‘Bubbly’ is sometimes a good thing. Bubbly people make for a fun social event, and no celebration would be complete without a glass of bubbly in hand! However, when it comes to adhesives, bubbly is definitely not something you want. Adhesive air bubbles can cause a ratio imbalance when dispensing, and an all-round poor bond as trapped air leaves weak spots in the joint. So, how do we avoid bubbles for the best bond possible?
Permabond, like many other adhesive suppliers, sell in cartridges as well as in bulk. A major benefit of cartridges, as well as their general ease of dispensing, is that the risk of bubbles forming in the adhesive is far less than with bulk. This is because our cartridges come with static mixing nozzles. These not only make sure you apply the correct ratio of resin to hardener, but also prevent the formation of air bubbles when dispensing.
With bulk, however, this is not the case. We supply bulk epoxy resin and hardener separately in big barrels or pails, meaning that parts A & B require mixing before bonding. You will also need to pour the adhesive once mixed. Both of these actions can lead to air getting into the adhesive and forming bubbles, which will need removing before any substrate bonding can take place.
To get rid of these adhesive bubbles, you could consider using a vibrating table after mixing. This brings the bubbles up to the surface of the adhesive, where you can then pop them! Sometimes, however, high surface tension in adhesives can mean that popping bubbles by hand isn’t possible. A simple trick here is to use a hot air gun, or even an everyday hair dryer – the heat generated causes the air bubbles to expand and pop in one or two seconds!
You could also use a vacuum chamber to remove adhesive bubbles. As the name implies, a vacuum chamber draws the air out of anything inside it. For this method, make sure to use a big enough container as this will allow the air to rise and expand outwards without leading any adhesive to flow out over the edge of the container. See our example below!
So, you’ve got your ready-to-go cartridge, or mixed and degassed your bulk product. Somewhat annoyingly, however, the problem doesn’t end there – there is always a risk of air getting into your adhesive joint during or after bonding.
One of the first things to mention here is not to shake your adhesive before dispensing! This might sound obvious, but shaking will disperse a lot of air bubbles into the adhesive, which could be very difficult to remove and affect both the strength and the appearance of the bonded parts.
When dispensing, opting for a zigzag pattern across the substrate, rather than a line around the edge or ring shape at the end, is a far better strategy to avoid air entrapment. Another option is to apply a bead across the middle of the substrate, which would then be pushed outwards towards the edge once bonded. And once you’ve clamped your substrates together, it’s incredibly important that you allow enough time for the adhesive to reach a handling strength before unclamping. Unclamping too soon can lead to a relaxation in the joint, which could lead to air ingress that will affect the cure and bond strength of your adhesive.
As a general rule, adhesives are made bubble-free. All Permabond bulk adhesives are manufactured and mixed in a vessel that has been vacuum-drawn, meaning that adhesive that leaves our factory should be fully free of air bubbles. However, remember what I mentioned about shaking earlier? An unavoidable fact is that freight shakes things around, therefore, by the time an adhesive gets to you, air bubbles may have already formed, even if these aren’t directly visible.
With this in mind, your vibration table and/or vacuum chamber will become your best friends in the fight against bubbles. By making sure to follow these guidelines, as well as those for proper dispensation, you will be giving yourself the best chance of a strong, lasting bond that fulfils your requirements.
For more information and support with your application, please contact our friendly technical support team.
