Dry ice blasting
The dry ice blasting is a compressed air jet method , in which solid as the blasting medium carbon dioxide , so-called dry ice , is used with a temperature of around -79 ° C. The process is used in surface technology for cleaning and deburring cast, sintered or thermoset parts.
General
Dry ice is electrically non-conductive, chemically inert , non-toxic and non-flammable. In contrast to other blasting media , dry ice changes directly from the solid to the gaseous state at ambient pressure without liquefaction - it sublimates .
For cleaning, the dry ice particles are accelerated with 5000 liters of air per minute, for example, and hit the material to be cleaned at the speed of sound. As a result, the layer to be removed is locally supercooled and embrittled. Subsequent dry ice particles penetrate the brittle cracks and sublime suddenly when they hit. The carbon dioxide becomes gaseous and increases its volume by about 700 to 1000 times. In doing so, it blasts off the dirt from the surface.
The advantages of this minimally abrasive and non-corrosive process lie in the low damage to the material to be cleaned and in the fact that no cleaning medium remains for disposal after processing, since the CO 2 evaporates in gaseous form in the ambient air. Because dry ice is relatively soft, many surfaces are not damaged; Sensitive electronic components can also be cleaned in this way, circuit boards with restrictions, as electrostatic discharge occurs. Due to the possibility of processing the smallest geometries with little damage and without dismantling, dry ice blasting is used, among other things, for cleaning casting molds, stripping paint from assemblies, removing underbody protection when restoring old and youngtimers, cleaning replacement engines and removing paint, rubber, oil and grease , Silicone, wax, bituminous coatings, release agents, binders and adhesives are used.
In monument preservation , paint can be removed without causing major damage, even inside buildings (here, for safety reasons, it is essential to ensure adequate ventilation). This technique is also used to remove paint, graffiti and remove the roots of ivy and wild grapevine on walls.
Abrasive dry ice blasting
Dry ice is a soft blasting agent (2-3 Mohs ). To ensure that stubborn impurities (e.g. paint on steel, rust scars in steel, patina on metals) are thoroughly removed, an additional blasting agent (glass beads, corundum, nutshells, plastic granulate ...) is added to the compressed air / dry ice mixture. This achieves the same cleaning results as with conventional abrasive blasting (sandblasting).
Properties of dry ice pellets
| Abrasives | spec. Weight (g / cm³) | hardness | Grain size (mm) | achievable surface roughness 1) |
|---|---|---|---|---|
| Dry ice pellets | 1.56 | 2 (after Mohs) | L: 5-10mm, d: 3-4mm | no surface roughening |
1) On uncoated ferrous materials and alloys.
See also
literature
- J. Haberland: Cleaning and stripping with dry ice blasting - Basic investigation of the CO 2 blasting tool and the procedure . (= Progress reports VDI. Series 2, No. 502). Dissertation . University of Bremen, 1999.
- C. Redeker: Removal with the dry ice jet . (= Progress reports VDI. Series 2 No. 639). Dissertation. University of Hanover, 2003.
- M. Krieg: Analysis of the effects of dry ice blasting . (= Reports from the Production Technology Center Berlin). Dissertation. TU Berlin 2008, ISBN 978-3-8167-7625-3 .
Individual evidence
- ↑ Steph Webb, Creare Communications Ltd: Frequently Asked Questions - Cryogenesis. In: www.cryogenesis.co.uk. Retrieved January 19, 2017 (English).