Film and paste adhesives, wet release layers, and potting compounds enable the aviation industry to utilize advanced materials that help reduce weight, improve design efficiency, and increase sustainability. #a350 #Boeing#787
From the early days of the aviation industry, aircraft structures have been made of metal. Gradually, aluminum has become the first choice for primary, secondary and tertiary structures because of its light weight, alloying ability, fatigue properties and lower production costs compared to other materials.
The latest generation of aircraft uses advanced composite materials that can be optimized for specific aircraft design requirements. By weight, both Airbus A350 and Boeing 787 are composed of approximately 50% composite materials.
Many benefits provided by composite materials have accelerated this evolution, such as:
One of the most important advantages of composite materials is lightweight. The reduction in aircraft weight provides a series of benefits. Lighter aircraft use less fuel, which contributes to sustainability and lower emissions.
Video: Benefits of composite materials
In addition, the continuing trend of optimizing raw material costs and related processing costs has accelerated the application of high-performance thermoplastic composites as alternatives to thermoset plastics. In addition to the many advantages provided by thermoset composites, high-performance thermoplastic composites also provide potential for process optimization by eliminating autoclave curing and refrigerated transportation and storage.
Paste adhesives are used to bond aluminum, stainless steel, titanium and composite materials in a rib design or honeycomb design.
The composite formulation can be customized according to the target application and performance challenges. The range of possible properties of composite materials, as well as consideration of other substrates to be bonded, requires careful selection of the correct bonding solution to maintain the structural integrity of aircraft components. Adhesives must meet the bonding requirements of different composite materials, joint types and functions, such as:
Aerospace adhesives are usually used in paste or film form. Films provided in roll or sheet form are preferred for large-area structural bonding applications, as well as composite parts with higher fiber content and lower resin content. The paste can form thicker bonding lines to fill and bridge the gaps between bonding surfaces.
Film and paste adhesives bring value to the design and manufacturing process in many ways. They can be used to bond two different materials. They also help disperse stress at the joint, absorb vibration, and are very suitable for connecting thin substrates.
The film adhesive is pre-catalyzed and can be provided in roll or sheet form according to the specified area weight. They are available in different formulations to provide superior performance under a variety of conditions, including high-temperature applications, provide the required toughness and durability, and the ability to co-cure with composite materials. The film can bond large or small parts, allows the use of precise amounts of adhesive, and can be used with automatic tape laying equipment.
Video: Thin film structural adhesives for aerospace applications
LOCTITE EA 9696 AERO is an example of an industry-leading film adhesive. It is a toughened film adhesive for bonding composite materials, honeycomb cores and panels, and metals. It provides 60 days of non-use time, but can cure in less than 90 minutes when heated (248°F/120°C).
Paste adhesives, such as films, can also meet various performance requirements. They are available in one-component and two-component systems, as well as room temperature and high temperature curing options. In addition, they have a variety of different packaging configurations for ease of use. In addition to meeting a wide range of bonding needs, there are also formulations suitable for use as liquid gaskets and low-viscosity wet laying applications.
LOCTITE EA 9394 AERO is a popular two-component adhesive with excellent mechanical properties. It can be cured at room temperature, or it can be cured within an hour at elevated temperatures. It can also be used as a liquid gasket and potting material. It is available in a variety of packaging sizes, from 55 gallon drums to gram kits.
Surface treatment is an important factor to ensure good adhesion. There are two main methods for the preparation of adhesive bonding on the surface of pre-cured thermosetting carbon fiber composites: surface abrasion and the use of peel-off fabrics. The peeling layer avoids labor-intensive grinding operations, while also creating a more uniform surface treatment than manual or machine abrasion.
LOCTITE EA 9895 WPP AERO wet release layer is a pre-impregnated polyester release layer product that does not require sanding, solvent wiping or any further processing steps. It provides a more durable bond than dry release layer fabrics. It is available in film form, compatible with the most advanced composite prepreg resin systems, and provides minimal residual release layer fibers on the bonding surface after curing and removal.
The situation is different for high-performance thermoplastic composite materials, such as carbon fiber reinforced polyether ether ketone (PEEK), which is a material with extremely low surface energy and is difficult to bond with adhesives. The surface treatment of such thermoplastic composite substrates (such as PEEK) is necessary to change the surface chemistry and improve the wettability. It is usually done through solvent cleaning, etching agents (such as chromic acid) and other methods. Plasma treatment is currently the preferred method used by many in the aerospace industry because it provides a stronger and more stable surface energy enhancement.
In a recent study, three film adhesives with high temperature curing systems were evaluated for bonding CFRP PEEK laminates; LOCTITE EA 9696, EA 9695 and EA 9658. In addition, two paste adhesives were also studied; room temperature curing adhesive, LOCTITE EA 9394, and high temperature curing paste adhesive, LOCTITE EA 9394/C-2.
Video: What kind of overlay film does Henkel offer?
The adhesive chemistry has a positive effect on the proficiency of each treatment method. Ultraviolet radiation proves that the use of LOCTITE EA 9658 improves the performance of CFR PEEK, while the use of LOCTITE EA 9695 proves that plasma activation is more effective. Compared with untreated, both treatments significantly improve the adhesion and bond strength. The peak efficiency depends to a large extent on the chemical properties and characteristics of the adhesive, for which specific surface treatment parameters can be customized.
Henkel's series of composite materials and assembly solutions for primary and secondary aerospace structures help define and advance the way modern aircraft are manufactured.
Henkel provides sustainable film adhesive solutions to improve the performance and safety of aircraft and the production efficiency of manufacturers.
In-flight damage caused by lightning and bird strikes is more common than most of us realize. Although such incidents are expected to cause in-flight damage, other incidents may also occur when the aircraft is parked at the gate. Catering truck collisions, thrown luggage, or even tools falling on components can cause enough damage to be repaired.
For airlines, the advantages of composite materials such as strength-to-weight ratio, light weight, and corrosion resistance are fully demonstrated and encouraged to use new materials in the fuselage. Incremental improvements in weight reduction increase the fuel efficiency of aircraft, which in turn reduces airline operating costs while preventing fluctuations in fuel costs.
Original equipment manufacturers are meeting the needs of their airline customers by switching to more composite airframes and parts.
Original equipment manufacturers are meeting the needs of their airline customers by switching to more composite airframes and parts. The inherent advantages of composite parts over aluminum parts have brought some additional costs and airline considerations. The damage of aluminum parts is more obvious than that of composite parts. Due to damage to hidden layers between layers or across surfaces, undue stress usually exceeds the visible impact on the composite part. Therefore, maintenance technicians need to inspect and expand the maintenance area to prevent further spread, which may lead to more catastrophic events during maintenance.
Due to the complex configuration of composite parts, consisting of multiple fiber layers, resins, adhesives, honeycomb or foam cores, which are combined to create a highly contoured structure, technical feasibility and material availability will drive the decision to repair or replace damaged part. If there are no readily available spare replacement parts for composite parts, airline operators must determine the safest, fastest, and most economical way to resolve composite damage.
For all these reasons, standardized maintenance practices and easily accessible maintenance materials are essential for airline operators to improve their punctuality and fleet utilization. Therefore, advanced technologies have been developed to meet the challenges of these maintenance scenarios. These include film adhesives and pastes that improve aircraft performance and safety, while meeting stringent OEM requirements for full-scale production and after-sales maintenance.
Whether it is damaged wing skins, cabins or cargo doors, if there are no ready-made spare parts, you can choose to repair or order replacement parts. Since the latter will allow the aircraft to stay on the ground longer, the repair route may be the best solution, especially for smaller but still necessary composite repairs.
Although up to 50% of the primary and secondary structures of modern aircraft may be composed of composite materials, the basis of maintenance evaluation and procedures follow the same method no matter where it is used.
The best practices of how to carry out this type of maintenance have prompted efforts to standardize maintenance technicians and their training requirements. This work is led by collaboration between key material suppliers, service providers, airline end users, and original equipment manufacturers. The integration and coordination of this activity is carried out through industry trade alliances and working groups.
A good example of this industry collaboration is the characterization of the leading structural film adhesive LOCTITE EA 9695 AERO in off-autoclave applications. LOCTITE EA 9695 AERO has multiple functions and advantages, making it ideal for maintenance applications.
This epoxy-based film adhesive has tested well on co-cured and pre-cured laminates and exhibited excellent environmental resistance. Its ability to cure at lower temperatures makes it suitable for the repair of composite structures, and its low flow characteristics can minimize the mixing of prepreg resins. It has consistent performance characteristics across a wide range of curing curves, allowing various structural component repairs in store autoclaves or wing vacuum bags with heating blanket applications. Therefore, various OEMs, airlines and MROs agree that this is a reliable aerospace-grade structural film adhesive, suitable for metal and composite repairs. OEM and industry specifications were written using LOCTITE EA 9695 AERO, making it an industry-wide ready solution.
The LOCTITE AERO structural adhesive film and paste adhesive series include a wide range of products that can provide performance for metal and composite substrates in various forms, viscosities and areal weights over a wide temperature range.
As the world's leading adhesive manufacturer, Henkel offers a wide range of potting, edge filling and encapsulation compounds for various substrates, operating temperatures and other environmental factors.
The most common repair applications usually require bonding and filling of various substrates in many different parts and structures. This has led to strong product requirements, as well as ease of use and material storage considerations that drive the selection process. Epoxy-based paste adhesive is preferred because it will provide the strength, toughness and high temperature resistance of a heat-curing film adhesive, but has greater flexibility and ease of use. When bonding substrates with different expansion coefficients, the low temperature curing of the paste adhesive is advantageous. These solutions can also be applied to large parts through controlled metering mixing distributors or double-cylinder static mixer kits.
Paste adhesives can also be used for potting repairs in honeycomb structures, which is a common demand in the MRO aftermarket. The preferred solution is a solution with a customizable characteristic range, which can be cured under ambient (70-77°F/21-25°C) temperature conditions and or lower temperature curing curves (about 180°F/82°C) ) Under curing. Paste adhesives with lower viscosity can be customized with fillers to adjust their flow and sagging characteristics for various repair situations.
In addition, there are paste adhesives for wet laminate repair applications, including lamination, injection, and coating. A low-viscosity mixture is required here to be injected into the pre-assembled part. The flexibility of these cured adhesives allows them to be used to bond different substrates.
Structural paste adhesives with curing temperatures up to 350°F/177°C are also used in aircraft propulsion applications, such as engine nacelles and cold section engine parts, which may be damaged by bird strikes or other foreign objects.
For maintenance technicians, it is important to have a range of options to ensure that the aircraft stays in flight throughout its 30-year life cycle.
For maintenance technicians, it is important to have a range of options to ensure that the aircraft stays in flight throughout its 30-year life cycle. As more and more composite parts are added to airlines in the commercial fleet, various proven adhesive films and pastes with specific application characteristics should be readily available, so maintenance is consistent and reliable And quickly. Standardized solutions will be selected based on the degree to which they meet and exceed the expectations of aircraft manufacturers. A well-defined aerospace authorized global distribution network further improves the commercial availability of the above solutions.
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