15 Mount Tom Ave., Holyoke, MA 01040 karen@invisiblast.com
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Commercial Dry Ice Cleaning & Restoration

F A Q

What is CO2 blasting?

  

It is a process in which dry ice particles are propelled at high velocities to impact and clean a surface.  The particles are accelerated by compressed air, just as with other blasting systems. Today, most applications are able to use standard shop air, in the 30 - 100 psi range.

How does it remove contaminants?

It depends on what you're cleaning. If you're removing a brittle contaminant such as paint, the process creates a compression tension wave between the coating and the substrate. This wave has enough energy to overcome the bonding strength and literally pop the coating off from the inside out. If you're removing a malleable or viscous coating such as oil, grease, or wax, the cleaning action is a flushing process similar to high pressure water. When the particles hit, they compress and mushroom out, creating a high velocity snow flow that actually flushes the surface.

How does this differ from how sandblasting works?

Sandblasting is similar to using an ice pick whereas dry ice blasting is similar to using a spatula. Sand cuts or chisels away the contaminant. Dry ice lifts it away. 

What happens to the dry ice once it strikes the surface?

It sublimates and returns to the atmosphere as carbon dioxide (CO2) gas. CO2 is a naturally occurring element that constitutes less than 1% of our atmosphere.

What happens to the contaminant?

People sometimes think it disappears too, but it does not. All cleaning involves the relocation of dirt. When you mop a floor, the dirt moves from the floor to the mop to the water in the bucket. With dry ice, the dirt moves from an undesirable area to an area where you can better deal with it. If it is a dry substance, it generally falls to the floor where it is swept away or vacuumed during normal maintenance.  If it is a wet substance like grease, you take a methodical approach similar to hosing down a driveway. You start at one end and guide the grease to the other end where it is vacuumed or squeegeed up. 

Does the process damage the substrate & Other Questions

Generally no, but it depends on the substrate. There is an energy threshold at which disbonding will occur and a threshold at which damage will occur. When the disbonding threshold is lower than the damage threshold, you can clean. If the reverse is true, damage can occur. Most of our applications deal with production equipment (cast iron, tool steel, tool grade aluminum), so there is no damage. We do have success with softer substrates such as plastics, wiring, pure copper, and fabrics, but these must be examined on a case-by-case basis.


Can CO2 be used to clean hot online?


The process cleans best hot. Most contaminants have weaker adhesive strength when hot. In many applications, you may be able to clean three to five times faster hot than cold. In addition, because dry ice sublimates on impact, entrapment of the blasting media is not an issue. Grit entrapment is an important reason those who clean with sand, walnut shells, or other grit media cannot clean online.


Does the CO2 cool the substrate?


Yes, but generally not as much as you might think. T he amount of cooling is dependent upon three main factors: mass of the targeted surface, dwell time, and ice usage rate. T ypically, a tire mold may start at 350°F and drop to 325°F during cleaning. With a very thin mold, the drop can be much greater. Generally, however, cooling is not a concern and only rarely does it affect cleaning performance.


Will the temperature drop damage the hot mold?


It depends on the mass of the mold. Large, heavy molds will not be harmed in any way because the drop in temperature is insignificant when compared to the mass of the mold. With thin molds where tolerances are critical, some testing may be required to determine if the drop in temperature would alter the structure of the mold.
 

Will the process create condensation?


Once again, it depends on the mass of the object you're blasting, your dry ice usage rate, and your dwell time. T here will be condensation if you cool the substrate below the dewpoint (the dewpoint varies depending on local climate). Of course, if you're cleaning a hot mold it is rare to have condensation because you seldom cool the mold below the dewpoint. Condensation is not a factor 80% of the time. When it is, it can be dealt with quite easily. Use of a hot air knife can be highly effective.


What are the best cleaning applications for CO2?


Delicate wiring in copy machines; conveyors; tire molds; dry ice blasting shines in cleaning production equipment online because it eliminates the need for masking, cool down and disassembly. Users minimize downtime which maximizes production efficiency. We have achieved outstanding results cleaning production equipment for foundries, molded rubber producers, food processors, printers, and the semiconductor industry. Dry ice blasting is also widely used in the nuclear industry for decontamination. Anytime waste volume or health risks are a concern, the viability of CO2 should be examined. Because CO2 disappears on impact, it creates no additional waste. Competing processes such 


Dry ice blastas grit blasting or solvents often present disposal problems or health hazards.


How is dry ice blasting used in foundries?


Dry ice blasting equipment is used in foundries worldwide to clean core boxes and permanent molds. Not only does dry ice blasting increase production by decreasing downtime, but it also eliminates mold damage, preserving the critical tolerances and greatly extending the life of the expensive tooling. 


What are some successful rubber molding applications?


Virtually every major tire manufacturer uses dry ice blasting equipment to clean tire molds. We also clean rubber molds for manufacturers of gaskets, o-rings, shoes, and many other products.  A good rule of thumb in the rubber industry is, if you can see it, you can clean it with CO2.


How is CO2 used in the food industry?


CO2 is perfectly suitable for use in this industry because it is food grade quality, the ingredient that provides the carbonation in soft drinks. It is used to clean ovens, conveyor belts, molds, dry mixers, laminators, and packaging equipment.
 

Can CO2 be used to remove paint?


Yes, however, the removal rate is dependent on a great many factors including: the underlying surface profile of the substrate; the thickness of the coating; the adhesive bond strength of the coating; and the cohesive strength of the coating (generally a function of age). Paint removal rates can vary dramatically, from 300 square feet/hour down to 1 square foot/hour. Generally speaking, if you have concerns with contamination, toxic substances, waste disposal, or substrate damage, dry ice blasting should be considered as a cleaning option. Otherwise, grit blasting is probably a more efficient method for paint removal.


Will CO2 remove greases, oils, or weld slag?


A methodical approach similar to hosing down a driveway is required if dry ice is to be effective on these and other wet contaminants. You must start at one end and work the grease to the other end where it can pass through a grate or be vacuumed or squeegeed for disposal. Some customers use a paper or plastic backdrop to catch the wet contaminant as it is removed from the substrate.  Dry ice doesn't dissolve the oil and doesn't make it disappear so you must have an acceptable way of handling it when it is relocated by the blasting process.


Can CO2 be used to remove rust?


It tends to remove the loosely adhered oxidation and salts, but will not remove the deeply adhered oxidation. You will not get a white metal finish. To do that you have to remove the surface metal, something the dry ice blasting process cannot do. Of course in many applications, this is a major advantage because it preserves the surface integrity of the substrate.


Will CO2 clean glass?


It can, but some prior testing is required to avoid shattering the glass.

Can CO2 be used to clean wood?


Yes. One of the exciting areas of dry ice use today is in mold remediation and fire restoration. Dry ice blasting will slightly raise the grain on the wood, leaving a finish similar to that of very light sandblasting. If you need a smooth wood finish, dry ice blasting will have to be followed by sanding or some other smoothing method. Because dry ice disappears as it strikes the surface, the only waste that must be disposed of is the removed contaminant and some wood fiber particles.


Does CO2 replace sandblasting / bead blasting / water blasting, etc.?


They are all tools in the toolbox. Consider that there are many types of hammers: ball peen; tack; claw; sledge; and so on. Could each do the job of the other? Perhaps, but the ideal toolbox would include each, because each has specific capabilities that it does better than any of the others.