Detonator Fuse Initiated Aqueous Slurry Explosive System

Abstract

A detonator cord-initiated slurry type inorganic oxidizer salt explosive system is provided, in which the slurry explosive charge is detonatable without substantial loss in detonation energy encountered heretofore, and which comprises a detonator cord having alternate high and low energy loadings extending in lengthwise contact with a mass of the explosive; a booster type detonator for the explosive within the mass and adjacent each high energy core section and detonatable by detonation energy transmitted from the adjacent high energy section; each high energy section being detonatable by detonation energy transmitted from an adjacent low energy core section which has a loading not exceeding about 18 grains PETN (or equivalent) per foot, and thereby laterally transmits insufficient detonation energy to the main charge to cause substantial lowering of the detonation energy thereof. The high energy section loading is at least 25 grains PETN (or equivalent) per foot. In one embodiment, the high energy section loading can be at least 200 grains PETN (or equivalent) per foot to constitute an integral unit of high energy section and adjacent booster without need for a separately disposed booster.

Description

This invention relates to detonator cord initiated aqueous slurry type inorganic oxidizer salt explosive systems having improved detonation energy characteristics.

Aqueous inorganic oxidizer salt explosives of the aqueous slurry type have been used extensively in recent years. These explosive compositions comprise an inorganic oxidizer salt or a mixture of such salts as the basic explosive ingredient, together with water, and, as a sensitizer, a high explosive such as TNT, tetry or PETN, a finely divided metal such as aluminum or a magnesium alloy, or smokeless powder. A gelation agent, or other suitable thickener, is generally included to impart additional consistency to preclude settling of the individual ingredients and to facilitate handling. These slurry type compositions are generally insensitive to detonating action of a No. 8 blasting cap and hence cap-insensitive, but are readily initiated by action of a suitable booster charge, generally a high explosive such as PETN, tetryl, composition B and the like, in turn initiated by action of a blasting cap, or a detonator cord, or fuse. Such inorganic oxidizer salt explosive compositions of the aqueous slurry type are well known, as exemplified in U.S. Pat. Nos. 3,235,425, 2,930,685, 2,836,484, and others.

The use of a detonator cord for initiation of the booster charge is often preferred inasmuch as it is reliable in performance and is readily handled during emplacement of the explosive system, and its use eliminates the need for electrical initiation means which are always susceptible to failure resulting from faulty circuiting, or misfire by static charge and/or stray currents, and at best require careful and time-consuming handling to assure satisfactory emplacement in the explosive system.

However, in the use of a detonator cord initiator in aqueous slurry inorganic oxidizer salt type explosives, it is generally required that the core loading be in order of at least 25 grains, more often 50 grains or higher, of PETN (or equivalent) per linear foot, to assure reliable detonation of the booster charge; and, when the detonator cord extends to the embedded booster, within, or along side of, the mass of emplaced main explosive charge, there is a loss in detonation energy of the main charge that is not encountered when the initiation is done by nondetonating cord initiator means. It has been observed that under such shooting conditions there is a lateral transmission of detonation energy from the cord to the adjacent, or surrounding, mass of main explosive charge with accompanying loss in detonation energy of the main charge. Although the phenomenum is not clearly understood, it appears that the detonation energy loss is due to compression, and accompanying density increase, of the main slurry charge, that takes place in response to force of the laterally transmitted energy.

I have found that such loss in detonation energy can be markedly reduced, or substantially eliminated, when the detonator cord contains alternate high and low energy loadings. My invention is based on the discovery that a requisite high loading can be disposed adjacent each booster charge in the system, in detonating relationship therewith, and that a markedly lower energy loading can be utilized along the remainder of the cord length which is sufficient for transmission of requisite detonation energy to the higher core loading in the booster area but insufficient for lateral transmission of any significant amount of detonation energy to the adjacent or surrounding mass of main explosive; and that under such conditions there is no appreciable loss of detonation energy from the main explosive charge. It is therefore an object of the invention to provide such an explosive system.

In accordance with the invention, a detonator cord-booster initiated cap-insensitive aqueous slurry type inorganic oxidizer salt explosive system, having markedly reduced detonation energy loss, is provided, which comprises a detonator cord having alternate core sections of high and low energy loadings extending in lengthwise contact with a mass of said explosive; a booster type detonator for said explosive within said mass and adjacent each high energy core section, and detonatable by detonation energy transmitted from said high energy section adjacent thereto; each said high energy core section having a loading of at least 25 grains PETN (or equivalent) per foot sufficient to provide detonation energy for detonation of said booster adjacent thereto, and detonatable by detonation energy transmitted from an adjacent low energy core section described below; and each said low energy core section having a sufficient loading to provide detonation energy for transmission to an adjacent high energy core section to cause detonation of same, but not exceeding about 18 grains PETN (or equivalent) per foot, whereby said system provides for detonator cord type initiation of said slurry type explosive without substantial loss in detonation energy of same.

Any suitable high energy core loading of at least 25 grains PETN (or equivalent) per foot is utilized, the high energy core per-foot loadings often being as high as 200 grains, and in preferred practice in the range of from about 50 to 100 grains. Any suitable low energy core loading not exceeding 18 grains PETN (or equivalent) per foot is utilized, the low energy core per-foot loadings often being as low as 0.2 grain, and in preferred practice from about 2 to about 12 grains.

In preferred practice, the mass of emplaced explosive is columnar and has a length of from 2 to 50 feet, and a plurality of booster charges is disposed along the length of the columnar mass, often successively spaced apart a distance of from 5 to 20 feet; the high energy core loadings are at least about 50 grains PETN (or equivalent) per foot, and the low energy core loadings are at least about 2 grains per foot. However, the system often contains a single booster charge, generally at or in close proximity to one end of the column with the low energy section of the cord leading from the booster to the adjacent upper end of the slurry mass for communication with an external initiator means, generally an electric blasting cap or a trunk line type of detonator fuse.

In another embodiment, the core loading of any one or more high energy core sections can be sufficiently high to constitute an integral unit of high energy core section and adjacent booster. In that embodiment, the loading of the high energy core section is at least 200, and preferably 300-700, grains PETN (or equivalent) per foot and eliminates the need for maintaining the booster adjacent thereto, as a separate unit.

The invention is illustrated with reference to the drawings, of which,

FIG. 1 illustrates an explosive system of the invention emplaced for shooting in a bore hole; and

FIG. 2 is a view along the line 2--2 of FIG. 1 showing a booster charge and high energy core section of the assembly of FIG. 1 in detonating relationship therewith.

Referring to FIG. 1, explosive system 10, in bore hole 11, comprises a columnar mass 12 of gelled aqueous slurry type inorganic oxidizer salt explosive 13, detonator cord 21 extending lengthwise within mass 12 and having continuous core 22 with alternate core sections b, d and f of high energy loading and a, c and e of low energy loading, and spaced booster type detonators 17, 18 and 19 within the explosive mass. Explosive 13 is detonated by detonation energy transmitted from boosters 17, 18 and 19 which in turn are detonated by detonation energy transmitted respectively from high energy core sections b, d and f; and high energy core sections b, d and f are respectively detonated by detonation energy transmitted from adjacent low energy core sections a, c and e.

Detonator cord 21 comprises a continuous core 22 of high explosive, such as PETN, covered with a suitable plastic type sheet 23 and extends, within mass 12, from the stemming level 14 substantially to the bottom 15 of the bore hole.

Boosters 17, 18 and 19 respectively contain passageways 17', 18' and 19' extending therethrough co-directionally with detonator cord 21; and cord 21 extends through each of passageways 17', 18' and 19'. Boosters 17, 18 and 19 are spaced so as to contain high energy loading sections b, d and f respectively within passageways 17', 18' and 19' and hence to position each booster type detonator adjacent each high energy section of core 22.

Each high energy section b, d and f is supported in position within the respective booster unit in any suitable manner such as by tapes 17a and 18a wrapped around cord 21 adjacent both the top and bottom ends of booster assemblies 17 and 18 respectively, tape 19a wrapped around cord 21 adjacent the top end of booster 19 and section g or cord 21 as a knot g' adjacent the bottom end of booster 19. Each tape is wrapped to a diameter greater than that of the respective passageways 17', 18' and 19' and knot g' is of cross-sectional dimension greater than the diameter of the passageway 19'.

Each high energy core section b, d and f has a loading of at least 24 grains PETN (or equivalent) per foot sufficiently high to respectively provide the requisite detonation energy for transmission to the boosters 17, 18 and 19. Each low energy core section a, c and e has a suitable loading below 18 grains PETN (or equivalent) per foot, which is sufficient to provide detonation energy for transmission to the adjacent high energy core section to cause detonation of same. Although end core section g does not function to initiate a high energy core section, it does not exceed the maximum for the core sections a, c and e in order to provide insufficient detonation energy for lateral transmission to the surrounding main explosive mass to cause any substantial detonation energy loss of the mass. Advantageously, the loading of small core section g is generally the same as that of sections a, c and e. If desired, means other than low energy section g can be utilized for support of detonator cord 21 in booster 19.

Section a' of detonator cord 21, outside mass 12, and having a core loading genrally about the same as that of the low energy core loadings within mass 12, extends upwardly from section a through stemming material 16 to connect with a trunk line 25 above ground as the initiating energy source, and is secured to line 25 by knot means 25a.

In the operation of the embodiment of FIG. 1, the "down line" or detonator cord 21 is initiated by detonation energy transmitted from trunk line 25 via extended end section a'. There is, of course, detonation along the entire length of cord 21, there being in succession, detonation of sections a, b, c, d, e, and f with no substantial lateral transmission of detonation energy to the surrounding slurry mass from the low energy loaded core sections, but with detonation of each booster charge and accompanying release of detonation energy lost heretofore due to lateral transmission of energy from the cord to the main charge 13.

The aqueous slurry inorganic oxidizer salt explosives of the system of the invention are generally those which are free from ingredients which are, per se, explosives, and contain dispersed gas particles to facilitate sensitivity. Gelled aqueous slurry explosives in which the thickener is guar gum in crosslinked form are often utilized.

A composite cord of unitary construction having a connecting portion of generally low brisance and a detonating portion of higher brisance for transferring low energy signals and capable of performing useful comparatively high energy work at one or more work stations is, per se, disclosed in U.S. Pat. No. 3,241,489.

The invention is further illustrated with reference to the following examples.

EXAMPLE 1

In each of three tests, a bagged columnar cap-insensitive aqueous slurry explosive 5 inches in diameter by 26 inches in length was packed, and detonated at 40.degree. F., in an iron pipe open at one end, in response to action of a 500 gram Pentolite booster charge (including a 3 gram PETN insert) embedded in one end of the columnar mass. In the first test, the booster was initiated by action of a No. 8 electric blasting cap supported in a well extending into the booster body in detonating relationship therewith, and connecting with an outside firing current source via the lead wires extending along side the columnar mass intermediate the side wall of the bag and the inner wall of the pipe; in the second test, the booster was initiated by action of a detonator cord having a uniform loading of 50 grains PETN (or equivalent) per foot and extending from initiating contact with a No. 8 electric blasting cap outside the mass, along side the columnar charge from the end thereof opposite the booster intermediate the side wall of the bag and the inner wall of the pipe, and then into a well extending into the booster body in detonating relationship therewith; in the third test, the booster was initiated by action of a detonator cord extending into detonating relationship therewith in the same manner as described with reference to the second test except that in this test the core loading of the cord within the booster well was 54 grains PETN (or equivalent) per foot and the core loading of the cord along its remaining length was 4 grains PETN (or equivalent) per foot. Density of the slurry explosive in all instances was 1.08 grams per cc. and results of the tests are summarized as follows: ##SPC1##

The above data demonstrate that when the main aqueous slurry type explosive charge was initiated by a detonator cord under conventional core loading conditions, the detonation energy was only 62 percent of that obtained under nondetonator-fuse initiating conditions and hence the loss was 38 percent; whereas, in a system of the invention, the detonation energy was 90 percent of that obtained under nondetonator-fuse initiating conditions and hence the loss was 10 percent, thus providing a substantial reduction in the loss of detonation energy of the main charge in detonator cord initiated aqueous slurry explosive systems heretofore.

EXAMPLE 2

In each of two tests, a 5 inch diameter .times. 26 inch length bagged columnar mass of aqueous slurry explosive was detonated in an iron pipe under hydrostatic pressure of 32 p.s.i.g. at 40.degree. F. by a 2-pound Pentolite booster (including a 3- gram PETN insert) embedded in one end of the mass. In the first test, the booster was initiated by action of a No. 8 electric blasting cap supported within the booster and connecting with an external firing current energy source. In the second test, the booster was similarly positioned and was initiated by action of a detonator cord, having a uniform core loading of 50 grains PETN (or equivalent) per foot, and extending from initiating contact with a No. 8 electric blasting cap outside the mass, first into the end of the mass containing the booster and then through a passageway extending through the booster, and on through substantially the remainder of the length of the mass. The slurry explosive mass was the same for both tests, as follows:

Ingredients Parts by Weight __________________________________________________________________________ Water 15.8 Ammonium nitrate 50.0 Sodium nitrate 15.0 Ethylene glycol 4.4 Silicon alloy (85 percent Si) 12.5 Guar gum* 1.4 Sodium nitrite 0.08 Specific gravity 1.06-1.07 __________________________________________________________________________

The results of the tests are further summarized as follows:

Test 1 Test 2 __________________________________________________________________________ Detonator for the boosters EB Cap Detonator cord No. 8 (50 grains PETN per foot) Detonation rate, m/sec. 4250 3100 (slurry explosive) Total energy, main explosive charge* 0.960 0.535 __________________________________________________________________________

The data of Example 2 further demonstrate the loss in detonation energy of the main explosive charge that takes place when the detonator cord of a conventional detonator cord-initiator system, for aqueous slurry type explosive, extends in contact with the main explosive mass -- within, and substantially along the entire length of the mass, in the present instance.

Any suitable detonator cord-sensitive booster type high explosive charge can be utilized as a booster in the explosive system of the invention, exemplary of which are composition B, Pentolite, TNT, Amatol, and PETN. Often such charges also contain a small portion of a supplemental explosive of sensitivity greater than that of the main booster charge, as an "insert", in detonating relationship with the detonator cord initiator and in turn with the booster charge to facilitate detonation of the booster charge in response to initiating action of the detonator.

Claims

What I claim and desire to protect by Letters Patent is:

1. A cap-insensitive aqueous slurry type inorganic oxidizer salt explosive system including a detonator cord-booster type initiator therefor, having improved detonation energy characteristics, comprising a mass of said explosive and a detonator cord having alternate core sections of high and low energy loadings extending in lengthwise contact with said mass; a booster type detonator for said explosive within said mass and adjacent each high energy core section, and detonatable by detonation energy transmitted from said high energy section adjacent thereto; each said high energy core section having a loading of at least 25 grains PETN (or equivalent) per foot sufficient to provide detonation energy for detonation of said booster adjacent thereto, and detonatable by detonation energy transmitted from an adjacent low energy core section described below; and each said low energy core section having a sufficient loading to provide detonation energy for transmission to an adjacent high energy core section to cause detonation of same, but not exceeding about 18 grains PETN (or equivalent) per foot, whereby said system provides for detonator cord type initiation of said slurry type explosive without substantial loss in detonation energy of same.

2. In an explosive system of claim 1 a columnar gelled aqueous slurry type explosive as said mass.

3. An explosive system of claim 2 wherein said slurry explosive is free from any ingredients which are, per se, explosives.

4. An explosive system of claim 2 wherein said slurry explosive contains dispersed gas bubbles to facilitate sensitivity.

5. An explosive system of claim 2 wherein the core loading of each high energy core section is up to about 200 grains PETN (or equivalent) per foot; and the core loading of each said low energy section is within the range of from about 2 to 12 grains PETN (or equivalent) per foot.

6. An explosive system of claim 2 wherein said detonator cord extends from said mass to an external initiator source therefor.

7. In an explosive system of claim 2 a plurality of said boosters spaced apart along the length of said columnar mass, each said booster containing a passageway extending therethrough, and a high energy section of said detonator cord disposed within each said passageway.

8. An explosive system of claim 2 containing only one booster, and said booster positioned within said columnar mass at substantially one end thereof.

9. A system of claim 7 wherein said boosters are spaced apart substantially equidistantly.

10. A system of claim 7 wherein the length of said columnar mass is in the order of from about 2 to 50 feet and said boosters are successively spaced apart a distance of from 5 to 20 feet.

11. An explosive system of claim 10 wherein said explosive contains a sensitizing proportion of dispersed gas bubbles, and guar gum in cross-linked form to provide a resulting column of gelled aqueous slurry explosive.

12. An explosive system of claim 1 wherein at least one booster and high energy core section adjacent thereto constitutes, as an integral unit, said high energy section having a core loading of at least 200 grains PETN (or equivalent) per foot.

13. An explosive system of claim 12 where said core loading is 300-700 grains PETN (or equivalent) per foot.

14. An explosive system of claim 2 wherein said detonator cord extends within said mass in said lengthwise contact therewith.