What is dry ice blasting ?

Dry ice blasting It’s a process where solid carbon dioxide particles (dry ice) are blasted at high speed to impact and clean a surface. The air velocity is a function of the cryogenic nozzle and air pressure and varies between:

– 60 to 120 m/s: venturi system

-Over 290 m/s: single hose system coupled with supersonic nozzle

What is the origin of the technique?
It regained its origins at Lockheed in the years 70 when Calvin Fong, the engineer of the coating machines, was looking for ways to rejuvenate the aircraft primer.
How it works ?

In general, cryogenic cleaning is a combination of 3 effects:

  • Kinetic Effect:

When dry ice particles strike a surface at the speed of sound, the contaminant on the surface is cracked.

  • Thermal effect:

The low temperature of dry ice-78,5 °c makes the coating brittle, it cracks and peels off.

The bonding is reduced between the coating and the underlying surface.

  • Explosive effect-sublimation:

Dry ice is projected using compressed air and cryogenic cleaning machines.

The dry ice penetrates the cracked and departed coating and sublimes immediately (from the solid state to the gaseous state in ratio 1 to 400. This results in an increase of 400 times in volume, an explosive effect that raises the surface coating.

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

For malleable or viscous contaminants such as oil, grease or wax, the cleaning action is a process comparable to high pressure cleaning. When the particles hit the surface, they are compressed and flattened, producing a 360 ° high-speed snow throw that cleans the surface.

What is the difference with sandblasting ?

Sandblasting works like a chisel, but dry ice blasting works like a spatula. The sand cuts or engravess the contaminant while the dry ice lifts it.

In addition the sandblasting generates a lot of dust and it is usually not possible to clean on the spot.

What happens to dry ice when it impacts the surface?
It sublimes (moving from the solid state to the gaseous state) and returns to the atmosphere as carbon dioxide (CO2). CO2 is an element of natural origin that constitutes less than 0.04% e our atmosphere.
What happens to the contaminant?

It is transferred from an unwanted place to a place where you can take care of the latter more easily.

Dry contaminants fall to the floor where a broom or blower can be used to pick them up.

For viscous contaminants like fat, it takes a methodical process like cleaning to hate pressure. You start at one end and you guide the contaminant to a pickup point.

Does dry ice cleaning damage the surface?

The decohesion takes place at a certain energy threshold. When the decohesion threshold is below the damage threshold you can clean safely. When it is higher, you could damage the item. Since the majority of the items cleaned with CO2 are production equipment (cast iron, tool steel, high quality aluminum), there is no damage. We can also clean softer substrates such as plastics, yarn, pure copper, and tissues but we need to analyze each application.

Example of application may be recommended: stripping of a marine quality varnish on a soft wood (pine, fir).

The necessary pressure defibers 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 cooling level depends on three primary factors:

The mass of the target surface

B. The duration of application

C. The rate of ice use.

A tire mold could typically drop from 350 º F to 325 º F during cleaning.

With a very thin mould, the temperature drop can be more important.

Cooling is not normally a reason to care and the cleaning performance is seldom affected.

The temperature drop, can it damage a hot mold?

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 critically tolerant thin substrates, you may need to test to determine if the temperature drop will affect the surface structure.

Will the process create condensation?
Only if you cool the substrate under the dew point which varies according to the local climate. If you clean a hot mold, it is unlikely that you cool the mold under the dew point. It is therefore rare to cause condensation.
How make dry ice?

From Liquid CO2. The CO2 under the liquid state only under high pressure. When the pressure drops to atmospheric pressure, 50% turns into gas and 50% in dry ice.

The dry snow is then compressed into blocks, sticks or pellets.

How make dry ice pellets?

Liquid CO2 under pressure is reduced to atmospheric pressure: dry ice is obtained.

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

The machine capable of doing this work is a pelletizer.

There are two versions: hydraulic version, mechanical version.

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

However, it is possible to work without a problem with a mechanical ice

How much air (voulime) do I need for dry ice blasting?

Normally, a minimum of 4000 L/min and a pressure of at least 5.5 bars are required, but it depends entirely on the application.

85% of applications are made at pressures of 7 bar 4000-5000 l/min.

What are the possible cleaning pressures?

Cryogenic cleaning pressures range from 2 to 15 bars

Some scrapers however are whacked at pressures of 7 see 10 bars

Prefer strippers, which can work at least up to 12 bars

Can the feed rate of dry ice be changed?

It all depends on the hardware manufacturer. Some machines are crazy to a certain consumption.

It is préférabe to be able to increase or decrease the consumption of dry ice depending on the contaminant and the pressure

Regarding maintenance...

CRYOBLASTER ® Cleaning units are designed to give you years of trouble-free operation with minimal maintenance. It is necessary to keep oil in the burette of the librificateur, check the filters from time to time and examine the Tuayux compressed air from time to time to check that there are no cracks or abrasions.

What are the best applications of dry ice blasting?

The range of CO2-jet cleaning applications is incredible. A small sample of our clientele highlights this easily.

Cryogenic cleaning is excellent for cleaning the production tools online because masking, or caulking, cooling and dismantling are not necessary. We have achieved exceptional results by cleaning the production materials of foundries, in plastics, in the agro-food industry, in printing, in the semiconductor industry. Cryogenic cleaning is also widespread in the nuclear industry for decontamination.



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