by White Lion dry ice blasting systems and compressed air, the pellets are jetted directly on the workpiece to be cleaned. The following basic physical factors
are largely responsible for the mode of action of this method.
Dry ice pellets that hit a component, lead to sudden precise hypothermia of the coating, to be removed or to be contaminated.
Due to the different thermal expansion coefficients of the impurity layer and the workpiece, thermal stresses arise between these two layers. These cause the decisive micro-cracking in the dirt layer.
Contamination becomes brittle and literally bursts.
The higher the difference in expansion coefficients, the higher the removal rate and thus the overall cost effectiveness of dry ice cleaning.
Phase effect
transformation – sublimation
The high kinetic energy of dry ice pellets causes not only their deformation and crushing when impacting the workpiece, but also microcracks in the dirt layer. Small particles of dry ice penetrate deep into these cracks and thereby break up the layer of dirt to be removed.
Kinetic effect:
coating blasting / contamination
Dry ice particles that have penetrated the fragile glands now suddenly sublimate (change from solid to gas). Due to the volume increase during sublimation about 700 to 1000 times, the layer, to be removed, completely separated from the workpiece.
The dry ice blasting medium is now gaseous.
Result: Cleaned, undamaged surface
Unlike traditional blasting techniques, dry ice blasting is a non-abrasive process. This means that there is no abrasion on the workpiece. The surface looks like new.
Advantages of a dry ice blasting system
With a dry ice blasting machine, pellets of dry ice are fired at the surface to be cleaned using air pressure, removing stubborn dirt without the use of abrasive material. Working with mineral organic blasting material such as sand, soda ash, granulated walnut shells or glass beads is still very common for tough cases. However, these approaches have two unpleasant side effects: On the one hand, the cleaned material can be attacked by the abrasive blasting material to the point of complete destruction. Second, the blasting material is not only blown into the area to be cleaned, but everywhere. At best, it will fall to the ground where it can be swept up and disposed of.
But it is much more likely that it settles in all corners, from where it has to be removed by lengthy cleaning. High-pressure water cleaning does not have this problem, but the effectiveness of a sharp water jet is limited and high moisture penetration during the cleaning process is an exclusion criterion for many applications.
When working with dry ice blasting, on the other hand, no blasting material or water is produced as waste. Pellets fired with a dry ice blasting system vaporize without leaving any residue. After treatment with a dry ice blasting machine, only loose dirt remains.