Particulate matter generated by grinding, sanding and cutting materials, such as carbon-fibre composites, paints and cadmium, is not only a potential FOD risk but also dangerous to maintenance engineers. One prevention method increasingly being used by OEMs and MROs is vacuum capture at the source.
GE Aviation’s composites plant in Batesville, Mississippi, is one facility that has sought to proactively reduce any dust they could because 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 plant produces the composite fan platforms and fan case assembly for the GEnx engine, which engine powers the 787 and 747-8 and is the world’s only jet engine with composite fan blades, fan platforms, and fan case assemblies.
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,” says 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 10-feet in diameter, weren’t practical to bring inside a containment booth,” says Curtis. “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 Fort Worth-based DCM Clean-Air Products equipment. DCM manufactures hand tools designed for source capture of airborne particulate, including a line of HEPA vacuums, sanders, grinders, drills, routers, buffers and shrouds.
“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,” says Curtis.
In 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 Malcomb, a JetBlue University instructor at Orlando International Airport, who teaches an advanced composites class. “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 US health and safety rules do 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 a report from the US Occupational Safety and Health Administration (OSHA), hexavalent chromium (Cr(VI)), 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. Furthermore, the airborne dust of many materials, such as aluminum, can ignite or explode if set off by a spark, blowtorch or other ignition source.
To control dust and debris from materials like aluminum the aerospace industry has long used vacuum extraction. Now vacuum capture of dangerous dust, FOD and particulate matter at the source is being extended as a best practice in materials 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 New-Jersey-based manufacturer of source capture tools and vacuum sanding equipment.
Associated Painters, an aerospace industry service provider for aircraft manufacturers, modification centres and airlines, for instance, 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, Environmental Protection Agency and OSHA regulation,” says Mike Wilkins, purchasing manager for Associated Painters.
Wilkins finds that preventing dust and particulate from circulating around the worksite is much more effective than the traditional approach of hosing down the floor and scraping waste material into trenches to collect later.
“Our operators are safer, more comfortable, and about eight to 10 per cent 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.”
Malcomb’s 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.”
The larger unit is a 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.
After Malcomb’s group of 20 to 25 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 MROs begin to use these systems, such equipment will move from best practice to standard procedure because of the way they help to optimise safety, quality and production.”
Image credit: Clayton's complete vacuum extraction system in use at Associated Painters