US3439617A

US3439617A - Igniter safe and arm

Info

Publication number: US3439617A
Application number: US607559A
Authority: US
Inventors: Aubrey B Boyd; Jarod L Baugh
Original assignee: North American Rockwell Corp
Current assignee: Boeing North American Inc
Priority date: 1967-01-05
Filing date: 1967-01-05
Publication date: 1969-04-22
Anticipated expiration: 1986-04-22

Description

IGNITER SAFE AND ARM Filed Jan. 5, 1567 INVENTORS. 405/967/5 50X@ BY 734,600 5406+/ United States Patent 3,439,617 IGNITER SAFE AND ARM Aubrey B. Boyd, Littleton, Colo., and Jarod L. Baugh, Loveland, Ohio, assignors to North American Rockwell Corporation, a corporation of Delaware Filed Jan. 5, 1967, Ser. No. 607,559 Int. Cl. F42c 15/00 U.S. Cl. M12- 70.2 3 Claims ABSTRACT 0F THE DISCLOSURE A safe and arm device for solid propellant igniters having a housing in which is disposed shock detonating material. Fuses leading to the igniter are xedly held in the housing adjacent the detonating material with a perforated rotor disposed between the fuses and the detonating material.

This invention relates to a safe and arm device. More particularly, the invention relates to a device for utilization with an igniter for solid propellant motors which is used as a safe and arm.

The present invention, relating to an igniter safe and arm, has particular use for the type of igniter disclosed in copending application Ser. No. 469,973 filed June 30, 1965, now abandoned. In the copending application, an igniter is disclosed formed of a mesh screen having attached thereto and wrapped about strands of explosive fuse material such as Pyrocore. The screen is then coated with a combustible mixture. Upon ignition of the Pyrocore, the combustible material and screen were ignited causing virtually instantaneous combustion of the entire igniter. The initial ignition of the igniter transpires from the igniting of the Pyrocore leads which extend from the igniter body. As with most igniters, it is imperative that the Pyrocore be prevented from accidental ignition prior to the desired set time. Thus, a safe and arm device is mandatory for the successful operation of the igniter.

Previous proposed concepts for safe and arm devices for remote ignition for the type of igniter described utilized devices where the charge for igniting the fuse material was in a rotor and thus subjected to rotary movement from a safe to an arm position. The mechanical arrangement of the previous devices has been quite complex and such devices have not been easily adaptable for placement outside of the motor case. Another disadvantage of prior art devices is that normally the electrical detonator is disposed in a line with the fuse, thus extending the axial length of the device.

Thus, it is an object of this invention to provide a simple safe and arm device for ignition of solid propellant igniters.

Another object of this invention is to provide a safe and arm device having a minimum of Working parts.

Still another object of this invention is to provide a safe and arm igniter device wherein no additional boost charge is present in the rotor.

The above and other objects of the invention will become apparent in the following description.

The device of this invention comprises an outer shell housing electrical detonators. Mounted on the shell is an electrical conductor for conducting current to the detonators within the shell. Means are provided in the shell or housing for permanently afxing the ends of the fuses which lead to the igniter. The ends of the fuses are affixed to shock sensitive detonating material and are circumferentally disposed adjacent the radially oriented electrical detonators. Disposed between the ends of the fuses and the electrical detonators is a rotor element having apertures there/ln corresponding to the number of fuses. In a safe position, the rotor is disposed so as to block passage of ICC shook energy from the electrical detonators if prematurely set off to the ends of the fuses. In an arm position, the rotor is rotated so as to align the apertures with the end of the fuses and electrical detonators such that when detonations occurs in the electrical detonator, the shock force will pass through the aperture to the fuses. Itis believed the invention will be better understood with regard to the following detailed description in which:

The figure is a cross-sectional View of the safe and arm device of the invention.

Referring to the figure, there is shown a safe and arm device 11 of this invention mounted on a forward case head 13 of a solid rocket motor. 'Such a location outside of the forward case head is a usual location for safe and arm devices in that it provides easy access for the arming of the motor, and is normally the shortest distance between the safe and arm device and the igniter which is normally disposed at the front end of the solid propellant grain. In this particular example, two pyrotechnic fuses 15 are shown which lead from the safe and arm device to the igniter for the solid propellant motor. Through-hole bodies 17 are integrally welded at their bases 19 to the motor case head and extend forwardly therefrom. Through the center 18 of these bodies 17 pass the fuses 15. The pyrotechnic fuse 15 has an insulation material 21 about the center fuse element 23. As shown the fuse element 23 extends past the end of the insulation at point 25 and meets and is imbedded in a material 27 sensitive to shock waves. An example of the material 27 is lead Styphanate. The shock sensitive material 27 and the end of the insulated fuse 15 extending through the body 17 is enclosed by a sleeve 29 of, for example, brass or thin guilding metal, which is crimped at 31 about the fuse train 15 so as to prevent movement thereof through body 17. The end of the sleeve 29 is flanged 33 and is enclosed by a nut retainer 35, which is in threaded engagement with the through-hole body 17. To ensure a tight fit, Oring seals 37 can be disposed in the body 17 adjacent the flanged end 33. The foregoing arrangement thus provides for securing the fuse in a fixed relationship outside of the motor case. Additionally the foregoing arrangement provides for securing in a fixed relationship the fuse to a shock detonating material which will eventually .cause the ultimate detonation of the fuse in rocket motor.

In the initial assembly of the device, a longer than necessary length of the insulated pyrotechnic fuse 15 is inserted through the body 17 so the forward case head 13 is moved forward for installation onto the main motor case. The insulated fuse 15 is in a slight friction fit within aperture 18 of the body 17 and is pulled tight from the outside of the head 13 after the head is installed in the motor case until all slack is removed. The friction fit holds the fuse in place while trimming the end before slipping the flanged sleeve assembly 29 onto the fuse and crimping it in place. The O-ring seal 37 is inserted in the end of the body 17 before the uncrimped flanged end 33 of the sleeve assembly is slipped onto the trimmed fuse. The nut retainer ring 35 or other suitable retaining device is then installed to lock the flanged end sleeve 29 in place.

After the previously described install-ation, the cylindrical housing 39 containing the electric detonator and rotor assembly is secured over the exposed fuse ends to the case head 13 by bolts 41. A seal 42 between the housing and the motor case prevents moisture and the like from entering the housing. Mounted on the shell 39 is an electrical connector 43 which serves to connect pairs of

leads

45 and 47 extending therefrom to 'an external battery source (not shown). Within the shall 39 the first pair of wires 45 affixed to the connector 43 pass through an electrical potting insulation 49 made of material such as silicone which serves to hold the wires in place and prevent any movement during the vibration of the motor prior to liring. Secured by screws 51 to shell 39 adjacent the potting composition 49 is an electric detonator assembly 53. The electric detonator assembly 53 is comprised of a metal outer shell 55. The electrical potting composition 56 serves to bond the wires 45 in place as they pass through the shell and insulate the material therein. A wire bridge 57 connects the leads 45 and is imbedded in a composition known in the art as the bead 59 which is sensitive and is detonated by heat. An example of such material 59 is lead styphanate. The layer adjacent the bead 59 and within the ceramic enclosure is the sustaining charge 61 which is of a material that is less sensitive than the bead and can be of boron-potassium nitrate composition.

As can be appreciated, the leads 45 with the bridge 57 therebetween are permanently affixed to and extend from the electric detonator body and are of sufficient length to pass through the potting composition 49 to the electrical connector 43. As shown a second pair of leads 47 pass through the potting composition 49 to a second potting composition 180 from the rst described assembly to a second potting composition 63 where the leads are connected to a second electrical detonator 65 disposed adjacent the other fuse in the shell. As is apparent, as many electrical detonators are used in the invention as the number of fuses require, there being one detonator per fuse. Thus, the device is arranged so that the electrical detonators are adjacent the crimped end of the fuses. Disposed between the crimped end of the fuse and the electrical detonator body is a rotor 67 which has a fiat base portion 69 and perpendicular extending side 71 that pass between the electrical detonator 53 and hanged sleeve assembly 31. An extension 72 of the base 69 of the rotor extends through the shell 39 to a rotor arm 73 mounted outside of the shell. To prevent any leakage of air or atmosphere into the housing, an O-ring seal 75 can be inserted in the portion of the extension 72 that extends through the shell. As shown in the drawing, the rotor is in the armed position wherein the apertures 76 in the wall 71 are aligned with the sleeve assembly 31 and electrical detonator 53. In this particular device, two such apertures would be provided, one for each fuse 180 apart. The number of apertures would always correspond to the number of fuses and detonators.

In operation, the rotor 67 is rotated manually by moving arm 73, or electrically if arm 73 is connected to a suitable means, from a safe position where there are no through-holes between the anged end sleeve assembly and the electrical detonator to an armed position as shown in th ligure where the through-holes are between the primer end and the electrical detonator. Upon command an electrical current through the electrical connector 43 activates an electrical detonator 53. The activation is caused by the current passing through the bridge 57 warming the material 59 to its ignition point detonating it and in turn detonating the sustaining charge 61.

This causes a significant shock force which passes through the apertures 76 in the rotor to the primer material 27 which is sensitive to such shock force, detonating this material, which in turn detonates fuse end 25 carrying such detonation to the main igniter.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. A safe and arming device for a combustible charge, comprising;

a support structure,

a fuse connected to the support structure,

a detonator positioned in xed relationship with one end of the fuse, the detonator being separated from said fuse end by a space defining a portion of the detonating path,

a rotor rotatably connected to the support structure,

an annular wall connected to the rotor extending parallel to the axis of rotation, the wall dening a hollow cavity in which said fuse end is disposed,

means in the wall forming an opening having an arcuate path of movement intersecting the detonating path,

whereby when the device is in its safe position the opening is misaligned with the detonating path and when the device is in its armed position the opening is aligned with the detonating path.

2. The device according to claim 1 wherein;

at least two detonators and two fuses are provided constituting at least two detonating paths,

the support structure is a housing that encloses the detonators and fuse ends,

a control is connected to the rotor and extends outside the housing, and,

the wall includes at least two openings that are simultaneously moveable into alignment with respective detonator paths.

3. The device according to claim 2 wherein;

the fuses are attached to shock sensitive material, and,

the detonators generate shock waves to ignite the fuses when the openings are aligned with their respective detonating paths.

References Cited UNITED STATES PATENTS SAMUEL FEINBERG, Primary Examiner. GERALD H. GLANZMAN, Assistant Examiner,