CA1068161A - Elongated, flexible detonating device - Google Patents

Abstract

ELONGATED, FLEXIBLE
DETONATING DEVICE
(Abstract of Disclosure) There is provided an elongated, flexible unitary detonating device of indeterminate length for detonating a selected explosive material within a bore hole. The detonating device includes, in combination, a detonating cord capable of detonating the selected explosive material when initiated while in direct contact with the selected explosive and a flexible energy absorbing layer formed around and carried by the detonating cord. The energy absorbing layer is formed from an energy absorbent ma-terial and has a radial thickness sufficient to preclude detonation of the selected explosive in direct contact with the energy absorbing layer when the detonating cord is initiated. In addition, an arrangement is provided for allowing stripping of the energy absorbing layer from the detonating cord at any selected position along the detonat-ing cord to expose a portion of the detonating cord.

Description

(Disclosure) This invention relates to the art of dQtonating devices for explosives of the type placed in bore holes and more particularly to an impr~ved elongated, flexible unitary detoDating device for detonating from the bottom of a bore hole without using blasting caps or other highly sensitive explosives in the bore hole.
The present invention relates to an elongated detonating device, similar in appearance to a detonating cord, which de-vice is primarily used for botton detonation of non-cap , .' .. , ~ ~, .

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;~'~ 10 68 1 61 sensitive explosives, such as NCN and certain slurries, placed in a bore hole. The invention will be described with particular reference to this application; however, ; the invention has broader uses and may be employed for detonating certain cap sensitive explosives.
BACKGROUND OF INVENTION
In many explosive applicat~ons, a series of elongated, deep bore holes are provided in the material to be fragmented.
Such bore holes are filled with an explosive material which is chosen on the basis of explosive characteristics and cost.
In many instances, NCN and a variety of slurries are used as an explosive material because of their low cost. When these explosives are used, dynamite or cast primers are the commonly employed detonating devices. It has long been known that ' 15 substantially more energy can be transmitted to the surround-ing burden, if the explosive in the bore hole is detonated ~;' ' from a lower position. Consequently, substantial development " work has been devoted to systems for detonating the explosive column at a lower position of a bore hole. The most widely used system for this'purpose involves the use of an electric blasting cap. An electric blasting cap includes a housing having an explosive charge, which is capablë of'being detonated by an electrically heated resistance wire connected to two wires known as "leg wires". The leg wires extend from the blasting cap to a remotely located source of electrical ; current. When using this type of detonating system, the electrical blasting cap can be positioned below the surface ; of the explosive column within a bore hole with the leg wires exten~ing from the blasting cap, through the explosive column ' ; 30 and to any remote position. A current source applied across . ~
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- 2 -^`` 1~:)68161 the leg wires fires the blasting cap and detonates the ex-plosive column. This type of electrical system has proven quite useful for lower detonation of bore holes; however, certain disadvantages have become apparen~. In blasting locations, electrically operated equipment is often used ; for various non-blasting work. Many tLmes ground cables must carry electrical current for operation of such equip-ment. In addition, certain equipment generates electrical current for use by the equipment itself. Since the blast- -ing sites are exposed to atmospheric condition, it is possi-ble to experience lightning and static electricity conditions.
It has also been found that when a number of leg wires are connected for simultaneous detonation of several bore holes, these conductive wires can form receiving antennas which will generate electrical currents when exposed to electromagnetic energy sources, such as radio transmitting antennas. All of these sources of stray electricity present a potential for inadvertent detonation of electrically actuated blast- ;
ing caps after the caps are placed into bore holes. To overcome the possibility of inadvertent detonation by stray lectricity at a blasting site, expensive precautions are required.
Because of the disadvantages of electrical blasting caps, it ls somewhat common practice to detonate the upper portion of the explosive column in bore holes. In this manner, standard detonating cord can be used with a primer located at the upper portion of the explosive column. The disadvantages of electrical ~-blasting caps are avoided; however, the additional explosive strength experienced with lower detonation of the explosive column is not obtained. To reslize the benefit of lower . , ' .

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` 10 6 81 61 detonation without using an electrical system, substantial effort has been devoted to development of a positive non-electrical system for detonating explosive columns at a position deep in a bore hole.
; 5 If a standard detonating cord, which does not present the basic disadvantages of an electrical system, is extended through an explosive column in a bore hole filled with NCN, slurry, dynamite or other explosive material, the explosive column is detonated from the top when the detonation wave in the cord reaches the explosive. This is due to the fact that the explosive wave of standard detonating cord is sufficiently strong to explode non-cap sensitive explosives in direct con-tact with the cord. For this reason, standard detonating cord can not be used for lower detonation of explosive columns in the confinement of bore holes.
To provide lower detonation of explosive columns, certain - modifications have been made in detonating cord. The first proposed modificati~n of detonating cord has been the develop~
ment of a low energy detonating cord, often known as LEDC, .
which includes a small continuous lead tube filled with standard high explosive material with an approximate d~stribution or load ~-; of 1-2 grains per linear foot. This compares with a standard ~ -distribution of 15-40 grains per linear foot for "economy" ~ ~-~`! cord and over 50 grains per linear foot for reinforced cord.
By using this low explosive loading, in a flexible lead tube, sufficient detonating energy is created at a cut end of the tube for the purpose of initiating a blasting cap. As is known, : a blasting cap is a standard component having a small primary, highly sensitive charge for converting a relatively small detonating force, such as created by a low energy cord, into . ' ' .. .. .. . - . ., , , .:. ~ .
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a higher force for detonating a secondary charge. The secon-dary charge has suf~icient bulk to detonate the explosive in a bore hole. This type of system requires a good physical contact between the lead tube and primary charge of the blast-ing cap. To assure a sound eonnection to the lead tube, the blasting cap is generally secured onto the detonating cord by a relatively expensive manufacturing operation performed at the manufacturerfs plant. Consequently, the cap and cord must be purchased as a unit with the approximate length of cord being attached. If the cord length is not proper, it is not possible to splice the cord for changing its length.
This caused difficulties in the field. This low energy type of system can be used for lower detonation if the proper con-nections are ~ade at the initiating end and the blasting cap end. However, because of the sensitivity required to initiate this detonating cord, this system does not produce uniform results. If the blasting cap is not initiated after placed in a bore hole, ~t remains at the bottom of the bore hole in a dormant condition. As is well known, care must then be taken if the blasting cap is to be removed. Since the ~lasting cap includes a very sensitive primary charge an ` ` inad~ertent blow can detonate the cap and any explosive adjacent thereto. Because of the uncertainty of ignition, the possibility of leaving a dormant blasting cap in the bore hole, and the high expense of this type of system, this system has not proven the ~olution to the problems outlined above, although the low energy wave of the detonating cord does allow it to pass through certain explosive material to the lower portion of an explosive column in a bore hole.
To overcome the disadvantage of requ~ring a demanding . .

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~068161 physical contact between the low energy detonating cord at both ends thereof and the eost contaminant thereto, a further type of lower energy detonating cord has been developed using the concept of a hollow plastic tube with the inner walls of the tube coated with a slight amo-mt of high explosive material.
This ~econd type of low energy detonating cord is described in United States Letters Patent 3,590~739. Approximately 0.5 to 2.4 grains per linear foot of explosive material is used on the inside surface of a hollow plastic tube for detonating purposes. By using this structure, it is possible to extend the hollow detonating cord through an explosive column to a lower portion of a bore hole; however, since relatively low energy is created by the small amount of high explosive within the cord, this system again requires a sensitive blasting cap in the bore hole itself. By requ~ring a blasting cap in the lower portion of the bore hole, as re-quired in the first low energy type of detonating cord, a very sensitive primary charge is used in connection with a secondary ~ primer charge. Thus, if detonation does not occur, expensive precautions are necessary to remove ~he blasting cap at the bottom of a bore hole.
The two prior attempts to provide a blasting cord which can pass through the explosive charge of a bore hole for lower detonation thereof each have co~mon disadvantages. They are both predicated upon the theory that a minute distribution `; or load of high explosive within the cord, less than about 4 grains per linear foot, is the proper procedure for prevent-ing detonation of the charge as the cord is exploded through ah explosive. The reduction of loading in the core of a blast-ir~ cord ~or reducing the probabiliey o pre_ ture detoration '' '' `~

in a bore hole causes substantial disadvantages. First, each low energy system requires a blasting cap in the bore hole.
The low energy cord has insufficient usable energy for d~tonat-- ~ng a cast primer without a highly sensitive charge found in a blasting cap. Since these low energy cords use the concept of reduced available energy, detonation is less positive, - especially in the variable ambient conditions within a bore hole. Another distinct disadvantage of low energy cord is the inherent inability to transmit a detonating wave to or from a standard detonating cord. Consequently, it is not practical to provide a standard detonating cord as a trunk line for direct connection to a low energy cord forming a down line of a bore hole. Thus, to initiate the low energy detonating cord, a strong positive initiating force must be exerted on the cord itself. This results in complications when multiple ore holes are to be shot simultaneously. In addition, low nergy cords can not detonate from one cord .
to another. Thus, splicing of such cords is not practical.
With all of ~he disadvantages inherent in using low energy . 20 detonating cord, relatively expensive blasting equipment is ; required and substantial expense is incurred by using such cord. Additional expenses are incurred to assure the 8afety of the site when an attempted detonation by low energy cord fails.
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SUMMARY OF INVENliON
The disadvantages of prior attempts to provide a detonat-ing cord which will detonate an explosive column within a bore hole at the lower position thereof are completely overcome by the present invention which relates to an elongated, flexible unitary detonating device of indeterminate length, which device :~.

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` has insufficient transverse energy to detonate an explosive ; column in a bore hole when the detonating device is extended throught~e bore hole to a lower position. The invention has sufficient~strength to provide a positive detonation at the lower portion of the bore hole without requiring an inter-mediate energy increasing charge, such as found in conventional blasting caps.
In accordance with the present invention, there is pro-vided an improvement in a detonating cord having an outer surface and including a center core of particulate high ex-~ plosive material, a tensile strength increasing layer surround-; ing the core and a moisture impervious layer surrounding the core. This improvement involves the use of an energy absorb-iDg layer surrounding the outer surface of the detonating cord ;
and releasably secured thereto. By utilizing an energy ab-sorbing layer surrounding the outer surface of a detonating cord, it is possible to preclude detonation of an explosive column in a bore hole, even though the cord extends through the explosive to the bottom part of the bore hole. By re-leasably securing this energy absorbing layer onto the afore-... .
mentioned outer surface of a detonating cord, it can be stripped at both the upper and lower ends so that a detonating wave may be initiated in the cord by either another standard detonating cord or other appropriate blasting machines. In the lower portion of the bore hole, exposure of the inner cord by stripping of the energy absorbing layer therefrom allows a substantial in~
crease in the transversely transmittable energy usable for detona-` tion. By this arrangement, lower detonation of a bore hole is made possible without the distinct disadvantages experienced when using .ow energy types of detonating cord having a grain ..
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` 10 6 81 6 1 load of less than about 4 grains per linear foot.
In accordance with another aspect of the invention, there ~ -is provided an elongated, flexible unitary detonating device of indeterminate length for detonating a selected explosive material within a bore hole. The detonating device includes, in combination, a detonating cord capable of detonating the selected explosive material when initiated while in direct contact with the selected explosive; a flexible energy ab-sorbing layer formed around and carried by the detonating cord, with the energy absorbLng layer being formed from an energy absorbent material and having a radial thickness sufficient to preclude detonation of the selected explosive material when in direct contact with the energy absorbing layer while the detonating cord is initiated; and, means for allowing manual stripping of the energy absorbing layer from the detonating cord at any selected position along the detonat-ing cord.
In accordance with the preferred embodiment of the invention, the arrangement for allowing stripping of the energy absorbing layer from the internal detonating cord is a loosely woven yarn covering the outer surface of the detonating cord and covered by an extrusion of plastic which does t extend through the yarn and into fixed engagement with the surface of the detonat- -ing cord. With this arrangement, any section of the elongated element ~ay be circumferential~y cut and stripped to expose the internal detonating cord, which cord is sufficiently high in explosive force to detonate the explosive through ~hich the cord extends. The loosely woven yarn provides a cushion be-tween the outer surface of the inner detonating cord and the 30 - o~ter plastic extrusion over the layer of yarn. This cushion of :
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compressible loosely woven yarn completely surrounding the - -inner detonating cord absorbs a certain amount of trans-versely transmittable energy, even though the yarn layer ;
serves the primary function of a separating seam or joint between the energy absorbing layer and the inner cord. The -outer plastic energy absorbing layer, which is relatively - thick, coacts with the yarn to dampen and reduce the trans-mitted energy available when the inner detonating cord is initiated.
In accordance with the invention, the inner detonating cord can have an explosive core with a longitudinal distribu-tion of particulate high explosive material in the general range of 6-20 grains per linear foot. In practice, the ex-plosive distribution is approximately 11-13 grains per linear foot. As can be seen, this type of cord, although it provides the bottom detonation characteristics, does not utilize the concept of reduced available energy, as previously used for lower detonation of bore holes. Thus, the present invention . . .
i~ a departure in kind from prior attempts to develop a non- -electrical cord which will extend through a column of explosive in a bore hole for bottom detonation.
In accordance with another aspect of the invention, the above mentioned invention is connected to a standard cast primer in the lower portion of a bore hole by a unique connect-ing arrangement wherein the energy absorbing layer of the in-vention is stripped from the lower end of the detonating element and tied to a standard detonating cord which can be threaded upwardly through the explosive column and through secondary ;
cast primers for successive upper detonation of the column after an initial lower detonation. The prior low energy .

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detonating cords for bottom detonation could not be used for this purpose sin~ce they can not, by themselves, transmit a detonating wave to or from a standard cord.
In addition, by using the present invention, a standard S cord may be provided as a tr~nk line with the down lines formed from the invention. This is made possible by stripping the releasable energy absorbing layer from a selected upper por-tion of the inventian and then intimately connecting this stripped portion with a standard detonating cord trunk line.
The standard detonating cord will initiate the invention, which forms the down line to each bore hole.
The primary object of the present invention is the pro-vision of an elongated, flexible detonating device, which device can extend through an explosive column in a bore hole for lower detonation of the column.
Another object of the present invention is the provision of an elongated, flexible detonating device, which device can extend through an explosive column in a bore hole for lower detonation of a column, without using a blasting cap at the point of detonation.
Still a further object of the present invention is the provision of an elongated, flexible detonating device, which device can extend through an explosive column in a bore hole for lower detonation of a column without requiring a high sensitivity primary charge for detonating a secondary primer charge preparatory to detonation of the column.
Another object of the present invention is the provision of an elongated, flexible detanating device, as defined above, which device does not depend primarily upon the use of small core loading for its ability to fire thrQugh a portion of an ,: ' .. . . .
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106816~

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explosive column in a bore hole without detonating the column.
; Yet another object of the present invention is the -provision of a detonating device as defined above, which device can transmit a detonating wave to and from a standard -detonating cord. , -Yet another object of the present invention is the provision of a flexible detonating device as defined above, '; which device includes an outer layer of an energy absorbing material formed as a unit onto an inner detonating cord, but selectively releasable from the cord.
In accordance with one broad aspect, the invention relates to a method of detonating an explosive in a bore hole having an innermost end and an outermost end, said method ;
comprising the steps of: (a) providing a first detonating -; cord having two ends and a transversely transmittable energy ' sufficient to detonate said explosive; (b) providing an elongated detonating device having first and second ends and including an inner second detonating cord and an outer energy absorbing layer which device adjacent said layer has a ;
, ; 20 transversely transmittable energy insufficient to detonate ~ said explosive and said first detonating cord; (c) stripping ;; said outer layer from first end of said elongated device;
(d) connecting said first end of said elongated device to one end of said first detonating cord; (e) placing said connected end adjacent said innermost end of said bore hole with said second end of said elongated device extending to a position adjacent said outermost end of said bore hole and said first -cord extending from said innermost end toward said outermost -end of said bore hole; and, (f) initiating said second end of , 30 .said element.
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: ; -~068161 These and oth,er objects and advantages will become . apparent from the following description taken~ together with the accompanying drawings.
. BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings accompanying this specification: :
. FIGURE 1 is a pictorial view showing the preferred embodiment of the p~esent invention;
FIGURE 2 is an enlarged cross-sectional view taken generally along line 2-2 of FIGURE l;
FIGURE 3 is an enlarged, partial cross-sectional view illustrating the stripping characteristics of the present invention;
; FIGURE 4 is an enlarged, partial cross-sectional view illustrating the stripping characteristics of the preferred embodiment;
FIGURES 5, 6 and 7 are enlarged, partial cross-sectional views similar to FIGURE 4 showing modifications of the ; preferred embodiment of the present invention;
,~ FIGURE 8 is a partial, schematic, partially cross-, 20 sectioned view illustrating one type of connection between the : present invention and a somewhat standard cast primer; .

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3Q ' , , .. - 12a - -FIGURE 9 is a view similar to FIGURE 8 showing another arrangement for connecting the present invention with a cast primer and illustrating the feature of the invention allowing transmission of a detonation wave to a standard detonating cord;
FIGURE 10 is a schematic, cross-sectional view showing a blasting system using the preferred embodiment of the present invention;
FIGURE 11 is a pictorial view showing a connection be-tween the present invention and a trunk line using a standard detonating cord; .
FIGURE llA is a plan view showing the structure illus- ~
. trated pictorially in FIGURE 11; : .
FIGURE 12 is a view similar to FIGURE 10 illustrating .
; 15 a blasting system using a further aspect of the present inven-tion; and, .
; FIGURE 13 is a view similar to FIGURES 10 and 12 illus-; trating still another system using the present invention for a decking type of bore hole charging.

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PREFERRED EMBODIMENT OF THE INVENTION
Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same, FIGURE 1 shows an elongated, flexible unitary detonating device or element A constructed in accordance with the present in~en-tion which element can be wrapped, tied and otherwise used in the same manner as a standard detonating cord. Detonating element A includes an indeterminate length which can be cut to provide two longitudinally spaced ends 10, 12, one of which can be connected to a standard initiating device and the other to a primer or other element to be detonated. In accordance with the invention, detonating element A includes an inner detonating cord 20 having an outer 5urface 22 a~d constructed in accordance with somewhat standard practice in the detonating cord art. Cord 20 is used for transmitting a detonating wave by high explosive particles, as in a standard detonating cord.
Surrounding surface 22 of detonating cord 20 there is provided ; an energy abcorbing layer, or sheath, 30 which functions to reduce the transverse transmitted energy caused during initia-tion of detonating cord 20, so that detonating element A can extend through a column of explosive material, such as NCN
and/or slurry, without detonating the same.
Referring now more particularly to the somewhat s~andard inner detonating cord 20, this cord is constructed in accord-ance with normal manufacturing techniques such as those de-scribed in United States Patent 3,726,216 The detonating cord 20, in the preferred embodiment of the invention, differs from the cord specifically disclosed in this prior patent in certain respects. For instance, .

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( ~F ;~, detonating cord 20 has an explosive distribution or grain load in the general range of 6-20 grains per linear foot, - -whereas the disclosed detonating cord in the prior patent ~ -has a grain load generally in excess of 15 grains per linear foot. In addition, with the lesser explosive distribution or grain loading, particles of explosive material, as will `
be explained later, are smaller in the present invention than in this prior patent. The outer textile wrapping of thread coated with a wax for tying purposes shown in the prior patent is omitted in the preferred embodiment of the present invention. It is appreciated that such a wrapping could be incorporated in the invention without departing from the intended scope. ;
Inner detonating cord 20 of the present invention in-cludes the centrally located explosive core 40 formed around ., .
a feed assisting thread or string 42 which enhances gravity feeding of the high explosive particulate material forming core 40. In practice? core 40 is formed from small particles of pentaerythritoltetranitrate (PETN), cyclotrimethylene-...
trinitramine (RDX), cyclotetramethylenetetranitramine (HMX), tetryl, ditrinitroethylurea, trineitrotoluene (TNT) and mixtures `` thereof. In the preferred embodiment of the present invention, , * .
Class II Tro~an (PETN) is used. This material has a grain size ; which allows a majority amount by weight of the PETN particles ~25 to pass through a 325 United States Standard screen. Indeed, `
i this material actually allows most of the PETN particles to pass through this relatively small screen to enhance the wave propagation characteristics of core 40 after initiation. The ;;
particle size of the PETN in the preferred embodiment is ~30 applicable for grain loading of approximately 6-12 grains per Trademark linear foot. If higher loading is used in detonating cord 20, a correspondingly larger PETN grain size could be used with an increase in the ease of feeding the particles into the core. As explained in the prior patent, the PETN particles are first dried and then treated with an appropriate flowing - or anti-static agent and an anti-wicking agent which are well known in the art. These agents facilitate easier gravity feed of the small particles around thread or string 42 and into core 40 during the formation of detonating cord 20, in accordance with standard practice and with standard detonating cord manufacturing equipment.
In accordance with somewhat standard practice, core 40 is supported by a carrier or tube S0 formed from longitudinally wrapped fibrous material, such as Crepe paper. Carrier or tube 50 provides a means for forming core 40 into a continuous flexible column which allows ~ropagation of a detonating wave therethrough. Although Crepe paper having a width of approx-~: imately 1/4 inch and thickness of approximately .002-.005 inches is employed in the preferred embodiment, other appropriate supportlng material could be used, such as plastic or fiberglass tape or ribbon. Disposed around the carrier 50 is a textile 1syer 52 which is used for increasing the tensile strength of detonating cord 20. This fibrous or textile layer 52 may in- ;
clude ten strands of thread wrapped around carrier 50. These strands can be formed from continuous lengths of various fibrous i~
' materials such as cotton, rayon, jute and the like. In practice ~
~, these strands have about 1500 filaments and a weight in the -` range of from about l,lO0 to about 2,200 Denier. To further increase the tensile strength of detonating cord 20, it is possible to wrap, in an opposite direction, a second layer of ' , ~ ~ ' :~. ' textile material over the first layer 52, although this is not illustrated in the preferred embodiment of the inven-tion. Around tensile strength increasing layer 52, there is provided a moisture barrier 60 formed from 8 mils of polyethy- -lene extruded around textile layer 52 and forming a moisture impervious barrier preventing moisture from contaminating the PETN of core 40. Of course, other extrudable materials, both plastic and elastomeric, could be used to provide the ` moisture barrier for core 40. Although polyethylene is used in the preferred embodiment, polyvinylchloride and poly-ethylene terethphalate or the like is also appropriate as a barrier. In accordance with normal practice, barrier 60 is extruded around core 40, although it is possible to use a ribbon or tape wrapped around fibrous layer 52 to provide ; 15 this barrier. As so far described, barrier 60 defines the . . .
outer surface 22 of detonating cord 20.
~ Although the high explosive material in core 40 may ; have a grain load or explosive distribution in the gêneral range of 6-20 grains per linear foot, in the prefer~ed em-bodiment of the invention, the grain load is about 11-13 grains per linear foot. In the example to be provided later, the grain loading is 11.8 grains per linear foot. As can ?,, be seen, general~y the grain loading of detonating cord 20 .. i9 below grain loading of a standard detonating cord and i 25 above the grain loading of low energy detonating cord.
There may be a slight amount of overlap between the lower loading for economy cord and the upper limit of the preferred loading of the present invention. When the present invention ~
i:~ approaches a loading of 15-20 grains per linear foot the energy abaorbing layer 30 becomes relatively large. This reduces the -. .
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economy of the invention and creates a relatively large channel through the explosive column. For these reasons, the upper practical limit of the invention may be approximately 20 grains per linear foot; however, higher loading is possible without departing from the invention if the remaining criteria are observed. The lower limit of grain loading is substan-tially above the previous low energy detonating cord. As will become apparent, cord 20 functions,for initiation and detonation purposes, as a standard cord. With loading less than about 6 grains per linear foot, special boosters and equipment, not contemplated by this invention, would be re-quired~ Indeed, loading below about 6 grains per linear foot would preclude needed initiation by a standard cord.
As so far explained, detonating cord 20 is constructed in accordance with well known detonating cord technology. In the manufacture of detonating cord, often surface 22 is pro-vid.ed with a thin thread wrapped around the surface and coated . with a wax. This thread is used to facilitate tying of the detonating cord which is easier when a waxed thread coating ~ 20 is used. Although this thread coating could be used in the ; present invention, it is not contemplated ln the preferred j embodiment.
; The cord 20, which is constructed in accordance with ~ -qtandard practice, includes a sufficient high explosive grain loading tô guarantee detonation of a standard 40-50 grain detonating cord when the cord is intimately associated with outer surface 22 by a knot or other cord connecting arrange-ment. Since cord in some instances may have a grain load as ' low as 15 grains per linear foot, the loading of core 40 may be increased to initiate to or from this-low load cord; however, -, ,~

`` ` 10~;8161 generally core 40 is loaded to initiate to or from a 40-50 grain cord. In practice, it has been found that a grain loading of 11-13 grains per linear foot will detonate a 40-50 grain detonating cord when a 8 mil barrier 60 is used for the cord 20. With this loading of the high explosive particles, cord 20 would have sufficient transverse detonating -energy to detonate an explosive in a bore hole, such as a blasting agent or siurry. Consequently, cord 20 by itself ;
can not be used for bottom detonation of explosive columns in bore holes. In accordance with the present invention, cord 20 is provided with an outer energy absorbing layer 30 releasably secured to surface 22. Energy absorbing layer 30 has sufficient energy absorbing characteristics, based upon the required loading of core 40, the material of layer 30 and the t!~ckness of the layer 30, to prevent detonation of an explos ve charge through which element A extends. This : energy absor?ing layer will be modified according to the ,, .
core loading required to obtain positive initiation and detonation for a particular application. If initiation is to be by a low loaded cord, core 40 will have a higher loading and layer 30 will have a high energy absorbing capability. A
variety of energy absorbing layers could be provided for meet-1;; ing this requirement. In a like manner, a variety of arrange-;l~ ments can be used for allowing selective removal of the energy absorbing layer from certain portions of element A to initiate the element and, when necessary, to detonate a cast primer or other detonating device in the bottom of a bore hole.
In accordance with the preferred embodiment of the in-vention, the energy absorbing layer 30 is formed from a heavier layer of plastic material which is the same as the plastic , ' ' ' ,, , .
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material forming barrier 60. This heavier layer is ex-truded around detonating cord 20 with a thickness of 35-45 mils. In practice, the nominal thicknes~ is approx-.,, - , - imately 42 mils. To allow stripping of the energy absorb-S ing layer from selected areas of element A, there is pro-. .: , ; vided a layer of fibrous material 70, which layer is formed - from rayon, cotton or other yarn. The primary function : ~ .
of layer 70 is to prevent tight adhesion between energy absorbing layer 70 and surface 22. In practice, a loosely woven rayon yarn designated 20/2 is used to create a separat-:, . .
ing seam 80 between the energy absorbing material and surface ` 22. This rayon yarn is formed from a number of short naps . .
' twisted together in two strands so as to create a loosely woven fiber layer 70 which is wrapped around surface 22 and ;; 15 does not fixedly adhere thereto. Layer 72 forms the primary -~ energy absorbing structure of layer 30 and is extruded around ;~
-~ the wrapped yarn layer 70. The plastic in layer 72 does not extend through the yarn layer and into adhesion with layer or barrier 60. Since the yarn forming layer 70 is loosely woven with numerous twisted short naps, this layer has an ,. : .. :
energy absorbing characteristic of its own. This is a secon-tary functian of layer 70. The space between plastic layers ~ 60, 72 which ~s filled by yarn Layer 70 has voids that dissi-;` pate energy attempting to be transmitted through this space.
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In some instances, it would be possible to provide between layers 60, 72 a yarn or thread similar to that provided in fibrous layer 52. This would prevent adhesion between plastic layers 60, 72; however, would be more expensive and would pro-vide less additional energy absorption. The preferred embodi-ment includes the loosely woven type of yarn for its added '.. ~ :.

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: 1068~61 energy absorbing characteristics. In addition, since this yarn sticks to neither layer 60 nor layer 72, the loosely woven yarn provides a convenient means for releasing outer energy absorbing plastic layer 72 from cord 20. This construc-tion of element A is schematically shown in FIGURE 2.
To remove energy absorbing layer 30, and more particularly - the heavier plastic tubular extrusion 72, from cord 20 it is only necessary to manually cut layer 72 circumferentially as indicated by cut 90 in FIGURE 3. This cut may be only par-tially through layer 72 and partially around the circumference - of layer 30. After a cut around about 3/4 of layer 30 is made, element A can be flexed at the cut to break away plastic layer 72. Thereafter, the layer may be slipped from the end of element A, as shown in FIGURE 3. This leaves only the ;
fibrous strands in layer 70 surrounding an exposed portion of cord 20. These strands may then be cut away or unwoven from !!! surface 22 and pulled away from the surface so that cord 20 may be tied to a trunk line or other initiating system. Cut 90 i9 generally made approximately 6-12 inches from an end of element A so that the exposed portion of cord 20 is sufficiently long to form a connecCion. -FIGURE 4 illustrates the releasing characteristic be--`~ tween layer 72 and barrier 60 at seam 80. In practice, an A! axial release is used instead of the illustrated circumferen-. . .
tial release which would be possible by making a longitudinal cut and a circumferential cut. A view similar to FIGURE 4 illustrating a modification of tke preferred embodiment of .. ..
; the present invention is shown in FIGURE 5 wherein elongated ` flexible element A' includes an inner detonating cord 20' which`differs from cord 20 by including an elastomeric barrier 100 . ' .

.

.:

;.. .

6816il instead of a plastic barrier 60, as used in the preferred embodiment. This elastomeric barrier could be tar, asphalt or other similar water impervious material coated or extruded around carrier 50. Except for this change in detonating .
cord 20, element A' is substantially the same as the preferred ~ embodiment of the invention. A further modification ls illus-; trated in FIGURE 6 wherein an elongated flexible detonating : element A" is provided with an inner detonating cord 20 corresponding to the detonating cord of the preferred embodi-ment. The outer energy absorbing plastic layer 72 of the preferred embodiment is replaced by an elastomeric energy absorbing layer ll0. This layer has sufficient thickness to perform the function attributed to energy absorbing layer 72 of the preferred embodiment. A further modification of the preferred embodiment is illustrated in FIGURE 7. In this modification, an inner detonating cord 20 is formed in ; accordance with the preferred embodiment of the invention.
The outer plastic energy absorbing layer 72 is releasably secured to surface 22 of cord 20 by a releasing material 120 which may be a plastic having a dissimilar melt index from plastic of layers 60, 72. Other materials could be provided between the energy absorbing layer 72 and barrier 60. Indeed, it is possible that the two plastic materials forming the energy absorbing layer 72 and barrier 60 could be so dissimilar that they would not adhere. When this type of structure is used, the space between layers 60, 72 is not filled by a fibrous layer.
Thus, it may be difficult to slip the severed portion of the energy absorbing layer from the end of the detonating element.
In that instance, a longitudinal cut may be used or required to sever the energy absorbing layer from the inner detonating ~' -:.
;: - 22 -., .
~`
- cord. It is apparent that various modifications are possible in the preferred embodiment of the invention without departing from the intended spirit and scope of the invention. For instance, various energy absorbing layers, releasing arrange-ments and detonating cords can be used to obtain the desired results of the invention. In all instances, the flexible ~` elongated detpnating element is a unitary structure whi~h can be wrapped on a reel and transported to a blasting site , ...................................................................... .
in accordance with standard transportation procedures for ^ 10 detonating cord. Thus, the two element structure is a unitary `
structure until the stripping process is performed.
FIGURE 8 illustrates a connection between the detonating ?h~
element A and a standard cast primer 130. In this illustrated ~ arrangement, the lower portion of element A is stripped to p,l 15 expose inner detonating cord 20. This cord is then molded into the cast primer 130 for subsequent use in the bottom of the bore hole in a manner to be explained later.
$~ FIGURE 9 shows another aspect of the invention wherein `~ ~ an improved connection is provided between detonating element A and a standard cast primer 140 having the usual axial bores 142, 144. Element A is stripped at portion 150 to expose i~ inner cord 20, which is connected to a standard 50 grain ~ "
tetonating cord 152 by an appropriate knot 154 or other -connecting arrangement. Standard detonating cord 152 ex-tends upwardly through bore 144 for a purpose to be explained later. When detonating element A is initiated, it may have ` 8ufficient transverse energy to detonate primer 140. If detonation does not occur, then the exposed detonating cord . . .
~ will positively detonate the higher energy standard detonating -;~ 30 cord 152 for positive detonation of primer 140 and any ., ~. .
; - Z3 -.. .
,, -- .

: ,: . - , ~0 68 16 additional primers located along cord 152. -;~- Referring now to FIGURE 10, cast primer 130 shown in FIGURE 8 is p~sitioned at the bottom of a bo~e hole 160 filled with a column 162 of explosive material, such ~ ;
as NCN, TNT, slurry, etc. The column and bore hole have ;
a lowermost end 164 and an uppenmost end 1660 Cast primer ` ` -130 is positioned ad3acent lowermost end 164 and element A ~-extends through the explosive column 162 to an upper blast-ing device 170 ad~acent the uppermost end 166 of the bore hole. The blasting device is only representative and ele~
ment A may be initiated by a trunk line, an electric initiator or other appropriate device. Before element A
can be initiated, the upper portion has the energy absorb-ing layer 30 stripped. In this manner, positive initiation to the inner detonating cord 20 is possible. U-on initiation ... . .
~ of element A, a lower detonation 180 occurs adjacent lower-`i~ most end 164 of bore hole 160.
A~ shown in FIGURE 11, the blasting deYice 170 of FIGURE
10 may be a standard trunk line 190 extending over bore hole 160. Element A forms the down line from the trunk line. A
.
connector 192, including diametrically opposite openings 194 .; .
and flexible lips 200, 202, is used to connect a bight 210 of cord 20 with the trunk line. This can be done by extending one end of element A through connector 192 and then forming ~'?''~ 25 bight 210 around trunk line 190. The free end of element A
~` is then threaded through the connector and the connector is ; shifted upwardly to engage trunk line 190 and resiliently -hold detonating cord 20 in tight, intimate wave transmitting contact with the trunk line. In this manner, the standard trunk line can be used to detonate a down line formed in ,.' , . .'. .
,. . .~ , ;~ . ..

.
, .:

~ :

accordance with the preferred embodiment of the present invention.
.
Referring now to FIGURE 12, a system utilizing ~he present ~
invehtion is illustrated. In this system, the cast primer 140, ~ -as shown in FIGURE 9 is positioned at the lowermost end 164 of bore hole 160. An initiating or blasting device 170 can be used for bottom detonation of cast primer 140. In accordance with the illustrated system, a plurality of axially spaced secondary primers 220 are positioned in the ~ore hole. Stand- ;
ard detouating cord 152 is threaded through the spaced secon-dary primers for further detonation of explosive 162 in bore hole 160. In practice, the secondary cast primers have a :", :.
lesser weight than the basic cast primer 140 in the lower portion of the bore hole. Initiation of element A detonates explosive column 162 in a manner clearly apparent by the drawings. A similar arrangement for using the structure shown ; ;
i in FIGURE 9 in a decking arrangement is illustrated in EIGURE
. 13. The secondary cast primers 220 are located in axially ~, spaced explosive charges 162a separated by dirt portions 230.
Initiation of element A by device 170 fires the explosive ~` charges 162a separately from the bottom of the bore hole to - the top thereof.
EXAMPLE AN~ TESTING r .1~
As an example of the present invention, the following .... . .
energy absorbing detonating device has been produced:
;j~ Element Process lbs/1000 ft , (a) Center String Fed longitudinally to assist in feed-ing PETN.................. 0.024 .

. ,. , . ~

' - , .

: . -. ,. , . ~ .

.i. ' - ' I'' 1068161 : :~
(b) PETN (11.8 Fed around center grains/ft) ~ supporting string............ .1.68 Class II :
~rojan*
(c) 1/4 inch Crepe Wrapped around said paper PETN core for support- `
0.003 inches ing core..................... Ø254 (d) 10 s~rands of Spun around paper 16~0 Denier tube for tensile ;
Rayon Thread with strength..................... .2.040 1500 filaments each.
(e) In~er Plastic Extruded around Water Impervious Rayon threads to layer (8 mils) protect core from ; (Polyethylene) mois~ure..................... .l.180 ---(Standard Manufacturing Steps to this condition)---(f) Overspin of Spun!around inner ~:
20/2 rayon yarn plastic layer.
Covers inner plas- ;
- tic layer to form -; releasable contact with inner plastic ~,' layer........................ .O.893 i' 25 (g) Outer Plastic Extruded over ¦~
', layer (42 mils) loosely woven (Polyethylene) rayon yarn................... ll.27 Enerby Absorbing layer. - -~- 30 TO~AL 17.34 . ' . ' .
,,. . ~ ~,~, . .
Trademark -, 26 -. ~ ,.

... . .

~:

~ ~ -1068161 ~: ~
.. . ~ .~ .
*Class II Trojan P~TN is a fine grain PETN wherein a ma~ority o the material passes through a 325 United States Standard screen.
~ Elongated detonating devices, constructed in accordance ; 5 with the above example, were initiated while extending in a confined column of ANF0 without detonating the column. Also, a length of the detonating element was twisted three times longitudinally around a lengeh of standard 40 grain/ft detonating cord which was then placed in a 2 inch diameter, 5 feet length of pipe. The pipe was filled with sand and the ;
detonating element was initiated. In these tests, the 40 ;
grain/ft detonating cord was not detonated by the device hav-ing the energy absorbing layer in place. To further test ~"i , .
the detonating capabilities of the detonating device with the energy absorbing layer in place, the device was spliced to a 50 grain/ft standard detonating cord. In five tests, only twice was the 50 grain cord initiated. Consequently, ~ . the detonating element was shown, by these tests, to be ,l a relatively ineffective initiator or detonator for a blasting ~20 agent or standard detonating cord when the energy absorbing layer or layers remained intact around the inner detonating cord. ~;
The outer energy absorbing layer~or layers were then 8tripped from the ends of the detonating element constructéd 2S in accordance with the above example. The element was spliced " with a standard 50 grain/ft detonating cord with the exposed `~ inner plastic layer in contact with the cord. In ten successive .~, . ., L'`'' tests, initiation of the invention csused initiation of the 50 grain cord. This indicates an increased detonating characteristic for the stripped portion of a detonating device constructed in -~
*Trademark . ." '`

. ..... ~,.

,:.', ` ~ ~
10~316 1 accordance with the example. In addition~ the detonating device was placed in a cast primer of standard PETN, composi-tion B,etc. construction. The initiation of the device was sufficient to detonate the primer without requiring any inter-mediate charge,such as needed in prior non-elec~ric detonating systems which can detonate in the lower portion of a bore hole.
The present invention was tested in 14 bore holes 70 feet deep filled with ANF0. An elongated element constructed in accordance with the invention extended through the ANF0 to a lower one pound cast primer. The upper portion of the elongated detonating device was stripped for initiation and initiated by a trunk line of 30 grain/ft standard detonating cord. Each of the bore holes was detonated from the bottom, `
indicating that the detonating wave through the invention ; propagated through the ANF0 to the lower cast primer with-out predetonation at the upper portions of the explosive ,~ column. The lower primer had no high energy charge required by other detonating elements allegedly capable of detonating ', 20 a bore hole charge from a location adjacent the bottom of the bore hole.
Attempts to initiate the detonation element constructed . . . . .
in accordance with the above example without removing the energy absorbing outer layer or layers have proven incon-sistent and generally ineffective. It has been found that . .
` the energy absorbing layer or layers used to allow bottom ~;~ detonation must be removed to obtain consistent initiation by standard detonating cord and other common initiating -` -~ devices.
~ -.
~ ' - -:
, ' ' ' '

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of detonating an explosive in a bore hole having an innermost end and an outermost end, said method comprising the steps of:
(a) providing a first detonating cord having two ends and a transversely transmittable energy sufficient to detonate said explosive;
(b) providing an elongated detonating device having first and second ends and including an inner second detonating cord and an outer energy absorbing layer which device adjacent said layer has a transversely transmittable energy insufficient to detonate said explosive and said first detonating cord;
(c) stripping said outer layer from first end of said elongated device;
(d) connecting said first end of said elongated device to one end of said first detonating cord;
(e) placing said connected end adjacent said innermost end of said bore hole with said second end of said elongated device extending to a position adjacent said outermost end of said bore hole and said first cord extending from said innermost end toward said outermost end of said bore hole; and, (f) initiating said second end of said element.

2. A method as defined in claim 1 including the additional steps of:
(g) providing a cast primer;
(h) extending said elongated device and said first detonat-ing cord through said cast primer; and, (i) positioning said cast primer adjacent said innermost end of said bore hole.

3. A method as defined in claim 2 including the additional steps of:
(j) providing additional cast primers;
(k) positioning said additional cast primers in said bore hole at longitudinally spaced positions therein; and, (1) extending said first detonating cord serially through said additional cast primers.