FREQUENTLY ASKED QUESTIONS

The dry ice blasting technique has its origins at Lockheed in the 1970s when coating machine engineer Calvin Fong was researching techniques for rejuvenating the primer on aircraft cabins.

Generally speaking, dry ice blasting is a combination of 3 effects:

Kinetic effect:

When dry ice particles hit a surface at the speed of sound, the contaminant cracks.

Thermal effect:

The low temperature of dry ice (-78.5 ° C) makes the contaminant fragile, it peels off: the bond between the coating and the underlying surface is reduced.

Explosive effect or sublimation:

Dry ice is projected using compressed air and dry ice blasting machines.

Dry ice penetrates into the cracked and peeled contaminant, and immediately sublimes (change from solid to gaseous state in a ratio of 1 to 400): an “explosive effect” occurs and blows the contaminant off the surface.

By blasting dry ice particles onto hard contaminants such as paint, varnish… the process produces a compression wave between the coating (contaminant) and the substrate (surface). This wave has sufficient power to break the cohesion and detach the contaminant, which by gravity ends up on the ground.

For malleable or viscous contaminants like oil, grease or wax, the cleaning action is a process comparable to high-pressure cleaning. As the particles hit the surface, they are compressed and flattened, producing a high-speed 360 ° spray that cleans surfaces.

Dry ice sublimates on impact (changing from a solid to a gaseous state or sublimation) and returns to the atmosphere as carbon dioxide (CO₂).

CO₂ is a naturally occurring element that makes up less than 0.04% of our atmosphere.

It is transferred from an unwanted place to a place where it can be more easily “taken care of”.

The dry contaminants fall on the ground (or on a plastic sheet): one can then use a broom, a vacuum cleaner or place everything in a container for reprocessing.

For viscous contaminants such as grease, it is necessary to act methodologically, such as high-pressure cleaning. Cryogenic firing is carried out from point A to point B, while guiding the contaminant towards the pickup point (B).

The decohesion or detachment of the contaminant takes place at a certain energy threshold. When the decohesion threshold is lower than the damage threshold, you can clean without danger. When it is higher, you might damage the surface.

The hardness of dry ice is comparable to that of chalk.

Since the majority of parts cleaned with CO₂ are production equipment (cast iron, steel, stainless steel, aluminium) there is no damage. You can also clean more fragile substrates (surfaces) such as plastics, electronic boards, monuments, copper, fabrics, etc.

A preliminary test will make it possible to define the feasibility of the dry ice cleaning project.

Example of application not recommended:

Stripping a marine-grade varnish on soft wood (pine, fir): the pressure necessary to loosen the varnish from the wood.

The level of surface cooling depends on three primary factors:

a) the mass of the target surface

b) the duration of application

c) dry ice consumption per hour

A tire mould would typically drop 175 to 162 ° C during the application of dry ice blasting.

With a very thin mould, the temperature drop may be greater.

The cooling of the tool is in the great majority of cases minimal.

This is unlikely, but it depends on the mass of the target object.

Heavy moulds, for example, will not be damaged at all because the temperature drop is insignificant compared to the mass of the mould.

With thin, critical tolerance substrates, you may need to do some testing to determine if the drop in temperature will affect the structure of the surface.

Condensation can only occur if you cool the substrate (surface) below the dew point, which varies depending on the local climate.

If you are cleaning a hot mould, you are unlikely to cool the mould below the dew point. It is therefore rare to cause condensation.

From liquid CO₂ under high pressure. When the pressure of liquid CO₂ drops to atmospheric pressure, 50% turns into gas and 50% turns into dry ice.

The dry ice is then compressed into blocks, sticks or pellets of 3 mm.

The pressurized liquid CO₂ is brought back to atmospheric pressure: carbon dioxide snow is obtained.

This snow is compressed and pushed through a die or die to form pellets.

The machine capable of doing this job is a pelletizer. There are 2 versions:

– hydraulic version,

– mechanical version

The first version (hydraulic) offers a higher density ice, therefore an increased stripping power.

However, it is possible to work without problem with a glass of mechanical origin.

Dry ice blasting pressures range from 0.3 to 15 bar (ATX25-E).

Some competing guns, however, are rated at maximum pressures of 7 or even 10 bar.

Prefer guns, which can work up to a pressure of 12 bar minimum.

Cryoblaster ATX working pressures:

• ATX nano: 3 to 12 bar
• ATX25-E: 0.3 to 15 bar
• ATX25: 3 to 15 bar

Cryoblaster ATX equipment is designed for cleaning operation with clean dry air (available in most factories).

Although the ATX series includes an internal micron filter as standard, an additional air dryer will be needed in exceptional circumstances:

– absence of compressed air treatment at the customer’s premises,
– rental of a compressor without a compressed air treatment system

You should always purge compressed air lines before connecting them to your ATX unit. This will remove any water and dirt that might be there (see methodology Instructions for use of your ATX).