This invention relates to a dual safety time delayed fuze, useful, for example, in conventional grenades, and particularly to a biased barrier between the pyrotechnic delay charge and the fuze ignitor charge. The barrier contains a flash-hole which is normally held out of alignment with the fuze powder train by a barrier latch. Upon ignition of the delayed charge, a heat motor, activated by the burning of the charge, expands against the barrier latch, displacing it, thereby allowing the biasing element to drive the barrier flash-hole into alignment with the delay and the ignitor. The barrier flash-hole may optionally contain a lead charge to insure ignition of the fuze.
What is claimed and desired to be secured by
U.S. Letters Patent is
1. In a time-delay fuze having a pyrotechnic delay charge and an ignitor charge adjacently disposed in longitudinal alignment, the improvement comprising:
2. The device of claim 1 wherein the flash-hole of the barrier contains a lead charge.
3. The device of claim 2 wherein said lead charge is lead azide.
4. The device of claim 1 wherein said heat motor includes naphthalene.
5. The device of claim 1 wherein said heat motor comprises naphthalene with copper powder disbursed therethrough.
6. A time-delay fuze comprising:
7. The device of claim 6 wherein said latch means includes a longitudinally slidable stop disposed between an end of said barrier and the internal wall of said housing, said stop adapted to be displaced longitudinally by said heat expandable means when said means expands to permit lateral movement of said barrier from the first to the second position.
8. The device of claim 7 further comprising a longitudinally slidable piston disposed between said heat expandable means and said stop, abutting adjacent faces thereof; a second bias means disposed within said housing engaging said stop for urging said stop longitudinally against said piston and for retaining said stop in an abutting relationship with said piston.
9. The device of claim 8 wherein the heat-expandable means includes naphthalene and the piston means is a slidable seal.
10. The device of claim 9 wherein the heat-expandable means is a heat motor comprising a mixture of naphthalene and copper powder.
Various heat motors have been known and used in a variety of temperature responsive mechanisms, wherein a controlled expansion responsive to heat is required. The main application prior to this time has been in automobile thermostats.
Heat expansive elements used in munitions are typified by U.S. Pat. No. 2,937,596; wherein a heat expansive element enclosed in a bellows is allowed to expand with aerodynamic heating to drive electrical contacts together to complete the ignition circuit for a missile.
Movable barriers, which interrupt fuze powder trains to prevent premature arming, are also known. However, they are primarily utilized in impact detonating devices, such as, the fuze delay described in U.S. Pat. No. 3,313,236; wherein a first firing pin ignites a charge which burns through to release a biased barrier, which then aligns the powder train, arming the fuze for impact denotation by a second firing pin.
These devices are not applicable for use with small arms, such as grenades or incendiary devices wherein a small, extremely reliable time delay mechanism is required to detonate a charge.
Conventional grenades usually provide a single safety, which comprises a pin. When the pin is released, a striker ignites the primer which in turn ignites a pyrotechnic delay charge. The delay charge burns over a preselected period of time, directly to the ignitor to detonate the charge. If the delay is defective, it will burn too rapidly and detonate the fuze early. This could be a dangerous weapon for the user and an altogether undesirable fuze for general use.
Accordingly, it is an object of this invention to provide a dual safety time delay fuze for detonating grenades and other explosive charges.
It is another object to provide a dual safety fuze regularly adaptable for use in a conventional grenade.
It is a further object to provide a movable barrier disposed between a pyrotechnic delay and the ignitor in a conventional grenade which, after a preselected period of time displaces to align the fuze powder train for detonation.
It is yet another object to provide a heat motor which, responsive to the heat generated by the burning of the pyrotechnic delay element, expands to displace a barrier and align the fuze powder train for detonation.
It is still another object to provide an additional safety device for a time-delay fuze which includes a biased barrier disposed in the powder train of a conventional fuze and a heat motor which displaces the barrier to align the powder train only after a preselected amount of heat has been generated by the burning of a delay charge.
These an other objects will be readily apparent with reference to the following drawings and description wherein:
FIG. 1 is a cross-sectional view of a conventional grenade prior to arming, having the device of this invention incorporated in the fuze body; and
FIG. 2 is a cross-sectional view of the grenade of FIG. 1 after the pyrotechnic delay has burned a sufficient time to allow the device of this invention to arm the grenade.
As shown in the drawing, the device of this invention may be implemented within the body 10 of a conventional grenade fuze. In a grenade, the safety pin (not shown) releases a lever (not shown) disposed in mounting 11 which causes the primer 13 to ignite a pyrotechnic delay charge 15. However, in the preferred embodiment of this invention, there is disposed between the delay 15 and the ignitor 17, which detonates the grenade, a barrier 19. Barrier 19 has a normally out-of-alignment flash hole 21 and is held in place by the barrier latch 23.
Latch 23 is a hollow cylinder, having 2 slots which form lips 25 and 27. Lip 25 extends upwardly to normally hold barrier 19 out of alignment, as shown in FIG. 1, and lip 27 carries a leaf spring 29, which normally urges barrier 19 to the left into a position where flash hole 21 is aligned between delay 15 and ignitor 17, as shown in FIGURE 2.
A heat motor 31 in the form of a hollow cylinder is disposed within the fuze body 10 to surround the pyrotechnic delay charge 15. The heat motor 31 is separated from barrier latch 23 by a seal 33 which may be neoprene washer. Latch 23 is normally held against seal 33 by compression spring 35, which should exert a force in excess of 10 pounds per square inch on the barrier latch 23. This would be sufficient to prevent accidental arming due to transportation vibration or dropping. Spring 35 surrounds ignitor 17 and is held in place by hollow plug 37 in fuze body 10. Plug 37 is also disposed to surround the ignitor and may be held in place by a crimp 39 in the fuze body 10.
As delay 15 burns, heat motor 31 expands, driving latch 23 downwardly, depressing spring 35. When the latch 23 is driven down a distance corresponding to the extra height of lip 25, barrier spring 29 drives barrier 19 to the left, aligning flash hole 21 with the flash-hole 41 in the delay charged base plate 43.
The fuze is them armed, and when the delay charge terminates, a flash will be transmitted to detonate the ignitor 17 and the grenade. The terminal flash from delay charge 15 will be transmitted through holes 41 and 21 to ignitor 17. It may be desired to place a lead charge (not shown) in flash-hole 21 to insure transmission of the flash. This charge may be any conventional flash material, such as, lead azide.
The safety device of this invention may be designed to fit the standard fuze well 47 of a military grenade, as shown in the drawings. In this embodiment the pyrotechnic delay charge 15 and the ignitor 17 would be that used by the standard military fuze, designated M204. An example of a pyrotechnic delay charge capable of transmitting a flash through the barrier hole 21 would be a conventional manganese, barium chromate, lead chromate mixture.
The heat motor of this embodiment may be of the type that employs a principal of volume change when the component material changes state from a solid to a liquid. An example of such a material is naphthalene, although several others are well known. Naphthalene changes from solid to liquid at 175° F. A conductive metal such as copper powder may be mixed with the naphthalene to increase stability and sensitivity. The motor may also include inert filler material.
The heat motor should be designed to displace the barrier arming the fuze when 0.5 to 1.0 seconds burning time remains in the pyrotechnic delay charge, or after a minimum of 3 seconds burning time, when the M204 fuze-delay charge is used. The expansion characteristics of the naphthalene heat motor increase rapidly as the material is heated. Approximate values are as follows:
a. Solid state (under 166° F.) 67.1×10-5 cubic inches per cubic inch per °F.
b. Critical state (166° to 188° F.) 461×10-5 cubic inches per cubic inch per ° F.
c. Liquid state (over 188° F.) 45.2× 10-5 cubic inches per cubic inch per ° F.
This heat motor would develop an output in excess of 20 pounds per square inch, and would produce a barrier latch travel of approximately 0.10 inches when heated from 166° F. to 188° F. The latch travel distance must be enough to allow depression sufficient for barrier 19 to clear lip 25.
The above distance provides adequate travel even when the grenade is stored at approximately 165° F.
The device of this invention is particularly useful as a second safety for a time-delayed fuze. The heat motor is particularly adapted for use in cylindrical form in a fuze well and the heat characteristics of the standard M204 pyrotechnic delay charge are adequate to provide the necessary impetus to displace the barrier latch in a minimum of 3 seconds burning time.
It must be noted that the device of this invention is not limited to the design herein disclosed, or the materials of the preferred embodiment. Any conventional heat motor having characteristics of expansion similar to those above numerated may be adapted in the manner of this invention for use with a time delay fuze.
Likewise, the safety device of this invention could be used in any time delay fuze or in combination with a source of heat other than that disclosed. The device will accordingly be easily adapted to a variety of uses within the scope of this invention.
The invention as disclosed in the preferred embodiment may be used in a conventional military grenade to provide an inexpensive and reliable second safety, or in any other time delay mechanism adaptable to utilize a heat motor which displaces a latch for releasing a barrier for alignment of the powder train.