AU2003270958B2 - Improvements in explosives - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "IMPROVEMENTS IN EXPLOSIVES" The following statement is a full description of this invention, including the best method of performing it known to us:

TITLE

"IMPROVEMENTS IN EXPLOSIVES" FIELD OF THE INVENTION This invention is concerned with modifications to or improvements in Australian Patent No 742653 relating to improved packaging of explosive compositions.

BACKGROUND OF THE INVENTION It is well known to package explosive compositions in purpose designed packages to assist in transportation and handling of explosive compositions including dry powder or granulated compounds, emulsions, slurries, water gels and the like.

These packages may be adapted to suit charge mass, borehole diameter, borehole length and the like.

Australian Patent Application AU-A-81802/87 describes the packaging, in non-porous plastic cartridges of from 25mm to 75mm in diameter and 1000mm long, an explosive composition comprising ammonium nitrate, paraffinic oil and foamed or expanded polystyrene beads.

British Patent No 882665 describes the packaging of ammonium nitrate compositions in paper wrapped cartridges.

British Patent No 1281421 also describes the packaging of an ammonium nitrate explosive in a thin flexible plastics sheath such as polyethylene. This product has a detonating cord extending throughout an elongate explosive filled sheath in a unitary charge up to 20m long. The specification discloses divisible charges in rolls of from 50m to 100m in length whereby charges of selected shorter length can be formed by clamping the sheath at closely spaced intervals and severing the charge therebetween.

The patent specification states that explosive charges according to the invention can be inserted into boreholes at up to 60" from vertical and moreover that with the aid of a bracket-shaped slide, these packages can be inserted into horizontal boreholes.

Experience has shown however that thin flexible sheaths of,

NNW=-

say 0.2mm in wall thickness are prone to perforation by puncture on rough borehole surfaces or by abrasion even on smooth borehole surfaces. If such perforations occur near the lower end of the charge being inserted, there is a risk that a substantial part of the freely flowing particulate explosive composition would fall to the bottom of the borehole beyond the end of the detonating cord without the knowledge of the personnel concerned. Only when the connected charges in adjacent boreholes were detonated would it be discovered that the mechanical and safety aspects of the integrated breaking pattern were compromised by the detonation failures in one or more boreholes.

These soft thin walled explosive packages were found to be difficult and time consuming to insert into horizontal boreholes and even more prone to puncture and tearing when pushed into the horizontal cavity.

A particular difficulty with such flexible, thin walled elongate explosive charges is that when rolled into conveniently sized coils for packaging, transportation and storage, the tubular sheath is prone to kinking or flattening in parts.

At the position of the kink or flattened region, the crosssectional area of the explosive charge is substantially diminished and with severe kinking, a discontinuity may be formed in the mass of explosive material. This kinking or cross-sectional area reduction can also occurwhen trying to insert elongate thin walled flexible tubular explosive charges into inclined or horizontal boreholes.

It is believed that severe reductions in cross-sectional area or discontinuity in the mass of explosive composition may give rise to a condition known as "gapping" where propagation of explosive energy along the charge column is interrupted.

In order to overcome such problems with prior art packaged explosives, particularly for use in perimeter hole blasting for tunnel shaping where the boreholes are horizontally drilled, it has been proposed to use short, rigid tubular packages adapted for end-to-end coupling to form a long unitary charge.

Originally such explosive packages comprised a stiff paper or cardboard cylinder about 900mm long and about 20mm in diameter filled with a highly viscous, non-flowable cap sensitive emulsion or water gel explosive. The paper or cardboard cylinder was open at opposite ends which were shaped to form a socket and spigot connection between adjacent packages.

Of more recent times these paper or cardboard cylinders have been replaced with a semi rigid plastics tube such as polyethylene with a wall thickness of about 1mm.

A difficulty encountered with these prior art modular explosives tubes is that a close face-to-face abutment of the explosive composition in adjacent tubes is required to ensure propagation of the explosive force throughout the entire assembly which may, for example, comprise six tubes joined by the socket and spigot fittings.

As typically these tubes are initially filled with a heated mix to reduce the viscosity of the normally non-flowable viscous emulsion, the tube contents undergo shrinkage on cooling and can create a gap of 5-10mm between the faces of explosive material when the tubes are joined.

Where "gapping" occurs between adjacent explosive masses, whether due to shrinkage in the tube or human error in assembly, an incomplete explosion can leave one or more portions of the explosive charge in the ground. This is an extremely hazardous situation with cap sensitive explosives in particular which may be accidentally detonated by impact from an excavator or subsequently in a crushing mill.

Another problem associated with prior art blasting techniques is that where it is required to increase the powder factor or energy factor in the "butt" or base of a borehole, it is common practice to first push a separate primer charge to the butt of the borehole.

Thereafter, a water gel or emulsion explosive is loaded into the borehole, typically in the form of spigot and socket joined tubes described above.

Again this procedure is prone to unreliability due to gapping between the primer and the end of the explosive charge and/or between adjacent tubes which can lead to ineffectual blasting, rifling of tubes from the borehole and unexploded explosives left in the borehole.

Yet another disadvantage associated with the abovementioned prior art explosive charges is the need to insert a stem plug to close off the borehole after the charge is loaded. This is a costly and time consuming process.

Australian Patent No 742653 overcame many of the abovementioned prior art problems referred to above by providing a relatively stiff plastics tube with an enlarged distal end having a diameter of from to 100% greater in diameterthan the tube itself. The enlarged distal end was sealed with a bung having a sealed cap well to receive a detonator and permitted the use of either a detonator cord extending through the explosive composition within the tube bore or a detonator insertable in a blind bore accessible from the outer end of the bung. A preferred embodiment described an explosive composition in the form of powdered ammonium nitrate with a detonating cord extending through the tube bore within the mass of powdered explosive. Another preferred embodiment described a liquid or paste explosive composition such as a water gel or emulsion explosive.

A difficulty encountered with the tubular explosive charges according to Patent No 742653 was that when the tubular explosive charges containing a water gel or emulsion composition were coiled for packaging, the flowable nature of the liquid composition permitted kinking in the tube with the risk of consequent "gapping" of the explosive in use. With a stiffer tube to avoid kinking during coiling it was not possible to obtain a coil with a compact packaging diameter. Moreover, in use, the "memory" of the stiff plastics tube interfered with the insertion of the charger into the borehole.

Another difficulty encountered with the explosive charges according to Patent No 742653 was a concern expressed by some users as to a non-cap sensitive explosive charge having a detonating cord extending therethrough. That concern was directed to the possibility that a powdered o ammonium nitrate based explosive charge with a detonating cord extending 0 'N therethrough could be severed by ground movement when adjacent charges were detonated. If the tubular charge was severed, this may prevent propagation of detonation through the distal severed portion with the result that an undetonated portion of the charge would then be at risk of subsequently detonation due to mechanical impact from earth-moving 00 equipment, rock crushing equipment or the like. Experience has shown that 1 unsheathed detonating cord can be detonated by mechanical impact.

0 It has been discovered that by utilizing sufficient sensitisers en 10 with the powdered (ammonium nitrate) explosive composition, it is possible 0 o to make the powdered composition cap sensitive and thereby avoid the use of an internal detonator cord. Instead of the internal detonator cord, it is now possible to utilize a detonator in the cap well of the bung together with an external signal tube such as a "Nonel" tube.

SUMMARY OF THE INVENTION It is an aim of the present invention to overcome or ameliorate at least some of the prior art problems associated with explosives packaged in tubular containers and/or otherwise to provide users with a convenient choice.

According to one aspect of the invention there is provided an explosive charge comprising:an elongate plastics tube having circumferentially extending ribs, said tube having a sealed closure at least at a distal end and an explosive composition occupying substantially an entire volume of the interior of said tube, said tube having an enlarged distal end portion with a diameter to 100% greater than the diameter of the tube, said closure having a sealed cap well adapted to receive a detonator therein; and, in use, a signal tube coupled to said detonator and extending externally of said tube between opposite ends thereof.

If required, the tube is selected from a stiffness range to permit easy insertion of the charge into horizontal or upwardly inclined boreholes.

Suitably, said tube, in use, permits formation of said charge into

OC

0 a coil having an inner diameter of 200mm or greater without kinking.

Suitably, said plastics tube has a wall thickness in the range of from 300p m to 1500 p m.

O Most preferably the tube has a wall thickness of 8 00 y m to 1200pm.

o Suitably, the tube has an external diameter in the range to

O

Preferably, the tube has an external diameter of from 18mm to n

O

o 10 The enlarged end portion preferably comprises a diameter greater than the diameter of the tube.

The enlarged end portion may have an axial length in the range 100mm to 1000mm.

Preferably, the enlarged end portion has an axial length in the range 200mm to 500mm.

If required, the enlarged end portion may be integrally formed with the tube.

Alternatively, the enlarged end portion may be removably attachable to said tube.

The explosive composition may be selected from flowable particulate materials, water gels or emulsions.

The explosive composition may be cap sensitive.

The tube may be sealed at opposite ends by any suitable means.

Most preferably, a proximal end of the charge includes a free end of said tube to enable, in use, the free end to be folded over to form a stemming plug.

If required, the proximal end of the tube may include a closure member to seal an opening therein.

Suitably, the packing density of the explosive composition is greater than 1.0 gm cm 3 Preferably, said tube may include a longitudinally extending 0 Sgroove in an outer surface thereof, in use, to locate a signal tube.

A plastics tube for the explosive charge according to the aforementioned aspect may comprise a longitudinally extending signal tube 00 groove formed on an outer surface of said tube.

A closure member for the explosive charge according to the 00 aforementioned aspect may comprise a hollow moulded body having an open neck portion adapted for attachment to a distal end of said tube, an 0 enlarged diameter portion and a closed base portion having formed therein a csealed cap well to receivably locate, in use, a detonator.

According to another aspect of the invention there is provided a N method of manufacturing an explosive charge, said method comprising the steps of:suspending said tube by a proximal end thereof from a filling station; progressively filling said tube with a flowable particulate explosive composition; and, sealing said proximal end of said tube.

Preferably, said tube is suspended from a vibratory suspension means.

Suitably, a free end of the tube extends beyond a proximal seal, to enable folding of the proximal free end, in use, to form a stem plug.

According to a further aspect of the invention there is provided a method of manufacturing an elongate explosive charge, said method comprising the steps of:supporting on a hollow mandrel a predetermined length of plastics tube having circumferentially extending ribs, said tube having a closure at a distal end, said closure having a sealed cap well adapted to receive a detonator therein; pumping a fluid explosive composition into said tube via said hollow mandrel to progressively displace said tube along said mandrel with a predetermined quantity of fluid explosive composition; and forming a closure in a proximal end of said tube.

0 BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood and put into practical effect, the invention will now be described with reference to 0O preferred embodiments illustrated in the accompanying drawings in which: FIG. 1 shows a coilable elongate explosive charge according to the invention; "f FIG. 2 shows a closure member for use in the charge of FIG. 1; o FIG. 3 shows an alternative embodiment of the invention; CFIG. 4 shows schematically one method of filling a coilable 0 10 explosive charge;

O

N FIG. 5 shows schematically another method of filling a coilable explosive charge; FIG. 6 shows an alternative configuration of a distal end closure.

FIG. 7 shows an alternative embodiment of a tubular charge housing; and FIG. 8 shows an explosive charge according to the invention when installed in a borehole.

For convenience, like reference numerals are employed for like features in the drawings.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, the explosive charge 1 comprises a 4.5m length of corrugated tube 2 having a diameter of about 20mm and a wall thickness of The tube 2 is sealed at its distal end 3 with a rubber, plastics or timber bung 4 having a sealed cap well 13 therein.

Corrugated or ribbed tube 2 may be formed from any suitable chemical resistant plastics material such as polyvinyl chloride, polyethylene, polypropylene or the like. If required, the plastics composition may include a conductive filler material such as carbon black to reduce the risk of a static electricity charge buildup on the surface of the tube during handling.

Conveniently, the tube may be similar to that currently employed as flexible electrical conduit by electricians and typically is manufactured by extruding a plastics tube between ribbed travelling mould blocks with an elevated pressure within the tube to form the ribbed wall. Alternatively, the ribbed tubing may be formed by incorporating a stiff helically wound metal or plastics filament on an inner or outer wall surface of the tubing. If required, the helical reinforcing rib may be incorporated within the wall of the tubing by forming an inner core, winding the helical reinforcing about the outer surface of the inner core and then extruding or winding an outer sheath thereover.

As used herein, the expression "ribbed or corrugated" tubing is intended to embrace tubular members reinforced against axial collapse or kinking when coiled for packaging and/or transportation.

By forming the explosive charge according to the invention with a ribbed or corrugated tube wall, it has been found that even with soft water gel or emulsion explosives, no kinking occurs when the charge is tightly coiled for packaging. Similarly, when being inserted into a borehole, the handling problems associated with tightly coiled stiff walled tubes due to "shape memory" are substantially diminished.

The ribbed tubing permits a relatively thick walled stiff plastics tubing to be employed to assist in handling of water gel or emulsion explosives compositions during insertion into a borehole yet allows significantly reduced packaging diameters than otherwise would be possible without kinking. Most importantly however, the use of a ribbed or corrugated tube wall allows a reinforcing of the tube wall to resist kinking with subsequent "gapping" of the explosive charge.

Although not as critical with particulate explosives which tend to resist kinking in a plastics tube, the ribbed or corrugated tube nevertheless provides a conveniently coilable tubular container for compact shipping purposes but which is still rigid enough to permit easy insertion into a borehole.

The closure 7 is conveniently a "Tipper Tie" (Trade Mark) in the form of a metal clip extending tightly around the tube 2 to form a waterproof seal. Alternatively, a plastics or cork bung may be employed.

A particulate explosive composition 5 which may comprise, for example, 80-85% ammonium nitrate (finely ground), 3-5% of a particulate carbonaceous fuel such as a coal dust, and 5-15% of a sensitizer such as aluminium powder, perchlorate, PETN, etc.

It is to be understood that the present invention is not limited to any particular explosive composition and may also comprise any known flowable particulate explosive, water gels and emulsions.

It is to be further understood that as used herein to distinguish the opposite ends of coilable semi rigid tubular explosive charges, "distal" means the remote end of the charge, in use, closest the butt of the borehole and "proximal" means the end of the charge opposite the distal end.

Typically, charges of the type described above will be used in perimeter hole blasting where horizontal boreholes are drilled for tunnel shaping, etc.

The charges used for perimeter hole blasting typically are from 2 to 5 metres long but often in the range 3-4 metres.

The boreholes are usually spaced at 750-800mm from each other and may be 30-50mm in diameter.

As shown in FIG. 1, a free end 8 of the tube extends beyond closure 7 for about 400mm in length. This enables the proximal free end, in use, to be folded over upon itself to form a stem plug when inserting the charge into a borehole thereby alleviating the costs associated with insertion of a separate stem plug as required with prior art charges of this type.

FIG. 2 shows a preferred form of distal end closure in the form of a plastics bung 9 having a cylindrical body 10 and an end flange 11.

Also located in bung 9 is a blind bore or cap well 13 adapted to receive a detonator (not shown) but otherwise to provide a waterproof closure for use in water filled boreholes and prevent explosives compounds exuding during transit.

FIG. 3 shows the bung of FIG. 2 fitted to an embodiment of the invention.

In this embodiment, the distal end 14 of tube 15 is radially increased from say 20mm to about 35mm over an axial length of from 100mm to 600mm to provide a charge region of increased powder or energy factor at the base or butt of a borehole.

The increased radial volume may accommodate an explosive composition having a higher explosive energy than that in tube 15 but preferably contains the same composition throughout the axial length of the charge.

Bung 9 is secured to the distal end 14 to tube 15 by heat sealing, adhesive or mechanical clamping means (not shown) before the explosive composition is inserted into the tube.

FIG. 4 shows a method of manufacture of a coilable explosive charge having a flowable particulate explosive composition.

In FIG. 4, a 4m length of 20 mm diameter smooth bore polyethylene tube 20 is closed at the enlarged distal end 21 thereof by means of a bung 22 as generally shown in FIG. 2.

Tube 20 is then suspended by its proximal end in a clamping gland 23 in filling station 24 with the neck 25 of a filling hopper 26 inserted into the open end of tube Valve 27 is opened and the filling station 24, mounted on resilient mounts 28 is vibrated by a mechanical or electromechanical vibrator 29 to assist in filling the tube with a flowable particulate explosive composition 30 from hopper 26.

Vibration is important during the filling operation to not only reduce filling time but also to ensure an even packing density of the particulate explosive composition over the entire length of tube A packing density greater than 1.0 gm cm 3 is desirable to ensure that the charge will not float in a water filled borehole.

When the tube 20 has been filled to a distance of about 400mm from the proximal end of the tube, valve 27 is closed and a "Tipper Tie" (Trade Mark) closure is secured around the tube 20 at the upper level of the explosive composition to form a waterproof closure to the tube.

Alternatively, a plastics or cork bung or closure may be employed to seal the proximal end of the charge.

Gland 23 is released and the tubular charge drops onto an arcuate guideway (not shown) leading on to a horizontal inspection and packing table (not shown).

The tubular charge is wound onto a mandrel of from 200- 250mm diameter to form a coil having an external diameter of about 450mm which is secured with a tie or adhesive tape to prevent unravelling.

Coiled charges are then packed in boxes in multiples of 10 to for safe transport.

It will be readily apparent to a skilled addressee that the above method enables custom manufacture of tubular charges to any required length without any change in apparatus set up or procedures.

FIG. 5 shows an alternative embodiment of the manufacturing process utilising a liquid or paste-like water gel or emulsion explosive.

In this embodiment, a slurry pump 30 such as a "Mono" (Trade Mark) is coupled to a four metre long hollow mandrel 31 over which a hollow ribbed plastics rube 32 is closely fitted.

The distal end of tube 32 is fitted with an enlarged end 33 which may be integrally formed by thermo-forming or it may be a moulded hollow body attachable to tube 32 by heat sealing, adhesive, threaded, pressed connection or the like.

A liquid or paste-like explosive composition 39 is then pumped under pressure into the distal end of tube 32 and as the interior fills, tube 32 is progressively displaced along the mandrel 31 and on to inspection and packing table Again, when the explosive composition occupies all but about the last 400mm of the proximal end of tube 32, pump 30 is stopped and a "Tipper Tie"(Trade Mark) or similar clamp is applied to the tube 32 by a clamping head 41 to form a waterproof closure about detonator cord 34 extending therefrom with an open "tail" above the closure in a manner similar to the sealing process described in relation to FIG. 4. Alternatively, the open end of the tube may be plugged or capped by a closure member.

After severing the tube 32 at a required position, the process is repeated and again, it will be readily apparent to a skilled addressee that this process is readily adapted to produce explosive charges of any required length.

FIG. 6 shows an alternative form of distal end closure in the form of a hollow moulded plastics body 50 having a neck 51 adapted for securing to a tubular charge body (not shown) by mechanical means, adhesive, friction welding or the like. Located in the enlarged bore portion 52 is a sealed cap well 53 adapted to receive and frictionally retain a detonator (not shown).

FIG. 7 shows an alternative embodiment of a tubular charge body or housing 55. To avoid the risk of mechanical damage to a "Nonel" signal tube coupled to the detonator and otherwise extending down a borehole outside the tube 55, a longitudinally extending groove 56 having a width and depth similar to a "Nonel" tube is formed in an outer surface of the tube. Partially fused indentation regions 57 form thin flexible retaining lugs to retain the "Nonel" tube in groove 56 and thereby provide a measure of protection when the charge is being inserted into a borehole. The outer groove 56 may be formed in both ribbed and smooth walled tubing alike.

FIG. 8 shows the installation in a borehole of a coilable explosive charge according to the invention.

An elongate tubular explosive charge 60, typically about 4m in length and about 20mm in diameter with an enlarged end 61 having a diameter of about 25mm is inserted into a borehole 62 about 30-35mm in diameter. A tamping rod 63 may be employed to push the charge to the base of the borehole.

In the enlarged distal end of charge 60 is located a closure plug 64 having a hollow cap well 65 locating a detonator 66. A signal tube 67 is secured in a slotted recess 68 in the plug 64 and otherwise runs freely down the outside of tubular charge 60. A proximal end of tubular charge 60 is closed by a plug 69.

To assist in locating the charge 60 within borehole 62, resilient plastics spiders 70 located adjacent the distal and proximal ends of charge assist in centring the charge 60 within the borehole.

In the various aspects referred to above, the semi-rigid smooth bored or ribbed tube may be comprised of any suitable material such as plastics or rubbers including polyvinyl chloride, polyethylene, polypropylene butyl rubber or any other homopolymeric or copolymeric materials suited for the intended purpose.

While it is important that the tubular explosives charges according to the invention are not so flexible that they cannot readily be loaded into inclined or horizontal boreholes, it is equally important that they be not so stiff that they cannot be coiled without kinking into conveniently sized packages for storage, transport and handling.

While the requisite properties of the semi-rigid smooth bored or ribbed tube may be modified by using a thinner wall with a more rigid polymer or vice versa, it is preferred to use a smooth bored tube for particulate explosives compositions and a ribbed tube for liquid or paste compositions such as water gels or emulsions.

In each embodiment described above, it is preferred that a retaining "spider", known in the art, is secured adjacent a proximal end of the explosive charge.

In the coiling of the elongate tubular explosive charges, it is important that the stiffness or rigidity of the tube is such that when coiled, the tube does not kink to form a reduction in cross-sectional area or even a discontinuity in the mass of explosive composition as this may create a situation analogous with gapping as in prior art systems.

It is equally important that when the charge is uncoiled, there is sufficient resilient recovery that the tubular charge readily assumes a substantially straight configuration to assist in insertion in boreholes.

In the practice of the present invention, it has been found that a low-medium density polyethylene tube having an external diameter of 21mm and a wall thickness of 1mm can be coiled over a 200mm winding mandrel without kinking and stored for long periods of time without developing a permanent set or "memory" which resists elastic recovery to a generally straight elongate tube. Ribbed or corrugated tube, whether filled with particulate or fluid explosives compositions tends not to develop any permanent set or "memory".

Claims (15)

1. An explosive charge comprising:- an elongate plastics tube having circumferentially extending 1- ribs, said tube having a sealed closure at least at a distal end and an explosive composition occupying substantially an entire volume of the interior 0 of said tube, said tube having an enlarged distal end portion with a diameter to 100% greater than the diameter of the tube, said closure having a sealed cap well adapted to receive a detonator therein; and, Nin use, a signal tube coupled to said detonator and extending externally of said tube between opposite ends thereof.

2. An explosive charge as claimed in claim 1 wherein the enlarged end portion has a diameter 50% greater than the diameter of the tube.

3. An explosive charge as claimed in claim 1 or claim 2 wherein the enlarged end portion has an axial length in the range 100mm to 1000mm.

4. An explosive charge as claimed in claim 3 wherein the enlarged end portion has an axial length in the range 200mm to 500mm. An explosive charge as claimed in any one of claims 1 to 4 wherein the enlarged end portion is integrally formed with said plastics tube.

6. An explosive charge as claimed in any one of claims 1 to 4 wherein the enlarged end portion is attachable to said plastics tube.

7. An explosive charge as claimed in any preceding claim wherein said tube is selected from a stiffness range to permit easy insertion of the charge into horizontal or upwardly inclined boreholes.

8. An explosive charge as claimed in any preceding claim wherein said tube, in use, permits formation of said charge into a coil having an inner diameter of 200mm or greater without kinking.

9. An explosive charge as claimed in any preceding claim wherein said tube has an external diameter in the range 10mm to

10. An explosive charge as claimed in claim 9 wherein said tube has an external diameter of from 18mm to

11. An explosive charge as claimed in any preceding claim wherein O 0 O ci 00-- 00- 0 ci en- the explosive composition is selected from flowable particulate material, water gels or emulsions.

12. An explosive charge as claimed in any preceding claim wherein a proximal end of the charge comprises a free tail of said tube to enable, in use, the proximal free end to be folded over to form a stemming plug.

13. An explosive charge as claimed in any one of claims 1 to 11 wherein the proximal end of the tube includes a closure member to seal an opening therein.

14. An explosive charge as claimed in any preceding claim wherein 10 the packing density of the explosive composition is greater than 1.0 gm cm- 3 A method of manufacturing an explosive charge according to any preceding claim, said method comprising the steps of:- suspending said tube by a proximal end thereof from a filling station; progressively filling said tube with a flowable particulate explosive composition; and, sealing said proximal end of said tube.

16. A method as claimed in claim 15 wherein said tube is suspended from a vibratory suspension means. 17 A method of manufacturing an explosive charge according to any one of claims 1 to 14, said method comprising the steps of:- supporting on a hollow mandrel a predetermined length of plastics tube having circumferentially extending ribs, said tube having a closure at a distal end, said closure having a sealed cap well adapted to receive a detonator therein; pumping a fluid explosive composition into said tube via said hollow mandrel to progressively displace said tube along said mandrel with a predetermined quantity of said explosive composition; and, forming a closure in a proximal end of said tube.

18. A method as claimed in claim 17 wherein said fluid explosive composition is pumped into a distal end of said tube. V. 18 O o DATED this Seventeenth day of May 2005. JOHNSON HI-TECH (AUSTRALIA) PTY LTD 00 by its Patent Attorneys FISHER ADAMS KELLY 00 Ci o 0 ci