Bonded caravan takes to the road

In recent years, Elddis had 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 any 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 felt 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 sectors confirmed the viability of this method and the company was keen to apply this technology in the leisure market. A strong working relationship between the companies was swiftly established and together they embarked on a three year development process to create a fully-bonded caravan.

'Seam welding' with adhesive

Henkel’s Macroplast UK 1366 B10/UK 5452 structural bonding adhesive was recommended for its ability to provide the elasticity needed to withstand the vibration caused by travelling across uneven road surfaces. 

Initially the panels of a caravan were butt joined with Macroplast; rigorous testing proved its strength. Next, a keyway joint on all mating surfaces was introduced, increasing the bond area 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 original, timber support structures have become redundant, allowing even more weight saving.

Road test

The next step was to road test the bonded caravan design at the Ford track at Lommel.  The fully loaded vehicle completed 27,000 miles, easily meeting the requirements of BS EN1645 Part 1, the master standard for caravan construction.  

The bonded structure was then put through tests that mimicked annual rain fall and also subjected to temperature extremes of -40 to 50°C. No sign of water ingress could be seen but that was insufficient proof for Elddis. Its engineers completely dismantled the structure to confirm all elements were dry and that there were no joint failures. On the strength of this, Elddis has been able to introduce its 10 years bodyshell warranty.

Still not content, the company returned to Lommel with another test caravan. This time it was overloaded by an extreme 500kg for another simulated 27,000 mile test. Yet again the caravan survived but the 4 x 4 tow vehicle had to be retired from service.

SoLiD in production

With the design proven, the Elddis SoLiD concept was put into production; SoLiD is the acronym the company has chosen for its Stronger, Lighter and Drier method of construction.  

With Henkel’s help Elddis chose dedicated dispensing equipment, a vital ingredient in ensuring the correct amount of adhesive is applied to achieve the joint elasticity required to absorb the forces. 

Elddis believes the bonded structure to be a major differentiator between the company and its competitors. It had its best ever order intake at the main industry exhibition in 2012 and even in a fairly flat market caravan sales are above target.  

Henkel know-how is part of the company’s forward plans. Alan Beel, business development manager at Elddis, says: "Our working partnership has been better than anyone expected. I have worked with many suppliers throughout my 30 years in industry and Henkel is by far the best.”