US2725821A - Circuit closing means and blasting assembly - Google Patents

Description

Dec. 6, 1955 H. w. COLEMAN 2,725,821

CIRCUIT CLOSING MEANS AND BLASTING ASSEMBLY Filed March 29, 1952 POWER SOURCE o o a u a u u a a I, n O l 2 3 4 5 O I Z 3 4 5 FIG-3 POWER SOURCE POWER 32 souncs 33 HOMER W-COLEMAN INVENTOR.

BY a. 69%

AGENT.

United States Patent CIRCUIT CLOSING MEANS AND BLASTING ASSEMBLY Homer W. Coleman, Wilmington, DeL, assignor to Hercules Powder Company, tion of Delaware Wilmington, Del., a corpora- This invention relates to the art of blasting and more particularly to improved methods, assemblies, and apparatus for use in delay blasting techniques.

The art has long recognized the benefits obtainable from the use of delay blasting initiators of various types. Until recent years the periods of delay employed between adjacent charges or groups of charges have been in the neighborhood of 0.5 of a second to several seconds. The original and basic object of the use of such delay periods between charges or groups of charges was to make it possible to explode a large quantity of 'high explosive at spaced intervals in a single shot and escape the undesirable effects normally obtained from exploding the same quantity of explosive instantaneously. In addition, the use of delay initiators enabled those engaged in quarry and cut blasting to break successive portions of the burden at timed intervals in a single shot. Likewise, in tunnel blasting the delay technique enabled the shooter to so time the initiation of the charges in the various boreholes that a cut is first made in the center of the tunnel face and then successive portions of the face are successively cleared by the other charges set off by the initiators having longer periods of delay.

In the more recent years it has been discovered that even better results are obtainable in some instances where the delay between adjacent boreholes or groups of boreholes is considerably reduced. This blasting technique is generally referred to as short-period delay shooting. The periods of delay normally employed for'optimum results are in the neighborhood of from -75 milliseconds. It has been found that this technique results in considerably less earth vibrations and in superior breakage. 7

As a result of the wide-spread use of both types of delay shooting, the major blasting initiator manufacturers throughout the world have undertaken the manufacture of conventional delay initiators and short-period delay initiators having varying periods of delay. Depending upon the type of blasting operations being conducted in the various localities, it is current practice to manufacture and sell delay initiators embodying the number of delay periods which are desired for use in the particular field of operations. In the United States, for example, about 16 periods of conventional delay and 16 periods of shortperiod delay are available. In some countries, on the other hand, as'few as six periods of short-period delay are available from domestic producers. It is apparent, therefore, that initiator manufacturers are required to produce caps embodying a large number of delay periods and the operators in the field are required to stock large numbers of initiators having the varying periods of delay in 'order to insure the availability of the desired number of delay periods for a particular shot. Where a shot is proposed which will require a greater number of delay periods than are readily available from domestic sources, initiators must, if possible, be obtained from foreign sources with additional inconvenience and at additional expense or else the benefits which would be derived from this added number of periods must be foregone. There fore, it would be desirable and advantageous from the standpoints of both the producer and user of delay electric initiators if it were possible to obtain the desired effects without the necessity of more than a relatively few periods of delay in either the conventional or shortperiod delay types.

An object of the present invention, therefore, is a blasting method in which it is possible to readily and economically obtain all of the benefits of a large number of delay periods while employing only a relatively few delay electric initiators.

A further object of the invention is a blasting assembly which will enable the use of any practical number of delay periods in a shot employing any practical number of boreholes while employing only a few delay initiators. An additional object of this invention is a blasting device which will initiate current flow at the desired time in successive blasting circuits which may individually contain any desired number of periods of delay.

Generally described, this invention resides in employing between individual blasting circuits which are to be successively fired, a delay device which contains a body of combustible, fusible composition which is conductive in the fused state, said composition being disposed between spaced electrical contacts which close the later firing circuit when these contacts are brought into conductive relationship. More specifically, the invention relates to a method of blasting which comprises charging a plurality of boreholes with explosive and dividing the holes into groups, priming a plurality of boreholes in each group by means comprising electric initiators, connecting the initiators in each group in a separate firing circuit, the first circuit to be fired being initially closed and the remaining circuits being initially open, connecting each circuit to be successively fired with its preceding circuit by means of a delay device containing a body of combustible, fusible composition which is conductive in the fused state, said composition being disposed between spaced electrical contacts which close the later firing circuit when said contacts are brought'into conductive relationship, and applying current to allcircuits, whereby the said combustible, fusible compositions are successively brought to ignition and the successive circuits are closed in predetermined order.

This invention further relates to a blasting device for establishing current flow in an electrical firing circuit comprising a shell, a first pair of insulated conductive leads entering the shell and being conductively connected adjacent their bared terminal ends by a resistance wire, a second pair of insulated conductive leads entering the shell, the terminal ends of which are not in conductive relationship, ignition composition disposed about the resistance wire, fusible ignition composition disposed between and contacting the terminals of the second pair of leads, said fusible composition being conductive in the fused state, and combustible, ignition propagating means disposed between the said ignition mixtures.

A further embodiment of the invention relates to a blasting assembly comprising at least two groups of charged boreholes, a plurality of holes in each group being primed by means comprising electric initiators, the initiators in each group being disposed in an electrical circuit connected to a power source; and a device em ployed between at least two such circuits which in combination comprises a shell, a first pair of insulated conductive leads entering the shell and being conductively connected adjacent their bared terminal ends by a resistance wire, said first leads being connected in a first circuit, a second pair of insulated conductive leads entering the shell, the terminal ends of which are not in conductive relationship, said second leads being connected in a second circuit, ignition composition disposed about the resistance wire, fusible ignition composition disposed between and contacting the terminals of the second pair of leads, said fusible composition being conductive in the fused state, and combustible, ignition propagating means disposed between the said ignition mixtures.

Having generally described the invention, specific embodiments of the apparatus, blasting assemblies, and methods in accordance with the invention will be more specifically described, for illustrative purposes, with 17-25 erence to the accompanying drawing. in the drawing, Figs. 1 and 2 are part-sectional, part-elevational views of devices which may be employed to establish current flow in a blasting circuit in accordance with the invention. In Figs. 3, 4, and 5 are shown schematic diagrams of blasing assemblies which may be employed in accordance with the invention.

In Fig. 1, a shell 10 is closed at either end by rubber sealing plugs 11 and 12. Passing through the sealing plug 11 is a pair of conductive leads 13, the bared ends of which are joined by a bridge wire 14. Passing through the sealing plug 12 is a second pair of leads 15, the terminal ends 16 of which are in spaced relationship within the shell 10. Disposed within the shell 10 and about the bridge wire 14 and the terminal ends 16 of the second pair of leads is a pulverulent combustible composition 17, such as a stoichiometric mixture of lead and selenium, which is conductive in the fused state. When a current is passed through the bridge wire 14, the combustible mixture is ignited and the mixture burns progressively toward the oppostie end of the device. When the mixture between the terminal ends 16 of the lead wires 15 becomes fused, the terminal ends are brought into conductive relationship enabling a current to pass from one terminal to the other.

In Fig. 2, a shell 20 is sealed at each end by rubber sealing plugs 21 and 22. Disposed immediately beneath the sealing plug 21 is a cavity ignition plug 23. A pair of lead wires 24 pass through the sealing plug 21 and bridge plug 23 and terminate in the cavity 25. The bared terminal ends of the lead wires 24 are bridged by a re sistance wire 26. Disposed about the resistance wire 26 is a conventional ignition composition 27. Immediately beneath the cavity plug 23 is disposed a delay fuse 28.

containing a delay train of combustible delay powder 29. A charge ofcombustible, fusible composition 30, which is conductive in the fused state, is disposed within the shell 20 between the delay fuse 28 and the sealing plug 22. A pair of electrical leads 31 pass through the sealing plug 22. The terminal ends 32 of the leads 31 are disposed in spaced relationship and are surrounded by the composition 30. A thin coating 33 of nitrocellulose lacquer is disposed about the terminal ends of the lead wires 32 and extends to the upper surface of the plug 22. When a current is passed through the leads 24, the ignition composition 27 is ignited by the bridge wire 26. The delay train 29 is ignited by the burning ignition composition 27 and the combustible composition 30 is ignited by the delay train 29. The coating of lacquer 33 is consumed by the burning composition 30. The fused residue of the combustible mixture 30 brings the terminals 32 of the leads 31 into conductive relationship and allows a passage of current therebetween.

In Fig. 3 is shown a blasting diagram wherein a row of twelve charged boreholes is disposed along a quarry face. As shown, the first hole is primed with an instantaneous or delay cap while the second, third, fourth, fifth and sixth holes are primed with delay initiators having delay periods of l, 2, 3, 4, and respectively. The seventh hole is charged with a 0 delay or instantaneous cap while the eighth, ninth, tenth, eleventh, and twelfth holes are primed respectively with delay initiators having delay periods of 1, 2, 3, 4, and 5, respectively. The initiators in holes one through six are connected in a separate circuit which includes the bridge wire of a device 50 such as that shown in either Fig. 1 or Fig. 2. The initiators in holes seven through twelve are connected in a separate circuit which includes the spacedapart terminals of a device 59 such as that shown in either Fig. l or Fig. 2. The first circuit is closed while the second circuit remains open until such time as the spacedapart terminals are brought into conductive relationship by fusing of the combustible composition. in the shot depicted in Fig. 3, the timing device 50 is characterized by a delay period of 6 in order that current flow will not be established in the second circuit until all of the initiators in the first circuit have fired. Both circuits are connected to a power source. Upon the application of a firing current holes one through six fire in order whereupon current flow is established in the second circuit by the device 50 and holes seven through twelve then also fire in order. It will be seen, therefore, that a row of twelve holes has been fired at desired intervals of delay by employing electric initiators having only 5 different periods of delay and one timed circuit-making device in accordance with the invention.

In Fig. 4 is shown a blasting diagram and assembly wherein a block of thirty-six holes disposed in six rows are to be shot. All of the holes in this shot are primed with branch lines of Prirnacord which are connected in detonating relationship to a trunk line of Primacord for each row. The trunk line of rows one and four are primed with instantaneous initiators, the trunk lines of rows two and five are primed with initiators having a period 1 delay, and rows three and six are primed with initiators having a period 2' delay. The initiators of rows one, two, and three are connected in one firing circuit while the initiators of rows four, five, and six are connected in a separate firing circuit. The first firing circuit includes the bridge wire of a timed circuit-making device 50 such as that shown in either Fig. l or 2, while the second circuit contains the spaced-apart terminals of such a device. Both circuits are connected to a power source. The device 50 in the shot depicted is characterized by a delay of period 3. Upon the application of a firing current to both circuits, rows one, two, and three shoot in order. 'The second circuit is then closed at the end of a period 3 delay by means of the conductive fused residue whereupon row four shoots instantaneously followed by rows five and six after a delay corresponding to periods 1 and 2. Fig. 4, therefore, shows a blasting assembly whereby six rows of boreholes can be successively fired at the desired timed interval by employing a circuitmaking device in accordance with the invention, instantaneous caps and initiators characterized by periods l and 2 of delay.

In Fig. 5, a blasting diagram is shown for shooting a rock cut such as might be made in highway construction. In the assembly illustrated, eight rows of charged boreholes are successively disposed inwardly from the face of the cut. The holes in the first, second, third, and fourth rows are primed by electric initiators having delay periods of 0, l, 2, and 3, respectively. All of the initiators in the first four rows are connected in series in a single circuit which includes the bridge wire of the device 50 such as that shown in Figs. 1 and 2. The initiators of rows four through eight are also characterized respectively by delay periods of 0, 1, 2, and 3. Rows four through eight are connected in a separate circuit which includes the spaced-apart terminals of a device 50 such as that shown in Figs. 1 and 2. In this assembly, the device 50 is characterized by a delay corresponding to period 4. Upon the application of a firing current, the first four rows will fire in order. At the end of the fourth period of delay the second circuit will be closed by means of the conductive fused residue of the device 50 and rows five through eight will fire in order. Thus, a shot of eight rows may be made by employing a device in accordance with the invention and electric initiators having delay periodsof 0, l, 2, and 3.

It will be apparent that in each of the shots depicted in Figs. 1 through 5, the number of holes, the number of rows, the number of delay periods and the number of circuit-makers may be varied at will in designing a shot of the desired pattern and size. All such shots, however, can be made by employing a greatly reduced number of different periods of delay initiators in accordance with the invention.

The timed circuit-making devices in accordance with the invention may be readilyand economically manufactured from readily available materials. The shells may be made of any desired materialalthough metal is preferred. The closure plugs shown in the drawings are formed from rubber but they may be formed from any of the materials currently employed by the art such as sulfur, resins, and the like In like manner, a series of closure bodies may be employed instead of the single body shown in the drawing. v

The lead wires employed will normally be conventional insulated blasting cap leadwires but, of course, may be of different types. Wire insulated with a thermoplastic resin, such as a cellulose derivative, various vinyl compositions, or nylon, is preferred, although other insulatory materials such as rubber, textiles, and the like may be employed. The bridge wires andbridge assemblies may be formed in accordance with the known procedures and from theknown materials of the art. A Nichrome alloy or platinum bridge wire ispreferred. Although the drawings show the use of loose and buttered ignition mixtures around the bridge wires, it is apparent that matchhead-type igniters may also be employed.

The combustible, fusible;composition which is conductive in the fused state is, preferably a mixture of lead or tin with selenium in proportions approaching stoichiometric equivalency. However, many similar mixtures may be employed and operable compositions are found generally in finely divided mixtures of a metal or metal oxide with a suitable reducingagent. The degree of conductivity of the fused residue of such a composition will, of course, be controlled at least in part by the proportions of ingredients employed. Examples of operable compositions are mixtures of lead and selenium, tin and selenium, lead and tellurium, tin and tellurium, iron oxide and boron, iron oxide and aluminum,-lead oxide and antimony phosphide, lead oxide and boron, and the like. Of all of these mixtures, lead selenium and tin-selenium are preferred in viewof the fact that these materials are relatively nonconductiveprior to fusing but when fused are excellent conductors. In addition, lead-selenium and tin-selenium have highly desirable ignition characteristics.

Where millisecond delay characteristicsare desired, and particularly in the lower periods of millisecond delay, it is preferred to employ a device such as that shown in Fig. 1 where the ignition composition around the bridge, the fusible composition surrounding the spaccd'terminals, and the ignition propagating means disposed therebetween, are made up of a single charge of a mixture which is conductive in fused state. Small amounts of burning accelerators, such as magnesium and the like, may be added to increase the speed of burning of the mixture. Since the amount and length of such a single charge is controlled by practical considerations, it is desirable to employ a separate fuse train such as shown in the device of Fig. 2 for longer periods of millisecond delay and for regular delay periods. Known delay powders such as barium peroxide-selenium, and the like, may be employed in such fuse trains in lengths and densities necessary to give the desired periods of delay.

In the device shown in Fig. 1, it is not necessary that the entire combustible charge be lead-selenium or other mixture which becomes conductive upon fusing. If desired, conventional ignition mixtures may be employed about the bridge Wire. The same is true of the device shown in Fig. 2 wherein conventional ignition compositions may be employed in the cavity plug. If a matchhead is emwhich is substantially gasless.

ployed, conventional matchhead compositions may be used. As in the case of delay initiators, however, the

problem of gas formation during burning of an ignition composition must be considered. If the shell of the device is vented, gas formation is not a problem.. If a ventless shell is employed, however, an air space may be employed nals in accordance with the invention normally burn withhas operated in its anticipated manner.

out substantial gas evolution.

As shown in Fig. 2, the spaced-apart terminals may be coated with a dielectric material which is readily combustible such as various waxes and lacquers. The purpose of such a coating is to prevent a voltage breakdown of the combustible, fusible composition across the open terminals of. the circuit-making device before the device Such a coating may be especially desirable in the structure shown in Fig. 1 if there is danger that the firing voltage which may be usedexceeds the breakdown voltage of the specific mixture employed about the spaced-apart terminals, When such a coating is employed on the spaced-apart terminals, the combustible, fusible mixture may be conductive in the unfused state under some circumstances, since current flow will be prevented until the coating is consumed. When employing the device of Fig. 1, it is also desirable that the initiator in each of the circuits after the first be connected between the device and the power line.

In the blasting assembly shown in Figs. 3 through 5, it will be apparent that the holes may be primed with different delay periods that those shown while still maintaining the desired interval between the detonation of those holes or rowsof holes. For example, in Fig. 3, the device 50 may have a period 5 delay if hole seven is primed with a period 1 instead of a period 0 initiator. In like manner,

the device 50 of Fig. 4 may be characterized by a period 2 delay if the initiator attached to the trunk line of row four is aperiod 1; while in Fig. 5, the device 50 may have a period 3 delay if the initiators in rows five through eight are primed with delay periods of 1 through 4. If desired, adjacent holes or adjacent rows may be primed with such periods of delay that they will shoot simultaneously.

It will beappreciated that in employing the devices, assemblies and methods of the invention, the firing current must be applied for a length of time necessary to the ignition of the ignition charges in all of the initiators employed.

It is apparent, therefore, that many variations of the devices, assemblies, and method disclosed are possible without departing from the scope of the invention. It is, therefore, intended that the invention be limited only by the scope of the appended claims.

What I claim and desire to protect by Letters Patent is:

l. A blasting device for establishing current flow in an electrical firing circuit comprising a shell, a first pair of insulated conductive leads entering the shell and being conductively connected adjacent their bared terminal ends by a resistance wire, a second pair of insulated conductive leads entering the shell, the terminal ends of which are not in conductive relationship, ignition composition disposed about the resistance wire, fusible ignition composition disposed between and contacting the terminals of the second pair of leads, said fusible composition being conductive in the fused state, and combustible, ignition propagating means disposed between the said ignition mixtures.

2. A device in accordance with claim 1 in which the ignition compositions and ignition propagating means consist of a single charge of ignition composition which is conductive in the fused state.

3. A device in accordance with claim 1 in which the o 7 ignition compositions and ignition propagating means con sist ofa single charge of lead-selenium. x v

4. A device in accordance with claim 1 in which the terminals of the second pair of leads in contact with the fusible ignition compositions are coated with a readily combustible dielectric material. a

5. A blasting device for establishing currentflow in an electrical firing circuit comprising a shell, a first pair of insulated conductive leads entering the she'lland being conductively connected adjacent their bared terminal ends by a resistance wire, a second pair of insulated conductive leads entering the shell, the terminal ends of which are not in conductive relationship, ignition composition disposed about theresistance wire, fusible ignition composition disposed between and contacting the terminals of the second pair of leads, said fusible composition being conductive in the fused state, and a delay fuse'train disposed in ignitible relationship between the ignition compositions.

6. A device in accordance with claim 5 in which the terminals of the second pair of leads in contact with the fusible ignition composition are coated with a readily combustible dielectric material.

7. A device in accordance with claim 5 in which both ignition compositions are lead-selenium. v V

8. A device in accordance with claim 5 in which the ignition composition surrounding the resistance wire is a mixture of diazodinitrophenol and potassium chlorate and the ignition composition disposed between the terminals of the second pair of leads is lead-selenium.

9. A blasting assembly comprising at least two groups of charged boreholes, a plurality of holes in each group being primed by means comprising electric initiators, the initiators in each group being disposed in an electrical circuit connected to a power source; and a device employed between at least two such circuits which incom bination comprises a shell, a first pair of insulated" conductive leads entering the shell and being conductively connected adjacent their bared terminal ends by a resistance wire, said first leads being connected in a first circuit, a second pair of insulated conductive leads entering the shell,- the terminal ends of which are not in conductive relationship, said second leads being connected in a second circuit, ignition composition disposed about the resistance wire, fusible ignition composition disposed between and contacting the terminals of the second pairof leads, said fusible composition being conductive in the fused state, and combustible, ignition propagating means disposed between the said ignition mixtures. V

10. An assembly in accordance with claim 9 in which the ignition compositions and ignition propagating means consist of a. single charge of ignition composition which is conductive in the fused state. I

11. An assembly in accordance with claim 9 in which 8 the initiators in each group are characterized by varying periods of delay. a V I v 12. An assembly in accordance with-claim 9 in which only part of the holes are primed by means comprising electric initiators characterized by varying periods of delay and the'remaining holes in each group are primed by detonating fuse leading from the holes in which electric initiators are employed. I I

13. An assembly in accordance with claim 9 in which at least part of the holes are primed by detonating fuse which, in turn, is primed by electric initiators haying varyingdelay characteristics. a

14. A blasting assembly comprising at least two groups of charged boreholes, a plurality of holes in each group being primed by means comprising electric initiators, the initiators in each group being disposed in an electrical circuit connected to a power source; and a device employed between at least two such circuits which in combination comprises a shell, a first pair of insulated conductive leads entering the shell and being conductively connectedadjacent their bared terminal ends by a resistance wire, said first leads being connected in a first circuit, a second pair of insulated conductive leads entering the shell, the terminal ends of which are not in conductive relationship, said second leads being connected in a second circuit, ignition composition disposed about the resistance wire, fusible ignition composition disposed between and contacting the terminals of the second pair of leads, said fusible composition being conductive in the fused state, and a delay fuse train disposed in ignitible relationship between the ignition compositions.

15. A device in accordance with claim 14' in which the initiators in each group are characterized by varying periods of delay.

'16. A device in accordance with claim 14 in which only part of the holes are primed by means comprising electric initiators characterized by varying periods of delay and the remaining holes in each group are primed by detonating fuse leading from the holes in which electric initiators are employed. a

17. A device in accordance with claim 14 in which at least part of the holes are primed by detonating fuse which, in turn, is primed by electric initiators having varying delay characteristics. 7 7

References Cited in the file of this patent UNITED STATES PATENTS McFarland Sept. 9,

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