MIL-PRF-24667C
4.5.1.4 Sled calibration. Since friction readings are a function of the surface condition of the steel sled rubber
surface, a steel sled with a new vulcanized neoprene rubber pad shall be used for each product tested. In addition,
sleds used for the different test conditions shall be used only for the same conditions. That is a sled used dry shall
only be used to test dry friction specimens, sleds used with water shall be used only with water friction specimens,
and sleds used to measure oily friction shall be used only for tests of friction on oily specimens. Sleds shall be
calibrated against a flat steel block having machined cross hatched v- shaped grooves having a nominal depth of
0.05 inch (1.27 millimeters) and a nominal groove peak to peak distance 0.01 inch (0.25 millimeter). Sleds may
continue to be used in testing the same product until repeat measurements on the calibration surface changes by
more than five percent (plus or minus). All calibrations shall be performed on the same calibration block since the
intent of the calibration blocks are only to determine reproducibility of readings by the rubber pad and thus rubber
pad replacement criteria. Calibration of sleds on different calibration blocks during the determination of friction
values on a test specimen is not permitted. Calibration shall be performed before and after test specimen friction
determinations and the values obtained recorded and reported with the test value.
4.5.2 Abrasion of arresting cable (composition L only). Three 12- by 6- by ¼-inch (300- by 150- by 6-
millimeter) (nominal) test panels shall be prepared as specified in 4.4.3. Each panel shall be conditioned by running
50 cycles in the cable abrasion tester specified herein before determination of the abrasion of the arresting cable.
Each panel shall then be abraded by a new -inch (3-millimeter) (nominal) diameter cold-rolled ASTM A229 Class
2 steel rod of sufficient length to completely span the width of the sample plate. Before use, the diameter of each
rod shall be measured to the nearest 0.1 mil (0.0025 millimeter) in a minimum of ten places that will come in contact
with the test panel. After completion of 200 cycles in the abrasion machine, the rod shall be removed from the jig
and the diameter of the rod shall be measured to the nearest 0.1 mil (0.0025 millimeter) in the same places as
measured before the rod was abraded. The mean difference in thickness of the rod shall be computed and that
number shall be recorded as the wear value for that rod. The average of the wear of the three rods shall be
computed, and this value shall be used to determine conformance to the requirements specified in 3.5. The device
used for the measurement of the rods shall have a minimum precision of 0.1 mil (0.0025 millimeter) and shall be
capable of measuring an irregular surface. One device that has the necessary measurement capability that may be
used for the measurement of the rods is a Nikon Instruments Inc. V-12B profile projector, or equivalent.
4.5.2.1 Cable abrasion test apparatus. The test apparatus shall be constructed so that there will be relative
motion between the steel rod and the test panel, and shall have the following features:
a.
A carriage or jig on which either the test panel or the steel rod is mounted. The test panel and the rod shall
be securely fastened to preclude movement within the carriage or jig during the test, and shall be moved in
a reciprocating motion 9 inches (225 millimeters) along the long axis of the sample panel.
b.
The steel rod shall be in contact with the test panel, with the axis of the rod horizontal and at a right angle to
the direction of the reciprocating motion. The clamps holding the rod shall not come into contact with the
test panel, and shall not permit the rod to bend, twist, or rotate during the test. The test apparatus shall be
constructed so as the contact force between the rod and the sample is 30±¼ pounds (13.6±0.1 kilograms)
during the test.
4.5.3 Impact resistance (types I-X). Four 6- by 6- by ¼-inch (150- by 150- by 6-millimeter) (nominal) test
steel, and reinforced plastic panels as specified in 4.4.2 shall be prepared as specified in 4.4.3 (prepared using the
highest primer thickness specified). Immediately before testing, two panels shall be subjected to each of the
following treatments: (a) no treatment and (b) 15 days of immersion at room temperature in either natural seawater,
or synthetic seawater in accordance with ASTM D1141. Panels that are immersed shall have an epoxy anticorrosive
coating applied to the edges and back side of the panels.
4.5.3.1 Impact test apparatus. The impact test shall be conducted with a device similar to that depicted in
ASTM G14, except that the v-block securing device shall be replaced with a steel base that is at least 1.5 inches (40
millimeters) thick, is capable of securing the sample plate without allowing movement when impacted and allows
alignment of the plate with the designated impact locations. A machinist's magnetic vice has been demonstrated to
have this capability. The tup nose shall have a -inch (15.875-millimeter) hemispherical head and the weight of the
tup shall be modified so that it is 4.0 pounds (1.8 kilograms).
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