(FLASHJET article is reprinted from Aerospace Digest,

Volume 40, Number 2, September 1993)

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MCDONNELL DOUGLAS

McDonnell Douglas engineer Dave Breihan and co-inventor of the FLASHJET Coating Removal Process, Wayne Schmitz, also of McDonnell Douglas, demonstrate the process on a composite wing of an AV-8B.

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RICH RAU

McDonnell Douglas, Cold Jet Ins., Maxwell Labora- tories lnc. team has developed and built an A environmentally friendly,

operator safe, and cost effective- method to remove paint from aircraft structures without damaging the underlying materials. This new process is called FLASHJET.

The Growing Challenge Underlying the development of an

environmentally compliant alternative to aircraft paint stripping are several key issues:

Increasingly stringent worldwide environmental regulations controlling the use, cost, and disposal of hazardous and toxic materials

safety Concerns over personnel health and

Aging airframe structural integrity Increasing use of composite materials

but collectively they pose some major challenges to the commercial and military aircraft support communities.

For instance, hazardous material landfills authorized to accept paint chips and spent chemical removers are rapidly approaching capacity. Meanwhile, additional waste is being generated by requirements to strip and structurally

fleet. Since opening more disposal sites to solve this problem seems unlikely, the cost of disposing hazardous waste is rapidly increasing and new environmental laws are making such waste the responsibility of the producer, even after it has been properly stored.

lightweight composite materials used in airframe construction are particularly susceptible to damage from existing chemical and abrasive media depainting

These are not new issues individually,

Adding to this challenge is the fact that

techniques. While chemical stripping of structurally insigniiicant composite components has been performed on a limited basis, impending environmental regulations dealing with chemicals and clean air laws will eliminate chemical usage for any depainting.

As these environmental and structural issues have become more pressing, alter- natives to using toxic media for stripping have been found. As explained in the next section, however, none of the recent alternatives entirely eliminates the prob- lems of disposing of hazardous chemical or solid waste or causing potential structural damage to aircraft. It was not until the FLASHJET Coatings Removal Process was developed that all of these problems have been solved.

of several safety, efficiency, and cost characteristics relative to federal govern- ment and industry goals concerned with:

Not compromising the structural integrity of surface and substructural components Not using hazardous media for stripping Reducing toxic waste (i.e., paint and worn-out or contaminated media) by 90 percent

and aircraft stripping cycle times by 50 percent Reducing overall stripping costs by 50 percent The results of the study are shown in

Figure 1, which includes the process that the FLASHJET team ultimately developed.

The matrix shows, as men- tioned, that many alterna- tives to chemical paint stripping have been avail- able. Prior to the develop ment of FLASHJET, however, only three tech- nologies - laser, Xenon flashlamp, and carbon dioxide (CO,) pellet blast- ing - did not rely on solid or liquid media to remove coatings.

By comparison, the problems with the media- based alternatives are greater. In general, they

Reducing maintenance man-hours

The Search

effective - as well as an environmentally and structurally safe -way to remove aircraft paint systems, the McDonnell Douglas, Cold Jet Inc., and Maxwell Laboratories Inc. team conducted an in- depth analysis of all current and emerging coatings removal technologies. These technologies were compared on the basis

TM ‘FLASHJET” is a trademark of the McDonnell Douglas Corporation

still yield a certain amount of hazardous - -. - . ~

waste to be disposed of and present

to aircraft structures. It seemed most reasonable, therefore, to look at processes that do not rely on these media. This led to a closer examination of the laser, xenon flashlamp, and CO, pellet blasting technologies. b

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Non-Phenol Sodium Based High Pressure Wheat Phenol Based Plastic {;$!,# COP Pellet Xenon Starch Chemical/ Media Laser fkSliF; Bicarbonate Chemical Water Jet Blasting Softener/ 32,000 psi Blasting Water Rinse Blasting (PMB) Blasting Flash,amp

Water Jet

Liquid/Solid-Media Based Characteristics Rating

Best Worst

Figure 1. Comparison of Paint Stripping Processes. Only four technologies do not rely on solid or liquid media for stripping, with FLASHJET proving to be the best overall.

Laser stripping is currently under development. However, it is generally felt that high cost, safety issues, and manda- tory robotics make it a viable alternative only in the long-term future. Near-term environmental concerns and the economics of military and commercial airline opera- tions make it necessary that a solution be implemented much sooner.

for nearly two decades and is used in a variety of cleaning, paint removal, and sterilization processes. The flashlamp consists of a quartz tube filled with xenon gas which, when electrically energized, emits a brilliant flash of light that is focused on the paint surface by a highly polished reflector. The light flashes, which can be regulated from 4 to 6 pulses per second, will heat a paint surface and turn it into a

Xenon flashlamp technology has existed

combination of fine ash particles and previously trapped volatiles in a process called pyrolysis.

In 1986, the US. Air Force Sacramento Air Logistics Center undertook a program to evaluate flashlamps for removing aircraft coatings. The equipment tested consisted of a handheld 9-inch laboratory prototype. The program concluded that while the flashlamp will strip paint from both metallic and composite substrates and can selec- tively strip to primer and stop, the tempera- ture rise of the substrate was a concern, the handheld, manually controlled unit was cumbersome and awkward, the effective- ness of the flashlamp and reflector was quickly reduced by a covering of ash, and further mechanical degradation testing of the specimens was required. Accordingly, not much was heard about flashlamps with regard to aircraft paint stripping until FLASHJET emerged.

CO, (dry ice)pellet blasting was devel- oped primarily as an environmentally compliant cleaning process. In 1989 McDonnell Douglas and Cold Jet Inc. investigated the effectiveness of CO, pellet blasting as an aircraft paint removal pro- cess. Initial testing on metallic substrates proved the process’s viability in removing coatings from metallic surfaces. However, the results on composites were less than encouraging-res required to cause paint removal were too high for the relatively fragile composite substrates.

however, lead the U S . Air Force Warner- Robins Air Logistics Center to undertake an extensive CO, paint removal program for F-15 metallic structures. This project concluded that CO, pellet blasting is fairly effective in removing coatings from metallic substrates, has a slightly better strip rate than other solid media techniques and, most important, has none of the problems

,

The results of the initial metallic testing, -

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associated with solid particulate media recycling and disposal. Still to be resolved, however, were the challenges associated with composite substrate stripping, stripping large military transport aircraft that utilize relatively thin-skinned metallic structures, and stripping rates.

So even though the two most viable alternatives at the time -Xenon flashlamps and CO, pellet blasting - offered benefits in terms of eliminating the use of haz- ardous media and the disposal of toxic waste, they nevertheless still presented problems with compromising structural integrity and demonstrating low strip rates and high costs.

The Solution

above challenges, the FLASHJET team saw the potential synergy of combining the flashlamp and CO, pellet technologies. This synergistic combination of the two technologies would allow the advantages of each to cancel out the disadvantages of the other to achieve effects that neither could by itself. These effects include high strip rates, damage free coating removal, finite process control, and significant reductions in maintenance man-hours, stripping cycle time, and stripping costs.

How FLASHJET Works A schematic of the FLASHJET process

(Figure 2) shows the pulsed light energy system, the dry ice (CO,) system, and the effluent capture system. (Not illustrated are a control sensor feedback system and the process applicator.)

The pulsed light energy source is produced by Maxwell Laboratories Inc. As its electrically energized, xenon-filled quartz tube emits pulses of light, the surface coating absorbs photon energy, heats to the point of pyrolysis, and changes into fine ash particles and previously trapped volatiles. At the same time, the dry ice system built by Cold Jet Inc. applies a Darticle stream to the surface to offset

In seeking a viable solution to all of the

Figure 2. FLASHJET Operation. The combination of pulsed light energy and low pressure dry ice achieves effects that neither technology can achieve by itself.

Figure 3. Strip Rate. FLASHJET's attractive strip rates result in reduced aircraft downtime.

strate by the effluent capture system and collected in pre-HEPA and HEPA filters. The remaining effluent vapors are collected in an activated charcoal air scrubber, leaving the resulting discharge totally clean

A color sensor, in turn, controls the depth of the stripping process. The sensor enables the flashlamp to fire only on selected colors and is capable of determin- inn the difference between topcoats, - I I

potentially damaging pyrolysis heating,

constant maximum light transmission, and sweep away coating residue from the

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an imi ng e azar ouswase isposa to ge v o ~ u m ~ o f ~ a i n t ~ a ~ c l e s ;,",,a i i the HEPA filters.

- pnmers, and substrates.

All of these process parameters can be preset for removing coatings at different rates and to specific depths. For instance, a 6-inch-lamp prototype system developed for the Air Force is capable of removing 1 mil (0.001 inch) to 2 mils of coating per pulse at 4 pulses per second. This rate equates to approximately 1 square foot of

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Figure 4. Comparison of FLASHJET with Chemical Technique. FLASHJETs significantly lower waste, throughput hours, and maintenance manhours results in significantly

lower costs for paint stripping.

Stripping Process Wash Mask Apply/Dwell Strip Rinse Demask

Comparison Clean Up

FLtlSHJET

Sodium Bicarb

0

0 0 0 0 0 Aquastrip

Media Blast

Figure 5. Stripping Process Comparison. FLASHJET eliminates the prestrip and poststrip requirements of other technologies.

0 0 0 0 0 0

0 0 0 0 0 0

coating removal per minute. A 12-inch- lamp production system is capable of removing 4 to 5 mils of coating per pulse at 6 pulses per second. This rate equates to approximately 4 square feet per minute.

aircraft through-put time is reduced by 70 percent. These reductions provide a combined savings in overall aircraft paint stripping costs of 66 percent!

Figure 5 compares the cost factors that

Chemicals

Water Jet

P

lamp production system is provided in Figure 3.

typical narrow body jet yields some very significant savings when compared with using a chemical system (see Figure 4).

Note that in addition to reducing haz- ardous waste by 99 percent, maintenance man-hours are reduced by 66 percent and

Applying this technology to stripping a

0 0 0 0 0 0 0

0 0 0 0

apply to chemical stripping and other media-based processes. This chart helps explain why significant cost savings and a significant reduction in waste can be achieved by FLASHJET. Further compar- isons are provided in Figures 6 and 7.

Applying FLASHJE T FLASHJET currently has two applica-

tion techniques: a power-assisted mobile manipulator and a dedicated stripping

booth. Which is used depends on the size and shape complexity of the aircraft parts to be stripped. Both, however, help reduce stripping cost and enhance personnel safety.

The power-assisted mobile manipulator shown in Figure 8 is used for total aircraft stripping. In this applicator, the effluent capture shroud is an integral part of the stripping end effector. Since aircraft paint stripping is removed from the critical paths of maintenance, other work can be safely performed simultaneously to reduce aircraft downtime.

For off-aircraft component stripping of either composite or metallic structures, the FLASHJET process can be conducted in a dedicated booth using a gantry device. In this application, effluent capture can be handled by booth ventilation.

Unlike several other emerging paint removal technologies, FLASHJET need not be applied or controlled using expensive robotics, nor is there a need for large hanger facilities to contain and handle residual media or removed paint. These features will allow current depainting facilities, which will soon require extensive equipment upgrades due to Clean Air Act regulations, to be converted to a normal maintenance facility.

Product Development The original idea for the FLASHJET

Coating Removal Process was developed in pursuit of the U.S. Air Force Large Aircraft Robotic Paint Stripping (LARpS) program. Although FLASHJET was not selected for this program, in 1991 Warner-Robins Air Logistics Center awarded the FLASHJET team the Producibility, Reliability, Avail- ability, and Maintainability (PRAM) contract to develop and deliver a proof-of- concept, prototype system (see Figure 9). The prototype consists of a &inch-long flashlamp, a Gnch-wide CO, particle delivery nozzle, a power supply, and a CO, pelletizer.

proof-of-concept system, the FLASHJET

performance system with its own funds and put it into operation at the Maxwell Laboratories Inc. facility in San Diego, California. The 12-inch-lamp system was initially used to strip numerous metallic and composite panels for the PRAM pro- gram, for the U.S. Navy Add-on program, and for Douglas Aircraft/FAA certification testing.

Nearly 700 metallic and composite specimens were processed for these three

In concert with the development of the

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Figure 6. Cost Savings. FLASHJET reduces paint Figure 7. Waste Reduction. FLASHJET reduces hazardous waste up to 99%. stripping cost up to 66%.

programs. Up to five striprepaint-strip cycles were performed on the sample panels prior to their being made into specimens for mechanical properties degradation tests. Most of the data presented in this article came from these demonstration programs.

The results to date of the US. Air Force and Navy programs, which were completed

of the FAA certification testing was a letter of approval in May 1993, allowing Douglas Aircraft unrestricted use of FLASHJET for stripping all Douglas commercial aircraft.

Meanwhile, McDonnell Douglas has begun operating the 12-inch-lamp system in a process application development and demonstration cell in St. Louis (see Fig- ure 10) to demonstrate the FLASHJET

horizontal stabilator. McDonnell Douglas is also using the cell to perfect FLASHJETS effluent collection system, color sensor process control system, and process application integration techniques.

FLASHJET Is NOW! FLASHJET is an exciting technology

designed to meet the aircraft supportability in July 1993, show no damage or loss of strength to the specimens. The result

process on composite structures, specifi- cally a carbon/epoxy AV-8B Harrier

needs of our military and commercial customers while providing a cleaner

Figure 8. Airframe Stripping Concept. FLASHJET's application flexibility eliminates the need for dedicated stripping facilities.

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Figure 9. Warner-Robins AFB Proof-of-Concept Installation

environment in which to live. Three prototype systems are currently in service, and demonstrations and preproduction tests have proven the technology non-

personnel, safe on all airframe outer

technology and will be happy to answer any questions and inquiries. For more information, please contact any of the following personnel:

St. Louis. Missouri

Dave Breihan has been a member of the McDonnell Douglas Product Support division for 27 years. His ex- perience includes preparing art and technical data for organizational level publica-

F/A-18 projects; developing rrl T 4 i - . . I

I *! I I J , I U

moldline surfaces when properly applied, and economical to use.

With first customer deliveries scheduled for December 1993, the FLASHJET team is actively marketing its

(314) 232-2921 Eugene Cooke I11 - Cold Jet Inc. Loveland, Ohio (513) 831-3211 Michael Plum - Maxwell Laboratories Inc. San Diego, California (619) 576-7602

logistics support data for the AV-8B and serving as the supportability member of the Advanced Materials and Structures group Dave is currently assigned to the Aircraft and Missile Support Systems division and has been a member of the

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FLASHJET Team since its beginning -~

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