Adhesives keep the rail industry on track

Characterised by well documented benefits, including a high strength-to-weight ratio, excellent fatigue and corrosion resistance, good impact resistance, design flexibility and lighter weight, composite substrates have grown to become the established material of choice. However, selecting the most suitable joining method is just as important as the design and choice of the composite materials themselves.

The rail industry

The land-transport sector, as a whole, accounts for about 25% of the European composites market. Composites provide lightweight solutions for rail vehicles compared with traditional metal counterparts. Lower overall weight translates into less energy costs in vehicle operation – important criteria for all vehicles including recent high-speed railway projects. According to a recent report from Lucintel, the rail industry for composites is forecast to grow at an average rate of 10.5% until at least 2015, with the industry’s focus firmly fixed on all the benefits outlined above, as well as better flame retardancy, smoke and toxicity (FST) performance.

This is an industry where composites and adhesives continue to play an even greater role, providing a solution to demands for more advanced and improved developments that help to sustain long term growth.

Vehicle composite bonding

The rail industry uses composite materials for making exterior and interior parts, as well as infrastructure components in combination with adhesive bonding replacing soldering or fastening solutions in the delivery of long term performance and durability. Simply speaking, structural adhesives enable the most efficient use of substrates and increasingly you won’t see one without the other.

Interior and exterior components made of composites include major items such as interior ceiling and side wall covers, corridor adapter frames, luggage bins or racks, drivers’ cabins, exterior panels, end cabs and more. With their high strength, impact resistance and outstanding combination of high lap shear and peel strength, epoxy adhesives are the type of adhesive most commonly used.

For exterior parts, Araldite AW 4859 / HW 4859 is an example of an epoxy adhesive which offers the advantages of good chemical resistance and thermal stability even in temperatures ranging as high as 140°C.

The three main types of structural adhesive from Huntsman all have a different chemistry with different structures and physical characteristics that make them suitable for targeted applications and specific processing requirements.

The methacrylate-based adhesives tend to be used in applications like bonding metal hinges to GRP interior panels, where their fast curing properties provide significant time saving advantages. By contrast, polyurethanes with their flexible properties are the material of choice for joining tough-to-bond engineering thermoplastics, rigid plastics and composites, finding application in frame bonding for example.

Araldite 2013 is an example of an epoxy adhesive that is increasingly being used to bond GRP train driver cabins because of its adhesion to substrates, high durability in ambient weather conditions, fatigue resistance and toughness.
It also supports greater design freedom, providing a fast and efficient bonding solution for producing the more complex and ergonomic shape of composite driver cabins now seen on the new generation of high-speed trains.

Innovation in adhesives

As much as innovation in adhesives is about improving mechanical properties, it is also about adding new features such as flame retardance, low smoke density and low toxic emissions.

Based on its long experience of working in the aerospace industry, Huntsman has developed products that meet stringent FST safety criteria. Araldite 2033 is an example of a recent development from Huntsman, which allows the possibility of using an adhesive with flame retardant properties.

Offering good adhesion on metals and composites, this UL 94 V-0 and NF F 16-101 I2 and F2 approved two component epoxy adhesive exhibits flame retardance, low smoke density and low toxic emissions.

The future

As the use of composites across the rail industry increases, structural adhesives will continue to be a key player in supporting new design methods where the conditions in service, greater efficiency in manufacturing and the type of stress and forces applied during service are critical.

Huntsman remains focused on delivering solutions for specific markets with R&D in adhesives ranging from improved toughness to better and even longer term performance with innovative flame retardance features.