GB2033553A - Electric priming devices - Google Patents

Abstract

Priming devices comprising a priming charge and two poles which are connected by a low resistance connection, such that when there is a current surge between the poles, the connection is destroyed and the charge is ignited, in which the connection comprises a conductive layer having a non-conductive portion which surrounds one of the poles and whose ends lie side-by-side and substantially parallel. <IMAGE>

Description

SPECIFICATION Electric priming devices This invention relates to improvements in priming or detonating devices, of known type, which comprise a priming charge and two poles which are connected by a low resistance connection, such that when there is a current surge between the poles, the connection is destroyed and the charge is ignited. Such priming devices have been employed for igniting explosives, particularly in explosive missiles such as shells and rockets. Known primer capsules comprise an electrically conductive casing, about 0.5 to 1.0 cm. in size, a pole pin extending into the casing and insulated therefrom except for an electrically conductive metallic connection, between the pole pin and the casing, having a relatively low resistance of the order of one to 20 ohms.Metallic connections which have been used include fine wires or priming charges or compositions which have been rendered conductive, or conducting igniters with a high resistance, which are in connection with a sparking device. The metallic connections melt under the current surge which is initiated in known manner on the impact of a missile, sparking occurs, and the priming charge ignites.

Conventional priming charges include known explosives such as nitropentaerythritol or combined priming charges comprising a primary primer, such as silver azide, and a secondary primer, such as nitropentaerythritol. Combined priming charges are usually preferred.

The sensitivity of metallic filaments and conducting igniters is often unsatisfactory for widespread use in the present-day munitions and explosives industries. There are limits to the fineness of such metallic connections, owing to increasing instability and the resultant possible danger. Further, known detonators cannot always be reproduced with the constancy which is required.

According to the present invention, in a priming device of the type described, the connection comprises a metallic conductive layer having a nonconductive portion which surrounds one of the poles and whose ends are not contiguous but lie side-byside and substantially parallel. It is preferred that the non-conductive portion sould be substantially circular. The non-conductive portion will generally be substantially linear and may, as desired, be curvilinear or comprise a number of rectilinear portions joined together.

The priming device of the invention may comprise one or two pole pins. The former, or "single-pole priming device", is more common and is preferred in this invention. One pole of the priming device is formed by a metal casing and the other pole is formed by a pin projecting from the casing. In the latter, or "two-pole priming device", the two poles are pins projecting from the priming device (and generally parallel to each other).

In the single-pole priming device, it is generally preferred for the non-conductive portion to surround and approximately to bisect the pin and the casing.

In a two-pole priming device of the invention, it is preferred for the non-conductive portion to surround one of the pole pins and, again, approximately to bisect the two poles.

The invention will now generally be described with reference to single-pole priming devices. The device generally comprises an electrically conductive casing, a pole pin disposed therein and insulated therefrom except for a thin metal layer which forms an electrically conductive connection between the pole pin and the casing. On one side of the metal layer is the pole pin and its surrounding insulation.

On the other side of the connection lies the priming charge. The resistance of the metal layer between the ends of the non-conductive portion will be chosen with regard to the ignition requirements of the priming device and will generally be of the order of one to 300 ohms.

The electrically conductive casing, the pole pin and the insulation are preferably of conventional type. For example, the pole pin and the casing may comprise a high-grade nickel-cobalt-iron alloy and the insulation may comprise a pore-free glass which is compatible with the given alloy.

The metal layer preferably comprises separate coatings deposited from the vapour state under high vacuum onto the end of the pole pin, the insulation and the casing, and comprises a conductive adhesive coating of a chrome-nickel alloy and a purely conductive coating of gold. The adhesive and conductive coatings may be, for example, 0.015 EL and 0.15 Il, respectively.The width of the non-conductive portion is generally from 20 to 100 , e.g. 50 Il, over its entire length, the distance between the ends of the non-conductive portion being from 20 to 100 Il, e.g. 40 ,u. When the ends of the non-conductive portion are desired to lie side-by-side, the length of the substantially parallel portions is generally from 100 to 1000 Il, and preferably about 500 11.

The non-conductive portion is preferably applied to the metal layer by photolithography. Further details of this method can be obtained from a publication issued by Holex Inc, Hollister, California, U.S.A. This method allows the size of the ignition section, i.e. the section between the ends of the non-conductive portion, to be adapted as required in particular practical instances, and also allows good reproducibility. The non-conductive portion may also be cut out of the conductive layer, particularly when that is metallic, using lasers. This tecnique may be especially appropriate when it is desired to achieve an angular non-conductive portion.

The same general points apply to two-pole prim ing devices of the invention.

The invention will now be described by way of example with reference to the accompanying draw ings, in which: Figure 1 is a cross-sectional schematic view of a single-pole priming device according to the inven tion; Figures 2 and 3 are cross-sectional views, in plan, of different embodiments of a priming device of the type illustrated in Figure 1; Figure 4 is a cross-sectiona schematic view of a two-pole priming device of the invention; and Figure 5 is a cross-sectional view, in plan, of a device of the type illustrated in Figure 4.

The device of Figure 1 comprises a pole pin 1 and an electrically conductive casing 2, mutually separated by an insulating layer 5 and connected via a conductive layer 3 over a priming charge 4. Two different embodiments of the conductive layer are shown in plan in Figures 2 and 3. In Figure 2, a substantially circular non-conductive portion 6 surrounds the pole pin 1. The ends of the nonconductive portion are separated by the ignition bridge 7. The slot 8 in the conductive layer represents a conventional opening for the venting of the priming charge. A similar arrangement is shown in Figure 3 but, in this case, the non-conductive portion is angular.

The two-pole priming device illustrated in Figure 4 comprises two pole pins 9 and 10, insulation 11, casing 12, conductive layer 13 and priming charge 14. Figure 5 shows the conductive layer in plan, with non-conductive portion 15 surrounding pole pin 10.

The two ends of the non-conductive portion are separated byan ignition bridge 16.

The illustrated embodiments of the invention function in the following manner; when, on the impact of a projectile, the circuit between a current source (not shown) and the two poles is completed, the resulting current surge between the poles melts the ignition bridge, with consequent sparking and ignition of the priming charge.

Claims (8)

1. A priming device comprising a priming charge and two poles which are connected by a low resistance metallic conductive layer, such that when there is a current surge between the poles, the connection is destroyed and the charge is ignited, in which the conductive layer includes a nonconductive portion which surrounds one of the poles and whose ends lie side-by-side and substantially parallel.

2. A priming device according to claim 1 in which one pole comprises a metal casing and the other pole comprises a pin projecting from the casing.

3. A priming device according to claim 1 in which each pole comprises a pole pin.

4. A priming device according to claim 2 or claim 3 in which the non-conductive portion is substantially circular.

5. A priming device according to claim 4 in which the substantially circular non-conductive portion approximately bisects the two poles.

6. A priming device substantially as described in either of Figures 2 and 3 of the accompanying drawings.

7. A priming device substantially as described in Figure 5 of the accompanying drawings.

New claims or amendments to claims filed on 7th January, 1980.

Superseded claims 1,6,7.

New or amended claims:- 1,6,7,8.

1. A priming device comprising a priming charge, two poles which are mutually separated by an insulating medium, and a metallic conductive layer connecting the two poles, in which the conductive layer includes a non-conductive portion which surrounds one of the poles and whose ends lie side-by-side and substantially parallel, and in which at least one pole and the insulating medium lie on one face of the conductive layer and the priming charge lies on the other face thereof.

6. A priming device according to any preceding claim in which the conductive layer has been deposited from the vapour state onto the poles, the insulating medium and the priming charge.

7. A priming device substantially as illustrated in Figure 1 and either of Figures 2 and 3 of the accompanying drawings with reference to the description herein.

8. A priming device substantially as illustrated in Figures 4 and 5 of the accompanying drawings with reference to the description herein.