MIL-DTL-24640C
4.7.4.3 Procedure. The specimen shall be straightened. If it does not remain straight of itself, it shall be held
straight by securing it (as with twine to a straight wooden bar). The straightened specimen (including wooden bar if
applicable) shall be placed within the refrigeration chamber and subjected to an air temperature of -20±2 °C (unless
otherwise specified, see 3.1) for a continuous period of not less than 6 hours. Prior to any change of chamber
temperature, the specimen shall be removed from the chamber (following detachment from the wooden bar, if
applicable) and one specimen end shall be inserted into a clip which has been affixed to (or adjacent to) the mandrel,
such that the specimen is both in contact with the curved surface of the mandrel and also perpendicular to the
mandrel center of curvature axis. The opposite end of the specimen shall then be bent circumferentially around the
curved mandrel surface through an arc of not less than 170 degrees. This bending shall be accomplished at a rate of
not less than 20 degrees per second. The period of time between the removal from the refrigeration chamber and the
completion of specimen bending shall be not greater than 40 seconds. Care shall be taken to avoid heating the
specimen, as by excessive handling, during removal from the refrigeration chamber and during bending. Following
bending, the specimen shall be secured to maintain its bent shape (as with a piece of twine stretch taut and tied
between each end of the specimen) and shall then be removed from the mandrel. Not less than two thirds of the bent
portion of the specimen shall then be dissected and each of its constituent components visually inspected for
deterioration.
4.7.4.4 Observation. Specimen failure shall be construed if the specimen either during bending or upon
dissection and inspection, exhibits distortion or cracking of any specimen component, or exhibits any other visible
deterioration of such a nature or extent as to impair the performance of the cable in service.
4.7.5 Drip. This test shall determine whether or not sealant will exude and drip from the cable ends when
cables containing sealant are subjected to high temperatures. Such sealant dripping may produce deleterious effects,
such as the coating or bridging of underlying electrical contacts.
4.7.5.1 Specimen. The specimen shall consist of an 18±½ inch length of completed cable.
4.7.5.2 Special apparatus. Apparatus shall include a heating chamber for supporting the requirements as
specified in 4.7.5.3. The chamber air temperature shall be measured in the immediate vicinity of the specimen.
4.7.5.3 Procedure. The specimen shall be straightened and shall be suspended from one end within the heating
chamber, such that the specimen hangs freely downward. The temperature within the chamber shall then be raised
to 95±1 °C. This chamber temperature shall be maintained for a continuous period of not less than 18 hours.
Provision shall be made to catch any material which may fall away from the lower specimen end during this test.
4.7.5.4 Observation. Specimen failure shall be construed if any material falls away from the lower specimen
end during the test.
4.7.6 Durometer hardness. This test shall be to determine whether or not jacketing material exhibits sufficient
hardness (see 4.7.6.4) for use in cable construction.
4.7.6.1 Specimen. The specimen shall consist of a block of material of the dimensions specified in
ASTM D2240, which shall have been cured in effectively the same manner as when used in cable manufacture.
4.7.6.2 Special apparatus. Apparatus shall include a Type A durometer, which shall be in accordance with
ASTM D2240.
4.7.6.3 Procedure. The specimen shall be tested in accordance with ASTM D2240.
4.7.6.4 Observation. Specimen failure shall be construed if the specimen exhibits a durometer hardness other
than that specified (see 3.1).
4.7.7 Flame propagation. This test shall be to determine the relative ability of grouped cable to resist the
propagation of fire along its length. The test shall be performed according to UL Flame Exposure of UL Standard
1685, without the smoke requirements.
4.7.8 Gas flame. This test shall determine the ability of completed cable to maintain electrical circuit integrity
in the presence of flame.
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