MIL-DTL-70438A(AR)
4.4 Testing.
4.4.1 Melting test of ternary eutectic alloy. Five (5)
samples of approximately one quarter pound each shall be randomly
taken from each lot of ternary eutectic alloy to be used in each
lot of fusible plug assemblies. The samples selected shall be
individually tested by placing each in a beaker of distilled
water at ambient temperature. The temperature of the water shall
then be raised at a rate not to exceed 10ºF per minute. The
water shall be stirred to assure uniform heating. A temperature-
indicating device such as a thermometer or thermocouple, suitable
for the required temperature range shall be inserted in the
water. When the alloy is observed to melt, the indicated
temperature shall be recorded. The measured temperature shall
then be compared with the value specified on dwg. 9215391 to
determine compliance or non-compliance of the sample with the
melting point requirement. If any sample fails to comply with
the specified melting point, the alloy lot shall be rejected. In
addition, all fusible plug assemblies containing the rejected lot
of ternary eutectic alloy shall be rejected.
4.4.2 Air pressure test of fusible plug assembly. Every
plug assembly shall be subjected to this test. The test shall be
performed by sealing the open end of the plug and completely
immersing the plug in water. The air pressure specified on dwg.
9345325 shall then be applied through the sealed end of the plug
for the specified time intended. Observation shall be made for
air bubbles originating from the area of the fusible alloy
indicating a leaking plug. All such leaking plugs shall be
classed defective and removed from the lot. The plug assemblies
shall be thoroughly dried after completion of this test. All
equipment used on this test shall be capable of performing the
test accurately and consistently. Equipment shall be calibrated
prior to the start of each shift. At the start of each shift and
every four (4) hours thereafter, the equipment operation shall be
verified with a known leaker. If the equipment fails to either
calibrate or verify, all plugs tested since the last satisfactory
check will be retested
4.4.3 Mechanical properties tests. Five (5) lifting plugs
shall be randomly selected from each lot after final heat
treatment and prior to the pouring of the alloy for these tests.
If any sample part fails to meet any requirement, the lot
represented by the failing part shall be rejected.
4.4.3.1 Tension. The lifting plug shall be screwed into a
threaded plate or other suitable fixture and a load of 8,000
pounds minimum applied through the medium of a ¾ inch diameter
bolt or pin passing through the eye of the plug. The full load
shall be transmitted through the screw threads of the plug.
4.4.3.2 Ductility. The plugs used in the tension test shall
be cooled to minus 40 degrees Fahrenheit (F.) for a minimum of 30
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