US3070013A - Electrical igniter for effecting the ignition of explosive charges - Google Patents

Description

Dec. 25, 1962 G. BAcKsTElN ETAL 3,970,013

' ELECTRICAL IGNITER FOR EFFECTING THE IGNITIO F EXPLOSIVE CHARGES May( 9, 1960 Fm B Ee.

Traxx/Veys B'l Patented Dec. 25, 1962 tice 3,07t),t13 ELEQTRECAL IGNITER FR EFFECTING TEE EGNTGN F EXPLGSVE CHARGES Gnter Backs'ein, Essen (Ruhr), and Fritz Berger, Dusseldorf, Germany, assignors to Firma Rheinmetall GJnhH., Dusseldorf, Germany Filed May 9, 1960, Ser. No. 27,747 Claims priority, application Germany May 15, 1959 1 Claim. (Cl. 102-28) The present invention relates to an electrical igniter for effecting the ignition of explosive charges, of the type comprising a capacitor in the form of a coiled package which consists of spirally wound metal foil with an insulating intermediate layer, the capacitor including inner and outer poles, the metal foil being formed at one end in such a manner as to provide a plurality of sparking gaps across which sparking occurs when the capacitor is discharged.

In the known electrical igniters of this type the outer pole of the ignition capacitor has been provided by a metallic outer casing enclosing the coiled foil package, and the inner pole by a metallic former illing the inside of the coil, both the outer and the inner poles being the same length as the coil so that the end faces of the poles and the end face of the coil which comprises the ignition zone, were substantially located in the same plane.

It has now been found in the course of practical tests carried out on such igniters that even if the charge is kept constant the intensity of the spark di'nfers greatly, so that reliable ignition of the primer charge is not always ensured.

it is an object of the present invention to provide an igniter which overcomes this drawback and which will generate a uniform and powerful spark so that reliable ignition of the explosive charge is ensured.

According to the present invention an electrical igniter of the kind referred to for effecting the ignition of an explosive charge is so arranged that the end face of the coiled metal foil which comprises the ignition Zone is insulated from the inner or outer poles or from both said poles.

The arrangement according to the invention prevents the tendency for a strong electric field to build up between the two pole ends in the neighbourhood of the ignition zone. This was particularly likely in previously known igniters if the coil had thin walls so that the two poles were close together. Such an electric field has an adverse effect on the spark formation when the capacitor was discharged, `since the capacitor coil located between the two poles tended, due to the skin effect obtaining in the vicinity of the ignition zone, to discharge wholly or in part through the poles themselves, and thus no, or only a feeble sparking would occur which was insuliicient for the ignition of the explosive charge.

By insulating the ignition zone, from the pole or poles the resistance between the two ends of the poles is increased to such an extent that the electric field is no longer suicient to interfere with the generation of sparks. Thus, all the energy stored in the capacitor is available for generating the sparking for igniting the charge. This has been conrmed by tests.

Due to the uniform ignition of the priming charge which can be achieved by means of the igniter according to the present invention, it is also possible to work with an electric output which is smaller than that used in known apparatus.

To enable the invention to be fully understood it will now be described by way of example with reference to the accompanying drawing in which:

`FIGURE 1 is a sectional View of an electrical igniter according to one embodiment of the invention, incorporating a coiled capacitor and an outer pole in the form of a strip located below the ignition zone,

FIGURE 2 is a section viewof another embodiment of the invention incorporating an outer pole in the form of a ring enclosing the coil, and

FIGURE 3 is a sectional view of an assembly including a further embodiment of the invention including an igniter with a chamber for the priming charge formed by an insulating ring.

The electrical igniters illustrated in FIGURES 1 to 3 of the accompanying drawing consist essentially in the manner known per se of a coiled capacitor 1 which is formed by two metal foils with an interposed dielectric. The two metal foils and their intermediate layer are coiled round part of a metallic former 2 which is connected electrically to the inner foil and e.g. to the positive terminal of a source of current. This former 2 constitutes the inner pole of the igniter. The outer metal foil is connected to the negative terminal of the source of current by means as described below.

The end face 3 of the capacitor 1 has the form of a coarsely cut surface, so that when a predetermined voltage is exceeded the energy stored in the capacitor will be discharged by sparking between the cut ends of the metal foils. To simplify manufacture and ensure that the end face 4 of the former 2 is in the same plane as the end faces of the foils the formation of the end face 4 may be effected at the same time that the end face 3 of the metal foils are out.

As shown in FIGURE 1 the outer pole takes the form of a metallic strip 6 partly enclosing the outer surface 5 of the coil and so located that contact is made at some distance below the end face Ii of the coil which comprises the ignition zone. In other words, the upper face 7 of the strip 6 is spaced at such distance from the end face 4 of the inner pole that the electric field building up between the poles cannot exert an adverse effect on the formation of sparks at the end face 3. Thus the air gap between the faces '3 and 7 forms an insulating layer.

In the embodiment according to FIGURE 2, the outer pole takes the form of a metallic ring 8 enclosing the coiled capacitor. The upper face 9 of this ring is spaced from'the ignition end face 3 of the coiled package so that an air gap is formed between the end faces 4 and 9 of the poles 2 and Thus, here again the air forms an insulating layer in the vicinity of the ignition end face 3 and the outer pole 8. An advantage of the ring Shaped pole is that it serves as a protection against damage. In order to eliminate the risk of damage to the outer foil when the ring 8 is passed over it, the bore of the ring is tapered as shown at 10. The inner pole 2 is separated from the outer pole 8 by a disc 11 made of electrically insulated material.

In the embodiment shown in FIGURE 3, the coil is enclosed in the vicinity of the ignition zone by a ring 12 made of an insulating material, preferably a synthetic plastic, whichl extends beyond the end face 3 of the coil so that it provides a chamber for accommodating a primer charge 13. The outer pole, which in this embodiment comprises an annular body 14, also extends beyond the end face of the coil its upper end terminating in the plane of the end face of the insulating ring. The member 14 has an annular recess which serves to locate the ring 12. In this arrangement the insulating ring 12 insulates the ignition zone from the outer pole 14, at and above the ignition zone. When the coiled capacitor is being discharged, a powerful spark is generated which ignites the priming charge 13 which then in turn detonates the explosive charge 16 located in the container 15. An important advantage of the embodiment illustrated in FIG- URE 3 is that it enables the priming charge 13 to be accommodated in the immediate vicinity of the point of Y a plurality of spark gaps, and an inner and an outer pole for the capacitor, a space adjacent the end face forming an insulating layer for the outer surface of the coiled capacitor to insulate the coiled capacitor on the outside from the outer pole and on the inside from the inner pole, the insulating layer being an electrically insulating ring provided near the ignition Zone and the coiled capacitor to enclose the latter and being composed of syntheticV plastic which extends beyond the end =face of the coiled capacitor VadistanCe to also form a chamber accommodating a priming charge. y

References Cited in the file of this patent UNITED STATES PATENTS 2,963,970 Schaadt et al Dec. 13, 1960

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