What factors influence the cleaning results of dry ice blasting?

How it works – briefly and clearly

Before we get to the specific settings, it is worth taking a quick look at the ‘why’ behind the effect. In dry ice blasting, CO₂ pellets strike the contamination at high speed (kinetics); the extreme cold of −78.5°C weakens the adhesion of the coating (thermal shock); and upon impact, the pellets immediately turn into a gaseous state, expanding rapidly (sublimation). This causes the loosened deposit to lift away, leaving behind a dry, clean surface – with no secondary waste. Limitations arise where contaminants are too firmly adhered or oxidised, such as in the case of rust
 

Why preparation determines the result

In practice, it is repeatedly evident that the blasting result is not determined on the surface, but is already decided during the planning stage. Anyone who clearly defines the target result (suitable for production, visually flawless, ready for painting), correctly classifies the material and coating, and checks the infrastructure has already done half the work before the first blast. This also includes sorting out the dry ice logistics, having suitable nozzles ready, and realistically assessing the available compressed air – including pipe diameters, drying and filtration.

Dry ice quality – freshness is a performance factor

Not all dry ice is the same: fresh pellets transfer more kinetic energy and intensify the thermal shock. Older dry ice pellets (older than 2 days or – depending on storage conditions) absorb a lot of ambient moisture; they appear glassy, partially collapse and are no longer clearly recognisable as pellets. In the blasting machine’s hopper, they tend to clump together and cause blockages at the inlet of the distribution unit. Moisture also settles on the surface of the object being cleaned – the surface becomes wet. The cleaning jet stalls and becomes uneven. This leads to an irregular cleaning result and wasted time.

The solutions are simple: short transport distances, insulated boxes, rapid processing and thorough dry-blowing before starting. Those who clean regularly also benefit from in-house production: fresh, dense dry ice pellets are available as and when needed, logistical dependencies and losses are reduced, and reproducibility increases.
 

The right nozzle – shaping the jet

The nozzle you choose determines the focus, energy density and air requirement – the following options have proven themselves in practice:

• Round nozzle (conical acceleration): It concentrates the blasting energy and produces the highest localised effect – ideal for selectively removing stubborn deposits. Its strength lies in the maximum energy density over a small area and the clean transitions. Depending on the task, orifices such as 10/11/13 mm are used; for particularly delicate surfaces, plastic variants are available.
   
• Flat nozzle: It distributes the energy over a wider area and ensures even, smooth transitions on large, flat surfaces. The spot power decreases, whilst the surface coverage increases.
   
• Angled nozzle: Where geometries are angular or work must be carried out at a distance, it facilitates access. Jet control is less precise than with round and flat nozzles, which is why it is suitable for selective applications – where accessibility is more important than perfect line definition. Or for small closing gaps, particularly in the plastics industry.
   
• Combi nozzle (Venturi principle): Where required, this allows the addition of fine abrasive media (up to approx. 0.3 mm) to break through localised resistance where dry ice alone is insufficient. It is not intended as a continuous sandblasting solution; its strength lies in providing targeted ‘boosts’ without compromising the nature of dry ice blasting.

Practical tip: Test nozzles on site – material, geometry and surface vary. A direct comparison reveals the best choice for the desired blasting result.

Compressed air – quality, volume and the right pressure

Compressed air is the carrier medium of the process and is often the limiting factor. Clean, dry air with a low pressure dew point prevents icing, pellet breakage and erratic blasting patterns. The flow rate is equally important: the machine, nozzle and desired output determine how much free air (m³/min) must actually reach the nozzle under load. If there is insufficient volume, the particle velocity drops – and the effectiveness drops noticeably. Only when the quality and quantity of the air are right is it worth increasing the working pressure: higher pressure increases the pellet velocity, but only works effectively in a stable air environment. A practical reference point from the plastics industry: 2.5–3 bar is often sufficient for removing release agents; for large-area cleaning or stubborn layers, higher pressures and larger nozzles are advisable. And during breaks: use up any ice, briefly blow dry – this keeps the system clear.

Fine-tuning – small adjustments with a big impact

Once the ice, nozzle and compressed air are under control, fine-tuning determines the speed and gentleness of the process. A slightly warm surface intensifies the relative thermal shock and accelerates the removal of release agents, paints or adhesive residues. The jet distance and angle determine the energy density: 90° to the object being blasted is ideal. Pellet dosage also needs to be carefully controlled – more is not automatically better. Often, the balance between pellet quantity and air velocity delivers the highest area output with moderate consumption. And finally, the match between material and coating: dry ice works particularly well when coatings react to temperature differences or impact (e.g. release agents, plastic and food residues, PU foam, adhesives, wax, bitumen). For firmly adhered oxides, the optional abrasive additive via the combination nozzle can provide the necessary extra power.

What this means for your day-to-day operations

Those who view dry ice blasting as a process rather than a one-off measure get more out of it: more consistent results, lower ice consumption, shorter set-up times and less downtime. The sequence is logical and practical: clarify the target, assess the object, secure the air side, ensure a fresh supply of ice, test the nozzle and fine-tune the parameters on the object. This turns a technology into a reliable standard in industrial cleaning – from mould maintenance to plant cleaning.

How ASCO supports you: We won’t leave you to it on your own. ASCO actively supports you – from the initial assessment directly at your site, through the air-side audit (quality, flow rate, ducting), to nozzle and parameter tests under real-world conditions. Our experts bring with them many years of expertise from a wide range of industries and work with you to develop a setup that suits your application and resources – including training and practical optimisation during ongoing operations.