Page 509 - Handbook of Adhesives and Sealants

Selection of Adhesives 441

11.6.1 Nature of the part or assembly
The assembly being bonded may consist of two simple parts; compli-
cated, multipart subsections; or fully developed products with several
subsections. They may be one-of-a-kind articles or mass production
units. The nature of the part being bonded may dictate the type of
adhesive or bonding process that could be used.
The method chosen for the application of the adhesive to the sub-
strate is determined by the size and geometry of the parts to be as-
sembled, the number of components to be bonded, and the dimensions
of the part, as well as by the physical properties of the adhesives. Most
adhesive types are available in forms ranging from thin liquids to
pastes and solids. The method of application may depend on the vis-
cosity of the adhesive. Table 11.5 lists available forms and processing
requirements for common types of adhesives.
The shape of the components often favors the use of a particular
form of adhesive. The joining of aluminum honeycomb structures to
flat metal skins is best accomplished with thermosetting film adhe-
sives that are supported on glass cloth. On the other hand, it is more
convenient to use a paste adhesive for the construction of heat ex-
changers formed from aluminum tubes and spiral copper fins. A low
viscosity, liquid adhesive is convenient to use for laminating parts that
have a large surface area.
High volume production items usually require that the adhesive be
of a form that can be handled by processing equipment designed for
fast assembly. Hand assembled units often employ adhesives in phys-
ical forms unsuited to mass production machinery. The assembly of
small, delicate parts is dependent on human skill, and the relatively
low volume requirements makes it feasible to consider a wider range
of adhesive types.

11.6.2 Production requirements
The production conditions under which the adhesive is to be applied
are also important criteria for the selection of the adhesive. Particular
production requirements could lead the user to choose a product that
will bond at a certain temperature or within a certain time. In fact,
such circumstances may be the major criterion in the selection process.
This is especially true in high volume assembly of low strength parts,
for example auto parts, clothing, and toys. Here, the method and time
of bonding may be more important than the adhesive’s strength or
environmental resistance. Often the use of fast-setting expensive ad-
hesives, such as cyanoacrylates, which avoid complex jigging of assem-
bly parts, may be an economic choice over a higher strength adhesive
that requires extended cure time.