Hew Stripping
Technique Minimizes
Hazardous Waste
By Kimberly A. Roy
W
ith a onetwo punch of heat
and cold, a new stripping
process removes paints and
other coatings without generating toxic
waste or damaging metal or composite
surfaces.
The technology, known as FLASHJET@,was developed as an alternative
to methylene chloride for stripping
paint and coatings from aircraft at McDonne11 Douglas Aerospace-East
(MDA-E St Louis). Besides damaging
the aircraft’s composite substrate,
methylene chloride is strictly regulated
and generates hazardous waste that is
costly to dispose, explains Wayne
Schmitz, MDA-E’s FLASHJP program manager.
Although the company initially did
not intend to develop a new technology, a review of available stripping
Effluent Capture System
Air
Dry Ice System
low-pressure Dry Ice
Particle Stream
June/July 1993
options failed to identi@ a cost-effective
alternative that would minimize h a ardous waste, reduce maintenance
time, and eliminate substrate damage
and corrosion, Schmitz says.
MDA-E eventually joined forces
with Cold Jet Inc. (Loveland, Ohio), a
developer of dry-ice blasting technologies, and Maxwell Laboratories Inc.
(San Diego), an advanced technical services company and manufacturer of
high-energy, pulsed-power technology
and systems. The prototype, which was
fabricated and tested in January 1991,
“did in fact work well,” Schmitz says,
and the trio applied for patents later
that year. Patents were pending at
press time.
The FLASHJP process uses a
high-intensity flashlamp (heat) to destroy a coating’s cohesive bonds and a
simultaneous particle stream of dry ice
(cold) to remove residue, and cool and
clean the surface. Without the dry-ice
stream, Schmitz says, the pulsed-light
energy from the flashlamp could cause
“a great deal of (structural) damage.”
(Using heat and dry ice together maintains surface temperature between 40
degrees and 100 degrees Fahrenheit.)
Pulsed-light energy is generated by
a quartz tube filled with xenon gas,
which, when electrically energized,
emits a brilliant flash of light, Schmitz
explains. As the paint or coating a b
sorbs the photon energy, its temperature rises rapidly to a point at which a
thii layer of paint is removed.
Dry ice, meanwhile, is produced
from carbon dioxide gas, which is
121
Paint Stripping Processes
Operator
Safety
Requirements
Ear/Eye
Protection
I I I I I 1
Ear/Eye
Protection
Lethal
El12y
Ear/Eye
Protection
Aircraft
Masking
Requirement
Aircraft
Damage
Potential
Paint
Stripping Rate
Eye
Protection
Breathing
Air, Eye
Protection
Chemical
Burn
Protection
(Whole Body)
+T
I
Chemicol
lethal
Blast
Pressure
Breathing
Air, Eye
Protection
Protection
(Whole Body]
Breathing
Air, Eye
Protection
Extensive
Extensive
Extensive
Extensive
High On
Composites,
Transparencies
Moderate
Moderate
Moderote
Moderate
Moderate
Post Stripping
Cleanup
Required
Yes
Yes
Media
intrusion
Potential
High
High
Yes
Yes
High
Yes
Yes
Yes
None
low
Aircraft
Thru-put Rate
Corrosion
Potential
Adjacent Comonent Damage
otential
t
Aircraft
Precleaning
Required
Media Recycle
Requirement
Media
Disposal
cost
Hazardous
Woste
Volume
Technolog!
Best
I
I
I
I
Characteristics Rating
J
Worst
collected from various industrial
processes, purified, converted to a liquid and compressed into tiny particles
before beiig delivered to the paint surface in a low-pressure air stream. The
pellets sublimate to a gaseous state on
impact leaving the surface clean and
ready for repainting.
The carbon dioxide also acts as a
shield that prevents oils or soils on the
surface from igniting, thus eliminating
the need to wash the surface or p r e
treat it before stripping. The continuous flow of dry ice also keeps the flashlamp clean, helping to ensure
maximum transmission of light energy.
A self-contained effluent capture
system (vacuum) is integrated with the
pulsed-light and dry-ice nozzles into a
common head (Figure 2). The capture
system carries removed paint and coatings to a series of filters, where they
are collected for incineration. Air from
the filters passes through a charcoal
tubscrubber before b e i i released to
the atmosphere.
uBy eliminating particulates, hazardous waste requiring disposal is r e
duced by 99 percent” reports Gregory
Gardner, MDA-E’s business develop
ment manager for the -WETS
program. Operators need only tinted
glasses and normal hearing protection,
and other technicians are free to perform maintenance on or in the aircraft
while the system is operating, he adds.
While easily adaptable to robotics,
the mobile system also can be con-
trolled with a pneumatic, mechanically
assisted manipulator, Schmitz says. In
other words, the operator can push
the system, which weighs about 50
pounds, across the Surface with assistance from a colorsensing device that
monitors stripping rate and provides
visual feedback. If the stripping head
does not contact the surface properly
or is moved too slowly, the system automatically shuts down.
According to Schmitz, strip rates up
to 4 square feet per minute are possible
when stripping to primer with a 12-inch
stripping head. A &inch stripping head
also is available.
size designation
indicates the area being stripped.)
FLASHalso provides a high
degree of control, Schmitz says, and
can remove as little as one one-thousandth of an inch of coating. It can be
used to remove complete finishing systems (top coats and primer) or select
layers of top coat, or for chemical-free
cleaning using only the dry-ice particle
stream. These variations are achieved
by modifying such operating parame
ters as pulsed-light energy density;
stripping head rate of travel and distance from the surface; and dry-ice d e
livery pressure and nozzle angle.
To date, no limitations have been
identitied, Schmitz reports, a d d i g that
tests have been conducted on “all
known paint and primer systems used
in the aviation business, as well as all
structures, including steel, aluminum,
titanium and various composites.”
Operating costs are estimated at
$4 per square foot compared to a minimum of $12 per square foot and a maximum of $25 per square foot for other
systems, Gardner says. Capital costs
have not been set.
At press time, the system was certified for use on all McDonnell Douglas
aircraft and was being certified for Air
Force and Navy a i r d Certification
tests were scheduled for this summer
for commercial aircraft manufacturers
in the United States and Europe.
‘We’re also very interested in other
applications,” Gardner says, “but no
c v c i - 1 tzzcetiqdus5es ‘law been
identi6ed at this time.” E!
me
June/July
123