Patent Grant
8042471
The present disclosure relates generally to safe and arm devices for explosives.
Safe and Arm (S&A) devices are used to prevent an explosive device's main charge from inadvertently detonating, e.g., while stored or handled. These devices allow the explosive to detonate when desired or intended, e.g., when delivered to a target.
Two military specifications set forth standards that relate to fusing: Mil-Std-1316 for fuses; Mil-Std-1455 for dispensed projectiles and submunitions. These specifications include the following standards:
Three known types of S&A devices make use of sliders, rotors, and shutters. A physical barrier (e.g., metal) separates a primary explosive from a secondary explosive in an explosive device. These devices can take up more than three times the amount of space as the explosive material's transfer diameter. The transfer diameter is the minimum diameter needed in intimate contact between primary explosive and secondary explosive to achieve a reliable detonation transfer from primary explosive to secondary explosive. For example, the transfer diameter for typical explosives is 0.11 inches. A rotor that eccentrically turns a primary material to be inline with the secondary would need to be about 0.375 inches in diameter to swing a 0.125 inch diameter in line.
A set back and spin S&A device can be used in gun rounds. For example, an artillery gun round S&A can use set back as environment 1. The set back environment pulls a pin out of a plate mounted eccentrically on a shaft. Removal of the set back pin allows the plate to rotate about the shaft. The gun round is spun up by rifling in its barrel while the set back is present, so the eccentric plate can swing a primary in line with a secondary to arm the device.
An example of an artillery gun round fuse containing the S&A device is 2.5 inches in diameter. Unfortunately, if you scale down these S&A devices to a smaller diameter, they no longer work. The environments (accelerations) they use are still there, but the mass of the tiny pieces are so small they may not reliably overcome friction and springs to enable the armed condition. Also, the transfer diameter is scaled below a level where it will function reliably. The M758 fuse used with the 25 mm M242 gun is an example of an S&A device that works correctly for its specific size, but may not scale to operation at a smaller size.
An exemplary safe-and-arm device is disclosed for an explosive device, and comprises a delay housing including a primary explosive or a booster explosive at an output end, the delay housing movable from a first position to a second position, wherein in the first position the primary explosive or the booster explosive is at a no-fire separation distance from a secondary explosive and in the second position the primary explosive or the booster explosive is at a distance less than the no-fire separation distance from the secondary explosive, a restraining element positioning the delay housing at the first position, the restraining element breakable under an applied force, and a target sensor protruding radially from an outer surface of the explosive device and connected to the delay housing to break the restraining element and to move the delay housing from the first position under a force applied to the target sensor.
An exemplary explosive device comprises a delay housing movable from a safe position to an arm position, a target sensor protruding from the explosive device and connected to move the delay housing from the safe position toward the arm position under an applied force, and a restraining element positioning the delay housing at the safe position, the restraining element breakable under the applied force.
An exemplary explosive train for an explosive device comprises a primer activated by contact with a firing pin, a delay housing movable from a safe position to an arm position, wherein the delay housing includes a deflagration-to-detonation material that is initiated by the activated primer, a target sensor protruding radially from the explosive device and connected to move the delay housing from the safe position toward the arm position under a force applied to the target sensor, and a secondary explosive, wherein the secondary explosive is detonated by the initiated delay housing.
An exemplary method to safe and arm an explosive device including a delay housing including a primary explosive or a booster explosive at an output end, a target sensor protruding from an outer surface of the explosive device and a safing channel in an outer surface of the explosive device, the safing channel adapted to receive a target sensor of an adjacent explosive device when the adjacent target sensor is in a first position, comprises safing the explosive device by a safing method including restraining the delay housing at the first position by a restraining element, wherein in the first position the primary explosive or the booster explosive is at a no-fire separation distance from a secondary explosive, and mating the target sensor to a safing channel in an adjacent explosive device.
The following detailed description of preferred embodiments can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:
An exemplary embodiment of an explosive device with an exemplary embodiment of a S&A device is shown in
Cutting the explosive device in half reveals the interior components of the explosive device, as shown in isometric cross-sectional view in
The side view of the sectioned explosive device shows major components of the explosive device and an exemplary embodiment of a S&A device.
The exemplary embodiment of a S&A device 22 also comprises a restraining element 110, such as pin positioning the delay housing 102 at the first position I. The restraining element 110, such as for example a shear pin, is breakable under an applied force as discussed further below.
The exemplary embodiment of a S&A device also comprises a target sensor 24 protruding from the explosive device 10, either from the outer surface 26, the dart 30, or both. The target sensor 24 is connected to the delay housing 102 to break the restraining element 110 and to move the delay housing 102 from the first position I under a force applied to the target sensor 24. In exemplary embodiments, the target sensor 24 is a rod, bar or the like, but other suitable embodiments can include a bearing, a disk or portion of a disk or any other solid projection against which a force can be applied. Also, in exemplary embodiments, the target sensor 24 is protruding radially, but can also protrude off-axis or eccentrically. The target sensor 24 has material properties such that the restraining element 110 breaks allowing movement of the delay housing from the first position I before the target sensor 24 would break under the applied force. In operation, the target sensor 24 preferably does not break under the applied force, at least not until the delay housing has been moved to the second position II and the secondary explosive detonated.
The target sensor 24 can translate in any direction under the applied force such that it moves the delay housing 102 from the first position I toward the second position II. For example and as shown in, e.g.,
Also shown in
In exemplary embodiments, the primary explosive 104 is a stacked multilayer explosive including a primary material in the form of a deflagration-to-detonation material and a booster layer in the form of a keeper layer as an outermost layer. For example, exemplary embodiments include an injection moldable explosive as a keeper layer positioned as an outer layer of the stacked multilayer explosive. In another example, exemplary embodiments of the stacked multilayer explosive include PBXN-301 as an injection moldable explosive and DXN-1 as a deflagration-to-detonation material. A typical stacked multilayer explosive is shown in
The deflagration-to-detonation material operates such that material on its input side (e.g., facing a primer) begins burning extremely fast but subsonic, called deflagration. By the time the burning wave front reaches the output side (e.g., facing a secondary explosive), the burning wave front achieves supersonic velocities, called detonation, and has the ability to detonate a secondary material in close proximity to it. Often times a deflagration-to-detonation material is referred to as a primary material (distinguished from a primer). The delay time is variable, determined by free volume and thickness of the slow burn delay material (such as but not limited to lead salt).
In an exemplary embodiment, pressure generated by the output gas of the primer 124 can contribute to the applied force to break the restraining element 110. Upon being struck by the firing pin 122, the primer 124 outputs heat and pressure. This pressure pushes against a surface 128 of the delay housing 102 and attempts to move the delay housing 102 from the first position I. This pressure also pushes against a surface 129 of the primary explosive 104 and tends to push the primary explosive 104 (or one or more layers of a stacked multilayer explosive) out of its position and into the no-fire separation distance D. To address this potential problem and to increase the reliability of the S&A device, a retainer that can withstand this pressure can be used in connection with the primary explosive. The retainer can be, as an example, a pressed-in metal washer or similar piece. An exemplary embodiment of a retainer is described in connection with a primary explosive that includes a stacked multilayer explosive. Metal aft of the primary 144 or injection moldable material 146 is not safe as these materials are powerful enough to create small metal shrapnel and accelerate them across the no-fire separation distance possibly detonating the secondary explosive 34 by impact. However, metal aft of the cushion disk 140 or aft of the delay material 142 but before the primary explosive 144 or booster explosive 146 is safe as these materials do not typically accelerate metal objects into the no-fire separation distance possibly detonating secondary explosive 34 by impact. As long as the stacked multilayer explosive 104 and its retainer take the pressure load, the primary explosive and/or booster explosive do not need retainers.
In an exemplary embodiment, the S&A device includes a stored energy device. The stored energy device is optional in the S&A device.
In an exemplary embodiment, the stored energy device can return the explosive device to the safe mode when the arming condition is removed. Here, for example, removal of the applied force to the target sensor 24 can result in the stored energy device 130 moving the delay housing 102 toward the first position I under the biasing force.
In an exemplary embodiment, an optional locking device can be included in the S&A device to lock the delay housing in an other than safe mode position, e.g., other than the first position I. For example and as shown in
In
In exemplary embodiments, the no-fire separation distance D can be determined as follows. Consider the extremes of the separation distance between the primary explosive and/or the booster explosive and the surface of the secondary explosive when in safe mode. If the no-fire separation distance D were very large, say 100 feet in length, it is virtually impossible to transfer from the primary explosive/booster explosive to the secondary explosive. If the no-fire separation distance D were very small, say 0.002 inches, transfer from the primary explosive/booster explosive to the secondary explosive would occur quite reliably. Using the Intermediate Value Theorem in a broad sense, one can understand there must be some value for the no-fire separation distance at which transfer does not occur more often than 1 in 1 million times, which is the goal of the interrupter required by the specifications. It would not be practical to actually attempt to detonate 1 million explosive devices, but it is possible to determine the value of the no-fire separation distance by statistical methods. The process essentially starts with an arbitrarily determined value for the no-fire separation distance. It then shortens the no-fire separation distance until a transfer occasionally occurs. Once this threshold is known, the statistical system tests other values for the no-fire separation distance incrementally smaller and larger than the threshold no-fire separation distance and determines statistically what no-fire separation distance would result in 1 in 1 million transfers.
Using the above method to statistically determine a minimum distance between the primary explosive and/or the booster explosive and the secondary explosive to minimize transfer while in a safe mode, an exemplary embodiment of the no-fire separation distance is estimated to be about 0.030 to 0.25 inches, e.g., typical distances between primary explosives (such as but not limited to DXN-1)/booster explosives (such as but not limited to PBXN-301) and secondary explosives (such as but not limited to PBXN-5) across which the detonation event can be transferred is about 0.030 inches or less, alternatively about 0.025 inches or less. Further, in exemplary embodiments the distance less than the no-fire distance, e.g., distance d in
In a specific exemplary embodiment, the explosive device contacts the target and continues to travel through the target quickly (e.g., at 1000 ft/sec). For a 1.375 inch distance from retracted sleeve to fully moved target sensor and a no-fire distance of about 0.25 inches, the target sense legs hit the target at 94 μsec after the trigger event and break the pin holding the delay housing at position I, which allows the delay housing to move, e.g., move linearly aft along the projectile's longitudinal axis, toward position II. The no-fire separation distance has been reduced and the primary explosive and/or the booster explosive is in intimate contact with the secondary explosives after about 115 μsec. At the 300 μsec mark, the detonation in the primary explosive/booster explosive occurs and detonation is transferred to the secondary explosive.
To better understand the arming process, a discussion of both arming environments follows. Before moving to the armed mode, two arming environments are sensed by the S&A device.
The first environment is the dispense separation event, e.g., the dispensing and separation of a plurality of explosive devices.
In an exemplary embodiment, the relationship between safing channels and target sensors and the operability of sating channels and target sensors when placed in a dispenser with other explosive devices having the exemplary S&A device can help to prevent and/or minimize errant packing of explosive devices in the dispenser if the exemplary S&A device is not in the safe mode, e.g, in the armed mode or at an intermediate condition between the safe mode and the armed mode. For example, a nesting pin and groove technique can be employed. In this exemplary technique, consider the plurality of explosive devices, e.g., submunition projectiles 202 in a dispenser 204 in the illustrated example, as being in adjacent rows as illustrated in
One way to accommodate this nesting pin and groove technique is to position the safe-and-arm module 14 at a staggered position, as seen in
Once the explosive devices are released and after safe separation has occurred, explosive devices move away from one another on the way to the target, at which time the target sensors 24 are free to move aft on contact with a target. If the arming environment is taken back away, the S&A device returns to safe mode. In this case, that can be interpreted as being packed back into the dispenser, and the S&A device would go back to safe mode if this occurred.
The second arming environment is target sense.
In an exemplary embodiment of the disclosed S&A device, the mating primary and secondary surfaces maintain their integrity, e.g., packing and surface integrity, even under harsh freefall and vibrational environments. In general, explosives are pressed to close to 10,000 psi in an assembly and a flat face is generated at the future interfacing surfaces. A keeper layer, such as a cup, retainer, or foil keeper, can be used to prevent and/or minimize interface crumble and break down. It is not safe to have crumbled primary material or crumbled secondary explosive in and around moving parts. Typically, a layer of foil over the interface serves as a keeper layer. However, with a no-fire separation distance, such as an air gap, foil can be dangerous on the output end of the delay housing. Foil on the output end of the delay housing could be accelerated by the primary explosive across the no-fire separation distance at speeds sufficiently high enough to cause the secondary explosive to detonate on impact. The same problem could exist for screen or mesh employed as a keeper layer if they involve metal objects that could be created and accelerated. Exemplary embodiments of the S&A device can be tested in what is commonly called the “jumble” test, as outlined in Mil-Std-331 referenced from Mil-Std-1316, to evaluate the integrity of the primary and secondary surfaces under certain conditions. In this test, the S&A device is put in a wood lined box and turned at 30 rpm for 3600 revolutions to simulate harsh freefall and vibration environments. In the test, the explosive materials in the S&A device must not detonate during the test, but does not need to be functional after the jumble test.
To promote and enhance the integrity of the primary and secondary surfaces, the stacked multilayer explosive 104 utilizes, in exemplary embodiments, an injection moldable explosive (such as but not limited to PBXN-301) as a keeper layer. This explosive has a putty-like or formable plastic-like consistency. It is sometimes described as “explosive silicone”. A thin layer of PBXN-301 could be used to keep the primary material in place. This keeper layer of injection moldable explosive then ultimately transfers to the secondary explosive. On the secondary explosive side, standard explosive manufacturing processes can be used to put a foil keeper on the interface. In this example, only the stacked multilayer explosive 104 has potential of creating accelerated masses, so a foil cover is fine for the secondary explosive. The injection moldable explosive can easily transfer through a keeper layer covering the secondary explosive as long as the transfer faces are substantially intimate, meaning within 0.030 inches.
In an exemplary embodiment, a fire-then-arm sequence is used in which the explosive device is fired, e.g., ignition of the primary is started, and then the explosive device is armed, e.g., the S&A device is placed in the armed condition. An exemplary explosive device employing a fire-then-arm sequence can choose an appropriate delay, such as e.g., 300 μsec, to allow the bulk of the explosive device payload to enter the target before it detonates, but any desired delay time can be utilized. The exemplary arrangements in
Other exemplary embodiments can use an arm-then-fire sequence in which the explosive device is armed, e.g., the S&A device is placed in the armed condition and then the explosive device is fired, e.g., ignition of the primary explosive is started. An arm-then-fire sequence can be useful when minimum delay is desired between a triggering event and actual detonation of the explosive device. Exemplary embodiments of an arm-then-fire system would be useful when an explosive device needing no delay at all is used. In such an exemplary embodiment, the deflagration-to detonation material, e.g., DXN-1 and keeper layer, e.g., PBXN-301, could be right behind the primer and the exemplary embodiment can eliminate the free volume, cushion disk and lead salt from the explosive train.
In
The S&A device 320 has some features consistent with embodiments described herein. Exemplary embodiments include a delay housing 322 that is movable from first position I′ toward a second position II′. In the first position I′, a primary explosive or booster explosive is at an output end 326 of the delay housing 322 and is separated from the secondary explosive 330 by a no-fire separation distance D. In the second position II′, the separation distance between the primary explosive and/or the booster explosive and the secondary explosive 330 is less than the no-fire separation distance D. Other features, similar to those described herein with respect to
In contrast to the fire-then-arm embodiments, the exemplary embodiments shown in
When an optional stored energy device 360 is present, the force applied to move the delay housing 322 overcomes the optional stored energy device 360. As shown in
In the exemplary embodiment shown in
Also shown in
The S&A device described herein is practical at any size scale, including down to small diameters, e.g., less than 1 inch diameters, .35 (0.35 mm) caliber, preferably .25 (0.25 inches) caliber. In addition, the disclosed S&A device can be used in other size explosive devices, such as .44 caliber and .50 caliber munitions.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20100031841 A1 | Feb 2010 | US |
