US2478415A - Blasting initiator - Google Patents

Description

Aug. 9, 3949. R. J. MILLER BLAS'I'ING. INITIATOR Filed May 22, 1948 mmvrox Ros J. Miller Patented Aug. 9, 1949 BLASTING INITEATOR Ross J. Miller, Woodbury, N. 3., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware 1 This invention relates to delay electric blasting initiators of a novel design adapted to overcome difficulties heretofore encountered under certain conditions, and more particularly to an improved form of electric blasting cap.

Delay blasting caps are caps in which the detonation takes place not instantaneously with the firing of the ignition charge but at a predetermined time interval thereafter. In designing delay caps, it is customary to have a series of these, designated for example as first to tenth delays, the delay period being longer in the higher numbered devices. In blasting operations, greatly increased emciency results in many cases when the detonation of the diiferent boreholes takes place in prearranged order.

It is important, therefore, that no conditions be present that will cause one of a series of delay caps to fire out of the predetermined order, or to fail completely. Since many of the blast holes, into which explosives are loaded, are at least partly filled with water, it is desirable that there be no opening in the cap shell through which water can enter during burning of the delay charge. Ventless delays have been introduced during recent years to satisfy this requirement, the explosive and delay charges being selected from compositions that evolve the minimum quantity of gaseous products on combustion.

Even the ventless type of delay cap has not been free from drawbacks in the foregoing respect, as experience has shown that whenthese are fired in parallel arrangement from high voltage power circuits, arcing between the bridge posts may burn holes in the shell wall. Thishas caused erratic timing and occasional failures in the field in both wet and dry holes because of the extinguishing of the delay powder, either from the sudden release of pressure within the shell or from the entrance of water. An arrangement and assembly that would make arcing failures impossible and that would make the cap performance indifferent to the results of arcing constitutes a decided advance in blasting technique.

An object of the present invention is a delay blasting initiator that is so designed that its performance is unaffected by shell punctures as a result of arcing. A further object is a delay electric blasting cap of such arrangement that shell perforation as a result of arcing, with 'consequent sudden release of pressure or influx of water, causes no impairment of the delay charge. Additional objects will be disclosed as the invention is described in greater detail hereinafter.

I have found that the foregoing objects are accomplished, and a blasting device is obtained of the desired advantages, when I assemble a delay blasting initiator comprising a metal shell, containing a main explosive charge at its base, initiating means at the other end of the shell, said means being in firing contact with an ignition charge, and a delay charge between the ignition charge and the main charge. The ignition charge is separated from the delay charge by a non-permeable metal partition and the delay charge is ignited by means of the heat generated from the ignition charge and other charges located on its side of said partition and transmitted therethrough to the delay charge. Desirably a special heat-producing charge will be positioned adjacent to the partition on the side toward the ignition charge and capable of initiation thereby, while a special heat-sensitive charge will be adjacent to said partition on the side toward the delaycharge, capable of becoming ignited by the heat transmitted through the metal partition and then of causing the firing of the delay charge. It will be apparent that, with such a design and arrangement, arcing in the vicinity of the bridge posts and any resultant puncturing of the shell wall will have no impairing effect on the functioning of the cap, since the delay cap is a twocompartment device with an impermeable metal wall between ignition and delay charges. The latter charge will have become ignited before the entrance of water into the chamber and will be completely out of contact with said water.

The attached drawings will serve to illustrate several embodiments of the delay initiator of the present invention and are, of course, not to be taken as limiting in any way.

Figures 1, 2, and 3 are elevations of three embodiments of the invention, showing electric blasting cap assemblies of special design.

In Figure 1, I represents a metal cap shell, for example of gilding metal, containing a pressed base charge 2 substantially of tetryl, with a primer charge 3 mainly of lead azide in contact therewith. At its otherwise open end, the cap shell is sealed b means of the'rubber plug 4 which is molded about the leg wires 5, which are covered with insulating material for the greater part of their length. The bared ends of the two leg wires, at a position beyond the inner surface of said plug, are connected by the small diameter bridge wire 6, which is embedded in a head I of flame-producing material ignitible on passage of the electric current through the bridge wire. A delay charge 8, comprising for example an 85-15 mixture of barium peroxide and selenium and located in the central chamber of the lead carrier 9, is positioned between the ignition charge I and the base charge 2. A cup-shaped receptacle l fits tightly within the cap shell with its base just above the top of the delay charge, said base serving as an impermeable metal partition dividing the shell interior into two compartments water tight to one another, the upper compartment containing the firing mechanism and the ignition charge and the lower compartment the delay, primer and base charges. In Figure 1, a heat-producing charge I I, comprising a few grains oi magnesium-barium peroxide-selenium mixture in a 3060-10 proportion respectively is positioned on the base of the metal capsule l0. Just below the base of the cup-shaped capsule also, an additional heat sensitive mixture I2 is placed just above the delay charge, this mixture comprising a. blend of tetrazene, selenium and bismuth in a 1-35,-64 proportion. With the assembly shown, the electric current, on application, fires the bead ignition mixture 1, the flame from which immediately ignites the heat-producing charge l2. The heat transmitted through the base of the capsule l0 fires the heat-sensitive mixture H. which in turn ignites the delay charge 8. The primer and base charges function in the usual manner. being initiated by the delay charge. It will be seen from the foregoing description and the drawing that arcing, even if it causes puncturing of the shell wall, will have no efiect on the functioning of the delay cap. By the time the shell has been opened up to permit entrance of water, the heat sensitive charge II will have brought to ignition the charges on the other side of the metal partition, which are out of reach of the incoming water because of the impenetrability of the partition. When arcing occurs, a hole will ordinarily be left in the shell wall at a point opposite the base ends of the leg wires emer ing from the bridge plug.

Figure 2 represents a similar two-compart-' ment dela electric blasting cap. Again a watar-impermeable partition is present separating the ignition composition from the dela charge and the main explosive charge. Instead of the upright capsule of Figure 1, an inverted cupsha ed metal capsule is present, designated as ill, the top of which constitutes the wall through which heat is transmitted to fire in turn the heat sensitive mixture I2, the delay charge 8, the primer charge 3, and the base charge 2.

Figure 3 represents a third embodiment of a delay electric blasting cap assembly. As in Figure 2, an inverted cup-shaped metal capsule I 0 is provided, to prevent the ingress of water into thecompartment containing the delay charge. Whereas the inverted capsule in Figure 2 was inserted sothat the side walls were outside the outer walls of the carrier 9, the capsule in Figure 3 has its side walls driven down into the metal of the walls of the lead carrier, whereby a tight joint is secured. Whereas'the carrier is of lead, it is essential in the arrangement of Figure 3 that the inverted capsule be of a metal harder than that of the carrier, for example copper, steel, a copper alloy, etc. An additional feature of Figure 3 is the metal sleeve 13, for example of a copper alloy, which will aid in the prevention of shell rupture from arcing.

The present invention is applicable to delay electric blasting initiators generally, whether used in electric squibs where the main charge will be a deflagrating'explosive capable of producing flame or in blasting caps, which will be the '4 more important place of employment, where the base charge will be a high velocity detonating explosive adapted to explode another high velocity explosive by shock wave.

Various compositions for explosive charges are suitable for use in the delay electric blasting caps of the invention. Any of the commonly used explosive compounds capable of high velocity detonation and possessing satisfactory strength may be used as base charges, for example tetryl, pentaerythritol tetranitrate, cyclonite, etc. As primer charge, materials and compositions will be employed that are capable oi. ignition by flame and of subsequently bringing the base charge to detonation, for example lead azide, mercury fulminate, etc. Various types of ignition charges may be used, a requirement being that they produce sufficient flame to fire the succeeding charge. The drawings have shown the ignition charge in the form of a bead suspended on the bridge wire, and this is a very convenient arrangement. A loose charge may be used, however, surrounding the bridge wire, or the concave plug or match head types of firing assembly may be employed. The invention is not limited as to composition of ignition charge.

The delay charge may be present in the bore of a metal carrier, of lead for example, such as is commonly used, or may occupy varyingportions of the shell volume.

The delay charge will be initiatedby an adjacent superposed charge and wilr'propagate combustion to another adJoining charge. The purpose of the charge is to-"produce a delay in the functioning of the cap of a predetermined order. Since the cap of the present invention is designed to be workable under wet conditions, it is important that the cap be ventless. delay charge must be one that burns with little or no gas evolution, so that no substantial rise in pressure will take place during combustion, which would produce irregularities in burning speed as well as other disadvantages. The examples have cited a barium peroxide-selenium mixture, and various analogous compositions may be used, such as potassium permanganate-antimony mixtures, mixtures of zinc and antimony with oxidizing agents, etc. The composition of the dela charge is likewise not part of the invention.

The essential feature of the invention is the impermeable metal partition separating the ignition charge from the delay charge and the main explosive charges. This partition comprises the base or top of a cup-shaped metal capsule, depending on whether this capsule is upright or inverted, secured in position within the shell to furnish water-tightness between the two compartments. A special heat-producing charge will desirably be located on the ignition charge side of the partition, which will become ignited by the flame from the ignition composition and will then transmit heat through the metal partition. This charge will therefore desirably be one characterized by high combustion temperature, for

" example one containing a metal having a high heat of combustion such as magnesium, aluminum, manganese, titanium, and the like. The examples cite a magnesium-barium peroxide-selemum composition.

A special heat-sensitive mixture will desirably be present intermediate between the metal partition and the delay charge. Such a charge will be capable of ignition by the heat transmitted through the metal partition wall and of bringing to combustion the delay charge.

Hence, the p Several devices have been shown adapted to serve for dividing the cap shell into two compartments. Cup-shaped capsules have been described either (1) in upright position, in which case the heat-producing charge will be located in the base of said capsule with the side walls extending upward inclose fittin relationship with the shell walls, or (2) in inverted position, when the heatproducing charge will be placed on the closed end of said capsule, with the side walls extending downward, either outside the wall of the carrier or driven into the soft metal structure thereof. In either case, or whatever the form of the partition, the two compartments should be substantially water tight with respect to one another.

The advantagesof the invention will be apparent from the foregoing, in that a delay electric blasting initiator is present in which the perforation of the side wall and subsequent sudden pressure release or insurge of water, which frequently takes place when such initiators are fired in parallel on high voltage power circuits, have no harmful consequences on the performance of the initiators.

The invention has been described at length in the foregoing, but many changes in assembly, compositions and details of procedure may be introduced without departure from the scope of the invention.

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

I claim:

1. A delay electric blasting initiator which comprises a metal shell, a main explosive charge within said shell, an ignition charge, and a delay charge between said main charge and the ignition charge, said ignition charge being separated from the delay charge by a non-permeable metal wall.

2. A delay electric blasting cap which comprises a metal shell, a main explosive charge within said shell and at the base thereof, an ignition charge, electrical firing means for said ignition charge, and a deflagrating delay charge between the main charge and the ignition charge, said ignition charge being separated from the delay charge by a non-permeable metal wall.

3. A two-compartment electric blasting initiator, said compartments being separated from one another by a metal partition, both compartments being contained within the same metal shell, one of said compartments containing electrical firing arrangements and an ignition charge in contact with a portion of said firing means, and the second compartment containing a main explosive charge at the base of the shell and a delay charge superposed thereon, said delay charge being in position to and of such nature as to become ignited by the heat resulting from a burning charge in the first compartment and transmitted to the delay charge through the metal partition.

4. A delay electric blasting cap which comprises a metal shell, 9, main detonating explosive charge within and at the base of said shell, an ignition charge and electrical firing means in contact therewith, a deflagrating delay charge between the main charge and the ignition charge, a nonpermeable metal partition between the ignition charge and the delay charge, and a heat-producing charge adjacent to said partition and in position to be fired by the ignition charge, said heat-producing charge being capable of combustion from the flame of the ignition charge and of transmitting heat through the metal partition and thereby igniting the delay charge.

5. The delay electric blasting cap of claim 4, in which an additional heat-sensitive charge is superposed on the delay charge in substantial contact with the metal partition, capable of ignition by the heat transmitted through said partition and of initiating combustion of the delay charge.

6. The delay electric blasting cap of claim 4, in which an upright cup-shaped metal capsule is positioned within the shell above the delay charge, the base of said capsule comprising the heatconducting metal partition.

'7. The delay electric blasting cap of claim 4, in which the delay charge is contained within the bore of a metal carrier and an inverted cupshaped metal capsule is positioned with its side walls surrounding the upper part of said metal carrier, the top of said capsule comprising the heat-conducting metal partition.

8. The delay electric blasting cap of claim 4. in which the delay charge is contained within the bore of a lead carrier and an inverted cupshaped metal capsule of a harder metal is positioned so that the top of said capsule comprises the heat-conducting metal partition, the side walls of said capsule being forced down into the lead walls of the carrier, whereby non-permeability is assured.

ROSS J.

No references cited.

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