ASSEMBLYADHESION
Figure 3: Two-part adhesives supplied in convenient side-by- side cartridges
Structural adhesives offer tremendous opportunities to the solar power industry Adhesives not only reduce the weight of an overall installation, but they also reduce maintenance and warranty costs, compared to using traditional nuts and bolts. Over time, bolts and screws will loosen and work themselves loose due to wind-induced and/or structural vibration, requiring periodic maintenance. Once a panel is bonded, the bond requires no additional maintenance.
Structural adhesives have been used to replace mechanical fasteners in solar frame assemblies, frame-to-rack installations, and rack-to-tracking systems. These replacements have resulted in a simpler, more robust installation process that produces an array that can survive the 25-year lifespan promised by many solar equipment manufacturers.
Selection Criteria 44 Figure 4:
Recommended “Dos” and “Don’ts” for joint design
When choosing a structural adhesive, it is important to consider cure times, and joint and process design. Paying attention to these parameters will ensure that the adhesive chosen will match the application. Two-component (resin and curative) adhesive systems provide the
broadest range of cure times. With this system, the components are separated until just prior to use. For small volume applications, the components are supplied in a side-by-side cartridge configuration (Figure 3) and dispensed through a manual or pneumatic caulk gun. For higher volume use, adhesives are dispensed through meter-mix units. Cure times range from minutes to hours, allowing users to select an adhesive that is optimal for their process. Faster-curing adhesives can reach handling strengths within minutes of application to the substrate.
If heat is applied, quicker cure times can be achieved. Slower curing adhesives can take several hours to acquire handling strength. Though many designs for traditional joining methods might not appear to be good candidates for structural- adhesive bonding, in reality it is not difficult to convert to adhesive bonding. When designing a bonded joint, it is better to design for shear and compressive loading, while avoiding peel and high-tensile loading. (Figure 4)
Cure speed and fixturing should be taken into account when implementing adhesives into the manufacturing process. The cure speed of the adhesive must be balanced to allow for easy application of the adhesive and optimum throughput of bonded assemblies. Fixturing allows assemblies to remain in the correct alignment during the curing process. Sufficient pressure applied to the bond line ensures intimate contact between the substrate and the adhesive.
A Solar Solution
While the primary function of a structural adhesive is the joining of two or more components, other benefits are of particular importance to the solar panel manufacturers. Providing protection against the elements, equally distributing stresses, eliminating galvanic corrosion, and improving structural rigidity are examples of additional benefits that make structural adhesives a wise alternative to traditional fastening methods.
In addition, don’t forget a major advantage - significantly reduces maintenance after the initial installation. Whether bonding frames to racking systems or racks to tracking systems, structural adhesives provide a simple alternative to the multiple mechanical fasteners used in joining metal components in solar installations.
© 2011 Angel Business Communications. Permission required.
www.solar-pv-management.com Issue V 2011
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