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What is Dry Ice?
Dry Ice is made of liquid CO2 (carbon di-oxide) and is
TOTALLY FREE OF WATER. Liquid CO2 is injected into a production cylinder
at 14 -17bar (200-290 psi), where it expands at atmospheric pressure into
CO2 snow. This snow is then compacted by rod & piston into solid CO2
= Dry Ice. Different types of Dry Ice machines produce various forms of
Dry Ice.
The most common forms of Dry Ice are:
Blocks
10-20kg p/block
Nuggets rod shaped, 10-16mm diameter, 15-30mm in length
Pellets rod shaped, 2.5-3.5mm diameter, 3-8mm in length
Disks square, usually 150x150x10-15mm (rare, only used by airline
caterers for some airlines.The trend is to use nuggets and pellets, which
are more comfortable to handle and cheaper to produce)
Dry Ice as an industrial product has been around for approximately 80
years and is mainly a consumable in the food production and transport
industries. Since its invention many other applications have been found.
A more recent application is Dry Ice Blasting.
Properties of Dry Ice:
Temperature
of -78.5 Celsius ( -173° F)
Specific Weight is approximately 1450kg/m3
Dry Ice is free of water (pure CO2 = 100% dry)
Dry Ice is not conductive
Dry Ice converts to CO2 vapor on surface impact
Dry Ice is free of oxygen (anti bacterial)
Dry Ice is not toxic (food grade CO2)
What is Dry Ice Blasting?
Dry Ice blasting is similar to sand blasting. Both use compressed air
as kinetic energy, feeding particles into a high velocity air stream from
a blasting unit, via a hose, through a nozzle onto a surface. Dry Ice
blasting does not compete with sandblasting. It has different properties.
Sand blasting is abrasive (corund, ash, steel shot, glass beads, etc.).
Along with the contaminate it removes surface material. It is therefore
ideal to remove rust corrosion, which Dry Ice cleaning cannot. Sand blasting
produces secondary waste, which needs to be disposed of at considerable
cost. Dry Ice blasting is not abrasive. It does not remove surface material
(given a trained operator). Dry Ice blasting does not produce secondary
waste. The Dry Ice material sublimes to CO2 vapor on impact. Only the
contaminates have to be managed.
The Cleaning Action of Dry Ice Blasting is because
of three reasons:
Kinetic Energy from compressed air propels the Dry Ice particles up
to sonic speeds. Though very light in weight, they puncture
the contaminate and chip away at it, thereby opening the surface of the
contaminate. On impact, solid CO2 absorbs energy and sublimes instantly to CO2
vapor.
Thermal
Differentials create an immediate and localized cold shock to the
contaminate, which contracts at -78.50°C versus a substrate, which
usually only cools down by up to 15°C to current temperature. This
promotes a contact break between contaminate and substrate. It is particularly
noticeable where hard resins have been applied to metal surfaces.
Sublimation: As the Dry Ice sublimes on impact,
it increases up to 700 times its volume from solid to vapor, when it enters
the cracks within the contaminate. This gas expansion, breaking up the
contaminate from within, is the major factor responsible for the Dry Ice
cleaning effect.
The advantages of Dry Ice Blasting are:
a) subtle to high aggression cleaning from 2 - 12bar ( 30 - 175psi)
blast air pressure.
b) 100% free of water
c) not abrasive
d) no secondary waste
The above advantages makes Dry Ice blasting so interesting and sensible
to many industries. It allows cleaning of machinery in line without harming
surfaces, parts or components and without interfering with electrics or
electronics. At the same time it can be aggressive enough to clean many
types of surfaces from hard contaminates without causing damage.
Different Dry Ice Cleaning Systems:
Two principally different systems exist today: 1-Hose AirLock and 2-Hose
Venturi delivery. Both are good. Both have their own pros & cons.
1-Hose Systems use an AirLock to feed Dry Ice particles from the
ice hold into a single air hose, which transports the work air / ice mix
from the blast unit to the blast gun. This method of delivery allows wide
ranges of blast nozzles. The very pointed delivery of the Dry Ice particles
makes 1-Hose Systems the more aggressive ones at the very top end of the
aggression scale.
Advantages: High / pointed aggression. Large amounts of nozzle
configurations possible. Long Dry Ice delivery hose length possible (safe
up to 30 m / 66 ft).
Disadvantages: High Dry Ice consumption (av. 50-80kg / 110-176lbs).
Too aggressive for "soft" jobs (hard contaminants on generator
windings, soft aluminum, sand stone), current rotary disk airlocks are
very sensitive to humidity and are therefore difficult to run under adverse
conditions.
2-Hose Systems utilize the venturi principle. Work air travels
from the blast unit through an air hose, straight to the blast gun. The
blast gun contains a venturi function, drawing Dry Ice particles through
the ice hose from the unit's ice hold into the blast gun. There, the Dry
Ice particles join the work air stream and are delivered to the surface
being cleaned.
Advantages: Very even ice flow. Low Dry Ice consumption (av. 20-40kg
/ 45-90lbs). Light and mobile. Allowing a broad range of applications
with one system.
Disadvantages: Lesser variety of nozzle configurations. Pointed
aggression limited to approximately 85% of 1-Hose capability. Hose length
is limited (safe to20m / 66 ft. with Fine Shot & 12m / 40 ft. useing
Rough Shot Dry Ice particles).
Bottom Line: From our perspective 2-Hose systems have so far been
the more user friendly and reliable ones. Covering the broad middle range
of industry's needs very well, while being more economical and easily
adapted to tackle contaminations on sensitive surfaces and components.
For this reason CMW has concentrated on perfecting such systems and bringing
them to their maximum potential. At the same time, knowing full well of
the advantages of 1-Hose systems, we are within months of introducing
a new 1-Hose AirLock system. This new AirLock is small, light and contains
few moving parts, making it very reliable in daily use even under adverse
high humidity conditions.
Crystal Particle vs. Pellet Blasting - What
is Crystal Particle Blasting?
Dry Ice pellets, blocks or nuggets are ground into fine or rough sugar
crystal like format by means of controlled mechanical stress. Specially
developed Dry Ice Management Systems build into our Mach1 Dual Pellet
Blaster and Mach2 Universal Blaster CO2 cleaning machines supply this
function continuously, optimizing the Dry Ice Crystal Particle size and
desired flow. This new Dry Ice Particle Flow is fed into the work air
stream by our proven and rugged 2-Hose Venturi delivery method.
What are the Advantages of Crystal Particle
Blasting?
1. Economy:
Slow motion video shows that approximately 60% of a Dry Ice pellet sublimes
to CO2 vapor on surface impact, when being blasted via a high velocity
air stream onto a targeted substrate. Only 40% of that pellet actually
does the job of removing coatings and contaminates.
When particles of a defined small granular size are being used for cleaning
(Dry Ice Crystals), solid CO2 pellets, blocks or nuggets are ground into
fine or rough sugar like crystal particles, increasing the impact points
per cm3 Dry Ice onto the substrate thousand fold and thereby drastically
reducing impact sublimation. This new format utilizes the Dry Ice media
more efficiently than any other method .......30-50% less Dry Ice consumption
!
2. Substrate Safety:
CMW CO2 Crystal Particle Cleaning systems create particles of substantially
reduced individual mass, compared to standard Dry Ice pellets without
any loss of cleaning power. It is the distribution of equal Dry Ice mass
over a much larger amount of impact points, which gives CO2 Crystal Particle
Cleaning the ability to clean very sensitive surfaces. For example your
generator and motor windings, electronics, circuit boards, semi conductor
tools, even wood or soft sand stone substrates are protected. ...Sensitive
surfaces are safe !
CMW Dry Ice Blasting Equipment:
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