AU2029402A - Explosive casing - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: Actual Inventor(s): Address for Service: Invention Title: Initiating Explosives Systems Proprietary Limited Bradley Kevin Beikoff and Rodney Wayne Appleby DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, Victoria 3000.

"Explosive Casing" Details of Associated Provisional Application(s): No(s): PR3515/01 dated 5 March 2001 The following statement is a full description of this invention, including the best method of performing it known to me/us: P.'OPERUcc SPECIFCATIONSTEXPLOSIVE CASING.2.dm-04'03/02 -1- EXPLOSIVE CASING The present invention relates to a casing for housing in close proximity a portion of a detonator cord and a detonator. The invention further relates to a method of loading a blasthole and to a method of blasting, each method employing the casing.

In underground mining tunnels are created by detonating explosives in an array of blastholes, the configuration of which mirrors the intended tunnel shape. Thus, the array typically consists of core (or centre) blastholes surrounded by a number of perimeter 10 blastholes. The core blastholes are detonated first followed by the perimeter blastholes in order to define the walls of the tunnel. Detonation of the core holes first creates a cavity into which material from the perimeter holes may be ejected. From a safety point of view g it is desired that the walls of the blasthole are as smooth and unbroken as possible. If the walls, and particularly the ceiling, of a blasthole is fractured or has loose attachments, this 15 can represent a safety hazard. The production of clean blasthole walls is also advantageous from an economic viewpoint as the removal of loose attachments is labour and time intensive.

o A number of methods have been proposed for underground mining. For example, it has been proposed to detonate conventional ANFO or emulsion explosives in blastholes.

However, these explosives tend to be of high energy and this can lead to the kind of damage to the walls of the tunnel it is desired to avoid. It has been proposed to replace this type of explosive with less energetic products. These have a lower energy output and thus cause less damage, but tend to be much less efficient.

As an alternative, it has also been proposed to carry out underground mining using, as explosive, lengths of detonating cord initiated using a detonator. However, loading of the cord and detonator can be problematic. For example, if the cord protrudes from the blasthole opening, detonation can lead to cratering damage to the wall at that point.

Furthermore, the detonator cord is prone to being pulled out of perimeter blastholes when the core blastholes are fired. This in itself can be hazardous as this sometimes leads to undetonated explosive being present in the muckpile generated by blasting of core P:'OPERJc'SPECIFICATIONS\EXPLOSIVE CASING-2UdOm-04'O0O2 -2blastholes.

The present invention seeks to provide an improved means of underground mining which does not suffer the disadvantages associated with conventional techniques. More specifically, the invention seeks to provide a means for underground mining which is efficient and safe and which results in tunnels having smooth and unfractured surfaces. In part, these advantages are achieved by use of a specially designed casing which enables housing in close proximity of a detonator cord and detonator which facilitates loading of a blasthole in a manner which gives beneficial results. In accordance with the present 10 invention the blasthole is loaded with the detonator at the toe and with detonator cord running back up the blasthole. The length of the detonator cord may be tailored to any given blasthole so that it is not in close proximity to the open end of the hole.

Additionally, in an embodiment of the invention, the detonator/cord assembly may be fixed at the toe of the blasthole thereby preventing dislodgment of the detonator/cord 15 assembly due to any separate detonation in another blasthole.

A fundamental aspect of the present invention is the casing which is used to accommodate the detonator adjacent to the detonator cord, as necessary for firing of the cord using the detonator. This casing is also especially adapted to allow blasthole loading. Accordingly, the present invention provides a casing comprising: a detonator cord receiving passage having detonator cord retaining means; a detonator receiving passage adjacent to or in communication with the detonator cord receiving passage; detonator retaining means; and loading member engagement means.

In use the detonator and a portion of the detonator cord are retained in the casing, in contact or in close proximity to each other. Typically, the end of the detonator cord will be contained by the casing. The casing is then pushed into the blasthole until it is positioned at or close to the toe of the blasthole. This is achieved using a loading member which engages the loading member engagement means of the casing.

P 'OPER'Jcc\SPECIFICATIONS\EXPLOSIVE CASING-2.do-.O4103/2 -3- The loading member may be a loading hose as is used for loading bulk explosive into the core blasthole. Alternatively, the loading member may be a tamping rod. Either way the casing is adapted to engage the loading member to facilitate positioning in a blasthole. In fact, and as discussed below, the casing may be fixed at the toe of the blasthole by bulk or packaged explosive and the way in which this is carried out has implications on the type of loading member which is used.

As the casing is pushed along the blasthole it pulls with it a length of detonator cord. The *length is chosen in advance based on the length of the blasthole so that when the casing is .i 10 in position at the toe of the blasthole, detonator cord does not protrude from the open end of the blasthole. Signal tube used to initiate the detonator runs from the neck of the detonator, where it is usually crimped in place, and back up and out of the blasthole. Both the detonator cord and detonator are retained in position in the casing.

15 The casing of the present invention allows one step loading of a blasthole which is advantageous from an efficiency viewpoint. The invention also enables loading of hard to access blastholes. A further benefit is that the casing protects the detonator, signal tube and the end of the detonator cord against abrasion and impact during handling and loading.

The detonator cord receiving passage is adapted to receive and retain a portion of detonator cord, usually the end portion. The cord is typically circular in cross-section and this is also usually the configuration of the receiving passage. Typically, the passage is cylindrical, and approximately 25 to 75 mm in length. The diameter of the passage is essentially the same as the detonator cord.

The detonator cord may be retained in the passage in a variety of ways. For instance, the passage may comprise one or more tabs which may be pushed into the surface of, and engage the cord when in position in the passage. Alternatively, the passage may comprise a longitudinal hinge which enables it to be opened in order to receive the detonator cord.

In this embodiment the inside surface of the passage includes one or more cord engaging projections which will grip the cord when the passage is closed by movement of the respective sides about the longitudinal hinge. In this embodiment the passage also P.\OPERkc'SPECIFICATIONS\EXPLOSIVE CASING.2.dmc-0413,02 -4comprises one or more tabs and corresponding tab-recesses to ensure that the passage does not open when the cord is in place.

For the assembly to function the detonator must be in close proximity to or in contact with the detonator cord so that firing of the detonator triggers detonation of the cord. This requirement obviously influences the arrangement of the detonator receiving passage relative to the detonator cord receiving passage. In one embodiment the detonator o. receiving passage and detonator cord receiving passage share a common boundary. For example, the passages may be cylinders which are joined along a common longitudinal .i 10 axis. In this embodiment, the space between the detonator and detonator cord, including the thickness of any material of the casing, should be as small as possible.

*o.

In a preferred embodiment, the detonator and detonator cord are contained in a single passage and are in direct contact with each other. Typically, the diameter of the cord is 15 larger than that of the detonator and there are a variety of configurations which permit the .555 two to be contained within a single passage. For example, the passage may comprise two mutually communicating cylindrical channels, one channel sized according to the cord and one channel sized according to the detonator. In this embodiment, the detonator and cord contact each other along a common longitudinal axis. In this embodiment the passage may be hinged as described above to allow insertion of the detonator cord. The detonator may be inserted in a similar fashion, or through a transverse end of the passage.

The detonator receiving passage includes means for retaining the detonator in place. The passage may include a transverse wall portion to prevent longitudinal movement of the detonator. If the casing includes a longitudinal hinge and the detonator is dropped into place rather than being slidably inserted from one end of the passage, the detonator passage may include two wall portions, the separation of which corresponds approximately to the length of the detonator. When the detonator is slidably inserted into the passage, the latter would include a single wall portion provided along the passage at least the length of the detonator away from the open end of the passage through which the detonator is inserted.

In this embodiment, the detonator may be retained in position by use of a restraining means for the signal tube.

P 'OPER'Jcc'SPECIFICATIONS\EXPLOSI'E CASING-2doc-04i03102 The restraining means may take the form of a flexible tab provided at, and covering at least a portion of, the open end of the detonator receiving passage. The tab is positioned such that an end of it is displaced (typically by the detonator) when the detonator is inserted into the detonator receiving passage. After the detonator has been inserted in the passage the tab springs back into its original position covering at least a portion of the open end of the passage thereby preventing the detonator from sliding out of the detonator receiving *i passage.

The restraining means may additionally or alternatively take the form of an arm around which the signal tube is passed before being fed back along the casing and out of the blasthole. Alternatively, the restraining means may take the form of a groove in an essentially planar portion of the casing. In this case the signal tube is passed through the groove before being fed back along the casing and out of the blasthole. It will be 15 appreciated that in these embodiments the restraining means would be present toward the leading portion of the casing, i.e. the end of the casing that would be inserted first when loading the blasthole. In other words, in these embodiments the detonator would be reverse primed. When the detonator receiving passage include two wall portions, one of these may include a channel or groove through which the signal tube may pass.

The detonator may be forward primed in which case the casing may comprise a signal tube restraining means at the end of the detonator passage remote from the leading portion of the casing.

The loading member engagement means facilitates insertion of the loaded casing in a blasthole, and may take a variety of forms. Thus, the engagement means may take the form of an elongated sleeve extending from the casing. The external diameter of the end portion of the sleeve may be tapered or stepped to enable a variety of loading members loading hose or tamping rod) to be used, the external diameter of the sleeve being at some point just less than the diameter of the loading member being used. This allows a single casing to be used with a variety of loading members with different diameters. In an alternative embodiment the loading member engagement means may comprise a P \OPERJccSPECIFICATIONSEXPLOSl\'E CASING-2 doc-04103102 -6substantially planar fin extending from the casing. The end of the fin is adapted to engage a loading hose and is typically sized such that at least a portion of the fin will be enclosed by the hose when loading of the casing takes place. The width of the end of the fin may vary so as to provide flexibility as to the dimensions of the loading hose which may be used. In this embodiment, for rigidity and to improve engagement with the end of a loading hose the fin may comprise one and preferably two further fins extending in perpendicular directions from it. The loading hose engagement means may additionally *i include one or more tabs to facilitate engagement with the loading hose.

In an embodiment the external diameter of the sleeve may be substantially less than that of the loading hose used to position the casing. In this case during blasthole loading the signal tube and/or detonating cord are tensioned in order to tilt the casing, and thus the sleeve such that the sleeve is caused to engage the inside surface of the loading hose.

Contact of the sleeve and loading hose in this way facilitates loading, although in this 15 embodiment it is likely that the end of the loading hose will also abut against the end of the detonator cord receiving passage and/or detonator receiving passage.

In another embodiment, the end of the casing remote from the loading member engagement means may comprise a guide means which helps to guide the casing over discontinuities and obstructions in the blasthole during loading. In this embodiment, the leading end of the casing would usually have a rounded end portion. For example, the casing may be provided with a nose cone. Alternatively, the casing may comprise a pair of perpendicular intersecting fins which define a rounded leading portion. The trailing portions of these fins may also be rounded to allow for easy removal of the casing from the blasthole if necessary.

The casing may also comprise means for centring and/or retaining the casing in a blasthole.

For instance, the casing may include blasthole engagement means in the form of legs which extend outwardly and rearwardly from the intended leading portion of the casing.

The legs are resilient and are deflected inwardly as the casing is pushed into a blasthole.

The legs assist in centring the casing in the blasthole and also prevent unwanted movement of it. The ends of the legs may be shaped to engage the blasthole walls, and thus include a P.OPERUkccSPECIFICATIONS EXPLOSI'E CASING.2.do-0410302 -7prong or spike. Alternatively, the ends of the legs may be rounded to avoid engagement with the blasthole walls, in order to allow the casing to be withdrawn from the blasthole if necessary. This means may be provided as a separate component which is attachable to the casing, or as integral to the casing.

The casing, and components thereof, may be made of a variety of materials including plastics and paper/cardboard. Typically, the casing will be made of an injection mouldable plastic, such as polypropylene or high impact polystyrene.

10 The invention further provides a casing loaded with detonator cord. It is envisaged that this is the form in which the product would be supplied to end-users. The end-user would then insert the detonator (and signal tube) and carry out blasthole loading as described.

The length of detonating cord associated with the casing may obviously be varied, and the end-user would select a suitable loaded casing based on the length of the blasthole in 15 which the cord is to be loaded.

Conventional types of detonator cord may be used. Typically, the cord has a diameter of 3-15 mm and a charge density of 2 g/m to 100 g/m. The charge density of the cord would be selected based on, amongst other things, the material being blasted. The cord contains an explosive such as pentaerythritol tetranitrate (PETN) or cyclo-l,3,5-trimethylene-2,4,6trinitramine (RDX).

In a preferred embodiment the detonator cord is sufficiently flexible so that it is not selfsupporting. In this embodiment when the cord is run along a horizontal blasthole it will fall under its own weight and lie along the lower surface of the blasthole. Depending on the blasthole diameter, positioning the cord in this way results in a space between the cord and the upper surface of the blasthole. In turn this helps to reduce the blast energy in that direction. This is particularly useful in perimeter blastholes which will when blasted lead to formation of the ceiling of a tunnel. Reduced energy in this direction may help to provide smooth, unfractured surfaces. The flexibility of the cord may be manipulated by varying the plastic used for the cord sheath and/or the yarn typically included in the cord to bind the explosive. The extent to which the explosive is compacted in the sheath may also P.'OPERJcc SPECIFICATIONS'EXPLOSIVE CASING.2 doc-04103)02 -8be influential.

The invention further provides a casing loaded with detonator cord and a detonator.

Conventional detonators may be used, although the design of the casing will obviously dictate the dimensions of the detonator which may be used, and vice versa. The detonator may be electric, non-electric or electronic.

o. The invention further provides a method of loading a blasthole with a detonator cord and detonator using the casing described herein. After the end of the detonator cord (of 10 appropriate length relative to the length of the blasthole) and detonator have been positioned in the casing a loading member is used to push the casing to the toe of a blasthole, the member engaging the loading member engagement means of the casing. As the casing is pushed along the blasthole it pulls detonator cord with it. It will be appreciated that the cord must be fixed firmly in the casing to facilitate this. Signal tube 15 running from the detonator is also pulled along the blasthole toward the toe. In a preferred embodiment, when the loaded casing is in the desired position at or in proximity to the toe of the blasthole, a volume of bulk explosive may be pumped through a loading hose thereby surrounding the casing. This can help to fix the casing in position in the blasthole but, more importantly, provides additional explosive energy at the toe of the blasthole, as is desired due to the greater confinement at that location. The result is improved performance on blasting. In this case the loading member will usually be a loading hose through which bulk explosive may be supplied when the casing is suitably positioned.

Conventional bulk explosives may be used. The same effect may be achieved by securing the casing at the desired position using a packaged explosive. In this case it is likely that the casing will be pushed along the blasthole using a tamping rod, the rod then also being used to position the packaged explosive and tamp it into position. The packaged explosive essentially locks the casing in position.

The invention further provides a method of blasting which comprises loading a blasthole as described herein and then firing the detonator via the signal tube. In turn this causes detonation of the detonator cord. The detonator may be initiated in conventional manner.

The invention is useful in any blasting operation where it desired to have a smooth profile.

P OPER'Jcc\SPECIFICATIONS\EXPLOSIVE CASING-Zdoc-04/03/02 -9- The invention is particularly well-suited to perimeter blasting in an underground mining operation, and to pre-splitting in rock or concrete (in civil applications).

Embodiments of the present invention as illustrated in the accompanying drawings in which: 0ooo oo:. Figure 1 illustrates a perspective view of a casing (open) of the present invention; and o Figure 2 illustrates a perspective view of a casing (closed) of the present invention.

o• Figures 1 and 2 illustrate a casing comprising a detonator cord receiving passage (2) S. having detonator cord retaining means in the form of a series of spike projections A So* detonator receiving passage is provided adjacent to the detonator cord receiving passage The passages are essentially cylindrical and are closed by movement of 15 respective portions about a longitudinal hinge. The detonator cord receiving passage (2) and detonator receiving passage have a common longitudinal axis The detonator receiving passage has an open end and a closed end A portion of the casing (1) which defines the detonator receiving passage is provided with tabs and another portion of the casing provided with corresponding tab-recesses (10) to allow secure closure of the passages 4).

The detonator (not shown) is retained in place in the detonator receiving passage by a flexible tab (11) the end of which will be provided over the open end of the passage (4) when the casing is in use. Insertion of a detonator into the passage displaces the flexible tab (11) until the end of the detonator moves beyond the tab At that point the tab (11) springs back into its original position thereby preventing the detonator from sliding out of the passage through the open end The casing also includes a slot (12) through which signal tube (not shown) may be passed before being fed back along the casing and out of the blasthole being loaded. The signal tube is typically crimped to the end of the detonator. Securing the signal tube to the casing also serves to secure the detonator in position.

P \OPER\kc'SPECIFICATIONS\EXPLOSIVE CASING-2 do-O,/30102 The casing also includes a loading member engagement means (13) in the form of two substantially planar fins (14, The casing shown is also provided with guide means (16) to assist in guiding the casing over discontinuties and/or obstructions in the blasthole. The leading edge of the casing is rounded.

In use detonator cord (not shown) is positioned in the portions of the open casing which 10 define the detonating cord receiving passage The passage is then formed by closure of the parts of the casing around the hinge The spike projections will grip the detonating cord and retain it in place. The casing is closed by means of the tabs and tab recesses In closing the casing in this way the detonator receiving passage is defined. The detonator may then be slidably inserted into the passage (4) 15 through the open end thereof The detonator may be secured in position as described.

Once loaded the casing may be positioned in a blasthole using a loading member to engage the loading member engagement means and subsequently detonated by initiation of the signal tube.

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 (15)

1. A casing comprising: a detonator cord receiving passage having detonator cord retaining means; a detonator receiving passage adjacent to or in communication with the detonator cord receiving passage; detonator retaining means; and S. loading member engagement means. ee 10 2. The casing of claim 1, wherein the detonator cord receiving passage is adapted to receive and retain a portion of detonator cord.

3. The casing of claim 1 or 2, wherein the detonator cord receiving passage comprises a longitudinal hinge which enables it to be opened in order to receive a detonator cord.

4. The casing of claim 3, wherein an inside surface of the passage includes one or more detonating cord engaging projections which will grip a detonating cord when the passage is closed by movement of the respective sides about the longitudinal hinge. The casing of any one of claims 1 to 5, wherein the detonator receiving passage and detonator cord receiving passage share a common boundary.

6. The casing of any one of claims 1 to 5, wherein the detonator receiving passage includes means for retaining the detonator in place.

7. The casing of any one of claims 1 to 6, wherein the loading member engagement means comprises an elongated sleeve extending from the casing.

8. The casing of any one of claims 1 to 6, wherein the loading member engagement means comprises a substantially planar fin extending from the casing.

9. The casing of any one of claims 1 to 8, wherein the end of the casing remote from the loading member engagement means comprises a guide means which helps to guide the casing over discontinuities and/or obstructions in a blasthole during loading. P' OPER\JccSPECIFICATIONSNEXPLOSIVE CASING-2 dc.04/03102

12- The casing of any one of claims 1 to 9, wherein the blasthole engagement means comprises legs which extend outwardly and rearwardly from the intended leading portion of the casing. 11. The casing of claim 10, wherein the ends of the legs are rounded to avoid engagement with blasthole walls thereby allowing the casing to be withdrawn from a blasthole. 12. The casing of any one of claims 1 to 1, wherein the loading member engagement means is adapted to engage a loading hose.

13. The casing of any one of claims 1 to 11, wherein the loading member engagement a means is adapted to engage a tamping rod.

14. A casing substantially as hereinbefore described with reference to the 15 accompanying figures.

15. A casing as claimed in any one of claims 1 to 14, loaded with detonator cord.

16. A casing as claimed in any one of claims 1 to 14, loaded with detonator cord and a detonator.

17. A method of loading a blasthole which comprises positioning a detonator and detonator cord respectively in the detonator receiving and detonator cord receiving passages of a casing as claimed in any one of claims 1 to 14 and positioning the casing in the blasthole by means of a loading member in contact with the loading member engagement means of the casing.

18. A method according to claim 17, wherein the casing is locked in place in the blasthole by a volume of bulk explosive or by a packaged explosive.

19. A method according to claim 17 substantially as hereinbefore described. P:'OPER\Jrc\SPECIFICATONS\EXPLOSIVE CASING.2.d-01403102 -13- A method of blasting which comprises loading a blasthole by a method as claimed in claim 17 or 18 and firing the detonator via a signal tube attached to the detonator. Dated this 4 t h day of March 2002 Initiating Explosives Systems Proprietary Limited DAVIES COLLISON CAVE Patent attorneys on behalf of the applicant.