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How it Works

History

The application of dry ice blasting started around 1980 in the United States as a method for removing paint from aircraft wings without damaging the delicate airfoil surfaces.

The early blasting machines were generally designed as complete self-contained plants. They converted liquid CO2 into dry ice, which was fed into a high-pressure carrier stream, and then through a flexible hose to a blast nozzle. The nozzle finally accelerated the dry ice particles to the surface to be blasted.

Today, dry ice is available from commercial sources in the form of small diameter pellets and blasting machines have developed from the older large integrated plants to smaller more mobile units that only transfer the pellets from a hopper to the nozzle. Modern blasters use a dry ice transfer system that has either one or two flexible hoses connecting the blast unit to the nozzle. They are generally known as single or dual hose blasters.

Single Hose Blaster (SHB)

This design of blaster uses a mechanical shuttle or rotating air lock to transfer dry ice pellets from a feeder system at atmospheric pressure to the carrier stream at high pressure. The shuttle or rotating air lock must have a good sealing system that is able to cope with the low dry ice temperature and mechanical wear. The moving parts are generally electrically driven. The dry ice is carried to the nozzle in the carrier stream, which typically would be compressed air flowing at around 200 ft3/min (5.7 m3/min) free air. At the nozzle, the exit velocity is increased by a restriction through which both the dry ice and the carrier stream flow.

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Dual Hose Blaster (DHB)

This design can be used in two ways. Either the entire carrier stream goes through one hose and the dry ice through the other, or some of the carrier stream is also used to assist the dry ice passage through the second hose. In the first case, the dry ice is moved from the blaster to the nozzle wholly by suction, but in the second case it is partly propelled or assisted in its travel to the nozzle.

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The Clean Surface System 2000 dry ice blaster is a dual hose machine, where the dry ice is transferred only by suction, and the entire machine is pneumatically driven and controlled. The dual hose design gives the System 2000 several advantages compared to single hose machines:

Advantages of the System 2000 Dual Hose Design

Low Dry Ice Transfer Losses: The dry ice travels from the machine hopper to the nozzle accompanied only by a small amount of naturally aspirated air. This reduces sublimation of the dry ice en route to the nozzle. Typically, single hose systems have a high dry ice consumption, often operating at up to 100 kg dry ice per hour, compared to the optimum rate of 30 kg/h for the System 2000. As the cost of dry ice is the major part of the total operating cost of a blasting system this makes the Clean Surface blaster one of the most economical available.

Low Risk of Blockage: The carrier stream and the dry ice come together at the last possible moment in the nozzle, making blockage of the machine or hoses, either by the dry ice, or by water ice formed within them, virtually impossible. Tests over multiple shifts have proven Clean Surface blasters work continuously without blocking for long periods. This allows compressed air, readily obtainable from standard hire compressors as used in the building industry, to be used as the carrier stream without the need for more than a standard oil filter, water separator and aftercooler.

Nozzle Design Advantages: The nozzle can be designed with a 90 degree angled outlet making it possible to blast two parallel mould halves in an open press. Most of the other systems cannot offer this facility as once accelerated the dry ice will be destroyed in an angled nozzle by a cleaning action on the inside of the bend.

Very High Availability: Apart from simple pneumatic control components, Systems 2000 blasters have very few moving parts powered by an air motor to provide a continuous smooth metered flow of dry ice to the point where it is further transported by suction. This drastically reduces the chances of mechanical failure when compared to complex systems in which the dry ice and carrier streams are mixed under high pressure conditions. In addition, as electrical power is not required to run or control the Clean Surface System 2000 blaster it can be used safely in remote locations.

Very Low Maintenance: The construction of the blast unit can be kept lightweight. At 55 kg the System 2000 blaster is light and easy to maneuver. The pneumatic control systems require only limited maintenance, and as all component parts are standard readily available items sourced from global suppliers, replacement in the event of failure is quick and straightforward.

Low Risk of Substrate Damage: Despite the above stated advantages of dual hose blasters single hose units are still widely used. They are considered to be more powerful than dual hose units when operating at the top end of their range, but care must be taken to ensure that large dry ice or water ice particles do not damage the substrate. The development of larger and more efficient nozzles has allowed Clean Surface dual hose blasters to match the top end performance of most single hose units on the market today, and because the size of the ice particles emitted by dual hose machines is considerably smaller, the risk of substrate damage is virtually eliminated.

Good Low Pressure Performance: The small pinhead sized dry ice particles emitted by Clean Surface dual hose units are also much better suited for operating at the lower end of their range when delicate substrates are involved. Special dual hose systems are regularly built to operate at 2.0 bar air pressure to enable them to be used for electronic applications or deflashing delicate plastic lenses without any risk of mechanical damage.

Even High Pressure Performance: The smooth flow of small dry ice particles coming through the System 2000 nozzles also creates a much smoother cleaning performance at the top end of the operating range. As single hose blasters emit an uneven flow of larger dry ice particles they tend to miss some areas, which then require to be re-cleaned at the inspection stage. This is generally unnecessary if a Clean Surface System is used, meaning the job is done quicker with a much lower ice usage.

Future Developments: New developments at Clean Surface are particularly customer orientated because the development engineers are constantly on site advising and assisting customers and finding out what the market needs. This has resulted in constant improvement to the CSL 2000 unit over the last 15 years, but in 2010 a new machine will be launched that will give users needing the ultimate in dry ice cleaning much greater flexibility and economy than they can find anywhere on the market today. Clean Surface is placed in a unique position to achieve this as it is the only UK based company capable of research, development, design and construction of dry ice equipment, all concentrated at one location where the important consumable, dry ice pellets, are also produced.

To find out more about dry ice systems past, present and future, please call +0116 224 0072 or e-mail sales@cleansurface.co.uk