US3817181A - Detonating cap - Google Patents

Abstract

This invention relates to a detonating cap for an explosive charge and devised to be initiated from a fuse of the type consisting of a flexible tube the inner wall of which is coated with a thin layer of a powder of a reactive substance. The detonation cap of the invention has the form of a sleeve containing at least one charge and a delay element interposed between the charge and the end of the fuse introduced into an open end of the sleeve. The delay element has a central channel for open communication from the end of the fuse tube to the charge. In order to prevent said channel from being clogged by powder particles detached from the coating of the tube or the free surface of the charge from being covered by such detached particles opposite the said channel, this latter is bridged over by a shield of a structure adapted to deflect detached powder particles or the gas impact wave rushing out from the fuse tube. This shield may be shaped as a valve initially closing the channel but opening it when actuated by the gas impact valve.

Description

United States Patent [191 Persson et al.

[ DETONATING CAP [75] Inventors: Per-Anders Persson, Stockholm,

Sweden; Gosta Lithner, Brugherio, Italy [73] Assignee: Nitro Nobel AB, Gyttorp, Sweden [22] Filed: Jan. 3, 1973 [21] Appl. No.: 320,833

[30] Foreign Application Priority Data June 18, 1974 Primary Examiner-Verlin R. Pendegrass Attorney, Agent, or FirmShlesinger, Fitzsimmons & Shlesinger 57 ABSTRACT This invention relates to a detonating cap for an explosive charge and devised to be initiated from a fuse of the type consisting of a flexible: tube the inner wall of which is coated with a thin layer of a powder of a reactive substance. The detonation cap of the invention has the form of a sleeve containing at least one charge and a delay element interposed between the charge and the end of the fuse introduced into an open end of the sleeve. The delay element has a central channel for open communication from the end of the fuse tube to the charge. In order to prevent said channel from being clogged by powder particles detached from the coating of the tube or the free surface of the charge from being covered by such detached particles opposite the said channel, this latter is bridged over by a shield of a structure adapted to defleet detached powder particles or the gas impact wave rushing out from the fuse tube. This shield may be shaped as a valve initially closing the channel but opening it when actuated by the gas impact valve.

6 Claims, 7 Drawing Figures I PATENTEDJUNI 81974 SHEET 1 0F 2 Fig. 2

Fig. 3

slenllal PATENTEDJuu I 8 e914 SHEET 2 BF 2 FIELD OF THE INVENTION This invention relates to a detonating cap for an explosive charge and devised to be initiated from a fuse.

THE PRIOR ART More particularly, this invention relates to a detonating cap intended for fuses of the type consisting of a flexible tube or hose, the inner channel wall of which is coated with powder of a reactive substance such as, e.g., an explosive or aluminium or a mixture of both said substances. Fuses of this kind are described in US. Pat. No. 3,590,739.

The cap comprises a sleeve-shaped casing provided with, beginning from its closed end, a charge, preferably in two or more layers, a delay element and a spacer element disposed between the delay element and the end portion of a tubular or hose-shaped fuse, which is inserted through, and retained in position in the open end of the casing. The delay element contains a pyrotechnical composition for the purpose of providing for a predetermined delay of time between the arrival of the gas impact or percussion wave emanating from the fuse and the initiation of the charge. The channel existing between the end of the fuse and the delaying composition, or the free interspace which is formed by the spacer element or within which said element is located, has for its purpose to reduce the scattering in timing for the ignition, which is of particular importance for the so-called interval blasting system, by preventing mechanical destruction, such as e.g., cratering of the pyrotechnical composition of the delay element.

It has been experienced that powder may detach from the innerwall of the fuse and fall through the open spacer element down onto the delay element, on the top of which it may accumulate as a kind of drift so that in many cases the detonation of the detonating cap fails to occur. Thus powder particles are detached from the channel wall of the fuse when this fuse is subjected to some types of rapid movements, and even if this has no detrimental effect on the operative function of the fuse, the gas impact wave produced by the fuse can under unfavourable conditions be prevented from igniting the delay composition.

OBJECTS, FEATURES AND ADVANTAGES OF THE INVENTION One main object of the invention is to eliminate this drawback.

According to a main feature of the invention the channel of the spacer element is bridged by a shield of such structure as to effect a deflection of powder or gas impact wave transferred from the fuse bore or channel towards the delay element. This results in that a coating on the pyrotechnical composition of the delay element is avoided, and the powder is caused to accumulate at least to a large extent laterally of said element.

A further advantageous effect of the invention is that the hot gas impact wave rushing out from the fuse passes over the surface of the composition in a vortex motion, and in this way blows off possible deposits of powder, while at the same time causing an increase of heat transfer to the composition enabling it to reach a value necessary for the ignition of the delay composition or even exceeding said value.

SHORT DESCRIPTION OF THE INVENTION Further objects, features and advantages of the invention will become apparent from the following description, when considered in connection with the accompanying drawings, which form part of this specification and of which:

FIG. 1 is a longitudinal sectional view of a detonating cap made in accordance with one embodiment of the invention,

FIG. 2 is a sectional view following the line "-11 of FIG. 1,

FIGS. 3 to 5 show three alternative configurations of that portion of the spacer element shown in section in FIG. 1,

FIG. 6 is a longitudinal sectional view of a detonating cap according to still another embodiment with the spacer element formed as a valve, and

FIG. 7 is a sectional view following the line VIl-VII of FIG. 6.

DETAILED DESCRIPTION OF ONE PREFERRED EMBODIMENT Referring now to the drawings, reference numeral M) denotes a sleeve or casing closed at its lower end and made of, e.g., sheet metal. Said casing is, commencing from its closed end in a manner known per se, provided with a secondary charge 12, a primary charge 14 and a delay element 16. The latter may be a sleeve 17 made of metal and having an internal channel of substantially smaller diameter than the inner diameter of the sleeve or casing 10. Disposed within the channel of the sleeve 17 is a pyrotechnical delaying composition 18 of known kind. Inserted into the open end of the casing 10, and retained therein, e.g., by crimping, is a flexible tube 20 of plastic material intended to retain and protect the free end of an initiating fuse 22 having the shape of a flexible hose, the inner channel of which, in the manner described in the patent specification referred to hereinbefore, is coated with a thin layer of a pulverulent reactive substance, primarily an explosive, even if it may consist of aluminium or a mixture of an explosive and aluminium. The quantity of explosive or reactive substance for producing a propagating hot gaseous impact or percussion wave in the channel is very little, but is applied in practice with an excess great enough to safeguard reliable operation.

Located between the delay element 16 and the inner ends of the tubes or hoses 20, 22 is a spacer element generally denoted 26, and preferably made of some suitable plastic material. In the embodiment shown in FIGS. 1 and 2 said element has opposed, segmental cylindrical portions 28, 30 presenting spaced, segmentlike cross-sections, said portions being interconnected by a transverse section or shield 32 which extends diagonally and part way only across the bore in sleeve 10 so that the element is formed with open passages on both sides of said shield. The shield! 32 has an inclined upper surface 34 which extends transversely across the bore in sleeve 10 for a distance greater than the diame ter of the inner channel 24 of the fuse 22 and also the diameter of the delay charge 18. In this embodiment, the shield in section has the form of a rhomboid with two shorter sides positioned in the longitudinal direction of the detonating cap between the upper inclined roof surface 34 and a lower surface 36 extending parallel to said roof surface 34. The shield 32 leaves free a passage at both its short sides.

If the fuse 22 is exposed to rapid motion so that some explosive powder is detached from the channel wall 24, such loose powder is prevented by the shield 32 from falling straight down onto the delay charge 18 and will either get caught by and adhere to the roof surface 34 or slide along said surface and be accumulated laterally of the top surface of the delay composition. The gas impact wave, when the fuse 22 is ignited, rushes with its high speed and temperature into the open passages of the spacer element 26, but will be deflected by the roof surface 34 to be whirled about the upper surface of the delay composition. Thereby, any explosive powder which possibly has been deposited on said surface will be removed therefrom, and in addition an intensive heat transfer is brought about and guarantees ignition of the delay composition.

DESCRIPTION OF OTHER PREFERRED EMBODIMENTS In the embodiment shown in FIG. 3 the shield of the spacer element 26 which bridges the two segments 28, 30 has the crosssectional shape of a wedge 38 with its base facing the delay charge 18 so as to interrupt the straight or direct communication between the fuse channel 24 and the delay composition. Powder material detached from the fuse will slide along the two wedge surfaces 40 to be accumulated laterally of the delay composition.

In the embodiment according to FIG. 4 the shield portion 42 of the spacer element extends from the outer circumference of the element in an inclined, inward direction over the centre of the element so as to form a surface which deflects both powder and the gas impact wave. The bottom side 36 of the wall 42 is parallel, or approximately parallel to the roof surface 34.

In the embodiment according to FIG. the shield 44 has the cross-sectional shape of a right triangle the diagonal of which forms the deflecting surface 34 which is met by the media rushing out from the fuse channel.

In the embodiment shown in FIGS. 6 and 7, the space between the delay element 16 and the adjacent end of the fuse 22 houses a valve-like member 46 which in the starting position entirely shuts off any communication between the inner channel of the fuse 22 and, said space..To this end the member 46 is under the action of a spring member 48 which keeps said member pressed against the end of the fuse. In this way detached particles of the pulverulent coating on the inner wall of the are prevented from falling down onto the delay composition 18. In the illustrated embodiment the valve member 46 is formed with a conical point 50 which fits into the bore in the fuse. The member 46 is preferably shaped as a disc made, e.g., of plastic material, and has diametrally opposite portions thereof flatted off to form thereon lateral, parallel surfaces 52. Moreover each portion of its circumference fits to the inner diameter of the cap so that its bevelled lateral surfaces 52 provide open passages for the gas impact wave rushing out from the fuse after having forced down the valve member 46 so as to uncover the discharge end of the fuse. This position of the valve member 46 is represented in FIG. 6. In this embodiment the valve member 46 constitutes both the spacer element and the shield according to the preceding figures.

While several more or less specific embodiments of the invention have been shown and described, it is to be understood that this is for purpose of illustration only, and that the invention is not to be limited thereby,

but its scope is to be determined by the appended claims.

What is claimed is:

l. A detonating cap intended for use with a tubular fuse the inner wall of which is coated with powder of a reactive substance, such as an explosive, comprising a housing having a bore open at one end,

a charge, a delay element, and a spacer element disposed one after the other in said bore with said spacer element facing the open end thereof, and

guide means on said housing for guiding one end of a fuse from outside the housing and through the open end of the last-mentioned bore to an operative position in which the fuse confronts said spacer element,

said spacer element providing at least one passage connecting said delay element with the open end of said bore and said fuse, when the latter is in its operative position, and

a portion of said spacer element forming a shield extending part way across said passage and being of such structure as to effect a deflection of powder and a gas impact wave transferred from a fuse toward the delay element.

2. The detonating cap as claimed in claim 1, wherein said spacer element has two passages therethrough on opposite sides of said shield, whereby the shield is devised to be passed on both sides by powder and/or a gas impact wave from a fuse.

3. The detonating cap as claimed in claim 1, characterized in that said shield has at least one inclined surface facing the open end of said bore to confront a fuse disposed in its operative position.

4. The detonating cap as claimed in claim 3, characterized in that said shield projects from one side of the spacer element and transversely across an imagined prolongation of the bore in a fuse, when the latter is disposed in said operative position.

5. The detonating cap as claimed in claim 1, wherein said shield is disposed normally to shut off the passage between the bore in the fuse and the delay element, when the fuse is in its operative position, and disposed to be forced by said gas impact wave to open said passage.

6. The detonating cap as claimed in claim 5, characterized in that said spacer element is formed as a spring-actuated valve member for closing the bore in the confronting end of the fuse, when the latter is in its operative position.

Claims (6)

1. A detonating cap intended for use with a tubular fuse the inner wall of which is coated with powder of a reactive substance, such as an explosive, comprising a housing having a bore open at one end, a charge, a delay element, and a spacer element disposed one after the other in said bore with said spacer element facing the open end thereof, and guide means on said housing for guiding one end of a fuse from outside the housing and through the open end of the lastmentioned bore to an operative position in which the fuse confronts said spacer element, said spacer element providing at least one passage connecting said delay element with the open end of said bore and said fuse, when the latter is in its operative position, and a portion of said spacer element forming a shield extending part way across said passage and being of such structure as to effect a deflection of powder and a gas impact wave transferred from a fuse toward the delay element.

2. The detonating cap as claimed in claim 1, wherein said spacer element has two passages therethrough on opposite sides of said shield, whereby the shield is devised to be passed on both sides by powder and/or a gas impact wave from a fuse.

3. The detonating cap as claimed in claim 1, characterized in that said shield has at least one inclined surface facing the open end of said bore to confront a fuse disposed in its operative position.

4. The detonating cap as claimed in claim 3, characterized in that said shield projects from one side of the spacer element and transversely across an imagined prolongation of the bore in a fuse, when the latter is disposed in said operative position.

5. The detonating cap as claimed in claim 1, wherein said shield is disposed normally to shut off the passage between the bore in the fuse and the delay element, when the fuse is in its operative position, and disposed to be forced by said gas impact wave to open said passage.

6. The detonating cap as claimed in claim 5, characterized in that said spacer element is formed as a spring-actuated valve member for closing the bore in the confronting end of the fuse, when the latter is in its operative position.

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