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TECHNICAL PAPERS

HOW TO COMPARE DRY ICE BLAST CLEANING SYSTEMS

Not all dry ice blasting systems are created equal. System comparison tests are suggested below that should help potential buyers distinguish between sales pitches and performance reality.

Initial Dry Ice Blast Cleaning Test Setup:

  1. Use your own air supply for all testing. If you don't have the required air supply necessary for your particular dry ice blast cleaning application, it's important to learn this "before" you purchase a system.
  2. The dry ice blasting systems to be compared should be hooked to the air supply at the same air supply junction point in order to ensure that the systems are seeing the same air resources. Also, to help extend the test long enough to expose any equipment freeze-up problems, it is best to simply hook and unhook each blasting machine at this junction point for each blast sample being test cleaned.
  3. Have multiple samples or critical clean components ready for test cleaning. The dirtier the better. Similar portions of the test samples should be equally sized for each system to be tested, and a stopwatch made available for recording blast times. Also, components within a physically restricting environment should be made part of the test to verify an appropriate blast applicator is available for cleaning such compounds.

Test dry ice pellet hopper feed reliability:
A poorly designed hopper will frequently encounter bridging, clumping, and feed port clogging, which will require the dry ice to be manually broken with a stick. This is not only frustrating and time consuming, it can often result in unnecessary damage to the dry ice blasting system. Inferior hopper design will not show itself with only a few scoops of fresh pellets; however, filling the hopper completely full of pellets and allowing the system to sit for 10-15 minutes before blasting will likely indicate any serious hopper design flaws.

How to Test: At the start of the test, completely fill the dry ice pellet hopper to the advertised capacity and wait about 10-15 minutes before blasting. Conclude testing with a final blast to empty any dry ice pellets remaining in the hopper.

Test blast cleaning performance relative to dry ice pellet consumption:
Since dry ice pellets are consumed during system usage, the ongoing cash flow justification of dry ice pellet cost is typically just as important as the initial cost justification for the dry ice blasting system . Therefore, the dry ice pellet consumption rate is typically just as important to determine as which available blasting system cleans the fastest, and what the dry ice consumption rate is that corresponds to this optimum blast performance. The point being, if System-A does just as well or better than System-B, but at only half the dry ice pellet consumption feed rate, then System-A's ongoing cash flow costs will be half that of System-B. Therefore, System-A could save $100's of dollars a week, $1000's of dollars a month, and tens-of-thousands of dollars annually for the same amount of work as that accomplished by System-B.

For given blast pressures and air flow rates, which are dictated by the air supply capability and the particular blast nozzle geometry being used, there is an optimum dry ice pellet feed rate that yields the maximum cleaning performance. It will take longer to clean a given test sample both above and below this optimum pellet feed rate. For standard industry air supply availability (150 scfm at 80 psi / 4.25 m3/min at 5.5 bar), the optimum pellet feed rate will likely be between 1-3 pounds (0.45 - 1.36 kg) per minute.

How to Test: Starting at 1 pound (0.45 kg) per minute, blast a designated portion of the sample while recording the blast time. Increase the dry ice pellet feed rate by ½ pound (0.2 kg) per minute, and repeat the test. Continue this until the time to clean per square inch of surface becomes constant or begins to increase over the previously recorded cleaning time.

 

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