Ammunition and explosives – Igniting devices and systems – Fuse cord
Patent
1995-06-21
1997-05-13
Nelson, Peter A.
Ammunition and explosives
Igniting devices and systems
Fuse cord
1022759, C06C 504, C06C 700
Patent
active
056294930
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a low energy fuse, comprising a plastic tube with a channel, the channel containing a reactive material able upon ignition to sustain a shock wave within the channel, the tube comprising at least two layers of plastic materials, a first plastic layer closer to the channel and a second plastic layer outside the first layer, at least the second layer containing a major amount of draw orientable polymer resin. The invention also relates to a manufacturing method for such a fuse and the fuse manufactured by the method.
BACKGROUND
A low energy fuse of the type referred to was first described in U.S. Pat. No. 3,540,729 and numerous subsequent patents have been published. In broad terms the fuse consists of a narrow plasic tube with a pyrotechnic or self-explosive reactive matter disposed within the tube channel. The amount of reactive material is sufficient to give a high speed shock wave in the channel, able to ignite secondary or functional pyrotechnical devices such as detonators or transmission caps for blasting networks. Yet the amount of reactive material is sufficiently small to confine the reaction within the tube without destroying, disrupting or even deforming it and to make the overall device safe, harmless and noiseless in use.
Although the device is simple in principle, the physical demands placed on it are not. A substantial radial strength is needed to resist the forces produced by the shock. Signal speed is lost, or the wave halted, if the tube is substantially defomed or ruptured. Radial strength is also needed to avoid compression and external damages and to allow crimp attachment of functional devices to the tube. Substantial axial strength with maintained elasticity is needed to take up forces involved in handling, network connection and charging operations. Overall toughness is needed to sustain the harsh field conditions before and during blasting. Further desired properties are suitable friction properties and impermeability to moisture and oil.
The reactive material is typically a powder introduced in the channel. For that reason a unique constraint on the fuse tube is that the interior surface must have suitable powder adhesion properties. A too weak attraction may mobilize the powder, giving signal interuptions due to material rarefactions or clogs. Too stong bonds counteracts rapid reaction and dust explosion.
The fuse tube is produced in considerable lengths and the tube materials must be inexpensive and the manufacturing methods cost effective.
The demands are partly contradictory and single-layered tubes tend to require a compromise between desired properties. It has been suggested in U.S. Pat. No. 4,328,753 to make a two-layer tube and select inner and outer materials of different properties but the materials are not optimally used solely thereby.
It has been suggested, in for example Canadian patent 1 200 718 and U.S. Pat. No. 4,817,673 to increase axial strength by incorporating longitudinal reinforcing filaments in the tube material. The resulting inelastic tube is unable to absorb elongation under field conditions and tend to break or disengage from its detonator when subjected to strain. The tube material is not efficiently utilized in spite of the increased costs for manufacture and reinforcements.
The U.S. Pat. No. 4,607,572 describes a manufacturing method in which an inner tube with suitable adhesive properties is first manufactuted and then elongated under overextrusion to increase manufacturing speed, minimize the amount of adhesive inner material and give an orientation to the elongated tube material. The respective materials are not efficiently used as orientation is concentrated to the inner layer, resulting in radial brittleness, whereas the outer layer contributes little to axial strength. A product inclined to fracture will result unless stretching is limited.
The European patent specification 327 219 describes a single-layer tube extruded from a mixture of a draw orientable polymer and a minor amount of a polyme
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Andersson Lars
Danertz Karl-Erik
Jidestig Goran
Nelson Peter A.
Nitro Nobel AB
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