Alpha
Wire Company offers a comprehensive, onsite flex testing service,
which provides life cycle test data for use in failure analysis
and fit for use comparisons. A state of the art rolling flex test
apparatus (Figure 1) is employed to provide rolling Flex Life data.
This device operates continuously in a 24 x 7 environment. Cables
are flexed at a rate of approximately 17 cycles per minute over
a 14-ft. length of travel. The cables are flex tested within a Cable Track system with a continuous 24 VDC electrical signal used to
measure conductor continuity. Cycle count accrues only if electrical
continuity fails. A single cycle is measured when the device completes
an "out and back" motion from 0-ft. to 14-ft. and back
to 0-ft. in the axis of motion.
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ROLLING
FLEX
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FIGURE 1 |
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the determination of bending and torsional Flex Life-cycle performance,
Alpha Wire Company employs MIL-C-13777G, General Specification
for Cable, Special Purpose, Electrical. |
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standard offers two distinct destructive test procedures that have
been found to provide accurate, comparative cable flex test results.
Sections 3.7.2, 4.5.4.1 and related figures 3 and 5, of the MIL-C-13777G
specification describe the test requirements for bend and twist (torsion).
In each instance the cables are tested at temperatures in the range
of 68° to 95°F. A 110 or 220 volt, 60 Hz, AC potential with
a prescribed load current of not less than .5 Ampere is used to permit
the determination of failure caused by broken conductors or by short
circuits between conductors. Failure due to either cause terminates
the test. Values obtained are derived from tests of a minimum of three
samples per test. If any of the samples tested do not comply with
the requirements, the test is considered a failure. |
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BENDING
FLEX
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FIGURE 2
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MIL-C-13777G bend test employs an apparatus which subjects the
cable test sample to bending ±90° about a mandrel,
with a radius of 5/8" for cables with a diameter of .750"
or larger, and 3/8" radius for cables with a diameter of
.749" or smaller. The test is performed using a cable test
specimen of 42" to which is fixed a weight of between 20
and 50 lbs., based on the circular mil area (CMA) of the copper
conductors in the cable sample. A weight to CMA chart is supplied
in the test procedure. The test cycle rate is 30 cycles per
minute. |
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TORSIONAL
FLEX
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FIGURE 3
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MIL-C-13777G torsional test is performed using a cable specimen
length of 66". The cable is weighted at one end using a
50 lb. weight for cables containing copper Circular Mil Area
(CMA) above 14000 and 20 lbs. for cables containing copper CMA
below 14000. 22" inches from the weighted end, the cable
is wound about a mandrel of between 3" and 9", depending
on cable diameter. The cable is affixed to a continuously rotating
arm driven at 30 cycles per minute. Torsion is applied to the
22" weighted end of the test sample using a helical travel
of ±90° over a length of 8". The torsional stress
applied to the cable is 8.2° of motion per inch.
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