Ammunition and explosives – Blasting – Contained blasting charge
Reexamination Certificate
1999-04-08
2001-02-13
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Contained blasting charge
C102S275400
Reexamination Certificate
active
06186069
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an explosives booster.
Explosives boosters are used for amplifying the explosion from a detonator in the direction of the main charge.
PRIOR ART TO THE INVENTION
The known boosters usually comprise an elongated hollow body, usually of cardboard or plastics, which is charged with an explosive material which is more sensitive to detonation than the main charge.
A common material for such booster charge is pentolite, which is a mixture of pentaerythritol tetranitrate (“PETN”) and trinitrotolune (“TNT”).
It is also known to employ a booster body which is of cone shape, with the arrangement such that the detonator is located towards the base of the cone, and the wider end of the cone faces the main charge.
The known detonator boosters suffer from various disadvantages.
Thus, for example, because of the relatively high concentration of the PETN component of the pentolite mixture, the known boosters are relatively expensive.
Other disadvantages relate to the configuration of the booster body and the dimensional interrelationship of its components, both which may adversely influence the effectiveness of the explosion and the resultant shock wave.
OBJECT OF THE INVENTION
It is accordingly an object of this invention to provide an explosives booster with which the aforesaid disadvantages may be overcome or at least minimised.
SUMMARY OF THE INVENTION
According to the invention an explosives booster intended for igniting a main explosive charge is provided which includes a first explosive charge which is sensitive enough to be ignited by the explosion of a charge of a detonator charge; and a second explosive charge which is less sensitive to ignition than the first charge, but more sensitive to ignition then the main charge.
With such an arrangement the detonator in use will ignite the said first charge, which in turn will ignite the said second charge, which in turn will ignite the said main charge.
It will be appreciated that with such an arrangement the said first charge may comprise a conventional 60/40 PETN/TNT pentolite mixture, while the said second charge may comprise a pentolite mixture with a lower concentration of PETN, such as, for example, a 40/60 mixture, which accordingly makes it less expensive.
Furthermore, because the only purpose of the said first charge is to ignite the said second charge, a relatively small first charge can be employed which further serves to reduce the costs of the arrangement.
Further according to the invention the booster includes a hollow body which is of substantially ice-cream cone configuration, in longitudinal cross section and which comprises a hollow cup of substantially semi-dome shape and a hollow elongated stem which projects radially outwardly from the apex of the dome; the stem being adapted to carry the detonator and said first charge in its bore, and the cup being adapted to carry said second charge.
Further according to the invention the said bore of the stem of the booster is of circular configuration in cross section, and its diameter where it is ignited by the detonator is at least twice that of the detonator.
Thus, for example, if a conventional type of detonator with a diameter of 7 mm is employed, the effective diameter of the bore of the stem at the ignition point is in the order of at least 14 mm.
Still further according to the invention the said cup is also of circular configuration in cross section, and its diameter at its widest part is at least four times that of the detonator.
Still further according to the invention the diameter of the cup at its widest part is not greater than the total height of the booster measured from the free end of the said stem to said widest part of the cup.
Applicant has found a booster of the aforesaid configuration to have the following advantages:
1. because the detonator is located in a position spaced from, but centrally relative to, the said second charge, optimum use is made of the directional detonation wave caused by the detonator explosion, while an advantageous pressure duration is also obtained;
2. the shape of the booster ensures that a planar shock wave is obtained;
3. the presence of dead zones in the charge behind the point of innitiation of the explosion is avoided, or at least minimised;
4. because of the aforesaid interrelated dimensions of the booster components, a full detonation wave, as well as proper reversed detonation (retonation), is obtained which, because of the gradual build up until the shock wave has fully formed and flattened out, ensures better and prolonged results.
Still further according to the invention the stem of the booster is releasably securable to the cup of the booster, so that differently sized cups may be employed with the same stem in order to provide boosters of, say, 200 g, 400 g and 800 g.
The cup and the stem may each be provided with said second and first charges respectively in any suitable manner such as, for example, by means of a casting operation.
Preferably, also, an inwardly extending detonator well may be provided towards the one side of the said second charge through which the detonator may be passed in order to allow it to be loaded from below into the bore of the stem of the booster while the latter is in position in the blasting hole.
Because of its particular location, such a well has no influence on the shockwave being formed by the explosion. Preferably, the hollow body of the booster is made of a suitable material such as cardboard or plastic.
REFERENCES:
patent: 3238876 (1966-03-01), Allen
patent: 3244103 (1966-04-01), Spickard
patent: 3713384 (1973-01-01), Turnbull
patent: 3880080 (1975-04-01), Cook
patent: 4331081 (1982-05-01), Cloutier et al.
patent: 4383484 (1983-05-01), Morrey
patent: 4938143 (1990-07-01), Thomas et al.
patent: 5714712 (1998-02-01), Ewick et al.
patent: 5780764 (1998-07-01), Wetch et al.
Ensign-Bickford (South Africa Proprietary) Limited
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Nelson Peter A.
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