US2671399A - Blasting method - Google Patents

Description

March 9, 1954 G. MORRIS 2,671,399

BLASTING METHOD Filed April 15, 1952 LLL INVENTOR.'

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d ATTORNEYS' Patented Mar. 9, 1954 BLASTING METHOD George Morris, Ardrossan, Scotland, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain Application April 15, 1952, Serial N0. 282,373

Claims priority, application Great Britain July 4, 1951 2 Claims.

The present invention relates to improvements in or relating to blasting methods for use Where it is necessary or desirable to re a large number of shots substantially simultaneously in a denite sequence.

In large scale blasting operations such as quarrying for the production of stone suitable for crushing, it is known that better' results are obtained for the same total amount of explosive charge, by iiring a large number of small shots than by ring a smaller number of larger shots. As the number of shots is increased, however, the cost increases due to increased drilling costs. Thus the ratio explosive charge per hole to total charge is determined by economic considerations. Such blasting operations are usually conducted by detonating explosive charges in a number of positions in a row behind and generally parallel to a face, for example, in bore holes drilled vertically behind the face or horizontally into it. In this system of blasting it is generally of the utmost importance for the shots to be red in the correct sequence. It is also well-known that if the shots in the individual bore holes in a single rng circuit are caused to detonate successively at very short intervals of time, the amount of ground vibration caused is much less than would be caused by the simultaneous detonation of the total weight of explosive charge at the same time and that better breaking is achieved with less need for subsequent secondary blasting to break up the resulting boulders. It has hitherto been the practice to achieve this by one of several methods, all of which are subject to severe limitations. Thus in one method a series of short interval delay detonators are used, all of which are initiated by the firing current at the same time. This method gives excellent results when the number of charges in the circuit is not very large, but it is not at present practicable to obtain a series of short delay detonators having a delay interval of less than about 25 milliseconds or a series having more than about 8 members so that the vring of a large round of shots, for example, of the order of two hundred, would require the use of a number of sets of delay detonators initiated at different times.

Another method which has been used is to use a switch, which may be motor driven, capable of making and breaking a number of circuits in any desired sequence. In using such a switch the negative leading wires of all the detonators are connected to the negative pole of the switch and the positive leading wire from each detonator is connected to a separate contact which is traversed by an arm which successively connects each of the series of contacts to the positive pole of the switch. This method necessitates the use of a large amount of Wire since it is necessary to have two Wires all the Way from each detonator to the switch. This necessitates the use of a large number of Wires and there thus exists a serious possibility of making a wrong connection and hence of the detonators failing to re in the desired order or at all. With this system there also exists the possibility of some of the wires being cut by flying debris before the detcnators connected thereto have been initiated. This is partly overcome by decreasing the time interval between successive shots. With commercially available switches however, this method is limited to use in blasts where only about 15 to 20 shots are being fired. A switch suitable for firing larger rounds of shots would require to be large and cumbersome and would not be easily transportable, and would also require very extensive wiring with the increased possibility of one or more wires being connected to the Wrong contacts, and the increased possibility of being cut and thus causing individual failures.

According to the present invention the method of ring a succession of 'shots by the firing of their corresponding detonators at a pre-set time interval and in a sequence prescribed by the blasting operation to be accomplished comprises arranging the detonators in an array of columns andi, rows, connecting together in each row one poleof each detonator to a common conducting element, connecting together in each column the other pole of each detonator to another conducting element, arranging that each row is contacted in desired sequence toa pole of a source of electricity, arranging that each column is contacted in desired sequence to the opposite pole of said source of electricity, and arranging that contact to a row is maintained while all the contacts or" a column are made in sequence.

The term row in the description and claims is intended to signify a line of shots which is substantially parallel to the face to be blasted.

More specifically according to the method of the invention there are m rows and 11l columns, a pole of each detonator in each row is connected to one of n bus-bars provided, each of the busbars is arranged to be contacted in desired sequence to a common wire through one of the n time control contact means provided to a pole of said source of electricity, the other pole of each of the n detonators of a row is connected to one of m bus-bars provided, each of these busbars is arranged to be contacted in desired sequence'through one of the m time control contact means providedto another common wire to the The present invention overcomes the aforemenze tionedtdic'ulties of the prior proposals and permits the ring of larger rounds of shots by ordinaryrelectric detonators.

A switch for use in carrying out the method ofA the invention comprises two rotor armsv each adapted to be mechanically driven and on rotation to make and break electric circuits by' making and breaking contact with contacts providedl for each arm in which switch the rotor arms. are geared together so that while one arm makes and breaks contact vin desired ,sequence with all its ,contractsv the. other arm makes and is in contact with. one of its contacts.

By this means it is 'possible to re a number of shotsv equal to the productl ofthe number of conin both series whereas by the former switch method the number of shots was limited' to the number of contacts`- In practice to wiresuch a network it is necessary only to lay long' lines of wires connected to the swtchjpositions then remore the insulation from each wire 4at appropriate intervals and connect the leading wires of each detonator to the twolwi'res chosen ,atY the nearest points whereV the insulation. has been removed. Thus the possi-k bility of connecting the detonator. leading, wires to the wrong switch positions is very small.

The individual shots may be fired at any suitable. tixneinterval, for example, l milliseconds.

Itis preferred, however, to fire the shots at inter-` vals or 3 milliseconds.

The inventiontis illustra-ted byI the diagrammatic sketch accompanying thev specification which shows a suitable arrangement for rin'g mn shots using a switch' havingonlwngwlfcontacts. lIn the diagramthel circuits are shown individual for` convenience of representation.), 'I-`he shots may be fired in any desired `orden-'thus by' closing switch R1 then switchesI S1 toY S11 in succession, followed by .closand S1 are closed. 1t might alternatively be preferable to fire the shots in some other order which could be easily arranged.

' It will thus be seen that using the method of the present invention a hundred shots could be red using onlyv twenty wires inI the; network, whereas using the prior switch methods one hund-red and one wires would be necessary. This effects fa considerable economy due to decreased cost of wire, greatly simplies the task of connecti-ngf up, decreases the possibility of incorrect connection and also decreases the possibility of any misres due to-wires broken duringv firing.

What,A I, claim,

l. A method of ring a succession of shots by theri-'ngoil' their corresponding detonators at a pre-set time interval and in a sequence prescribed ther blasting operation to be accomplished which comprises arranging the detonatcrs,` in an `array of columns and rows, connecting together in each row one pole of each detonator to a common conducting element, connecting tog-ether' in each column the other pole of each detcnator to another conducting element, arrangingv that each row is contacted in desired sequence to e. pole oi a source of electricity,4 .arranging that each column is contacted in desired sequence to the opposite pole of said source of electricity, arranging that contact to a row is maintaincdwhile all the contacts of a column are madev in sequence.

` 2. A method as claimedv infclaim 1 wherein there are .m rowsy and "n: columns, wherein a pole of each detonator each row is connected to one, of n bus-bars provided',V wherein each of the bus-bars is arranged to be contacted in desired sequence to a .common wire through one or" the :n time control contact means provided to a pole of said source of electricity, wherein the other pole of each of the n detonators of a row is convnected to one of m leus-bars provided, wherein y in desiredY sequence through one of the m time control contact means provided tol another co1 each of the row contacts mon wire-to the other pole of said source oi" electricity, andwherei'n all the time control contact means are interrelated so that all'the columns are contacted during the time interval for which is maintained. v

GEORGE MORRIS.

References Cited in the le of this patent UNITED STA'I'ES PATENTS 21,609,750 McFarland Sept. 9,

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