US 3638572 A
A delay train for an ordnance fuse having a body with two tandem chambers at the front end communicating via an axial bore with the main charge located in the rear end. A cup with an apertured bottom fits in the first of the tandem chambers and, except for the aperture, closes the second of the tandem chambers. A primer mix fills the cup and a delay composition fills the second chamber. Initiation of the primer mix by a firing pin is propagated via the cup aperture to the delay composition which reacts at a known slow rate, thus contributing the greater part of the time delay. Lead azide in the axial bore is initiated by the delay composition and, in turn, initiates a length of pyrocore along which the initiation is propagated to a main charge.
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Description (OCR text may contain errors)
United States Patent Menichelli 1 Feb. 1, 1972 154] DELAY TRAIN FOR ORDNANCE FUSE Primary Examiner-Benjamin A. Borchelt  inventor. glrrfent .I. Menieheiii Panorama City, mum Exammfl .rhomas H. Webb Attorney-R. S. Sciascia and J. A. Cooke  Assignee: The United States of America as represented by the Secretary 0! the Navy ABSTRACT  Filed; Feb. 18, 1969 A delay train for an ordnance fuse having a body with two tandem chamber: at the front end communicating via an axial PI N05 800,203 bore with the main charge located in the rear end. A cup with an apertured bottom fits in the first of the tandem chambers [52 us. Cl .102/75 l02/85 |02l86.5 Chm sewn [511 int. Cl. ..F42c 9/10 F42l; v04 F 42c 1910a chamber A P'imfir mix culP a Composifion  dd 0 Search j 85 86 5 fills the second chamber initiation of the primer mix by a firlng pin is propagated via the cup aperture to the delay composition which reacts at a known slow rate, thus contributing [s6] Rem-em cued the greater part of the time delay. Lead azide in the axial bore UNITED STATES PATENTS is initiated by the delay composition and, in turn, initiates a length of pyrocore along which the initiation is propagated to 1,369,476 2Il92l Semple ...lO2/75 a main charge. 2,441,248 5/l948 Morris et al. 102/865 3,i62,127 l2ll964 Breslow et al. 102/85 2 Claims, 1 Drawing Figure l4 zz-g PATENTEI] FEB I I972 INVENTOR Vincent J. Menichem' BY A RNIiY DELAY TRAIN FOR ORDNANCE FUSE BACKGROUND OF THE INVENTION This invention relates generally to ordnance fuses and more particularly to a millisecond delay train for a fuse providing for detonation after target penetration.
The destructiveness of projectiles fused by many presentday mechanically initiated fuses is limited because projectile detonation is effected on contact with the surface of a target. Since detonation within the interior of the target is vastly more destructive than surface detonation, various attempts have been made to impose a time delay between projectile impact and detonation.
Mechanical timing mechanisms have been used but are usually large and bulky and often incapable of consistently and reliably providing small time delays, such for example, as of 50 milliseconds. Moreover, they tend to be complicated, susceptible to mechanical failure and expensive. Electronic time delays are generally satisfactory for use with electrically initiated explosive devices, but not with mechanically initiated explosive devices.
Pyrotechnic delay trains have been employed in the past and have proved generally satisfactory in their particular applications in large ordnance such as rockets. In this application, a large, complicated, expensive delay train is satisfactory because the percentage contribution to the cost of the projectile is small. However, in small caliber ordnance which typically is expended in vast quantities, a large, complicated and expensive design is economically prohibitive. The particular requirements which the instant fuse was designed to satisfy precluded use of any of the known fuses and necessitated the research that culminated in this invention.
The requirement for a small, sturdy, inexpensive and reliable S-millisecond range delay train for a fuse arose because of the nature of the target and the nature of the projectile. It was found that in use against targets hidden in foliage or in buildings, a microsecond range delay known in the art did not permit sufi'lcient penetration and the detonation was premature. Also, the projectiles for which this fuse was designed were too small to accept existing fuses, and would accommodate only a very small fuse assembly. Further, the available SO-millisecond range delay fuses did not produce consistent delay times. Finally, existing fuses that might have been modified for the instant requirements were prohibitively expensive for use in small caliber ordnance.
One persistent problem encountered in the design of delay fuses is the baflle between the initiator or primer and the delay composition. The baffle must serve four functions. Firstly, it isolates the delay composition column from the brisance of the primer and prevents breakup agitation, voids, compaction and other undesirable disturbance to the desired density and distribution of the delay composition column. Secondly, the baffle prevents particles of the exploding primer from penetrating into the delay composition column. If a par ticle were to penetrate half the length of the delay composition column, for example, the delay imposed thereby would be efiectively cut in half since the reaction would begin halfway down the column. Thirdly, the nature of the delay composition which, although it is called gasless," in fact does produce a certain quantity of gas which, if not vented, will build up pressure and temperature in the delay composition chamber and unpredictably affect the rate of reaction of the delay composition. Moreover, the housing for the fuse would need to be strengthened to support the increased pressure, thus increasing the cost and weight. The fourth function of the baflle is to prevent the separation of the reacting front of the delay composition column from the unreacted remainder thereof. The reaction products are in the form of a frothy slag which, if not confined, would tend to expand away from the reacting material and actually cause a separation of the reacting front from the body of the material, thereby extinguishing the reaction.
SUMMARY OF THE INVENTION Accordingly an object of this invention is to provide a new and improved mechanically initiated, pyrotechnic, time delay for a fuse.
Another objective of the invention is to furnish a pyrotechnic fuse having a consistent and reliable delay in the millisecond range between initiation and detonation.
Yet another object of the present invention is to provide a novel pyrotechnic time delay for a fuse that is of a suitable size for use in relatively small caliber ordnance.
A still further object of the instant invention is to provide an improved unobturated pyrotechnic time-delay fuse with a simple design which is relatively inexpensive to produce.
Still another object of the invention is the provision of a rugged and dependable pyrotechnic time-delay fuse that can sustain high-impact stresses without operational failure.
Another still further object of the present invention is to provide a delay fuse in which blowby of particles of the primer into or through the delay composition is effectively prevented while the delay composition is isolated from primer brisance, constrained from unwanted expansion and vented from pressure increase.
Briefly, in accordance with this invention, these and other objects are attained by providing an explosive train for a fuse wherein two axially aligned chambers separated by an aper tured base of a cup fixedly secured in the upper chamber. The cup contains a primer mixture and the lower chamber contains a delay composition. The apertured base serves as a baffle between the primer mixture and delay composition and also to vent the lower chamber.
DESCRIPTION OF THE DRAWING A more complete appreciation of the invention and its many attendant advantages will develop as it becomes better un delstood by reference to the following detailed description when considered in connection with the solitary FIGURE of the drawing, which is an elevational, partly sectional view, of a preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, the fuse is embodied in a generally cylindrical body 10 which may be secured in a shell, grenade, bomb or other explosive projectile, usually in its hose and directly in line or alignable with a firing pin 12. The body is secured in the projectile in any appropriate manner, such as in an arming rotor or fixed in line with arming drop leaves, for example.
A frontal chamber 14 is formed in the forward portion of body 10 having generally cylindrical walls and extending axi ally into the body about one third of its length. Adjacent to the frontal chamber and axially aligned therewith is a generally cylindrical central chamber 16 extending axially into the body and having an axial depth and a cross-sectional diameter both somewhat less than the corresponding dimensions of the frontal chamber. An axial bore 18 is formed in body 10 to provide communication between the bottom of the central chamber and the rear end of the fuse body.
A cylindrical bafile cup 20 having a diameter substantially the same as the frontal chamber fits snugly therein and rests against the shoulder 22 formed at the junction of the two chambers by the difference in diameters thereof. An axial aperture 24 is formed through the bottom, or baseplate, of cup 20 provides communication between the interior of the cup 20 and the central chamber 16.
Overlying the top edge 26 of the cup 20 and covering the open top thereof is a frangible disc 28 of any suitable material, such as thin steel or aluminum. The entire top edge of body it) is crimped inwardly at 30 over the peripheral edge of the disc 2!, thereby securely clamping the disc against the top edge 26 of the cup sidewall and effecting thereby a secure seal of the cup. The inward crimp 30 is also effective to hold the bottom edge of the cup 20 securely against the shoulder 22, thereby preventing any relative motion, or play of the cup 20 within the frontal chamber 14.
The cup is filled with a suitable primer mix 32 such, for example, as 33 percent potassium chlorate, 33 percent antimony sulfide, 28 percent lead azide and 6 percent carborundum, which will be initiated when the firing pin 12 stabs through the frangible disc 28. The aperture 24 may be filled with the primer mix, a suitable igniter, or it may remain empty.
The central chamber 16 is filled with a suitable delay composition 34 such, for example, as 49 percent tungsten, 41 percent barium chromate, percent potassium perchlorate and 5 percent diatomaceous earth, which may be initiated by the primer mix via the aperture 24. The delay composition 34 reacts at a known constant rate, contributing the greater part of the time delay and then initiates the contents of the axial bore 18 which may be lead azide and, either directly or by way of an intervening pyrocore, initiates the main charge of an ordnance device.
The success of this small, simple, stab-initiated unobturated millisecond range delay train for a fuse in achieving consistent and reliable delay times, pomible in the past only by complicated, cumbersome and expensive designs, is believed to be largely achieved by the cup 20 and its support and securement within the body. The form of the baffle cup 20 inherently prevents blowby of particles of exploding primer around the edge of the baffle. The small aperture 24 in the cup bottom, or baseplate, pennits initiation of the delay composition in the central chamber and also permits venting of gases therefrom, yet is sufficiently small to enable the cup bottom to shield the composition from the brisance of the exploding primer and to prevent excess expansion of the delay composition reaction products and reaction front away from the remaining unreacted composition. This cooperative combination of cup, aperture and body efficaciously performs all the functions of the baffle and does it simply, inexpensively and reliably.
The delay time of the fuse may be shortened by partially filling the central chamber 16 with a fast reacting substance, such as lead azide, and then filling the remainder of the central chamber with the delay composition. The delay time is thereby adjustable, within certain limits, when the fuze is assembled. Also, the percentages of the components of the delay composition may be altered to produce different rates of reaction.
Obviously numerous other variations and modifications of the above-described best mode or preferred embodiment of the invention, defined in the claims, may be made in light of the above teachings.
What is claimed as new and desired to be secured by Letters Patent of the United States is:
l. A delay train for a mechanical fuse comprising:
a body having defined therein adjacent frontal and central chambers, the frontal chamber opening to the front of said body and the central chamber opening to the rear of said frontal chamber, and a passage leading from the rear of said central chamber to the exterior of said body;
a cup having sidewalls and a bottom secured in the frontal chamber of said body;
said cup bottom having an aperture defined therethrough and covering said central chamber,
a frangible disc secured in said body and covering said frontal chamber;
a primer mix disposed in said cup and in its aperture and initiatable by a firing pin penetrating the frangible disc;
a delay composition completely filling said central chamber whereby said delay composition is contiguous with and initiatable by said primer mix via said aperture; and
a pyrotechnic composition disposed in said passage initiatable by said delay composition and by way of which the initiation is propagated to a main charge.
2. A stab-initiated, millisecond range, pyrotechnic timedelay fuse comprising:
a generally cylindrical body having a front end and a rear end and having defined therein at least two chambers and an axial bore;
the first of said chambers communicating with the front end of said body;
the second of said chambers to the rear of and contiguous to said first chamber and communicating therewith;
said axial bore communicating between said second chamber and said body rear end;
said first chamber containing a baffle cup having a sidewall and an apertured baseplate, the cross-sectional dimension of said cup being substantially the same as the cross-sectional dimension of said first chamber;
said second chamber cross-sectional dimension being less than said first chamber cross-sectional dimension so that a front facing shoulder is formed between said first and second chambers;
said cup baseplate resting on said shoulder and securely held thereagainst by said sidewalls;
a frangible disc of substantially the same dimension as the cross-sectional dimension of said first chamber and positioned therein and overlying the top edge of said cup sidewall;
said body front end being crimped over said disc and said cup sidewall top edge, whereby said disc is securely clamped over and covering the mouth of said cup and said cup is securely fixed in position against said shoulder;
said cup and its aperture containing a primer initiable by the stab of the firing pin through said frangible disc and into said primer;
said second chamber being completely filled with a delay composition whereby said delay composition is contiguous with and initiatable by said primer via said aperture, said delay composition having a reaction rate substantially slower than the reaction rate of said primer;
said axial bore containing a pyrotechnic material contiguous with and initiatable by said delay composition and having a reaction rate substantially faster than said delay composition reaction rate.