US3021786A - Blasting device - Google Patents

Description

R. J. MILLER ET AL BLASTING DEVICE Filed July 21, 1958 Feb. 20, I962 JET 5.1

INVENTORS ROSS JAY MILLER GEORGE ADELBERT NODDIN ATTORNEY .detonating fuse leading to the explosive charge.

3,021,786 BLASTING DEVICE Ross Jay Miller, Pittman, and George Adelhert Noddin, Seweil, N.J., assignors to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed July 21, 1958, Ser. No. 749,848 3 Claims. ((21. 10227) The present invention relates to a novel delay initiator. More particularly, the present invention provides a nonelectr'ic initiator and assembly including such initiator. This application is a continuation-in-part of the copending application Serial Number 619,991 filed on November 2, 1956, and now abandoned.

The art of delay blasting has been practiced for many years. In the earlier times, the primary purpose of providing an interval between the initiation of the main explosive charges was to permit burden loosened by each preceding blast to clear before the following blast occurred. In certain cases, the delay between shots also permitted a count to ascertain whether or not all shots had actually fired. For the foregoing purposes, delay intervals of from /2 to several seconds were desired and used. .In more recent years, delay shooting to reduce ground vibration and to improvefragmentation has been widely practiced. For this purpose, delay intervals of from 5 to 100 milliseconds are desired and used. A relatively'high degree of accuracy is required for millisecond delay blasting, since a slow or undesirably fast initiation of one charge will prevent the desired vibration reduction and may have a deleterious effect on the fragmentation. For the longer interval delays, close precision is less important. a

Three means have been used in the past to achieve the desired delayed initiation of the explosive charges. The

first known means involved a mechanical arrangement for controlling the application of electrical energy to the individual" electric blasting caps. This means, with many refinements, is in use at the present time, particularly for millisecond delay shooting, and provides excellent accuracy of timing and a relatively good selection of timing intervals. The next means developed was a delay electric blasting cap in which the delay interval was provided by a delay train interposed between the electrically-ignited charge and the detonating charge of the cap. This means is widely used at present, both for long-period delaysand for millisecond delays. The most recent means developed is the interpositioning' of a delay connector in a line of This means has been applied only to millisecond delay blasting and has become increasingly accepted for above-ground blasting. I

All of the foregoing procedures and assemblies have their advantages and disadvantages. The chief advantage of the delay electric blasting cap is that the delay interval is produced in the immediate vicinity of the charge. In a shot in which a number of charges are fired in a predetermined sequence by means of delay electric blasting caps, a single electrical impulse will initiate all of the caps. Thus, no danger exists that ground movement or fragment throw from an earlier detonation might prevent ignition of a. subsequent charge by severing or shortcircuiting the line leading to the subsequent charge. On the other hand, the electric delay blasting cap is subject to the disadvantage of all electric initiation devices, i.e., complicated electrical circuits and the ever-present danger of accidental ignition by extraneous electricity, i.e., electricity from a source other than the firing device. It is because of the hazards inevitable with direct electric initiation of the explosive charges that detonating fuse has gained wide acceptance for above-'ground-blasting. Deto- 3,02i,78 Patented Feb. 20, 1962 nating fuse lines are simple to connect and are free from the hazard of accidental initiation. However, the brisance of the detonating fuse is such that the delay connector must be positioned a distance from a cap-sensitive explosive charge to avoid having the charge initiated by the detonating fuse prior to the delay. Even if this distance is only small, the danger of cut-off due to ground movement or fragments from an earlier detonation cannot be eliminated. Such cut-off results in failure to initiate the charge, thus disrupting the entire pattern and leaving an unexploded charge in the blasted area. Detonating fuse cannot be used for bottom hole priming of cap-sensitive explosive charges, a procedure gaining increased acceptance in present day blasting.

7 Delay blasting using a mechanical timing device is subject to both the danger of accidental ignition of the electrical initiators by extraneous electricity and to cutoff from previous blasts, since the electrical firing impulse does not go to a later initiator until the previous charge has been fired. f

Thus, a need has long existed for a delay blasting means wherein the delay interval occurs in the immediate vicinity of the explosive charge and which is not susceptible to accidental initiation; in other words, a non-electric delay device and assembly which can be positioned in contact with the explosive charge. 7 Accordingly, an object of the present invention is to provide such a delay device and assembly. A further object is to provide a delay device of high accuracy. A still furtherobject is to provide an assembly suitable for use for bottom-hole priming of explosive charges. Other objects will become apparent as this invention is more fully described.

The foregoing objects are achieved by providing a delay initiator which can be actuated by means of low energy connecting cord of the type described and claimed in copending application Serial No. 744,586 filed June 25, 1958, by D. J. Andrew, R. W. Felch, and-G. A. Noddin, now Patent Number 2,982,210, and assigned to the present assignee. prises a central continuous core of a high-velocity detonating' explosive encased in a metal sheath, the core containing less than 10 grains of the explosive per foot of length. Preferably, the metal, sheath will be countered with a fabrie orsynthetic polymeric material nitroglycerin dynamite charge even when taped lengthwise to the cartridge.

Thus, the present invention includes a delay initiator adapted to be initiated by the described low-energy connectingcord wherein none of the charges except the priming and/or base load will initiate a cap-sensitive explosive composition, and also an assembly of the delay initiator and a length of low-energy connecting cord containing from 0.5 to 2 grains of explosive per foot of length.

In order to more fully describe the present invention, reference now is made to the accompanying drawings which are illustrative only, the invention not being limited thereto. Each of the figures depicts modifications of the basic assembly. Throughout the figures, the same number has been used to indicate the equivalent part of the element.

The low-energy connecting cord comsembly illustrated in FIGURE 1.

Referring now to the figures, and particularly FIG- URE 1, 1 represents a tubular shell having one integrally closed end, 2 represents a. base charge of a detonating explosive, 3 represents a primer charge of a heat-sensitive detonating explosive, 4 represents an exothermicburning composition, 5 represents an openended metal capsule having a central aperture 6, 7 represents an air gap, .8 represents the terminal end of a length of lowenergy connecting cord which is held in place by peripheral crimps 9. In this figure, the connecting cord 8 isshown in partial section, showing the explosive core 10., the metal sheath 11, and the countering 12.. The assembly depicted in FIGURE 2 is identical to that, of FIGURE 1 except that a delay carrier 13 containing a delay composition 14 is interposed between the primer 3 and the exothermic-burning composition 4. The initiator illustrated in FIGURE 1 can be designed to provide a precise delay periodof from 1 to 1.000 milliseconds, depending on the depth of the exothermic-burning composition 4. In operation, the sequence is as follows for thisassembly. The initiating impulse from the detonation of the explosive core jumps the air gap 7 enclosed by the capsule 5, passes through the aperture 6, and ignites the exothermic-burning composition 4. This composition burns at a constant rate, and when thehot front reaches the. priming charge 3, the latter is ignited. The priming charge, in turn, initiates the base charge 2. The initiator depicted in FIGURE 2 provides a longer delay, i.e. 1-20 seconds, than that provided by the as- The sequence of operation of the modification illustrated in FIGURE 2 is identical to that described for FIGURE 1 except that the exothermic-burningcomposition 4 ignites the slow-burning' train of, delay composition 14, This delay composi tion 14, in turn ignites the primer 3.

In order to illustrate our invention further, reference now. is made to the, following examples.

EXAMPLE 1 A delay initiator was prepared utilizing an. aluminum shell 1.03 inch in length, 0.277 inch in outside. diameter, and having a 0.010-inch wall thickness. As abase charge, 7.2 grains of PETN was: charged to the shell and corn pacted at 200 pounds by a pointed pin. On top of this charge, 3.0 grains of lead azide, as. the primer, was loaded and compacted at the-same pressure as the base charge by a flat pin. The exothermic-burning composition, 3.0 grains of a 2/98 mixture of boron/red lead, grained with neoprene, was charged to the. shell and. compacted at 200 pounds by a dimpled pin. The dimpled pin consisted of a conventional solid cylinder designed to fit snugly into the aluminum shell and, at: the end which, was inserted adjacent to the base charge, a second cylinder 0.047 inch long and 0.114 inch indiameter. centrally positioned and protruding from the first cylinder. An open-ended aluminum capsule 0.187 inch long and having a central aperture OLOStI-inch, in: diameter was inserted on top of the, exothermicrburning composition with the open end directed away from the loaded charges.

When this initiator was .tested, a low-energy connecting cord having 1 grain of PETN per: foot of length was inserted into the assembled initiator until it reached the capsule, thus leaving an air gap of 0.187 inch between the end of the. cord and the exothermic-burning composition. When fired, the initiator gave a delay period of 9.9 milliseconds.

EXAMPLE 2 Delay initiators were assembled as described in Example 1' except that the amount, percentage composition, and compacted shape of the exothermic-burning composition were varied. The delay periods obtained when firing these initiators are reported in Table I.

Table I Boron-Red Lead Mixture Shape of Dcluv Compacting Period Amount (gr.) Percent Pin (ms Composition EXAMPLE 3 A long-period delay initiator was assembled in an aluminurn shell having essentially the same dimensions as the shell discussed in Example 1 except that a longer length was required in order to accommodate the charges. PETN and lead azide, as the base and priming charge, respectively, were loaded and compacted as described in Example 1. A delay carrier having a length of 0.25 inch and a shell' wall thickness of 0.063 inch and containing a central core of an /15 barium peroxide/selenium mixture, as a slowburning delay composition, wasplaced adjacent to the primer; of the exothermic-burning mixture identical to that described in Example 1 was loaded and compacted at 200 pounds by a Hat pin. The open-ended aluminum capsule was inserted as previously exemplified.

When the assembled initiator was tested, low-energy connecting cord containing 1 grain of PETN per foot of length was inserted into the loaded shell until it reached the aluminum capsule. Upon being tired, the initiator gave a delay period of 1.40 seconds.

scribed in Example 3 varying only the length of the delaycarrier. The. delay periods obtained on firing these initiators are reported in Table II.

Table Il Delay Delay Train Length (in.) Test Conditions IZeriogi The particular compositions selected for the various charges are not critical to the present invention, provided 1that the selected compositions function as desired; Thus,

for the base charge, any of the usual base charge compositions may be used, e.g., RDX, lead azide, PETN, nitromannite, TNT, or HMX. As the priming charge, heatsensitive detonating compositions such as lead azide, diazodinitrophenol, or mercury fulminate may be used. Obviously, when the priming composition and the base charge are identical, only one load is required; For the exothermic-burning composition, an exothermic-reacting mix* ture of a metal and an oxidizing agent such as is com monly used in ventless delay initiatorsis preferred, e.g., boron-red lead,magnesium/barium peroxide/cement, or silicon-red lead. For the long-period delay initiators, the delay composition contained in the delay carrier may be any conventional gasless delay composition which burns On top ohthecarrier, 1 grain bowaxes, are also suitable.

charges is varied depending on the effect desired. The composition of the rigid tubing surrounding the charges or spacing the charges also is not critical, butlead or any pressure which is sufficient to retain the charges in.

the shell. and not sufficient to cause desensitization of the charges is suitable.

The pressure and shape of the pin used for the cornpaction of the exothermic-burning composition is not;

critical to the ability of the initiator to function. However, the delay period is dependent upon the depth of the delay charge and amount of compaction of the exothermic-burning composition. Thereby, changes in these variables from those illustrated will produce a change in the delay period. The limits of pressure utilized to compact this charge are identical to the limits of pressure for the base and priming charge, i.e., sufficient pressure to retain the composition in the shell and not desensitize the charge. 1

As illustrated in the examples, the exothermic-burning composition preferably is grained prior to use, as exemplified by the treatment of the boron-red lead composition with neoprene. It is to be understood, however, that graining agents known in the art, such as solutions of gum, shellac, polyethylene glycol, .Thiokol, and car- Although a graining agent usually is desired to facilitate loading, the presence or absence thereof is not critical to the functioning of the device.

In the preferred embodiment of our invention, the open-ended metal capsule enclosing an air gap and having a central aperture is positioned with the open end directed away from the loaded charges. This positioning 2-inch length, one hundred percent performance was obtained on testing the initiators of the present invention. Obviously, this allowable variance is an asset in the use of the initiators in the field.

Thus, the initiator of the present invention for use with a'low-energy connecting cord having an explosive core of from 0.5 to 2 grains of explosive per foot of length, hasically comprises a tubular shell closed at one end and containing in order starting at the closed end, a base charge, a priming charge, a delay-ignition composition, and an openended metal capsule. For a longer delay period, ie 1-20 seconds, a delay train within a rigid tube is interposed between the delay-ignition composition and the primer. Many modifications, other than those herein described, will be apparent to those skilled in the art. Therefore, the invention is limited only by the following claims.

We claim: g

l. A non-electric delay initiator in combination with and adapted to be initiated by a low energy connecting cord having an explosive core of from 0.5 to 2 grains per foot of length comprising a rigid tubular shell integrally closed at one end and containing in sequence a base charge "of a detonating explosive at said closed end, a priming is recommended because the rounded corners of the capsule thus inserted serve to retain the adjacent exothermicburning composition. However, if desired, the capsule may be positioned in the reverse manner, i.e., so that the open end is directed toward the charges. Varying the diameter of the aperture in the capsule does not interfere with the functioning of the initiator. The functioning of an initiator in which a sleeve, i.e., a capsule having the maximum aperture diameter, is substituted for the preferred capsule which has partial lower closure, is within the scope of this invention. An aperture is present in the capsule in order to permit easy transmission of the initiating impulse from the detonation of the connecting cord to the delay composition. Thus, as long as there is an opening in the capsule, this condition will be satisfied.

The depth of the capsule may be varied. In addition,

the low-energy connecting cord may be inserted in the device until it reaches the bottom of capsule'or may be spaced away from the bottom of the capsule provided that the distance from the end of the cord to the delay composition does not exceed 0.57 inch. A greater separation results in unreliable functioning of the device. Within this range, however, contact up to 0.57 inch, which is considerable in shells generally having less than a charge of a heat-sensitive detonating explosive, a delay charge of an exothermic-burning composition and a tubular capsule positioned axially within the said shell contiguous tothe said delay charge, said capsule having a closure at one extremity provided with a central orifice therethrough and one, open extremity positioned in abutting relationship with said connecting cord.

2. The delay initiator of claim 1 wherein a delay carrier comprising a tube of rigid material containing a central core of a gasless delay composition is interposed between the said priming charge and the said delay composition.

3. An initiator delay assembly comprising a rigid tubular shell integrally closed at one end and containing in sequence a base charge of a detonating explosive at the closed end of said shell, a priming charge of a heatsensitive detonating explosive, a delay charge of an exothermic-burning composition, a tubular capsule positioned axially within the said shell contiguous to the said delay charge, said capsule having a closure at one extremity provided with a central orifice therethrough and one open extremity, and a length of low energy continuous connecting cord positioned in abutting relationship with the open extremity of saidcapsule, said cord comprising a central core of from 0.5 to 2 grains of high velocity detonating explosive per foot of length and a metal sheath encasing the said core.

References Cited in the file of this patent UNITED STATES PATENTS Re. 20,190 Lewis Dec. 1, 1936 868,876 Lheure Oct. 22, 1907 882,154 1 Lheure Mar. 17, 1908 2,360,698 Lyte Oct. 17, 1944 2,402,235 Burrows June 18, 1946 2,424,374 Taylor July 22, 1947 2,475.875 Burrows July 12, 1949 2,619,035 Lewis Nov. 25, 1952 2,796,834 McCalfrey June 25, 1957 FOREIGN PATENTS 747,878 Great Britain Apr. 18, 1956

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