MIL-PRF-55371B(CR)
4.5.4 Tensile strength of ribbon. The tensile strength of the ribbon shall be determined for
compliance with the tensile strength requirements of 3.5.7.1 as follows: Four specimens, each
0.6 foot long shall be cut from the ribbon. Each specimen shall be creased transversely in two
places 0.1 foot apart near the center of the specimen. The creases shall be made by folding the
tape 180° with firm finger pressure on the crease. One fold shall be made back to back and the
other to front, the front being the face with the numerals. The folds shall then be straightened
with finger pressure and the specimen placed in the tensile tester with the section containing the
straightened folds between the jaws.
4.5.5 Abrasion test. Three specimens 21 inches long shall be cut from the ribbon of each
sample tape. One of these tapes shall contain and have this test performed on a frequency
marking. The other two specimens shall contain and have this test performed on graduations.
The other two specimens shall contain and have this test performed on graduations. The
specimens are to be tested as follows: Immerse the brush bristles in water at 77° to 86°F for 30
minutes to a depth of one-half inch, and then rub Bon Ami cake soap into the brush for about 30
seconds, working the soap well into the bristles by using the corners and edges of the cake. The
brush should be turned on its back during this operation so that no more than a minimum amount
of water is lost. Mount the three specimens on the glass washability panel with waterproof tape,
insert the brush in its holder and start the motor. The brush shall travel at a rate of 45 ± 5 cycles
(90 separate strokes ° 10 strokes) per minute. After each 150 cycles, wash and resoap the brush.
After a total of 1000 cycles, the 150 cycles, wash and resoap the brush. After a total of 1000
cycles, the outline of any number, letter or graduation in the center eight inches of scrub stroke of
each specimen shall be completely discernible. (See 3.5.7.2).
4.5.6 Holding strength at reel. Each sample tape shall be supported at the reel and with the
ribbon and connecting strip fully pulled out, a 25 pound load shall be applied to the ribbon for
not less than five minutes. The ribbon shall not be loosened from the reel. (See 3.5.10).
4.5.7 Finger ring test. Each sample tape shall be supported at 4-1/2 inches from the tip of
the finger ring and a 40 pound test load applied across the finger ring to 75 percent of its width,
for not less than five minutes. The tape shall not break or be pulled out of the chip which fastens
the finger ring, and the finger ring shall not break or deform. (See 3.5.7.3).
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