The aerospace industry utilizes vehicles that must function at peak performance levels in environments with extreme temperatures and pressures. Because of these constraints, aerospace technology and all supporting materials and tools must function at high level specifications as well. This includes aerospace adhesives, which are used in vehicle construction as well as maintenance on a wide variety of aerospace parts, including pipes, panels, fixtures and tools. Many companies produce different kinds of adhesives that function to various specifications for everything including hobby planes to space vehicles.
Adhesives are classified by their adhesion principles, based on the chemical properties of the adhesive itself. Adhesives that are non-reactive do not require a chemical interaction within the adhesive, but another element to harden, such as heat or pressure.
Drying Adhesives require air drying to solidify. This occurs when the solvent evaporates, and the adhesive hardens. Examples include white glue and rubber cement.
Pressure Sensitive Adhesives require applied pressure between the adhesive and adherend to form a molecular bond between the two elements. These adhesives are not usually intended to form permanent bonds. Examples includes adhesives on sports tapes and bandaids.
Contact Adhesives are rubber variants that can attach to a surface relatively quickly. Once the bonds are formed to the surfaces, the rubbers can be pressed together and bond quite rapidly. Examples include neoprene and certain kinds of laminates.
Hot-melt Adhesives are applied in molten form. When they cool, they form bonds between different surfaces. Examples: hot glue guns
One-part and Multi-part Adhesives are reactive adhesives that use chemical reactions that form internally or as part of a mix of components. One-part adhesives have a latent chemical reaction that can be catalyzed through the application of an outside energy source, like heat or ultraviolet rays. Multi-part adhesives form bonds when two components are mixed together and applied to a surface. One-part adhesives are generally lighter than multi-part adhesives.
Natural adhesives are formed from animal gelatin or vegetable material, like flour, and are categorized as basic glues.
Synthetic adhesives are often reactive adhesives, and are comprised of a wide variety of materials, such as plastics and emulsions. Examples include epoxies, polyurethane, and acrylic polymers.
Adhesives in the Aerospace Industry
Adhesives are not typically used for structural sealant purposes in aerospace designs, but there are plenty of adhesive applications in aircraft and spacecraft. For instance, many circuits in aerospace applications require electrically conductive or thermally conductive adhesives, so there are many options. These adhesives usually feature metal flakes, such as silver, which is spread into the adhesive to be conductive.
Typically, aerospace adhesives are available in numerous formulations to allow for flexibility in application. Additionally, adhesives can often be custom formulated to assist with optimal application. They are available for:
Transducer seals Fuel assemblies Metal and fiber composites Electronic assemblies Antennas Optical fibers Sensors
Adhesives Over Mechanical Fasteners
Adhesives are often used over mechanical fasteners like bolts or screws when weight factors are important to structural integrity and function, which are common issues in aerospace design and manufacturing. In some instances, mechanical fastening methods must be used, but in many cases, both options are available. Adhesives can be applied to achieve certain aesthetic design or function benefits. For one, adhesives can often be hidden from view, allowing smoother body shape. This can be beneficial for aerodynamics. Additionally, some aerospace designs require very thin, fragile material use. These materials cannot undergo welding or bolting easily, but adhesives can bond materials of all shapes and sizes. Finally, adhesives generally offer lighter weight contributions to the overall vehicle weight, which is another important consideration for aerodynamics and fuel consumption.
Adhesives cannot withstand all kinds of pressures, temperatures, and function stresses. Large, bulky materials that undergo function stress cannot be attached with many types of adhesives because these pressures can wear down and tear at adhesive bonds. Additionally, in cases where adhesives must be cured, the curing method may not interact well with the other materials, resulting in damage or wear. Likewise, environmental and production techniques that structural materials are exposed to may have adverse effects on many types of adhesives.