2006-06-01 - The Cold Clean of Dry Ice
As part of this month’s comprehensive look at the Carbon Dioxide Market, we invited Cold Jet, a pioneer in the development of dry ice technology, to write about dry ice blasting. Cold Jet has been continuously improving the efficiency and effectiveness of this environmentally safe cleaning method that uses CO2 since 1986. Cold Jet provides the equipment to produce the highest density dry ice available, manufactures a proprietary line of dry ice production and blasting equipment, and provides rental services to industrial and commercial customers worldwide.
To download the full article in CryoGas International: The Cold Clean of Dry Ice
WHAT IS DRY ICE BLASTING The dry ice blasting process uses solid CO2 or "dry ice" as its blast media. Dry ice particles are accelerated to high velocities by a stream of compressed air and the blast stream is directed at the surface to be cleaned. There are three things that happen when the accelerated dry ice particles hit the surface:
- The Kinetic Effect: dry ice particles have very little mass and sublimate at the contact of air and immediately upon impact with a surface, which is why dry ice blasting is a non-abrasive process. Velocity is a key contributor to the success of the dry ice blasting process as it provides the kinetic energy required to maximize the thermal shock and gas expansion effects.
- Thermal Shock Effect: as the dry ice particles at -110 F impact the surface, which is relatively hot in comparison, there is a temperature gradient created between the contaminate (on the surface) and the substrate, which releases the bond between the two. This is a surface effect only as the dry ice particles sublimate immediately upon contact causing the gas expansion effect to occur.
- The Gas Expansion Effect: when the dry ice particles impact the surface and sublimate, their volume expands 800 times, causing a mini explosion that breaks the contaminate into pieces and pushes it away from the surface.
Unique features of the dry ice blasting process are that it is a dry process, and therefore a non-conductive process, it is a non-abrasive process and it creates no secondary waste as the media sublimates upon impact. The benefits are that it is a fast process that can be used to clean equipment while it is hot and online, thereby eliminating prolonged production shutdown times. Equipment life is prolonged through lack of abrasion, trapped media, and damage during transport to cleaning area or misalignment during reassembly. There is also no secondary cleanup required.
Equipment used and technology There are several types of dry ice blasting systems available – each with its own individual features and advantages that allow for solutions for various needs. Nozzle technology is a critical feature on dry ice blasting systems. The choice of nozzle will have an effect on sound level, density of the blast stream (i.e. the rate at which the pellets sublimated through the nozzle), and the rate of cleaning. For example, Cold Jet supplies a range of over 100 different nozzles to match as the many applications for blast systems.
Pellets vs Block The dry ice media used for blasting comes in two forms: pellets or blocks. Pellets often allow for a more aggressive clean as the particles blasted tend to be larger and more irregularly sized. Shaved block ice produces much finer and more consistently sized particles allowing for more delicate surfaces to be cleaned without damage.
Single hose vs Dual hose Early dry ice blasting systems used dual-hose technology, a system that uses the Venturi effect to accelerate the particles. With dual hose technology compressed air is supplied to the blast applicator (or gun) through one hose. A second hose runs from the applicator to the hopper that stores the dry ice. The passage of the compressed air through the applicator causes a suction effect on the other hose that pulls the dry ice particles from the hopper into the compressed air stream at the applicator level. The dry ice particles and compressed air are then blasted together. As the dry ice particles are only actually accelerated the length of the applicator by the compressed air, the dual hose system has a relatively small kinetic effect and offers a much less aggressive clean than the newer single hose technology.
Single-hose technology was pioneered and introduced by Cold Jet in 1986. In single-hose systems there is one hose leading from the hopper to the applicator and a feeder system that feeds the dry ice particles and compressed air into that hose. As a result the dry ice particles are accelerated by the compressed air stream the length of the hose, dramatically increasing their kinetic energy and therefore the aggressiveness of the clean.
Electric vs Pneumatic Electric dry ice blasting machines require regular power outlets (110V or 220V) to function whereas pneumatic systems work without electrical power.
What are the applications
Dry ice blasting is used in a large number of industries. Some of the most popular and successful industry applications for dry ice blast cleaning include:
- Disaster Restoration (mold remediation, fire and historic restoration)
- Automotive (plastic and rubber molded parts – seals & gaskets, brake pads, dashboards, vent covers, rubber-to-metal bonded engine parts, etc. process equipment - weld lines, pain shops, etc.)
- Printing (ink removal from printing presses for general maintenance or refurbishment and repair)
- Food processing (baking ovens, food conveyors, mixing vats, etc.)
- Packaging (packaging equipment cleaning – dust, grease, product removal from conveyors and machines, ink and glue overspray removal from boxers and baggers)
- Plastic & Rubber Molding (food and packaging containers, medical devices, lenses, etc.)
- Rubber tire molding
- Foundry (permanent molds, semi-permanent molds, core boxes, die castings, etc.)
- Wood (OSB press cleaning, dryers, etc.)
How is the dry ice made Dry ice is made by taking liquid CO2 (LCO2) and compressing it by applying pressure. This causes the LCO2 to solidify into a snow. The snow is then either compressed to form blocks or compressed and extruded to form pellets. The equipment used to make the dry ice is called pelletizers and block makers.
HD pellets Dry ice blasting uses High-Density (HD) pellets versus the "regular" pellets used for storage or shipping. High-density pellets are created using specialized pelletizers that create a homogenous CO2 pellet as opposed to the "regular" pellets, which result from compacted snow. These specialized high-density pelletizers were created twenty years ago by Cold Jet to meet the needs of dry ice blasting customers as 3 mm standard blasting pellets were not available in the marketplace.
Latest technology Dry ice blasting has evolved tremendously over the past 5 to 10 years. We often meet customers who felt that dry ice blasting was not a solution for them based on their experience with it 5 years ago: it was to noisy, too large, too unwieldy… all of those have elements been greatly reduced since then.
Today, Cold Jet has advanced dry ice blasting technology even further with the creation of the first, unique and revolutionary precision cleaning system: the i³MicroClean. Traditional dry ice blasting offers blast swaths ranging from ½" (12.7 mm) up to 13" (330 mm) whereas the i³MicroClean nozzles range in size from 1/8" (3.2 mm) to ½" (12.7 mm). The i³MicroClean can reach where traditional blasters cannot, i.e. small rims, complex geometries, grooves and crevices; it can direct the blast flow into small or tight areas that the larger traditional blasters cannot access. The i³MicroClean is also much smaller than traditional blasters and as a result consumes much less compressed air and produces far less noise. It is the perfect cleaning tool for manufacturers needing to clean delicate surfaces (circuit boards, electrical panels, ceramic plates) and the perfect production tool for those wanting to maintain superior part quality through more production cycles (online cleaning of rims and edges of plastic and rubber mold cavities producing high-tolerance precision parts). The i³MicroClean eliminates the use of small metal brushes and scrapers on delicate mold surfaces thereby extending the life of the molds. It also provides cool relief from the heat of the molds in production without causing any temperature losses to the mold. By increasing the number of shots for each mold it reduces the frequency of disassembly for complete mold cleaning and as such represents a tremendous complement to both traditional dry ice blasting systems as well as other blasting methods used for mold maintenance.