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.
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.
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?
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. 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.
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 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.
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..
How is block dry ice converted to blastable granules?
When you pull the trigger on the SDI-5, 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. The SDI-5 is a patented system, the only blasting unit on the market capable of starting with block dry ice to create a blastable medium.
Does block dry ice have advantages over pellets?
Yes. It is easier to transport. Block dry ice 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 sublimate (turn into a gas) faster than block. Pellet machines are larger and more complex and consequently are much more expensive to purchase and operate.
Are there differences in the cleaning effectiveness of dry ice pellets vs. the granules produced by the SDI-5?
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.
How much dry ice do we 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. We use approximately 1½-2 pounds per minute while the trigger is engaged. Of course, when you are cleaning, you won't be pulling the trigger constantly. At a rate of 2 pounds per minute with 50% trigger time, you would use 60 pounds of dry ice in an hour.
How do we store dry ice?
Since dry ice is -109°F, putting it in a freezer doesn't really help. The best way to extend the shelf life is to store the ice in an insulated bin. Depending on the quality of the bin and how much ice you are storing, your loss due to sublimation should range from 2% to 10% per day. Premier Line Services bins are insulated and it holds up to 570 pounds of pellets. It features a hinged lid and includes casters to make it easy to move around the shop floor. The tote was specially designed to withstand the extreme temperatures, payload, and rugged use associated with the dry ice industry.
How did the dry ice blasting technology originate?
Dry ice blast cleaning originated at Lockheed in the 70's when a coatings engineer, Calvin Fong, was researching ways to strip paint off aircraft. The technology did not become commercially available until Alpheus bought the license and patents from Lockheed and introduced it to the marketplace in 1987.
How much air will Premier Line Services need to clean effectively?
It is typical to operate at about 90 psi with 130 cfm, however your needs will depend on your application. Premier Line Services uses nozzles that clean effectively while using as little air as possible.
What blasting pressures are possible?
Most of our standard gun configurations are rated up to 125 psi which is well above the 90-100 psi used in the vast majority of applications.
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 80 - 130 db. Hearing protection is required.
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. We 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.
