Do structural adhesives really work?

Categories : Glues

On the one hand are rivets, bolts, welds. All methods which clearly their working methods, mechanical technologies which are extremely easy to understand, and have been known for a long time. No one needs any explanation on how to fasten a bolt, or how this mechanism can hold two pieces of metal tightly together. Moreover, we are used to seeing ships, buildings, and even bridges being held together by huge bolts, just as we take for granted that two pieces of metal must be joined together via welding. For all these reasons, we are naturally inclined towards usage of these “simple” mechanical fastening solutions. And this while being aware that, in many industrial sectors, in the most diverse needs, the same rivets, bolts, and welds have often been replaced by structural adhesives. These glues have become the default solution for the fastening of metals, plastics, and many other materials due to the various guaranteed advantages, such as increased lightness, instant fastening, absence of pre-drilling, clean aesthetics, and so on. These features are all true for high performance double-sided adhesive tapes as well and, therefore, not just for structural adhesives. Yet, doubt can often still arise: do structural adhesives really work? Are they actually strong enough to replace the rivets, bolts, and welds? Let’s have a look.

Structural adhesives: a summary

We have already outlined what structural adhesives are, and so this section will be brief: in a nutshell, they are simply, in a way, extremely strong glues. When giving a qualitative definition, it is possible to describe a structural adhesive as a glue which creates a bond at least as strong as the materials it is used to join. But, when it comes to endurance, performance and safety, quality definitions are likely to be insufficient. In the United States, therefore, adhesives with a shear strength greater than 7 megapascals are defined as structural, whereas in Europe the requirement is even higher: structural adhesive can only be called such in the case of glue with a shear strength of higher than 10 megapascals.

A typical structural adhesive is liquid, thermosetting, but it must be noted that there are several variants. And, it has to be stressed, too, that this is not something which came on the market just recently. These are, in fact, tried-and-true products. Consider that 3M launched the first neoprene-based contact adhesive in 1942 and that, in the 1960s, it brought the first flexible structural epoxy adhesive to the market, as well as the first liquid adhesive spray. In short, structural adhesives are well-established and well-regulated: let’s have a look at how well they can actually work.

Structural adhesives really work: here are the test results

To understand how and how much structural adhesives work, there is really nothing better and more useful one can do than comparing these glues with all those classic fastening solutions that they are called, in the most appropriate cases, to replace.

Here, the most important data used to express the power of a fastening solution is the already named shear overlap resistance: what solution, between flux welding, spot welding, rivets, bolts, or structural adhesive leads to higher strength? Well, the famous rivets are at the bottom of the list, with the worst marks. They, it is known, are quite cheap, and fast enough to use, but they certainly do not stand out for the design freedom and aesthetic result they offer. Then there are bolts which, like rivets, can certainly ensure a high resistance at the very point where they are installed, failing in any way to “work” on the remaining, uncovered surface. It is slightly better to carry out spot welding, but it is still a fastening method that really only works on distinct points. The fastening methods ensuring the highest resistance to overlapping shear are two: flow welding and structural adhesives, as they appear to be able to do up to 3 times better than the “weaker” rivets.

For any kind of use

The tests prove it, structural adhesives work, as much and, often, better than more classic fastening solutions. And they can be used in many different cases: to fasten metals, plastics, and composites, for stable and flexible surfaces, to withstand very high or very low temperatures, and so on. We therefore invite you to discover the best structural glues inside our e-commerce website, to find the one that best suits your business processes!

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