Metal alloys and polymer-matrix composites (PMC) or advanced composites are material components principally found in commercial and military aircraft. Despite their remarkable mechanical properties and light weight, the manufacture of these components requires dust / fume collection to remove heavy metal / resin contaminants from the work environment.
Civilian space programs - Military defence
Aerospace manufacturing is a constantly evolving technology industry that often benefits from public-private joint ventures. Civilian space programs such as the National Aeronautics and Space Administration (NASA) in the USA, the Canadian Space Agency (CSA) and the European Space Agency (ESA) are but a few institutions committed to coordinate / promote research and industry-related initiatives dedicated to the exploration of space. Government-run programs foster innovative and globally competitive defence-related industries to produce state of the art military air vehicles. In the wake of these developments, a multitude of businesses manufacture tools, components and complex artefacts such as aircraft, drones, spaceships and satellites.
Metal alloys and polymer-matrix composites (PMC)
Metal alloys and polymer-matrix composites (PMC) or advanced composites are material components principally found in commercial and military aircraft. Their remarkable high-strength, high-stiffness and low weight characteristics make them suitable candidates not only for aerospace manufacturing, but also for a wide variety of industries. While aerospace remains the predominant player for advanced composites fabrication, the gradual decrease in manufacturing costs over time has driven PMC penetration into the automotive market as well as the sports industry, namely in the production of high-tech commodities for golf, tennis, fishing and archery.
In this section, we will focus on aerospace manufacturing.
Common processes / sources and hazards
Metal alloy machining - Part assembly - Health hazards
Metal alloys are cut, shaped, drilled and formed with computer numerical control (CNC) machining centers. Aluminum, titanium and beryllium offer light weight, high strength and high melting point that are of value as structural components in aircraft. They are often assembled as a honeycomb sandwich which offers superior resistance to bending at the fraction of the weight of a metal plate of comparable thickness. Machining these materials produce chips and fine dust particulate that, if not controlled, will clutter the work environment. Beryllium, for example, is a notorious health hazard; exposure to particles, fumes, mists from beryllium-containing materials promotes skin sensitization, injury to the eyes, lungs and other vital organs; it is a confirmed human carcinogen by the International Agency for Research on Cancer (IARC).
Advanced composites or PMC manufacturing - Machining - Part assembly
Polymer-matrix composites (PMC) or advanced composites are privileged for their high strength, rigidity, low weight and superior corrosion / heat resistance. They are manufactured with carbon or hydrocarbon fibers, on occasion with metallic strands or particles, and bonded using polymer resins to produce sheets or fiber-wound strands. The individual sheet elements are stratified in metal, wood or plastic molds using adhesives and can be found in wing skins and aircraft fuselages. Cylindrical and spherical components are CNC precision-manufactured by winding fiber on a mandrel with resin gradually injected to form the part with subsequent resin curing; they are found in aircraft / rocket motor housings, fuel tanks and ventilation ductwork
Resins in the manufacture of composites - Dermal and inhalation hazards
Employee exposure to resins used in the manufacture of composites or generated as by-products remains the principal work-related hazard. Some resins present both a dermal and inhalation hazard. Thermosetting resins, which are predominantly used in PMC fabrication, include epoxies, polyurethanes, phenolic / amino resins, bismaleimides (BMI, polyimides) and polyamides. The potential for respiratory exposure increases when the resin is sprayed or when curing temperatures are high enough to volatilize the resin. Polyurethane resins pose a significant hazard, in particular to the eyes, respiratory tract and skin. Phenol-formaldehyde resins, urea-formaldehyde resins, bismaleimides (BMI) and polyamides are potential carcinogens and must be handled with adequate ventilation. (OSHA)
Fiber reinforcement added to resins - Dermal, ocular and inhalation hazards
Fiber reinforcement added to resin matrix improves the mechanical resistance of the finished part. Potential worker exposure is higher among those plants that manufacture fibers or use them to produce prepreg material. Most fibers are classified as nonrespirable; however, they may cause eye, skin and upper respiratory tract irritation due to the nature of the fibers. (OSHA)
Exposure limits for PMC dust-generating processes
The most common PMC dust-generating processes are the machining and finishing of cured parts and the repair of damaged parts. The sub-micron particulate contains few fibers and should be considered respirable; exhaust ventilation should be maintained to ensure dust concentrations remain below the permissible exposure limit (PEL) of 15 mg/m3 set for inert or nuisance dusts.
Dust collector design
Separate process areas and dedicated enclosures with local exhaust ventilation (LEV) are commonly employed to control dust emissions. Due to the nature and composition of dusts, customized dust collection with special precautions and protective devices may be required in order to meet air quality and/or worker health and safety regulations.
Dust collectors adapted for individual processes
AIrex successfully supplied and implemented fume / dust collection systems for the following processes:
- Grinding aluminum
- Polishing aluminum
- Forming and flame / torch cutting titanium
- Landing gear – Finishing
- Airplane wing – Finishing
An Airex solution for a well-known problem: Aluminum dust collection
Aluminum cutting, boring and drilling generate dusts that are not easily removed from the work environment with dry collection systems due to the risks associated with fire. The metal dusts are “apparently” not combustible, but they may burn or explode if the particles are correctly-sized and in the right concentration. Should the particles disperse in air and the dust cloud confined, an ignition source may cause a deflagration.
In response to this problem, Airex designed and developed a wet collector in line with NFPA health and safety recommendations. The Airex Wetrex Series collectors employ water baths to scrub the polluted air stream and thereby remove aluminum particulate in a safe and secure manner. An innovative, inexpensive solution with NO fire hazard.