By Julie Miller
Adhesives have been applied to surfaces as bonding agents for centuries. While today’s adhesives operate on the same basic principles, designers have a number of variables to consider. Load-carrying capacity is often the deciding factor in choosing an adhesive product for a particular application. The load-carrying capacity is defined by the maximum load an adhesive-bonded joint can bear without failing.
When considering load-carrying capacity, adhesives can be classified as:
Structural adhesives demonstrate strengths from 1000 lb-force per square inch (psi) up to as high as 4000 psi. They are typically durable enough to tolerate environmental exposure and maintain performance integrity (within design limits) when a bonded joint is stressed to its yield point.
Because of their high strength, structural adhesives are used for long-term, permanent attachment. Automotive, aerospace, consumer appliance, construction, electronics, medical device manufacturing and other industries rely on structural adhesives—particularly as an alternative to mechanical fasteners.
The advantages of structural adhesives include:
- Reduced assembly size and weight;
- Fewer parts per assembly;
- Ability to join dissimilar materials;
- Adaptability to automated processes;
- Productivity gains with fast-setting formulations;
- Improved aesthetic design; and
- Lower cost.
Chemistries of structural adhesives can include acrylics, cyanoacrylates, epoxies, rubber and urethanes. With liquid or paste application, a consistent bead of adhesive on the substrate ensures the strongest bond. Delivery of liquid-type adhesives ranges from contact-bond and hot-melt to aerosol and cylinder spray. Tape or film formats are also appropriate in some applications, where the right amount pressure must be applied to ensure the tape fully adheres and fills the gap between surfaces.
Another advantage of structural adhesives is that they provide strong attachment for a variety of substrates, including metal, composites, and both rigid and flexible thermoplastics. Additionally, structural adhesives can fill gaps between substrates, sealing out environmental exposure.