Dry ice blasting cleaning effectiveness and when to use it?

The particle blasting method of cleaning can be utilised effectively across a wide range of surfaces using CO2 pellets due to the compound’s poor conductivity, but how does this work? Daniel Took from Kärcher explains

Dry ice blasting is a particularly effective cleaning solution for cleanrooms as it produces reliable results without producing by-products in the process. This particle blasting method of cleaning can be utilised effectively across a wide range of surfaces using CO2 pellets as the blasting agent.

Unlike most other blasting media, for example sand, whose solid aggregate state remains unchanged throughout, the frozen CO2 pellets sublimate into gas on collision with the surface. This lack of residuals makes dry ice blasting an excellent cleaning application for cleanrooms.

The cleaning action of dry ice blasting is based on three physical effects

The blasting process works as the rapid decompression of liquid CO2 produces dry ice that is then compressed into small pellets, at minus 79°C in temperature. During the production process, liquid carbon dioxide flows into the pressing cylinder of the pelletiser and is turned into dry ice snow by the pressure drop. A hydraulic cylinder compresses this dry ice snow, which is then pressed through an extruder plate. This causes rods of dry ice to form, which are then broken down into pellets.

The pellets measure 3 mm in diameter and can be broken down into even smaller pieces to target delicate surfaces during the blasting process using the front-end scrambler. The pellets are accelerated to the speed of sound in a jet of compressed air and sublimate immediately upon impact with the surface to be treated.

Closed rooms or blasting cubicles must be fitted with a ventilation system and CO2 alarm

The use of liquid CO2 compressed into small snow pellets offers many positive characteristics due to the poor conductivity of CO2. After blasting, there are no wastewater, chemicals or blasting agent residues requiring disposal, as the pellets dissolve and return to the atmosphere as CO gas, leaving only the containment behind.

Depending on quantity and composition, they can either be blown away, using the compressed air on site, or vacuumed up.

How does it clean surfaces?

The cleaning action of dry ice blasting is based on three physical effects:

  1. As with many other blasting methods, the accelerated particles emit kinetic energy on impact allowing for the breakdown of stubborn agents including silicone, rubber, dyes and paints. The Mohs hardness (scale of mineral hardness) of the pellets produced during dry ice blasting is approximately the same as that of plaster, ensuring a potent clean.
  2. Thermal energy from the abrupt cooling to -79°C causes a thermal shock effect and produces fine cracks in the top layer of material to be removed causing it to go brittle and crumble away from the surface.
  3. Some of the frozen carbon dioxide penetrates the cracks in the dirt crusts caused by the thermal shock where it sublimates, increasing 400-fold in volume and, on a microscopic scale it literally blasts these dirt layers off. Through these three physical effects, dry ice blasting is able to remove unwanted paints, oil, grease, tar, bitumen, ink, resin, adhesives, wax, silicon and rubber residues, chewing gum and a wide variety of dirt encrustations from diverse substrates.

The ability to clean effectively without damaging surfaces and not leaving vast amounts of waste, makes dry ice blasting is another reason why this can be an effective solution for tackling dirt found within cleanrooms. The fact that dry ice blasting uses no chemicals and leaves no wastewater, also makes it an environmentally friendly solution for areas where cleaning with water is prohibited, including electrical wiring.

Dry ice blasting is non-abrasive and can be controlled for regulated for use on hard or delicate surfaces making it an effective cleaning solution within controlled environments.

It also does not require supplementary chemical agents within the cleaning process, making it highly effective for cleaning on the sensitive materials that may be found in regulated cleanrooms.

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Safety considerations for use

Dry ice blasters, such as the Kärcher IB 7/40 Adv, are portable and have pneumatic tyres and castors enabling them to be transportable like a porter's trolley even across uneven ground, across thresholds and up and down stairs without much effort. The blasting gun and dosing unit are electrically, rather than pneumatically, driven, so there is no risk that they will become iced up and fail. The aluminium blasting nozzles have rubber insulation and can be changed even when they are icy.

The different nozzle geometries and sizes make the machine highly adaptable, allowing it to be used on varied structures of very different designs and dimensions.

The acoustic pressure of a dry ice blasting machine is not inconsiderable. Depending on a variety of operating parameters, it varies between 75 and 125 dB(A), so the operator must wear ear protectors. Since dry ice is extremely cold, touching it can damage the skin.

The dry ice blasting gun and dosing unit are electrically, rather than pneumatically, driven

For safety's sake the operator's equipment must therefore also include an overall, goggles or a helmet with visor, and gloves. The MAK (maximum workplace concentration) of CO2 is limited to 0.5% by volume, which is not a problem in the open air or in a factory shed.

However, closed rooms or blasting cubicles must be fitted with a ventilation system and a CO2alarm, and operatives must wear respiratory protection.

The compressed air used should meet the requirements for at least purity class 3 (ISO 8573-1). Since even newer compressors often fail to deliver this, using a water and oil separator attachment kit with the XX is recommended. Depending on the specific application, a mobile or stationary air compressor with a pressure of 1.0-1.4 MPa and a volume flow of 8-10 m³ is required for the Kärcher dry ice blaster. Please note, these figures are for extremely stubborn dirt.

Dry ice blast cleaning can be a faster, more efficient, safer and environmentally friendly process when compared with many other cleaning methods. The use of dry ice blasting ensures manufacturers can effectively clean their equipment and facilities in in a shorter period whilst using fewer resources, making it the most suitable process for the cleaning of cleanrooms.

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