Page 3 - us2869463

2,869,463
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The internal structure of the cartridge is comprised of preferred form, that the delay train is made up of a
four parts, usually made of brass, and assembled in order series of layers or pellets, each of which is less in thick-
from firing to discharge end,..and illustrated in perspective ness (in the direction of fire travel) than in its trans-
in Figure 2, as follows: a ·spacer 18 enclosing a shock verse dimension. Thus, in~the embodiment of Figure 1,
chamber 19; a support screen 20 for supporting a delay 5 each of the cylindrical pellets 31 to 36 has an axial thick-
train 21 comprised of a column of pellets of slow burn- ness less than its diameter. This structural arrangement
ing material; a delay tube 22 for housing the delay train has been found to produce more reliable cartridges since
21; and a propellant cup 23 used to contain the propel- the consolidation pressure applied to each layer during
lant 24, which delivers the output energy when dis- manufacture can be more effective, and the delay train
charged. Preferably, a moisture proof varnish is applied 10 so constructed seems to survive vibration and firing better
around the edges of the primer capsule 16 and flano-e 15 by virtue of it.
at 25 and 26 to provide a seal. "' The delay train 21 may be manufactured by introduc-
As seen in Figure 1, the assembly provides an enclosed ing powder for each successive layer into the delay tube
burning path from the primer 16 to the propellant 24. A 22 as powder and consolidating each layer under pres-
small concentric )101~ 27 in the base 11 provides an open 15 sure. However, it is a preferred method of fabricating
passage commumcatmg between the primer and the shock the cartridge to make up each layer as a pre-consolidated
chamber 19. The volume of the chamber 19 is enlarged pellet, assemble the pellets in the delay tube 22, and
?Y holes 23 in spacer rn and by the space between the reconsolidate the entire delay train 21 on a ram. An-
mner wall of the case :rn and the outer walls of the spacer other feature of the pelletized construction illustrated in
and the d lay tube 22. The annular inter-wall space may 20 Figure 1 is that several of the pellets are formed with
7
be a considerable percentage of the total shock absorbing mating recesses and projections on their adjacent faces
volume .since both spacer 18 and delay tube 22 ordi- so as to increase the strength of the delay train column.
na~ily are made to fit rather Ioosely into the case 10. The consolidation pressures most successfully used have
T_h1s volume may be further increased by reducing the been in the range of 20,000 to 50,000 pounds per square
2
diameter of the delay tube 22 for part of its length near 5 inch. However, density can be slightly increased by
the firing end as indicated at 29. The reduced diameter pressures up to 100,000 pounds per square inch if timing
29 also facilitates assembly since it avoids binding be- of the delay train requires it.
tween the delay tube and the case HI as a result of the Another method of manufacture is to load the :first :fire
draft taper normally produced in shell casings by the and after :fire as powder, and the time delay powder in
forming dies. 3 o pellet form and then consolidate the delay train.
The support screen .20 in cartridges of the .38 caliber In most cases, pelletizing at least the delay powder
size is preferably about twenty mesh and woven of wire will be found desirable in order to reduce the tendency
about .016" diameter. The screen must be of sufficient of the powder to pick up moisture from the air and
strength to support the delay train 21 during a great thereby become erratic in burning rate.
many hours of aircraft engine vibration and during :firing, 35 A delay train having a given time of burning can be
but must be porous enough to permit ready ignition of produced by properly selecting three variable factors: the
the delay train. ingredients and their proportions in the delay powder; the
The propellant cup 23 is provided with a hole 30 in length of the delay train in the direction of burning; and
its bottom to provide open communication between the the density to which the layers or pellets of the delay
discharge end of the delay train 21 and the propellant 24. 40 train are consolidated under pressure. The column·
When the cartridge of Figures 1 and 2 is fired by length is the major manufacturing variable. It will gen-
striking the percussion primer capsule 16, the primer erally be fourid most practical to select a preferred delay
explosion bursts the capsule at the hole 27 and fills the powder composition, a standard consolidation pressur~,
shock chamber 19 with hot gases. The pressure within 45 and then varying time delay by drilling the delay tram
the shock chamber suddenly rises, but the chamber column to a predetermined length in the delay tube, and
muffles the shock of the explosion to some degree and :filling up the remaining space with afterfire powder.
prevents it from damaging or altering appreciably the Using this method of manufacture, and selecting spacer
time characteristic of the delay train 21. and delay tube lengths as required, it has been found
The hot gases produced by the primer expl'osion pene- 50 comparatively simple to manufacture cartridges having
trate the support screen 20 and ignite the firing end of the any desired time delay between ¾ of a second and five
delay train 21. The delay train illustrated in Figure 1 is seconds in a standard .38 caliber case, or any time delay
comprised of a first fire pellet 31 which ignites readily between five and eight seconds in a long case ( 1.07'' over-
and quickly and reliably initiates burning of a series of all length). Of course, it will be understood that ?ev-
four pellets of time delay powder 32 to 35. After these 55 eral experimental runs must be made for each combma-
four have been consumed one by one in turn, an after- tion of variables in order to properly select manufac-
fire pellet 36 is ignited by the :final burning of the last turing standards to produce a desired time delay. ·
time delay pellet 35, and produces heat and combustion The preferred propellant is a double base powder of
products which pass through the hole 30 and detonate nitroglycerine colloided with nitrocellulose, such as the
the propellant 24. 60 Hercules Powder Company's "Unique" brand. However,
The powders of pellets 31 to 36 are ordinarily referred nitrocellulose alone can be used. Preferably, the propel-
to as "gasless" since they are supposed to burn solely lant powder is :finely divided with a maximum of surface
by the transfer of oxygen between solids and without the area, for example by slicing extruded rods of the material
evolution of any gaseous combustion products. How- into small discs about .002" or .007" thick and about
ever, some gas is inevitably produced by unavoidable or- 65 .030" in diameter. In the typical delay cartridge of the
ganic impurities, and it is a second important function of .38 caliber size,. the propellant work output is about 35
the shock chamber 19 to contain these gaseous combus- to 50 foot pounds, sufficient to move a small piston about
tion products within the case 10 during combustion of .35" in diameter through a stroke of about 2½" against
the delay train 21 without an excessive pressure rise, a 200 pound dead load.
which might introduce unpredictable variations in the 70 The embodiment of Figure 3 illustrates two variants
time delay. It will be understood that the chamber 19 from the cartridge of Figure 1. A cartridge 37 is shown
might be filled with some structural aid having many fragmentarily since it differs from Figure 1 only in the
open spaces and interstices and still be "empty" in the primer arrangement and in-the discharge end. Instead of
sense of providing space for gas. being fired by percussion as in the cartridge of Figure 1,
It is an important feature of the invention, in its 7o the cartridge 37 is fired electrically. The primer pellet