Adhesive tape passes road test
A high-strength adhesive bonds panels
to posts on custom trailers
By Karen Auguston Field, Executive
Although the rivets used to attach the aluminum skins
to the frames of Featherlite's custom trailers protrude
a mere 0.20 inch, some discerning customers were asking
for a smoother surface.
"If you're looking at the trailer straight on, you
don't notice it so much," says Bob Gast, engineering
manager. "But if you're looking down the side, the rivets-which
are located between 2 and 8 inches center-to-center
(depending on the construction criteria)-break up the
contour somewhat. Companies who want to put high-end
graphics on our trailers were telling us they wanted
the sides of the trailer to be as smooth as glass."
A high-bond-strength adhesive tape from 3M looked like
a good alternative to rivets in this panel bonding application.
Featherlite engineers were familiar with the double-sided,
acrylic foam adhesive, which they had used on some interior
lining applications in the past. One major requirement,
however, was that the tape perform well under a wide
range of operating temperatures-from frigid Minnesota
winters to the summertime heat of Death Valley. The
tape also had to provide a sufficiently strong bond
to withstand the tensile and shear stresses produced
by air flow and trailer movement.
An invisible fastener. As a builder of custom
and specialty products, Featherlite builds trailers
in a variety of sizes and formats. The typical frame
is a rigid structure consisting of hat-shaped side posts
located on approximately 18-inch centers attached to
top and bottom rails. Mounted to this frame are aluminum
side panels or skins measuring approximately 4-ft-wide
and anywhere from 0.04 to 0.09 inch thick.
After prepping and cleaning the areas to be bonded,
an operator applies the tape with uniform pressure along
the length of each side post. Then he or she removes
the liner from the tape and puts the aluminum panels
in place. To make sure that uniform pressure is applied
over the length of the section, Kevin Weinacht, senior
design engineer, explains that Featherlite built its
"There is an immediate adhesion, and then a full cure
that takes 36 hours," says Weinacht. "One of the things
we've learned is that the extent to which tape performs
depends highly on the quality of the assembly process.
If you don't do your homework in the factory, you are
not going to get good performance in the field."
Temperature also plays a role in that process, since
to form a strong bond the pressure-sensitive adhesive
cold flows across the surface of the substrate.
Another temperature-related benefit stems from the
fact that the tape is more forgiving than a mechanical
fastener in allowing the posts and panels to move independently.
Small, differential movements are caused by the different
thermal expansion rates of the two metals (aluminum
vs. steel), and also because the outer panels heat up
faster in the sun than the inner posts.
A mechanical fastener is used to attach the panels
to the top and bottom rails of the frame, lending strength
to the design. But the tape's dynamic tensile strength
still has to withstand the forces of the wind on a trailer
as it is zipping along the highway. Although the exact
magnitude of the forces cannot be easily quantified,
the strength of the tape used by Featherlite in the
assembly process appears to be more than enough as no
failures in the field have been reported.
In fact, so good is the tape's peel strength that
removing the tape has been more of a challenge than
getting it to stick. "Actually, 3M has an abrasive wheel
that works well, as does an air chisel. It's really
more of an issue of bond accessibility with our interlocking
panels," says Weinacht. One last unique property of
the tape is that it is viscoelastic in nature, and therefore
is a great energy absorber. "We're catering to a different
type of customer and their expectations are a little
higher across the board. They are sensitive to even
minor vibrations or rattles," says Gast. He explains
that the tape has helped to reduce both noise levels
inside the trailer and vibrations, leading to a quieter,
more comfortable ride.
In a typical panel bonding application, the frame is
a rigid structure consisting of upright side posts attached
to top and bottom rails. Load-bearing and non-load bearing
aluminum side panels are mounted to the posts, using
an acrylic, pressure-sensitive, double-sided adhesive
tape. Mechanical fasteners add strength to the assembly,
although the tape has sufficient strength to withstand
tensile stresses on the joint. "Bonding panels onto
frames is a common application for 3M's VHB Tape across
a variety of industries," says Ted Steiner, technical
service manager, 3M's Bonding Systems Division. "Any
application that involves putting skins over the surface
of a frame or box is a good application for these tapes,
because they have fantastic strength."