Swivel type through bulkhead initiator

The acceptor charge is initiated from the side and the donor charge is contained in a full circle swivel assembly. This allows the initiator to be used where little head clearance is available and use, also, of the initiator to transmit a shock wave through a solid barrier or bulkhead to a relatively movable body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to pyrotechnic systems, and more particularly, to 
such systems in which an ignition reaction or shock wave is transmitted 
through a solid barrier or bulkhead to initiate explosive functions. Such 
systems have utility in igniters, gas generators, explosive devices, and 
actuators. 
2. Description of the Prior Art 
Through bulkhead initiators are known and used in the prior art in ordnance 
applications which have an explosive transfer line to initiate a 
pyrotechnic type of ordnance device. Such initiators accept an explosive 
signal from the ordnance transfer assembly and converts it to a hot gas 
output on the downstream side of a solid barrier or bulkhead. This barrier 
provides a pressure seal during operation of the ordnance item. The 
barrier or bulkhead must have the structural integrity to withstand both 
the detonation sequence and the operational pressure of the ordnance 
device and desirably, therefore, may be made of a material such as 
stainless steel. 
The initiation stimulus is transmitted through the sealed metal bulkhead 
through shock waves. The shock wave generated by detonation of the donor 
charge is transferred to the metal bulkhead and is propagated therethrough 
to an acceptor charge. The metal bulkhead is not structurally degraded by 
the passage of the shock wave. Sufficient energy is contained in the shock 
wave to cause a detonation reaction to the acceptor charge. This reaction 
is transmitted to an output charge where it is transformed into a 
deflagration reaction. 
The through bulkhead initiators of the prior art are characterized in being 
in-line, rigid systems which require considerable head clearance for 
installation. Thus, there has been a need for a through bulkhead initiator 
where little clearance is available. There has also been a need for such 
an initiator for transmitting a shock wave through a solid barrier or 
bulkhead to a relatively movable body, such, for example, as the gas 
generator of an airbag system mounted on an automobile steering wheel. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide, for initiating various explosive 
functions, a through bulkhead initiator characterized by low body height 
and having particular utility in ordnance applications where there is 
limited space. 
A further object of the invention is to provide a through bulkhead 
initiator wherein the acceptor charge is initiated from the side and the 
donor charge is contained in a full circle swivel assembly whereby the 
initiator is operable in applications having little head clearance to 
transmit a shock wave through a solid barrier or bulkhead to a relatively 
movable body. 
Another object of the invention is to provide such an improved through 
bulkhead initiator that provides a pressure seal during the operation of 
the ordnance item. 
In accomplishing these and other objectives of the invention, there is 
provided an improvement in through bulkhead initiators that incorporates a 
swivel action. This swivel action allows the initiator to be used where 
little head clearance is available. Novel features of the improved 
initiator include side initiation of the acceptor charge, the donor charge 
being contained in a full circle swivel assembly, and a low overall 
initiator height.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawing the through bulkhead initiator 10 of the invention is 
illustrated in conjunction with an end portion 12 of an ordnance transfer 
line 14 which forms part of an ordnance transfer assembly (not shown). The 
ordnance transfer line 14 comprises a confined detonating cord 16 
contained within and protected by a braided cover or shield 18. The end 
portion 12 has a confined detonating fuze 20 at its end and is provided 
with a protective cover 22 and with suitable attachment means for 
facilitating the attachment thereof to the input side, indicated generally 
at 24, of the through bulkhead initiator 10. Such attachment may be 
effected, as shown in the drawing by a flexible locking nut 26 and an 
adapter fitting 28 having first and second ends with a screw thread formed 
on each end. Thus, an internal screw thread on a first end 27 of the 
adapter fitting 28 is in engagement with an external thread on the 
flexible locking nut 26 and is operative to cause the locking nut 26 to 
squeeze and firmly retain therein the protective cover 22 and thereby the 
end portion 12 of the ordnance transmission line 14. The screw thread on 
the second end 29 of the adapter fitting is used to attach the end portion 
12 of line 14 to the input side 24 of initiator 10 in a manner described 
hereinafter. 
A donor charge 30 of Pentaerythritoltetranitrate (PETN) is provided in the 
open end 32 of the locking nut 26, adjacent the confined detonating fuze 
20. Other donor charge explosives such as hexanitrostilbene (HNS) and 
Hexogen (cyclonite) (RDX) can be used for the donor charge 30. The open 
end 32 of the locking nut 26, as shown in the drawing, extends somewhat 
beyond the end of the adapter fitting 28 when nut 26 and fitting 28 are in 
assembled operative relation, as shown. The donor charge 30 is sealed with 
a thin closure at the open end 32 of nut 26. This surface is in close 
proximity with a barrier 54 described hereinafter to insure efficient 
transmission of the explosive shock wave to a steel bulkhead barrier 68. 
The input side 24 of initiator 10 includes, as part of a full circle swivel 
assembly indicated at 34, a swivel sleeve 36 having a cylindrical bore or 
opening 38 therein that is arranged to receive for relative angular or 
swivelling movement a cylindrical portion or hub member 40 of an initiator 
body 42. Body 42, desirably, may be made of steel. A retaining ring 44 is 
provided, as shown, for retaining swivel sleeve 36 on initiator body 42. 
Disposed at a right angle to the axis of cylindrical opening 38 of sleeve 
36 and formed integrally therewith is a sleeve fitting 46 having an 
internal screw thread that is adapted to receive in threaded engagement 
therewith an external screw thread on the second end 29 of adapter fitting 
28. The arrangement is such that, when assembled, the end of flexible 
locking nut 26 is flush with the inner cylindrical surface 32 of the 
opening 38 of swivel sleeve 36. 
Formed in the initiator body 42 is a cavity 48. Cavity 48 includes 
communicating bores 50 and 52 having a common axis with the bore 52 being 
smaller in diameter and entending part way only through the hub member 40 
of the initiator body 42. There is thus formed at the upper end of hub 
member 40, as seen in the drawing, an end closure and sealing barrier 54 
for cavity 48. This barrier 54 together with the cylindrical walls of 
cavity 48 serve as a pressure seal for the ordnance device to be 
activated. A cylindrical wall 56 that is associated with bore 52 and 
swivel sleeve 36 desirably has a substantially uniform cross section. 
Contained within the bore 52 is an acceptor charge 58 of PETN. Other 
acceptor charge explosives such as HNS and RDX can be used for the 
acceptor charge 58. An ignition or output charge 60 of suitable explosive 
material is contained within bore 50, the output charge 60 being located 
adjacent to and in communication with the acceptor charge 58. An orifice 
plug 62 and closure plate 64 for the initiator body 42 may also be 
provided, as shown. Additionally, an attachment screw thread 66 may be 
provided on the lower end of body 42, as seen in the drawing, for 
attaching the initiator 10 to an ordnance device (not shown) to be 
activated. 
With the foregoing arrangement, the cylindrical wall 68 of uniform cross 
section comprises the barrier or bulkhead through which a shock wave 
generated by detonation of donor charge 30 is propagated to the acceptor 
charge 58. The wall 68 may be made of steel and is not structurally 
degraded by the passage therethrough of the shock wave. The energy 
contained in the shock wave causes a detonation reaction in the acceptor 
charge 58. This reaction is transmitted to the ignition or output charge 
60 where it is transformed into a deflagration reaction. 
Thus, there has been provided, according to the invention, an improved 
through bulkhead initiator 10 which has a low overall height and 
incorporates a swivel action to allow use of the initiator where little 
head clearance is available. Its novel features include side activation 
through the solid metal barrier or bulkhead, wall 68, with the donor 
charge 30 being contained in an assembly allowing the transmission of a 
shock wave through the solid barrier or bulkhead to a relatively movable 
body, and in particular, allowing a full circle swivel action while 
providing a pressure seal.