TM 1-1500-204-23-11
a. Types of Injection Repair. There are two types
reduced at higher temperatures; however, heating the
of injection repair: positive pressure injection and
adhesive causes an increase in the rate of polymer-
vacuum injection. Positive pressure injection involves
ization, reducing the work life of the material. As the
drilling holes into the delaminated area and injecting
adhesive is mixed and brought up to temperature, the
them with resin. It is used when a leak path exists,
viscosity drops to its minimum value. For EA 956,
i.e. a delamination open to an edge or a blister. The
for example, this is about 20 minutes. After reach-
vacuum injection method involves using a vacuum to
ing minimum viscosity, gelation occurs rapidly. Again
remove air from the delaminated area, allowing resin
for EA 956 this occurs in about 10 more minutes.
to low into the void. It is used in areas where little
The resin becomes too viscous for successful injec-
or no airlow is possible and the delamination is too
tion to occur. There is a trade-off between insuring a
close to an edge to allow drilling injection holes, such
reasonable viscosity for injection and insuring an ade-
as small area delaminations in and around fastener
quate pot life to complete the injection. Heating the
holes.
adhesive to its minimum viscosity temperature before
injection may result in gelation occurring too quickly.
Instead, heat the delaminated area to the minimum
b. Adhesive Characteristics. Injection repairs uti-
viscosity temperature prior to performing the injection
lize a low viscosity liquid adhesive to facilitate low
to facilitate adhesive low and ensure suficient work
into tight matrix cracks and delaminations. The vis-
life prior to adhesive gelation.
cosity of most adhesives at room temperature is too
high for successful injection. Adhesive viscosity is
Figure 7-32. Impact Damage Injection Repair
Figure 7-33. Injection Repair
c. Damage Classiication. NDI must irst be per-
d. Positive Pressure Injection Repair. This meth-
formed on the component to determine location,
od is used when positive airlow through the laminate
depth and perimeter of the damage. The informa-
is possible. The method involves drilling injection
tion obtained from NDI will determine which injection
holes, heating the delaminated area to the minimum
repair method is to be used.
viscosity temperature of the adhesive, and injecting
