Pollution prevention, sustainability, and source reduction opportunities abound in the aerospace industry and its supply chain, from reduction of toxics use and emissions, to reduction energy, water, solid or hazardous wastes, and greenhouse gas emissions.

Note that a good environmental management strategy for OEMs is to assist their supply chain with information, training, and clear expectations for environmental stewardship during manufacture of parts supplied to the OEM. The following pollution prevention opportunities may be applicable through the entire supply chain.

The opportunity areas discussed below include:

Energy

• Institute an energy management program with risk management, cost control, quality assurance, employee recognition, and training.
• "Right-size" energy systems for the facility as a whole, e.g. upsizing cooling towers, while downsizing certain other components, especially heating, ventilation, and air-conditioning (HVAC) systems.
• Design and operate redundant air handlers, scrubbers, and cooling tower units in parallel to reduce pressure drop and power requirements, yet provide backup capacity when needed.
• Sequence chillers for maximum efficiency.
• Install variable-frequency drives on fan motors (supply and exhaust), and other motors across the plant.
• Size the boiler plant to minimize energy use while idle and eliminate boiler reheat requirements through heat recovery. (Different sized boilers - with integrated seasonal switchover - minimizes idle energy use during low-load periods).
• Minimize pressure drop in air delivery system with low-pressure-drop filters and lower face velocity unit coils.
• If vending machines are provided, (common for shifts that run around the clock), install vendormisers and pull the lamps and ballasts from the machines.
• Instill a company policy to unplug cell phone/blackberry/radio chargers when batteries or devices are not being charged.
• Implement leak detection for compressed air, vacuums, and any specialty gas delivery systems.
• Replace incandescent "exit" signs with LED lighting.

Water Efficiency/Conservation

• Institute a water management program with cost control, quality assurance, employee recognition, and training.
• Facility-wide water efficiency suggestions are provided in North Carolina's 2009 Water Efficiency Manual (Chapter 2).
• If hose washing or spraying is required, install high pressure, low-volume nozzles.
• Avoid or eliminate water wall or wet spray booths. Use fiber or deep bed air filters.
• Install water supply control valves to regulate water feed rates.
• Look for ways to reclaim, recycle, and reuse water streams.
• Minimize water contamination of solvent wastes and acid wastes.

Wastewater

• Reduce waste water by reducing water use in general as discussed in the Water Efficiency section above.
• Separate dye penetrants from water.
• Look for viable reclaim and reuse opportunities for filtered, separated process water.

Equipment & Process Modifications

• Install impervious covers on cleaning tanks to prevent vapor loss
• Install a vapor level control device for automatic sump shut-off
• Use super-heated vapor degreasers to facilitate drying and minimize solvent drag-out
• Use dry pumps on vacuum equipment to eliminate use of oil
• Use counter-current cleaning methods where possible
• Preclean parts by wiping instead of rinsing
• Centralize and consolidate cold cleaning operations to minimize vapor losses
• Increase drain times for parts before & after washing - to reduce dragout
• Use conductivity controls to minimize makeup and rinse changeout in water rinses, chillers, and boilers
• Extend solvent life by avoiding unnecessary solvent additions
• Extend life of cleaners through filtration
• Design experiments to determine the most dilute bath chemistries
• Use in-line solvent recovery on vapor degreasing

Loss Prevention and Housekeeping

• Implement and practice preventive maintenance on equipment to minimize opportunities for leaks, spills, evaporative losses, and other releases of potentially toxic chemicals.

• Implement 5S in work areas - to save time and reduce chances of misusing or losing equipment, chemicals, or materials.

Solid and Hazardous Waste

• Maximize recycling of any recoverable wastes, industrial and office.
• Research less toxic alternatives for cleaners, solvents, paint pigments and stabilizers, foam propellants, fire retardants, etc.
• Implement and practice waste segregation and separation to avoid mixing different types of wastes and especially avoiding the mixture of hazardous wastes with non-hazardous wastes.
• Recycle glycol coolant, hydraulic oil.
• Install halogenated solvent recovery system.
• Frequently inventory & reduce use of shelf-life sensitive material to save material, money, & costs of disposal for outdated hazardous materials.
• If disposable clean or PPE suits are used, consider replacing with suits that can be laundered and reused. If Tyvek suits are used, find a recycler.
• Use a rag laundering service in lieu of disposable rags.
• Evaluate opportunities with suppliers to take back packaging materials, and/or implement reusable packaging systems with suppliers.
• Use material exchanges to evaluate the possibility of finding another company that may use relatively clean streams (such as caustics, acids, solvents) as a feedstock. Depending on level of contamination, these may be valuable feedstocks for another company.
• Recycle and reuse packaging as possible.
• Recover spent solvent (in house or off-site).

Subset Manufacturing Processes within the Aerospace Industry

Metal Fabrication and Machining - See Metal Fabrication and Machining topic hub Pollution Prevention Opportunities page.

Metal Finishing - See Metal Finishing topic hub Pollution Prevention Opportunities page, and/or the Spray Painting section below.

Fiberglass Manufacturing - See Fiberglass Fabrication topic hub Pollution Prevention Opportunities page.

PCB Manufacturing

• Minimize the amount of water used for rinsing
• Recover copper sulfate from etching & stripping processes by cooling & crystallization
• Substitute drip pans for rinse tanks in circuit board facility
• Look for alternatives to isopropyl alcohol, such as spin drying of certain components, or use deionized water for cleaning.
• See potential additional opportunities at Semiconductor Manufacturing topic hub Pollution Prevention Opportunities page.

Spray Painting

Spray painting is a significant contributor of VOCs at an aerospace manufacturing facility. The following are suggestions to reduce the toxicity and quantity of paint and associated materials and resources used.

Paint Mixing

In batch production with manual application of the coating, determine precise methods to estimate the amount of paint needed for a job. Note that the amount of paint needed may be able to be reduced via efficient spray techniques and application equipment described below.

Application Equipment

To effectively reduce paint waste (via overspray, bounceback, over-use, etc.), and produce a quality coating, proper application techniques should be supplemented with efficient application equipment. Through the use of equipment with high transfer efficiencies, the amount of paint lost to overspray is minimized.

If conventional air gun spraying is still used, consider upgrading technology to one of the following technologies which are described below, followed by potential environmental benefits:

High Volume Low Pressure (HVLP) Spray Guns - The HVLP spray gun is similar to a conventional air spray gun but with modifications and special nozzles that atomize paint at very low air pressures. The atomizing pressure of HVLP systems is often below 10 psi.

Advantages: Improved transfer efficiency and reduced overspray than that of conventional air guns. The low application pressure decreases excessive bounceback and allows better adhesion of the coating to the substrate

Airless Spray Guns - Instead of air passing through the spray gun, an airless system applies hydraulic pressure to the liquid paint. As the paint passes through the nozzle, the pressure atomizes the paint and it is carried to the substrate by its own momentum. The paint is usually supplied by a pump located at a remote supply at pressures of up to 2000 psi. Airless tips are designed to shoot at about 12" from the substrate surface, which makes it more efficient for painting large objects, such as aircraft and ship parts, as long as the operator uses good techniques and does not have to paint the surface a second time. Airless can atomize higher viscosity coatings better than other guns. 

Advantages: Increased production rate, reduced bounceback and resultant decrease in overspray, and the ability to spray higher viscosity coatings without thinning using a solvent.

Electrostatic Spray - Electrostatic spray systems use paint droplets that are given a negative charge in the vicinity of a positively charged substrate. The droplets are attracted to the substrate and a uniform coating is formed. This system works well on cylindrical and rounded objects due to its "wrap-around" effect that nearly allows the object to be coated from one side.

Advantages: Very little paint is lost to overspray, and it has been noted to have a transfer efficiency of over 95%.

Heated Spray - When paint is heated, its viscosity is reduced allowing it to be applied with higher solids content, thus requiring less solvent. When the paint is heated in a special container and supplied to the gun at 140 to 160 degrees Fahrenheit, coatings of 2 to 4 millimeters dry-film thickness can be applied in one operation, resulting in considerable savings in labor cost.

Advantages: Reduces solvent use (but does require energy input).

Plural Component Systems - A common problem that facilities face when working with two-part coatings is over-mixing. Once the component parts of a catalyst coating are mixed, the coating must be applied. Otherwise, the excess unused coating will cure and require disposal. Additionally, the coating equipment must be cleaned immediately after use.

Advantages: Elimination of paint waste generated by mixing an excess amount of a two part coating, and cleaning wastes associated with mixing for each use.

Spray Technique

A good manual coating application technique is very important in reducing waste. If not properly executed, spraying techniques have a high potential for creating waste in the form of overspray and higher build than necessary. Here are several techniques for reducing overspray as offered in Spray Technique Analysis and Research (STAR®):

1. Triggering: Trigger the paint gun at the end of each pass instead of carrying the gun past the edge of the surface before reversing directions.
2. Air Pressure: Avoid excessive air pressure.
3. Spraying Angle: Use a perpendicular spray angle, pointing the gun directly (at 90 degrees) toward the substrate.
4. Overlap: Overlap the previous pass by 50 percent, which means that for every pass that the operator makes with the spray gun, 50 percent of the area covered by the previous pass is also sprayed. If less than a 50 percent overlap is used, the coated surface may appear streaked. If more than a 50 percent overlap is used, the coating is wasted and more passes are required to coat the surface.
5. Paint Proportioning: Mix batches of paint on an as-needed basis, whether through the use of a paint proportioning machine or otherwise. Record keeping requirements to track the amount of paint and thinner used can also help conserve materials and prevent waste.
6. Build Efficiency: Determine optimal paint build thickness and measure to ensure operators are not applying excess paint to the substrate.

Alternative Coatings

Powder coatings - Powder coatings are 100 percent paint solids in a powder form, and require specialized application equipment and heated curing. Transfer efficiencies can reach 95 percent to 99 percent while achieving a durable, corrosion-resistant finish. Product overspray collected in the paint booth exhaust system can be recovered and reused. Powder coating is extremely sensitive to part cleanliness, making multi-stage washers a prerequisite.

High solids paints - High solids paints are solvent-based products with 50 percent or more solids content. Because of the higher solids content, the desired film thickness can be accomplished with fewer spray applications. Quality characteristics include improved abrasion and mar resistance. High solids paints are sensitive to temperature and humidity and may require heating to obtain an acceptable cure time.

Water-borne paints - Water-borne paints use water as the primary solvent, which reduces volatile emissions compared to conventional coatings. Some may contain from 2 to 30 percent petroleum-based solvents. Water-borne paints can often use water as a thinner, and lines may be flushed with water (versus solvent).

UV / EB Coatings - Coatings systems that are curable by ultra violate light or electron beams (UV/EB). The resins used in these coatings are basically the same as those used in conventional high performance coatings which have been modified to make them polymerizable by UV or EB energy.

Paint Booth

• Ensure filtration meets new NESHAP requirement of 98% efficient filters. The best filtration options are fiber or deep bed air filters.
• Use air flow measurement to ensure filters are not changed more frequently than necessary.
• Water-based filtration consumes significant water. One advantage of water-based filtration in booths is the collection and separation of overspray, so that only the paint particulate becomes waste, versus drumming up and replacing filters along with particulate matter. Water-based filters are generally efficient at capturing the particulate as well. If water-based filtration is used, the options are:

Wet-Vacuum Filtration which consists of an industrial wet-vacuum head on a steel drum containing a filter bag. The unit is used to vacuum paint sludge from the booth. The solids are filtered by the bag and the water is returned to the booth.

Tank-Side Weir which can be attached to the side of a side-draft booth tank, allowing floating material to overflow from the booth and be pumped to a filtering tank for dewatering.

Consolidator which is a separate tank into which booth water is pumped. The water is then conditioned by the introduction of chemicals. Detacified paint floats to the surface of the tank, where it is skimmed by a continuously moving blade. The clean water is recycled to the booth.

Centrifuge or Hydrocyclone: The hydrocyclone is used to concentrate solids. The paint booth water enters a cone-shaped unit under pressure and spins around the inside surface. The spinning imparts an increased force of gravity, which causes most of the solid particles to be pulled outward to the walls of the cone. Treated water exits the top of the unit and the solids exit from the bottom.