AU2017101164A4 - Low Energy and Full Strength Explosive Charge Combination - Google Patents

Abstract

The present invention relates to an explosive charge for breaking rock during open pit mining, comprising at least one first type of cartridge and at least one second type of cartridge in longitudinal alignment and containing an explosive substance, wherein the first type of cartridge comprises a lower concentration of the explosive substance when compared with the concentration of the explosive substance of the second type of cartridge. Also described is a method of breaking rock during open pit mining using the above-mentioned explosive charge. Fig. I

Description

2017101164 25 Aug 2017 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR AN INNOVATION PATENT (Original) APPLICATION NO: LODGED: COMPLETE SPECIFICATION LODGED: ACCEPTED: PUBLISHED: RELATED ART: NAME OF APPLICANT: Explosives Manufacturing Services Pty Ltd ACTUAL INVENTOR(S): Duncan Minto ADDRESS FOR SERVICE: LORD AND COMPANY,

Patent and Trade Mark Attorneys, of PO Box 530, West Perth,

Western Australia, 6872, AUSTRALIA.

INVENTION TITLE: “LOW ENERGY & FULL STRENGTH EXPLOSIVE CHARGE COMBINATION”

The following Statement is a full description of this invention including the best method of performing it known to me/us: 2017101164 25 Aug 2017

TITLE “LOW ENERGY & FULL STRENGTH EXPLOSIVE CHARGE COMBINATION”

FIELD OF THE INVENTION

[0001 ] The present invention relates to an explosive charge comprising a combination of low energy and full strength explosive.

BACKGROUND

[0002] In order to provide a safe place of work, and assist with the economic extraction of mineral-bearing rock, open pit mines need to have sound final walls in place. Part of this outcome is achieved by lightly blasting to remove the last of the rock to develop the pit perimeter to its final limit. To achieve the final slope, and to leave sound terraces to help prevent rock from falling into the pit and potentially damaging equipment and hurting operators, berms are developed. The crests, or edges, of these berms should be very solid and stable and mined to a pre-determined dimension.

[0003] The current selection of explosives available to miners designed for this type of blasting are composed of a single formulation of explosives throughout the length of the charge. Some degree of customisation has been developed by explosives suppliers to save operators at mines from adapting a standard explosive into one that is suited specifically to their operational requirements. Aspects of customisation at present include: - Doubling of cartridges to create a stronger charge located at the bottom of the drill hole where more explosive energy is required to successfully blast the rock to within design limits. - The addition of load bearing twine or rope to the charge, which supports the weight of the explosive charge when it is suspended in the blast hole. - Additional length of detonating cord at the top of the charge enabling the top of the explosive column to be located at a set distance below the hole collar/final crest in order to reduce damage to the residual rock. The detonating cord is then 2 connected to a trankline that initiates the charge. 2017101164 25 Aug 2017 - The inclusion of empty cartridges near the top of the charge to lower the amount of explosive energy at, or close to, the top of the hole.

These efforts have been met with some success but products remain imperfect and at times prohibitively expensive (especially in the case of manufacturing charges with empty cartridges).

[0004] Despite efforts to offset the top of the charge from the crest position at the top of the drill hole, it is very common for the residual rock located at the hole collar, i.e. the crest of the berm which remains, to be damaged by the explosive during blasting. This results in wedges of rock falling from the crest thus rendering the crests less effective with a corresponding impact on safety in the pit. However, if the top of the explosive charge is located too deep in the hole, effective rock breakage will not happen with undesirable outcomes resulting from this ineffective breakage, such as, the possibility that rock located at the top of the hole will merely be partially broken, thus having it remain on the wall but in a destabilised condition. This can be a danger to people and equipment working below as it could loosen and fall. Remaining rock may also require mechanical removal, which is hazardous and time consuming, thus slowing down the mining cycle and increasing costs.

[0005] The present invention attempts to overcome at least in part the aforementioned disadvantages of previous explosive charges.

SUMMARY OF THE INVENTION

[0006] In accordance with one aspect of the present invention, there is provided an explosive charge for breaking rock during open pit mining, comprising at least one first type of cartridge and at least one second type of cartridge in longitudinal alignment and containing an explosive substance, wherein the first type of cartridge comprises a lower concentration of the explosive substance when compared with the concentration of the explosive substance of the second type of cartridge. 3 [0007] The charge may comprise a plurality of the second type of cartridges, wherein at least one of the second type of cartridges may be disposed adjacent to another one of the second type of cartridges so as to form adjacently aligned pairs of the second type of cartridges. 2017101164 25 Aug 2017 [0008] The charge may comprise a plurality of the first type of cartridge, a plurality of the second type of cartridge in singularity, and a plurality of the second type of cartridges in adjacently aligned pairs.

[0009] The charge may comprise a detonating cord, at least part of which is internal of the cartridges, traversing substantially the full length of the charge.

[0010] The lower concentration of the explosive substance of the first type of cartridge may be achieved by filling the first type of cartridge with a combination of the explosive substance and an inert filler.

[0011] The first type of cartridge may possess an explosive strength of about 60% of an explosive strength of the second type of cartridge. The first type of cartridge may possesses an explosive strength of between about 60% and 100% of an explosive strength of the second type of cartridge.

[0012] The charge may comprise a suspension means extending from an upper end thereof, for use in suspending the charge at a desired height within a hole in the rock.

[0013] In accordance with a second aspect of the present invention, there is provided a method of breaking rock during open pit mining comprising the use of the above-mentioned explosive charge.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of an explosive charge in accordance with one embodiment of the present invention; 4

Figure 2 is a sectional view of part of the explosive charge of Figure 1; and Figure 3 is a schematic representation of a typical presplit blast layout. 2017101164 25Aug2017

DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] Referring to the Figures, there is shown an explosive charge 10 comprising a combination of low energy and full charge explosives. With specific reference to Figure 1, a preferred embodiment of an explosive charge 10 is shown. The charge 10 comprises a number of cartridges 12 in alignment with one another in and end-to-end arrangement, resulting in an elongated column charge 10 in a continuous cartridge 12 form.

[0016] At a lower end 20 of the charge 10, a number of cartridges 12 are disposed adjacent to another cartridge 12 respectively, to create a high energy portion 18 of the charge 10. This high energy portion 18 effectively comprises a length of pairs of cartridges 12, or a ‘doubling-up’ of cartridges 12, at the lower end 20 of the charge 10.

[0017] The charge 10 further includes, at an upper end 22 thereof, a length of suspension means 14 and a length of external detonating cord 16. The suspension means 14 and external detonating cord 16 extend upward from the uppermost cartridge 12 adjacent one another. It is preferred that the suspension means 14 comprises rope.

[0018] With reference to Figure 2, each cartridge 12 comprises an explosive 24 internal portion, wrapped in a skin 26, preferably comprising laminated polyethylene film of a thickness between about 70 and 120 microns. The explosive 24 may be selected from, but not limited to, a water gel explosive, emulsion type explosive or ammonium nitrate/fuel oil (ANFO) explosive. It is preferred that the explosive 24 possesses a velocity of detonation of about 4300 m/s. If required, inhibited explosive 24 maybe used for instances where the charge 10 is to be used under reactive ground conditions. The diameter of the cartridge 12 and other measurements of the charge 10 may be dimensioned to suit the conditions for use of the charge 10. Each terminal end of the cartridge 12 is sealed with a clip 28, preferably constructed of aluminium wire. 5 [0019] An internal detonating cord 3 0 is disposed at the internal portion of the cartridge 12. The internal detonating cord 30 extends from the external detonating cord 16 at the upper end 22 of the charge 10, through all of the cartridges 12 to ensure, during use, the complete functioning of the entire length of the cartridges 12. At the lower end 20, the internal detonating cord 30 reverses direction to continue extending through the additional cartridges 12 at the high energy portion 18. The internal detonating cord 30 may comprise an approximately 11 g/m, 6500 m/s velocity of detonation, detonating cord constructed of appropriate material. It would, however, be understood by the skilled person for the detonating cords 16,30 to be appropriately structured and composed to suit each specific application of the charge 10. 2017101164 25 Aug 2017 [0020] As shown in Figure 1, at least one of the cartridges 12 at the upper end 22 of the charge 10 comprises a mixture of the explosive 24 and inert filler resulting in a lower strength of explosive. Accordingly, the charge 10 comprises a low energy portion 32 at its upper end 22, the high energy portion 18 at its lower end 20 and between die two, a standard formulation explosive fills the cartridges 12 for a fall strength portion 34 at the mid-length of the charge 10.

[0021 ] The explosive 24 within the one or more cartridges 12 of the low energy portion 32 is preferably provided in an amount from about 60% to 100% of the total volume of the internal portion of the cartridge 12. However, the proportion of explosive 24 is selected to suit each specific application and use of the charge 10. The inert filler used within these cartridges 12 is any material that does not contribute to the explosive chemical reaction and may be chosen from, but is not limited to, polystyrene beads, sawdust, bentonite or salt.

[0022] In use, the charge 10 according to the present invention is utilised during pre-split blasting of a perimeter wall 36 of an open pit mine, as represented in Figure 3. The charge 10 is most suited to hard rock operations where smaller holes are drilled, but can be adapted for use elsewhere, as would be understood by a skilled person. The charge 10 is inserted into pre-split holes 3 8 drilled into the ore, or material to be mined, along a line 6 to become the crest of the berm 40 that remains after blasting. Normal production blasting can occur in the rock between the pre-split line and the current crest, as is appropriate to a given mining situation. 2017101164 25 Aug 2017 [0023] The charge 10 is lowered into a pre-split hole 38, starting with its lower end 20, such that the high energy portion 18 is at the lower end of the hole 38. Accordingly, the low energy portion 32 at the upper end 22 of the charge 10 is proximal to the upper, open end of the hole 38. The suspension means 14 and external detonating cord 16 extend from the charge 10 within the hole 38 to above and beyond the hole 38 and the suspension means 14 is fixed at an appropriate location such that the charge 10 hangs from the suspension means 14 and is suspended within the hole 38 at a desired height. As a result, the charge 10 can be ideally positioned within the hole 38 to have the best effect during blasting.

[0024] Once the charge 10 is ideally positioned, the external detonating cord 16 is connected with a suitable initiator as would be well known. If required, an additional length of detonating cord, or trunkline, may be used to connect the external detonating cord 16 of the charge 10 with the initiator. Once the charges 10 are fully prepared and appropriate safety checks have been completed, detonation is initiated.

[0025] As described above, the high energy portion 18 of the charge 10 is at the lower end of the hole 3 8. Accordingly, during the blast, more energy is delivered to the bottom of the hole 38 to achieve optimal design results, and the full strength portion 34 at the mid-length of the charge 10 also delivers desired outcomes. Similarly, the presence of the low energy portion 32 at the upper end 22 of the charge 10 proximal to the top of the hole 38 ensures adequate rock breakage while ensuring a stable and reliable berm 40 and crest remain after blasting. The charge 10 of the present invention, comprising a combination of low energy and standard strength explosive in the same continuous charge 10, results in optimal post-blast rock conditions. Additionally, the charge 10 is cost-effective to manufacture as production requires merely an alternate filling material 7 for the cartridges 12 within the low energy portion 32, compared with the remainder of the cartridges 12. 2017101164 25 Aug 2017 [0026] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. For example, as previously described, the cartridges 12 in the low energy portion 32 comprise the explosive 24 mixed with inert filler in variable proportions to suit the rock being blasted by a user. The explosive strength at the low energy portion 32 can therefore be selected as dictated by site requirements. Further, the length of the charge 10, or number of cartridges 12 within the low energy portion 32, can also be varied. Similarly, the length of the charge 10, or number of cartridges 12 within the high energy portion 18 and/or the fiill strength portion 34 are selected to suit user requirements. 8

Claims (9)

1. An explosive charge for breaking rock during open pit mining, comprising at least one first type of cartridge and at least one second type of cartridge in longitudinal alignment and containing an explosive substance, wherein the first type of cartridge comprises a lower concentration of the explosive substance when compared with the concentration of the explosive substance of the second type of cartridge.

2. An explosive charge according to claim 1, comprising a plurality of the second type of cartridges, wherein at least one of the second type of cartridges is disposed adjacent to another one of the second type of cartridges so as to form adjacently aligned pairs of the second type of cartridges.

3. An explosive charge according to claim 2, comprising a plurality of the first type of cartridge, a plurality of the second type of cartridge in singularity, and a plurality of the second type of cartridges in adjacently aligned pairs.

4. An explosive charge according to any one of the preceding claims, comprising a detonating cord, at least part of which is internal of the cartridges, traversing substantially the full length of the charge.

5. An explosive charge according to any one of the preceding claims, wherein the lower concentration of the explosive substance of the first type of cartridge is achieved by filling the first type of cartridge with a combination of the explosive substance and an inert filler.

6. An explosive charge according to any one of the preceding claims, wherein the first type of cartridge possesses an explosive strength of about 60% of an explosive strength of the second type of cartridge.

7. An explosive charge according to any one of claims 1 to 5, wherein the first type of cartridge possesses an explosive strength of between about 60% and 100% of an explosive strength of the second type of cartridge.

8. An explosive charge according to any one of the preceding claims, compri sing a suspension means extending from an upper end thereof, for use in suspending the charge at a desired height within a hole in the rock.

9. A method of breaking rock during open pit mining comprising the use of an explosive charge according to any one of the preceding claims.