AU687051B2 - Initiation system - Google Patents

Description

WO 94/25820 PCT/IAU9400204 1 INITIATION SYSTEM The present invention relates to a redundant initiation system and method of use.

Detonators are devices which contain a small amount of very sensitive explosive, the initiation of which can be safely controlled from a distance.

Initiation systems housing electrically wired circuits, signal tube or detonating cord are commonly used to connect the detonators to the shot firer's position from which detonations may be triggered.

The initiation of detonators may be instantaneous, that is occurring within microseconds of the shot firer triggering the exploder box, or the initiation may be delayed by a delay device incorporated in the detonator and/or ir, the initiation system. These delays are commonly of any length up to about seconds.

Shot firers plan the location of detonators and charges in the ground to be blasted and use the delays to achieve firing of detonators at selected intervals in a predetermined sequence known as a blast sequence. The firing of detonators in a pattern gives control over rock fragmentation, direction of throw and the intensity of ground vibration and the associated air blast and noise. Overbreaking of rock can be reduced, generally resulting in an improved, smoother finish to the walls of a mine or excavation.

In mining operations significant importance is given to the sequencing and timing of the initiation of each blasthole. A number of techniques exist to ensure that each hole is initiated at a time that results in the optimum displacement and fragmentation of the blasted ground. In recent times a large number of mining operations have adopted surface initiation systems based on signal tube utilising delay detonations between rows of boreholes and between boreholes within a row. Such systems have been collectively called trunkline delay systems and the BLASTMASTER system described in Australian Patent No. 17732/88, Atlas Powder Company is an example of one such system.

(BLASTMASTER is a trade mark).

A benefit of these systems is that they give the shotfirer a great deal of flexibility in assigning differing delay times to a large number of boreholes.

Furthermore, such systems have an advantage in reduced inventories because SUBSTITUTE SHEET (Rule 26) WO 94/25820 PCTIAU94/00204 2 instead of having to maintain a supply of dozens of detonators of differing delay times, the shotfirer need only keep a few different units which can be connected in a variety of ways to give different delays.

Signal tube and low weight detonating cord are particularly favoured for use in initiating systems because they propagate the initiating wave virtually noiselessly ano Lnerefore they are more acceptable than detonating cord in noise coriscious areas. A major drawback of the trunkline delay is that there is only a single communication path from the point of blast initiation by the shotfirer and each borehole so that any failure in the path or "cutoff" of the initiating wave results in failure of the detonator to explode. Such incidents are termed "misfires" and tend to cause poor blasting results because areas of rock are left unbroken or only partially broken. Unfired detonators and associated explosive compositions in blastholes present a costly safety hazard.

Systems such as the BLASTMASTER system are known as "redundant" systems as they have a second line of communication to each detonator to ensure that in the event of a failure, all detonators are initiated. However, such prior art systems have the disadvantage that the time sequence is altered or compromised in the event of a failure or misfire of the first communication path.

The initiation system of the present invention provides the significant advantage of not only being redundant but, in the event of failure of the 'irst communication path, retaining the intended initiation sequence of the first communication path with essentially unchanged timing.

The initiation system of the current invention provides significant benefits in the event of a failure or misfire because it returns a blast pattern to the intended initiation sequence far more quickly than the initiation systems of the prior art, ensuring every blasthole is detonated and thus preserving the blast performance.

The current invention therefore provides a redundant initiation detonation system comprising, SUBSTITUTE SHEET (Rule 261 WO 94/25820 PCT/AU94/00204 3 a male connector comprising a well housing a delay detonator connected to a length of signal tube and at least one channel adapted -o receive at least one signal tube in close proximity to said delay detonator; a female connector comprising a well housing a delay detonator connected to a length of signal tube; a dual connector comprising a male connector comprising a well housing a delay detonator and at least one channel adapted to receive at least one signal tube in close proximity to said delay detonator and a female connector comprising a well housing an instantaneous detonator and wherein said delay detonator and instantaneous detonator are connected to opposite ends of a length of signal tube; wherein said male and female connectors are interconnectable and said male, female and dual connectors are joined in such a manner that the control row of boreholes are linked by male connectors, the back row of boreholes are linked by female connectors and the echelon rows of boreholes between the control and back rows are linked by dual connectors.

The initiating system of the current invention includes the use of malefemale type connectors which house detonators. It will be readily apparent to a person skilled in the art that the term delay detonator also includes detonators having a delay time of zero. The detonators may be located and held within the connectors by any convenient method including clips or friction. Three basic types of connectors used a male connector housing a delay detonator, a female connector housing a delay detonator and a dual connector comprising a female connector housing an instantaneous detonator and a male connector housing a delay detonator. In a preferred embodiment the dual connector further comprises a channel in the male connector which channel is adapted to hold the tail of the delay detonator such that the delay detonator can initiate the signal tube by end on initiation. The male connector of the dual connector unit may be the same as the male connector of the single unit. It will readily be apparent to the person ski!led in the art that the terms "male" and SUBSTITUTE SHEET (Rule 26) WO 94/25820 PCT/AU94/00204 4 "female" connectnrs are relative terms only and merely serve to indicate the opposite interlocking nature of the connectors.

It will also be readily apparent to a person skilled in the art that a detonation front is communicated through the initiation system of the current invention by signal tube hence all references to detonators relate to signal tube detonators. The term "tail" refers to a single piece of signal tube or detonating cord or the like which is attached to a detonator. Where used herein the term "signal tube" refers to signal tube or low weight detonating cord or the like.

Blasting patterns in general are described in terms of rows of blastholes.

Initiation systems usually comprise a "control row" which is the first row along which the initiating detonation front is transmitted. Branching from the control row are "echelon" rows along which the initiating detonation front is transmitted from the control row. A "back row" may also be included to act as a second control row should the intended control row or echelon row misfire.

The redundant initiation detonation system of the current invention further provides a method of detonating a blast pattern which comprises at least one control row, at least one echelon row and at least one back row.

Using the initiation system of the current invention, the control row comprises male connectors, each male connector being connected to the tail of the detonator of an adjacent male connector. Where an echelon row branches off from the control row, the connector of the control row is connected to units in the echelon row.

The echelon row of the initiation system of the current invention comprises double ended units connected together. At one end of the echelon row is a female connector of a dual connector which is connected to a male connector of the control row. At the other end of the echelon row is a male connector of a dual connector which is connected to a female connector of the back row. The back row comprises female units connected together.

Signal tubes connected to male connectors enable transmission of a detonation signal down boreholes to detonators often located in primers which detonate the larger body of bulk or packaged explosive in the borehole.

The male connector necessarily includes provision for connection to signal tube or the like including the tail of other detonators. Signal tubes so connected SUBSTITUTE SHEET (Rule 2b) must be located in close proximity to the detonator and in such a manner that a detonation front issuing from the detonator will be propagated in the signal tube. This propagation of the detonation can be achieved by either locating the signal tube along the side of the detonator or across the end by what is referred to as "end on" initiation. The latter is preferable because it facilitates the use of detonators which include smaller quantities of charge in the detonator. Where used herein the term "end on" initiation means initiation of signal tube by a detonator, the longitudinal axis of the signal tube being located substantially perpendicular to the longitudinal axis of the detonator.

When the male and female units are connected it is necessary that the detonators are located such that the initiation of the detonator in one connector will cause initiation of the detonator in the other connector.

In a further embodiment the invention comprises a method of blasting using the redundant initiated detonation system of the current invention.

15 A preferred embodiment of the method of use of the present invention will now be described by way of the following example and with reference to the accompanying drawings in which Figures 1(a) and 1(b) depict simple blast patterns; Figure 2 is a perspective view of the connectors used in the current invention; Figure 3(a) is a plan view of a male connector and delay detonator, Figure 3(b) depicts a longitudinal cross-section of male connector housing a delay detonator connected to a female connector housing an instantaneous detonator and Figure 3(c) depicts a longitudinal cross section of male connector housing a delay detonator connected to a female connector housing a delay detonator; Figure 4 is a schematic representation of a blast pattern showing 25 how the connectors and units are arranged.

Figure 1 illustrates simple initiation patterns of the prior art for blasting at rock faces The arrows indicate the direction of propagation of the initiation travelling from the initiation hole and the numbers indicate the length of delay between initiation at the initiation hole(2) and the detonation at a particular blast hole The control rows and echelon rows are clearly seen. Figure 1(a) depicts a multiple row initiation of 5 rows in a square pattern.

Figure 1(b) depicts a sequential hole by hole initiation of 5 rows in an offset pattern.

1A LLI Figure 2 depicts the connectors used in the initiation system of the T 0a WO 94/25820 PCTIAU194100204 6 current invention. Figure 2(a) shows a male connector into which has been inserted a delay detonator attached to signal tube A channel is provided in the connector for the insertion of signal tube in close proximity to the detonator. Figure 2(b) shows dual connector comprising a male connector and delay detonator attached to one end of a piece of signal tube and, at the other end of the signal tube, a female connector (11) housing an instantaneous detonator Figure 2(c) shows a female connector (12) housing a delay detonator (13) housing a female connector As delay detonators comprise a delay element in addition to charges they are usually longer than instantaneous detonators and the relevant female connectors may be of different sizes.

Figure 3 depicts various connectors and their relationship to detonators.

Figure 3(a) is a section (front) view of a delay detonator (14) located within a male connector The detonator is held within a well or channel (16) of the connector and the signal tube (17) for initiating the detonator is curled around and held by the connector. Using this embodiment, initiation of the detonator will lead to propagation of a detonation front through the signal tube. This embodiment also has the further advantage that the detonator is firmly located and there is little chance of accidentally pulling the signal tube out of the detonator even if it is strongly pulled. The connector also includes another well or channel (18) in which one or more signal tubes may be located in close proximity to the end of the detonator where the explosive charge of the detonator is located. As the detonator initiates, the main explosive front is sufficient to initiate an explosive front in the signal tubes.

Figure 3(b) is a longitudinal cross-section of male connector housing a delay detonator (14) which is in turn connected to a female connector (19) in which is located an instantaneous detonator (20) attached to signal tube The channel or gutter (22) into which signal tubes (23) have been inserted can be clearly seen.

Figure 3(c) is a longitudinal cross-section view analogous to Figure 3(b) except that the female connector and instantaneous detonator have been replaced by a female connector (24) in which is located a delay detonator Figure 4 illustrates a particularly preferred embodiment of the redundant SUBSTITUTE SHEET (Rule 26) WO 94/25820 PCT/AU94/00204 7 initiation detonation system of the current invention. From the initiation hole (26) the initiation front runs along the control row branching off along echelon rows The back row (29) acts as a second safety control row in the event of a misfire. The lines with arrows indicate directions in which the initiation front may run. The lines with single arrowheads at one end only represent boreholes linked by male connectors, each male connector being connected to the tail of the detonator of an adjacent male connector. Signal tubes connected to male connectors ,ransmnit the detonation signal down the boreholes to detonators which initiate inhole detonators and thus the bulk or packaged explosive which fills the borehole.

It will be readily apparent that in this conformation, under normal conditions a blast front travels along the control row, branching off along the echelon rows and also travelling along the back row. The echelon rows can therefore be initiated from either end. If a blast front from the control row runs along an echelon row and stops due to misfire, the rest of the detonators in the row will be initiated by the blast front travelling along the back row. The blast front from the back row will also detonate the next echelon row and then the control row. This means that control of the blast rapidly returns to the control row and that the blast front does not miss any detonator of the pattern.

Figure 4 uses the conventional method of the art for indicating different connectors. The lines having a single arrowhead at one end and a double arrowhead at the other end represent the male and female connectors respectively of the double ended units which link boreholes of the echelon row.

The lines having a single arrowhead and line indicate boreholes of the back row linked by female units. The tail of the delay detonator of each female connector is connected to the male connector of the double ended unit of said echelon row and the female connector which precedes it. The control row comprises male connectors only and these are indicated by single arrowheads.

Another benefit of the surface initiation system of the current invention is that it retains a large degree of common features with the existing systems and can function as a standard, non-redundant trunkline delay system without modification. The benefits in terms of inventory and training will be obvious to the skilled practitioner.

SUBSTITUM SBEET (Rule 2b) WO 94/25820 PCT/AU94/00204 8 While the invention has been explained in relation to its preferred embodiments it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification.

Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.

SUBSTITUTE SHEET (Rule 26) L L

Claims (4)

1. A redundant initiation system for detonating a blast pattern comprising at least one control row, at least one echelon row and at least one back row wherein said redundant initiation system further comprises: a male connector comprising a well housing a delay detonator connected to a length of signal tube and at least one channel adapted to receive at least one signal tube in close proximity to said delay detonator; a female connector comprising a well housing a delay detonator connected to a length of signal tube; a dual connector comprising a male connector comprising a well housing a delay detonator and at least one channel adapted to receive at least one signal tube in close proximity to said delay detonator and a female connector comprising a well housing an *e 15 instantaneous detonator and wherein said delay detonator and instantaneous detonator are connected to opposite ends of a length of signal tube; wherein said male and female connectors are interconnectable and said male, female and dual connectors are joined in such a manner that the 20 control row of boreholes are linked by male connectors, the back row of ao• boreholes are linked by female connectors and the echelon rows of boreholes between the control and back rows are linked by dual connectors.

2. A redundant initiation system according to claim 1 wherein the channels in said male connectors are located so that said delay detonators initiate signal tube within said channels by end on initiation.

3. A redundant initiation system according to claim 1 or 2 wherein said dual connector comprises a further channel in said male connector which further channel is adapted to hold the signal tube from the delay 4\ Rdetonator of said male connector.

15-11R"~ 4. A redundant initiation system according to claims 1 to 3 wherein the female connector of a dual connector at one end of said echelon row is connected to a male connector of said control row; the male connector of a dual connector at the other end of said echelon row is connected to a female connector of said back row; and signal tubes connected to male connectors of the, control and echelon row enables transmission of a detonation signal down boreholes. A method of blasting comprising initiation of explosive compositions in blast tioles using the redundant initiation system of any of the preceding claims. 6. A method of detonating a blast pattern comprising at least one control row, at least one echelon row and at least one back row using the redundant initiation detonation system of any of claims 1 to 3 wherein o* said control row comprises male connectors housing delay detonators, said echelon row comprises dual connector units and said back row comprises female connectors housing delay detonators. 0 e o IL L- II