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Application Tips for Sign Adhesives Part 2: Adhesive Bonded Joint Design

( 09/05/2019 ) Written by: Carolee Nail

In “Selecting the Right Sign Adhesive for the Job,” you learned how various substrates affect adhesive performance. Now that you’ve selected the right adhesive for your project, how can you apply it to get best results? In this four-part blog series, we’ll show you how.

Bonded joints should be designed so that the basic stress is primarily shear, tensile  or compressive, with cleavage and peel stresses minimized on the bondline. The entire bonded area should equally share the load. The illustrations below depict both recommended joint designs as well as designs that should be avoided.

As the figures show, lap joints are the most practical design and are best for bonding thin materials. Lap joints enhance joint strength by reducing the potential for peel stress. Butt joints, which experience tensile stresses, are impractical and are not recommended. Angled designs convert applied loading to compressive forces and result in stronger joints. For additional information on joint configuration, refer to our Fixturing Guide for Metal Bonding Applications.

For optimal performance of joints bonded with structural adhesives, care should be taken during the mating and curing processes. During part mating, align the pieces properly. If the materials need to be re-positioned after mating, slide the pieces into position. Do not lift or separate the pieces as this can allow air into the bondline and create voids, causing a potential reduction in coverage and strength. Immediately after the parts are positioned correctly, they must be weighted with even pressure until handling strength is achieved. (Avoid applying pressure in areas that allow the assembly to bow.)

  • Boards can be used to apply even pressure across the bondline on flat assemblies.
  • Weight bonded signs with sand bags, bean bags or other formable materials to distribute weight evenly.
  • Mechanical fasteners (screws, rivets and/or bolts) can be used to affix particularly difficult-to-clamp areas and can be removed after handling strength is achieved.
  • Braces can be used to hold odd-shaped signs in place while curing.

Illustrations of the above weighting methods are shown in the Fixturing Guide for Metal Bonding Applications.

As with other steps involved in the structural adhesive application process, attention to detail can result in longer life for installed signage. Explore our sign adhesive solutions, and don’t forget to check out part one of our blog series on adhesive application tips for the sign industry:

 

ABOUT THE AUTHOR MORE BY THIS AUTHOR
Carolee Nail

Carolee Nail is a Technical Service Representative at LORD, assisting customers with highly reliable adhesive solutions for assembly, manufacturing and repair with a focus on the sign industry. Our technical support provides product recommendations and application support via chat, web and phone.

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