FASTENINGS & ADHESIVES FEATURE


Composite materials are used for a wide range of applications – from lightweight vehicles to architectural structures. Huntsman Advanced Materials explains how adhesive bonding enables the most efficient use of these materials


SEE THE LIGHT with adhesive bonding


C


omposite materials influence many aspects of our everyday lives – from


helping to safely extract and distribute energy to our homes to delivering better performing and lightweight vehicle designs. They can be formed into any shape and deliver stiffness, strength and weight savings to different structural designs, all facilitated through the latest technologies which make the fast production of high quality composite materials more commercially viable and attractive than ever before. In one unusual application,


the first-ever all-composite lighthouse has recently been constructed and installed at the port of Valencia in Spain. The lighthouse project has


overcome perceived limitations for composites, opening the way for other applications requiring light, tall structures to benefit from utilising Huntsman Advanced Materials’ proven material innovations. Combinations of hybrid, CFRP


and GFRP composites were selected for the tower’s principal components, calling for the development of new material systems and processes to fulfil the design engineer’s vision for the 35m tall tower structure. The lighthouse’s structural column


is made up of eight 35m long CFRP pultruded tubes, with an outside diameter of 250mm and 20mm thickness. ACCIONA INFRAESTRUCTURAS, which led the project, had to develop a special pultrusion process to achieve production of high quality and very thick pultruded profiles combining carbon tows and heavy carbon fabrics. While the lightweight GFRP floors


were subject to certain aesthetics and chemical resistance factors, architectural requirements stated they should also not exceed 20cm thickness. So, resin infusion was selected as the preferred process for the floors. As manufacturing needed to be fast, a resin system with low viscosity, long pot life and low


Alongside the


construction industry, Huntsman provides adhesives for industrial and consumer applications


exotherm, which was also capable of meeting the desired chemical and mechanical properties, was developed by Huntsman Advanced Materials. In order to achieve low weight, low


maintenance, smooth surface, chemical resistance and aesthetics, metal fasteners were not a preferred solution to join pultruded CFRP tubes with GFRP tubes. A new system needed to be designed that could not only meet the criteria but also the complex structural and geometric requirements – and within budget. A structural design for optimum material utilisation, low cost mould, a fast process which was independent of labour skill and capable of reproducing the parts with the same quality, was needed Carbon and glass fibre hybrid stiffeners


were designed and developed using the user-friendly and low exotherm resin solution developed by Huntsman Advanced Materials. The project also required the


production of slip-free, lightweight (<25Kg), chemically and mechanically resistant, GFRP stairs that would not exceed 20cm thickness. Composites made by resin transfer moulding (RTM), using resin from Huntsman Advanced Materials, were identified as providing the optimum solution.


ADHESIVE SOLUTIONS In keeping with the design concept and performance aims, ARALDITE adhesives were selected to bond the lighthouse’s composite components together. The industrial adhesives have been used extensively in the construction sector


for decades, primarily on applications such as crack injection, bonding old concrete to new, segment bonding and concrete strengthening where they are specified for a combination of performance characteristics, including high mechanical strength, high chemical and water resistance and their effectiveness even in adverse weather conditions. They work across a range of substrates


with formulations developed to cover the bonding of dissimilar materials – such as metals from mild or galvanised steel, to aluminium, brass and ferrite, many modern plastics, ceramics, glass, rubber and wood. Variations in formulations will deliver


a precise product profile matched to a specific process, assembly or manufacturing need with variables such as pot life, sag resistance, cure time, gap filling and shrinkage taken into account. When adhesive and composite systems are used in combination they deliver excellent mechanical performance capabilities to structures. Combining a long pot life with fast curing, and thixotropic properties that facilitated easy application on the tower’s vertical surfaces, the ARALDITE epoxy based structural adhesive specified for this project delivered significant cost and production time savings. It also added to the strength of the composite structure and contributed to its lightweight and aesthetic appeal.


MEETING REQUIREMENTS Before the lighthouse was commissioned, final tests had been conducted to ensure it met load and wind requirements. In comparison to concrete builds which typically require 28 days to be fully cured and an additional 21 days to install, the all-composite lighthouse was fabricated off-site while the site preparation was taking place and was installed in less than 20 days. Due to its advantageous size-to-weight ratio – 20 tonnes for the 35m tower – a lightweight crane installed the structure in less than six hours. With the lighthouse, an outstanding result was achieved which went on to win one of the prestigious 2016 JEC World Innovation Awards.


Huntsman Advanced Materials www.huntsman.com/ advanced_materials


Other partners involved in this project, working with ACCIONA INFRAESTRUCTURAS S.A. and Huntsman Advanced Materials, included Autoridad portuaria de Valencia, Siegrist & Moreno S.L, AIMPLAS, DOW, SAERTEX and Owens Corning


 DESIGN SOLUTIONS | MAY 2016 25


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