BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

110 Birgit Kjærside Storm
A fresh anodized surface does not need any treatment if it has not been
touch before bonding.
5. Adhesive Bonding
An adhesive bonding shall be constructed so the forces on the bonding is the
best possible for the bonding. An adhesive bonding like a shear stress and
dislike a direct tension. In Fig. 3 the two types of forces are sketched.
Fig. 3 – The figure shows to the left, the shear force and to the right, the tension [3].
The adhesive bonding dislikes a peeling, but in practice it is difficult to
create a bonding, where peeling is not possible. The peeling is the weakest point
for an adhesive bonding and is often the limitation for making the bonding. If it
is possible the bonding shall be constructed so the forces are shear forces and
peeling cannot occur.
6. Structural Adhesives
Adhesives used for aluminium will be a structural adhesive. With a
structural adhesive means an adhesive with a high strength. The perfect bonding
will be a bonding where the bonding will have a strength which is the same as
the aluminium. The bonding shall not break in interphase between the
aluminium and the adhesive but in the aluminium or in the adhesive layer. If the
break will be in the interphase, the wetting has normally not been good enough,
or the cleaning of the surface has not been sufficient, or the forces in the surface
of either aluminium or the adhesive have not been sufficient.
Structural adhesives can be many different polymers. All of them are
polymers which will cure up under cross linking. All of them will have an
opening time. The opening time – the time from the adhesive has been added to
the product until it will start the cross linking - depends on the curing system
and can be regulated to be short or long depending on the application of the
product. There are of course limitations for how short and how long the opening
time for the adhesive can be. The structural adhesives have no green strength,
which means that for several applications it is necessary to use a tool to fix the
products until the adhesive has obtained the strength. The structural adhesives
are epoxy adhesives, polyurethane adhesives, acrylic adhesives or other
adhesives which can cross link. In Fig. 4 the curing reaction of an epoxy