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Bootstrap Aircraft is restoring to flight the Chance Vought F4U Corsair fighter aircraft. This World War II aircraft holds the distinction of being the only fighter designed and built by one corporation, United Aircraft. Pratt & Whitney supplied the R-2800 Double Wasp engine, Hamilton Standard provided the Hydromatic propeller, and Sikorsky built the airframe as part of Vought-Sikorsky. In fact, the F4U Corsair was designed in East Hartford in what is now the IAE Building. Less than 20 aircraft are flyable worldwide, out of 12,751 produced.

Due to the extremely rare nature of this aircraft, and the availability of spare parts, every method available to clean the aircraft was thoroughly explored. Our concerns were focused on our need to remove over 50 years of grease, oil, carbon, dirt, paint and any corrosion with little or no substrate damage. Chemical stripping was ruled out due to environmental and safety concerns. Mechanical removal such as sanding and scraping was never considered. The remaining choices centered on media blasting.

The various commonly used forms of media were investigated, such as plastic bead, glass bead, walnut shell and sand. Each had their benefits, as well as their drawbacks. The most significant obstacle for us was the fact each form of media would require its own blasting cabinet. In addition, to avoid contamination, the different materials being cleaned would require us to use several different cabinets, even though they were using the same form of media. Waste disposal was also a major problem. The concern of causing substrate damage was highlighted by the use of all of these various cabinets, as the inadvertent use of an aggressive media on a delicate part was possible with all of these cabinets and forms of media in use.

Our investigation lead us to the Armex Cleaning and Coating Removal System. Armex is made by the world known Arm & Hammer division of Church & Dwight. This water-soluble media blasting system met our initial requirements, specifically not causing any substrate damage and by providing easy waste disposal. The added benefits were even more impressive. The basic product, sodium bicarbonate, can be mixed with additives to give characteristics not normally found in the media. There are currently 14 different formulae, ranging in abrasiveness from extremely mild to very aggressive. This meant we would only need to invest in one cabinet, and could easily switch back and forth between various grades of media as required. Contamination in not a concern, as the blasting system is one pass only, and is not recirculated within the cabinet. Also, the use of this system allows us to blast parts without having to pre-clean them, as we would have to do with other systems. The Armex media literally sweeps away grease and oil, and does not impact into the grease and become lodged. The media fractures upon impact, and does not cause crack closure, in fact it aids in revealing cracks. The water soluble nature of the media ensures passages can be thoroughly cleaned after blasting.

The first major project cleaned with Armex was the Corsair engine, the R-2800 Double Wasp. This engine was shipped from Pratt & Whitney on May 17, 1945. It was installed in the F4U Corsair, and accumulated 917 hours prior to its removal in the mid 1950s. Once removed, it was sealed in a container, and remained there until 2000. The engine was simply preserved and sealed in the container without having any cleaning or re-work done. Our purposes in restoring the engine were several fold: To inspect the engine for its future flight use, to preserve the engine until it undergoes a certified overhaul, to create a functioning display showcasing Pratt & Whitney's piston engine heritage, and to provide a build-up fixture, centered on the engine, to restore the powerplant portion of the Corsair. To do this, we needed to disassemble, clean, paint and re-assemble the engine. The Armex system allowed us to clean the various parts, economically and easily. We used no solvents or chemical cleaners, and were able to retain the original finishes found on the engine. For instance, the steel parts of the engine cylinders were sprayed with a proprietary aluminum type coating to prevent corrosion. During aftermarket overhauls, this is usually removed with media blasting, and is replaced with paint. We were able to leave this coating intact, having cleaned them with Armex and 15 PSI of air pressure. The formula we used leaves anodizing intact, as well as other platings and coatings on steel and other materials.

We restored this engine, having done no machine work or parts replacement. Since the engine will eventually be overhauled before flight, we wanted to leave as much information for the overhauler as possible such as witness marks or heat damage. The exhaust valves, which see the most heat, were cleaned of all carbon at 5 PSI, and retained their coloration.

Maintaining the cabinet is quite simple. We acquired the cabinet as a used unit, and we believe the glass window is about 10 years old, and is as clear as new. The nozzles are at least several years old, and show no wear. The cabinet uses a cyclone to trap the heavier particles, and a filter housing to catch any finer dust. These are both dropped into sealed 55 gallon drums. Routine daily maintenance takes about 2 minutes, and the system reliability is extremely high, as the sodium bicarbonate is formulated to be water resistant prior to blasting and is almost impervious to moisture intrusion within the system. We have had water get into the compressed air lines, and it just blew all the way through the system and came out of the nozzle within the cabinet, causing no clogging.

We had no other methods available to clean this engine, and found this system extremely efficient and cost effective. An added benefit was that we have found a secondary use for the used media in the clean up of chemical spills elsewhere in the plant. As operators, we feel comfortable working with the Armex system, as the media is non-toxic, non-hazardous and biodegradable prior to its being used. We also found that our used media proved to be non-hazardous after cleaning the engine, as the measured parts per million of contaminants were below established limits.

The engine was painted using the exact colors from the WWII era, and all external parts were replated to the original specifications. It is currently on display in the Pratt & Whitney Aircraft Engine Museum, and looks exactly as it did on the day it was shipped. This would not have been possible with more aggressive types of media. The entire restoration project, including the engine and the Armex system can be seen on our website at http://www.bootstrapaircraft.com.

ARMEX, a formulated sodium bicarbonate, has been utilized for over 15 years as a cleaning and coating removal media. The process was originally introduced to remove surface corrosion from soft metallic surfaces without damage or distortion. Church & Dwight Co., Inc. makers of ARM & HAMMER products and leader in bicarbonate technologies has carefully engineered this process to maximize efficiencies in applications where substrate preservation is essential. While this technology employs the extraordinary physical characteristics of the sodium bicarbonate crystal, other chemical benefits and properties such as its benign nature, low pH and water solubility have contributed to its successful application and preferred use on high value parts and critical components. As a formulated sodium bicarbonate, ARMEX has filled a very important niche within the aerospace industry

Though utilization of ARMEX may seem limitless, there are specific niche applications where it works best. Four years ago Jimmy Nixon, Lead Technical Advisor of American Eurocopter, Grand Prairie, TX was intrigued with ARMEX's potential for stripping aluminum parts. Working with the ARMEX Distributor, Laster Castor, DeSoto, TX, the two companies embarked on a long endeavor of testing and proving the system.

Previously specified were liquid caustic strippers which were posed worker and environmental concerns and were time consuming as well. The liquid stripper method required that the part be covered with the chemical, left possibly for hours for the chemical to soften or loosen the paint. Then it would be cleaned of chemical and paint residues. In some instances cleaning would be incomplete and the process would have to be repeated.

The one-step, thorough results of using ARMEX were immediately evident. A part that used to take the caustic stripper up to 3 hours to prepare was done in 10 minutes. Coupled with the inherent worker safety and environmental advantages, the time savings was another indication of tremendous cost savings potential. The manufacturing, parent company however, was still insisted on a thorough approval process. Over a three-year testing period the time saving and thorough cleaning benefits were confirmed and the group discovered the further advantages of the ARMEX process's versatility. Applicators found that as they learned to operate the system with finesse they could remove coatings in layers potentially eliminating follow-up steps. For example, ARMEX could easily remove just the top-coat leaving the primer intact. For the required magnetic particle inspection the water-solubility of ARMEX made crack exposure simple. There was no peening on the surface or residue lodged in fissures.

American Eurocopter has since approved and specified the process for numerous cleaning applications involving 60-70 dynamic components. What used to take up to 8 hours has been reduced to 1.5. Compressor side turbines usually have a coating on the blades that must be removed for inspection purposes (FPI or NDT testing). Coatings removal is typically done with hazardous chemicals and hand tools under a chemical fume hood. The process is tedious and slow, sometimes taking several hours to accomplish. There is a risk of further damaging the part with hand tools and/or insufficiently cleaning the part for inspection. In either case the part would then be scrapped. Hazardous waste disposal not only contributes to the cost but further complicates regulatory and safety concerns.

In comparison ARMEX can accomplish the same task in twenty minutes completely contained in an inexpensive glove box unit. The process does not cause crack closure, peening or other damage to the surface. As little as one half pound of non-hazardous, non-toxic ARMEX is required per minute of blast time. Although testing of the waste stream should be performed, our research has determined that most waste tests non-hazardous and can be disposed of in a sanitary landfill. The result is a very clean turbine, with no substrate damage, accomplished with a process that is both economical and without environmental or user hazards.

While ARMEX is comprised primarily of sodium bicarbonate, its uniqueness results from the purity and more importantly the uniformity of particle size combined with formula additives for flowability and rinseability, and other specific surface preparation requirements. ARMEX Blast Media is extremely stable under normal storage conditions and will retain its blasting and efficacy properties indefinitely. ARMEX will not burn or inflame at any temperature in fact it will act to retard flame propagation.

Another unique feature for ARMEX is its water solubility. This characteristic allows for complete removal from any macro or micro area on sensitive machinery or hardware. In any surface preparation operation there is a chance that errant media will be left behind on the surface either in the form of a light dusting or in blind holes of recessed areas. ARMEX media is the only soft-abrasive material that allows for complete removal through water rinsing.

Finally with sodium bicarbonate being mildly alkaline with a pH of 8.2 it can be useful in aqueous buffering and in neutralization of acidic materials during surface treatment or in the waste stream

For more information contact us at 1-800-332-5424 or 609-497-7220.

Application Overview:

AlliedSignal Aerospace's Anniston, Alabama facility overhauls commercial aircraft. This involves cleaning dirt, oil, rust, corrosion, carbon and grease residue from aerospace components such as cooling turbines, main engine starters and pneumatic valves. The components range in size from 5 to 18 inches. The facility cleans approximately 2,200 whole assemblies (including impellers, shafts, etc.) each month.

Substrates:

The majority of the aerospace components cleaned at the Alabama facility are hard anodized-coated aluminum. Other components are titanium or stainless steel.

Previous Methods:

AlliedSignal was using alkaline soap and hot water to hand scrub components as an interim alternative to chloroflurocarbon (CFC) degreasers. This provided satisfactory results, but raised some waste disposal concerns.

Special Concerns:

The Anniston facility was interested in minimizing process waste and complying with increasingly stringent federal and local environmental regulations [i.e. regarding waste disposal] – without sacrificing cleaning efficiency and performance.

Alternative Cleaning Method Evaluation:

The engineering department launched a comprehensive evaluation of alternative cleaning technologies and waste disposal options, including an ultrafiltration and pH manipulation system for oil removal.

Equipment Specifications:

AlliedSignal selected the ARMEX® Blast Cabinet Process, fitted with a #6 fixed nozzle. A smaller #4 nozzle is used for cleaning larger items that are difficult to clean under the fixed nozzle. The media chosen for this application is ARMEX® Maintenance Formula XL with SupraKleen® Rinse Accelerator. This patented, baking soda-based ARMEX Blast Media formulation is composed of all food grade materials and is approved by the United States Department of Agriculture as an A1 cleaner suitable for use in FDA-regulated facilities.

AlliedSignal operates the Blast Cabinet Process every day, using approximately 50 pounds of media per day. The Blast Cabinet Process is operated for a total of 48 hours per month. Most cleaning operations are performed using wet blasting at an air pressure of 20 psi.

Results/Benefits Summary:

The new process has resulted in numerous benefits, including:

Convenient Waste Disposal

A built-in waste filtration system captures insoluble materials for easy disposal. The remaining effluent (with a moderate pH averaging 8.4) is discharged directly to the onsite waste treatment facility for final disposal. Other benefits include an air recirculating system that virtually eliminates the need for outside venting.

Improved Cleaning

Checked by visual inspection, the aircraft parts are noticeably cleaner than with the previous soap-and-water method. The mild abrasivity of the ARMEX process enables it to clean and depaint high tolerance parts without altering the surface characteristics of most aerospace materials or without causing crack closure. Water-soluble ARMEX also is ideal for cleaning components, such as valves, where passageways need to be free from potential blockage.

Better Productivity

Previously, two workers on each of AlliedSignal's two shifts manually washed the components. Even so, the company typically had a day-and-a-half backlog of parts to be cleaned. Now, just one employee per shift cleans parts, and there is no backlog. The new process also requires less maintenance than the manual method – only one hour a week.

Enhanced Worker Safety

The former cleaning method used caustic cleaners, such as alkaline soap, as well as some harsher rust and corrosion removers required for some hard-to-clean parts. The non-toxic, non-hazardous ARMEX Blast Media eliminates the handling risks associated with these industrial chemicals and cleaners.

Application Overview:

At the end of every runway in the world there is one really tough cleaning job: the landing zone. This portion of the runway takes a pounding -- and a bit of each tire -- from every aircraft that lands. The Subang Airport Authority, Kuala Lumpur, Malaysia, faced the task of removing the accumulated layers of rubber, oil, grease, and grime from landing zones in order to restore the original FAA-approved surface texture in these areas. The runway is 14,000 feet long and 150 feet wide. The target area at each end is approximately 4000 feet long and roughly 60-80 feet wide (in the middle of the runway).

Substrate:

Bitumen with granite aggregate.

Special Concerns:

The management of the Airport had two primary concerns: that the refinished surface meet strict FAA guidelines for surface texture (FAA Circular #150/5320-12A, "Grease Patch Test to Determine Thickness of Rubber Deposits") and that the substrate show no evidence of damage or breakdown. A runway should have a targeted surface roughness of less than 250 microns; otherwise, two major problems may occur. Aircraft tires can wear too quickly or aggregate can be exposed and pose a danger to aircraft engines or other equipment.

Scheduling work posed a unique problem, too. Understandably, the airport could not shut down for several days while work progressed; yet work could not proceed with jumbo jets thundering down into the job site. The resulting schedule made the areas available two nights a week between the hours of 1:00 am and 5:30 am.

Previous Methods:

Chemical stripping, which is now prohibited for environmental reasons; and water blasting, which caused unacceptable damage to the runway, violating FAA surface guidelines.

Project Schedule:

January through February 1995. The overall schedule reflects the fact that contractors had a total of 9 hours each week to perform work.

Equipment Specifications:

In all, four ACCUSTRIP SYSTEM® delivery devices were used: two Model 13P units, one Model 16W unit, and one Model 12SX unit; all units were fitted with #8 Profile Performance Nozzles. The media used was ARMEX Maintenance Formula XL with SupraKleen Rinse Accelerator. It was estimated that the job would require 20 tons of media. Two trailers were set up to be self-contained workstations. Each trailer carried two ARMEX units, an Airman 830 CFM @ 150 psi compressor, holding tanks for blast water, and an array of electric lights driven by a diesel generator.

Containment:

No containment was used, or was necessary. The work was performed outside, in early hours of the morning, far from airport personnel and structures.

Results/Benefits Summary:

Blasting at 90 psi and using a media flow rate of 1.5lbs/minute, workers were able to maintain a nozzle rate of ten square feet/minute/nozzle. After blasting, a fire hose was used to wash spent ARMEX media, rubber residue, grease, grime, and oil into the drainage system beside the runways. The job was completed on time and the surface easily met FAA specifications. The substrate suffered no damage.