TM 1-1500-204-23-11
(c) Control may be established by either the
via conduction. Consequently, the heat blanket must
leading (hottest) thermocouple or lag-
conform to and be in 100 percent contact with the
ging (coldest) thermocouple automat-
part. This is usually accomplished using vacuum bag
ically. It is typically used when one
pressure. Lack of contact between the heat blanket
does not want to either exceed a tem-
and the area to be cured will result in inadequate
perature value (leading) or when one
heating of the repair area and an over-heating of
wants to ensure a minimum temper-
the heat blanket. For example, excessive height in a
ature is obtained in the entire repair
core plug being bonded into place causes an air gap
area (lagging). This method is highly
at the edges of the core plug and correspondingly
dependent upon thermocouple place-
inadequate heating at the plug s edge. In addition,
ment which should be determined by a
heat loss occurs around the outer perimeter of the
thermal survey of the repair area.
heat blanket causing the temperatures on the outer
portion of the repair area to be less than the center.
See igure 6-40 and igure 6-35 for proper placement
(4) Alarm. A hot bonder provides the operator
of a standard heat blanket over the repair as well
with the capability to set an alarm condition in which
as temperature variations that may exist in the repair
the actual measured temperature or vacuum varies
area due to edge effects, heat sinks, insulated areas,
from that speciied in the programmed cure cycle. In
and variations in part thickness. Refer to paragraph
most cases, this alarm will put the controller into a
6-19.e.4 and paragraph 6-18g, Thermal Survey, for
HOLD situation until the alarm condition is corrected.
ways to identify and mitigate uneven heating and for
the proper number and placement of thermocouples.
g. Heat Blanket. Heat blankets are a common
Heat/vacuum blankets allow application of the heat
method used to apply heat for repairs in the ield.
blanket without a vacuum bag. They are much less
See Chapter 3, Tools, Equipment, and Supplies for
lexible than standard heat blankets and are usable
information on heat blanket construction, selection, and
only on relatively lat surfaces.
storage. Heat blankets are usually used in conjunction
with a hot bonder. Heat is transferred from the blanket
6-78