METHOD

Field of the Invention The invention relates to the reduction of failures in initiation of detonation of explosives in blasting operations, such as in underground mining operations.

Background to the Invention

The inventor is aware of a problem related to the use of electronic initiation systems in blasting operations, in particular in underground mining, wherein when an electronic detonator detonates explosive material in a hole in a rockface which is adjacent to a series of holes filled with explosives and in which electronic detonators have been placed for a predetermined blasting pattern of the explosives in the holes, the explosion alone or together with subsequent explosions displaces the electronic detonators in adjacent holes or holes in the rockface thereby causing failures in detonations of some of the explosives in some of the holes.

The electronic detonators are connected by wires to a bus whereby the detonators form a wired network to a control module. The detonation of explosives in the holes causes the rock face to move thereby pulling on the wires and displacing the detonators in the holes or even out of their holes. l The inventor thus identified a need to reduce these failures and increase productivity of blasting using electronic ignition systems which use electronic delay detonators. Summary of the Invention

In this specification the following terms have the associated meanings unless the context clearly indicates the contrary:

EDD- Electronic delay detonator;

Electronic Initiation System (EIS); Wire - the conductive material which electrically connect the EDD to an electronic control system, whether directly or indirectly; and

Bus - is a communication system that transfers signals and/or data between components of a network or between networks. This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocols.

The invention thus provides an electronic ignition system which includes an electronic detonator and a wire connecting the detonator to a source of detonation signal, wherein a frangible portion of the wire has a reduced breaking strength relative to other portions of the wire, wherein the breaking strength of the frangible portion is from 1 : 10 to 1 :2 of the breaking strength of the other portions of the wire so that, in use, when a force is exerted on the wire remote the detonator, the wire breaks preferentially at the frangible portion before the detonator is withdrawn from a hole in which it is located. The breaking strength may be less than half of the force required to break the wire at a detonator crimp or to pull it out from the detonator crimp.

The breaking strength may be less than the force required to dislodge the detonator from a hole charged with explosives.

According to a further aspect of the invention, there is provided a method of reducing the risk of an electronic detonator being dislodged from a hole charged with explosives into which it has been placed, the method including providing a reduced breaking strength portion on the wire between the detonator crimp at a position outside the hole and a bus interface clip, so that in use, when there is a force exerted on the wire pulling the detonator out of the hole, prior to initiation of the detonator, the wire breaks in said portion thereby reducing said risk and leaving the detonator in the hole. According to a third aspect of the invention, there is provided an electronic ignition system which includes an electronic detonator and a wire assembly for connecting the detonator to a source of detonation signal, wherein a join portion of the wire has a breaking strength less than the breaking strength of the wire, wherein the breaking strength of the join portion is from 1:10 to 1:2 of the breaking strength of the wire so that, in use, when a force is exerted on the wire remote the detonator, the join portion breaks preferentially to the wire before the detonator is withdrawn from a hole in which it is located.

Description of Embodiments of the Invention

The invention can be described by way of non-limiting examples only, with reference to the accompanying diagrammatic drawings. In the drawings.

Fig 1 shows an electronic initiation system having an electronic delay detonator, a wire and a bus clip, said wire having a frangible portion; and Fig 2 shows an electronic initiation system having an electronic delay detonator, a wire and a bus clip, said wire having a join portion between the detonator and the bus clip.

Thus, generally in accordance with the invention, there is provided an electronic initiation system 10 having an electronic delay detonator 12, a wire 14 and a bus clip 16, said wire having a frangible portion 18. The bus clip 16 is connected to bus 20 which connected the electronic detonator 12 to a control system.

The electronic delay detonator 12 is inserted into explosives 22 in a hole 24.

The frangible portion 18 of the wire 14 has a reduced breaking strength relative to other portions of the wire 14, wherein the breaking strength of the frangible portion 18 is 25% of the breaking strength of the other portions of the wire 14 so that, in use, when a force 26 is exerted on the wire14 remote the detonator 12, the wire breaks preferentially at the frangible portion 18 before the detonator 12 is withdrawn from the hole 24 into which it is located.

With reference to Figure 2, the frangible portion 18 of Fig 1 is replaced by a join portion 28 of the wire which has a breaking strength less than the breaking strength of the wire 14 with a breaking strength of 40% of the breaking strength of the wire 14 so that, in use, when a force 26 is exerted on the wire 14 remote the detonator 12, the join portion 28 breaks preferentially to the wire 14 before the detonator 12 is withdrawn from a hole 24 in which it is located by the pulling force 26.