Myth #3: “I’ve tried one so I’ve tried them all.”

Disproved: Different adhesives offer different properties.

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Different adhesive families bond differently, so it’s important to understand why an adhesive failed.

Understanding Adhesive Properties

If an adhesive failed to work in the past, the decision to trial another adhesive can be difficult. This is especially true if historically there has been success with traditional fastening methods. Before giving up on structural adhesives, it’s important to investigate why the previous option failed to meet expectations.

Initial Considerations

Surface Preparation

The manner in which a surface is prepared, or even if it is prepared at all, can affect the performance of an adhesive.

Dispensibility

Ensuring ease of dispensing and accurate mixing ratios are met is critical to any structural adhesive application.

Cure Time

As cure times can vary greatly, it is important to know exactly how long the adhesive you are using needs to properly cure.

Mechanical Properties

Some adhesives work better on certain materials, or perform better on materials that stretch, bend, or undergo sheer or peel strains.

Environmental Resistance

Different adhesive chemistries perform better in different environments.

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Knowing which adhesive best suits your needs to be paramount. For instance, the three main families of structural adhesives — acrylic, epoxy and polyurethane — while they’re all strong, each has different benefits. Acrylics build strength the fastest, epoxies have higher overall strength and superior environmental resistance, and polyurethane-based products provide energy absorption and vibration damping. Processing characteristics such as shelf life, rate of strength build and the amount of surface preparation required can also affect how well a structural adhesive works for a given assembly.

More to Consider

Viscosity: 1-180,000 cP

Viscosity affects how an adhesive stays in place when applied. Low-viscosity self-levelling adhesives can pool to fill gaps but will run on non-horizontal surfaces. High-viscosity non-sag adhesives will stay in place even ‘underneath’ the substrate but may need to be spread at application to achieve coverage.
Overlap Sheet Strength: 1,000-4,600 psi

1,000 psi overlap shear strength is the minimum for an adhesive to be considered structural, but many applications require significantly stronger adhesives. Knowing how much strength you need can help you test and select the right adhesive without risking bond failure or overengineering your bonding solution.
Work Times: Instant - 25 min.

Instant adhesion allows zero work time, so parts must be applied correctly the first time but are then strong enough to move to the next processing step. Longer work times allow greater opportunity to adjust part placement while the adhesive is still workable. The work times of certain adhesive chemistries can be adjusted by slight variations in the formulation.
Elongation/Flexibility: 2-860%

Elongation measures how much an adhesive bond will stretch or flex before failing, and of course different applications have vastly different requirements. Very stiff bonds will transfer nearly all applied energy. Other applications may be better with a more flexible bond that can absorb energy to reduce noise and vibrations, or can flex with normal movement while still maintaining integrity.