Adhesives + new joint design = many performance advantages
Although the construction of caravans is a niche application for adhesives, the benefits of this method are relevant to all manufacturers seeking to make structures stronger, lighter and leak proof. By either replacing or supporting mechanical fixing, structural bonding not only improves the performance of structures but also gives designers the freedom to join dissimilar materials and enhance the aesthetics of their product.
In recent years the British caravan maker, Elddis, has sought to cut the weight of its caravans to allow customers to use a lighter tow car and add accessories without exceeding weight limits. Another design aim was to eliminate leak paths, always the main bugbear of a screw-fixed construction.
Elddis wanted more than lightweight and watertight construction however. Its goal was the freedom to design products of any size or shape, unhindered by the construction technique.
It had explored the use of various composite materials to reduce weight but quickly realised that they were not compatible with traditional coach building techniques. Instead, the use of adhesives with current materials emerged as the most compelling option.
Henkel's experience in structural bonding in the aircraft and automotive sector confirmed the viability of this method. Elddis was keen to apply this technology to the leisure market and a strong working relationship between the companies was swiftly established.
The Henkel LOCTITE adhesive selected for 'seam welding' provides the necessary elasticity to withstand the vibration caused by travelling across uneven road surfaces. Initially panels were butt joined with the product but thanks to the subsequent introduction of a keyway joint on all mating surfaces the bond area was increased by 63%.
The resultant, bonded construction is more than 10 times stronger than the original. Flimsy panels are now stiff structural components so many of the timber support structures have become redundant, allowing even more weight saving.
Having easily met - and in several respects greatly exceeded - the requirements of industry-standard durability tests, the bonded caravan was then put through tests that mimicked annual rain fall and also subjected to temperature extremes.
The caravan was then de-constructed to confirm all elements were dry and there were no joint failures. And on the strength of these findings, Elddis has been able to introduce its 10 year bodyshell warranty - an industry first.
With the design concept well and truly proven, the world's first structurally bonded caravan was put into production. And here too, the Henkel partnership proved invaluable. Henkel assisted in the specification of dispensing equipment, a vital ingredient in ensuring the correct amount of LOCTITE adhesive is applied to achieve the toughness and joint elasticity required to absorb the forces.
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