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THE BASICS

EFFECTIVENESS

DRY-ICE

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Lets start with what CO2  blasting is:

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 80 - 100 psi range.

 
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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.

 
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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.

 
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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.

 
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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 squeegee up.

 
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Does the process damage the substrate?

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.

 
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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.

 
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Does the CO2  cool the substrate?
Yes, but generally not as much as you might think. The amount of cooling is dependent upon three main factors: mass of the targeted surface, dwell time, and ice usage rate. Typically, 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.
 
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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.

 
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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. There will be condensation if you cool the substrate below the dewpoint (the dew point 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 dew point. Condensation is not a factor 80% of the time. When it is, it can be dealt with quite easily. One method is to introduce heated air into the blast stream which usually eliminates condensation. This is a patented method possible only with phoenix two-hose system. A second method is the hot air knife which is also highly effective.

 
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How is dry ice made?

It is made from liquid carbon dioxide. Dry ice exists as a liquid only under high pressure. When it drops to ambient pressure (the normal pressure that surrounds us), approximately half turns to gas and half turns to solid. The solid, usually in the form of fluffy snow, is then compressed to form dry ice blocks, pellets, or nuggets.

 
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How are dry ice pellets made?

Pellets are made by taking liquid CO2  from a pressurized storage tank and dropping it to ambient pressure to produce snow. The snow is then pushed through a die to make pellets. The system is a mechanical, circular process in which the pellet extrudes very slowly before coming into contact with a pin which breaks it off at a very uniform length. The other type of system uses a hydraulic ram to form "spaghetti" which breaks off at random lengths as it passes through the die.

 
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How is block dry ice converted to blastable granules?

When you pull the trigger on Enviroblasts equipment, an actuator engages the ice, pushing it into the cutting face (the granulator) which produces particles that look much like raw sugar crystals, about 10 mils in size. Because the granulator only operates when the trigger is engaged, you only make granules as you need them. Any block that remains at the end of a given job can then be stored until the next job. Sublimation rates vary from 2-10% per day depending on storage conditions. A full block, properly stored, can still be useable several days later even after normal loss due to sublimation. The SDI-5 is a unique, patented system, the only blasting unit on the market capable of starting with block dry ice to create a blastable medium.

 
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Does block dry ice have advantages over pellets?

Yes. Perhaps the most important advantage of block dry ice is consumption. The SDI-5 can clean more effectively at 1½-2 pounds of block per minute than our competition can at 4-5 pounds of pellets per minute. Over the course of a year, this could save tens of thousands of dollars in ice costs alone. Block has many other important advantages over pellets. It is easier to transport because pellets tend to compact in transport, causing them to clump. Block tends to be easier to get and is generally sold at a lower cost per pound than pellets. Block dry ice also has a longer shelf life. Pellets have a higher surface-to-mass ratio which makes them more hydroscopic, meaning they attract water. When stored, this causes them to clump, making them unusable. Additionally, the higher surface-to-mass ratio causes the pellets to sublimate (turn into a gas) faster than block.

 
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Are there differences in the cleaning effectiveness of dry ice pellets vs. granules?

In about 75% of the applications, users do not choose dry ice media based on its cleaning effectiveness because there is little or no difference. In the remaining cases, pellets work better in some of the applications, granules in others. Generally speaking, pellets are more effective with thick hard to remove contaminants as the greater mass behind each individual particle more readily travels all the way through the contaminant to disbond it. Because the granules are smaller than the pellets, they produce a significantly greater number of surface impacts and are therefore better at removing paint. In addition, they are better for cleaning intricate patterns or tiny openings such as microvents in coreboxes.

 
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Why is pellet uniformity important?

It is critical in ensuring repeatability of performance. There are many applications where pellets of a certain size and density deliver optimal performance. Once you determine the size and density that best suits a given application, only phoenix systems can consistently deliver pellets to those precise specifications. Other pelletizing processes produce pellets with a much broader variance in pellet length and density, even within the same batch.

 
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What is the difference between a one-hose system and a two-hose system?

In the phoenix two-hose system, the dry ice travels in one hose and the high pressure air in another. The two are not mixed until just before the pellets exit the end of the nozzle. In a one-hose system the pellets and air are mixed together in one hose.The primary advantage of our two-hose system is reduced ice consumption. We deliver virtually all of our ice to the surface being cleaned. The one-hose system can stake no such claim. In U.S. government testing, it was determined that the one-hose system with a 25-foot hose lost 50% of its ice before reaching the surface. When the hose was lengthened, the losses increased. The phoenix system can often save tens of thousands of dollars annually in dry ice costs alone when compared to one-hose systems.

 
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How did the dry ice blasting technology originate?

It originated in the 70’s when a coatings engineer was researching ways to strip paint off aircraft. The technology did not become commercially available until it was introduced it to the marketplace in 1987. Phoenix continues to lead the way with many technological advances that have significantly impacted the industry.

 
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How much dry ice should I expect to use?

This is an important question to ask because the amount of dry ice you need to clean effectively can vary dramatically within the industry. With Enviroblast equipment, most customers need 1½-2 pounds per minute while the trigger is engaged. Of course, when we are cleaning, we won’t be pulling the trigger constantly. At a rate of 2 pounds per minute with 50% trigger time, we would use 60 pounds of dry ice in an hour.

 
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How is dry ice blasting used in foundries?

CO2  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. You don’t have to be an industrial giant to enjoy the cost benefits of CO2 . There are a large number of small to medium-sized foundries in the U.S. and abroad who successfully Enviroblast equipment to clean online.

 
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What are some successful rubber molding applications?

Virtually every major tire manufacturer uses CO2  blasting equipment to clean tire molds. Enviroblasting is also useful to 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 .

 
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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.

 
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What are some examples of applications where CO2  does not work well?

Dry ice Blasting Will not etch or profile most surfaces. If you need to clean large quantities of small parts, CO2  is not as efficient as other alternatives such as ultrasonic. Because dry ice blasting is primarily a line-of-sight cleaning process, if you can’t see what you need to clean, you probably can’t clean it with dry ice.

 
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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.

 
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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 squeegee 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.

 
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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.

 
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Will CO2  clean glass?

It can, but some prior testing is required to avoid shattering the glass. We have a customer who uses the technology to clean glass monitors before applying a non-glare coating. We have others who use it in general maintenance to clean oil and grease off of glass dials on control panels. To clean glass, it is important to remember that a certain impact energy is required to disbond the contaminant. If that energy level is high enough to also shatter the glass, you cannot clean using this process.

 
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Can CO2  be used to clean wood?

Dry ice blasting will raise the grain on the wood, leaving a finish similar to that of sandblasting. If you need a smooth wood finish, dry ice blasting is not the answer. The primary interest here has been in lead paint abatement. We are currently working with the Air Force to develop a program to remove lead paint from wooden buildings. Most other removal methods create too much additional toxic waste. Because dry ice disappears as it strikes the surface, the only waste that must be disposed of is the paint itself.

 
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Does CO2  replace sandblasting/beadblasting/ waterblasting, 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. phoenix equipment should be in your toolbox if you are concerned with downtime, entrapment, waste volume, or equipment damage.

 
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Is the system noisy?

Yes. Noise is a function of air volume and air velocity. Within the nozzle, the stationary air is sheared by the high velocity air causing turbulence which creates noise. The level can range from 85 - 130 db. Hearing protection is required.

 
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Do the contaminants or dry ice particles ricochet?

As long as it strikes the surface head on, dry ice does not ricochet because it sublimates (turns into a gas) on impact. As for the contaminant, you usually do not see or feel it as it disbonds and leaves the substrate, however, it is removed with some force which is why eye protection is recommended at all times.

 
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Does the process generate static electricity?

Yes. Any dry air process will generate static electricity and dry ice blasting is no exception. All phoenix equipment is designed with grounding devices. As long as both the blasting unit and the piece you are blasting is properly grounded, you are unlikely to have static discharge problems.

 
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Is it okay to blast in an enclosed area?

Yes, with proper ventilation. Because CO2  is 40% heavier than air, placement of exhaust vents at or near ground level is recommended when blasting in an enclosed area. In an open shop environment, existing ventilation is sufficient to prevent undue CO2  buildup.

 
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