Heat transfer initiator

Details Heat transfer initiator Heat transfer initiator

2001-08-20

2003-04-01

Jordan, Charles T. (Department: 3641)

Ammunition and explosives

Igniting devices and systems

Fuse cord

C102S205000

Reexamination Certificate

active

06539869

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to heat transfer initiators for propellant, pyrotechnic, and explosive devices. In particular, the present invention is directed to initiators that utilize heat transfer to ignite an non-detonating autoignition material to act as a thermal switch to reliably and precisely control the time to function of propellant, pyrotechnic, and explosive devices, and may also be used to reliably and precisely control the time to function of such devices. The initiators of the present invention are particularly useful as through-bulkhead initiators.
BACKGROUND OF THE INVENTION
Various initiators that are actuated by a pyrotechnic, electronic, or mechanical input are known in the art for the control of the function of propellant, pyrotechnic, and explosive devices. Initiators are used in a variety of applications, including, but not limited to, passive vehicular safety systems, fire suppression systems, rockets, and munitions. When actuated, the initiator provides a thermal output, typically, in the form of heat, hot gas, hot particulates, and/or flame. Actuation of a prior art initiator is typically achieved electrically, or mechanically.
In many applications, where a reliable electrical actuation signal is available, such as in vehicular air bag systems, a pyrotechnic squib may be used as an initiator. Pyrotechnic squibs such as those disclosed in U.S. Pat. No. 6,168,202 to Stevens, are well known in the art. A typical pyrotechnic squib includes a pair of electrical leads, connected by a bridge wire, which is in thermal contact with an ignition composition. Passing an electrical signal through the electrical leads and the bridge wire, heats the bridge wire, and ignites the ignition composition. The thermal output from the reaction or combustion of the ignition compound ignites a pyrotechnic material within the squib that provides the desired thermal output used to initiate function of a main propellant, pyrotechnic, or explosive charge. Pyrotechnic squibs will only function properly in applications where an electrical actuation signal is reliably available.
A mechanically actuated initiator is disclosed in U.S. Pat. No. 5,913,807 to Bak. The disclosed initiator uses a percussion primer, of the type used in bullets, which, when struck ignites a second charge that provides the desired thermal output. However, such mechanical actuation systems can be complicated and unreliable.
U.S. Pat. No. 3,945,322 to Carlson et al. discloses a through-bulkhead initiator for causing an explosion on one side of a bulkhead by initiating an explosion on the other side of the bulkhead, and transmitting the shock wave from the first explosion through the bulkhead. However, the use of an explosion and the resulting shockwave may be undesirable in many applications where the explosion and shockwave can damage equipment, or where an output of heat and/or flame is required.
Similarly, U.S. Pat. No. 4,503,773 discloses a through bulkhead initiator for use with a rocket motor. The initiator consists of a thin metal bulkhead with a small explosive charge on either side of the bulkhead. The first explosive charge is detonated by a confined detonating fuse, producing a shock wave that passed through the bulkhead without breaking the bulkhead. The shock wave then detonates the second explosive charge on the other side of the bulkhead, initiating combustion of a flame output charge.
Pyrotechnic, electronic, and mechanical initiators that control the time to function of propellant, pyrotechnic, and explosive devices are known as delays, and are frequently used to control functions of munitions, such as self-destruct and self-disable, and the propellant ignition time of a rocket or rocket assisted projectile, where the timing of the ignition of the propellant is critical in achieving maximum range. Pyrotechnic initiators that provide a delay time generally rely on the controlled burning of a pyrotechnic material, acting essentially as a fuse, such that the length of the column of pyrotechnic material and the burning rate of the material determine the time of the delay. That is, the delay time is the time between the ignition of the pyrotechnic column and the ignition of the propellant, pyrotechnic, and explosive device by the heat and/or flame output generated by the combustion of the pyrotechnic column. For example, in a projectile having a range extending propellant, the initial end of a pyrotechnic delay column/ignition train is ignited as the shell is fired. The range extending propellant grain is then ignited by the heat and/or flame output of the pyrotechnic delay column/ignition train when the burning portion of the delay column/ignition train reaches the propellant. The delay time is then the time between the ignition of the pyrotechnic delay column/ignition train and the ignition of the range extending propellant grain by the output of the pyrotechnic delay column/ignition train.
Such pyrotechnic initiators that provide delays typically require a rapid burn rate for reliability. Slower burning pyrotechnics are harder to ignite than fast burning pyrotechnics, and, typically, do not burn at a constant rate. Therefore, the delay time of slow burning pyrotechnics is less reliable than faster burning pyrotechnic delays, and reliable longer delay times are not easily obtained.
Control of the delay time of reliable, fast burning pyrotechnic delays is achieved by determining the burn rate of the pyrotechnic material and the length of pyrotechnic material that is needed to burn for the required time. As a result, the use of pyrotechnic delays in timing munition events is primarily limited by the space requirements of the munition, i.e., by the length of the column that will fit in the munition. Therefore, extended delay times are difficult to achieve because of the excessive length of pyrotechnic material required and/or the need for a slow burning pyrotechnic material. Typical size limitations for pyrotechnic delays using burn rate and column length to control the delay are driven by a nominal lower burn rate of about 0.1 inch (2.5 mm) per second for pyrotechnic columns having a cross section of about ⅛ inch (3 mm) for columns up to about ⅜ inch (9.1 mm), with cross-sections of about ¼ inch (6.4 mm) for longer columns. The burn rate, heat loss, and column cross section are all closely interrelated, and, thus, the column must be carefully tailored to obtain reliable performance at or near the limits described above.
Electronic delays are typically used in situations where pyrotechnic delays are inadequate. The requirements for the self-destruction of munitions dictates long delay times, i.e., in excess of 30 seconds. For long delay times, electronic delay mechanisms are typically utilized because pyrotechnics cannot provide the delay time required within the packaging constraints. For time delays greater than 30 seconds, electronic delays offer greater packaging efficiency than pyrotechnic delays, but at a significant cost premium. In addition, electronic delays are much less durable than pyrotechnic delays, being comparatively fragile and, thus, susceptible to damage by the high acceleration or “g” loading experienced when the projectile is fired or the munition is launched or ejected.
Mechanical delays are less common for timing munitions because of their poor reliability. In particular, pre-wound spring mechanisms fatigue over time, and complex winding or other energizing mechanisms are inherently less reliable.
Although unique pyrotechnic initiators that utilize heat transfer through various media to provide a thermal output with a short delay time, i.e., less than about 0.5 seconds, are known in the art, there is no known disclosure of pyrotechnic initiators having a non-detonating thermal output that are capable of providing a reliable delay time of greater than 0.5 seconds. For example, U.S. Pat. No. 2,506,157 to Loret discloses a delay action blasting cap that allows a series of blasting caps to be produced having delays that differ one f

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