ASSEMBLYADHESION
the ability to join dissimilar materials; enhanced sealant properties; and increased structural rigidity. Structural adhesives are defined as load-bearing adhesives – they can withstand a constant load on the bond without undergoing creep or losing adhesion. The most common structural adhesives are available in three chemistries: acrylic, epoxy and urethane. Service temperature, environmental exposure, and curing temperature and time will determine which adhesive is suitable for a particular application. Generally, acrylics are ideal for bonding unprepared metals, composites and thermoplastics. Epoxies and urethanes typically are used to bond prepared metals and composites. For higher service temperatures, acrylics and epoxies will provide the best performance.
Proven Applications
Adhesive bonding is an established joining method, proven in a variety of end-use markets, including automotive, exterior signage and transportation. In each of these industries, the benefits of structural adhesives have helped to reduce manufacturing costs, decrease production times and increase the structural rigidity of components. In the automotive industry, adhesives are used both during the initial assembly process as well as for aftermarket repair. Door panels bonded with structural adhesives have significantly more impact resistance than welded doors. Using structural adhesives has improved the corrosion resistance of automobiles by eliminating hundreds of welds. (Figure 1)
Sign manufacturers have found that using structural adhesives offer a considerable time savings during the assembly process compared to traditional fastening methods and/or welding operations. In the sign industry, structural adhesives are used in the assembly of sign extrusions; to mount letters and raceway brackets; and to adhere sign-mounting attachments. (Figure 2)
For the transportation industry, structural adhesives have demonstrated excellent durability in harsh environments over an extended period to time. The adhesives are widely used where structural integrity is required on roof, sidewall, door, and floor assemblies on trailers, medium-duty trucks, specialty and recreational vehicles, and buses.
Reliable and Durable As noted earlier, environmental resistance is especially important to solar installations. Structural adhesives have demonstrated outstanding environmental resistance in real-world applications. In a large heliostat installation, an acrylic adhesive was used to bond corner clips (to
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reinforce the panel’s metal frame), channels for sealants, and module support doublers. After more than 25-years of operation, the adhesive has provided excellent durability with no failures. Similarly, adhesives have been successfully used for many years to construct aluminum satellite dishes, commercial signage and military transport vehicles, where excessive thermal and mechanical stresses create fatigue conditions.
Accelerated fatigue testing has proven that structural adhesives are successfully resistant to the thermal and mechanical stresses posed on these assemblies. In one example, an adhesively bonded specimen was tested for its ability to withstand various loads applied to the joint. The bonded specimen surpassed 10,000,000-cycles of repeated loadings of 900 psi.
Figure 1: Adhesives provide superior structural integrity in applications for the automotive industry
Figure 2: Using a handheld cartridge, a worker easily applies adhesive during sign assembly
www.solar-pv-management.com Issue V 2011
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