What is dry ice blasting ?
It is a surface cleaning process where solid particles of carbon dioxide (dry ice or dry ice) are propelled at high speed to impact and clean the surfaces.
The air speed depends on the dry ice blaster, the pressure, the air volume, the type of nozzle and varies between:
– 60 to 120 m/s: two-hose or venturi system
– more than 290 m/s: one single hose system coupled with a supersonic nozzle
What is the origin of the technique?
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.
How it works ?
Generally speaking, dry ice blasting is a combination of 3 effects:
When dry ice particles hit a surface at the speed of sound, the contaminant cracks.
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.
What is the difference with sandblasting ?
Sandblasting works like a chisel, but dry ice blasting works like a spatula. The sand cuts or chisels the contaminant, while the dry ice lifts it after loosening it.
In addition, sandblasting generates a lot of dust, and it is generally not possible to clean in place.
What happens to dry ice when it impacts the surface?
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.
What happens to the contaminant?
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).
Does dry ice cleaning damage the surface?
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.
Can the hot equipment be cleaned on site?
You can clean up to three or five times faster when the equipment is hot. Adherence to the majority of contaminants is lower at higher temperatures. The dry ice sublimes at the time of impact, unlike the sandblasting that leaves the abrasive media trapped.
Abrasive cleaning methods are generally banned on-site in the industries.
Does CO2 cool the surface?
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.
The temperature drop, can it damage a hot mould?
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.
Will the process create condensation?
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.
How make dry ice?
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.
How make dry ice pellets?
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.
How much air (volume) do I need for dry ice blasting?
Normally, you need a minimum of 4000 l/min (4 m3/min) and a pressure of at least 6 bar, but this depends entirely on the application and the type of blaster (dry ice blasting machine). ).
85% of applications are carried out at pressures of 6-7 bar 4000-5000 l/min, but many applications require much less air:
Example 1: electrical cabinet cleaning with ATX nano – Required air volume 800 to 1500 l/min (pressure see Instructions for use)
Example 2: car seat cleaning with ATX nano – Required air volume 1200 to 3100 l/min (pressure see Instructions for use)
Example 3: machine tool degreasing with ATX25-E – Required air volume 4000 l/min (pressure see Instructions for use)
What are the possible cleaning pressures?
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
Can the feed rate of dry ice be changed?
It all depends on the device manufacturer. Some machines are priced at a certain consumption.
It is preferable to be able to increase or decrease the consumption of dry ice depending on the contaminant and the pressure.
The Cryoblaster ATX series includes a dry ice consumption regulator as standard:
- ATX nano: 0 to 35 kg/h
- ATX25-E: 0 to 75 kg/h
- ATX25: 0 to 65 kg/h
Do you need an air dryer?
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).
Cryoblaster® cleaning units are designed to give you years of trouble-free operation with minimal maintenance:
– 100% pneumatic dry ice blaster (ATX25): check the pneumatic oil level and the filters from time to time.
– electro-pneumatic dry ice blaster (ATX nano, ATX25-E): no maintenance
What are the best applications of dry ice blasting?
The range of dry ice blasting applications is incredible.
A small sample of our customers easily shows this: Révillon (chocolate factory), Renault Trucks (trucks), ITW (electronic cards), Pyxidis (medical), Groupe SAB (aluminum foundry) …
Dry ice blasting is excellent for cleaning in-line production tools because masking, or caulking, cooling, and disassembly is not required. We have obtained exceptional results by cleaning production equipment in foundries, in plastics, in the food industry, in printing …
Dry ice blasting is also widely used in the nuclear industry for decontamination.
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