MIL-DTL-24643C
d. An oven, for accommodating the gauge with the specimen inserted and for supporting the requirements as
specified in 4.8.15.3. The oven air temperature shall be measured in the immediate vicinity of the specimen.
4.8.15.3 Procedure. The initial insulation thickness of each specimen (T in the formula below) shall be
determined (see a(1) and b(1) below) and the oven shall be preheated to 121±1 °C. This oven temperature shall be
maintained for the remainder of the test. The gauge foot shall then be loaded with weights (see a(2) and b(2) below)
and the gauge placed within the oven. Not less than one hour later, one specimen shall be selected and also placed
within the oven. Not less than one hour after placing the specimen within the oven, the specimen shall be placed
beneath the gauge foot such that the gauge indicates the specimen thickness. Not less than 1 hour after placing the
specimen beneath the gauge foot, the final specimen thickness or diameter (as appropriate) shall be read from the
gauge and the final insulation thickness (t in formula below) determined (see a(3) and b(3) below). In an identical
manner, the remaining specimens shall also be tested. The percentage heat distortion of the insulation shall then be
calculated by using the following formula:
Percentage heat distortion = Median value of 100 (T-t)/T for all tested specimens.
Where:
T
=
Initial insulation thickness of the specimen, in thousandths of an inch (see a and b below).
t
=
Final insulation thickness of the specimen, in thousandths of an inch (see a and b below).
The following additional details apply:
a.
Rectangular strip specimens:
(1) The initial insulation thickness (T) shall be the initial specimen thickness, as measured with the gauge,
prior to loading the gauge with weights and prior to inserting either the gauge or the specimen into the oven
(2) The gauge foot shall be loaded with 2000±100 grams.
(3) The final insulation thickness (t) shall be the final specimen thickness, measured as specified.
b.
Insulated conductor specimen:
(1) The initial insulation thickness (T) shall be defined as ½ of the difference between the measured
overall specimen diameter and the measured specimen conductor diameter. Measurements shall be made using the
micrometer. The overall specimen diameter shall be measured in the same radial direction as will be measured
when the final insulation thickness (t) (see b(3) below) is determined.
(2) The gauge foot shall be loaded as follows:
(a) Specimens with a conductor cross-section of not more than 3999 circular mils nor less than 2700
circular mils: 400±20 grams.
(b) Specimens with a conductor cross-section of not more than 21,999 circular mils nor less than 4000
circular mils: 500±25 grams.
(c) Specimens with a conductor cross-section of not more than 94,999 circular mils nor less than
22,000 circular mils: 750±35 grams.
(d) Specimens with a conductor cross-section of not more than 189,999 circular mils nor less than
95,000 circular mils: 1000±50 grams.
(3) The final insulation thickness (t) shall be defined as ½ of the difference between the final specimen
diameter, measured as specified and the previously measured specified conductor diameter.
4.8.15.4 Observation. The specimen shall be construed to have failed the test if the percentage heat distortion
is greater than that specified on the applicable specification sheet.
4.8.16 Hydrostatic (open end). This test shall determine the ability of completed cable, which is intended to
pass through watertight bulkheads, to prevent the longitudinal flow of high-pressure water when properly installed
in a bulkhead penetrator.
4.8.16.1 Specimen. The specimen shall consist of a 60±2 inch length of completed cable.
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