Structural adhesives have become an increasingly popular choice for many applications due to their long-lasting strength and versatility. However, you may be wondering whether they are actually worth considering as a joining method.
Here at Forgeway, we manufacture over 3000 tonnes of industrial adhesives. We believe structural adhesives are the best bonding method. But, we know that sounds biased as we manufacture them.
That’s why we put our knowledge into this article.
While they have numerous advantages, we aren’t blind to the fact that there are several disadvantages to using structural adhesives too. It is important to understand the pros and cons of using structural adhesives to make an informed decision about the best joining method for your project.
This article will provide an overview of the advantages and disadvantages of using structural adhesives, so you can weigh the pros and cons to decide if this joining method is right for your application.
So you want to assess structural adhesives. But first, why are they becoming so popular? There are several advantages of using structural adhesives.
We have summarised them down to three main advantages; structural adhesives have high strength, they can withstand movements and vibrations, and they are extremely versatile.
Read this section to find out more about these advantages.
One of the main advantages of using structural adhesives is that they offer a high level of strength. In fact, some structural adhesives have such high bond strength, that they offer a very reliable connection between materials that is comparable to that of a weld.
The bond strength of structural adhesives is measured in terms of psi, or pounds per square inch. Here at Forgeway, we assess adhesive strength in terms of MegaPascal, or MPa. 1 MPa is the same as 145 psi.
The strength of an adhesive depends on the type of structural adhesive. For example, Epoxy adhesives are the highest-strength adhesives. Some epoxy adhesives can reach strengths over 60 MPa/9000 psi (the same as a weld).
So, if you are concerned that structural adhesives are not strong enough, the recent developments in adhesive technology will put your mind at rest. Structural adhesives can rival the strength of a weld.
Another advantage of using structural adhesives is that some adhesive manufacturers have developed formulations to be very durable and withstand movements and vibrations.
This added flexibility may take away some of the strength, but it means that any impact or vibrations don’t cause bond failure. As we often tell our customers, flexibility is just as important as strength when it comes to choosing an adhesive.
This ability to withstand vibrations and movement makes structural adhesives suitable for many different types of applications. For example, you want to reduce the noise caused by vibrations on a bus. Or maybe those vibrations are causing the paint to crack (ultimately leading to filiform corrosion).
A flexible adhesive can reduce the vibrations as it absorbs them rather than transferring them onto the substrate. You can reduce (sometimes eliminate) those noise and corrosion problems by having a flexible adhesive.
The main advantage of using structural adhesives is that they are very versatile. As you might have gathered already, you are almost guaranteed to find a structural adhesive that will meet your needs.
Need a high-strength, fast-curing adhesive that has chemical resistance and impact resistance? We know just the one.
Need a slow-curing adhesive that has lots of flexibility but also good strength and chemical resistance? That option is also available.
Whilst there are limitations (more on that later), there are so many options available. You are highly likely to find a structural adhesive that meets most of your requirements.
Even if you can’t find the perfect structural adhesive off the shelf, most adhesive manufacturers can tweak formulations to match your requirements.
Whilst structural adhesives are increasing in popularity, there are some clear drawbacks of using them. There are three main disadvantages of using structural adhesives; The need for adhesives to cure, there are always limitations, and the bonding process can be difficult to understand.
This section goes over those three points in more detail.
One of the main disadvantages of using structural adhesives is that they need time to cure. The exact amount of time varies depending on the type of structural adhesive.
When looking at a structural adhesive’s cure time, the most important number to look at is the handling time. This refers to how long it takes the adhesive to reach handling strength (0.4MPa/60psi).
As soon as the adhesive has reached handling strength, you can put it into light operation; knowing it won’t come undone. Some structural adhesives can reach handling strength very fast (within fifteen minutes).
However, it will often take more than 24 hours for an adhesive to reach full cure. This can make it difficult to work with structural adhesives, as you need to plan for enough time to wait for them to cure and reach sufficient strength before you can finish your project.
While structural adhesives are very strong, they have their limitations. Some types of structural adhesives are suitable for connecting certain materials, while others are not.
For example, low surface energy (LSE) plastics (like polypropylene) are notoriously difficult to bond. You will need a specialist adhesive or extensive surface treatment before you can create a strong bond to LSE plastics.
You also have to be aware that if you prioritise one characteristic from an adhesive, you may have to sacrifice in other areas. The best example of this is strength and flexibility.
You cannot get a very high-strength adhesive that also has very high flexibility. This means you will need to decide which characteristic is more important from your adhesive.
It is important to understand the limitations of structural adhesives to select the right structural adhesive for your application.
While many people use structural adhesives, not everyone knows how they work. Structural adhesives are fairly complicated chemical mixtures. It can be difficult to understand how they work, especially if they are relatively new to you.
So where do you gain knowledge on adhesives and the bonding process?
Thankfully, more and more adhesive manufacturers are starting to share their knowledge on adhesives. Here at Forgeway, we have made it our mission to share our experience and knowledge on adhesives.
We created a guide ‘The Fundamentals of Adhesives’ to make a complicated subject, easy to understand. If you are looking for information on adhesives and the bonding process, downloading the eBook version is a very good place to start.
However, as more adhesive manufacturers are sharing their knowledge, it is becoming increasingly easier to find the answers to your adhesive questions online.
The other option is to request training from an adhesive manufacturer. Training is the best way to understand a topic and gain internal knowledge.
Whilst the question is always difficult to answer, we would say that if you are joining two pieces of material together, a structural adhesive is the best choice.
Nonetheless, this decision comes down to you. It’s up to you to decide whether structural adhesives are going to be the best choice. We have given you the information to help you make that decision, now it’s up to you.
If you’re still unsure, you can look at some of the alternative joining methods like welding or mechanical fasteners. We recommend reading our article about whether you should choose mechanical fasteners or adhesives.
Or, you can get in touch with an adhesive expert who will help you make the decision. A member of our team would be glad to help you decide whether structural adhesives are the best choice for your application.
If you have seen enough and want to know more about structural adhesives, it’s time to look at the different types of structural adhesives in more detail. You now need to decide which type could be the perfect match.
Epoxy adhesives and methyl methacrylate adhesives are the two most common structural adhesives. We recommend exploring those two options further.