The characteristics of structural adhesives: how to choose the perfect glue

How should you choose the ideal structural adhesive for your internal procedures? In the section dedicated to structural glues of our e-commerce website, you can choose from dozens of different products: some are acrylic adhesives, other epoxy, and all boast the most varied compositions. There is no doubt that, for those who are accustomed to using only mechanical fastening solutions, such as welds, bolts, rivets, and so on, finding what you need among all these products for industrial fastening is anything but simple. Today we want to provide a guide to choose the perfect glue, kicking off this article with the analysis of the characteristics of structural adhesives.

First of all: are structural adhesives really the best solution?

Before anything else, it should be noted that, sometimes, structural adhesives are not the ideal solution. At times, it might be more convenient and straightforward to use a more traditional option, such as a rivet. Other times, it might be better to use high-performance double-sided tape. You might need to fasten panels to one another, create small, highly resistant joints, place gaskets on the door of an appliance, seal cracks, apply insulation coatings, and so on. It is best to start from an analysis of the general characteristics of the structural glues in order to understand if these are the best product for your needs.

The characteristics of structural adhesives: surfaces and materials they are designed for

Once you are aware that what you need is a structural industrial double-sided adhesive tape, it is paramount to find out which one you should buy, knowing that each surface is different, each substrate having different peculiarities. Let’s consider the different degrees of surface energy of various materials: metals are, for example, characterized by high levels of surface energy, so as to be particularly suited to be glued with adhesives; plastics, on the other hand, have a lower surface energy, and therefore require specific adhesives.

Furthermore, depending on the type of surface and object to be glued, it will be necessary to choose a more or less viscous double-sided adhesive tape: the more liquid ones will be able to make their way inside narrower nooks and crannies, while the more viscous ones definitely will not. The characteristics of the best structural double-sided adhesive tapes on the market respond to the peculiarities of different situations, and it is, therefore, a good idea to carefully read the description provided by the manufacturer.

The characteristics of structural adhesives: different timings of use

When choosing the industrial glue you wish to use, it is also best to consider the characteristics of the structural adhesives related to the timings of use. Sometimes, you’ll need to make very fast and sequential fastenings, while other times you’ll need to carry out one single, very important fastening, to which you can dedicate a lot of your time. Other times yet, you’ll need to continue working on the product for a longer time. In short, processing, handling, and curing times must also be taken into account. Specifically:

·         Processing time: this expression indicates the time between the mixing of the two components of the adhesive and the final fastening;

·         Handling time: it indicates the time of fastening, i.e. the period of time at the end of which you are allowed to remove the clamps and start manipulating the object.

·         Curing time: it indicates the period of time necessary for total polymerization, and therefore for the adhesive to reach its maximum strength.

For example, it is possible to have a structural double-sided adhesive tape that has a processing time of about 30 minutes, within which it is absolutely necessary to use the mixed adhesive. Once glued, there may be a handling time of 90 minutes, at the end of which it will be possible to handle the glued piece without fear of displacement or breakage; From there, it could take several hours to reach the maximum strength of the structural adhesive.

There are instant adhesives and much slower, more workable ones: which one do you need?

The characteristics of structural adhesives: resistance to overlapping shear

Some structural adhesives are more powerful, and therefore more durable than others. To be defined as structural, an adhesive must have an overlap shear strength of more than 7 megapascals (in the United States) or 10 megapascals (in Europe). But sometimes you may need even more strength, knowing that there are adhesive fastening solutions which reach up to 60 megapascals. A megapascal, to give a point of reference, corresponds to one newton per square millimetre; or, approximately, to 10 kg/cm² (142,23 lb/in²). A structural adhesive boasting a resistance of 10 megapascals, therefore, can hold up to 100 kg/cm² (1422,33 lb/in²), a resistance which can be more than enough for a very high number of industrial applications.

The conditions of use of the glued piece

Finally, to understand which characteristics of the structural adhesives to be enhanced, it is best to consider what the actual use of the piece will be, once assembled. Will it piece need to be flexible and extendable, or perfectly rigid? At what temperatures will it be exposed? Will it face threats such as moisture, ultraviolet rays, or chemical attacks?