| 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) 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. Corpus Christi Army Depot (CCAD) is also implementing an automated
laser decoating system to strip composite helicopter rotor blades.
|
| 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 meet the requirements of waste reduction under
RCRA, 40 CFR 262, 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 of SARA Title III for solvents (40 CFR 300, 355, 370, and 372;
and EO 12856) is reduced.
The Compliance Benefits
listed here are only meant to be used as a general guideline 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.
|
| Materials
Compatibility: |
Proper optimization
of laser decoating systems allows control of the process to effectively
strip even sensitive substrates without damage. As a result, this technology
is applicable for removing organic coatings from composites, plastics,
fiberglass, and metals.
|
| Safety
and Health: |
The use of Class
C lasers requires the use of protective eyewear, and all operators should
be properly trained. Consult your local industrial health specialist and
your local health and safety personnel prior to implementing this technology.
|
| Benefits: |
- Reduced environmental
impact from elimination of the use of hazardous chemicals and reduction
of solid waste generated for disposal.
- Reduced health
and safety risks due to the elimination of exposure to hazardous chemicals
and decoating residues.
- Decreased operating
costs due to reduced labor, materials use, damaged parts, and waste
disposal costs.
- Enhanced capability
to apply advanced coating systems to a variety of metallic and non-metallic
substrates by providing an efficient means to remove them.
|
| Disadvantages: |
- High capital costs.
- Few vendors of
commercially available systems.
- Line-of-site technology
(although it can strip moderately contoured parts - up to approximately
a 45-degree angle).
|
| 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 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. This will improve
the LADS utilization rate, which is currently only 20 percent.
Economic Analysis
Summary:
A summary of the financial implications for implementing a laser decoating
process as a replacement for chemical stripping of a radome is shown in
the following table.
Comparison
of Radome Stripping Methods
| |
Chemical
Strip |
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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|
| Approving
Authority: |
The Army has approved
the use of laser technology to strip composite rotor blades provided that
a color recognition system is used to selectively remove coatings down
to the primer. The Navy has authorized the use of lasers for removal of
paint from Passive Counter Measure System (PCMS) materials installed on
the topside structure of U.S. Navy surface combatants. The use of a laser
has been approved by various weapon systems managers for use on radomes.
|
| NSN/MSDS: |
None Identified.
|
| Points
of Contact: |
Air Force:
Mr. Steven Fairchild
Wright Patterson Air Force Base
Army:
Mr. Jim Holiday
Corpus Christi Army Depot
SIOCC.ES.IE M/S 35
308 Crecy Street
Corpus Christi, TX 78419
Phone: (512) 961-4617
Fax: (512) 939-4691
Other:
Ms. Heather Moyer
Concurrent Technologies Corporation (CTC)
100 CTC Drive
Johnstown, PA, 15904
Phone: (814) 269-6474
Mr. David Keranen
Ogden Air Logistics Center
Phone: (801) 775-3120
|
| Vendors: |
SLCR Lasertechnik
GmbH
Willi-Bleicher-StraBe 11
D-52353 Duren
Phone: +49(0) 2421/ 91 50-0
|
| Sources: |
Concurrent Technologies Corporation.
"Investigation of Laser Based De-Coating Technology. Final Report."
March 12, 1999.
|
