US3020844A - Explosive device - Google Patents

Description

Feb. 13, 1962 R. J. MILLER 3,020,844

EXPLOSIVE DEVICE Filed Dec. 29, 1958 INVENTOR. ROSS J. MILLER 3,2,84t Patented Feb. 13, teen 3,020,844 EXPLOSIVE DEVICE Ross J. Miller, Pitman, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed Dec. 29, 1958, Ser. No. 783,454 Claims. (Cl. 102-27) The present invention relates to a novel blasting initiation assembly. More particularly, the present invention relates to a novel connecting assembly whereby a detonation impulse is transmitted from low-energy connecting cord to detonating fuse.

Often in blasting operations, the detonation impulse is transmitted to the main explosive charges by means of detonating fuse which contains from 40 to 120 grains of high explosive per linear foot. This transmission is accomplished by a trunk line of fuse to which are attached branch lines of the same fuse leading down into the individual boreholes. Due to the high brisance produced by the exploding core of the described detonating fuse, these attachments may be made satisfactorily by knot-ting the branch detonating fuse to the trunk line. However, the noise and destructive violence produced by the explosion of such detonating fuse on the surface of the earth has resulted in much dissatisfaction with its use as a trunk line. The unpleasing noise level reached by an exploding length of conventional detonating fuse in air is very high. Many users of such fuse in populated areas have received complaints from individuals who have been discomforted by the noise produced. In many instances in rural areas, complaints that blast noise has had an adverse effect upon livestock have resulted in suspension of operations and law suits. Due to the psychological nature of these complaints, they are much more difficult to deal with than are complaints arising from actual damage. A further, and more restrictive, disadvantage of such detonating fuse trunk lines is that they cannot be used in operations where the line of initiation must pass objects which will not withstand a shattering explosive force. Expensive, elaborate, and time-consuming shielding methods such as, for example, covering the entire length of the trunk line with earth, must be employed in order to circumvent these undesirable effects.

Under many circumstances, the use of a more recently developed device, low-energy connecting cord, instead of detonating fuse, as the trunk line has been found to be advantageous. This connecting cord, described in detail in copending application Serial No. 744,586 filed June 25, 1958, now Patent Number 2,982,210 by D. J. Andrew, R. W. Felch, and G. A. Noddin, comprises a continuous core of 0.1 to 2 grains of a cap-sensitive high explosive per foot of length confined within a metal sheath, which preferably is countered with a strengthening and protective coating. The described cord is capable of propagating detonation at the velocity of conventional detonating fuse but without the accompanying destructive shattering or annoying noise. However, owing to the reduced brisance, transmission of detonation from a low-energy connectingcord trunk line to a conventional detonating fuse branch line cannot be achieved by the methods ordinarily employed with detonating fuse, i.e., knotting the ends or taping the lengths side-by-side. Therefore, a need exists for a means of reliably transmitting a detonation impulse from low-energy connecting cord to a detonating fuse branch line with an essentially simultaneous continuation of the detonation impulse in the trunkline.

Accordingly, an object of the present invention is to provide an easily practiced means of initiation for cordlike explosive devices, such as detonating fuse and the like. Another object of the present invention is to provide an assembly for connecting low-energy connecting cord and detonating fuse in such a manner that the detonation impulse is transmitted reliably to the detonating fuse from the low-energy connecting cord. A further object of the invention is the provision of an efficient blasting method wherein no objectionable noise or above-ground shattering is encountered. Other objects will become apparent as the invention is more fully described.

' We have found that the foregoing objects may be achieved when we provide as a connector for low-energy connecting cord and detonating fuse a blasting initiation assembly which comprises a tubular metal shell integrally closed at one end and containing a cap-sensitive detonating explosive therein and concentrically disposed around at least a portion'o-f said shell and contiguously joined therewith a cylindrical sleeve, the end portion of said sleeve opposite said shell having an inside diameter essentially 7 equal to the inside diameter of said shell, and having in tion of detonating fuse of sufiicient length through the apertures provided. Under circumstances where no tension is encountered, crimping of the sleeve may be omitted as the sleeve has been provided with an extension the I inside diameter of which is essentially equal to the outside diameter of low-energy connecting cord and which can retain the cord firmly, particularly if alternate means for retaining the cord are provided in the surface of this portion of the sleeve. The cord should be crimped in the shell to insure initiation of the explosive charge in the shell and to provide a water-tight junction.

In order to described more completely the nature of the present invention, reference is now made to the accompanying drawings, in which the same number has been used to indicate the equivalent parts of the assembly and FIGURE 1 is a top view of one embodiment of the assembly of the present invention,

' FIGURE 2 is a schematic View, partially in cross-section, of the assembly with a length of detonating fuse and two lengths of low-energy connecting cord inserted,

FIGURE 3 is a top view, partially in cross section, of the assembly provided with an aperture which is pear shaped and a shell having a delay element interposed adjacent the explosive charge.

Referring to the drawings in more detail, and particularly FIGURE 1, 1 is a metal shell having one integrally closed end and containing explosive charges 9 and 10. 2 represents a cylindrical metal sleeve having one end concentrically disposed around the closed end portion of shell 1 and having a pair of apertures 3 which form an opening of at least the diameter of detonating fuse and are located in sleeve 2 so as to be contiguous to the closed end of shell 1. 4 represents the other end portion of sleeve 2 and has an inside diameter essentially equal to the inside diameter of shell 1.

In FIGURE 2, l, 2, 3, and 4 are the same as in FIGURE 1. 5 and 7 represent terminated lengths of low-energy connecting cord inserted into the assembly, the terminal end of cord 7 being retained in the assembly adjacent to the primer charge of a heat-sensitive priming explosive 9 by a circumferential crimp 8. 6 is a length of conventional detonating fuse inserted through the apertures 3. The primer charge 9 is initiable by cord 7 and is above the base charge of a detonating explosive 10 which is disposed at the closed end of shell 1 and which initiates detonating fuse 6. 16 represents the explosive core of the low-energy connecting cord 5. 17 is a metal sheath surrounding the core 25, and 18 is a nonmetallic countering around sheath 17. The explosion of detonating fuse 6 immediately initiates the adjacent low-energy connecting-cord trunk line 5. Care must be taken so that the connecting cord is essentially abutted against the length of detonating fuse 6 and that detonating fuse 6 is adjacent the closed end of shell 1 in order to assure continuation of the detonation. Therefore, aperture 3 is preferably somewhat wider than the diameter of ordinary detonating fuse in order that a visual inspection may insure that the terminal portion of cord 5 is closely adjacent to detonating fuse 6, detonating fuse 6 then being firmly maintained between the closed end of shell 1 and the end portion of cord 5 by being squeezed between these two.

In FIGURE 3, 1, 2, 3, 4, 9, and 10 are as in FIGURES 1 or 2. 11 are inwardly directed prongs provided as an aid in retaining the low-energy connecting cord in the portion of smaller diameter 4 of sleeve 2. 12 represents a circumferential crimp which joins shell 1 and sleeve 2 integrally. 13 represents a delay element comprising an exothermic-burning mixture of boron and red lead in terposed adjacent the primer charge 9. 14 represents an open-ended metal capsule having a central aperture 15 interposed adjacent the delay element 13 and which provides static resistance.

In applying my invention to blasting operations, the low-energy connecting-cord trunk line is severed and one cut end inserted into the open end of the shell, and the shell is crimped. Then detonating fuse of a suitable length is threaded through the apertures provided therefor, one end of the detonating fuse extending to the bottom of the borehole. Next, the other cut end of the low-energy connecting-cord trunk line is inserted into the end portion of the sleeve, firmly abutted against the detonating fuse, and crimped. Optionally, inwardly directed prongs may be provided in the Wall of the portion of the sleeve having a smaller diameter in order to retain the low-energy connecting cord during the crimping operation. The end of the detonating fuse not extending to the bottom of the borehole is buried in the stemming or is taped or tied to the longer extension to insure against the withdrawal of the fuse from the assembly. The as-, sembly thus formed may be buried to eliminate the escape: of noise from the detonating fuse.

Low-energy connecting cord has a larger outside diameter than that of detonating fuse in order to insure against the use of the cord in an assembly or fitting designed for use only with the fuse or vice versa. In order to provide the maximum side wall and corresponding strength at the portion of the sleeve containing the apertures, the apertures must be in that portion having the larger diameter.

The exemplified shell containing an explosive charge is necessary, due to the low brisance produced by exploding low-energy connecting cord, in order to initiate the detonating fuse. Within the shell are disposed at the closed end a base charge of a cap-sensitive detonating highexplosive of the type conventionally used as the base charge of initiators, i.e., PETN, RDX, lead azide, picryl sulfone, etc., and adjacent the base charge a primer charge of a high explosive which is readily initiated by the low-energy connecting cord. Examples of such priming compositions are lead azide, diazodinitrophenol, and mercury fulminate. If a time delay is desired in the blasting operation in order to provide improved and more predictable burden movement, as'is often the case, a delay charge may be included adjacent to the primer charge as is shown in FIGURE 3. Such a delay device is described in copending application Serial No. 749,848 filed on July 21, 1958, by R. J. Miller and G. A. Noddin and assigned to the present assignee and contains as the delay element a layer of a mixture 'of boron and red lead. The low-energy connecting cord and the detonating fuse will have explosive cores comprising a cap sensitive high explosive, for example, PETN, RDX, lead azide, or picryl sulfone.

It is not necessary that the sleeve cover more than a portion of the shell. However, it may be extended as far as that portion of the shell which is to be crimped. Furthermore, the means by which the two elements are permanently engaged is not critical. An adhesive, :1 circumferential crimp, a friction joint, or any other of the commonly used joining means may be employed.

In practice, two of the above described assemblies may be used in conjuncture, i.e., tied or taped side-by-side, in order to insure detonation of the charge in the borehole. In this way, if one trunk line fails, completion of the blast will be achieved by the second assembly and without the necessity of the dangerous and expensive task of reconnecting the holes. With such duplicate assemblies the propagation of the detonation in each of the trunk lines is assured by the brisance produced by the explosion of the detonating fuse.

Many variations of the above described assembly are within the scope of this invention. For example, the sleeve may be provided with a second shell containing an explosive charge at the end of smaller diameter, the:

second shell also being abutted against the detonatingv With such an assembly detonationv fuse branch line. from either end of the trunk line is practicable. In complicated and interconnected blasting designs, detonation of the trunkline from either end is often highly desirable.-

Furthermore, the cylindrical sleeve need not be of' metal as described in the exemplified embodiment of the invention. reinforced paper, or any other material having adequate rigidity also would be suitable.

The invention has been described in detail in the fore-- going; however, it will be apparent to those skilled in the art that many variations are possible without departure from the scope of the invention. I intend, therefore, to be limited only by the following claims.

I claim:

1. A blasting initiation assembly for cordlike explosive devices which comprises a tubular metal shell closed at one end and containing a cap-sensitive detonating explosive charge and a tubular sleeve having a portion of larger diameter than said shell, one end of which portion is disposed around at least the closed end portion of said shell, and the other end portion of said sleeve being of reduced diameter and having an inside diameter essentially equal to the inside diameter of said shell, said sleeve having a pair of apertures disposed directly opposite each other in said portion of larger diameter so that the axis of said apertures is normal to the longitudinal axis of said sleeve, each of said apertures forming an opening of at least the diameter of conventional detonating fuse and being so located that the closed end of said shell is essentially contiguous to said apertures.

2. A blasting initiation assembly according to claim 1 wherein the boundary of each of said apertures is represented by a pear-shaped configuration.

3. A blasting initiation assembly according to claim 1 wherein the said tubular sleeve is a sleeve of a ductile metal.

4. A blasting initiation assembly for joining lengths of low-energy connecting cord and for transmitting a detonation impulse from said low-energy connecting cord to detonating fuse which comprises a tubular metal shell having a closed end and an open end, the closed end containing a cap-sensitive detonating explosive and the open end adapted for insertion therein of a low-energy connecting cord for transmitting a detonation impulse to said detonating explosive, a tubular sleeve having a portion of larger diameter than said shell, the end of which portion is disposed around at least the closed end portion of said shell, and the other. end portion of said sleevebeing of reduceddiameter and having an inside A moldable or extrudable plastic material,

diameter essentially equal to the inside diameter of said shell to permit insertion therein of a low-energy connecting cord, said sleeve having a pair of apertures in said portion of larger diameter located directly opposite each other and having a portion of their periphery adjacent to said closed end of said shell to permit insertion through said openings, in a direction normal to the longitudinal axis of said sleeve, of a length of detonating fuse contacting said closed end of said shell.

5. A blasting initiation assembly according to claim 1 wherein said tubular metal shell contains, in addition to 1,887,122 Dufiy Nov. 8, 1932 1,991,856 Motte Feb. 19, 1935 1,991,857 Lewis Feb. 19, 1935 2,424,374 Taylor July 22, 1947 2,739,535 Rolland Mar. 27, 1956

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