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Aerospace best practice: Clean as you go
In aerospace, the latest composite materials, like the carbon fiber used in Boeing’s 787 Dreamliner and Airbus’s A350, may be up to 20% lighter than conventional aluminum, leading to better fuel efficiency and longer flights. Yet to take full advantage of these materials, aircraft manufacturers and maintenance repair organizations (MROs) still have to contain their airborne dust, foreign object debris (FOD), and particulate when grinding, sanding, and cutting.
To optimize operations, one aerospace manufacturer and MRO best practice is increasingly to clean as you go. From composites to hexavalent chromium to cadmium, vacuum capture of dangerous dust, FOD and particulate at the source is enhancing aircraft safety, quality and production.
GE Aviation’s Batesville, Miss. composites plant sought to proactively identify and reduce any dust they could, since cleanliness is a vital part of their quality manufacturing process.
“We’ve had everyone from 60 Minutes to FAA quality inspectors tour our site, and our product requires us to have clean rooms,” says Curt Curtis, who is technical leader of the Batesville plant’s manufacturing shop.
The Batesville plant produces two composite parts for GE’s GEnx jet engine: fan platforms (installed between the engine’s front fan blades) and the fan case assembly (a large circular structure that encases the front fan). The GEnx engine powers Boeing 787 and 747-8 aircraft, and is the world’s only jet engine with composite fan blades, fan platforms and fan case assemblies.
Compared with conventional aluminum airframe components, composite components provide engine weight savings and greater durability, resulting in better aircraft fuel efficiency as well as reduced maintenance and replacement costs. For instance, Curtis says that compared with a typical aluminum fancase with titanium blades, the composite GEnx engine fancase and fanblades save over 300 lbs. per engine.
According to Curtis, the composite process has a significant amount of handwork involved to finish the product properly. After curing the material, certain areas require blending, smoothing and removal of excess material (called flash), typically using handtools such as sanders and grinders.
“Our rule is to capture dust at the point it’s created because cleanliness is our first line of defense against any potential quality issues,” states Curtis.
Curtis says the Batesville plant brings smaller composite parts inside a dust containment booth to finish them. “But larger composite components like our fan cases, which are about 10ft in diameter, weren’t practical to bring inside a containment booth,” he says. “That’s when using a tool shroud is critical since that essentially becomes the dust containment booth.”
After the Batesville plant conducted an aerospace industry literature study and evaluation, it chose equipment from DCM Clean-Air Products, a Fort Worth, Texas-based manufacturer of power hand tools designed for source capture of airborne particulate.
“To enhance quality and safety, we required strong, reliable vacuum suction with HEPA filters and tool shrouds to capture any composite dust at the source,” explains Curtis.
Safer, better, faster
In aircraft MRO operations, sanding, grinding, sawing or drilling can launch a plume of dust, FOD and small particulate across the aircraft and worksite. Often this can endanger worker safety, while hindering quality and production if work must be stopped to thoroughly clean the product and worksite.
“When doing a composite repair, cutting out an area, and grinding it down, you’re putting particulates and volatiles in the air,” explains David “Scott” Malcomb, a JetBlue University instructor at Orlando International Airport, who teaches an advanced composites class to a select group of technicians. “While those doing the repair usually wear respirators, gloves, goggles, and sleeves, everyone around them typically isn’t wearing protective equipment, so they’re getting exposed.”
Though OSHA has not required PPE for exposure to most composite reinforcement fibers, as they do not pose a health risk in dry fabric form or when cured in a resin matrix, machining a cured laminate can get short fibers airborne. This is a potential concern if the short fibers are breathed in and damage lung tissue.
“While airborne composite materials aren’t officially considered a respiratory hazard, safety managers would be wise to remember that asbestos was once considered safe,” says Malcomb. “Best-practice technique is to vacuum-extract composite dust and debris at the source so it doesn’t get airborne, scatter as FOD, or have to be cleaned up later.”
Besides composites, other dusts and debris can be even more important to control. According to an OSHA report, hexavalent chromium (Cr(VI)), a toxic form of chromium, for instance, is often used in the form of zinc chromate as an aerospace paint primer, varnish and pigment. It is toxic when inhaled as an airborne dust, fume, or mist, and can cause lung cancer in those who breathe it.
The OSHA report states, “Surfaces contaminated with Cr(VI) must be cleaned by HEPA-filtered vacuuming or other methods to minimize exposure to Cr(VI).”
Cadmium dust and FOD from frozen fasteners drilled out during maintenance can be toxic and dangerous as well. The airborne dust of many materials such as aluminum, in fact, can ignite or explode if set off by a spark, blowtorch, or other ignition source.
FOD damage is estimated to cost the aerospace industry US$4bn a year. FOD can not only cause product rejection by aircraft OEMs and suppliers, but also catastrophic failure if it interferes with mission-critical equipment.
To control dust and debris in materials like aluminum in past decades, the aerospace industry has used vacuum extraction. Now vacuum capture of dangerous dust, FOD and particulate at the source is being extended as a best practice in materials ranging from composites to hexavalent chromium to enhance safety, quality and production.
“Since the product is only as strong as its weakest link, today vacuum capture increasingly follows a whole-system approach, usually involving everything from the abrasive to the tools, hoses and vacuums, ensuring that harmful dust and debris is safely handled at each step of the process,” says Brad Clayton, vice president of Clayton Associates, a Lakewood, NJ-based leader in source capture tools and vacuum sanding equipment.
Associated Painters, an aerospace industry service provider for aircraft manufacturers, modification centers and airlines, uses a complete vacuum extraction system to control dust and particulate when mechanically removing old paint with sanders before repainting.
“Capturing dust and particulate at the source protects everyone across the entire worksite, improves the quality of the paint job, and helps us comply with FAA, EPA and OSHA regulation,” says Mike Wilkins, purchasing manager for both Associated Painters and Leading Edge Aviation Services, another aerospace service provider.
Wilkins finds that preventing dust and particulate from circulating around the worksite is much more effective than traditionally hosing down the floor and using squeegees to scrape waste material into trenches to pick up later.
“Our operators are safer, more comfortable, and about 8 to 10% more productive using Clayton sanders with tool shrouds and DustMaster vacuums with custom hoses,” says Wilkins, whose operators still wear protective suits and respiratory masks as a work precaution. “Our paint jobs are better since there’s no dust or particulate getting kicked up to settle on the paint. There is no dust or particulate to clean up after we use the vacuums.”
David “Scott” Malcomb’s JetBlue University advanced composites class also uses a complete vacuum extraction system to control particulate when grinding and removing a damaged section of carbon fiber or fiberglass material.
“In an enclosed area like our class or a shop, controlling particulate at the source is even more important,” says Malcomb. “We run four people at a time on a repair, three on our Clayton DustMaster unit, and another on a single unit.”
According to Malcomb, the larger unit is a complete, lockable, HEPA filter vacuum system configured for aerospace maintenance, with three hoses for simultaneous use. A safe filter change process allows workers to change filters without re-introducing dust and pollutants into the air.
Since both the larger and smaller units are portable, advanced composites class students will use them for repairs in the field as well. “Our students will not only use the vacuum extraction units in the training room but also will roll them out to do on-wing repairs on the hangar floor,” says Malcomb.
According to Malcomb, after his select group of about 20 to 25 advanced composite class students are fully trained, they will be stationed in New York City, Boston and Orlando to do necessary JetBlue light check composite repairs.
“Safety, environmental, and production managers need to look into source=capture vacuum equipment,” concludes Malcomb. “As aircraft MROs begin to use these systems, they will move from best practice to standard procedure because of the way they help to optimize safety, quality and production.”
26 January 2015