[0002] A conventional shock tube is capable of enabling communication in one direction only i.e. a fire signal that is transmitted from a blasting machine, via the shock tube, to an explosive charge. Communication from a detonator to the blasting machine is not possible. Thus, the status of the detonator prior to sending the fire signal cannot be confirmed, prior to detonation, using the shock tube. Additionally a shock tube cannot convey information, other than the fire signal, to a detonator. [0003] An aim of the current invention is to address, at least partially, the aforementioned situation.

SUMMARY OF INVENTION

[0004] The invention provides a shock tube for propagating an initiating signal to an explosive charge, the shock tube including a body that is connectable to a blasting machine and at least first and second elongate flexible conductors on or in the body which enable two-way communication between the explosive charge and the blasting machine.

[0005] Each conductor may be in the form of a coating or a deposit made from a stretchable electrically conducting material. The material may be an organic/polymeric conductive material, a metal oxide-based material, or may be made from a mixture of an organic/polymeric conductive material and a metal oxide-based material.

[0006] Each conductor may be printed using a suitable technique on or in the body. Each conductor may be printed in a pattern which is suitable to flexing or stretching deformation of the shock tube, without breaking the conductor. [0007] Each conductor may be printed on a respective layer of material that surrounds an energy propagating core of the shock tube. Preferably, a first conductor is printed on a first layer of material that surrounds the energy propagating core and a second conductor is printed on a second layer of material which surrounds the first layer of material. [0008] The first and the second conductors may culminate in a suitable connecting member which is connectable to a connector located in or on a detonator.

[0009] The invention also provides a connector for connecting a shock tube of the aforementioned kind to the explosive charge which, preferably, is a detonator.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] The invention is further described by way of example with reference to the accompanying drawings wherein ;

Figure 1 is a cross-sectional view of a conductive shock tube according to the invention; and

Figure 2 is a schematic representation of a connecting member for connecting first and second conductors of the shock tube of Figure 1 to a detonator.

DESCRIPTION OF PREFERRED EMBODIMENT

[0011] Figure 1 of the accompanying drawings illustrates a shock tube 10 which includes an elongate tubular body 12 which defines a bore 18 housing a core 20 made from or containing an energy propagating material 20A.

[0012] The energy propagating material 20A is surrounded by a first protective layer 22 and a second protective layer 24. Each layer 22, 24 consists of a suitable material having appropriate electrical insulating, waterproof and abrasion-resistant properties. [0013] A first elongate flexible conductor 26 and a second elongate flexible conductor 28, each in the form of a conductive coating, are printed on the first and the second layers respectively. Each of the conductors 26 and 28 completely surrounds the respective layer 22, 24. This is by way of example only and is non-limiting. [0014] The first and second conductors 26 and 28, at an end 30 of the shock tube which, in use, is to be connected to a detonator 32, culminate in a connecting member 34 which is connectable to a connector 36 of the detonator- see Figure 2. The connecting member 34 includes a cap 38 which is fitted onto the end 30, a support structure 40, and contacts in the form of a first conductive pin 42 and a second conductive pin 44 which extend to one side of the support structure (to the left in Figure 2). Each pin 42, 44 is embedded in or penetrates the first conductor 26 and second conductor 28 respectively.

[0015] A first contact or conductive nub 46 and a second contact or conductive nub 48 are connected to the first and second pins 42 and 44 respectively which extend through the support structure 40. The connector 36, on the detonator, has annular conductive surfaces 50 and 52 which respectively oppose the conductive nubs 46 and 48.

[0016] The cap 38 is attached to the end 30 in any suitable way e.g. by means of a crimping member 54. The cap 38 includes an external thread 56.

[0017] The connector 36 includes a formation 58 which is complementary to the cap 38 and has an internal thread 60 which is threadedly engageable with the thread 56. In use, the formation 58 and the cap 38 are threadedly secured to each other to hold the nubs 46, 48 and the surfaces 50 and 52 respectively in electrical contact with one another.

[0018] Electrical leads 64 and 66 extend from the surfaces 50 and 52 to electronic components (not shown), in the detonator 32. [0019] As an alternative to the tubular conductors 26 and 28, the first and second conductors may each be printed in a wavy or spiral pattern on respective tubular substrates or layers e.g. the layers 22, 24. These patterns allow for flexing and stretching of the shock tube, without leading to breaking of the conductors. [0020] The first and second layers 22, 24 could each be coated with the material which forms the first and second conductors, using techniques that do not require alteration of existing shock tube manufacturing techniques.

[0021] The conductors 26 and 28 are made from an organic/polymeric conductive material, or a metal oxide-based material, or a mixture of the organic/polymeric conductive material and a metal oxide-based material. This type of material can be "stretched" to a substantial degree without breaking.

[0022] In the drawings the conductors 26, 28 are shown enlarged. This is for illustrative purposes only. In practice the conductors are thin, particularly if formed by means of a printing technique, and the shock tube 10 would have a diametrical dimension substantially equal to that of a conventional shock tube.