The technical scope of the present invention is that of plasma torches and more particularly torches used to ignite the propellant charge of a piece of ammunition.
A plasma torch is a system that enables high pressure (around 500 MPa) and high temperature (over 10000 K) gases to be generated by a high voltage (around 20 kV) electrical discharge made between two electrodes.
Plasma torches are used in industry, for example, to cut conductive materials, or else to destroy certain products or materials, or to carry out metallic deposits. They are also used in the field of armaments to generate pressure allowing a projectile to be fired.
Known plasma torches comprise an anode and a cathode separated by a capillary tube made of a material that is both electrically insulating and able to decompose in order to generate a plasma (for example a plastic material). The electrical discharge between anode and cathode is excited by means of a copper fuse or other conductive material. The electric arc thus created produces a plasma, which ablates the capillary tube wall, thereby causing the generation of light high-pressure high temperature gases.
These gases are used either to directly accelerate a projectile, or to vaporise a working fluid (for example, water) allowing the volume of the gas to be increased.
Patents FR2754969 and FR2768810, which describe plasma torches used to ignite the propellant charge of a piece of ammunition, may be consulted.
One drawback to known plasma torches lies in the fragility of the fuse wire allowing the plasma to be excited. Such a fuse wire has a diameter of 0.1 to 0.5 mm. It may break further to thermal and mechanical stresses (vibration, impacts) that occur during the storage and implementation phases of the ammunition elements.
Moreover, the manufacture of known torches is made difficult and costly by the operation to mount such a fuse.
The aim of this invention is to overcome such drawbacks.
Thus the torch according to the invention has improved mechanical strength thereby increasing its reliability. Moreover, it is simple in structure and may be manufactured at low cost.
The torch according to the invention may be manufactured at different lengths without difficulty.
A further subject of the invention is an igniter squib implementing such a plasma torch, such squib facilitating the diffusion of the plasma towards the propellant charge and this for load configurations that are very different from the point of view of mass or geometry.
Thus, the invention relates to a plasma torch comprising at least two electrodes separated by an insulating cylindrical case delimiting an inner volume, said torch wherein the electrodes are separated by a sufficiently small distance for an igniting arc to appear between the electrodes when a serviceable voltage supplied by a generator is applied between them, the distance between the electrodes and the serviceable voltage of the generator being selected such that the electrical field appearing between the electrodes is of around 1 Megavolt/meter.
The torch may comprise a rear electrode and a front electrode, the rear electrode incorporating an axial tip oriented towards the front electrode and the front electrode incorporating a thinned crown oriented towards the rear electrode as well as an axial perforation.
The front electrode""s axial perforation may be nozzle-shaped incorporating a convergent conical profile open at the rear electrode side and followed by a divergent conical profile open towards the outside of the torch.
According to a variant embodiment, the torch may incorporate a block of energetic material placed between the electrodes.
The block may be ring-shaped.
The torch will generally incorporate a metallic body having an axial bore inside which the electrodes and insulating case are placed.
The bore in the body may incorporate a shoulder onto which the front electrode is applied, the insulating cylindrical case being in axial support, firstly on the front electrode and secondly on the rear electrode, and insulating closing ring being screwed at a rear threading of the body ensuring the axial joining of the electrodes and insulating case with the body.
The closing ring may incorporate a lip surrounding a thinned extension to the insulating case.
The front electrode may incorporate a cylindrical seat onto which the insulating case will be fitted.
The torch may incorporate a spacer ring coaxial to the insulating case and placed between the front electrode and the energetic block, the latter pressing on a countersink made in the insulating case.
A further subject of the invention is an ammunition squib wherein it comprises such a plasma torch.
The squib may comprise a tubular nozzle perforated by at least one hole and integral with the torch at its front part so as to receive the plasma generated by the torch.
The nozzle may incorporate at least two holes evenly spaced angularly and/or axially and perforated according to the radial directions of the nozzle.