|
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:
- 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.
- 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.
- 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.
|
