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THE FUNDAMENTALS OF DRY ICE BLAST CLEANING

Today, CO2 / dry ice blasting is being effectively used in a wide array of applications from heavy slag removal to delicate semiconductor and circuit board cleaning. Imagine a process that can be used on-line without damaging equipment or requiring a machine "teardown". Unlike conventional toxic chemicals, high-pressure water blasting and abrasive grit blasting, CO2 / dry ice blasting uses dry ice particles in a high velocity air flow to remove contaminates from surfaces without the added costs and inconvenience of secondary waste treatment and disposal.

History
In the early 1930's, the manufacture of solid phase carbon dioxide (CO2) became possible. During this time, the creation of "dry ice" was nothing more than a laboratory experiment. As the procedure for making dry ice became readily available, applications for this innovative substance grew. Obviously, the first use was in refrigeration, and dry ice is still widely used in the Food Industry for packaging and protecting perishable foods today.

1945 saw stories of the U.S. Navy experimenting with dry ice as a blast media for various degreasing applications. In May 1963, Reginald Lindall received a patent for a "method of removing meat from bone" using "jetted" Carbon dioxide particles. In November 1972, Edwin Rice received a patent for his "method for the removal of unwanted portions of an article by spraying with high-velocity dry ice particles". Similarly, in August 1977, Calvin Fong received a patent on "Sandblasting with pellets of material capable of sublimation".

The work and success of these early pioneers led to the formation of several companies in the early 1980's that pursued the development of dry ice blasting technology. In 1986, Cold Jet®, Inc. was founded in the State of Ohio by Mr. Newell Crane.

Dry ice pelletizers and dry ice blasting machines entered the industrial markets in the late 1980's. At that time the blasting machines were physically large, expensive, and they required high air pressure for operation (pressures greater than 200 psi or 13.8 bar). As the CO2 / dry ice blasting technology advanced, the dry ice blasting machines' size and cost dropped, and today, the latest nozzle technology has made blasting effective at shop air pressures (80 psi or 5.5 bar).

What Is Dry Ice?
Dry ice is the solid form of Carbon Dioxide (CO2), which is a colorless, tasteless, odorless gas found naturally in our atmosphere. Though it is present in relatively small quantities (about 0.03% by volume), it is one of the most important gases we know of.

CO2 is a natural media that serves many life sustaining purposes. It is a key element in the carbon cycle; it is the only source of carbon for the carbohydrates produced by agriculture; it stimulates plant growth; and it helps to moderate the temperature of the earth overall. Animal respiration is believed to add 28 million tons of Carbon Dioxide per day into the atmosphere. By contrast, the U.S. CO2 industry can supply only 25,000 tons per day and 95% of this amount is from by-product sources, or less than 0.04% of the other sources combined.

With a low temperature of -109° F (-78° C), solid CO2 (dry ice) has an inherent thermal energy ready to be tapped. At atmospheric pressure, dry ice sublimates directly to vapor without going through a liquid phase. This unique property means that the blast media simply disappears, leaving only the original contaminant to be disposed of. In addition, blast cleaning in water sensitive areas is now practicable.

The grade of carbon dioxide used in dry ice blasting is the same as that used in the food and beverage industry and has been specifically approved by the FDA, the EPA and the USDA. Carbon dioxide is a non-poisonous, liquefied gas that is both inexpensive and easily stored at work sites. Of equal importance is its non-conductive and non-flammable nature.

CO2 is a natural by-product of several industrial manufacturing processes such as fermentation and petrol-chemical refining. The CO2 given off by the above production processes is captured and stored without losses until needed. When the CO2 is returned to the atmosphere during the blasting process, no new CO2 is produced. Instead, only the original CO2 by-product is released.

Listed in Table 1 are the physical properties and conversion factors for CO2 in its various forms:

Table 1. Carbon Dioxide (CO2 ) properties.

Molecular Weight	44.01
Density (Solid)	97.5 lbs/ft3 at -109° F / 1565 kg/m3 at -78° C
Density (Liquid)	63.7 lbs/ft3 at 0° F / 1022 kg/m3 at -18° C
Density (Gas)	0.123 lbs/ft3 at 32° F / 1.974 kg/m3 at 0° C
Melting Point	-69.9° F at 75.1 psia  / -56.6° C at 5.2 bar absolute (triple point)
Boiling Point	-109.3° F / -78.5° C (sublimates)
Liquid-to-Gas Conversion Rate	8.726 scf (gas)/lb / 0.544 m3 (gas)/kg (liquid at 0°F / -18°C and 305 psia / 21 bar absolute)
Liquid-to-Snow Conversion Rate	.46 lb snow / lb liquid at 0° F / .46 kg snow / kg liquid at -18°
	.57 lb snow / lb liquid at -55.0° F / .56 kg snow / kg liquid at -48°C

Media Manufacture
In dry ice blasting, there are several methods used to manufacture the dry ice blasting media. One technique is to shave dry ice granules from a solid CO2 (dry ice) block at the blasting machine. This generally produces sugar-crystal sized dry ice granules, which must be used quickly due to rapid sublimation (which is due to their high surface area-to-volume ratio).

Another technique is to manufacture hard pellets of dry ice in a pelletizer then immediately blast with the pellets or store the pellets in an insulated container until they are needed. These dry ice pellets are generally on the order of 0.08" to 0.12" (0.2cm to 0.3cm) in diameter, and 0.1" to 0.4" (0.25cm to 1cm) in length.

Pelletized dry ice is manufactured by flashing pressurized liquid CO2 into snow, and then compressing the snow into solid form. The snow is either directly nuggetized into pellets (mechanical compression) or is extruded into solid pellet form through a die under hydraulic pressure. The latter process allows for a more efficient conversion from the liquid phase to the solid phase. Generally, it is desirable to have dry ice pellets that are well compacted to minimize the entrapment of gaseous CO2 and/or air which may affect product quality.

As seen in Table 1, the yield achieved when flashing liquid carbon dioxide into snow increases as the temperature of the liquid CO2 decreases, so it is important to pre-chill the incoming liquid CO2 via heat exchangers with the outgoing CO2 vapor. Figure 1 is a block diagram showing a basic pelletization process.

Several manufacturers make dry ice pelletizers, which may prove beneficial to have on-site for customers with high pellet demand. Facilities required for such an arrangement are generally as follows: a refrigerated liquid CO2 tank, a pelletizer, and liquid CO2 lines to reach the equipment.

Some manufacturers make combined dry ice pelletizer/blast machines, which manufacture the dry ice and then blast it all in one operation. Facilities required for such an arrangement are: An air compressor (typically either 120 psi at 250 SCFM / 8.3 bar at 7.1 m3/min or 350 psi at 250 SCFM / 24.1 bar at 7.1 m3/min), a liquid CO2 tank, a pelletizer/blast machine, a compressed air hose and liquid CO2 lines to reach the equipment, a blast hose from the machine to the blasting operation, and the appropriate nozzle(s) for the application. This equipment is best suited to high-volume, continuous dry ice blasting applications where the cost savings of manufacturing pellets on-site justifies the capital expenditure for the system. ( See: Cold Jet's Integrated Systems and FlashJet®).

How Does Dry Ice Blasting Work?

The Basic Process
Dry Ice blasting is similar to sand blasting, plastic bead blasting, or soda blasting in that a media is accelerated in a pressurized air stream (or other inert gas) to impact the surface to be cleaned or prepared. With dry ice blasting the media is solid carbon dioxide (CO2) particles. One unique aspect of using dry ice particles as a blast media is that the particles sublimate (vaporize) upon impact with the surface. The combined impact-energy dissipation and extremely rapid heat transfer between the dry ice pellet and the surface causes the instantaneous sublimation of the solid CO2 / dry ice into gas. The gas then expands to nearly eight hundred times (800x) the volume of the dry ice pellet in a few milliseconds in what is effectively a "micro-explosion" at the point of impact. Because of the solid CO2 vaporizing, the dry ice blasting process does not generate any secondary waste. All that remains to be collected is the contaminate being removed.

As with other blast media, the kinetic energy associated with dry ice blasting is a function of the particle mass' density and impact velocity. Since CO2 / dry ice particles have a relatively low hardness, the process relies on high particle velocities to achieve the needed impact energy. The high particle velocities are the result of supersonic propellant or airstream velocities.

Unlike other blast media, the CO2 / dry ice particles have a very low temperature of -109° F (-78.3°C). This inherently low temperature gives the dry ice blasting process unique thermodynamically induced surface mechanisms that affect the coating or contaminate in greater or lesser degrees, depending on the coating type. Because of the temperature differential between the dry ice particles and the surface being treated, a phenomenon known as "fracking" or thermal shock can occur. As a material's temperature decreases, the material becomes embrittled, enabling the particle impact to break-up the coating. See Figures 2 and 3.

FIGURE 2. Thermal shock induces micro-cracking in the surface coating

FIGURE 3. CO2 gas expansion and pellet kinetic effects break away and remove coating particles.

Also, the thermal gradient or differential between two dissimilar materials with different thermal expansion coefficients can serve to break the bond between the two materials. This thermal shock is most evident when blasting a non-metallic coating or contaminate bonded to a metallic substrate.

Quite often companies examining the dry ice blasting process are concerned with the effect the thermal shock will have on the parent metal. Studies have shown that the temperature decrease occurs on the surface only, so that there is no chance of thermal stress occurring in the substrate metal. To illustrate this principle, an experiment was performed where thermocouples were imbedded into a steel substrate at varying depths (flush with the surface to 2 mm deep). See Figure 4.

FIGURE 4. Thermocouple Distance From Plate Surface.

A CO2 / dry ice blast jet was constantly swept across the test specimen for 30 seconds (a relatively long dwell time for this process) and the thermal couples recorded the changing temperatures at the various depths. As shown in Figure 5, the surface-mounted thermocouple shows a temperature drop each time the blast jet passed directly upon the it (50° C in about 5 seconds). In contrast, the thermocouples imbedded at various depths in the substrate recorded a slow gradual drop in temperature corresponding to the overall test plate temperature drop. The thermocouple 2mm deep only dropped 10° C after 30 seconds. This curve illustrates that the "Thermal Shock" occurs only at the surface where the coating or contaminate is bonded to the substrate (Reference 1) and has no detrimental effect on the substrate.

FIGURE 5. Temperature Response Of Thermal Couples Placed At Various Depths In The Substrate

Another approach to looking at thermal stress is by studying the use of dry ice blasting in the molded rubber industry. Here, hot steel molds operating at 300+ °F (149+°C) are blasted with -109 °F (-78.3°C) dry ice particles. The temperature difference between the hot mold and cold Dry Ice will not cause cracking. There are two reasons for this phenomenon. First, as seen above, the temperature gradient occurs at the surface. Second, the thermal stresses involved are much less than those encountered during normal heat treatment.

The thermal stress due to a temperature differential can be estimated using equation 1 where sy is stress (psi), DT is temperature gradient (°F), a is coefficient of expansion and g is Poisson's Ratio.

            1.0

The corresponding parameter values are

            2.0

and the thermal stress (psi) is

            3.0

where the temperature differential will be 135 °F / 57.2°C (Based on Figure 5). This temperature gradient leads to a low tensile stress of 30,240 psi / 2085 bar. Even if the mold temperature was brought down to the temperature of the ice (an unrealistic extreme), the temperature gradient would be -109 °F - 350 °F which gives 459 °F / 237.2°C, for which the corresponding tensile stress is 102,800 psi / 7088 bar. This calculated stress is below the yield point of steel in the hardened condition. Again, these thermal stresses would be far less than those encountered during normal heat treatment where the temperature differentials would exceed 500 °F / 260°C (Reference 2).

Even at high impact velocities and direct "head-on" impact angles, the kinetic effect of solid CO2 / dry ice particles is minimal when compared to other media (grit, sand, PMB, etc.). This is due to the relative lack of hardness of the dry ice particles and the almost instantaneous phase change to a gas on impact, which effectively provides an almost nonexistent coefficient of restitution in the impact equation. Because dry ice blasting is considered non-abrasive and relies on the thermal effects discussed above, the process may be applied to a wide range of materials without damage. Soft metals such as brass and aluminum cladding can be dry ice blasted for the removal of coatings or contaminates without creating surface stresses (pinging), pitting, or roughness (Reference 3).

Blast Machine Types
There are two general classes of dry ice blasting machines as characterized by their method of transporting pellets to the nozzle: the two-hose and the single-hose systems. In either type of system, the proper selection of blast hose is important because of the low temperatures involved and the need to preserve particle integrity as the dry ice particles travel through the hose.

In the two-hose system, Dry Ice particles are delivered and metered by various mechanical means to the inlet end of a hose and are drawn through the hose to the nozzle by means of vacuum produced by an ejector-type nozzle. Inside the nozzle, a stream of compressed air (supplied by the second hose) is sent through a primary nozzle and expands as a high velocity jet confined inside a mixing tube. When flow areas are properly sized, this type of nozzle produces vacuum on the cavity around the primary jet and can therefore draw particles up through the Ice hose and into the mixing tube where they are accelerated as the jet mixes with the entrained air/dry ice particle mixture. The exhaust Mach number from this type of nozzle is, in general, slightly supersonic. Advantages of this type of system are relative simplicity and lower material cost, along with an overall compact feeder system. One primary disadvantage is that the associated nozzle technology is generally not adaptable to a wide range of conditions (i.e. tight turns in a cavity, thin-wide blast swaths, etc.). Also, the aggression level and strip rate of the two-hose system is less than comparable to single-hose blast machines.

In a single-hose system, particles are fed into the compressed air line by one of several types of airlock mechanisms. Reciprocating and rotary airlocks are both currently used in the industry. The stream of pellets and compressed air is then fed directly into a single hose followed by a nozzle where both air and pellets accelerate to high velocities. The exhaust Mach number from this type of nozzle is generally in the 1.7 to 3.0 range, depending on design and blast pressure. Advantages of this type of system are wide nozzle adaptability and the highest available blast aggression levels. Disadvantages include relatively higher material cost due to the complex airlock mechanism.

Dry ice blasting machines are also differentiated into Dry Ice Block Shaver Blasters and Dry Ice Pellet blasters.

The Block Shaver machines take standard 60 lb (27.3 kg) dry ice blocks and use rotating blades to shave a thin layer of ice off the block. This thin sheet of dry ice shatters under its own weight into sugar grain sized dry ice particles. These particles then fall into a funnel for collection. A two-hose delivery system (see above) is used to transfer the particles at the bottom of the funnel to the surface to be cleaned. The low mass of these particles combined with the inefficient two-hose system limits the block shavers to light duty cleaning. Because the shaved ice machines deliver a dry ice particle blast with high flux density (Number of particles striking a square area of surface per second), they are effective on thin, moderately hard coatings such as an air dried oil based paint. The disadvantage of the ice shaver is that the dry ice particle's size and flux density, as well as its velocity, are fixed.

In contrast, Pellet Blasting machines have a hopper that is filled with pre-manufactured CO₂ / dry ice pellets. The hopper uses mechanical agitation to move the pellets to the bottom of the hopper and into the feeder system. As stated earlier, the pellets are extruded through a die plate under great pressure. This creates an extremely dense pellet for maximum impact energy. The pellets are available in several sizes, ranging from 0.04" to 0.12" (0.1 cm to 0.3 cm) in diameter. With a single-hose delivery system, the final pellet size and blast flux density exiting the nozzle is governed by the type of blast hose (hose diameter and interior wall roughness) and nozzle used. Because of its design, the single-hose dry ice pellet blasting units are capable of "dialing-in" the correct blast type needed for a wide range of individual coatings or contaminate removals.

For example, soft coatings such as rubber, silicone, foams and waxes, release agents, food ingredients, etc. need large dry ice pellets with low flux density for maximum strip rate and efficiency. These coatings require maximum thermal energy (i.e. dry ice pellets with large mass) and large spacing between the pellets (i.e. low flux density) for optimum cleaning performance. In contrast, hard coatings such as paints, varnish, baked on sugars, carbon build-up, etc. require smaller particle size with high flux density and high particle velocity.

Dry ice blasting machines are further differentiated into all-pneumatic and electro-pneumatic types.

All-pneumatic machines have a pneumatically operated dry ice particle feed mechanism and controls. This may include the use of air motors. The advantage of such a machine is the availability of compressed air at the blast locations, especially outdoors. One disadvantage is that the operation of the machine may be susceptible to disruption due to moisture or contamination in the compressed air supply. In addition, these machines are more prone to freeze-ups and are better suited for light duty spot cleaning applications. Also, if the machine is powered by an air motor, it will have a continuous exhaust of oily air. This same air motor can easily be flooded with water if the air system is not adequately dried.

Electro-pneumatic machines are truly "Environmentally Friendly" because there is no oily exhaust and these machines are more tolerant of moisture and contaminants in the air supply. The electro-pneumatic machines rarely freeze-up which makes them ideal for automated line applications where around-the-clock dry ice blasting is required. Also, these machines provide pulse free blasting for uniform cleaning and efficient use of the dry ice. There is, however, a slight inconvenience factor associated with supplying both electrical power and compressed air to the machine at each blast location.

One of the most challenging technologies associated with either type of blast machine is the achievement of smooth, continuous pellet feed. One surprising property of dry ice is that it is not smooth or slippery like water ice nor is it smooth-flowing like sand or glass bead. Instead it is somewhat resistant to flow. Because of this, dry ice blast machines tend to have various agitators, augers and other devices in the hopper to improve pellet flow. Generally, the poorer the quality of the dry ice - containing, for example, water ice build-up or a large percentage of CO2 "fines" or snow - the more difficult its flow through a system. An additional property of dry ice is that it is extremely cold and will draw moisture out of the surrounding air in the form of frost. Therefore, the machine must be tolerant of repeated freeze-thaw cycles and the associated moisture accumulation that will take place over time.

Generally, the difference between a high-quality dry ice blasting machine and a mediocre one lies in the unit's ability to do a cleaning job quickly, cost-effectively, and with the reliability of smooth and continuous dry ice pellet flow under real-world conditions.

Nozzle Technology
The nozzle is where the dry ice particles are accelerated to the highest velocity possible in order to create an effective dry ice blast stream. Figure 6 shows the schematics of the two types of nozzles used for dry ice blasting. The science of two-hose ejector nozzles compared to single-hose convergent-divergent supersonic nozzles operating under the same conditions (i.e., air volume, pressure, temperature, CO2 particle mass...etc.), shows a significantly higher efficiency capability for the described single-hose type nozzles. This difference in capability is directly related to the two-hose ejector nozzle's overall supplied energy being used not only to accelerate the CO2 / dry ice particles, but also to create the vacuum pulling the secondary pellet flow through the secondary hose. Then, more energy is drained to mix this low velocity particle flow with the high velocity jet flow in order to accelerate the dry ice particles through the two-hose nozzle. In simple terms, the net resultant energy available for pellet acceleration is inherently lower for two-hose systems because much of the available energy is lost simply in combining the CO2 / dry ice particle flow with the air-jet flow.

Figure 6. CO2 / Dry Ice Blasting Nozzle Types

When sand or any similar media with a very small diameter is used in blasting, the size of the nozzle throat is very large compared to the blast media. In dry ice blasting, however, the nozzle throat may only be slightly larger than the dry ice particle being accelerated.

Table 2 is a chart indicating the approximate size of a round nozzle throat for four different levels of blast pressure at a constant airflow of 200 Standard Cubic Feet per Minute (SCFM) / 5.7 m3/min, a typical flow rate available for blasting operations. At higher pressures, the dry ice particle size needs to be smaller to correspond with the smaller throat size. The high-pressure blast stream is described as high-velocity small particles with high flux density. Again, this particle blast profile is best suited for removing hard coatings such as paint. The chart shows a larger nozzle throat diameter corresponding to low pressure operations. As stated above, large pellets impacting the surface with low flux density is ideal for cleaning soft coatings.

Table 2. Pressure To Nozzle Throat Diameter Relationship

Blast Pressure (psi)	Throat Diameter (in)
80	0.360
120	0.302
250	0.216
300	0.198

Dry ice blasting nozzles tend to be long as a result of the requirement to accelerate particles to as high a velocity as possible. Therefore, a very long nozzle with a small throat tends to have a high scrubbing-surface-area per unit airflow. This explains the higher efficiency of low-pressure dry ice nozzles compared to high-pressure nozzles. A minimum cost dry ice blasting system for industrial use has a design point at 80 psi / 5.5 bar, a typical pressure for a plant air system.

Benefits of CO2 / Dry Ice Blasting technology

Cost Reduction
The natural sublimation of dry ice particles eliminates the cost of collecting the cleaning media for disposal. Containment and collection costs associated with water/grit blasting procedures are also eliminated.

Because CO2 / dry ice blasting systems provide on-line maintenance capabilities for production equipment (online cleaning), time consuming and expensive detooling procedures are kept to a minimum. Dedicated cleaning cycles are no longer required as preventive maintenance schedules can be adopted, which allow for equipment cleaning during production periods. As a result, throughput is increased without the addition of labor or production equipment.

Extension of Equipment's Useful Life
Unlike sand, walnut shells, plastic beads and other abrasive grit media, dry ice particles are non-abrasive. Cleaning with dry ice will not wear tooling, texture surfaces, open tolerances, or damage bearings or machinery. In addition, on-line cleaning eliminates the danger of molds being damaged during handling from press to cleaning area and back.

A Dry Process
Unlike steam or water blasting, CO2 / dry ice blasting will not damage electrical wiring, controls, or switches. Also, any possible rust formation after cleaning is far less likely with dry ice blasting than with steam or water blasting. Also, when used in the Food Industry, dry ice blasting reduces the potential for bacteria growth inherent to conventional water blasting.

Environmental Safety
Carbon dioxide is a non-toxic element which meets EPA, FDA, and USDA* industry guidelines. By replacing toxic chemical processes with CO2 / dry ice blasting systems, employee exposure and corporate liability stemming from the use of dangerous chemical cleaning agents can be materially reduced or eliminated completely. Since CO2 gas is heavier than air (CO2 gas displaces oxygen), care must be taken if blasting in enclosed areas or down in a pit.

Current CO2 Blast applications

Molded Products
Dry ice blasting cleans unwanted release agents ("parting agent") and/or residual material build up from the mold's contact surfaces. That is to say that the build-up of release agents or residual product from the hot mold are easily removed. Dry ice blasting allows the tools or molds to be cleaned while the mold is hot and still in the press. This reduces "press downtime due to cleaning" by 80% to 95%. Since the process is non-abrasive, CO2 / dry ice blast cleaning will not wear the tools or open critical tool tolerances. Furthermore, "micro vents" are typically cleaned by dry ice blasting. This eliminates the hand-drilling of plugged vents needed for optimum gas escape. Examples of molds/mixers cleaned by Cold Jet are:

• Rubber Molds
• Tire Molds
• Urethane Molds
• High Density Polyethylene Molds
• PET Molds
• Foam Molds
• Banbury Mixers

Dies
There are many types of dies and sometimes the word "die" is practically synonymous with "mold". And, as with molds, the dry ice blasting application is usually quite successful. Both molds and dies usually operate at elevated temperatures, which increases the cleaning rate and the attractiveness of on-line cleaning. Examples are:

• Aluminum Foundries
• Core Boxes
• Paper Plate manufacturing

The Food Industry
Residual sugars left behind after baking can be readily removed from fixtures in most cases. Here, as with molding, heat may enhance removal speed and characteristics. In many cases the dry ice blasting application may be performed on-line.

A key benefit of using dry ice blasting to replace some of the general cleaning (done with water, detergents and sanitizers) is moisture reduction. Indeed, moisture promotes the growth of bacteria -- particularly salmonella -- whereas dry ice blasting actully inhibits bacteria growth. Furthermore, economics have led to the on-line cleaning of fixtures including wafer plates, waffle irons and other similar batter or dough baking and product forming fixtures, oven bands and conveyor belts.

CO₂ / dry ice blasting has been proven to remove and/or destroy significant biofilm build-ups of listeria and salmonella. Typical applications include:

• Cookie Oven Bands
• Baking Ovens, Shelves and Trays (without shutting down or disassembly)
• Wafer plates (Carbon build-up removal)
• Flight & Conveyor Cleaning
• Tanks and Vessels (removes Ingredient build-up)
• Screws and Augers

• Cleaning Conveyor Components
• Cleaning Hoppers
• Cleaning Car Carriers
• Removing weld slag from Robotics, Fixtures, Carriers
• Removing Oils and Grease from chains, machinery, etc.
• Cleaning Packaging Equipment
• Removing Adhesives

The Printing Industry
In the Flexographic Printing Industry, inks and varnish polymers are designed to adhere to most surfaces, resist scratches, and, in some instances, be solvent resistant. These characteristics, which make their use so attractive, also make the removal of dried ink very difficult. Ink buildup on the gears and deck guides causes poor alignment and results in low print quality. To compensate for this phenomenon, plate mounting generally needs to be adjusted several times in order to register critical graphics to produce an acceptable quality level. Generally, each "press run" to check the register of the colors results in thousands of feet of wasted material. This inherently wasteful process can now be eliminated due to the on-line precision cleaning ability of dry ice blasting.

The Future
We can't predict the future, but with environmental issues and legislation becoming more and more stringent, one thing is certain: the successful shops of the future will have fully incorporated the CO2 / dry ice blasting process into their operations.

* EPA: Environmental Protection Agency, FDA: Food and Drug Administration, USDA: United States Department of Agriculture

References

1. The Production Engineering Research Association of Great Britain (PERA), Cold Jet® Thermal and Surface Cleaning Characteristics, June 1988.
    
   
2. James A. Snide, CO2 Pellet Cleaning—A Preliminary Evaluation, Materials & Process Associates, Inc., October 12, 1992.

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