Dry ice blasting

Process for the cleaning with solid carbon dioxide (CO2, see Dry ice). The dry ice blasting method can generally be used for removing any type of material exhibiting intense reactions to temperature differences, such as oils, waxes, separating agents, but also paints, varnishes, adhesives, bitumen and plastic deposits. These can be readily removed without any damage to the surface.

Since dry ice blasting is considered to be non-abrasive, it is particularly suitable for gently cleaning molds and casting tools of any kind (e.g. gravity dies, core boxes, die casting molds, etc.).

Process principle

In the dry ice blasting unit, the dry ice pellets (Fig. 1ASCO Kohlensäure AG) are accelerated to a speed of approx. 300 m/s by means of compressed air and impinge upon the object to be cleaned, creating a point thermal shock. This causes the covering to be removed to contract and detach from the base material. The resulting kinetic energy removes the covering. Upon impact, the dry ice pellets immediately transition to the gaseous state (sublimation), leaving a dry surface. What remains is the detached coating or impurity, and there are no abrasives that need to be disposed of. As the pellets have a hardness of only approx. 2 Mohs, the surface quality is maintained and not damaged or altered (Fig. 2ASCO Kohlensäure AG). The Movie shows examples

Advantages of the process

  • Gentle: in contrast to conventional blasting methods using sand or glass beads, the cleaned surfaces are not damaged or altered. As an example, closing surfaces in gravity dies are not rounded, avoiding burring to occur.
  • No dismantling: the process can be applied directly to the molds/systems. Even hot gravity dies can be directly cleaned using this process without a noticeable cooling effect so that production can be resumed immediately after cleaning.
  • No blasting material residues: since the dry ice pellets immediately evaporate upon impact on the surface, there are no abrasives requiring disposal after cleaning.

Examples for the application of dry ice blasting are shown in Figs. 3 and 4 (ASCO Kohlensäure AG).

Literature references:
Website of ASCO Kohlensäure AG
Wikipedia, entry on “dry ice

  • Fig. 1: Dry ice pellets with a diameter of 3mm, source: ASCO Kohlensäure AG, Romanshorn, CH
  • Fig. 2: Process principle of ASCOJET dry ice blasting, according to ASCO Kohlensäure AG, Romanshorn, CH1) Thermal shock: the coating (impurity) contracts due to the sudden drop in temperature.2) Crack formation: the contraction of the coating causes cracks and the material becomes brittle due to the exposure to cold.3) Cleaning: the dry ice pellets impinging upon the surface at high speeds remove the detached covering.
  • Fig. 3: Dry ice blasting of a low-pressure gravity when hot, source: ASCO Kohlensäure AG, Romanshorn, CH
  • Fig. 4: Cleaning of a core box using dry ice, source: ASCO Kohlensäure AG, Romanshorn, CH
Movie 1