AU6662300A - Explosive cartridge - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

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Name of Applicant: Actual Inventors: Address for Service: Invention Title: Orica New Zealand Limited Mr Bruce McLennan Mr Matthew Monaghan Mr David Miller DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, Victoria 3000.

"Explosive Cartridge" Details of Basic Convention Application: New Zealand Patent Application No. 500525 filed 20 October, 1999 The following statement is a full description of this invention, including the best method of performing it known to me/us: P:\OPER\Joe\SPECIFICATIONS\EXPLOSIVES CARTRJDGEdoc-1910/00 -2- EXPLOSIVE CARTRIDGE The present invention relates to a cartridge for containing an explosive charge and to cartridges loaded with an explosive charge. More specifically, the present invention relates to a cartridge which is adapted to contain a charge of a liquid explosive and which may be connected in series with like cartridges thereby forming a column of connected cartridges. The invention also relates to a method of blasting employing such a column.

In certain operations it is necessary to carefully control the magnitude of an explosive blast. For instance, when laying charges to generate a seismic wave in seismic exploration, blast control is especially important in order to obtain meaningful readings from seismic monitoring equipment. One aspect of blast control involves using a deliberately chosen quantity of explosive charge.

.*15 Operations such as seismic exploration tend to take place in remote locations where accessibility may be limited. This can present problems in terms of explosive transportation. Transportation of bulk explosive to the site of use followed by loading of the explosive is impractical and the explosive is typically transported in containers as 0 discrete charges. For example, in seismic applications where transport to the required site may be by helicopter, the explosive tends to be packaged in individual containers which may be connected together prior to insertion into a blasthole. However, such containers may leak, especially after the rigours of transportation. For obvious reasons, leakage tends to be more of a problem when the explosive is a low viscosity fluid. As well as being potentially dangerous, leakage of the explosive may have a detrimental effect on blast control. Leakage can also result in incomplete detonation of the charge due to poor propagation between adjacent connected charges due to the presence of air pockets in the containers. It has been proposed to encapsulate the explosive in a sheath but this can be time consuming and increases cost. There is therefore the desire to provide an explosive container which overcomes these disadvantages and, in particular, provides leakage resistance.

P:%OPER JccSPECIFICATONS\EXPLOSIVES CARTRIDGE.d-1JIQ'O -3- In light of this background, the present invention seeks to provide a cartridge (container) for an explosive charge which avoids leakage of the charge during transport. In turn, this overcomes the detonation and propagation problems mentioned. The invention also seeks to provide a cartridge which may be connected with ease to other like cartridges in order to form a column of explosive charges, and which is therefore especially well suited for seismic exploration and other operations where it is desired to form a series of connected explosive charges.

SoAccordingly, the present invention provides an explosive charge cartridge which is adapted S• 10 to be connected to like cartridges in order to form a column of explosive charge cartridges, the cartridge comprising an elongate body portion which defines a chamber for receiving an explosive charge and which comprises an open end and a closed end, and a sealing means to prevent leakage of the explosive charge when present in the chamber, wherein the closed end of the body portion comprises a first connector portion, wherein the sealing 15 means is adapted to be inserted into the open end of the body portion and sealingly engage an inside surface of the body portion, and wherein the sealing means comprises a second connector portion which is adapted to engage a first connector portion of the closed end of the body portion of an adjacent like cartridge thereby enabling the cartridge and the S: adjacent like cartridge to be connected together.

The body portion of the cartridge is an elongate body which defines a chamber. In use an explosive is supplied to the chamber via the open end of the body portion and the sealing means inserted into the open end of the body portion thereby sealing the chamber and preventing leakage of the explosive. The body portion is usually cylindrical. The walls of the body portion are relatively thin and the chamber is usually of a similar shape to the body portion. The chamber is therefore also typically cylindrical. The chamber usually extends the length of the body portion. The opening of the chamber is the open end of the body portion and the chamber terminates at the closed end of the body portion.

P;\OPERcc\SPECIFICATIONS\EXPLWSIVES CARTRIDGE.doc-18/10/00 -4- The first connector portion of the body portion of the cartridge and the second connector portion of the sealing means are adapted to engage each other so that adjacent cartridges may be connected together. Thus, the sealing means serves to seal the chamber and provides a means for connection to a first connector portion of an adjacent cartridge. A variety of connector means may be provided the first and second connector means are mutually engageable. Preferably, once engaged the connector means are releasable thereby allowing adjacent cartridges to be separated, if necessary.

The first and second connector means may constitute an interference fitting wherein one of the first and second connector means may be inserted into the other so as to provide an •interference fit. Alternatively, the first and second connector means may constitute a snap fitting arrangement whereby one of the first and second connector means may be inserted into the other such that a tab on one engages a corresponding recess in the other. In a preferred embodiment, the first and second connector means are releasably engaged by a screw fitting. Thus, one connector means comprises an external screw thread and the other comprises a complementary internal screw thread. It is possible to employ a combination of these means of connection so that, for example, the first connector means may comprise an external screw thread and a tab and the second connector an internal screw thread and a recess for the tab. Typically, the first connector means comprises a male-type connector means and the second connector means comprises a female-type connector.

The sealing means sealingly engages by contact with an inside surface of the body portion when inserted into the open end of the body portion. This means that the seal is located within the body portion between the open and closed ends. The seal may be formed at any location within the body portion between the open and closed ends but in practice, in order to maximise the volume of explosive charge present in the chamber, the seal will be located in proximity to the open end.

Usually, the sealing means comprises a sealing portion which is specifically sized and shaped to form a seal as an interference fit between the sealing means and an inside surface of the body portion. Thus, if the chamber is circular in transverse cross-section, as would P:\OPER\Jcc\SPECIFICATIONS\EXPLOSIVES CARTRIDGE.doc-18/10/0 be the case with a cylindrical chamber, the sealing portion of the sealing means is also circular in transverse cross-section and of slightly greater diameter. This embodiment is particularly useful where the sealing portion and/or the walls of the body portion are elastically deformable, for instance when the body portion and/or the sealing portion are formed of a plastic. In this case, the sealing portion may conveniently comprise an enlarged distal head. To save material and provide structural rigidity the sealing portion may include a neck portion between the enlarged distal head and the engagement means.

The sealing means may also comprise an engagement means which is adapted to engage a complimentary engagement means provided on an inside surface of the body portion. The latter will usually be situated in proximity to the open end of the body portion. In use the engagement portions are intended to secure the sealing means in the body portion and prevent rotational and longitudinal movement of the sealing means within the body portion when a first connector portion, for instance of an adjacent cartridge, is brought into engagement with the second connector portion of the sealing means.

The sealing means usually takes the form of a sleeve which may be inserted into the open end of the body portion. The sleeve is typically cylindrical when the chamber into which the sealing means is inserted is so-shaped. The sleeve usually includes engagement means provided on an outer surface of the sleeve and the body portion comprises engagement means provided on an inner surface in proximity to the open end. The engagement means may be complementary screw threaded portions formed on the sleeve and body portions.

The sleeve portion may include recesses which are intended to engage corresponding recesses (when present) on the inside surface of the body portion. These recesses are intended to enhance fastening of these two components.

In an embodiment of the invention when the sealing means is in the desired location within the body portion, the sealing means does not extend beyond the open end of the body portion. This helps to reduce the gap between adjacent explosive charges when cartridges are connected.

P:\OPER\kc\SPEC1FICATIONS\EXPfLSIVES CARTRIDGE.do-1/IO/OO -6- The cartridge of the present invention may be used on combination with a variety of explosives. Usually, the explosive material will be a fluid explosive such as a water-gel or an emulsion. The cartridge is particularly well suited for use with low viscosity fluid explosives which are more prone to leakage than corresponding fluids having a greater viscosity. When measured by Brookfield Viscometer, model RVT, while utilising spindle "TF" at 5 RPM at 80 0 C, preferred emulsion explosives will exhibit viscosity values of no more than 600,000 cP. However, most preferred emulsions will have a viscosity in the range of 100,00 to 400,000 cP.

o° The exact composition, of the explosive is not critical to practice of the invention and one skilled in the art would be familiar with the kinds of explosive typically used in applications where use of the cartridges of the invention would be suitable. Thus, the present invention may be used for various explosives including gelatines based on nitroesters, dynamites, explosively sensitised water gels and slurries, liquid explosives oo based on nitroaromatics, fluid blasting agents, or even pourable granulated solid explosives. However, the invention is most suited for the contemporary water-in-oil emulsion explosives of liquid or fluid consistency. Any water-in-oil emulsion explosive formulation of a suitable sensitivity may be used in the practice of the invention. It is preferable to employ water-in-oil emulsion formulations comprising paraffin oil or combination of paraffin oil and wax as a continuous organic fuel phase. These types of formulations are more economical and exhibit better detonation sensitivity than comparable wax only based emulsions. The high wax content emulsions are also suitable to be used in the cartridges of the invention. However, the process of manufacture and handling tends to be more difficult in terms of processing and filling the plastic cartridges.

In some applications, conditions of high temperature may cause solid explosive material to melt, or compositions originally with high viscosity may exhibit lower viscosities due to the effect of enhanced temperature. It is possible to encounter temperatures of the order of to 100 0 C (or even higher) at the bottom of the boreholes. This may be due to high rock temperatures caused by reaction of the rock with the environment, volcanic activity or other cause. Under these conditions, the present inventions ensures containment of P:\OPERUc\SPECIFICATIONSEXPOSIVES CARTRIDGE.doc-18/O/O -7explosives materials within the cartridge and hence good performance and safety. For instance, leakage of explosive material into the borehole may cause reaction between the rock and explosive in hot or reactive environments. Considering that the explosive cartridge is typically initiated by the action of high explosive booster (cast PETN/TNT compositions), it is advantageous to employ explosives of lower intrinsic sensitivity.

In use individual cartridges are supplied with explosive to a predetermined volume and the sealing means inserted into the open end of the body portion, thereby sealing the chamber and preventing leakage of the explosive. The sealing means is retained in the body portion either by an interference fit with the body portion or by engagement means provided on the body portion and on the sealing means. The loaded cartridges may then be transported to the site at which they are to be used. At the site the cartridges may be connected via the first and second connector portions of adjacent sealed cartridges to form a column of loaded cartridges. Preferably, the thickness of materials between adjacent charges of explosive should be minimised so as to avoid detonation and propagation problems.

The column may be formed as it is being inserted into a blasthole and detonated in the usual way. A detonator may be used and this may be inserted though the sealing means of the uppermost cartridge in the column. The sealing means may be adapted to be punctured by a detonator, for instance by including a thin membrane. Alternatively, the explosive charge in a cartridge may be primed by use of an explosive booster. Typically, the booster is provided in a booster shell which comprises a connector portion which is adapted to engage a second connector portion of the sealing means of a cartridge. This enables the booster to be attached to the uppermost cartridge in a column. It will be appreciated that the booster will have a connector portion similar to the first connector portion described above in connection with the body portion. The booster may include an enlarged head which may be compressible. This is intended to prevent damage to the primer charge contained in the booster shell. The booster may be detonated in a conventional manner and used to trigger detonation of the entire column. The booster shell may be provided with a handle to facilitate easy handling. The booster may be initiated by a signal tube and the booster shell may be adapted to receive such a tube, for example through an aperture or P:XOPERVkc\SPEOFCATIONS\EXPLOSIVES CARTRIDGE.d-1/IOIOO -8hole. Conventional initiation means may be employed, i.e. electric, non-electric or electronic means.

The various components making up the cartridge, i.e. the body portion and the sealing means, and the booster, may be formed by injection moulding of a plastics material. Any plastics material may be employed provided it imparts a desired level of structural rigidity to the components. A degree of flexibility may also be required to assist seal integrity. As plastics which may be used polyethylenes and polypropylenes may be mentioned. The S•rigidity and robustness of the body portion may be enhanced by providing it with 10 longitudinal reinforcing ribs. These may be integral to the body portion and are usually provided on its outer surface.

As a practical illustration the cartridges of the invention are typically cylindrical with a nominal diameter of approximately 60 mm and a length of approximately 700 mm. Such cartridges usually contain around 1.7 kg explosive material. In seismic exploration the number of cartridges which are connected (and thus the total weight of explosive) will be determined by the instrumentation being used and the signal required.

S•The invention further provides a sealed cartridge as described herein loaded with an explosive charge.

The invention yet further provides a method of blasting which comprises detonating a column of cartridges loaded with explosive charge as described herein. Detonation may be achieved using a booster. The column may be assembled beforehand and inserted into a blasthole or assembled on insertion into the blasthole. The present invention is particularly suited to seismic exploration where blast control is important.

The present invention will now be described with reference to the following non-limiting drawings.

Figure 1 is a side view of the body portion of a cartridge of the present invention; P:\OPER\jcc\SPECIFICATIONS\EXPLOSIVES CARTRDGE.doc-18/O/00 -9- Figure 2 is another side view of the body portion shown in Figure 1; Figure 3 is a top view of the body portion of Figures 1 and 2; Figure 4 is a bottom view of the body portion of Figures 1 and 2; Figure 5 is a side view of a sealing means of a cartridge of the present invention; Figure 6 is another side view of the sealing means of Figure Figure 7 is a perspective view of the sealing means of Figures 5 and 6; Figure 8 is a top view of the sealing means of Figures 5, 6 and 7; Figure 9 is a bottom view of the sealing means of Figures 5, 6 and 7; Figure 10 is a cross-sectional representation of a cartridge of the present invention showing 10 the body portion and the sealing means; Figure 11 is a side view of a booster; Figure 12 is another side view of the booster of Figure 11; Figure 13 is a perspective view of the booster of Figures 11 and 12; Figure 14 is a top view of the booster of Figures 11, 12 and 13; Figure 15 is a bottom view of the booster of Figures 11, 12 and 13; Figure 16 is a cross-sectional view showing a column of connected cartridges provided in a blasthole and primed with a booster.

Figures 1, 2, 3 and 4 show a body portion comprising an open end and a closed end The body portion is elongated and generally cylindrical. The body portion (1) comprises a first connector portion provided towards the closed end The first connector portion comprises an external screw thread The cylindrical section of the body portion includes a ribbed section which is intended to provide structural P:\OPER\Jc\SPECIFICATIONS\EXPLOSIVES CARTRIDGEAd-IIO/OO rigidity. The cylindrical section also includes a smooth labelling surface The open end and closed end are disposed at opposite ends of the body portion The body portion also includes an engagement means which is adapted to engage a sealing means (not shown). In the embodiment shown the engagement means is an screw thread provided on the inside surface of the body portion The closed end (3) terminates in an extension to the first connector portion Figures 5, 6, 7 and 8 show a sealing means (10) which includes a seal portion (11) in the *form of an enlarged distal head. The sealing means comprises a sleeve portion (12) and an :engagement means (13) which is adapted to engage the second engagement means as shown in Figures 1 and 2. The engagement means (13) shown is in the form of a screw thread which is complementary to the screw thread of the engagement means The sealing means (10) includes a necked portion (14) disposed between the engagement means (13) and the sleeve portion The sleeve portion (12) includes recesses which may engage corresponding recesses provided on the inside surface of the body portion (not shown). It is evident from Figure 9 that the sealing means (10) is hollow and includes a second connector portion (16) which is adapted to engage a first connector portion of a body portion (as shown in Figures 1 and or a first connector portion ofa booster.

4 Figure 10 illustrates a sealing means (10) positioned within the body portion thus sealing the chamber This is achieved by an interference fit between the sealing portion of the sealing means, i.e. the enlarged distal head and the inside surface of the body portion The body portion includes engagement means which engages a complimentary engagement means (18) provided on the exterior surface of the sealing means These engagement means 18) allow the sealing means to be secured in position within the body portion after an explosive charge has been supplied to the chamber The sealing means (10) includes a second connector portion (19) which is provided on the inside surface of the sealing means (10) and which is adapted to engage a first connector portion of a body portion or a first connector portion of a booster.

Figures 11, 12, 13, 14 and 15 illustrate a booster (20) which includes a first connector P:\OPER\Je \SPECIFICATIONS\EXPLOSIVES CARTRIDGEdo-1/10/0O -11portion (21) and which is adapted to engage the second connector portion (19; not shown) of a sealing means In the embodiment shown the booster (20) includes a screw thread as the first connector means This is capable of engaging a complementary screw thread provided as the second connector means (19) of the sealing means The booster includes an enlarged head (22) which is adapted to protect the primer charge which would be present in the body (23) of the booster The booster (20) typically includes an aperture (not shown) to receive a signal tube (not shown). The booster (20) includes a handle (24) which allows easy manipulation of the booster (20) and aids insertion of the booster (20) by screwing into the sealing means The booster includes recesses .9 4 10 which may engage corresponding recesses provided on the sealing means 9. 0 Figure 16 illustrates how the present invention would be used in practice. In this figure a column consisting of five sealed cartridges is positioned in a blasthole Each cartridge consists of an elongated body portion which defines a chamber The chamber includes an explosive charge. The charge is sealed within the body portion by a sealing means (10) having, as a sealing portion, an enlarged distal head The sealing means toe.

000 o(11) includes an engagement means which cooperates with and engages a complimentary engagement means provided on the inside surface of the upper end of the body portion 9: *This arrangement is shown in greater detail in Figure 10. The uppermost sealing means of o, the column engages a booster The booster (20) comprises a first connector portion S S which engages a second connector portion of the sealing means The booster may be triggered by a signal tube (not shown).

Throughout this specification and the claims 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.

Claims (16)

1. An explosive charge cartridge which is adapted to be connected to like cartridges in order to form a column of explosive charge cartridges, the cartridge comprising an elongate body portion which defines a chamber for receiving an explosive charge and which comprises an open end and a closed end, and a sealing means to prevent leakage of the explosive charge when present in the chamber, wherein the closed end of the body portion comprises a first connector portion, wherein the sealing 0 means is adapted to be inserted into the open end of the body portion and sealingly engage an inside surface of the body portion, and wherein the sealing means comprises a second connector portion which is adapted to engage a first connector portion of the closed end of the body portion of an adjacent like cartridge thereby enabling the cartridge and an adjacent like cartridge to be connected together.

2. A cartridge according to claim 1, wherein the body portion and chamber are cylindrical.

3. A cartridge according to claim 1 or 2, wherein the first connector portion and second connector portion are releasably engageable. .0

4. A cartridge according to any one of the preceding claims, wherein the first and second connector portions are complementary screw threads.

5. A cartridge according to any one of the preceding claims wherein, in use, the sealing means forms a seal in proximity to the open end of the body portion.

6. A cartridge according to any one of the preceding claims, wherein the sealing means comprises an engagement means and wherein the inside surface of the body portion comprises a complementary engagement means adapted to engage the engagement means of the sealing means.

7. A cartridge according to any one of the preceding claims, wherein the sealing means is in the form of a sleeve comprising an enlarged distal head. P:\OPER\kec\SPECIFICATIONS\EXPLOSIVES CARTRIDGE.doc.18/10/00 -13-

8. A cartridge according to any one of the preceding claims further comprising a booster.

9. A cartridge according to claim 8, wherein the booster comprises a booster shell comprising a connector portion which is adapted to engage the second connector portion of the sealing means.

A cartridge according to any one of the preceding claims comprising an explosive sealed in the chamber by the sealing means.

11. A cartridge according to claim 10, wherein the explosive is a fluid explosive having a viscosity of no more than 600,000 cP (when measured by a Brookfield 10 Viscometer, model RVT, while utilising spindle "TF" at 5 RPM at 80 0 C).

12. A column of explosive charges comprising at least two cartridges as defined in claim 10 or 11 wherein the first connector portion of one cartridge is connectably engaged with the second connector portion of an adjacent cartridge.

13. A method of blasting which comprises detonating a column of explosive charges as claimed in claim 12.

14. An explosive charge cartridge substantially as hereinbefore described with reference to the accompanying drawings.

A column of explosive charges substantially as hereinbefore described.

16. A method of blasting substantially as hereinbefore described.