Flame-retardant adhesive on board

Twenty years ago, only 2% of an aircraft’s structure was made of composite materials. Today, these materials account for more than 50%. Metal parts are being replaced more frequently by composite materials, such as carbon fiber reinforced polymer (CFRP), making adhesive bonding the preferred joining method.

Austrian aviation composites supplier, FACC Operations GmbH, produces lightweight composite components installed in a variety of aircraft models.

Convenient, functional

For aircraft passenger interiors, original equipment manufacturers (OEM) demand light weight and longevity for overhead stowage bins, entertainment systems, and lavatories.

Airbus uses FACC overhead stowage compartments in its A380 and A320 families. The company’s interior division relies on honeycomb composite panels to build these compartments. Aramid fibers, such as Nomex or Kevlar, are coated with phenolic resin to make the material light and robust. A transparent, decorative polyvinyl fluoride film is then applied to the surfaces. This decorative film makes the compartments dirt- and chemical-resistant, pleasant to the touch, and attractive.

The composite sandwich panels are lightweight, offer high torsion resistance, and are completely flat as semi-finished products. Further machining is required if bent or angled structures are needed. The design and manufacture processes for these components takes place in the FACC Operations Interiors plant located in Ort im Innkreis.

Using ditch-and-pot technology, the honeycomb structure is cut from the back of the composite sandwich panel, allowing the panel to be bent or angled at that point. The resulting cavity is then filled with adhesive. Once cured, the adhesive permanently keeps the sandwich panel in the desired shape.

Processing time for manual operations

Panels used in luggage storage compartments need to be rugged, so FACC relies on large volumes of high-strength adhesives. The company prefers a two- component type with a mixing ratio of 1:1 to simplify production.

Because of the manual production process and finishing work on the component, the processing time of a 100g batch of adhesive should be at least 30 minutes, while curing time until initial strength at room temperature should not exceed 5 hours.

Flame protection

After intensive testing, FACC Operations opted for DELO-DUOPOX AB8390, an adhesive for ditch-and-pot applications on sandwich panels in aircraft interiors. The versatile construction adhesive is also suitable for bonding load-bearing joints with inserts.

The adhesive’s double chamber cartridge dispensing system allows thixotropic epoxy resin to be quickly applied, similar to a one-component adhesive. It fully cures at room temperature within the given parameters. Curing can be accelerated by increasing the temperature to 60°C, allowing production cycle times to be reduced without affecting final strength.

This versatile adhesive fulfills national aviation authority mandates, including fire protection in aircraft interiors that’s guaranteed by the Flame-Smoke-Toxicity (FST) test. It complies with RoHS Directive 2015/863/EU.

White adhesive

As a flame-retardant adhesive, DELO- DUOPOX AB8390 features good strength and high chemical resistance at temperatures ranging from -55°C to 85°C, which is suitable for aircraft. The tensile shear strength of two sand-blasted, bonded standard samples made of aluminum is 25MPa. This value is nearly reached even after 500 hours of storage at 70°C in a reference fluid for Skydrol (tri-n-butylphosphate).

It is extremely colorfast, keeping its white color after 1,000 hours of storage at 70°C and in air humidity of 85%.

FACC operations can rely on consistent colors to maintain the appearance of their aircraft components, like those used for luggage storage compartments.

DELO
www.delo-adhesives.com

www.facc.com