Booster for commercial blasting

Abstract

A booster assembly for commercial blasting, including: a housing containing an explosive substance; and a guide for receiving an initiator for initiating the explosive substance.

Description

BOOSTER FOR COMMERCIAL BLASTINGTECHNICAL FIELD

[0001] The present disclosure relates to an explosive device and a method for generating a shock wave, and more particularly, though not exclusively, to a booster assembly for initiating a main explosive charge in commercial blasting operations.BACKGROUND

[0002] Blasting has a number of important commercial, industrial, and civil uses, including commercial blasting applications associated with mining, quarrying, and civil tunnelling, in which a substrate such as rock is fractured and / or displaced to facilitate substrate excavation, removal, and processing.

[0003] To increase safety, the bulk explosive material used during these applications is typically insensitive to initiation by a detonator. Instead, the bulk explosive material is initiated using an “explosives train”, in which an intermediate charge or “booster”, which can be initiated by a detonator, is placed within or adjacent the bulk explosive material. When the intermediate charge or booster is initiated, a shock wave, or detonation wave, propagates into the bulk explosive material and thereby initiates the bulk explosive material.

[0004] Existing boosters typically include a hollow body that contains an explosive material and a slot or chamber, known as a “detonator well”, for receiving and appropriately positioning a detonator so as to ensure reliable initiation of the explosive material of the booster; however, it is common for existing boosters to misfire — i.e. fail to initiate.

[0005] The causes of misfire events can include low quality components in the initiating system, low quality explosives used in the booster and the bulk explosive material, improper mining practices, movement of the ground prior to blasting, adverse weather events, and failures in blasting equipment.

[0006] Misfires pose a significant safety risk in blast recovery operations that are performed after blasting such as ore recovery, removal of waste rock, removal of coal, and quarrying. For example, contact between a shovel of an ore recovery unit and a booster that has failed to initiate has the potential to trigger the detonator within the initiating system which in turn may initiate the explosive material contained within the booster. Detonation of the booster can in turn initiate anyun-exploded bulk explosive material, which can result in blasting of the surrounding earth. This creates a high-risk environment for operators and personnel in the immediate area and may lead to major injury or fatality.

[0007] Existing methods for reducing the risk of unexpected explosions focus on reducing the likelihood of a misfire event For example, detonator wires of increased strength can be used to reduce the risk of accidental wire cutting during the blast loading or subsequent processes before the blast is initiated. While these methods may reduce the likelihood of a misfire event, they do not reduce the consequence of an unexpected detonation if a misfire event does occur.

[0008] Existing boosters typically provide sufficient energy fluence and peak pressure to initiate bulk explosives used in commercial blasting, e g., in explosive columns used in mining and quarrying. In some applications, however, existing boosters may generate the energy fluence and peak pressure inefficiently, thus requiring excessive explosive material in the booster to produce the required energy fluence and peak pressure.

[0009] It is desired to address or alleviate one or more problems / limitations in the prior art, e.g., the above-identified problems, or to at least offer a useful alternative. Alternatively, or additionally, an example of the present invention seeks to at least provide the public with a useful choice.SUMMARY

[0010] Disclosed herein is a booster assembly for commercial blasting, including:a. a housing containing an explosive substance; andb. a guide for receiving an initiator for initiating the explosive substance, wherein, in an armed configuration, a distal end of the initiator is secured proximate to or in contact with a proximal surface of the explosive substance such that the distal end of the initiator can move away from the explosive substance when the housing deforms or fails mechanically such that the booster assembly is no longer in the armed configuration.

[0011] Disclosed herein is a booster assembly for commercial blasting, including:a. a housing containing an explosive substance; andb. a guide for receiving an initiator for initiating the explosive substance, wherein the housing is configured to break and dislodge the initiator from an armed configuration to a dislodged configuration in response to an external force applied to the booster assembly during blast recovery operations.

[0012] Disclosed herein is a booster assembly for commercial blasting, including:a. a housing containing an explosive substance;b. a guide for receiving an initiator for initiating the explosive substance; and c. a retainer disposed on an external surface for holding and guiding an initiator cable during assembly,wherein the retainer directs the distal end of the initiator upward when the booster assembly is lowered into a blasthole.

[0013] Disclosed herein method for initiating bulk explosive material for commercial blasting, including:a. providing a booster assembly containing an explosive substance;b. arming the booster assembly by securing an initiator therein so that a distal end of the initiator is secured proximate to or in contact with a proximal surface of the explosive substance without substantially extending into the explosive substance, wherein the initiator is secured such that a gap between the distal end of the initiator and the proximal surface of the explosive substance is not greater than about 10 mm, preferably not greater than 8 mm;c. lowering the armed booster assembly into a borehole; andd. activating the initiator to generate a shock wave and thereby initiate the column of explosives.

[0014] Disclosed herein is a method of arming a booster assembly for commercial blasting, including:a. providing a housing having an explosive substance therein;b. inserting an initiator into the housing; andc. securing the initiator in the housing so that a distal end of the initiator is proximate to or in contact with a proximal surface of the explosive substance without substantially extending into the explosive substance; andd. providing a cable connected to the initiator and securing the cable to the housing so that the distal end of the initiator is biased towards the explosive substance.

[0015] Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Some embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:Figure 1 is a perspective view of a booster assembly according to an embodiment of the present disclosure;Figure 2 is a front view of the booster assembly shown in Figure 1 ;Figure 3 is a rear view of the booster assembly shown in Figure 1,Figure 4 is a first side view of the booster assembly shown in Figure 1 ; Figure 5 is a second side view of the booster assembly shown in Figure 1; Figure 6 is a top view of the booster assembly shown in Figure 1;Figure 7 is bottom view of the booster assembly shown in Figure 1;Figure 8 is cross-sectional view of the booster assembly along line A-A in Figure 6 without an initiator;Figure 9 is a cross-sectional view of the booster assembly along line A-A in Figure 6 with an initiator located in a first armed configuration;Figure 10 is a cross-sectional view of the booster assembly along line A-A in Figure 6 with an initiator located in a second armed configuration;Figure 11 is a cross-sectional view of the booster assembly along line A-A in Figure 6 with an initiator located in a third armed configuration;Figure 12 is a partially exploded cross-sectional view of the booster assembly along line A-A in Figure 6 showing a first portion of a housing partially removed from a second portion of the housing;Figure 13 is a front perspective view of the booster assembly shown in Figure 1 showing the first portion of the housing separated from the second portion of the housing;Figure 14 is a schematic diagram of a blast recovery operation;Figure 15 is a cross-sectional view of the booster assembly along line A-A in Figure 6 showing the housing breaking due to a force applied during the blast recovery operation illustrated in Figure 14;Figures 16 to 19 are perspective views of a booster assembly according to an embodiment of the present disclosure showing steps for securing the initiator within the housing;Figure 20 is a schematic diagram of a booster assembly according to an embodiment of the present disclosure in a blasthole or borehole;Figure 21 is a flowchart that schematically outlines a method of arming a booster assembly; andFigure 22 is a flowchart that schematically outlines a method of initiating a column of explosives.DETAILED DESCRIPTION

[0017] Disclosed herein is a booster assembly 10 for commercial blasting that can reduce the risk of unplanned or unexpected initiation during blast recovery operations, and / or can reduce the amount of explosive substance required to provide sufficient energy fluence and peak pressure. Embodiments of the booster assembly 10 include a housing 12 containing an explosive substance 26. The housing 12 also includes a guide for the initiator 22, e.g., in the form of a passage 24, for receiving an initiation device or initiator 22 (e.g., a non-electric, electric, or electronic detonator, an optical- or laser-based initiation device, or another type of initiation device depending uponembodiment details) for initiating the explosive substance 26. The initiator 22 is configurable, configured, or activatable for initiating or triggering the release of explosive energy by the explosive substance 26, such that the explosive substance 26 correspondingly or responsively generates a self-propagating explosive shock wave or detonation front. The passage 24 is an elongate structure that extends from an opening or aperture formed at an upper or proximal end 33 of the housing 12 towards the explosive substance 26 and may also be referred to as a well, a detonator well (or “detwell”), a cap well, channel, pocket, slot, chamber, or cavity. The passage 24 has a generally cylindrical shape and may include structures or features that aid in retention of the initiator 22. In some embodiments, the passage 24 has a length of approximately 118 mm, and a diameter of approximately 8 mm. In an armed configuration, a distal end 23 of the initiator 22 is located proximate to or in contact with a proximal surface 27 of the explosive substance 26 (e g., the distal end 23 may abut the proximal surface 27). The combination of the initiator 22 and the booster assembly 10 (with the initiator 22 therein) may be referred to as a “primed booster” or “primer”. The proximal surface 27 is the surface of the explosive substance that is close to the distal end of the initiator in the armed configuration and may also be referred to as an upper, top, end, or peripheral surface of the explosive substance 26. The distal end 23 does not extend substantially into the explosive substance 26 (e g., in some embodiments the distal end 23 does not penetrate through the upper surface, and the initiator 22 is not embedded within the explosive substance 27). The proximal end of the initiator 22 is also not transversely surrounded by or embedded within the explosive substance. The booster assembly 10 may have a length of approximately 223 mm, a width of approximately 56 mm or 67 mm, and a mass of approximately 425 g. When the booster assembly 10 is deformed by an external force in the armed configuration, the distal end 23 of the initiator 22 can move away from the explosive substance 27 when the housing 12 deforms or fails mechanically. In some embodiments, the distal end 23 of the initiator 22 moves transverse to a longitudinal axis of the explosive substance 27 when the housing 12 deforms or fails mechanically. In other words, the initiator can move in a direction that is substantially transverse (e.g., cross-axially) to a longitudinal axis (shown as axis L in Figures 2 to 5) of the booster assembly 10, thus dislodging the initiator from the explosive substance, and thus disarming the booster assembly. As would be understood by a person skilled in the art, in some embodiments, where the booster assembly and / or the explosive substance are not elongated in shape (e g., embodiments that do not include a longitudinal axis as shown in the Figures), when the housing deforms or fails mechanically the initiator moves in a direction that is away from the explosive substance so that there is an increased or expanded gap between the initiator and the explosive substance. The increased or expanded gap is large enough to prevent the initiator frominitiating the explosive substance (i.e., to reduce or minimise the risk of an unplanned or unexpected explosion during recovery operations).

[0018] Compared to at least some existing boosters, the booster assembly disclosed herein reduces the risk of unplanned or unexpected initiation propagating to a full explosive blast during misfire recovery operations by: minimising the contact area between the initiator and the explosive substance; and providing an arrangement in which the initiator can be readily dislodged from the armed configuration when the housing is deformed / broken by an external force (e.g., applied by an excavator shovel), including not having the initiator 22 substantially extend into the explosive substance 27 so the initiator 22 can move transverse to the explosive substance when the housing is deformed / broken.

[0019] Moreover, the housing of the booster assembly disclosed herein includes a region that is designed to be relatively weaker, thinner, or more likely to break than the remainder of the housing. This region is sufficiently strong to protect the initiator during normal handling and under normal operating conditions (e.g., including from dynamic pressure from surrounding blasts) but is easily broken in more energetic handling processes such as recovery of ore following a misfire. Accordingly, the housing will break and move the initiator away from its position proximate to, or in contact with, the explosive substance before the initiator will initiate Because the booster assembly is configured to dislodge the initiator when the housing is broken, even if the initiator is triggered (which, by itself, poses negligible risk to people and equipment) by the recovery operations, the booster will not be initiated, and therefore, the bulk explosive will also not be initiated (it is standard practice in many commercial blasting operations to use bulk explosives that are not detonator sensitive (as an inherent safety practice)).

[0020] Standard blasting practice using existing boosters includes locating the initiator 22 substantially within the explosive substance to maximise the chance that the initiator will initiate the explosive when fired. Existing boosters also include initiator or detonator retention technologies that are designed to ensure the initiator will be within the explosive substance when it is fired. These technologies are not always reliable. It is common for initiators to move in response to knocks or movement during transport and / or loading in a blasthole. The present disclosure provides an improved mechanism for retaining the initiator within the booster assembly, without needing to embed or otherwise contact the initiator with the explosive substance, and thereby reduces the risk of a misfire event due to movement of the initiator during handling

[0021] Booster assemblies according to the present disclosure are suitable for use in a variety of applications and industries, such as iron ore mining, surface metal mining, construction, quarrying, surface coal, underground construction, underground mining, and civil infrastructure / demolition. The booster assembly 10 is recommended to be used in blastholes or boreholes with a diameter larger than 102 mm (the booster assembly is also suitable for use in blastholes of other sizes, for example a diameter of 89 mm or 76 mm). The booster assembly 10 can function in temperatures up to 70°C and when submerged or immersed in water. Moreover, booster assemblies according to the present disclosure may have excellent water and oil resistance can be used in a variety of hole conditions, including dry, dewatered, wet, hard rock, hot and / or reactive ground, jointed ground, and dynamic shock.

[0022] As shown in Figures 1 to 5, the housing 12 (also referred to as a cannister, a container, or a tube) includes a first or upper portion 14 and a second or lower portion 16. The first portion 14 may also be referred to as a cap and the second portion 16 may also be referred to as a shell. The shell 16 may include a generally cone-shape portion for containing the explosive charges. During manufacturing of the booster assembly 10, the cap 14 is typically connected to the shell 16 after the shell 16 has been filled with the explosive substance 26. Both portions of the housing 12 are typically formed from a rigid structure and can be manufactured from one or more types of polymer or plastic materials. The housing may be manufactured using various methods, such as by way of molding (e g., injection molding), machining, and / or additive manufacturing (e.g., three dimensional (3D) printing) techniques, processes, or procedures.

[0023] Figures 1 to 5 also illustrate a cable-locking mechanism provided in the housing 12. The locking mechanism includes channels or recesses 18 and a centre slit 35 in the first portion 14 that are configured to grip a cable 32 connected to the initiator 22, thereby locking the cable to the housing 12. The cable 32 is connected to a proximal end 29 of the initiator 22 and is configured to transmit an initiation signal. The cable may also be referred to as a signal tube, a lead wire, a downline, or a detonator cable. In some embodiments, the channels 18 are arranged so that the cable 32 can be wrapped around and secured to the housing 12. In the embodiment shown in Figures 1 to 5, the channels 18 are arranged so that the cable 32 can be wrapped around the housing 12, and secured thereto, in an approximately figure-of-eight configuration. This arrangement allows the cable 32 to be securely held or locked to the housing 12. This arrangement also allows the cable 32 to be secured in the locking mechanism such that the distal end 23 of the initiator 22 is biased towards the upper surface 27 of the explosive substance 26. Biasing of the initiator 22 towards the explosive substance 26 ensures that the distal end 23 of the initiator 22 remainsproximate the explosive substance 27 during handling and loading for reliable initiation of the explosive substance 27.

[0024] Figures 6 and 7 show a top end view and a bottom end view of the booster assembly 10, respectively. In the embodiment shown in Figure 6, the passage 24 is centrally located. As shown in Figure 7, the shell 16 may include a generally cone-shaped portion for containing the explosive charges, and an end cap 19 that is configured to be couplable, securable, or attachable / fixable to the shell 16. The portion for containing the explosive charge may also have a generally conical profile or tapered cylindrical structure. The end cap 19 can include a set of engagement structures, such as snap-fit or rotational or screw-type engagement structures, that enable mating engagement with the shell 16. Alternatively, the end cap 19 can be adhesively secured to the shell 16. The end cap can include or be formed from the same material as the housing — e g., plastics. The end cap 19 can additionally provide a chemically resistant barrier between the interior of the booster assembly 10 and the bulk explosive or other material or substrate when in use.

[0025] Like the end cap 19, the cap 14 is couplable, securable, or attachable / fixable to the shell 16. Cap 14 can include a set of engagement structures, such as snap-fit or rotational or screwtype engagement structures, that enable mating engagement with the shell 16. Alternatively, the cap 14 can be adhesively secured to the shell 16. In the embodiments shown in Figures 8-13, the cap 14 is coupled to or connected to the shell 16 using a snap-fit-type interference fit, and is held in place by engagement structures including protrusions 15 provided in the cap 14 and correspondingly shaped notches 25 provided in the shell 16.

[0026] Figures 8-12 show cross-sections of the booster assembly 10 taken along line A-A shown in Figure 6. As shown in Figure 8, the passage 24 extends from an opening in the upper surface 33 of the cap 14 and extends through the cap 14 towards an upper peripheral surface 27 of the explosive substance 26. Also shown in the figures are a non-explosive member or wave shaper 36, and a second explosive substance 28 The second explosive substance 28 may be referred to as a puck or the second, lower, or acceptor charge mass (hereafter “acceptor charge”), and the explosive substance 26 may be referred to as the first, upper, or donor explosive charge mass (hereafter “donor charge”). The donor charge 26 resides above (e.g., directly above) the wave shaping structure 36 when the booster assembly 10 is arranged to direct its output wave downwards; and the acceptor charge resides below (e g., directly below) the wave shaper 36. The acceptor charge 28 is configured to amplify a detonation wave generated by the donor explosivecharge 27 and thereby generate a shock wave that propagates in a generally outward direction from the booster assembly 10. Together, the donor explosive 26 and the acceptor charge 28 may be referred to as a set of explosive charge masses (or “explosive charges” for brevity), each of which can be defined as an “active” device component in that each explosive charge mass is capable of generating an explosive shock wave by way of releasing internally-stored explosive energy (e.g., each explosive charge mass itself within the set of explosive charge masses is detonable).[00271 Each of the donor charge 26 and the acceptor charge 28 includes at least one type of energetic formulation or explosive composition or compound. The explosive composition is cast, pressed or assembled into the cone-shaped plastic shell 16. A wide variety of explosive compositions or compounds are suitable for use in explosive boosters 10 in accordance with embodiments of the present disclosure. Suitable explosive compositions include molecular explosives such as pentaerythritol tetranitrate (PETN); a blend of trinitrotoluene (TNT) and PETN, e.g., 50% TNT and 50% PETN, generally referred to as Pentolite, which can vary in the relative proportions of the two main components and can include other components; Composition B (50% trinitrotoluene (TNT) and 50% cyclotrimethylenetrinitramine, where cyclotrimethylenetrinitramine is generally referred to as Research Department eXplosive (RDX); pressed RDX, which is a combination of RDX and a wax (e g., 90% RDX and 10% wax); and PBX (92% PETN and 8% inert polymer). The donor charge 26 and the acceptor charge 28 may each be formed from the same type of explosive composition, or from different explosive compositions. For example, in some embodiments, the donor charge 26 is formed from melt-cast 60% PETN and 40% TNT and the acceptor charge 28 is formed from pressed RDX. In other embodiments, the donor charge can be formed from detonator-sensitive ammonium nitrate emulsion formulation. The bulk blasting agent (e.g., pumped, augured and packaged explosives) typically includes ANFO and emulsion blends

[0028] In some embodiments, the booster assembly 10 can produce sufficient energy fluence, and a peak pressure above a detonation pressure threshold, with much less explosive mass than conventional boosters. For example, modelling results comparing the booster assembly 10 using 110 grams of high explosives with a conventional booster using 400 grams of explosives are shown in the table below. In addition, the booster assembly 10 according to the present disclosure can produce the required peak pressure using a 40% TNT and 60% PETN composition by mass. This reduces the cost of manufacturing and producing booster assemblies.|0029| The housing 12 includes a set of internal volumes, chambers, or cavities in which the set of explosive charges 26, 28 and the wave shaping structure 36 reside. The set of explosive charges 26, 28 and the wave shaping structure 36 are cooperatively structured and disposed relative to each other such that the explosive device or explosive wave shaping device outputs explosive energy exhibiting a quasi-planar wave front at or adjacent (e.g., directly adjacent) to a principal output end 31 of the housing 12. Portions of this quasi-planar wave front can travel quasi-unidirectionally (e.g., in a upward direction when the booster assembly is located in-situ in a blasthole) as the quasi-planar wave front propagates away from the principal output end 31 of the housing 12, thereby significantly, greatly, or dramatically enhancing the amount of explosive energy that propagates in an intended or target direction, and / or which is couplable or coupled into an intended or target material, substrate, or environment (e.g., geologic substrata) above and below the booster’s principal output end 31 compared to a conventional explosive device that outputs explosive energy exhibiting a spherical, hemispherical, or approximately hemispherical type of wave front at an analogous output end rather than a quasi-planar wave front. While the quasi-planar wave front propagates away from the principal output end 1, the booster assembly 10 also propagates a component of the explosive energy in other directions, so that the bulk explosive material located under and around the sides of the booster 10 (including in the toe-region of the blasthole) detonates

[0030] The non-explosive wave shaping structure 36, which can be defined as a “passive” device component in that the wave shaping structure itself does not or need not include any explosive composition therein, and does not or need not internally store explosive energy (e.g., the wave shaping structure itself is non-detonable, or explosively inert from a chemical composition perspective). The wave shaping structure 36 is configured to receive downwardly (in the orientation shown in Figures 8-12) propagating portions of the donor charge wave front; altering, transforming, or reshaping the spatial profile or distribution of those portions of the donor charge wave front; and outputting a substantially downwardly (in the orientation shown in Figures 8-12) propagating transformed shock wave having a wave front that exhibits a non-hemispherical, quasi-planar spatial profile or distribution, and which can serve as a shock initiation source for initiating the acceptor charge 28. In response to its initiation by the quasi-planar wave front received from the wave shaper 36, the acceptor charge 28 generates explosive energy providing an acceptor charge wave front that correspondingly has a similarly non-hemi spherical, quasi-planar spatial profile or distribution, and which can be coupled into a target material, substrate, or environment external to the explosive device 10.[00311 Further details of the internal geometry, including the shape of the donor charge, and the composition of the explosive charges are described in International Patent Application WO2020263194A1 (Petrovic et al., entitled "Deployment of quasi-planar shock wave generators in association with seismic exploration"), and United States Patent Number 12,104,887 (Johnson et al., entitled “Explosive device configured for producing a quasi-planar shock wave) the as-published specifications of which are hereby incorporated by reference herein in their entireties.

[0032] Also shown in Figures 8-12 is a sleeve 21 for protecting the initiator from external forces, such as dynamic shock or dynamic pressure. The sleeve 21 is arranged to at least partially surround the initiator 22. In other embodiments, the sleeve 21 may fully surround the initiator 22. In some embodiments, the sleeve 21 includes, or is formed from, a metal material such as steel. The sleeve 21 may also be fully encased in plastic.

[0033] The sleeve 21 also protects the initiator 22 from direct damage from contact during recovery operations after a misfire event. For example, when a force is applied to the housing 12 by an excavator shovel, if the booster assembly does not include a sleeve 21, the force from the shovel may be transferred from the housing 12 to the initiator 22 thereby damaging the initiator 22 sufficiently for it to be initiated. However, if the booster assembly includes a sleeve 21, the force from the shovel will be transferred from the housing 12 to the sleeve 21 which can distribute the force that is transmitted to the initiator 22 more evenly along the initiator 22, thereby reducing the pressure on the initiator 22 and reducing the risk of unexpected initiation. As a result, the sleeve 21 can assist in moving the initiator 22 away from its location proximate to or in contact with the explosive substance 27 to reduce the risk of unexpected initiation further. In other words, the sleeve 21 can assist in dislodging the initiator 22 from immediate contact with the explosive substance 27 when the booster assembly 10 is impacted during recovery operations.

[0034] In the embodiments shown in the figures, the sleeve 21 is a substantially homogeneous cylinder or tube. It is to be understood that the sleeve 21 could be provided in other forms whilestill performing the functions outlined above. For example, the sleeve 21 can include a mesh-like tube, a cage formed from a series of strips (e.g., wires), and / or a pair of concentric cages including an inner cage and an outer cage where gaps between solid portions in the inner cage are overlaid by solid portions in the outer cage. It is preferred that the sleeve 21 has sufficient radial strength to resist significant bending in response to forces applied to the housing 12 during recovery operations. For example, the radial strength of the sleeve 21 prevents the sleeve 21 from failing in bending in response to forces large enough to break the housing 12 and dislodge the initiator 22.

[0035] Figures 9-11 show the initiator 22 in the armed configuration (for simplicity, the cable 32 is not shown in these figures but would ordinarily be present in the armed configuration). In Figure 9, the distal end 23 of the initiator 22 is in contact with the upper (or proximal) surface 27 of the explosive substance 26. In other words, the distal end 23 of the initiator 22 abuts or sits on top of the donor charge 26, and does not extend into or penetrate the periphery of the donor charge 26. Correspondingly, the passage 24 does not extend into the donor charge 26. This configuration provides reliable initiation of the donor charge 26; however, the Applicant has achieved reliable detonation when the distal end 23 of the initiator 22 is displaced so that there is a gap 30 between the distal end 23 and the surface 27 of the donor charge 26 (as shown in Figures 10 and 11).

[0036] As shown in Figures 10 and 11, in the armed configuration, there may be a gap 30 between the distal end 23 of the initiator 22 and the upper surface 27 of the donor charge 26. In preferred embodiments, the gap is not greater than about 10 mm, and preferably not greater than about 8 mm when the gap 30 is filled with air. Testing by the Applicant has demonstrated that when the gap 30 is larger than 10 mm in air, the initiator 22 will not reliably initiate the donor charge 26. The size of the gap 30 for reliable initiation is reduced in the presence of water (e.g., if there is water, an emulsion, or another liquid in the blasthole). Where the gap 30 is filled with water or an emulsion, the maximum gap size for reliable detonation is about 5 mm, and preferably not greater than about 3 mm.

[0037] In some embodiments, a region of overlap 17 between the cap 14 and the shell 16 is located near, or close to, an interface between the initiator 22 and the donor charge 26. In other embodiments, the cap 14 and the shell 16 may be connected by other means (e.g., using an adhesive or a threaded fitting) so that the region of overlap 17 extends a shorter distance along the longitudinal direction of the booster assembly 10.

[0038] The booster assembly includes a region or plane of relative weakness near the interface between the initiator 22 and the donor charge 26. This region or plane allows the housing to break at a predictable location and therefore dislodge the initiator 22 during recovery operations, as is discussed in more detail below. The housing 12 also includes an internal cavity 34 for receiving the initiator 22 when it is dislodged by an external force during recovery operations.

[0039] Figures 12 and 13 show partially exploded views of the booster assembly 10.100401 Figure 14 schematically illustrates a recovery operation in which machinery 44 is used to collect substrate 40 (e.g., a “muck pile”) from a blasting operation. During such operations, machinery 44 impacts the substrate 40 at locations 42, and if a booster has failed to detonate, the machinery 44 may also impact the failed booster. When these forces impact a conventional booster assembly, it is likely that the force will lead to an un-planned or unexpected initiation of the booster, which is hazardous to people and equipment in the vicinity of the recovery operation A booster assembly 10 according to the present disclosure is configured to break or fail in response to these forces, and therefore reduce the risk of an unexpected detonation.

[0041] As illustrated in Figure 15, when a force F is applied to a side of the housing 12 (e g., a force that is transverse to the longitudinal axis L, or a cross-axial force), the housing 12 is configured to break and dislodge the initiator 22 from the armed configuration to a dislodged configuration. It is to be understood that forces applied to the housing 12 in directions other than the direction of force F may also break the housing 12 and dislodge the initiator 22. This “failsafe” design includes a region of the housing that is relatively weaker than the rest of the housing (e.g., a region with relatively thin sidewalls), so that the housing will readily deform / break in a predictable location (associated with the interface between the initiator 22 and the donor charge 26) as a result of contact with equipment during blast recovery operations. The internal cavity 34 provides sufficient space for the initiator 22 to dislodge from the surface of the donor charge 26 before it initiates. In the dislodged configuration, a distance between the distal end of the initiator 22 and the upper surface 27 of the donor explosive 27 is greater than a threshold distance, which is greater than the distance for reliable initiation of the donor charge. For example, the threshold distance is at least 10 mm.

[0042] In the embodiments shown in the Figures, the housing is configured to fail in the region where the cap 14 and the shell 16 are coupled together when assembled. It is to be understood that the point of failure is not necessarily required to be at the location of coupling so long as theinitiator 22 is reliably dislodged from its position proximate to or in contact with the donor charge 26. For example, in embodiments where the housing 12 is formed from one portion only, a region with relatively thin walls can be provided and / or imperfections (e.g., grooves) located at the desired point of failure.

[0043] In all embodiments, it is understood that the distal end 23 ofthe initiator 22 is dislodged from its proximity with the upper surface 27 of the donor charge 26 in a manner that is similar to shear failure. That is, the external force from the machinery 44 creates a stress along a (“failure”) plane that extends between the distal end 23 and the upper surface 27 and is perpendicular to the longitudinal axis L of the booster assembly 10. When the stress is sufficiently high, a fault zone will develop between the distal end 23 and the upper surface 27 and each of these components will move relative to each other. In other words, the distal end 23 will slip or slide past the upper surface 27.

[0044] Importantly, the upper surface 27 is configured so that the distal end 23 can move freely in any direction transverse to the longitudinal axis L of the booster assembly 10, or equivalently, in a direction that is substantially parallel with the upper surface 27.

[0045] Figures 16 to 20 illustrate steps for arming the booster assembly 10 by securing the initiator 22 within the housing 12. These steps in combination with the arrangement of recesses 18 in the cap 14 bias the distal end 23 of the initiator 22 towards the upper surface 27 of the donor charge 26 so that when the booster assembly is lowered into a borehole filled with a bulk explosive material, the distal end 23 of the initiator 22 remains in contact with, or in close proximity to (e.g. within approximately 10 mm) of the upper surface 27 of the donor charge 26. This ensures reliable detonation of the donor charge.

[0046] Figure 16 shows a first step of passing the initiator 22 with the cable 32 connected to its proximal end through retainer 20 and, in a second step 102, inserting the initiator 22 into the passage 24. In the embodiments shown in the figures, the retainer 20 is provided in the form of a tunnel on an external surface of the housing and is configured to guide and hold the cable 32 during assembly and deployment. It is to be understood that the retainer 20 can take other forms while still performing the required function of retaining the cable 32. Figure 17 shows a third step 103 in which the cable 32 is wrapped clockwise around the cap 14 in corresponding recess 18 and a fourth step 104 in which the cable 32 is pulled through centre slit 35. Figure 18 shows fifth and sixth steps 105 and 106 in which the cable 32 is wrapped in an anti-clockwise direction around thecap 14 in corresponding recess 18 and back into centre slit 35. Figure 19 shows steps 107 and 108, in which the cable 32 is pulled to taught to secure the cable 32 in the centre slit 35. This figure-of-eight wrapping provides a downwards force on the initiator 22 in the direction of arrow 107 in Figure 18.

[0047] In some embodiments, the housing 12 includes embossed arrows to assist an operator when wrapping the cable 32 around the housing to secure the initiator 22. The wrapping method also allows for safe removal of the initiator 22 if required. In addition, the recesses 18, the guide tunnel 20, and the centre slit 35 act to protect the cable 32 from damage during handling or while lowering the booster assembly 10 into a blasthole.

[0048] As shown in Figure 20, once the cable 32 has been wrapped around the cap 14 to secure the initiator 22, the booster assembly 10 can be inverted and lowered into a blasthole 46 containing a main explosive charge 38 (e g., bulk explosive). This arrangement can be used in various commercial blasting applications, including on applications on a mine site.

[0049] As shown in Figure 20, the retainer 20 is arranged to direct the distal end of the initiator 22 upward when the booster assembly 10 is lowered into the blasthole 46, thus directing the initial shockwave upwards into the main explosive charge 38.

[0050] As shown in Figure 21, a method 200 of arming a booster assembly in accordance with the present disclosure includes the following steps.a. Providing a housing 12 having an explosive substance 26 therein (step 202). b. Inserting an initiator 22 into the housing 12 (step 204)c. Providing a cable 32 connected to a proximal end of the initiator 22 and securing the cable 32 to the housing 12 by wrapping the cable 32 around the housing and securing it in correspondingly shaped recesses 18 so that the distal end 23 of the initiator 22 is biased towards the explosive substance 26 (steps 205, 206). d. Securing the initiator 22 in the housing 12 so that a distal end 23 of the initiator 22 is proximate or in contact with a proximal surface 27 of the explosive substance 26 without substantially extending into the explosive substance 27 (step 208).

[0051] Importantly, the booster is armed when the distal end 23 of the initiator 22 is in contact with, or proximate to, the end or upper surface 27 of the donor explosive 26. In other words, the initiator does not need to be embedded within the donor charge 26 for the booster to be armed

[0052] As shown in Figure 22, a method 300 for commercial blasting in accordance with the present disclosure includes the following steps.a. Providing a booster assembly 10 containing an explosive substance 26 (step 302). b. Providing a cable 32 connected to the initiator 22 and wrapping the cable 32 around the booster assembly to secure the cable 32 in correspondingly shaped recesses or channels 18 in the booster assembly 10 and securing the cable 32 to the booster assembly 10 so that the distal end 23 of the initiator 22 is biased towards the explosive substance 26 (steps 303, 304).c. Arming the booster assembly 10 by securing an initiator 22 therein so that a distal end 23 of the initiator 22 is secured proximate or in contact with a proximal surface 27 of the explosive substance 26 without substantially extending into the explosive substance 27 (step 305). In this step, the initiator 22 is secured such that a gap 30 between the distal end 23 of the initiator 22 and the proximal surface 27 of the explosive substance 26 is not greater than about 10 mm, preferably not greater than 8 mm.d. Lowering the armed booster assembly 10 into a borehole 46 and immersing the booster assembly 10 completely in the column of explosives 38 (steps 306, 307). e. Activating the initiator to generate a shock wave and thereby initiate the column of explosives (step 308).f. In a subsequent step, in the event that a booster misfires, the method may also include breaking of the misfired booster assembly during blast recovery operations, which dislodges the initiator from its secured position to reduce the risk of an unexpected initiation.

[0053] In the lowering step 306, the complete booster assembly is lowered to the desired location in the blasthole with the cap 14 pointing downwards. Operators should avoid walking on the cable 32 when the booster assembly 10 has been lowered into the blasthole in order to avoiddamaging the cable 32. It is preferable that the primed (eg., armed) explosive booster 10 is completely immersed in the bulk explosive 38, which may be achieved by either pulling the primer up into the explosive, or suspending the primer above the bottom of the hole during loading. Large diameter packaged explosives should be lowered on top of the primed booster 10, rather than dropped from the blasthole collar. The cable 32 should be kept taut during charging and stemming, to prevent damage and minimise abrasion. However, if a primed booster begins to float on top of a rising column of bulk explosive, the cable 32 can be slackened temporarily, and then, once the surface of the explosive column has risen past the primed booster 10, tension can be reapplied to the cable 32.Interpretation

[0054] For purpose of simplicity and clarity with respect to the description hereinbefore, the terms “upper,” “above,” or the like (e.g., “top,” or “on top of’) correspond to or define a spatial region, position, location, or site that is closer in relative terms to the proximal end 33 of the housing 12 than the distal end 31 of the housing 12; and the terms “lower,” “below,” or the like (e.g., “beneath” or “under”) correspond to or define a spatial region, position, location, or site that is closer in relative terms to the distal end 31 of the housing 12 than the proximal end 33 of the housing 12. The terms “downward” and “downwardly” correspond to or define one or more spatial directions away from the proximal end 33 of the housing 12 toward and / or beyond its distal end 31 ; and the terms “upward” and “upwardly” correspond to or define one or more spatial directions away from the distal end 31 of the housing 12 toward and / or beyond its proximal end 33. Additionally, the terms “inward,” “inwardly,” or the like (e.g., “inner”) correspond to or define one or more spatial directions toward the central longitudinal axis L of the booster assembly 10, and the terms “outward,” “outwardly,” or the like (e.g., “outer”) correspond to or define one or more spatial directions away from the central longitudinal axis A of the booster assembly 10. The terms “thickness,” “height,” or “depth” are defined as distances parallel to or along the central axis L. Additionally, the terms “lateral” and “radial” are defined with respect to a plane (e.g., an x-y plane) that is perpendicular to the central longitudinal axis L of the booster assembly 10.

[0055] The aforementioned relative spatial location or direction related terms are used for purpose of simplicity and aiding understanding. Individuals possessing ordinary skill in the relevant art will understand that these relative spatial location or direction related terms can be defined in a different manner for a given booster assembly 10 in accordance with an embodimentof the present disclosure, yet regardless of such terminology difference(s), the explosive device's structure remains fundamentally consistent, unchanged, or the same

[0056] While components and method steps will be described below for use in combination with each other in the preferred embodiments of the present invention, it is to be understood by a skilled person that some aspects of the present invention are equally suitable to be used interchangeably between one or more embodiments of the present invention and / or suitable for use as standalone inventions that can be individually incorporated into other devices and methods not described herein.

[0057] The word “about” or “approximately” when used in relation to a stated reference point for a quality, level, value, number, frequency, percentage, dimension, location, size, amount, weight or length may be understood to indicate that the reference point is capable of variation, and that the term may encompass proximal qualities on either side of the reference point.

[0058] As used herein, the word "substantially" may be used merely to indicate an intention that the term it qualifies should not be read too literally and that the word could mean “sufficiently”, “mostly” or "near enough” for the patentee's purposes.

[0059] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, a limited number of the example methods and materials are described herein.

[0060] In the description in this specification, reference may be made to subject matter which is not within the scope of the appended statements. That subject matter should be readily identifiable by a person skilled in the art and may assist in putting into practice the invention as defined in the presently appended statements.

[0061] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates.

[0062] Throughout this specification and the statements which follow, unless the context requires otherwise, the word ‘comprise’, and variations such as ‘comprises’ and ‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.LIST OF REFERENCE NUMBERS

Claims

CLAIMS1. A booster assembly for commercial blasting, including:a housing containing an explosive substance; anda guide for receiving an initiator for initiating the explosive substance,wherein, in an armed configuration, a distal end of the initiator is secured proximate to or in contact with a proximal surface of the explosive substance such that the distal end of the initiator can move away from the explosive substance when the housing deforms or fails mechanically such that the booster assembly is no longer in the armed configuration2 The booster assembly of claim 1 , wherein the initiator is secured such that a gap is provided between the distal end of the initiator and the proximal surface of the explosive substance.

3. The booster assembly of claim 2, wherein the gap is not greater than about 10 mm, preferably not greater than 8 mm.

4. The booster assembly of claim 2 or claim 3, wherein the gap is filled with a water or an emulsion.

5. The booster assembly of claim 4, wherein the gap is not greater than about 5 mm, preferably not greater than about 3 mm.

6. The booster assembly of any one of claims 1 to 5, further including a cable connected to a proximal end of the initiator for transmitting an initiation signal, the cable being securable to a locking mechanism provided in the housing such that the distal end of the initiator is biased towards the proximal surface of the explosive substance.

7. The booster assembly of claim 6, wherein the locking mechanism includes channels or recesses configured to grip the cable and thereby lock it to the housing.

8. The booster assembly of claim 7, wherein the channels or recesses are arranged so that the cable can be wrapped around the housing and secured to the housing9. The booster assembly of claim 8, wherein the cable is wrapped around the housing, and secured thereto, in an approximately figure-of-eight configuration.

10. The booster assembly of any one of claims 6 to 9, wherein the housing includes a retainer disposed on an external surface for holding and guiding the cable during assembly.

11. The booster assembly of claim 10, wherein the retainer comprises a guide tunnel on an external surface on the housing.

12. The booster assembly of any one of claims 1 to 11, wherein the housing is configured to deform or fail mechanically and thereby dislodge the initiator from the armed configuration to a dislodged configuration as a result of contact during blast recovery operations.

13. The booster assembly of claim 12, wherein the housing includes an internal cavity for receiving the initiator in the dislodged configuration.14 The booster assembly of claim 12 or claim 13, wherein, in the dislodged configuration, a distance between the distal end of the initiator and the proximal surface of the explosive substance is greater than a threshold distance.

15. The booster assembly of claim 14, wherein the threshold distance is at least 10 mm.

16. The booster assembly of any one of claims 1 to 15, wherein the housing includes a first portion and a second portion.

17. The booster assembly of claim 16, wherein the guide extends through the first portion and / or the explosive substance is disposed within the second portion.18 The booster assembly of claim 16 or claim 17, wherein, in response to forces applied to the housing during blast recovery operations, the housing is configured to fail in a region where the first portion and the second portion are coupled together when in an assembled configuration.

19. The booster assembly of any one of claims 1 to 18, further including a non-explosive member configured to alter the shape of a detonation wave travelling therethrough from a generally spherical wave to a quasi-planar wave20. The booster assembly of claim 19, wherein the non-explosive member comprises a non-compressible material.

21. The booster assembly of any one of claims 1 to 20, further including an acceptor charge configured to amplify a detonation wave generated by the explosive substance and thereby generate a shock wave that propagates in a generally outward direction from the booster assembly.

22. The booster assembly of any one of claims 1 to 18, wherein the housing further includes a sleeve for protecting the initiator, the sleeve being arranged to at least partially surround the initiator.

23. The booster assembly of claim 22, wherein the sleeve is formed from metal.

24. The booster assembly of any one of claims 1 to 23, wherein the housing includes inert material such as plastics and / or cardboard.

25. The booster assembly of any one of claims 1 to 24, wherein the booster assembly is configured for use in a column of explosives on a mine site26. The booster assembly of any one of claims 1 to 25, wherein the explosive substance includes a composition of at least 40% TNT with the remainder PETN by mass, or the explosive substance includes a composition of other molecular explosives.

27. The booster assembly of any one of claims 1 to 26, wherein, when initiated, the booster assembly produces an energy fluence of at least 3500 kJ / m2and / or a peak pressure of at least 14 GPa.

28. The booster assembly of any one of claims 1 to 27, wherein a proximal end of the initiator is not embedded within the explosive substance.

29. The booster assembly of any one of claims 1 to 28, wherein the distal end of the initiator can move transverse to a longitudinal axis of the explosive substance when the housing deforms or fails mechanically.

30. A method for initiating bulk explosive material for commercial blasting, including: providing a booster assembly containing an explosive substance;arming the booster assembly by securing an initiator therein so that a distal end of the initiator is secured proximate to or in contact with a proximal surface of the explosive substance without substantially extending into the explosive substance, wherein the initiator is secured such that a gap between the distal end of the initiator and the proximal surface of the explosive substance is not greater than about 10 mm, preferably not greater than 8 mm;lowering the armed booster assembly into a borehole; andactivating the initiator to generate a shock wave and thereby initiate the column of explosives.

31. The method of claim 30, further including providing a cable connected to the initiator and securing the cable to the booster assembly so that the distal end of the initiator is biased towards the explosive substance.

32. The method of claim 31, further including wrapping the cable around the booster assembly and securing the cable in correspondingly shaped recesses or channels in the booster assembly.

33. The method of any one of claims 30 to 32, further including immersing the booster assembly completely in the column of explosives.

34. The method of any one of claims 30 to 33, further including breaking the booster assembly during ore recovery operations and thereby dislodging the initiator from its secured position to reduce the risk of an unexpected initiation.

35. The method of any one of claims 30 to 34, further including inverting the booster assembly before lowering the booster assembly into the borehole36. A method of arming a booster assembly for commercial blasting, including:providing a housing having an explosive substance therein;inserting an initiator into the housing;securing the initiator in the housing so that a distal end of the initiator is proximate to or in contact with a proximal surface of the explosive substance without substantially extending into the explosive substance, andproviding a cable connected to the initiator and securing the cable to the housing so that the distal end of the initiator is biased towards the explosive substance.

37. The method of claim 36, further including wrapping the cable in an around the housing and securing the cable in correspondingly shaped recesses in the housing.

38. A booster assembly for commercial blasting, including:a housing containing an explosive substance; anda guide for receiving an initiator for initiating the explosive substance,wherein the housing is configured to break and dislodge the initiator from an armed configuration to a dislodged configuration in response to an external force applied to the booster assembly during blast recovery operations.

39. A booster assembly for commercial blasting, including:a housing containing an explosive substance;a guide for receiving an initiator for initiating the explosive substance; anda retainer disposed on an external surface for holding and guiding an initiator cable during assembly,wherein the retainer directs the distal end of the initiator upward when the booster assembly is lowered into a blasthole.

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