Extreme conditions require high performance aerospace coatings
The aerospace sector is one of the most demanding sectors for coatings and materials. Aerospace coatings need to provide protection from corrosion, abrasion, weather, UV radiation, erosion, temperature variations, and more in the most extreme conditions. The aerospace industry can be divided into space, commercial aviation, military and defence, and business aviation. Across these segments, coatings come in a range of technologies for use in both exterior and interior applications – from wing coatings to heavy-duty cabin coatings – for OEM (Original Equipment Manufacturer) and MRO (Maintenance, Repair, and Overhaul/Operations). With aerospace coatings, the sky is the limit.
In this article we look at the different aerospace segments and the coatings that serve them, as well as the companies and products available in Pakistan.
Sectors that use aerospace coatings
Aerospace coatings cover such a range of substrates and purposes it is easy to be confused about how the different sectors use them. Below we look briefly at the aerospace sectors and the coatings they use.
- Military and defence – The military sector requires specialty applications including for camouflage, chemical agent resistant coatings, infrared reflective coatings, and anti-static coatings.
- Space – Satellites, launch vessels, and other space-bound vehicles need specialty coatings to deal with the very specific nature of their use. These include solar reflection coatings, conductivity coatings, and even Vantablack.
- Business aviation – Private jets and general aviation is a growing industry, and the emphasis for coatings is on appearance – high quality aesthetics with as little downtime as possible.
- Commercial aviation – At any given time there are 5000 commercial airplanes in the sky. The commercial sector relies on coatings for protection but also for brand recognition, so colour is a hugely important factor. Long-lasting and durable coatings are needed to withstand the constant usage.
A quick guide to aerospace coating applications
It might be a surprise just how many surfaces in aircraft use coatings for protection or decoration (or both). Coatings for interior and exterior are exposed to different stresses and have different requirements in terms of finish and performance. Though solvent-based coatings are still the most common choice, air pollution regulations mean that water-based coatings are on the rise. Below we outline the different needs of interior and exterior coatings.
Interior coatings – cabins and cargo holds
Suitable coatings: polyurethane as a topcoat due to its durability, attractive finish, and soft touch properties
Last year, airlines ferried four billion passengers to destinations around the world. Cabin coatings need to deal with the knocks and scrapes of all these passengers day in, day out, year round and still look and feel good. The cabin interior uses a wide range of coatings for the ceiling panels, walls, seats, and equipment like galley carts. Not only do these coatings need to be protective and attractive, they need to comply with strict regulations regarding fire safety and flammability. Because of its durability, attractive finish, and soft touch properties, polyurethane topcoats are a coating of choice for cabin coatings.
Internal structural coatings – engines to fuel tanks
Suitable coatings: thermal barrier coatings and ceramic coatings for engines (heat resistance), epoxies and polyurethanes for other internal structures (chemical and corrosion resistance)
The internal structures of an aircraft are complex and it is vital that their function is maintained at the highest possible standard. Many of these structures have limited accessibility, so it is important that a coating is long lasting and hard working. The substrates range from airframe and engines to fuel tanks, each with different requirements. For jet engines it is of paramount importance that a coating can deal with, and protect from, extreme heat, as well as controlling wear and corrosion. Thermal barrier coatings and ceramic coatings are used for this purpose.
For internal structures such as airframe, fuel tanks, landing gear, and others, corrosion resistance and chemical resistance are key factors. These substrates are exposed to a range of corrosive substances such as anti-ice and hydraulic fluids and the coating needs to be highly resistant. They also need a coating able to deal with a high level of abrasion and wear. For these substrates epoxies and polyurethanes are used for their corrosion resistance, chemical resistance, abrasion resistance, and durability.
Exterior coatings – nose, wings, tail and everything in between
Suitable coatings: polyurethanes, acrylics and epoxies
The exterior of an aircraft needs to withstand incredibly harsh conditions. A passenger airline experiences a temperature range of over 90°C within a very short space of time, and at the same time the coatings need to deal with the flexing of the substrate and UV radiation. Not to mention the corrosive fluids (hydraulic fluid, fuel, and de-icer) and environments. The coatings also need to be lightweight so that they only minimally affect fuel and energy usage. Technologies for these coatings include polyurethanes, acrylics, and epoxies, though polyurethane is the most popular choice due to its UV resistance.
The coatings systems used for aircraft exteriors include primers, intermediate coats, and topcoats. There is also a special base coat/clear coat system which is modelled after the automotive coating system. The base coat is highly pigmented and provides more colour with less paint, while the high gloss clear coat extends service life and provides a smoother, easier-to-clean surface. Together the coatings cut down on application time and material, therefore cutting down on aircraft fuel costs. They are also more durable, which extends the repainting cycle, and are easily repaired.
Specialty coatings – anti-glare, anti-erosion and selectively strippable solutions
Suitable coatings: polyurethane for strippable and anti erosion coating as well as nanocoatings as anti-glare solutions
Airlines repaint their planes every 5-8 years. This process is costly, time consuming, and puts the aircraft out of operation for 10 days. A selectively strippable coating system reduces this downtime by including a primer that is not removed during the repaint process – the intermediate and topcoats are stripped and then replaced, leaving the primer in place. This not only cuts down on time, it cuts costs, and it also provides environmental benefits by cutting down on the amount of paint and paint remover.
Anti-glare coatings for the cockpit are another important coating used by the aerospace industry. They prevent glare from obscuring the vision of instrumentation and dashboards, allowing pilots to perform their jobs more safely. Anti-erosion coatings work to prevent the constant impact of rain, ice , dust, and other particulates causing erosion on exterior surfaces, especially the leading edge of wings and other strike areas. These are commonly polyurethane.
Aerospace coatings Pakistan – Manufacturers and their products
AkzoNobel, PPG, and Sherwin-Williams are the top three vendors in the aerospace coatings industry, and all three operate in the Pakistani market. The manufacture, development, and supply of coatings for the OEM (original equipment manufacturer) and MRO (maintenance, repair, and overhaul/operations) sectors of the aerospace market is a big business, and there are many companies that provide products for it. AkzoNobel products include the Eclipse, Alumigrip, Aerobase, and Aerodur lines, PPG produces Desothane, Andaro, and Desoto, and Sherwin-Williams aerospace coatings include the JetFlex, SKYscapes, and Soft Swade lines.
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