Page 209 - Handbook of Adhesives and Sealants

180 Chapter Five

Conformance to a specification does not mean that the adhesive or
sealant will perform perfectly in service. It only means that the prod-
uct conforms to the specification. Bonding or sealing specifications
should not only account for the adhesive or sealant, but they should
also define the adherends and the ancillary processes for preparing
the adherends and the joint assembly.
The product specification writer must try to put into the specifica-
tion the requirements that, if met, will provide the greatest likelihood
of success. These requirements should be standard tests that are
agreed upon by both the supplier and the user. The tests should be
indicative of how the adhesive is used in production and how the fin-
ished joint is to be used in service. Tests that are not directly related
to the specific application should not be included. Tests should not be
used simply because they are standard test methods or have been used
in the past. Specifications from other sources (e.g., ASTM, military,
etc.) may be used if they are applicable.
Specifications may require different categories of testing. For ex-
ample, there may be extensive series of tests that are required for
initial verification or qualification of the adhesive and supplier. These
tests would be used to approve a certain product at the onset. Other
receiving tests may be used to verify the consistency of the product
from lot to lot. A typical specification has the following format: title;
scope; general requirements; performance requirements; test methods;
controls; reference documents; and approved source list.
In addition to the staff, the operational facilities must be well pre-
pared before the use of adhesives or sealants. The plant’s bonding area
should be as clean as possible prior to receipt of materials. The basic
approach to keeping the assembly area clean is to segregate it from
the other manufacturing operations either in a corner of the plant or
in isolated rooms. The air should be dry and filtered to prevent mois-
ture or other contaminants from gathering at a possible interface. The
cleaning and bonding operations should be separated from each other.
If mold release is used to prevent adhesive flash from sticking to bond-
ing equipment, it is advisable that great care be taken to assure that
the release does not contaminate either the adhesive or the adherends.
Spray mold releases, especially silicone release agents, have a ten-
dency to migrate to undesirable areas.

5.2.2 Quality control of the incoming
materials
Acceptance tests on adhesives or sealants as well as adherends should
be directed toward assurance that incoming materials are identical
from lot to lot. The tests should be those which can quickly and ac-
curately detect deficiencies in the product’s physical or chemical prop-