Ammunition and explosives – Igniting devices and systems – Fuse cord
Reexamination Certificate
1998-07-10
2001-05-08
Jordan, Charles T. (Department: 3641)
Ammunition and explosives
Igniting devices and systems
Fuse cord
C102S275600, C102S275110, C149S037000, C149S108600
Reexamination Certificate
active
06227116
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the art of detonators of the kind comprising a shell with a base charge comprising secondary explosive arranged at one end of said shell, igniting means arranged at the opposite end thereof and an intermediate part with a pyrotechnical train being able to convert an ignition pulse from the igniting means to a detonation of the base charge. More specifically the invention relates to novel compositions of pyrotechnical charges to be used as ignition charges in such detonators and for the ignition of secondary explosives in general.
BACKGROUND OF THE INVENTION
Detonators are used for various purposes, both military and civilian ones, but will here be described mainly in relation to applications for commercial rock blasting where typically a plurality of detonators from an assortment with different internal time delays are connected in a network of electric or non-electric signal conductors.
In such detonators pyrotechnical charges may be used for different purposes in a pyrotechnical train converting an ignition pulse from igniting or signaling means to a detonation in a base charge, e.g. as a rapid transfer or amplifying charge, a slower delay charge, a gas-impermeable sealing charge or an ignition charge for detonating said base charge.
One example of a pyrotechnical charge in a pyrotechnical train is given in U.S. Pat. No. 2,185,371, which discloses a delay charge with an alloy of antimony as a specific fuel. Other examples are given in GB-A-2 146 014 and DE-A-2 413 093, which disclose a pyrotechnic fuel composition for severing conduits and an explosive mixture, respectively. As an example of a method of producing pyrotechnical charges reference is made to EP 0 310 580, which discloses the production of delay and ignition charges.
Common to all this prior art is, however, that it does not disclose or even suggest the use of our specific ignition charge to quantitatively and reliably detonate secondary explosive charges.
Ever increasing demands are placed on all the parts of the pyrotechnical train. A main requirement is that the charges shall burn with well defined and stable reaction rates with limited time scatter. The burning rate must not be significantly influenced by ambient conditions or ageing. The charges shall have reproducible ignition properties but yet be insensitive to shock, vibrations, friction and electric discharges. The nominal burning rate should be adjustable with minor charge modifications. The charge mixture has to be easy and safe to prepare, dose and press and not too sensitive to production conditions. In addition thereto there is a growing requirement that the charges must not contain toxic substances and that preparations can be made without health hazardous conditions such as use of solvents.
Although pyrotechnical charges in general can be regarded as mixtures of a fuel and an oxidant, and accordingly many compositions should be potentially available, the above described requirements together significantly limit the choice of suitable compositions for each of said charges. A need exists, however, for further improvements, both in respect of performance and because hitherto established compounds for the purpose, such as lead or cromate compounds, are becoming less available and accepted.
GENERAL DESCRIPTION OF THE INVENTION
The main object of the present invention is to provide a detonator, and pyrotechnical charges useful therein, with improved performance and properties in the above mentioned respects.
A more specific object is to provide a detonator with a pyrotechnical train having the capability of igniting a secondary explosive in a qualitative and reliable way.
Another object is to provide a detonator with stable properties in respect of burning rate, ageing and environmental influence in manufacture, storing and use.
A further object is to provide such a detonator with reliable properties but yet safe against unintentional initiation.
Another object is to provide such a detonator with less health hazardous components.
Yet another object is to provide such a detonator allowing safe and environmentally harmless conditions.
Still another object is to provide use of a pyrotechnical charge for ignition of secondary explosives in general and even without any primary explosive being present in connection therewith.
These objects are reached by the characteristics set forth in the appended claims.
Thus, according to the invention it has unexpectedly been found that a specific combination of metal fuel and metal oxide oxidant possesses the ability of quantitatively and reliably igniting secondary explosives, especially in detonators of the type specified in the opening part of this specification, and even in a case where there is no primary explosive present.
In this context qualitative ignition or similar means an ignition of a secondary explosive not with any laminar combustion where the burning front is flat but with a convective burning stage where the burning is extremely non-homogenous.
A very important finding in connection therewith is that in spite of said combustion or burning mechanism a very reliable ignition of the secondary explosive has been obtained, the remaining functions of the pyrotechnical train not being negatively influenced upon.
Furthermore, the qualitative ignition accomplished allows for a considerable shortening of the detonation development (time from deflagration to detonation) of the detonator, which in turn enables a considerable reduction of the length of the pyrotechnical train, or the initiation element, and/or a reduction of the strength or thickness of the shell, without any impairment of the function of the detonator.
Without being restricted to any theory as to reaction mechanisms, the invention seems to be based on the generation, by the novel ignition charge, of extremely hot gases with a high thermal capacity and under high pressure. Probably the igniting gases essentially consist of vapours from the metals present in the ignition charge. Only these properties seem to secure a qualitative ignition of a secondary explosive.
More specifically the invention relates to a detonator comprising secondary explosive at one end thereof, igniting means arranged at the opposite end thereof and an intermediate pyrotechnical train converting an ignition pulse from the igniting means to the base charge to detonate the same, the pyrotechnical train comprising an ignition charge comprising a metal fuel selected from groups 2, 4 and 13 of the periodic table and an oxidant in the form of an oxide of a metal selected from periods 4 and 6 of the periodic table, the metal fuel being present in an excess relative to the amount stoichiometrically necessary to reduce the amount of metal oxide oxidant, said ignition charge generating a hot pressurized gas that is able to ignite said secondary explosive of the base charge into a convective deflagrating state to reliably detonate the same.
Thus, by use of the defined ignition charge, which generally reacts by “inversion” of the metal/oxide system under heat generation, and which can be considered a thermite charge, the abovesaid objectives are met. Metal is present before, during and after reaction, securing high electric and heat conductivities. Electric conductivity means reduced risks for unintentional ignition through static electricity or other electrical disturbances. High heat conductivity means low risks for unintentional ignition through local overheating through friction, impact or otherwise, while good ignition properties from the reacted charge are secured by high and sustained heat transfer. Presence of molten metal in the reaction products amplifies the latter properties. Metal oxides are generally stable products also in the presence of water and so are the metals, often through surface passivation, which gives good ageing properties and allows for charge preparation in water suspensions, and which perhaps also explains observed reaction rate invariability in presence of moisture. The reactants of the thermite charge are
Baker Aileen J.
Burns Doane , Swecker, Mathis LLP
Jordan Charles T.
Nitro Nobel AB
LandOfFree
Pyrotechnical charge for detonators does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pyrotechnical charge for detonators, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pyrotechnical charge for detonators will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2497722