US3626850A

US3626850A - Explosive assembly

Info

Publication number: US3626850A
Application number: US464802A
Authority: US
Inventors: Clyde Oliver Davis
Original assignee: EI Du Pont de Nemours and Co
Current assignee: ETI EXPLOSIVES TECHNOLOGIES INTE
Priority date: 1954-10-26
Filing date: 1954-10-26
Publication date: 1971-12-14
Anticipated expiration: 1988-12-14

Abstract

The invention is an explosive assembly having a flat metal plate in contact with a flat surface on a high-density charge of high explosive.

Description

Bite States Patent [n1 m 72] inventor Clyde Oliver Davis [52] US. Cl 102/24 Wenonah, NJ. [51 Int. Cl F42b 3/00, [2!] Appl. No. 464,802 I F42b 3/l0 [22] Filed Oct. 26, 1954 [50] Field of Search 102/24, 56 [45] Patented Dec. 14, 1971 [73] Assignee E. I. du Pont de Nemours and Company [56] Re'e'ences Cited Wilmington, Del. UNITED STATES PATENTS Continuation-impart of application Ser. No. 23 5 703 12 194 Landen ct 231,773, June 15, 1951, now abandoned which is a comlnuauomlmpan 0 Primary Exammer-Verl|n R. Pendegrass application Ser. No. 768,547, Aug. 14. WW-James 1947, now abandoned. This application I954 64302 ABSTRACT: The invention is an explosive assembly having a flat metal plate in contact with a flat surface on a high-density charge of high explosive.

[54] EXPLOSIVIE ASSEMBLY 10 Claims, 2 Drawing Figs.

Patented Dec. 14, 1971 3,62,50

INVHN'IOR CLYDE 0. DAVIS ATTOR NEY EXPLOSIVE ASSEMBLY This application is a continuation-in-part of my copending application, Ser. No. 23l,773, filed June l5, 1951 and now abandoned. the latter being a continuation-in-part of my application Ser. No. 768,547, filed Aug. l4, 1947, now abancloned.

This invention relates to an explosive assembly adapted for breaking rock, ore, cement or other rigid material into smaller pieces and more especially to a unitary assembly of a charge and a missile of particular effectiveness because of its design and method of use.

In underground and other mining operations, the breakage of rock or ore by means of the explosive used results frequently in the presence in the material blasted down of boulders of too great size for effective handling. This difficulty in handling is particularly grave, for example, when the blasted rock is moved from the working places to the haulage ways through chutes, because in such a procedure the oversize boulders frequently become wedged in the chute and block further passage therethrough. Boulders of undesirable proportions may be present likewise during road construction projects, in the fields, etc.

The methods heretofore used in fragmenting or reducing the size of such objectionable boulders have comprised practices known as blockholing, mudcapping and the like. In blockholing, the blasting method has consisted of drilling a hole into the boulder, charging the hole with dynamite and thus breaking up the rock. Mudcapping comprises ordinarily packing a mass of dynamite or other high explosive on the surface of the boulder, covering this with a confining layer of wet earth, and cracking the rock by means of the strong impact of the explosive action thereon. While much successful fragmenting has been carried out by these methods, no satisfactory procedure has been known for cracking boulders that are relatively inaccessible to the operator. In the case of boulders wedged in chutes, for example, it is necessary for the shot flrer to make a hazardous approach to the wedged rock from below and to place the explosive charge in the proper position adjacent to the rock surface. In the usual methods used, breakage of the boulders has been efiected by means of the gas pressure from the explosive. When attempts have been made to use hollow charges for breaking boulders, it has frequently been found that the jet from the charge penetrates the boulder without breaking it.

An object of the present invention is an explosive assembly adapted for the breaking up of rock, ore, or other rigid material under the influence of a missile directed against said material by the firing of the explosive charge. A further object is such an assembly comprising a high-density charge of detonating explosive packaged in contactwith a missile in position to be propelled against the target material. A still further object is a method of breaking rigid objects at a distance from the explosive assembly by means of the projected missile. Additional objects will be disclosed as the invention is described more at length in the following.

I have found that the foregoing objects are accomplished when I employ a blasting assembly or unit comprising a highdensity charge of high-velocity explosive with desirably a substantially flat surface on one side thereof, a metal missile maintained in contact with said flat surface over the greater part of its area, and an initiating charge in a generally central position on the side of the explosive charge opposite to that on which the missile is located, said. explosive charge, initiating charge, and missile being enclosed in a unitary package. Whereas the high-density charge in contact with the missile may be of a low order of sensitivity such that it cannot be exploded by the usual types of initiators, it will be capable of detonation by means of the initiating charge, which itself will be sufficiently sensitive to be tired by means of a commercial blasting cap or detonating fuse. The high-density explosive may comprise a cast charge, for example of amatol, pentolite, or cyclotol (a cast blend of TNT and cyclotrimethylenetrinitramine, commonly designated cyclonite) or the like, or may be a compressed charge, such as a cyclonite-wax composition, a 50/50 pentolite composition (TNT/PETN), or it may be a gelatin dynamite of high density, for example a dynamite of a density greater than 1.35 g./cc. The initiating charge may comprise a 50/50 pentolite composition or other explosive capable of picking up rapidly to its maximum velocity on initiation. The explosive charge will have a length of from 40 percent to percent of its width or diameter.

One flat face of the explosive charge will be backed by a disk, plate, or other missile of metal or other suitable tough, dense, solid material having a thickness equal to from 5 to 20 percent of its width or diameter, this missile being in substantial contact with the greater part of the area of the explosive surface and being secured thereto by any desired means. A slight dishing of this contact surface of the explosive, rather than complete flatness, may at times be desirable. When the assembly of the type described is tired, the metallic missile will be projected in a direction parallel to the axis of the charge, that is, the line leading from the initiating charge through the center of said missile. While such an explosive assembly may be used under various conditions in the breaking of rock or other rigid material, the most advantageous field of application comes in the fragmenting of rock or ore at a considerable distance from the explosive charge, especially where such rock to be broken is in a relatively inaccessible location. This will be the case, for example, where rock or ore has been moved by gravity down a chute or raise in an underground blasting operation and has become wedged in said chute. By means of the method of the invention, the missile can be aimed from an appreciable distance at the boulder to be broken, the explosive charge fired, and the rock be readily fragmented and dislodged.

The invention will be clearly understood by reference to the accompanying drawings which show a cross section of two embodiments in accordance with my invention.

In FIG. 1, a high-density, high-velocity explosive charge comprising 2% lb. of cast amatol consisting of a 60/40 blend of ammonium nitrate and TNT is represented by l. The charge has a diameter of 5 inches and a height of 2 3/16 inches. An initiating charge 2 of a cast pentolite charge, 50/50 mixture of TNT and PETN, three-fourths lb. in amount, is in detonating relationship with the main charge, the block of pentolite being embedded in the cast amatol in a generally central position. A short length of Primacord" 3, knotted for convenience, is inserted in the initiating charge. At the end of the main explosive charge opposite the initiating charge, a steel plate 4 of in. thickness and of the same cross-sectional dimensions as said charge is butted up thereto, and the whole assembly of explosive charges and steel plate is enclosed as a unit and held together by a paperboard container 5 provided with firmly attached paperboard slipcovers 6 and 7 at each end.

In actual use, an assembly such as that illustrated is placed at a predetermined distance from a boulder or other rigid object to be broken, for example 12-30 ft. away. The aiming of the gun consists in sighting from the center, or initiating point, of the primary charge through the center of the main charge to the target. When properly aligned, firing takes place by means of the length of Primacord," and the steel missile 4 strikes against and fragments the boulder in question. The effectiveness of the assembly is such that under the conditions described, cement blocks and quarry stones of Al-Vt cu.yd./lb. explosive are broken into a number of smaller pieces by one shot.

The embodiment shown in FIG. 2 is as follows. A high-density, high-velocity explosive charge comprising 156 grams of a pressed cyclonite-wax composition is represented by 11. This charge has a diameter of 2 inches and a height of 2 inches. An initiating charge 12 of pressed cyclonite, 18% grains in amount enclosed in a capsule 16 is abutted in detonating relationship with the main charge in a generally central position. An electric blasting cap [3 is positioned adjacent to the initiating charge 12. At the end of the main explosive charge opposite the initiating charge, a steel plate 14 of %-in. thickness and 2-in. diameter is butted up to the said charge. The initiating charge and blasting cap are maintained in position by a wooden plug 17 and the assembly is enclosed as a unit within a paperboard container 15. This embodiment was used in making the tests described later and is used similarly to the embodiment described in FIG. 1 except that the charge is initiated by means of the blasting cap.

The requirements for the main explosive charge of the assembly are that it be of high bulk strength and high velocity under priming action of the initiating charge. High density is therefore necessary. Amatol compositions are well adapted for use, and a 60/40 composition is readily castable and otherwise suitable. Other high-density compositions may be used, however, such as cast mixtures of TNT and PETN (pentolites), cast blends of TNT and cyclonite (cyclotols), highdensity pressed charges of cyclonite-wax compositions, gelatin dynamites of density greater than 1.35, in fact any high-bulkstrength explosive capable of high-velocity detonation when unconfined.

The initiating charge should be one capable of firing by means of the usual detonating devices and of picking up rapidly to maximum velocity. Pentolite of 50/50 composition has been cited in the example and is well adapted for use. Other compositions may be employed, however, such as TNT/cyclonite blends, cyclonite by itself, and others, either in cast or pressed form but desirably at high density. The primary initiation may take place by means of commercial blasting caps or detonating fuse, for example, by Primacord."

The metal missile will be substantially in contact with the main explosive charge over the greater part of the surface area facing the target. Desirably this missile will be a steel plate because of the tough, dense characteristics of this metal, but other metals of suitable properties may be used.

Explosive charges and missiles both square and round in cross section have been used effectively, and other regular shapes may also be used.

The explosive assembly may be packaged in any convenient manner. For example, a paperboard container having a paperboard slipcover fastened at the top and base, as illustrated in the accompanying drawing (FIG. 1), is a suitable means of keeping the explosive charge in contact with the flat missile. A wrapper of heavy paper or foil or strips of heavy gummed tape would likewise serve. It is preferable, however, that materials which would produce dangerous fragments on explosion of the explosive charge not be used. If desired, the explosive charge and the flat metal missile may be shipped separately and combined in a unitary package at the place of use.

There are certain critical ratios of explosive charge length and width or diameter and metal missile thickness and width or diameter. Thus, the length of the explosive charge must be from about 40 percent to 100 percent of the width or diameter of the charge and the thickness of the missile must be from about 5 to 20 percent of the width or diameter of the missile. If the explosive charge has a length of less than about 40 percent of its diameter, the detonation wave resulting from central initiation will reach the central portion of the missile and propel the missile away from the charge before the full effectiveness of the charge can be attained. In some cases, the missile will be broken as a result of the central impact. On the other hand, if the length of the charge is in excess of about I percent of its diameter, the explosive force produced may disintegrate the metal plate instead of propelling it.

With respect to the missile thickness, if the thickness is less than about percent of its width or diameter, the explosive force over the surface area will disintegrate the metal plate and the fragments thus produced will not have the capacity to provide the desired impact on the target. On the other hand, when the missile thickness exceeds about percent of its width or diameter, its mass is such that the explosive force distributed only over the area of one surface will either fail to in- :luce sufficient velocity for satisfactory impact, or the metal will be fractured and cratered by the explosive instead of being hurled effectively as a missile.

The following examples illustrate the effect of the foregoing ratios. In the examples, the assembly shown in FIG. 2 was used. The charge and steel disk had a diameter of 2 inches, the charge consisted of percent cyclonite and 5 percent wax compressed at a pressure of 10,000 lbs. p.s.i., (density approximately l.69/cc.) and the ignition charge consisted of pressed cyclonite. The tests were made by firing the assembly towards an l8-in. thick reinforced concrete wall and measuring the average diameter and greatest depth of the crater produced. The volume was calculated using the formula for the volume of a cone:

The surprising characteristic of the explosive assembly of my invention is the fact that the missile itself is not shattered by the detonation of the high-velocity detonating explosive contiguous thereto but is propelled intact at very high velocity in a predetermined direction.

The invention has been described adequately in the foregoing and discloses a blasting assembly of unusual potentialities and a novel method of blasting that accomplishes by a simplified procedure, results that heretofore could be attained only by complicated and hazardous operations. It will be understood that many variations in details of assembly, explosive charges and procedures may be introduced without departure from the spirit of the invention.

I intend to be limited, therefore, only by the following claims:

1. An explosive assembly adapted for breaking rigid materials which comprises a high-density charge of an explosive capable of detonating at high velocity when unconfined, said charge having a substantially flat surface at one end thereof, and'having alength of from 40 percent to percent of its width, a flat metal missile in contact with said flat surface of explosive over the greater part of its area, said missile having a thickness of from 5 percent to 20 percent of its width, and a cap-sensitive initiating charge in a generally central position on that side of said explosive charge opposite to said missile, said explosive, metal missile, and initiating charge being enclosed in a unitary package, whereby, upon initiation, said missile is adapted to be hurled intact at high velocity in a predetermined direction toward said rigid materials to break the same.

2. The explosive assembly of claim 1, in which theexplosive charge in contact with the missile is in highly compressed form.

3. The explosive assembly of claim 1, in which the explosive charge in contact with the missile is in cast form.

4. The explosive assembly of claim 1, in which the explosive charge in contact with the missile is amatol.

5. The explosive assembly of claim 1, in which the explosive charge in contact with the missile is pentolite.

6. The explosive assembly of claim 1, in which the explosive charge in contact with the missile is cyclotol.

6 7. The explosive assembly of claim 1, in which the explosive 9. The explosive assembly of claim 1, in which the initiating charge in contact with the missile is a gelatin dynamite having rge i comprised Of cyclonite. a density greater than 1.35. 10. The explosive assembly of claim 1. in which the initiats. The explosive assembly of claim 1, in which the initiating s charge is embedded in the castmain explosive g charge is a pentolite composition. 5 w a a a

Claims

1. An explosive assembly adapted for breaking rigid materials which comprises a high-density charge of an explosive capable of detonating at high velocity when unconfined, said charge having a substantially flat surface at one end thereof, and having a length of from 40 percent to 100 percent of its width, a flat metal missile in contact with said flat surface of explosive over the greater part of its area, said missile having a thickness of from 5 percent to 20 percent of its width, and a cap-sensitive initiating charge in a generally central position on that side of said explosive charge opposite to said missile, said explosive, metal missile, and initiating charge being enclosed in a unitary package, whereby, upon initiation, said missile is adapted to be hurled intact at high velocity in a predetermined direction toward said rigid materials to break the same.

2. The explosive assembly of claim 1, in which the explosive charge in contact with the missile is in highly compressed form.

7. The explosive assembly of claim 1, in which the explosive charge in contact with the missile is a gelatin dynamite having a density greater than 1.35.

8. The explosive assembly of claim 1, in which the initiating charge is a pentolite composition.

9. The explosive assembly of claim 1, in which the initiating charge is comprised of cyclonite.

10. The explosive assembly of claim 1, in which the initiating charge is embedded in the cast, main explosive charge.