MIL-DTL-398D
ni = # of negatives at each log height
N = sum of ni
A = sum of (i*ni)
B = sum of i*i*ni
C = log interval of lowest drop height
M = C + 0.1(A/N + 0.5)
Height (at 50% explosion) = 10 raised to the power of M
S (standard deviation, log units) = 0.162*[(NB - A*A)/N*N
+ 0.0219]
The ERL type 12 impact machine shall be tested for accuracy each
day that it is used for testing RDX in accordance with the
specification. For this purpose an RDX sample having a known
sensitivity range shall be used. The results shall be recorded
on a chart showing the minimum and maximum values for the sample
(control limits) and the mid point of the control limits range.
If the test result for the control sample falls outside or near
the minimum or maximum value of the control limits, the impact
machine shall be checked and adjusted if necessary to assure that
the platform for the anvil is level and the guide rails for the
drop weight is upright. Drop height is also checked periodically
with a vertical weighed line to ensure that the impact machine is
upright. Drop tests with carbon paper for determination of
points of impact shall be conducted, and impact machine shall be
adjusted as required.
4.7.8.4 Holston impact sensitivity. The Holston impact
sensitivity of RDX shall be determined using a Holston impact
machine.
4.7.8.4.1 Holston short impact method. Pass a dry sample
of RDX through a sample splitter or roll and quarter on glazed
paper until a representative sample of about 5 grams is obtained.
Position 13 brass percussion caps (0.303 inch diameter and 0.20
inch in height) with open end up on a flat surface. Fill a 0.025
g loading spoon with RDX, remove the excess material by passing
the flat edge of a wooden spatula across flat surface of the
spoon and transfer the portion remaining in the spoon to one of
the percussion caps. Repeat the RDX loading procedure until all
of the percussion caps are loaded. Be sure the RDX is evenly
distributed in each of the percussion caps. Turn on the exhaust
fan in order to remove the dust and fumes from the impact machine
enclosure. Using laboratory tongs place a loaded percussion cap
on the anvil of the impact machine. Insert a plunger through the
guide hole above the anvil and into the open end of the
percussion cap. Turn the electromagnet power switch on. Turn
the gear handle until the base of the lower electromagnet arm
coincides with the 33 cm mark on the right guide bar. Lower the
safety shield and lift the weight vertically until it is held in
place by the electromagnet. Face the opposite direction of the
impact machine and turn the electromagnet switch to the OFF
position allowing the weight to fall and strike the plunger.
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