WO1993023718A2

WO1993023718A2 - Electric initiating means for a shock tube

Info

Publication number: WO1993023718A2
Application number: PCT/GB1993/001009
Authority: WO
Inventors: Peter Christian Shann
Original assignee: Explosive Developments Limited
Priority date: 1992-05-21
Filing date: 1993-05-18
Publication date: 1993-11-25
Also published as: AU4081193A; GB9210845D0; ZA933560B; WO1993023718A3

Abstract

The invention relates to a method of, and apparatus for, initiating the ignition of shock tubing. In one described embodiment a passageway, defined by a bore (13), is closed at one end and arranged with its open end (11c) adjacent an end (18a) of the shock tubing (18) to be ignited. The passageway includes two electrodes (12, 14), axially spaced within the bore (13), and an electrical circuit including a battery means (16) and a capacitor (17) is arranged to generate a spark between the electrodes (12, 14) to generate a high energy compression pulse within the bore (13), and which high energy compression pulse is directed by the bore (13) into the end (18a) of the shock tubing (18) to effect ignition of the tube (18).

Description

ELECTRIC -CNITIATING MEANS FOR A SHOCK TUBE

This invention relates to initiating means and, more particularly, to a method of and apparatus for initiating the ignition of shock tubing.

Shock tubing is well known in the art and generally comprises a length of flexible, resilient plastics tubing coated internally with a material capable of sustaining a dust explosion when initiated by means of a high energy compression pulse. Ignition of the tubing coating at one end produces a self-sustaining "dieselling" reaction at velocities common to gas phase shock transmissions (in the region of 2000 meters per second) and the energy pulse produced at that end of the tubing remote from the initiated end may conveniently be used to initiate a delay or non-delay detonator.

The prior art initiating means for igniting shock tubing generally comprises a percussion or the like detonation cap, adjacent the open end of the tubing, or an electrical spark generated in the tubing, for example as disclosed in the applicant's co-pending patent application No 9108502, filed 20th April 1991.

The present invention seeks to provide a method for initiating ignition of shock tubing and which method is safe, reliable and economical in use.

According to the present invention there is provided a method for initiating ignition of a shock tubing comprising the steps of generating a high energy compression pulse at a location spaced from an adjacent end of the shock tubing and directing said high energy compression pulse to and into the said adjacent end of said shock tubing.

Preferably the said method includes the steps of generating the said high energy compression pulse by electrical means.

In one embodiment the said high energy compression pulse is generated by an electrical spark.

In such an embodiment the electrical spark preferably has a length greater than 1 mm., more preferably greater than 1.75 mm. and most preferably greater that 2 mm.

In another eπώodiment the said high energy compression pulse is generated by an exploding bridgewire.

Preferably the method includes the steps of directing the high energy compression pulse along a passage extending from the location at which the high energy compression pulse is generated to the said adjacent end of the shock tubing.

In one such embodiment the method includes the steps of arranging said passage to be of uniform cross-section throughout its length, with a cross-section substantially identical to the cross-section of the shock tubing to be ignited.

In another embodiment . said passage is of truncated conical form and the method includes- the steps of generating the high energy compression pulse between the large end of said passage and the small end thereof.

Preferably the method includes the steps of bringing that end of the passage from which the high energy compression pulse is to issue substantially into close relationship with the adjacent end of the shock tubing.

Preferably the method includes the steps of axially aligning the passage with the adjacent end of the shock tubing.

In one embodiment the method includes the steps of introducing a barrier element into the path of the high energy compression pulse to define a safe condition for the initiating means and removing said barrier element when said initiating means is to be armed.

In another embodiment the method includes the steps of arranging said passage and the adjacent end of the shock tubing to be out of axial alignment, whereby to define a safe condition for the initiating means, and bringing the said passage and the said end of the shock tubing into adjacent axial alignment to define an armed condition for the initiating means.

The invention also envisages apparatus for initiating ignition of a length of shock tubing, said apparatus comprising passage defining means and means for generating a high energy compression pulse within said passage, said passage being totally closed at one end and having its open end alignable with the bore of a shock tubing to be detonated.

Preferably said high energy compression pulse is generated by a spark generating means.

Preferably said spark generating means comprise two electrodes, spaced apart within the said passage defining means.

Preferably said electrodes are spaced apart to generate a spark having a length in excess of 1 mm, more preferably in excess of 1.7 mn and most preferably a length in excess of 2 mm.

Preferably the apparatus includes a circuit for generating a spark across said electrodes and said circuit includes a capacitor means, arranged to discharge at a voltage in excess of 2000 volts, more preferably in excess of 3500 volts, and most preferably in excess of 5000 volts.

In another embodiment in accordance with the invention the high energy compression pulse is^"generated by an exploding bridgewire in the said passage defining means and the apparatus includes an electrical circuit for causing the bridgewire to explode.

Preferably the electrical circuit is powered by a battery means.

In one embodiment the said passage defining means defines a passage of substantially uniform cross-section and more preferably said passage has a cross-section substantially identical to the cross-section of the shock tubing.

In another embodiment the said passage defining means defines a passage of truncated conical form and the means for generating the high energy compression pulse is arranged to generate said pulse between the large end of said passage and the small end thereof.

Preferably the apparatus includes means for locating one end of the shock tubing adjacent, and in axial alignment with, the open end of the said passage.

In one embodiment in accordance with the invention the apparatus includes means for blocking the said passage, or the open end of said passage, or the adjacent end of said shock tubing.

In another eπibodiment said means for blocking comprises a valve having a valve port which, in one condition for the valve, defines part of said passage and in another condition for the valve closes said passage.

In one e bodiment the apparatus includes means for displacing the passage and the shock tubing out of adjacent axial alignment, to define a safe condition for the apparatus, and means for bringing the said passage and the shock tubing into adjacent axial alignment to define an armed condition for the apparatus.

The invention will now be described further by way of example with reference to the accompanying drawings in which; Fig. 1 shows, in longitudinal cross-section, one device for initiating ignition of a shock tubing in accordance with the invention.

Fig. 2 shows, in longitudinal cross-section, a second embodiment for an ignition initiation means.

Fig. 3 shows a third embodiment for an ignition initiating means and,

Fig. 4 shows, diagrammatically, a safe/armed arrangement for the embodiment illustrated in Fig. 1.

In the embodiment illustrated in Fig. 1 a length of tubing 11, of substantially uniform cross-section, has a first electrode 12 inserted into one end 11a of its bore 13 and a second electrode 14 inserted through an opening llb_ in the wall of tubing 11. The distance A between the electrodes 12 and 14 determines the length of the spark to be generated across the electrodes 12, 14 and the distance B defines the distance between the spark and the open end lie of the tube 11.

Electrodes 12 and 14 are connected to a circuit, generally indicated by numeral 15, which includes a battery means 16, which may conveniently comprise one or a plurality of batteries, and a capacitor 17, arranged to discharge at a voltage sufficient to generate a spark across the electrodes 12 to 14.

A length of shock tubing 18 has one end 18a_ in abutting, axial alignment with the end ll£ of tube 11.

With the above arrangement, and with the battery 16 charging the capacitor 17 to that voltage at which the capacitor 17 on discharge generates a spark across the electrodes 12 and 14, the resultant spark generates a high energy compression pulse within the tubing 11 and said pulse travels along the bore 13 of tubing 11 and into the adjacent end 18^ of the shock tubing 18, where said pulse causes the material dusting the bore of the shock tubing 18 to ignite.

With ignition of the dust at one end of the shock tubing 18 the ignition of the dust on the bore 18 progresses along the tubing 13 to deliver a high energy pressure pulse from the end of the tubing 18 remote from end 18a^

It has been found in practise that with the spacing A between the ends of electrodes 12 and 14 in the region of 1 mm. and the length B of the tube 11 in the region of 2 to 4 mm, the high energy compression pulse delivered is sufficient to ignite the dusting material on the bore of the shock tubing 18. When the distance A is 2 mm the distance B can be in the region of 5 to 8 mm and the high energy impulse developed will ignite the dusting on the bore of shock tubing 18. With the distance A in excess of 2 mm the distance B can be in excess of 20 mm and the high energy compression pulse will still ignite the dusting on the bore of the shock tubing 18.

In the arrangement illustrated in Fig. 2 a cylindrical body 21 of PTFE has a small axial bore 21a entered into one end, an enlarged bore region 21b partially extending axially into the opposite end of the body 21 and a truncated conical passage 21c_, having its small end open to the bore 21a and its large end terminating at a radial shoulder 21d between the said large end of the conical passage 21c and the enlarged bore region 21b_.

The bore 21a has a first electrode 22 inserted thereinto and the bore 21b has a second electrode 23 inserted thereinto.

The electrode 23 comprises an annular electrode, the outer diameter of which is a push fit in the enlarged bore 21b_, and the said electrode 23 locates against the shoulder 21d to define the distance between the electrode 23 and the electrode 22, and which distance defines the desired length for the spark generating the high energy compression pulse.

The electrodes 22 and 23 are connected to an electrical circuit generally indicated by a numeral 24, and which essentially includes a battery means 25 and a capacitor 26, arranged to discharge at a sufficiently high voltage as to generate a spark within the conical passage 21c between electrode 22 and the electrode 23.

The enlarged bore 21b has a diameter substantially equal to the outer diameter of a shock tubing 27 to be initiated, and whereupon said shock tubing 27 can be pushed into the bore 21b_ to abut the electrode 23.

The bore through the electrode 23 has a diameter substantially equal to the diameter of the bore of the shock tubing 27.

With the above arrangement, and on actuation of the electrical circuit, the capacitor 26 charges to that voltage at which a spark can be generated between the electrodes 22 and 23 and, on discharge of the capacitor 26, the resultant spark generates a high energy compression pulse which passes through the bore of the electrode 23 and into the bore of the shock tubing 27 to initiate ignition of the dusting on the bore of the shock tubing 27.

Thus, as with the first embodiment, the means generating the high energy compression wave are spaced from the adjacent end of the shock tubing by a passage, in the Fig. 2 embodiment defined by the bore of electrode 23.

In the arrangement illustrated in Fig. 3, a valve body 31 rotatably supports a cylindrical valve member 32, the valve member 32 has a circular port 33 passing therethrough, and the valve member 32 has a spindle 34 projecting axially therefrom to pass out of the casing 31 to handle 35 by which the valve member 32 can be rotated within the body 31.

The valve body 31 includes diametrically opposite openings 31a, 31b_, the central axes of which lie in the same plane as the axis of the valve port 33, and the body 31 presents a cylindrical wall 31jc surrounding the opening 31a and a cylindrical wall 31d surrounds the opening 31b_.

The bore defined by cylindrical wall 31c has a diameter substantially equal to the external diameter of a tubing 36, whereby the tubing 36 can be frictionally retained in the wall 31ά, and the bore defined by cylindrical wall 31d has a diameter substantially equal to the external diameter of a shock tubing 37 to be ignited, whereby the tubing 37 can be frictionally retained in the wall 31d.

The bores of the openings 31a, 31b_ and the port 33 have substantially the same cross-section, and which cross- section is substantially equal to the cross-section of the bore of tubing 36 and the bore of the shock tubing 37.

The tubing 36 is identical to the tubing 11 shown in Fig. 1, and has electrodes 12 and 14 (only the electrode 14 is shown in Fig. 3, and electrical circuit 15 arranged to generate a spark across the electrodes 12 and 14 in identical manner to the Fig. 1 embodiment.

Thus, when the handle 35 is turned so that the axis of the valve part 33 is at right angles to the axes of the openings 31a_ and 31b_, the member 32 is blocking the passage between the bores of tube 36 and shock tubing 37 and a high energy compression pulse generated by a spark in tube 36 will be blocked by member 32 to prevent ignition of the shock tubing 37. This position defines a "safe" condition for the apparatus.

When now the handle 35 is turned to align the axis of port 33 with the axes of the tube 36 and shock tubing 37, the port 33 forms part of the passage between the spark generating means 12, 14 and the shock tubing 37, thereby defining an armed condition for the apparatus.

In a modified form, the casing 31 may not include the opening 31a and a cylindrical wall 31c, and the member 32 may include means for supporting an exploding bridgewire across the port 33, with conductors extending from the ends of the bridgewire to a circuit for loading the bridgwire to cause said bridgewire to explode.

With such an arrangement, and with the means for generating the high energy compression pulse (the exploding bridgewire) located in the port 33, the member 32 can be rotated to isolate the exploding bridgewire from the opening 31b_, defining a safe condition for the apparatus, and rotated to expose the bridgewire to the opening 31b to define an armed condition for the apparatus.

In the embodiment illustrated in Fig. 4 a tubing 41, identical to the tubing 11 shown in Fig. 1 and having the associated electrodes 12 and 14 and the spark generating circuit 15, is held on a base board 42 by a clamp 43.

A length of shock tubing 44 passes through a friction clamp 45 attached to the baseboard 42 and the clamps 43 and 45 are arranged to generally support their respective tubing 41 and shock tubing 44 is axial alignment.

A solenoid 46 comprises windings 47, secured to the baseboard 42, a core 48 axially displaceable relative to the windings and an arm 49, secured to the core 48 and carrying a ring 49a on its end remote from the core 48. The solenoid 46 further includes a compression spring 50, which continuously urges the core 48 outwardly of the windings 47.

The adjacent end of the shock tubing 44 passes freely through the ring 49a_ and, when setting up the apparatus, the solenoid is operated to draw the core 48 into the windings 47 and the shock tubing 44 is drawn through the friction clamp 45 until the end of tubing 44, positioned by the ring 49a_, is adjacent to and axially aligned with the tubing 41. This condition defines the armed condition for the apparatus.

When, from the set-up armed condition the power to the windings 47 is removed, the spring 50 urges the core 48 outwardly from the windings 47 and the displacement of the core 48, transmitted to the ring 49a_, causes the adjacent end of the shock tubing 44 to be displaced out of axial alignment with the tubing 41, thus defining a safe condition for the apparatus. From the safe condition it is only necessary to supply power to the windings 47 to bring the apparatus to the armed condition.

It will be observed that in all the above described embodiments the electrical circuit means and the high energy compression pulse generating means are isolated from the explosive material, whereupon the apparatus is effectively proof against ignition caused a stray or induced currents.

Claims

1. A method for initiating ignition of shock tubing comprising the steps of generating a high energy compression pulse at a location spaced from an adjacent end of the shock tubing and directing said high energy compression pulse to and into the said adjacent end of said shock tubing.

2. A method according to claim 1 characterised in that the method includes the steps of generating the high energy compression pulse by electrical means.

3. A method according to claim 2 characterised in that said high energy compression pulse is generated by an electrical spark.

4. A method according to claim 3 characterised by the steps of generating said electrical spark to have a length greater than 1mm.

5. A method according to claim 3 or 4 characterised by the steps of generating said electrical spark to have a length greater than 1.75mm.

6. A method according to claims 3, 4 or 5 characterised by the steps of generating said electrical spark to have a length greater than 2.00π-m.

7. A method according to claim 2 characterised in that said high energy compression pulse is generated by an exploding bridge wire.

8. A method according to any one of the preceding claims characterised by the steps of directing the high energy compression pulse along a passage extending from the location at which the high energy compression pulse is generated to the said adjacent end of the shock tubing.

9. A method according to claim 8 characterised by the steps of arranging said passage to be of substantially uniform cross-section throughout its length.

10. A method according to claim 9 characterised by the steps of arranging the cross-section of said passage to be substantially identical to the cross-section of the shock tubing to be initiated.

11. A method according to claim 8 characterised by the steps of arranging said passage to be of truncated conical form, with the largest diameter end of said truncated form adjacent the end of the shock tubing and the smallest diameter end of said truncated form remote from the shock tubing.

12. A method according to claim 11 characterised by the steps of generating the high energy compression pulse between the large diameter end of said passage and the small diameter end of said passage.

13. A method according to claims 8 to 12 inclusive characterised in that the method includes the steps of locating that end of the passage from which the high energy compression pulse is to issue substantially into close relationship with the adjacent end of the shock tubing and substantially into axial alignment with the bore of the adjacent end of said shock tubing.

14. A method according to any one of the preceding claims characterised by the steps of introducing a barrier element into the path of the high energy compression pulse to define a safe condition for the apparatus and removing said barrier element when the apparatus is to be armed.

15. A method according to any one of claims 1 to 14 inclusive characterised by the steps of arranging said passage and the adjacent end of the shock tubing to be relatively displaced and out of axial alignment to define a safe condition for the apparatus and into axial alignment to define an armed condition for the apparatus.

16. Apparatus for initiating ignition of a length of shock tubing characterised by a passage defining means and means for generating a high energy compression pulse within said passage, said passage being totally closed at one end and having its open end alignable with the bore of a shock tubing to be detonated.

17. Apparatus according to claim 16 characterised in that said means for generating a high energy compression pulse comprise means for discharging a spark generating means.

18. Apparatus according to claim 17 characterised in that the spark generating means comprise two electrodes in spaced apart relationship within said passage.

19. Apparatus according to claims 17 or 18 characterised by a spark generating means including a capacitor means, arranged to discharge at a voltage in excess of 2,000 volts.

20. Apparatus according to claim 19 characterised in that said capacitor is arranged to discharge at a voltage in excess of 5,000 volts.

21. Apparatus according to claims 16 or 17 characterised by means for supporting an explodable bridgewire within said passage and said high energy compression pulse is generated by exploding said bridgewire within said passage.

22. Apparatus according to any one of claims 16 to 21 inclusive characterised in that the electrical circuit for generating the high energy compression pulse is powered by a battery means.

23. Apparatus according to claims 16 to 22 inclusive characterised in that the said passage defining means defines a passage of substantially uniform cross-section and said passage has a cross-section substantially identical to the cross- section of the shock tubing.

24. Apparatus according to claims 16 to 22 inclusive characterised in that the said passage defining means defines a passage of truncated conical form and said high energy compression pulse ^*is generated between the large diameter end of said passage and the small diameter end of said passage.

25. Apparatus according to claim any one of claims characterised in that the apparatus includes means for locating one end of the shock tubing adjacent, and in axial alignment with, the open end of the said passage.

26. Apparatus according to any one of the preceding claims characterised in that the apparatus includes means for blocking the said passage, or the open end of said passage, or the adjacent end of said shock tubing to define a safe condition for the apparatus.

27. Apparatus according to claim 26 characterised in that aid means for blocking comprises a valve having a valve port which, in one condition for the valve, defines part of said passage and in another condition for the valve closes said passage.

28. Apparatus according to claims 16 to 26 inclusive characterised in that the apparatus includes means for displacing the passage and the shock tubing out of axial alignment, to define a safe condition for the apparatus, and means for bringing the said passage and the shock tubing into adjacent axial alignment to define an armed condition for the apparatus.

29. Apparatus for initiating ignition of a length of shock tubing substantially as hereinbefore described with reference to the accompanying drawings.