Dry ice blasting is a relatively new process which gets rid of even stubborn dirt residues in a particularly gentle and above all environmentally friendly way. Offering speed, flexibility and mobility in its use, dry ice blasting increasingly represents a cost-saving alternative to other cleaning processes. Plus it has even more advantages for its users.

Dry ice blasting has already replaced other cleaning processes in many industrial sectors. For example, it is used for cleaning printing machines, motors, engines, facades and molds in plastic and rubber manufacturing. “Carbon dioxide in its solid form is suitable for removing lacquers, paints, oils, carbon black, plastic residues and many other stubborn residues,” says Thomas Böckler, Technology Manager Industry at Messer and contact person on matters relating to dry ice blasting.Blasting with dry ice can be compared to sand blasting, only it is much gentler. Grains of dry ice are small, solid and cold. When these pellets hit the contaminated surface with pressure, the dirt contracts under the cold conditions, breaks loose from the surface and is then simply blown away by the air pressure and the pellets that follow. Rod-shaped pellets with a diameter of approximately three millimeters and a length of one centimeter are used for this.

EFFECTIVELY DISSOLVED INTO THIN AIR
The principle of this blasting process is to embrittle the dirt by transferring the cold energy stored in the dry ice pellets, and then to break it up and remove it under pressure. In addition to the quantity of pellets, crucial factors for the cleaning process include the material properties of the object to be cleaned, such as the starting temperature, thermal conductivity as well as the type and thickness of the dirt. Optimal results can be achieved by adjusting the quantity of pellets and the acceleration pressure to suit the cleaning conditions. The advantage of dry ice as a blast medium is that the cold pellets, which have a temperature of minus 79 degrees, are converted to gaseous carbon dioxide during application and effectively dissolve into thin air. The result is no sand and no contaminated water – all you have to do after blasting is sweep up the dirt.

PERFECT IN MANY AREAS
The process cleans monitors, leaving them residuefree, and removes oils and fats from gauges without damaging the sensitive devices. Residues caused by welding robots are easy to get rid of as only a little kinetic energy is needed to remove them. For the cleaning of circuit boards, printing machines or casting molds, a grinder is used, which grinds the pellets into sugar-sized grains. The crystalline particles accelerate the subcooling of the base material and increase the removal rate without abrading the surface.Dry ice blasting is an alternative for cases where toxic substances have to be removed, since the contaminants are not mixed with other substances, making disposal much easier. “If the surface to be cleaned must not be damaged, sensitive parts cannot be removed or environmental regulations must be complied with, then dry ice blasting is the method of choice,” explains Thomas Böckler. “Applications that call for abrasive blasting, or where the base material and the layer to be removed have already started to form a chemical bond, achieve better results with a sand or glass blaster,” the dry ice expert adds.

FROM CO₂ TO DRY ICE
The different physical states of substances – solid, liquid and gaseous – are particularly well-known with regard to water: ice, liquid water and water vapor. Carbon dioxide, too, occurs in these states. Gaseous carbon dioxide is either extracted from ground sources or recovered as a waste product from a range of industrial processes. This means that the CO₂ that is used for dry ice blasting does not result in an additional increase in CO₂ emissions into the atmosphere. To turn the CO₂ into a solid, i.e. to change its physical state, it is first liquefied under pressure. Dry ice snow is then produced by sudden expansion. The snow is either pressed into blocks or pellets, the latter by using perforated plates.

SUCCESS DEPENDS ON PRESSURE TOO
The effectiveness of dry ice blasting depends on the amount of cold energy and the kinetic energy. In order to remove heavy contamination, an optimum nozzle as well as an air pressure of more than ten bar is usually necessary. The nozzle and jet pipe of the gun are adapted to the compressed air conditions. “The Messer experts check all the parameters on-site and fine-tune them in order to achieve an optimum and efficient cleaning result,” says Thomas Böckler, describing the support Messer provides to customers.