Page 214 - Handbook of Adhesives and Sealants

Quality Control and Nondestructive Tests 185

TABLE 5.2 Faults Revealed by Mechanical Tests
Fault Cause Remedy
Thick, uneven glue Clamping pressure Increase pressure. Check that clamps
line too low are seating properly
No follow-up Modify clamps or check for freedom of
pressure moving parts
Curing Use higher curing temperature
temperature too Check that temperature is above the
low minimum specified throughout the
curing cycle
Adhesive exceeded Use fresh adhesive
its shelf life,
resulting in
increased viscosity
Adhesive residue Excess air stirred Vacuum-degas adhesive before
has spongy into adhesive application
appearance or
contains bubbles
Solvents not Increase drying time or temperature
completely dried Make sure drying area is properly
out before bonding ventilated
Adhesive material Seek advice from manufacturers
contains volatile
constituent
A low-boiling Curing temperature is too high
constituent boiled
away
Voids in bond (i.e., Joint surfaces not Check treating procedure; use clean
areas that are not properly treated solvents and wiping rags. Wiping rags
bonded), clean must not be made from synthetic
bare metal fiber. Make sure cleaned parts are not
exposed, adhesive touched before bonding. Cover stored
failure at interface parts to prevent dust from settling on
them
Resin may be Replace resin. Check solids content
contaminated Clean resin tank
Substrates Check for distortion; correct or
distorted discard distorted components. If
distorted components must be used,
try adhesive with better gap-filling
ability
Adhesive can be Adhesive not Use higher curing temperature or
softened by properly cured extend curing time. Temperature and
heating or wiping time must be above the minimum
with solvent specified throughout the curing cycle.
Check mixing ratios and
thoroughness of mixing. Large parts
act as a heat sink, necessitating
larger cure times