ELECTRICALLY DETONATED EXPLOSIVE SQUIBS

Abstract: An electrically detonated explosive squib for a fire extinguisher head comprises a rigid plastics cap (5) threaded to a rigid plastics body (3), with an O-ring seal (22) interposed between the cap and body. A chamber (7) defined between the cap and body contains explosive powder (9) and a fuse head (11). The construction provides an effective seal for the chamber (7) which prevents penetration of moisture into the chamber even with rapid pressure changes as may be encountered with high flying military aircraft.

Description: ELECTRICALLY DETONATED EXPLOSIVE SOUTHS The present invention relates to electrically detonated explosive squibs and more particularly to explosive squibs for use in fire extinguisher heads. Fire extinguisher heads incorporating an explosive squib include a plug which seals extinguishant under high pressure within the body of the extinguisher. Upon actuation of the squib on receipt of an electric signal, a portion of the plug is sheared to permit release of extinguishant, normally within a few milliseconds. Fire extinguishers of this type are often incorporated in aircraft and military vehicles. Traditionally, explosive squibs have been constructed so that an insulating soft rubber sleeve encapsulates both the explosive powder and fuse end of the main body. An outer sleeve, generally a brass pressing, fits over the insulating inner sleeve and a rolling operation is performed which seals an internal O-ring onto the mid-section of the body. A second sealing operation at the connector pin end of the body comprises of soldering the outer case to a ring rigidly attached to the body. A problem with this form of squib is that at rapid altitude (and hence pressure) changes as may be encountered in high flying aircraft, particularly military aircraft, inadequate sealing allows moisture to penetrate into the interior of the fuse, rendering the explosive powder ineffective. A further difficulty with traditional squibs is that on firing, the gas pressure within the outer sleeve increases rapidly, permanently distorting the outer sleeve. Consequently, it is very difficult to remove an exhausted squib from a housing in which it is mounted. According to the present invention there is provided an electrically detonated explosive squib comprising a rigid plastics body, a rigid plastics cap projecting from one end portion of the body and defining therewith a. chamber containing an explosive charge and a fusehead, the cap being threadedly secured to the body, with sealing means compressively interposed between the cap and the body to provide an hermetic seal between the cap and the body. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is an end view of the explosive squib in accordance with the invention. Figure 2 is a sectional view -of the explosive squib along line A-A of Figure 1. Figure 3 is a part sectional view of the explosive squib fitted inside a cartridge body. The electrically detonated explosive squib 1 shown in the drawings comprises a rigid plastics body 3 of solid construction that can be threadedly secured to a rigid plastics cap 5. Preferably, the body and cap are each composed of an acetyl homopolymer such as that sold under the tradename "DELRIN". A chamber 7 defined by the plastics cap 5 and plastics body 3 contains explosive powder 9 and fuse heads 11 which are carried by the body 3. The fuse heads 11 are electrically connected to connector pins 13 by means of a connector strip 15 which extends through a passage in the body 3. A sealant 16 prevents entry of moisture into the chamber 7 from the remote end of the body via the connector assembly. The cap 5 has a tubular sidewall threaded at its inner end portion 18 for threaded engagement with the body 3. Beyond the inner end portion 18 the internal diameter of the side wall of the cap 5 is reduced, with an inclined transition surface 20 extending between the threaded inner end portion 18 and the remainder of the cap 5. An O-ring 22 is seated within a groove 24 axially beyond the screw thread on the body 3 and initially stands proud of the groove 24. When the cap 5 filled with explosive powder 9 is screwed onto the body 3 the O-ring 22 is compressed radially inwardly upon meeting the transition surface 20 and is retained in its compressed state by the reduced diameter portion of the cap 5. The O-ring 22 thus provides an effective seal against ingress of moisture into the cap. The end wall of the cap 5 is of reduced thickness so that the cap preferentially shatters at the end wall when the charge is fired. The explosive squib 1 is fitted within a cartridge housing 26 (Figure 3) which is in turn fitted to a fire extinguisher head. The cap end of the squib projects into a chamber of the fire extinguisher head which includes the plug that seals pressurized extinguishant within the body of the extinguisher. A second O-ring seal 28 on the body 3 provides a friction fit between the cartridge housing 26 and the explosive squib 1. This friction fit prevents inadvertent dislodgement of the squib during installation of the cartridge housing 26 to the extinguisher head as may occur when the extinguisher is mounted within an area which is difficult to access. If the cartridge housing 26 were to be bolted to the head with the squib displaced, the squib may become jammed in the housing thus impeding its subsequent removal. O-ring seal 28 also ensures that after firing the squib will be maintained within the cartridge housing 26 and not left within the head of the fire extinguisher. The described construction of the electrically detonated explosive squib enables operation at higher altitudes because of the improved sealing of the explosive charge. Furthermore on detonation, the plastics body and plastics cap remain inflexible and do not permanently distort. Thus the likelihood of the body jamming in the cartridge housing is severely reduced. The embodiment has been described by way of example only and modifications are possible within the scope of the invention.

Claims: CLAIMS : - 1. An electrically detonated explosive squib comprising a rigid plastics body, a rigid plastics cap projecting from one end portion of the body and defining therewith a chamber containing an explosive charge and a fusehead, the cap being threadedly secured to the body, with sealing means compressively interposed between the cap and the body to provide an hermetic seal between the cap and the body. 2. An explosive squib according to Claim 1, wherein the cap comprises a tubular wall having a closure at its inner end, the tubular wall including an internally-threaded portion at its inner end for engagement with an external thread on the body, said wall having axially outwardly of the threaded portion, an internal surface of a smaller diameter than that of the threaded portion, said sealing means being interposed between said smaller diameter internal surface and an adjacent portion of the body. 3. An explosive squib according to Claim 2, wherein the sealing means is an O-ring retained within a groove formed in the adjacent portion of the body. 4. An explosive squib according to Claim 3, wherein the wall of the cap includes an inclined transition surface extending between the threaded portion and the smaller diameter internal surface, said O-ring prior to application of the cap to the body having an external diameter less than the internal diameter of the internally threaded portion of the cap and greater than that of the smaller diameter internal surface whereby initial compression of the O-ring is effected by the transition surface as the cap is screwed onto the body. 5. An explosive squib according to any one of Claims 1 to 4, wherein the body is a solid body which mounts the fusehead at one end, the body including a passage through which electrical connection means extends from the fusehead to a connector at the opposite end of the body, the passage being sealed against ingress of moisture into the chamber from the said opposite end of the body. 6. An explosive squib according to Claim 1, wherein the body is a solid body and the cap comprises a tubular wall having at its inner end portion a thread for engagement with the body, a closure at the outer end of the body, the closure being a wall integral with the tubular wall. 7. An explosive squib according to any one of Claims 2 to 6, wherein the cap closure is weakened relative to the tubular wall of the cap whereby the cap preferentially shatters at the closure upon firing of the charge. 8. An explosive squib according to any one of Claims 1 to 7 in combination with a cartridge housing for mounting the squib to a fire extinguisher head, the squib being a friction fit within the housing whereby to prevent d i splacement of the squib during attachment of the housing of the fire extinguisher head.

Inventors: MCCULLOCH ALISTER LESLIE, MCCULLOCH, ALISTER, LESLIE
Applicants: MCCULLOCH ALISTER LESLIE, MCCULLOCH, ALISTER, LESLIE
Application year: 1989
Main classification: A62C35
IPC codes: A62C37, F42B3