Explosives with embedded bodies

Details Explosives with embedded bodies Explosives with embedded bodies

2000-09-11

2003-01-21

Nelson, Peter A. (Department: 3641)

Ammunition and explosives

Powder form

Having embedded reinforcing or burning control means

C102S288000, C102S290000, C102S318000, C149S093000

Reexamination Certificate

active

06508177

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is concerned with explosives comprising a continuous phase of a first explosive having embedded therein discrete bodies of a second explosive. More particularly, the present invention is concerned with cast explosives of the type commonly referred to as booster explosives.
2. Related Art
Booster charges are solid explosive charges used to initiate blasting agents such as ammonium nitrate-fuel oil (ANFO) mixtures. Such booster charges are available in a variety of sizes and shapes, e.g., cylindrical, conical, etc., typically having weights from, e.g., 5 grams to 88 ounces, lengths of 4 to 30 inches and diameters of 0.5 to 5 inches. Booster charges may be composed of trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclo-trimethylene trinitramine (RDX), cyclotetramethylene tetranitramine (HMX), pentolite (a mixture of PETN and TNT), other types of explosives such as fuel-oxidizer mixtures, and various mixtures of these explosives. In addition, stabilizers, emulsifiers and other additives may be present in the explosive mixture of the booster charge. These explosives all have individual characteristics in terms of ease of initiation, explosive energy, brisance, shelf life, solidification point and other factors which impact safety and usage of the booster charges.
Booster charges are conventionally made by pouring into a container, which serves as a mold, a molten or otherwise pourable explosive material and solidifying it within the container. Solidification of the liquid explosive may be by means of cooling, polymerization, crystallization, chemical reaction, hydration, curing or other methods known in the art. The resulting charge may be of any suitable shape including cylindrical, conical, irregularly conical, spherical and polygonal. One cast booster charge representative of the prior art weighs about 12 ounces and may be about 4.7 inches long with a diameter 1.9 inches.
A suitable fixture may be placed within the container prior to pouring the pourable explosive therein to provide one or more initiator seats such as one or more bores (which may comprise passageways open at both ends or wells open at one end only) within the cast booster charge. An energetic initiation device or “initiator”, such as a low-energy detonating cord (LEDC) and/or a detonator, is placed within the initiator seat so that upon initiation of the initiator, the cast booster charge is detonated. Cast booster charges are conventionally used to detonate a larger mass of a blasting agent such as the well known ammonium nitrate-fuel oil mixture (“ANFO”).
As used herein, the term “contact surface” or “initiation surface” refers to a surface on the booster charge, optionally at an initiator seat (e.g., a bore, passageway, well, groove, indentation, etc.) configured to receive an initiator, which receives the initiation signal from the initiator.
The art has been concerned with, among other things, preparing cast booster charges of sufficient sensitivity so that they may be reliably initiated by low-energy initiators such as low-energy detonating cord and relatively low-energy or small detonators. For example, in a typical environment of use, one or more cast booster charges are placed within a borehole which is partially filled with ANFO. The borehole may also contain some stemming material such as crushed gravel to seal the top of the borehole and/or to divide the borehole into two or more stages or “decks” of ANFO. In any case, if the booster charges or detonators contained within the cast booster charges are to be initiated by detonating cord, the detonating cord must pass through the ANFO or other blasting agent. It is therefore desirable to use a low-energy detonating cord to avoid the possibility that detonation of the detonating cord will initiate the ANFO prematurely or alter its explosive properties prior to initiation of the cast booster charge.
FIGS. 1 and 1A
(prior art) show a prior art expedient for increasing the sensitivity of a cast booster charge. To prepare charge
10
, PETN
14
a
may be contained as a powder within a balloon which is wrapped around a straw
12
a
around which the main body (the continuous phase) of charge
10
is cast as an annular-shaped body
14
b
of a TNT-containing explosive such as pentolite or composition B (a mixture of RDX and TNT). In use, a low-energy detonating cord may be passed through passageway
16
as an initiator, and may be knotted below straw
12
a
in order to prevent its slipping out of passageway
16
. The PETN therefore defines at least a portion of the initiation surface of charge
10
. PETN is more sensitive than is the cast TNT-containing explosive, but it is also significantly more expensive. However, by providing PETN at the initiation surface, the reliability of initiation from the initiator is significantly improved. Upon initiation of the low-energy detonating cord (not shown) within passageway
16
, the sensitive PETN
14
a
is detonated, which in turn detonates the less sensitive cast body
14
b
. Cast booster charge
10
is typically used to detonate a larger mass of a still less sensitive blasting agent such as ANFO, as is well known to those skilled in the art.
The prior art embodiment of
FIGS. 1 and 1A
has several drawbacks, including high production costs because of the necessity to fill balloons with the PETN and position and retain the balloon about the straw
12
a
and within a cylindrical container
12
. Should the PETN balloon be omitted from one or more containers, the result would be a less sensitive, all TNT or TNT-based (or other explosive) cast booster charge which may not be sufficiently sensitive enough to be initiated by a low-energy detonating cord placed within passageway
16
. The balloon may be misplaced, causing unreliable initiation. The invention eliminates this problem, and may incorporate the more sensitive explosives into a continuous phase to define the initiation surface. Optionally, the explosive material in the continuous phase may have a low permeability to water and so may not require isolation from water.
FIG. 1B
is a cross-sectional view of another booster charge
600
according to the prior art. Cast booster charge
600
comprises TNT pellets
640
, explosive filling
642
and a pentolite core
644
. Pellet
640
and filling
642
are both composed of TNT only.
FIG. 1C
is a cross-sectional view of still another prior art booster charge
700
. Cast booster charge
700
comprises pentolite filling
750
and a less sensitive TNT-containing mixture for filling
752
. There is no mixture of pentolite and TNT in this prior art charge. Note that if a detonator does not contact pentolite filling
750
, sensitivity of the charge may not be sufficient to insure detonation.
It is further known in the art to make the booster explosive from a first explosive such as TNT and to contact or line the passageway with a second explosive which is more sensitive to initiation than the first explosive.
U.S. Pat. No. 4,776,276, issued to M. E. Yunan on Oct. 11, 1988 and entitled “Cast Explosive Primer Initiatable By Low-Energy Detonating Cord”, discloses a cast booster charge which contains PETN disposed in a sleeve about the passageway through the charge where a detonating cord passes. The PETN about the passageway is more sensitive to initiation than the rest of the explosive material of the cast booster, so its close proximity to the detonating cord increases the reliability of initiation. Other prior art expedients include embedding a length of detonating cord at the passageway or providing a core of high PETN content surrounded by an annular body of a less sensitive explosive. The more sensitive, second explosive emplaced at the passageway is more reliably initiated by the detonating cord or detonator placed within the passageway and in turn initiates the remainder of the booster explosive.
U.S. Pat. No. 4,000,021, issued to Voigt, Jr. on Dec. 28, 1976 and entitled “Process For Suspending Particulate Additives In Molten TNT”, di

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