EXPLANATIONS OF THE dry ice blasting PROCESS
Dry ice cleaning: how does it work? The cryogenic cleaning technique represents a tremendous advance in industrial cleanliness. However, it remains a mystery to many neophytes, and maybe even you are one of them. Discover in this article and this video the explanations of the dry ice blasting process
Dry ice blasting in a few words …
Dry ice blasting is a cleaning technique that uses dry ice and its physical properties as a means of an instantaneous detachment of pollution or dirt.
Since dry ice (solid carbon dioxide) has the hardness of chalk, this process gently cleans surfaces. To discover all the advantages of this industrial cleaning technology, click on the link at the bottom of the page, “Advantages of dry ice blasting”.
The Cryoblaster® process uses the projection of dry ice by blasters and compressed air. See the illustration below.
Dry ice in the form of 3 mm pellets is introduced into the blaster inside the tank or hopper (1).
After connecting the compressed air supply (compressor or factory pressurized air network) (2) and switching “on” the dry ice blasting unit, the dry ice is mixed with the compressed airflow inside the blaster (3), then is propelled to the work of a blasting hose(4).
Finally, the dry ice is projected onto the surfaces to be cleaned using a gun with a spray nozzle at supersonic speed (5).
Dry ice blasting is based on the simultaneous action of 3 physical phenomena
See video below
1- Kinetic energy
Dry ice in the format of pellets with a diameter of 3 mm is projected at a very high speed onto the surfaces to be treated thanks to compressed air and the use of supersonic nozzles (convergence/divergence).
Dry ice is thus charged with kinetic energy (Ec = 1/2mV²).
Upon impact, the pellets generate a localized shock wave which facilitates the de-cohesion of the pollution on the treated surface.
However, it is important to remember that the energy transfer on the support is minimal and this for 2 reasons:
– First: the hardness of dry ice is comparable to that of chalk. Less dense, less heavy, dry ice is non-abrasive.
– Second: the almost instantaneous transition (or thousandths of a second) from the solid-state to the gaseous state of dry ice, therefore, allows the only minimal transfer of energy, as indicated above.
2- Thermal differential
The very low temperature of the dry ice pellets of -78.5 °C gives the cryogenic cleaning process undeniable thermodynamic properties!
Depending on the type of pollution or the contaminant treated, the temperature difference between the dry ice and the substrate, or thermal shock may occur. As the temperature of a contaminant or pollution decreases, it becomes brittle, allowing the impact of the pellets to break up the pollutant.
The thermal gradient or the difference between two different materials with different thermal expansion coefficients can also facilitate the decohesion of the pollutant from the support. This thermal shock or thermal differential is more evident during dry ice cleaning of a non-metallic coating (ex: electrical cabinets covered with dry residue) or of a contaminant linked to a metallic substrate (ex: coating on a foundry mould)
The hotter the temperature of the surface to be treated, the faster and more economical the dry ice cleaning process (ex: aluminium foundry gravity mould).
Many companies are interested in the cryogenic cleaning process but are worried about the reaction of their tools to the cold of dry ice: studies have shown that the temperature drop only occurs on the surface, so that ‘there is no risk of thermal stress in the metal mass of the support. Ex: plastic moulds.
On impact, dry ice sublimes (changing from a solid-state to a gaseous state) in a ratio of 1 to 700. We can speak of micro-explosions.
The dirt is blown away. All you have to do is vacuum up the dirt or residue. The treatment is dry and does not generate secondary waste, unlike the use of a high-pressure cleaner or a sandblaster.
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