Dry Ice Blasting - An Overview
Dry ice blasting (also known as CO2 blasting) is a relatively new cleaning process using solid CO2 pellets (known as dry ice). It is primarily used for industrial use in a variety of applications. The pellets sublimate (convert directly from a solid blast pellet to a vapor (CO2) leaving no residue. The process is superior to sand blasting, glass bead blasting and other types of cleaning methods for numerous reasons (see chart below).
Today, the dry ice method of cleaning is quickly becoming favored for environmental as well as production reasons. Because of tremendous environmental regulations, industry has needed to minimize wastes. Also, there is a growing consciousness that many are placing now on the global environmental impact of their production practices. However, these benefits are accentuated due to the tremendous performance gains through dry ice blasting -- little or no production downtime, quality of clean and minimized damaged to equipment.
What Is Dry Ice?
Dry ice pellets are made by taking liquid carbon dioxide (CO2) from a pressurized storage tank and expanding it at ambient pressure to produce snow. The snow is then compressed through a die to make hard pellets.
The Process
With the dry ice blasting process, dry ice (CO2) particles are propelled to supersonic speed impacting and cleaning a surface. The particles are accelerated by compressed air, just as with other blasting methods. Overall, there are three steps involved in dry ice blasting. Also, it can viewed in diagram form (see below).
Step #1 - Energy Transfer
Dry ice pellets are propelled out of the blasting gun at supersonic speed and impact the surface. The energy transfer knocks off the contaminant without abrasion. The force of this impact is the primary means of cleaning.
Step #2 - Micro-Thermal Shock
The cold temperature of the dry ice pellets hitting the contaminant creates a micro-thermal shock (caused by the dry ice temperature of -109F) between the surface contaminant and the substrate. Cracking and delamination of the contaminant occurs furthering the elimination process.
Step #3 - Gas Pressure
The final phase has the dry ice pellet explode on impact, and as the pellet warms it converts to a harmless CO2 gas, which expands rapidly underneath the contaminant surface. This forces off the contaminant from behind. The contaminant is then relocated, typically falling to the ground. Since the dry ice evaporates, only the contaminant is left for disposal.
Operating Details
To operate dry ice blasting equipment a few details need to be considered. First, though using dry ice is extremely safe, basic safety matters need to be followed including wearing hand, eye and ear protection. First, the process is noisy and ear protection should be used. Second, the temperature of dry ice is -109 degrees Fahrenheit. Gloves should always be worn when working with it. Thirdly, in dusty areas, a mask is recommended for eye and nose protection. Otherwise, wearing standard eye and ear protection would be acceptable just as with sand blasting or pressure washing. Fourthly, the gun should never be pointed at another individual or serious injury could occur.
Also, blasting in an enclosed area is safe with proper ventilation. Because CO2 is 40% heavier than air, placement of exhaust fans at or near ground level is necessary when blasting in an enclosed area. In an open shop environment, existing ventilation is sufficient to prevent undue CO2 buildup.
Further, though a large number of applications using dry ice blasting equipment only require between 80 to 100 psi and 120 to 150 CFM, an evaluation of your system air would be necessary to determine if your facility has sufficient capabilities to run the equipment at the levels desired for your applications.
Dry Ice Blasting Compared to Traditional Methods
For a brief comparison of dry ice blasting with other traditional cleaning methods, consider the following:
Dry ice blasting generates no waste for disposal, is not abrasive, is not toxic, and is not electrically conductive.
Whereas...
* Sandblasting, glass beads and corn cob generate a tremendous amount of waste for disposal and are abrasive.
* Pressure washing is electrically conductive.
* Solvents generate waste for disposal, are toxic and oan be electrically conductive.
Benefits of Dry Ice Blasting Technology
Dry ice blasting benefits can be broken down into six general areas. Following each benefit is discussed:
Benefit #1 - Decreased Downtime through Cleaning In-Place
Typical cleaning procedures require that equipment be disassembled and moved to an assigned area for proper cleaning. That is not the case with dry ice blasting. Equipment can be cleaned in-place and hot in most situations. Because of that, many time-consuming, labor-intensive steps, which were required with other methods such as sand blasting, can be eliminated including:
* Cool down
* Disassembly
* Transport of the equipment to and from a dedicated cleaning area
Reassembly
* Reheating time
* Dry ice blasting can shorten the downtime for cleaning from days down to hours.
Benefit #2 - Faster and More Thorough Cleaning
With dry ice blasting, a superior cleaning can be achieved while reducing hours when compared to scrubbing with abrasive pads or wire brushes. A tremendous labor savings is accomplished. In addition, the dry ice blasting method cleans in crevices that can't be reached by hand. As a result, equipment runs more efficiently and potential leaks are revealed possibly preventing major system failures.
Benefit #3 - Elimination of Equipment Damage
Cleaning methods such as sandblasting leave an aggressive and abrasive effect on the surface. They can actually remove part of the surface, changing the surface structure considerably. Dry ice is non-abrasive to surfaces and does not change a surface's structure. It lifts the contaminants away. Secondly, because equipment can now be cleaned in place, potential damage from moving equipment to and from a dedicated cleaning area is eliminated.
Benefit #4 - Reduction or Elimination of Solvents
No solvents are used when using CO2 pellets. This can be a critical need for certain companies in order to comply with environmental regulations or to improve worker safety. There are no issues pertaining to toxicity.
Benefit #5 - Reductions in Waste Disposal
With other cleaning methods, whether it be with solvents, sand blasting or some other means, the cleaning agent becomes a secondary contaminant and must be disposed of as toxic waste along with the primary contaminant. However, with dry ice blasting because the CO2 pellet vaporizes upon contact, the only waste created is the contaminant itself. This alone can result in significant waste reduction.
Benefit #6 - Increased Safety
CO2 blasting pellets are non-toxic, non-hazardous creating advantages to the environment, your employees, and production facility:
* No secondary waste
* Safe for the environment
* Safe for employees
* Safe for end products
* Safe for equipment
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