| Overview: |
Laser de-coating is a non-intrusive, non-kinetic energy process
for removing organic coatings from a variety of substrates, including
composites, glass, metal, and plastics. The high level absorption of
energy at the surface of a coating material results in the subsequent
decomposition and removal of the coating. Since the applied energy is
mostly absorbed and utilized in coating decomposition (i.e., instant
evaporation, which carries away most of the radiation energy), the
substrate experiences only a minimal increase in temperature.
A laser de-coating
system consists of a laser, beam delivery system, manipulation system,
feedback control system, and waste management system. A laser is a device
that generates very pure (monochromatic), coherent light that can be
focused and concentrated into a narrow, intense beam of energy. Pulsed
lasers use various methods to output photons in surges instead of
continuously. In coating removal applications, short, intense pulses of
laser energy quickly scanned over the surface volatilize coatings without
damaging the substrate. Currently, most lasers used to remove organic
coatings are transversely excited at atmospheric pressure (TEA) carbon dioxide (CO2)
industrial lasers, emitting infrared light with a wavelength of 10.6
microns. The optimal energy level and pulse frequency of the laser beam
depend on the type of coating to be removed.
The laser beam
delivery system transfers the laser output to the work surface with the
appropriate spot size and shape for delivering the energy density required
for efficient coating removal. A manipulation system controls the position
of the laser as it moves over the substrate surface, allowing each area to
cool before being exposed to the beam again. An optional feedback control
system allows the selective removal of primers, paints, topcoats,
sealants, and other surface coatings.
As a coating is
volatilized, decomposition by-products are thrown into the laser beam and
incinerated to produce carbon dioxide, water, inorganic pigment ash, and
trace amounts of other compounds. The organic constituents are exhausted
into the atmosphere, and particulate matter is collected in conventional
filters for future disposal. Therefore, the amount of waste to be disposed
of represents only a fraction of the original coating volume.
Materials testing
conducted by the NDCEE showed that laser decoating technology was
effective at removing even the most difficult coatings, including
powdercoats, electrocoats, chemical agent resistant coatings (CARC), and
specialty coatings such as Rockhard stoving enamel. Removal rates vary
between 5.8 and 17.5 ft2/hr (250-W system) and 46 and 140 ft2/hr (200-kW
system). An automated laser decoating workcell system is currently being
implemented in the NDCEE demonstration factory for further demonstration
and testing.
Laser decoating is
currently being used to strip radomes at Ogden Air Logistics Center
(OO-ALC), Hill AFB, Utah. Corpus Christi Army Depot (CCAD), Texas, is also implementing
an automated laser decoating system to strip composite helicopter rotor
blades.
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| Compliance Benefit: |
The use of laser
decoating systems reduces hazardous materials usage and hazardous waste
for disposal by 100%. The only solid waste generated for disposal consists
of the ablated inorganic particulates, which represents only a fraction of
the volume of paint removed. All organics are converted to gases that can
be exhausted directly to the atmosphere. The decrease in hazardous waste
helps facilities to meet the requirements of waste reduction under RCRA, 40 CFR
262; the Pollution Prevention Act (42 USC 13101-13109); and Executive Order (EO)
13148; and may also help facilities reduce their generator status and
lessen the regulatory burden (e.g., recordkeeping, reporting, inspections,
transportation, accumulation time, emergency prevention and preparedness,
emergency response).
In addition to
hazardous waste reduction, facilities will decrease the amount of solvents
on site and therefore, the possibility that a facility will meet any of
the reporting thresholds for solvents under SARA Title III (40 CFR 300, 355,
370, and 372) and EO 13148 is significantly reduced.
Moreover, since solvents
are not used, hazardous air pollutants (HAPs) and volatile organic compounds
(VOCs) associated with the process are eliminated,
which may lessen the likelihood that a facility will require an air permit
under 40 CFR 70 and 71. Eliminating HAP and VOC emissions may also help a
facility to comply with or avoid the requirements of the National Emission
Standards for Hazardous Air Pollutants (NESHAPs) (40 CFR 63).
The compliance
benefits listed here are only meant to be used as general guidelines and
are not meant to be strictly interpreted. Actual compliance benefits will
vary depending on the factors involved, e.g., the amount of workload
involved.
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| Economic Analysis: |
OO-ALC currently uses a laser de-coating system in their aircraft
maintenance facility. The Laser Automated Decoating System (LADS) is used
to remove epoxy and polyurethane coatings from aircraft radomes. The CO2
laser is attached to a robotic arm that can be programmed to adapt to a
number of complex parts. Radomes are placed on a 65-foot lathe bed and
rotated as the laser ablates and removes the coatings. The LADS laser
operates at 70 kV and approximately 100 to 300 pulses/second at 30
J/pulse. The spot size is approximately 1.5 to 2 inches diameter. The
following is a comparison of radome stripping using LADS versus
conventional chemical stripping, based on actual observations.
Assumptions:
Laser Decoating
Process
- Process time to
strip one radome: 2 to 3.5 hour laser strip followed by light sanding (9
flow days total)
- Material usage for
one radome: approx. 125 to 150 ft3 laser gas
- Waste generated:
less than a pound of solid (non-hazardous waste)
Chemical
Stripping Process
- Process time to
strip one radome: 16 hour soak followed by hand sanding (31 flow days
total)
- Material usage for
one radome: 25 gallons methylene chloride
- Waste generated:
100 to 300 gallons hazardous waste
Capital
Cost:
The capital cost for laser decoating will vary considerable
depending upon the process configuration required for the particular
stripping application. The capital costs for a laser decoating system for
depot level maintenance activities was estimated at $0.5 million to $1.5
million.
Operational
Cost:
Operating costs for laser decoating will vary considerable
depending upon the process configuration required for the particular
stripping application. Operating costs for laser decoating of a radome are
estimated at $4,000 per radome, as compared to $42,000 per radome for
conventional stripping.
Payback
Period:
The estimated payback period for investment in the
equipment/process: <5 years.
Annual
Savings:
Use of the LADS to strip radomes saves the facility
approximately $700,000 annually in operating costs. This amount does not include
the additional savings from reducing the number of scrapped parts. Using
conventional stripping methods, an average of 10 radomes per year are
scrapped due to substrate damage from extensive hand sanding. The LADS can
also accommodate flat panel components, such as vent stabilizers, flaps,
and body panels. Current efforts at OO-ALC are focused on programming the
robot and setting up the LADS work cell to strip more flat panel
components. These efforts will improve the LADS utilization rate, which is
currently only 20 percent.
Comparison of Radome Stripping Methods
| |
Chemical
Stripping |
LADS |
| Process
time: |
16 hour soak
followed by hand sanding (31 flow days total). |
2 to 3.5 hour
laser strip followed by light sanding (9 flow days
total). |
| Materials
usage: |
25 gallons
methylene chloride. |
approx. 125 to
150 ft3 laser gas. |
| Waste
generated: |
100 to 300
gallons hazardous waste. |
less than a
pound of solid (non-hazardous waste). |
| Cost: |
$42,000 per
radome. |
$4,000 per
radome. |
CCAD is currently
implementing a laser de-coating system to strip helicopter rotor blades
(main and tail). This process has been approved for composite rotor blades
provided that a color recognition system is used to selectively remove
coatings down to the primer and the surface temperature does not exceed
170°F. The 2-kW, 200 Hz CO2 laser system has a robotic arm that moves
along the rotor blade to remove topcoats and rain erosion coatings.
Traditionally, rotor blade coating removal is done completely by hand
sanding, which is very labor intensive and takes 8 to 15 hours. The laser
system can strip an entire blade in 3 hours. CCAD anticipates that this
will increase the throughput rate in the rotor blade shop by at least 30
percent.
Economic Analysis
Summary:
- Annual Savings for
the LADS: $700,000
- Capital Cost for LADS: $1,000,000
- Payback Period for Investment in Equipment/Process: <5
years
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