How to prove structural bonder's speed, strength and durability

Structural bonding is fast gaining popularity over conventional joining methods for several reasons. The ability to join dissimilar materials such as plastics and metals is one significant benefit, as it enables different combinations of materials to be chosen for their performance qualities without having to consider the joining method. A bonded joint is also sealed so it prevents leakage and corrosion and, as there is no visible sign of the join, it looks good too.

Then there is the question of strength and durability, and it is here that adhesive manufacturers are often met with a degree of resistance. Even though structural adhesives are used in some of the toughest applications - automotive and aerospace manufacture to name but two - some people remain unaware of the true scope of structural bonding. Others doubt its suitability over traditional joining methods.

The challenge

So, when Henkel started to explore the best way to convey the merits of its latest Loctite structural bonding development, it set its sights on creating a demonstration that would really make industry take notice. Henkel engineers decided to show the strength and durability of new and patented Loctite hybrid adhesive technology by designing a bonded coupler that would pull freight train wagons weighing 208 tons.

The new adhesive chosen to showcase this technology was Loctite HY 4070. It is one of the new breed of adhesives that combine the critical attributes of several adhesive technologies to achieve an excellent combination of bond strength, durability and cure speed. These qualities are also complemented by improved health and safety credentials.

Good impact resistance makes Loctite HY 4070 a great choice for joining the elements of products that are subject to drop testing or shock loading. It also provides good elasticity, which is an important consideration when joining parts subject to relative movement - and the train application is a great example! Fixture and cure speeds of this product are similar to those of an instant adhesive and this is achievable even when there is a relatively large gap between mating parts.

Selecting the best adhesive for the job, however, was only part of the story. As with all applications, the design of the rig that connected the engine to the lead wagon had a huge bearing on the outcome.

Austin Campbell, one of the engineers who designed the rig, explains: "208 tons is a lot of weight on a small bonded assembly. We therefore incorporated springs in the mounts to accommodate movement and, to add strength, we specified toughened pins to hold the rig under the knuckle couplers."

Having cleaned and sanded the steel plates, all it took was just 3g of Loctite HY 4070 and one hour of cure time to create the bonded assembly. Theoretically the join was 'man enough' for the job, but how would it fare in practise?

Austin Campbell summarised: "The train started to move, pulling 208 tons of wagons along the track, up hills and over bridges. Ultimately the steel plates bent but the adhesive join held firm. It was a tremendous effort by all the Loctite teams involved. Making a success of such a powerful demo was a great feeling."

Follow the link to find out more about the new Loctite Universal Structural Bonders and Henkel's patented hybrid technology that gives the adhesives their exceptional properties. You can also watch a video of the train coupling demonstration.