TM 1-1500-204-23-11
the sealant has been removed,
technicians to accurately estimate internal patch and
except for the sealant in the
bondline temperatures by observing the perimeter TC
crevices and fastener recesses.
readings.
All sealant remaining should be
lush with the repair surface. Be
(b) Thermal Variations. Thermal variations
careful not to remove too much
in the repair area occur for many reasons. Primary
sealant, as this would allow the
among these are material type, material thickness,
leaks to continue. The appli-
and underlying structure in the repair zone. For
cation of heat can signiicantly
these reasons, it is important to know the structural
shortened the amount of time
composition of the area to be repaired. Substructure
required to cure the sealant.
existing in the repair zone will conduct heat away
from the repair area resulting in a cold spot directly
Perform the vacuum integrity
c
above the structure. Thin skins heat quickly and can
testing process in paragraph
easily be overheated. Thick skin sections absorb heat
slowly and take longer to reach soak temperature.
The thermal survey will identify these problem areas
4
If a leak path exists which cannot
and allow the repair technician to develop the heat
be isolated using a backside vacuum
and insulation setup required.
bag and a minimum vacuum of 20
inches of mercury cannot be main-
(c) Maximum Temperature Control. The
tained, use an envelope vacuum bag.
heat generated by the heating source must be con-
trolled so that it will not damage aircraft systems and
g. Thermal Survey Procedure. A heat survey is
degrade surrounding coatings, sealant, and wiring.
performed on parts requiring an elevated temperature
A thermal survey will help determine the maximum
heat cycle during the repair process. In order to
temperature required for a cure in order to overcome
achieve maximum structural properties in a bonded
heat sinks in the structure.
composite repair, it is essential to cure these materials
within the recommended temperature range. Failure
(2) Facilities, Tools and Materials. Before per-
to cure at the correct temperatures can produce weak
forming the thermal survey, the aircraft or part should
patches and/or bonding surfaces and can result in
be positioned in the same location the actual repair
a repair failure during service. A thermal survey
will be performed; usually an area that is thermally
should be performed prior to installing the repair
stable and wind free. If this is not possible, a tem-
to ensure proper and uniform temperatures can be
porary shelter should be erected to protect the area
achieved. The thermal survey determines the heating
from the elements. The repair location should be
and insulation requirements as well as thermocouple
convenient to electrical power, vacuum source, and
(TC) locations for the repair area. The thermal survey
compressed air. If the repair location is not within
is especially useful for determining the heating method
easy reach of shop air and electricity, a generator
and monitoring requirements in cases where heat sinks
and air compressor will be needed. Collect all equip-
(substructure for instance) exist in the repair area. It
ment, tools, and consumable materials before starting
should be performed for all types of heating methods
the thermal survey procedure. Ensure all methods of
to preclude insuficient, excessive or uneven heating
heating (hot air modules, heat lamps, heat blankets,
(e.g., repair near the edge of a part, low ambient
etc.) that will be used for the repair are tested during
temperature, etc.). It is required when speciied by a
the thermal survey. If heat lamps are to be used
system speciic technical manual, engineering direction
for the repair, bafles may have to be constructed
or when the ability to obtain the proper cure cycle
to ensure adequate heating of the repair area. If a
parameters is in question.
heating blanket is to be used, ensure the repair area
has been vacuum sealed so vacuum bag integrity can
(1) Thermal Survey Considerations. When
be maintained for the thermal survey. Refer to earlier
performing a thermal survey, considerations must be
in this chapter for procedures on vacuum sealing the
taken for estimating bondline temperatures, thermal
repair area.
variations and temperature controls.
(a) General Rules. These rules apply to the
(a) Bondline Temperature Estimation. Du-
use of tools used during thermal survey.
ring a cure, no TCs may be placed in the bondline;
consequently, the only source of information during a
Use one TC for approximately each
1
cure is the TCs placed around the repair s perimeter.
10 square inches of patch area. Use
Because these TCs are not in the actual bond area,
a minimum of three control TCs per
they may not accurately relect the temperatures within
patch.
the repair zone. Thermal survey data will allow repair
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