US2636075A

US2636075A - Blasting control device

Info

Publication number: US2636075A
Authority: US
Inventors: Luther F Miller
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-10-17
Filing date: 1947-10-17
Publication date: 1953-04-21
Anticipated expiration: 1970-04-21

Description

April 2l, 1953 L. F. MILLER BLASTING CONTROL DEVICE 2 SHEETS--SHEET l Filed Oct. 17, 1947 L C INVENTOR April 21, 1953 l.. F. MILLER 2,636,075

BLASTING CONTROLI DEVICE Filed Oct. 17, 1947 2 SHEETS-SHEET 2 INVENTOR Lai/Lei' Miller NEYS Patented Apr. 21, 1953 UNITED STATES TENT OFFICE 11 Claims.

This invention relates to blasting control devices, and more particularly to circuits and apparatus for control of sequential multiple-shot blasting.

In some blasting operations, for example in quarrying or construction work in inhabited areas, there is a definite limitation on the quantity of explosive which can be simultaneously detonated. This limit is principally imposed by the hazard to building structures in the vicinity from excessive earth tremors. It has heretofore been found that, where, as is customary, a plurality of charges are employed, by ring them in rapid sequence instead of simultaneously, comparable or even superior blasting effectiveness can be achieved while limiting the seismic effect to that which would be produced by firing only a .single charge of magnitude equal to, or even less than, that of the largest of the several charges. Thus, this sequential or delayed action blasting procedure permits the use in each charge of a quantity of explosive equal to the total quantity permitted for a simultaneous multipleshot blast without any increase in hazard from earth tremors. This results in a considerable increase in the speed and effectiveness of such blasting operations.

Various devices for controlling such sequential blasting have heretofore been used, most of them built around a manually operated multiplecontact switch. In such devices, the time intervals between successive shots is ascertained by the speed with which the movable arm of the switch is actuated by the operator-at best an indeiinite and erratic determinant.

Another expedient frequently employed is that of delayed-action caps. These not only are subject to occasional failure, but to inaccuracy and to limitation of the minimum time delay of which they fare capable.

It has now been discovered that there exists a somewhat critical time interval between successive blasts in a sequence at which markedly superior results may be achieved. This time interval has been evaluated largely by empirical methods, and depends on such factors as the 'spacing of the holes in which the charges are placed, the density of the soil or stone, and the like. Within the favorable range of time interval values, there apparently is some interference or cancellation effect between the several compressional waves emanating from the Various explosions, which effect materially reduces the amplitude of their resultant or summative wave. Also, for reasons which do not fully appear, the blasted stone is more thoroughly fragmented; this is particularly advantageous in quarrying work, as it lessens or eliminates the after-break- .ing otherwise required to reduce the stone to 'the desired size. The above discussed blasting control devices have been found incapable of vaccomplishing the accuracy of time interval requisite to achievement of these superior results.

It is accordingly among the objects of the invention to provide a control device capable of supplying igniting electrical impulses to a vSeries of blasting charges at definite and uniform time intervals. Another object is that of providing a blasting control device in which the hazard of accidental, premature or anachronistic detonation is substantially eliminated. A more particular object is the provision, in such a device, of means for assuring that the sequence of detonations is commenced at the proper charge in the line of charges. A further object is that of minimizing the length and number of interconnecting cables required among the various units in the system.

These objects and others apparent hereinafter, are accomplished by the present invention, a suitable `embodiment of which is described herein and shown in the appended drawings, in which Figure 1 is a perspective of a blasting site, with a control device embodying features of the inven- Figure 2 is a partially schematic diagram of the principal electrical components of said device.

Referring to Figure 1, a typical quarrying 'opperation is shown in which a control device ecnstructed in accordance with this invention is in use. There is illustrated at A a wall or lface of stone on which the blasting is to be performed. As is customary -in such practice, a row of vertical holes B is drilled in the upper ground level a short distance behind the face A to receive a series of explosive charges. The spacing 'between the holes B, their common spacing from .the face A and the quantity of explosive used in each hole is determined by such considerations as the inature ofthe stone, the location vof the quarry, the desired size of the fragments andthe like. llift-urtning along the line -of holes B and `connected to one terminal of the -igniter element of each charge is a common electrical .conductor .24., which in turn is connected by means .of a lconductor .25 with one of the Vterminals y2li on an output terminal `board 28 of a switching unit, :general-ly indicated at lC and suitably located some 1-00 or 150 feet from the row of holes B. The other terminals of the igniter elements :are econ ne'cted by means of -separate .conductors 251 Itofone ef the terminals -l-20 on the output terminal board 12B of switching unit C.

In order to Vascertain whether allot the charges have been fired, i. e. whether any live vcharges remain unexploded after the firing, it is ra frequent practice to Iemploy a camera to photograph the explosions. In Figure '1, such a camera LD is shown so Vloca-ted and vdirected as to view e 3 entire row oi noles B, and it is adapted, by means hereinafter described, to have its shutter tripped and its film exposed immediately after the last of the series of charges has been detonated. Due to the rapidity of the firing and the operation of the camera, D, there will appear on the picture taken by camera D a smoke puff or similar visible indication above each of the holes B whose charge has been detonated. It is thus possible to ascertain whether any, and if so which, of the explosive charges has not been fired so that its safe removal may be effected. For purposes of actuating the camera D a two-conductor cable 3| connects the shutter actuating mechanism of the camera with terminals 25 and 35 of output terminal board 28 of switching unit C.

A control unit, generally indicated at E, is located in a protected spot, for example some 150 to.300 feet from switching unit C. The two units C and E-are interconnected by means of a four-conductor cable 32 between the input terminal board 33 of switching Iunit C and the output terminal board'34 of control unit E. With this arrangement, the operator controlling` the blasting is located at the control unit E* some 250 to. 45() vfeet from the row of charges and out of the range of personal hazard. However, since only a single cable 32 is employed for a major .portion of the distance between the operating position and the row of holes B, i.'e. from the control unit E to the switching unit C, so that the multiple conductors which fan out to the various holes extend considerably less than half of the -total distance, i. e., from the holes B to switching unit C, it will be seen that an economy Oflength and number of conductors is achieved. As shown in Figure 2, switching unit C includesV a switch, indicated generally at 34, havlgnaplurality, in this case twenty-two, xed contacts or points |-22,A arranged in an arc about ahe axialof e, shaft 35 which'carries e, radialv arm 36 arranged to be driven to sweep around said arc and `engage said contacts in sequence. Shaft 35 is rotatably mounted on the frame of switching unit C and is arranged to be drivenby a suitable electric motor 31 through a variable speed transmission 35a, which may be interposed between the motor and the shaft 35 forcontrolling the-angular velocity of rotary arm 36.V The terminals 3B and 33 of motor 31 are-connected by means of conductors 45 and 4| with tWo of the

terminals

42 and 43, respectively, on the input terminal board 33 of switching

unit C. Terminals

42 and 43 are, in turn, respectively connected by means of two conductors 44 and 45 inthe four-conductor cable 32 with two of the terminals 46 and 41 of the output terminal board 34 'of the Icontrol unit E. Within control unit E, terminals 46 and 41' are each respectively connected to

terminals

48 and 49 of the input terminal board 53 of this controlunit through one pole of a double-pole-single-

throw switch Terminals

48 and 49 of input terminal board 5|] provide connections for a suitable source of electric power P. An indicator lamp .52 is connected across

terminals

48 and 49 and is illuminated to indicate the availability of electric power at that point. When switch 5| is closed, power will be supplied from the source P to 'motor 31 through

terminals

48 and 49, switch 5|, terminals 45 and 41, conductors 44 and 45,

terminals

42 and 43, conductors 40 and 4| and terminals 38 and 35, to cause motor 31 to rotate and drive arm 35 continuously. A second indicator lamp 53 may be connected across terminals 46 and 41 in control unit E to indicate that switch 5| has been closed to supply power to the motor 31. The Variable speed transmission 35a is preset to provide that angular velocity of rotary arm 36 which will afford theoptimum time interval between successive blasts in the sequence, which interval is determined as hereinbefore described.

The greater portion, in this case twenty, of

. the fixed contacts |-20 of rotary switch 34 in 'switching unit C are connected by conductors 54 to respectively numbered terminals |-20 on the output terminal board 28 of switching unit C. For clarication, only one of such conductors 54 has been shown. A brush or similar resilient wiping contact 55 bears against shaft 35 and affords electrical contact from the rotary arm36 through a conductor 55 to one contact 51 of one pole of a.double-pole-single-throw solenoid-controlled switch or relay 58, referred to herein as the safety switch. The contact 53, which cooperates with contact 51, is connected by means of a conductor 50 with the conductor 4| which in turn is connected as previously described to one terminal of the power source P.

One terminal of the solenoid or winding 6| which actuates safety switch 58 is connected to the conductor 4t associated with the opposite terminal ofthe power source; the opposite terminal-of solenoid 6| is connected by means of a conductor 62, a terminal 63 on input terminal board 33, a conductor 64 in cable 32, and a terminal 65 on output terminal board 34 of control unit Eto one side of a single-pole-single-throw switch 65, referred to as the firing switch. The opposite side of firing switch 56 is connected by means of a terminal 61 on terminal board 34, a conductor 68 in cable 32, a terminal 69 on terminal board 33, a conductor 10 and the conductor 56 to contact 51 of safety switch 58. One of the contacts 22' of rotary switch 34 is connected by means of a conductor 1| to the conductor 4| associated with the power source. y The operation of this circuit is as follows: when switch 5| is closed, motor 31 is supplied currentl and runs continuously, driving arm 3B repeatedly around the arc of contacts I to 22 at a speed determined by the setting of transmission 35a. Solenoid 6| is not energized as long as firing switch 66 remains open, therefore safety switch 58 remains open and the rotating arm 36 is electrically dead. This is the preparatory or standby condition of the system, and is eifectuated immediately prior to firing. rotary arm 36 will normally make a number of revolutions during this standby period, and, as it repeatedly brushes the xed contacts |-22, it functions to wipe them clean of any dust, corrosion or other impediments so that, before the ring switch 66 is closed, on each revolution the rotary arm is establishing positive electrical'engagement with every one of the contacts.

When it is desired to fire the series of charges, firing switch 66 isclosed, connecting one side of solenoid 6| to rotary arm 36. This produces no change in the system until the next time the r'otating arm 36 engages contact 22. When this happens, arm 36 and its associated end of solenoid 6| will be electrically connected to conductor 4|, effectively bridging solenoid 6| across conductors 40 and4| and thence across the power source P, and energizing solenoid 6| to close safety switch ,58. The closure of switch 58 serves to maintain solenoid lenergizedafter rotary arm 36u15,- engagescontact 22,since rotaryarm 36 andiits associated rend. of solenoid 16 now'. are connected The to conductor 4l and therefore to the power source P through

contacts

51 and 59 of switch 58. In other words, contacts 5l and 5S `function as a keep alive for solenoid Sl.

Rotary arm 35, being thus connected to conductor lll and one terminal of the source P accordingly energizes each of the igniter elements on its next sweep past the series of contacts -20'. The return circuit through the igniter elements is completed by the common leads 24 and v25 (Fig. 1) which are connected through output terminal 2S of control .switch C and a conductor 'i2 to one contact 13 of the remaining pole of safety switch 5S; cooperating contact M of this pole of safety switch 5E is connected by means of a conductor l5 to the conductor dll and the other terminal of the power source P. The section i3- l cf safety switch 5t functions to open the return circuit through the igniter elements as long as solenoid t! is deenergized so that neither terminal of an igniter element is connected to the power source until the desired ring time, to eliminate the possibility of acciden-tal detonation by a short circuit in the portion of the circuit associated with one of the terminals oi' the igniter elements.

Since solenoid @I is not energize-d and switch 58 is not closed until the rst time rotary arm 35 engages contact 22' after the ring switch is closed, the ring sequence can only comM mence at the charge associated with contact i of switch 34. Also, since the camera is connected to contact 2| of switch 3 its shutter can be tripped only after the entire row of charges has been fired.

Generally, contact l or" switch 34 will be ccnnected to the charge in the hole at an extreme end of the row of holes B and the successive holes along the row of holes will be connected respectively to the successively numbered contacts of switch 34 so that the charges will be fired progressively along the row of holes B. It has been found that this type of nring produces a tearing or peeling action of the face A, an effect wherein face A gives the appearance of a large stone door swinging open. In this type of action, since the separating force is applied progressively along the face A and is entirely concentrated against the resistance of only a very small portion of the face A at any single instant, enicient separation may be achieved with a good economy of explosive. The contrast between such progressive separation and that which would be eiected by firing the entire row of charges simultaneousiy may be compared to that between removing a strip of adhesive tape from a iiat surface on which it is laid down by peeling gradually from one end and by attempting to pull it oli' at all points simultaneously.

Also, since the cleavage slightly precedes the explosions along the row, as each charge after the rst explodes, it expands outwardly against a wall already slightly separated from it and therefore somewhat yielding. The reactive force, which is evidenced as earth tremor, is thus considerably diminished.

In this type of blasting, it is extremely important that the sequence of blasting commences at an extreme end of the row of holes and progresses toward the other, rather than commencing, for example, at the center of the row, working its way to one end, then resuming at the other end and working back toward the middle of the row. The hazard of such a staggered sequence is that the iinal charges near the center oi the row may be completely or partially exposed before firing with the possible result that stones may be propelled some distance from the blasting site with injury to personnel or property. The characteristic of the control system herein described of incapability of commencing the firing sequence except at a certain point, namely at the charge associated with contact l of switch 34, completely eliminates this hazard.

There will thus be seen to have been provided a system which allows the operator at the control unit E to be located at some distance from the row of holes .B for complete personal safety, and the switching unit C to be located close to the holes B to achieve economy of cable length, while providing every reasonable assurance against accidental or untimely detonation of charges despite the remote position of the operator with respect to the switching unit C.

Accordingly, it will be appreciated that the present invention accomplishes the aforemen tioned and other desirable objects. However, it should be emphasized that the description and showing herein is intended as merely illustrative and not as restrictive of the invention.

Iclaim:

1. A blasting control device comprising a switch having a plurality of contacts arranged in an arc and a rotatable arm operable to engage said contacts in sequence, a safety switch operable to connect said arm to va source of electrical power, a solenoid for operating said safety switch, means to connect said solenoid to said source when said arm engages a certain one of said contacts, an electric motor operatively connected to rotate said arm, and a remotely located switch operable to connect said motor to said source.

2. A blasting control device comprising a multiple Contact rotary switch whose fixed contacts are respectively connected to igniter elements of a series of blasting charges, a relay operable to connect the rotary arm of said switch to a source of electrical power, means including a first remotely located switch for connecting the winding of said relay to said source when said arm engages a certain one of said contacts, an electric motor operatively connected to rotate said arm, and a second remotely located switch to connect said motor to said source.

3. A blasting control device comprising a multiple contact rotary switch which has one fixed contact adapted to be connected to one terminal of a source of electrical power, and a plurality of other fixed contacts adapted to be respectively connected to one of the terminals of the igniter elements of a series of blasting charges; a twopole relay having one pole operable to connect the other terminals of said igniter elements to the other terminal of said source and the other pole operable to connect the rotary arm of said switch to the former said terminal of said source, the winding of said relay being connected between said rotary arm and the latter said terminal of said source; an electric motor operatively connected to rotate said rotary arm; and a remotely located switch operable to connect said motor across said source.

4. A blasting control device comprising a multiple contact rotary switch which has one fixed contact adapted to be connected to one terminal of a source of electrical power, and a plurality of other fixed contacts adapted to be respectively connected to one of the terminals of the igniter elements of a series of blasting charges and another xed contact adapted to be connected to the shutter actuating mechanism of a camera, and a rotary arm adapted to engage said xed contacts in the order named; a two-pole relay having one pole operable to connect the other terminals of said igniter elements to the other terminal of said source and the other pole operable to connect said rotary arm to the former said terminal of said source, the Windingof said relay being connected between said rotary .arm and the latter said terminal of said source; an electric motor operatively connected to rotate said rotary arm; and a remotely located switch operable to connect said motor across said source.

5. A blasting control device comprising a multiple contact rotary switch which has one fixed contact adapted to be connected to one terminal of a source of electrical power, and a plurality of other xed contacts adapted to be respectively connected to one of the terminals of the igniter elements of ya series of vblasting charges; a twopole relay having one pole operable to connect the other terminals of said igniter elements to the other terminal of said source and the other pole operable to connect the rotary arm of said switch to the former said terminal of said source, vthe Winding of said relay being connected between said rotary arm and the latter said terminal of Vsaid source; an electric motor; a variable speed transmission operatively connecting said arm to Y said motor; and a remotely located switch operable to connect said motor across said source.

6. A blasting control device comprising a multiple contact rotary switch which has one xed -contact adapted to be connected to one terminal ofa source of electrical power, and a plurality rof other fixed contacts adapted to be respectively connected to one of the terminals of the igniter elements of a series of blasting charges and another fixed contact adapted to be connected to the shutter actuating mechanism of a camera, and a rotary arm adapted to engage said ilxed contacts in the order named; a' two-pole relay Vhaving one pole operable to connect the other terminals of said igniter elements to the other terminal of said source and the other pole operable to connect said rotary arm to the former said terminal of said source, the winding of said relay being connected between said rotary arm and the latter said terminal of said source; an electric motor; a variable speed transmission operatively connecting said arm to said motor; and a remotely located switch operable to connect said motor across said source.

7. A blasting control device comprising a switch having a rotary arm and a plurality of xed contacts, one of which is adapted to be connected to the rst terminal of a source of electrical power and a plurality of the others of which are adapted to be respectively connected to the igniter elements of a series of blasting charges, an electric motor operatively connected ,to drive said rotary arm, a remotely located switch operable to connect said motor across said source, a relay operable to connect said movable arm to the rst terminal of said source, the winding of said relay being connected between said rotary arm and the other terminal of said source, whereby when said rotary arm makes contact with said one xed terminal, said winding will be energized and said relay will be actuated to maintain the energization of said winding and to connect said rotary arm to said source Sothat, on the next revolution of said rotary arm, said charges will be serially detonated.

8. A system for testing and controlling the energization of a group of similar electric circuits, comprising a multiple contact switch having a plurality of spacedfelectrical contacts and a contact arm adapted to move from one contact to the other successively, means connecting said contacts one to each of said similar electric circuits, means for moving said contact arm over said multiple contacts, and means controlled by the motion of said arm over one of said contacts for completing the connection of said contact arm to a power source for energizing said similar electric circuits in successive order according to the travel of said contact arm.

9. A system for testing and controlling the energization of a group of similar electric circuits comprising a, multiple contact switch having operative connecting means to each of said electric circuits for successively .bringing potential to the same from a supply source, an interlocking relay having operative connecting means to apply power to said multiple contact switch, means for operating said multiple contact switch, and means controlled through one of said contacts of said switch for actuating said interlocking relay to apply said power to said contacts.

10. A system for testing and controlling the energization of a group of similar electric circuits, comprising a multiple contact switch having a plurality of spaced electrical contacts and a contact arm adapted to move from one contact to the other successively, means connecting said contacts one to each of said similar electric circuits, means for moving said contact arm over said multiple contacts, a, remote control switch for said similar electric circuits, and means controlled by the motion of said arm over one of said contacts after said remote control switch has been closed for completing the connection of said contact arm to a power source for energizing said similar electric circuits in successive order according to the travel of said contact arm.

11. A system for testing and controlling the energization of a group of similar electric circuits,

' comprising a multiple contact switch having a plurality of spaced electrical contacts and a contact arm adapted to move from one contact to the other successively, means connecting said contacts one to each of said similar electric circuits, a remote control sweep circuit switch and a remote control switch for the similar electric circuits, means operative by the closing of the sweep circuit switch for moving said contact arm over said multiple contacts, and means controlled by the motion of said arm over one of said contacts after the remote control switch for energizing the similar electric circuits has been closed, for completing the connection of said control arm to a power source for energizing said similar electric circuits in successive order in accordance with the travel of said contact arm.

LUTHER F. MILLER.

References cited in the sie of this patent UNITED sTATEs PATENTS