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From automotive bumpers to disk drive components, bicycle frames
to air/fuel breather valves, plastic railings to refrigeration
coils, structural adhesives are available for thousands of
manufacturing applications. With ongoing advances in adhesive
formulation, designers in every industry have diverse options
for bonding metal, composites, plastics, rubber, glass, and
more. A wide choice of epoxies, acrylics, and urethanes enable
design engineers to more easily achieve the right balance of
strength, heat resistance, and productivity. This article
describes epoxy, acrylic, and urethane structural adhesives,
including their strength, heat properties, creep resistance, and
the most appropriate applications.
Advantages of structural adhesives
In general, these structural adhesives have enough cohesive
strength and creep resistance to permanently bond high-strength
materials, and they have the potential to replace mechanical and
fusion fastening in many applications. Practical bond strength
is at least 7 MPa in overlap shear at 24°C. (Less than 7 MPa in
overlap shear is generally considered too low for structural
bonding.) Beyond having the load-bearing strength to do the job,
structural adhesives offer other styling, performance, and
production reasons for replacing mechanical or fusion fastening.
•Distribute stress over the entire bonded area: The
concentrated stress of rivets, bolts, spot welds, and similar
fastening techniques is eliminated. A design engineer can
specify lighter, thinner materials without sacrificing strength.
•Bond dissimilar materials: Laminates of dissimilar material
can often produce combinations superior in strength and
performance to either material alone. Adhesive flexibility
compensates for different coefficients of expansion between
substrates such as aluminum and glass, for example. Adhesives
also provide a film barrier to reduce or prevent bimetallic
corrosion between different metals.
•Maintain the integrity of assembled substrates: Mechanical
fastener holes are eliminated, as are surface marks from spot
welding and brazing. With this virtually...
...Continued
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