MIL-DTL-24640C
4.7.11.2 Special apparatus. Apparatus shall include an abrading machine which shall support and secure the
specimen such that it is straight and horizontal, and which shall abrade the specimen printed identification by means
of a motor driven, transversely reciprocating steel pin. This steel pin shall have a diameter of 0.025+0.001 inch
where it abrades the specimen, and shall have a surface roughness of not less than 2 micro inches, as specified in
ANSI B46.1. (A selected sewing needle may satisfy these requirements.) One possible arrangement for the
abrading machine is shown on figure 8. The steel pin shall be horizontal and perpendicular to the specimen axis,
shall ride along the top of the specimen, and shall be weighted to bear down on the specimen with a force of 1+1/16, -0
pound at all times during the test. This pin shall be reciprocated at a rate of 60+2 cycles per minute, such that the
pin is drawn along the specimen for a distance of +1/16, -0 inch in each direction (¾ inch minimum total excursion)
during each cycle. The abrading machine shall incorporate an automatic counter to total the number of times that
the specimen is abraded by the steel pin during the test.
4.7.11.3 Procedure. The specimen shall be wiped with a clean, dry cloth to remove any lubricant or dirt, and
shall be secured in the abrading machine with the specimen printed identification facing upwards, where it is to be
abraded by the steel pin. The automatic counter shall be set initially to zero. The abrading machine motor shall then
be turned on, allowing the steel pin to reciprocate and abrade the specimen printed identification either until the
printed identification is no longer legible in the abraded region, or until not fewer than 250 abrasive cycles have
been completed, whichever occurs first. The number of abrasive cycles completed shall then be noted. This test
shall be repeated four more times (five times total), subjecting a fresh portion of the specimen printed identification
to abrasion each time.
4.7.11.4 Observation. Specimen failure shall be construed if the median value of the number of abrasive cycles
completed during each of the five tests is less than that specified (see 3.1).
4.7.12 Physical tests on jacket. This test shall determine whether or not various jacketing materials have been
properly processed, by means of tension measurements. This test makes provision for making tension
measurements both before and after these materials have been artificially aged.
4.7.12.1 Specimens. Each specimen shall consist of a single piece of jacketing, which shall have sufficient
length for use in the test as specified in 4.7.21.
4.7.12.2 Special apparatus. Apparatus shall include a forced fresh air circulating oven for supporting the
requirements as specified in 4.7.12.3.a. The oven air temperature shall be measured in the immediate vicinity of
specimens.
4.7.12.3 Procedure. Specimens shall be maintained at ambient temperature for a period of not less than 30
minutes immediately prior to any accelerated aging or testing. Each of the specified physicals (aged) accelerated
aging procedures shall be performed as follows, using one specimen for each procedure. The same specimen shall
not be used for more than one physicals (aged) procedure. Each of the specified physicals (unaged) test shall be
performed as specified in 4.7.21.
a. Air oven accelerated aging: each specimen shall be freely suspended vertically, secured by one end, within
the oven. The air temperature within the oven shall then be raised to 136±2 °C and shall be maintained at this value
for a continuous period of not less than 168 hours. Each specimen shall then be removed from the oven and tested
as specified in 4.7.21.
4.7.12.4 Observation. Any of the following shall constitute specimen failure:
a.
A specimen tensile strength which is less than that specified (see 3.1).
b.
A specimen elongation which is less than that specified (see 3.1).
4.7.13 Tear strength. This test shall determine the ability of elastomeric jacketing material to withstand the
propagation of a cut passing through a portion of its length.
4.7.13.1 Specimen. Each specimen shall consist of a piece of jacketing material, which shall have been cut to
the dimensions specified in ASTM D470. Specimens shall be removed from completed cables. Not fewer than five
specimens shall be required.
4.7.13.2 Special apparatus. Apparatus shall include the following:
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