US3537399A - Method and device for blasting - Google Patents

Description

I nlted States Patent [1113,537,399

' [72] Inventor Paul H. Miller 2,961,583 11/1960 Sorenson 317/80 'lamaqua, Pennsylvania 3,011,096 11/ 1961 Wallack et a1. 317/80 [21] Appl. No. 733,634 3,141,114 7/1964 Jenkins et al.. 317/80 [22] Filed May 31,1968 3,167,014 1/1965 Kopito 102/28 Patented Nov. 3, 1970 3,288,068 11/1966 Jefferson et a1 1021702 [73] Asslgnee w g f a industries Primary Examiner-Verlin R. Pendegrass m g e aware Attorney- Kenneth E. Mulford, Roger R. Horton and Ernest a corporation of Delaware CL Amy [54] METHOD AND DEVICE FOR BLASTING 14 Claims 4 Drawing 8g ABs Tll A C T: A method and blasting device are disclosed for use in initiating up to about 150 blasting caps disposed in a [52] U.S.Cl l02/70.2 parallel circuit The blasting device includes a capacitor f F42) 3/12 delivering preferably an energy output of between about 210 Fleld of Search 102/28, to about 400 watt seconds f energy over a relatively Short 22, 317/ period of time, and a voltage sensing switch for releasing energy from the capacitor when the required level of energy out- [56] Reta-em. Cned put is available. The output energy, although sufficient to in- UNITED STATES PATENTS itiate up to about blasting caps disposed in a parallel cir- 2,644,117 6/1953 Schmitt el al. 317/80 cuit, is insufficient to cause malfunction by internal arcing of 2,892,128 6/1959 Wolf 317/80 as few as one electric blasting cap disposed in the parallel cir- 2,908,847 10/1959 Bickel et a1 317/80 cuit.

Patented 0v. 3, 1370 3,537,399

Sheet 1 of 2 INVENTOR Paul H. Miller ATTORNEY Patented Nov. 3, 1970 Sheet INVENTOR Paul H. Miller mw v0 ATTORNEY METHOD AND DEVICE FOR BLASTING such a circuit permits rapid connection of the blasting caps with minimal possibility of error. Typically, the electric blasting caps are initiated with electric energy received from a readily available AC power line.

One cause of malfunctioning of electric blasting caps and in particular those of the delay type is the large amount of heat generated by an electrical are which occurs within an electric blasting cap when an excessive electrical current is supplied. Although it is recognized that excess current may be usefully channeled in the parallel circuit by inclusion of additional blasting caps, both delay and inconvenience result unless a simple device is available which is operable for initiation of either as few as one or as many as about 150 blastcaps disposed in a parallel circuit.

Malfunctioning of electric blasting caps may occur when gases within the detonator are heated rapidly and a high internal pressure is soon built up. The heat and high pressure conditions within the blasting capcause a speed up in the delay.

timing. If the internal pressure builds up sufficiently, an outward rupture of the cap wall or a violent dislodging of the cap seal may result which rapidly releases the contained hot gases. The effect of this action on the blasting operation is unpredictable and varied. The sudden release of the gases may create conditions under which the burning of the delay element may be retarded, in which case the delay timing will be slow. Under some conditions, the burning delay element may be extinguished in which case the delay element will then fail to initiate the explosive charge of the detonator. Release of hot gases and flame from within a detonator can ignite the surrounding explosive which may burn at first but could eventually convert to detonation within the confines of a borehold.

' If the delay element is extinguished and the surrounding explosive charge is ignited, many minutes may elapse before heat from the burning explosive either causes detonation or initiates the explosive charge of the blasting cap which initiatcs the remainder of the burning explosive. Heat generated by the burning explosive may decompose the explosive charge of the blasting cap and, in such case, the surrounding explosive may, unpredictably, either burn completely or detonate at any point before it is completely consumed by burning. If the burning element is extinguished by the sudden release of the entrapped gases, and the explosive charge is not ignited by the hot gases, the shot may fail completely. Thus, the occurrence of a violent electrical are within a delay electric blasting cap may result in various types of malfunctions such as, for example, erratic delay timing, misfire, or a delayed detonation commonly known as a hangfire.

The various malfunctions caused by arcing occur more frequently when any of the'various parallel circuit arrangements such as normal parallel, reverse parallel, and closed loop parallel are used with a continuous source of electrical energy of high potential such as a power line. When electric blasting caps are connected in parallel, the voltage across the bridgewire terminals frequently is high enough to sustain an electrical arc after the bridgewire melts and when a power line of high current capacity is used, the arc may generate enough heat within the blasting cap prior to detonation to cause malfunction. Parallel circuit arrangements of delay detonators are often used in the blasting art and the convenience and advantages of a power line as a source of electrical energy are well known. Thus, the majority of arcing difficulties encountered in blasting operations occur when a commonly used circuit arrangement is combined with a commonly used source of electrical energy.

One approach to solving difficulties encountered in initiat ing electric blasting caps disposed in a parallel circuit is disclosed by MacFarland in U.S. Pat. No. 3,056,349. MacFarland teaches a blasting circuit for initiating, in parallel arrangement, delay electric detonators by generally applying firing energy insufficient to cause malfunction of detonators by internal arcing. Firing current is received from a continuous source of electric energy, and a quick trip switch is employed to restrict the time interval over which the current is applied.

Various other approaches for limiting malfunctioning by arcing of electric blasting caps disposed in a parallel circuit such as limiting the magnitude of the firing current and reducing the resistance inside the electric blasting caps have realized limited success. These approaches have attempted to limit the energy available for initiating electric blasting caps disposed in a parallel circuit based on the fact that energy is a direct function of the square of the firing current, times the internal resistance of the cap, times the duration of time the current is applied.

There are several reasons why various prior art methods of initiating from one up to about 150 blasting caps disposed in a parallel circuit by a single device have not been completely successful in eliminating arcing malfunctions. One reason is that some of these methods attempt to control only one of the three contributing factors that determine the amount of heat generated inside the cap. If one, or both, of the other contributing factors become excessive, the limiting effect of the one being controlled may be overridden. Another reason is that other solutions depend on a human decision or action. Hence, human error easily negates their effectiveness.

An approach that has been tried in an attempt to eliminate the arcing problem when firing delay electric caps in parallel is to use a commercially available condenser-discharge blasting machine as the power source. Such blasting machines have been disclosed by Wolf in U.S. Pat. No. 2,892,128 and Bickel et al. in U.S. Pat. No. 2,908,847. This solution suffers from the disadvantage that these blasting machines can fire only a limited number of caps connected in parallel while avoiding malfunctioning when as few as only one blasting cap is initiated.

Heretofore, no commercially available blasting machine has been available which is rated to fire more than about 50 blasting caps connected in a parallel circuit. This situation is unsuitable because operators employing parallel circuits of blasting caps desire to employ more than 60 caps and many would desire to employ more than caps in a single shot by a device which is also capable of initiating as few as one blasting cap without circuit modification and malfunctioning problems.

It has now been found that by the practice of the present invention, from one to about electric blasting caps may be initiated in a parallel circuit arrangement without encountering arcing malfunctions. This may be accomplished without the necessity of a human decision or action; and, hence, misfires due to human error are eliminated. The present invention uses output energy as a function of the capacitance and voltage of a condenser-discharge blasting device. v

Generally stated, the present invention provides a blasting device for initiating up to about 150 electric blasting caps disposed in a parallel relation by combining an energy output means capable of delivering between about 2l0 to about 400 watt-seconds of energy over a relatively short period oftime from a capacitor having a preferred capacitance of about.2.8 X l0 farads to about 5.0 X 10- farads. A voltage sensing switch is also desirably included in the blasting device for sensing the voltage of the charge on the capacitor and, after the desired voltage level is reached, for discharging the capacitor and providing the discharged energy to initiate the electric blasting caps of the parallel circuit. Thus, by using a voltage sensing switch, the present blasting device may be operated without opportunity for human error. In an embodiment of the present invention, other voltage sensing means may be employed in the circuit although with less reliability due to opportunity for human error.

The invention will be further described in connection with the accompanying drawings which illustrate schematically a circuit which may be used in the practice of the present invention.

In the drawings:

FIG. 1 illustrates a circuit which may be employed for converting an alternating current to a direct current;

FIG. 2 illustrates a circuit of the present invention for obtaining a condenser discharge with controlled energy output;

FIG. 3 illustrates electric blasting caps which may number from one up to about I50 disposed in parallel relation; and

FIG. 4 illustrates in greater detail a preferred embodiment of the blasting device ofthe present invention.

In the drawing of FIGS. 1-3, terminals and 12 are illustrated for receiving an alternating current from, for example, a power line, an alternating current generator or other source capable of supplying an AC voltage sufficient to charge the capacitor system described hereinafter. Switch 14 may be included in the circuit to control the flow of current into the system. Indicator light 16 may be also included for indicating the flow of electricity between lines 18 and 20, which lines connect bridge rectifier 22 for conversion of the alternating current to a direct current passing to terminals 24 and 26.

Resistor 28 may be included for limiting the flow of current in line 30 to switch 32 having charging position 34 and discharging position 36. When switch 32 is in charging position 34, direct current is received from terminals 24 and 26 for charging capacitor 38. Capacitor 38 may appear as one or as a bank of capacitors as desired.

Desirably included in the circuit is electromagnetically operated unit 40 exemplified by either a relay coil or solenoid for use in conjunction with switch 32 to serve as a voltage sensing switch. The voltage sensing switch may also be any suitable electronic circuit capable of opening switch 32 when sensing a particular voltage applied to the energy storage capacitor. Optionally included in the circuit is voltage monitoring system 42 which may be either a voltmeter for visually reading the potential applied to capacitor 38 or a simple indicator lamp which may light when the required potential is applied to the capacitor.

In operation, when the required voltage is received from terminals 24 and 26 for charging capacitor 38, electromagnetically operated unit 40 causes switch 32 to flip from charging position 34 to discharging position 36. Energy is thus released within about 0.25 second from capacitor 38 to terminals 44 and 46 for initiating from one to about 150 electric blasting caps 48 disposed in parallel between bus wires 50 and 52 without malfunction of as few as one blasting cap because of arcing.

The voltage across terminals 24 and 26 for charging capacitor 38, although illustrated in the drawing to be received from an AC source, may be received from a DC power line, battery, DC generator or the like provided that sufficient DC voltage ofa magnitude of about 400 to about 500 volts and preferably about 450 volts is available for'charging capacitor 38. The charged capacitor upon discharging provides about 210 to about 400 watt-seconds of energy within about 0.25 second to initiate from one up to about 150 electric blasting caps disposed in a parallel circuit arrangement.

FIG. 4 illustrates, in greater detail, a preferred blasting device prepared by the practice of the present invention. Terminals 54 and 56 may receive an alternating current from, for example, a standard 115 volt AC outlet. Connected between lines 55 and 57 is a power-on indicator light 58, exemplified by a NE-S 1H neon indicator lamp, in series with resistor 60, exemplified by a 47,000 ohm, 0.5 watt, wire wound resistor. Line 55 joins one terminal post 62 of switch 66, and line 63 joins a second terminal post 64 of switch 66. Switch 66, exemplified by a spring return, double-pole, double-throw toggle switch having a rating of 6 amperes and 125 volts, is illustrated in normal circuit position when connected to terminal posts 68 and 70. Line 69 from terminal post 68 is electrically joined to resistor 72, exemplified by a 500 ohm, 50 watt, wire wound resistor; and line 71 from terminal post 70 is electrically joined to bridge line 73. Bridge line 73 connects into bridge rectifier 74 formed, for example, of four diodes 76, exemplified by General Electric IN5062 silicon diodes. Adjacent diode connection lines 75 and 77, to that of bridge line 73, receive an electric current from the high potential side of a step-up transformer 78, exemplified by a Thordarson-Meissner 24Rl00 transformer. Electric current to the low potential side of transformer 78 is received from lines 57 and 63 when switch 66 is in position providing a closed circuit across terminal posts 62 and 64.

Corresponding to bridge line 73 for receiving rectified current from bridge rectifier 74 is bridge line 79 electrically joining resistor 80, exemplified by a 1,000 ohm, I00 watt, wire wound resistor, which joins line 81 illustrated connected to charging position 82 of power relay switch 84. Illustrated in phantom is switch 84 when connected to capacitor discharging position 86. Line 87 receives current from capacitor discharging position 86 when discharging capacitor 88 for releasing energy to terminals 90 and 92 by lines 73 and 87. The supplied energy to terminals 90 and 92 may be received by the circuit illustrated in FIG. 3 when initiating from one up to about 150 electric blasting caps disposed in parallel circuit arrangement.

Power relay 84 usefully includes switching coil 94 electrically positioned between lines 89 and 91. An example of a usefully employed power relay is that commercially available from Rowan Controller Co. under the designation B-32l-SP1 having a l 10 volt AC coil.

Power relay 84 forms a capacitor discharging element of the voltage sensing switch generally illustrated as switch 32 in FIG. 2, and auxiliary relay 96 forms the voltage sensing element thereof. Auxiliary relay 96 is exemplified by that available from Potter and Brumfield, identified generally as a plate relay and illustrated in combination with variable resistor 98 to obtain a 450 volt pull-in capability when combined with power relay 84.

Connected to power relay 84 is line 83 joining capacitor 88 and line 93 from resistor 72. Capacitor 88 is further connected to line 73 by line to complete a charging circuit connection. Capacitor 88, disposed between- lines 83 and 95, may be formed of eight 400 microfarad, 500 working volt DC electrolytic capacitors connected in parallel; i.e., a total capacitance of about 3.2 X 10- farad.

Usefully disposed in parallel to capacitor 88 is voltmeter 100 connected by line 101 to line 93 and by line 103 to line 73. voltmeter 100, exemplified by a 0 --500 DC voltmeter, is usefully included for visually reading the potential applied to capacitor 88.

In operation, the blasting device of FIG. 4 receives alternating current from a conventional outlet by terminals 54 and 56. When switch 66 is in the illustrated normal position, a drain of any residual charge on capacitor 88 is effected through resistor 72 and connecting lines 69 and 71 which is a closed circuit with lines 73 and 95 on one side of capacitor 88 and lines 83 and 93 on the opposite side thereof. A safety feature thus results in the capacitor drain circuit in that capacitor 88 is maintained without charge during nonuse of the blasting device.

When switch 66 is advanced to terminals 62 and 64, current is permitted to flow through lines 63 and 57 to the low potential side of transformer 78. On the high potential side of transformer 78, current is received through lines 75 and 77 by bridge rectifier 74 which converts alternating current to direct current for charging capacitor 88 by lines 73 and 81 when power relay 84 is in the capacitor charging position 82. When the required charge is on capacitor 88, auxiliary relay 96, operated by a minimal amount of current, closes switch 102 with terminal 104 and makes available alternating current from line 105 and line 91 to coil 94 of power relay 84. Power relay 84 is thus caused to rapidly switch to capacitor discharging position 86 to release energy from capacitor 88 through lines 87 and 73 and provide energy at terminals 90 and 92 for initiating up to about 150 blasting caps 48 disposed in parallel circuit between lines 50 and 52 of FIG. 3.

Conveniently disposed between lines 87 and 73 is discharge indicator 106, exemplified by a NESlH neon lamp, in series with a resistor 108, exemplified by 140,000 ohm, 2 watt, wire wound resistor, positioned along line 109. Discharge indicator 106 usefully visually indicates when capacitor discharge is effected.

The invention is further illustrated by the following example:

EXAMPLE Delay electric blasting caps in the number indicated in-the following table were connected according to standard blasting procedures in a parallel circuit arrangement and initiated by a blasting device having an energy discharge of a magnitude in the amount indicated from a capacitor having a rating also indicated.

b. Voltage sensing means for sensing a voltage between" about 400 and about 500 volts across said capacitor means; and

c. Means for automatically discharging said capacitor means into the firing line of said electric blasting caps when said voltage sensing means senses a voltage of between about 400 and about 500 volts across said capacitor means and such that the energy discharged from said capacitor means is between about 210 and about 400 watt-seconds.

5. The blasting device of claim 4 wherein the capacitor means has a capacitance of about 3.2 X t'arads.

6. The blasting device of claim 4 wherein the voltage sensing means is an electromagnetically operated unit.

7. The blasting device of claim 6 wherein the electromagnetically operated unit is a relay coil. 8. The blasting device of claim 6 wherein the electromagnetically operated unit is a solenoid.

TABLE Energy No. of Caps Capacitance Voltage (Watt- Connected Test No. (Famds) (Volts) seconds) in Parallel Results 1 2, 840 l0- 500 355 1 Cap fired normally. 2. 2, 840xi0- 500 355 All caps fired normally. 3 xltH 450 303 1 Cap tired normally. 4. x1 450 393 20 Allcaps tired normally. 5. 4, 970x10 400 398 1 Cap iii'ed normally. 6. 4 .l70)(10- 400 398 20 All caps fired normally. 7. 3, 000 (l0- 450 304 1 Cap fired normally. 8. 3, 000X10- 450 301 20 All cops fired normally. 9 3, OOOXlO- 450 304 150 Do.

It is apparent from the foregoing example that the present blasting circuit releases energy from a capacitor sufficientto initiate up to about 150 electric blasting caps disposed in a parallel circuit arrangement while being an energy level ins'ufficient to cause malfunction of any one electric blasting c'ap disposed in parallel circuit by internal arcing.

it is understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from this invention.

lclaim:

l. A blasting device for firing one to about 150 bridgewiretype electric blasting caps in parallel comprising:

a. Capacitor means capable of discharging between about 210 and about 400 watt-seconds oi'ene'rg'y; and

b. Means for automatically discharging said capacitor means into the firing line of said electric blasting caps when said capacitor means has been charged suificienitly to discharge about 2l0 to about 400 watt-seconds of energy. I

2. The blasting device of claim I wherein said means for sintomatically discharging said capacitor means is an electromagnetically o erated unit.

3. The b asting device of claim I wherein said means for antomatically discharging said capacitor means discharges said capacitor means within about 0.25 seconds.

4. A blasting device for firing one to about 150 bridgewiretype electric blasting caps in parallel comprising:

a. Capacitor means having a capacitance of about 2.8 x

10- farads to about 5.0 X 10- farads;

electric blasting caps in parallel comprising charging a capacitor means, said capacitor means being capable of discharging between about 2 10 to about 400 watt-seconds of energy, and automatically discharging said capacitor means into the firing 1 line of said electric blasting caps when said capacitor means has been charged sufficiently to discharge about 2l0 to about 400 watt-seconds of energy.

ll. The method of claim 10 wherein an elcctromagnetically operated unit is used to automatically discharge said capacitor means when said capacitor has been charged to between about 210 to about 400 watt-seconds of energy.

12. The method of claim 10 wherein said energy is discharged within about 0.25 seconds.

13. A method of firing one to about 150 bridgewire-type electric blasting caps in parallel comprising charging a capacitor means having a capacitance of about 2.8 X 10- t'arads to about 5.0 X 10- iarads, sensing the voltage across said capacitor as said capacitor is being charged, and automatically discharging said capacitor into the firing line of said electric blasting caps when the voltage across said capacitor has been sensed to be at a value between about 400 and about 500 volts such that the energy discharged from the capacitor means is between about 210 and 400 watt-seconds.

14. The method of claim 13 wherein the voltage across said capacitor is sensed by an electromagnetically operated unit.

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