Sign Builder Sticks with Adhesives

Building a sheet-metal structure? It's likely you might first think of welding when picking an assembly technique. But for some applications, durable adhesives deliver the desired aesthetic. Tooling Research Inc. (TRI), Walpole, Mass., primarily designs and builds custom electrical, mechanical, and pneumatic equipment and controls as well as machining metal and plastic components. But the company also has a growing business building signs and sculptures from conceptual sketches for architectural firms and sign companies. When TRI was tapped to provide outdoor signs for a college campus, the plans called for thin sheets of aluminum to be mounted on a structural framework. The finished sign panels had to be lightweight and removable, as well as weather resistant. Typically, such sheets are welded to a structural backing. But welds distort the sheet metal, leaving divots on the surface. Sign makers must repair the dents with body filler. Filling and smoothing can take several applications and add time and expense to the project. Mechanical fasteners also deform sheet metal. Sheets must be drilled or punched before joining, and installers still have filling and smoothing tasks to perform afterwards. Fasteners are also prone to leak or loosen from weather and vandalism. For the college-campus signs, TRI used Metal Welder adhesive from Devcon, Danvers, Mass. The two-part, 10:1 methacrylate mixes as workers dispense it from manual or pneumatic mixing nozzles. There's no need for a primer, and bonds attain functional cure in an hour at room temperature. Once the adhesive is fully cured, which takes 24 hr, it can hold 2,450 psi in tensile shear using a 0.020-in. bond-line on gritblasted substrates. The adhesive spreads loads over the structural framework instead of concentrating them at fastening points. This adds strength. The adhesive also acts to separate substrates electrically, diminishing the likelihood of corrosive electrolysis. The Metal