Syntactic pastes can also be used to seal and close-out honeycomb edgesto enclose inserts in cored parts such as aircraft luggage lockers orwhen produced in sheet formcan be used as core or linings.
The benefits of adhesive bonding for aircraft manufacture including weight reductioncost savingselimination of stress points and the elimination of mechanical fastenings and drilling.
Structural adhesives evenly distribute stresses over a wide areaact as sealants and also reduce noise and vibration. Nearly all adhesives used in aerospace interior applications must also exhibit the required flame retardancy and FST (fire/smoke/toxicity) resistancerequired by federal regulations.
The most commonly used materials are 1 or 2 two component flame retardant paste epoxy adhesiveswhich offer a good balance of FST and mechanical properties. These materials can be cured at either room temperature or elevated temperatures and exhibit good mechanical properties on both metal and thermoplastic substrates. They have good environmental resistance and show excellent stress crack resistance on thermoplastic substrates.
The EU’s ABiTAS programme (Advanced Bonding Technologies for Aircraft Structures) is now focusing on the development of a new generation of adhesives for use on commercial aircraft to replace film adhesive which allow bond to to bonding of the autoclave.
Adhesive pastes in the form of liquid shims are commonly used for levelling or filling gaps between two component surfaces or parts. Composite aerospace structures are very stiff and often parts cannot be machined closely enough to mate perfectly.
Soliquid shim adhesives are used to fill the small gaps around mechanical fastenings. They cure to form hardstrong fillers that prevent stress concentration at mechanical fastening points.
The tools used for forming composites can be made from a variety of materials including epoxy boards and seamless modelling pastes (SMP).
SMP offers a range of benefits including increased production ratelower costlightweight and easy to handleeasy machinabilitygood surface finish quality and minimal waste. The most recently developed paste also maintains dimensional stability at higher temperatures making it a viable alternative to traditional toolmaking. For exampleHuntsman has recently introduced a High Temperature SMPRenPaste4633. This cost-effective epoxy SMP has a heat deflection capacity of up to 180¢ªC for high temperature resistant tools.
Maintenance and repair of aircraft is a major cost issue for the aerospace industry. While most aircraft repair shops are familiar with the repair of aluminium skinned aircraftcomposite components require a different repair strategy. A range of low and room temperature curing epoxy and polyurethane adhesives and pastes as well as laminating systems are available to cover a broad range of needs to effect quickreliable infield repairs. For exampleHuntsman offer a range of wet laminating resins for repairs including Epocast50-A1/B which is a toughenedflame retardantlow viscosity resin that gives high flexural strength while still being easy to handle on random repairs.
