Choosing a High Strength Structural Adhesive

A structural adhesive is an adhesive that forms a bond which bears a structural load.  Two of the most common types are epoxy adhesives and acrylic adhesives.  Often both types will work for structural metal bonding application.  Choosing the best type of high strength structural adhesive for the application depends on several factors.  Understanding the characteristics of each type helps to determine the best fit.

Epoxy Adhesive Characteristics

• Generally low odor
• Highest temperature resistance
• High strength on metals
• Excellent chemical and environmental resistance
• Cure mechanisms include – Single component heat cure, Two-component room temperature cure, & Two component heat cure
• Most epoxy adhesives are fairly rigid. However, modified epoxy adhesives are soft and flexible.

Acrylic Adhesive Characteristics

• Many formulations are low odor. However, MMAs have a distinct strong odor
• High-temperature resistance
• High strength on metal, MMAs have very high strength on plastics, Specialty grades such as Permabond TA4610 has excellent strength on difficult to bond plastics such as polyethylene and polypropylene.
• Excellent chemical and environmental resistance
• Cure mechanisms include – Surface activated, Two-component static mix, Two-component bead on bead, External mix, Single component (with active metal)

If bonding metal only, either are high strength structural adhesives.  Special grades are available with low read through for thin panel bonding.

When bonding metal to plastic or other materials, acrylic adhesives may be the better choice.

Similarly, for high-speed automation, some acrylics offer fast strength development.

In addition to carrying a structural load, there are a variety of reasons to choose a high strength structural adhesive over a mechanical joint or weld – some of these reasons play into whether an epoxy adhesive or an acrylic adhesive is the best fit.

1. Maintain the integrity of the components.  Eliminate drilling holes for fasteners.  Eliminate post welding polishing and painting.
2. Distribute stress to reduce component fatigue.  Choose a cure mechanism that allows covering the desired bond area to eliminate any focused stress points.
3. Seal the joint. In addition to bonding if you want to seal the joint consider the gap between the components.  Surface activated acrylic adhesives have a maximum gap fill of 0.5 mm (0.02 inch).  For larger gaps, consider an epoxy or a two-component acrylic adhesive.

Contact Permabond for assistance in selecting an adhesive to suit your needs.