Page 210 - Handbook of Adhesives and Sealants

Quality Control and Nondestructive Tests 181

erties. ASTM lists various test methods that are commonly used for
adhesive or sealant acceptance. Many of the more common test meth-
ods were described in the previous chapter.
A receiving inspection program consists of comparison of the pur-
chase order with what is received. If the vendor’s test reports are re-
quired with the shipment, it is verified that they were received and
that the test values are acceptable as defined by the original material
specification.
It may also be necessary to test the incoming bulk product in-house
for fundamental properties. These inspections usually consist of an
evaluation of physical and chemical properties such as: color, viscosity,
percent solids, weight per gallon, pot life, open time, and flow.
Test specimens may also be made to verify strength of the adhesive.
These specimens should be stressed in directions that are represen-
tative of the forces which the bond will see in service, i.e., shear, peel,
tension, or cleavage. If possible, the specimens should be prepared and
cured in the same manner as actual production assemblies. If time
permits, specimens should also be tested in simulated service envi-
ronments, e.g., high temperature and humidity.
Because of cost and time required for extensive in-house testing, the
trend today is to have most of the quality control tests done by the
supplier. The supplier then provides a certified test report with ship-
ment of the product. The test program used by the supplier, his inter-
nal controls, etc. are usually verified and approved by the user on a
periodic basis, such as once per year.
Once identified and approved for receipt, all incoming material
should be labeled with a receipt date. This date will be prominently
shown on the container or material while it is in inventory. Precau-
tions must be taken to assure that the oldest material is used first
and that the shelf life of the product does not expire before it is used.
The date stamp on the product is the most reliable method of doing
this.

5.2.3 Quality control of surface treatment
Generally, some sort of surface preparation is required for reliable
adhesion. The extent of the actual surface preparation process will
vary depending on the performance characteristics desired, the nature
of the adherend, and time and cost considerations.
Surface preparation processes must be carefully controlled for reli-
able production of bonded parts. If a chemical surface treatment is
required, the process must be monitored for proper sequence, bath
temperature, solution concentration, and contaminants. If sand or grit
blasting is employed, the abrasive must be changed regularly. An ad-
equate supply of clean wiping cloths for solvent cleaning is also man-