BLASTING CARTRIDGE

A cartridge (10) is provided having a receptacle (12) with propellant (14) therein and an open end with a stemming device (16) secured to the open end to form a substantially closed container. The stemming device (16) is operable to result in radial expansion thereof and has a static member (18) secured to the receptacle (12) and a piston (20) movable, at least partially within the container, relative to the static member (18) and the receptacle (12). The cartridge is configured such that ignition of the propellant (14) causes movement of the piston (20) to operate the stemming device (16) and cause radial expansion thereof before the receptacle (12) ruptures.

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Description
FIELD OF THE INVENTION

This invention relates to rock breaking and more specifically to cartridges used for breaking rock.

The term “rock” as used herein covers natural rock and also includes concrete or similar structures that are to be broken up.

BACKGROUND TO THE INVENTION

Traditional methods of blasting or breaking rock in quarries and mines make use of high energy explosives, often referred to as detonating explosives. High energy explosives crush and pulverise the rock which can then be removed for either retrieving the sought after mineral within the rock or for disposal of the rock.

The problem with detonating explosives is that the ignition of the explosive is followed by a violent shockwave which may cause rock fragments to be projected from the explosion site. The projected rock fragments pose a great risk to mine workers, thus commonly requiring a large area surrounding the blasting site to be cleared. Furthermore, the pulverisation of the rock may create a thick cloud of dust to surround the blasting site, making it impossible to work at the site for extended periods of time.

The problems associated with the traditional methods of blasting or breaking rock resulted in the development of rock breaking explosives commonly referred to as non-detonating explosives. Non-detonating explosives function by containing and directing rapidly expanding gases within and against the rock, thereby causing the rock to break without the violent shock wave and pulverisation of the rock.

Non-detonating explosives are used by drilling boreholes into the rock, inserting non-detonating explosive cartridges containing a gas generating compound, commonly a propellant, into the boreholes and igniting the cartridges. Prior to ignition of the cartridge, the borehole must be stemmed by packing particulate material, usually sand, into the borehole after insertion of the cartridge. The packed particulate material keeps the gases created by the cartridge within the borehole once the cartridge has been ignited resulting in high pressure being created within the borehole.

A drawback of non-detonating explosives is that adequate stemming of the borehole is of utmost importance, failure of which may cause some of the gas to escape thereby reducing the pressure exerted onto the rock and causing the cartridge to be less effective. Furthermore, stemming of boreholes that run at a downward slope may be difficult thus often being very time consuming to achieve. Also, stemming material needs to be transported to the blasting site.

A self-stemming cartridge is proposed in U.S. Pat. No. 8,342,095. One embodiment of the cartridge disclosed in the patent has a sheath which is tapered radially inwardly at one end and which houses a gas generating compound and a cone. The patent discloses that the cone is forced in the direction of the taper upon ignition of the gas generating compound and forces the sheath outwardly, thereby stemming the borehole.

Drawbacks of the disclosed cartridge include the cartridge having a plug at one end which will be ejected from the cartridge prior to stemming, thus causing the stemming operation to stop and the cartridge to be ejected from the borehole without breaking any of the rock.

Furthermore, the sheath is of a solid construction. This will permit gas to escape about the periphery of the cone when the sheath flexes outwardly after ignition and from the gas pressure within the cartridge. It is thus highly unlikely that the cone will operate to expand the sheath. Also, such flexing will cause the development of empty pockets within the sheath into which the gas can move, thus causing a drop in pressure within the cartridge and resulting in a cessation of combustion of the gas generating compound.

A further disadvantage of the cartridge disclosed in U.S. Pat. No. 8,342,095 is that the sheath is a solid tube and thus unlikely to expand sufficiently to stem the hole. Also, the detonator cord runs between cone and sheath creating a gap which will permit gas to escape and thus prevent proper working of the cartridge during manufacture and handling. The gap will also permit the propellant to leak out of the cartridge. Furthermore, the detonator must be inserted into the cartridge before it can be filled with propellant. This will create an inherently dangerous situation during assembly as there is a possibility of the detonator igniting the propellant during assembly.

There is no evidence of the cartridges proposed by U.S. Pat. No. 8,342,095 being commercially available and the applicant believes this to be a result of these not being capable of functioning for the reasons given above.

In this specification, “propellant” shall have its widest meaning and include any suitable gas producing material, and “igniter” shall mean any device capable of causing the propellant to produce gas.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a cartridge comprising a receptacle for holding a propellant therein and having an open end with a stemming device secured to the open end to form a substantially closed container, the stemming device being operable to result in radial expansion thereof and having a static member secured to the receptacle and a piston movable, at least partially within the container, relative to the static member and the receptacle, and configured such that ignition of the propellant causes movement of the piston to operate the stemming device and cause radial expansion thereof before the receptacle ruptures.

Further features of the invention provide for an igniter to be secured within the stemming device with an operating cord extending therethrough; for the igniter to be preferably located in a socket in the piston; for the stemming device to be shaped to provide a sliding fit within a borehole; and for the receptacle to be cylindrical.

Still further features of the invention provide for the receptacle to be made of a plastics material; for the piston to be partly located within the receptacle; for the part of the piston located within the receptacle to provide a sliding fit within the receptacle.

Yet further features of the invention provide for the static member to be secured over the open end of the receptacle; for the static member to provide a snap fit over the receptacle; for the static member to have a plurality of holes therein for receiving buttons on the receptacle; alternately for the static member to provide a screw fit on the receptacle.

Further features of the invention provide for a nozzle to extend from the piston at the end of the piston that is located within the receptacle; the nozzle being radially inwardly stepped from the end of the piston; and for the nozzle to operatively extend into the propellant held within the receptacle.

Still further features of the invention provide for the piston and static member to have cooperating bearing surfaces, at least one, preferably both, of which is tapered such that relative movement causes radially outward expansion of either the static member or the piston.

Yet further features of the invention provide for a stemming device to be secured to opposite ends of a tubular receptacle; for either or both stemming devices to have an igniter associated therewith; and for the stemming devices to be of the same or different configuration to each other.

According to one aspect of the invention the static member has a tapered bore and at least one longitudinal slit therein to permit radial expansion thereof.

Further according to this aspect of the invention the static member has a plurality of circumferentially spaced slits, each slit extending substantially the length of the tapered bore.

According to a further embodiment of the invention the static member of the stemming device has a tubular body with a number of ports therein and an anchor member associated with each port such that movement of the piston causes radially outward displacement of each anchor member; for each anchor member to have a lug which extends centrally from one side of a panel, each lug providing a complementary fit within a port and the panels configured to extend over a part of the outer surface of the body; for the ports to be elongate and extend longitudinally along the body near its free end; for the end of the piston engaging the lugs to be tapered; and for the free end of each lug to have a complementary taper to the piston.

The invention also provides a piston for a cartridge substantially as defined above, the piston having a cylindrical section providing a sliding fit within a tubular receptacle and a tapered section which is movable within an expansion sleeve to cause radial expansion thereof, with a bore extending substantially axially through the piston and a nozzle extending from the end of the piston locatable within the receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only with reference to the accompanying representations in which:

FIG. 1 illustrates a side elevation of a cartridge according to a first embodiment of the invention;

FIG. 2 illustrates a longitudinal section of the cartridge illustrated in FIG. 1;

FIG. 3 illustrates a side elevation of the receptacle of the cartridge illustrated in FIG. 1;

FIG. 4 illustrates a longitudinal section of the receptacle illustrated in FIG. 3;

FIG. 5 illustrates a side elevation of an expansion sleeve forming a static member of the cartridge illustrated in FIG. 1;

FIG. 6 illustrates a longitudinal section of the sleeve illustrated in FIG. 5;

FIG. 7 illustrates an end view of the sleeve illustrated in FIGS. 5 and 6;

FIG. 8 illustrates a plan view of one of the two parts of a first embodiment of a piston;

FIG. 9 is a section through the part of FIG. 8;

FIG. 10 illustrates an end view of the part illustrated in FIG. 8;

FIG. 11 illustrates a three-dimensional view of an alternative embodiment of a piston;

FIG. 12 illustrates a longitudinal section of the piston illustrated in FIG. 11;

FIG. 13 illustrates a side elevation of a cartridge according to a second embodiment of the invention;

FIG. 14 illustrates an exploded three-dimensional view of a cartridge according to a third embodiment of the invention housing the piston of FIGS. 11 and 12;

FIG. 15 illustrates a three-dimensional view of the cartridge illustrated in FIG. 14;

FIG. 16 illustrates a three-dimensional view of a cartridge according to a fourth embodiment of the invention;

FIG. 17 illustrates a longitudinal section of the cartridge illustrated in FIG. 16;

FIG. 18 illustrates an exploded three-dimensional view of the cartridge illustrated in FIG. 16 housing the piston of FIGS. 11 and 12;

FIG. 19 illustrates an end view of a stemming device of the cartridge illustrated in FIGS. 16 to 18;

FIG. 20 illustrates a longitudinal section of the stemming device of the cartridge illustrated in FIG. 19;

FIG. 21 illustrates a longitudinal section of a cartridge according to a fifth embodiment of the invention;

FIG. 22 illustrates a longitudinal section of a cartridge according to a sixth embodiment of the invention;

FIG. 23 illustrates a longitudinal section of a cartridge according to a seventh embodiment of the invention;

FIG. 24 illustrates a longitudinal section of a cartridge according to an eight embodiment of the invention; and

FIG. 25 illustrates a side elevation of a cartridge according to a ninth embodiment of the invention.

 DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

The invention provides a cartridge having an elongate, preferably cylindrical, receptacle which holds a propellant and has an open end with a stemming device secured to the open end to form a substantially closed container. The stemming device has a static member, typically a sleeve, which is secured to the receptacle and a piston which is operable to move, at least partially within the container, relative to the static member and the receptacle to result in radial expansion of the stemming device. To this end the piston and static member have cooperating bearing surfaces, at least one, preferably both, of which is tapered such that relative movement causes radially outward expansion of either the static member or the piston.

An igniter is secured within the stemming device, preferably within a socket in the piston, with an operating cord extending therethrough. Ignition of the propellant within the receptacle causes production of gas within the container which in turn causes movement of the piston. This results in operation of the stemming device and radial expansion thereof.

The receptacle and stemming device are configured to resist rupture until at least partial, preferably complete, operation of the stemming device has been achieved. To this end the receptacle and stemming device are made of a rigid plastics material, but any suitable materials can be used. Complete expansion of the stemming device is that permitted by the borehole and compression or deformation of the material of the stemming device.

To achieve proper operation of the stemming device, it is also necessary to prevent the receptacle from disengaging from the stemming device after ignition of the propellant. One manner of achieving this is for the stemming device to provide a snap fit over the end of the receptacle through radially outward resilient deformation of the stemming device over a corresponding formation or formations on the receptacle. With the cartridge in position in a borehole, disengagement can be prevented by ensuring a sliding fit of the stemming device in the borehole which prevents outward deformation thereof. It will be appreciated, however, that the stemming device can be secured to the receptacle in any suitable manner, including through a screw or bayonet-type fit.

Shaping the stemming device to have a sliding fit within a borehole also has the result that minimal radial expansion of the device is required for it to be effective in stemming the borehole. It will be appreciated that the receptacle need not have the same outer dimensions as the stemming device. This has the advantage that one receptacle size can be used with different sized stemming devices, each of which provides a sliding fit within a different sized borehole.

The two-piece configuration of the cartridge of the invention, the receptacle with stemming device secured thereto, offers numerous advantages. Safety is greatly enhanced as the receptacle can be filled with propellant and transported separately from the igniter and stemming device. These can be fitted on-site so that minimal risk of accidental ignition of the propellant is achieved.

Also, the same stemming device can be fitted to cartridges containing different amounts of propellant and vice versa; the same cartridge can be secured to different diameter stemming devices intended for use with different borehole diameters. Thus multiple cartridge configurations can easily be achieved. This provides for both ease of manufacture and ease of use.

Furthermore, the two-piece configuration permits different materials to be used for the receptacle and stemming device. Thus, the receptacle can be made of a plastics material which permits it to undergo relatively large outward deformation before bursting while the stemming device can be made of a harder material which is more resistant to deformation and forms and effective plug within the borehole. Gas can thus be contained within the receptacle, which expands and conforms to the dimensions of the borehole, while the stemming device is being operated by the pressure of the gas.

Various embodiments of a cartridge are now described, by way of example only.

A cartridge (10) is shown in FIGS. 1 and 2 and includes a cylindrical receptacle, in this embodiment a tube (12), filled with a propellant (14). A stemming device (16) having a static member (18) and a piston (20) movable relative to the static member is secured to the tube (12). In this embodiment the static member (18) is provided by a split expansion sleeve and the piston (20) has a cone at one end. The tube (12) and stemming device (16) together define a substantially closed container.

The tube (12) has a domed closed end (22) and is open at the other end (24). At a zone approximately one quarter of the length of the tube (12) from the open end there is a circumferentially extending rib (26) which is bounded by an inclined surface (28) (FIGS. 3 and 4) and a radial surface (30).

The sleeve (18) has a securing end (32) and a free end (34) and has longitudinally extending slits at both ends. More specifically there are four slits (36) in the securing end (32) and three slits (38) which extend approximately half way along the sleeve (18) in the free end (34). The slits (36, 38) in both ends are equally spaced around the sleeve. Of course any suitable number of slits can be provided. For example, there can be a single slit at the securing end and two slits or more than three slits at the free end.

Adjacent its securing end (32) the sleeve (18) has an internal groove (40) the shape of which matches that of the rib (26). The section of the sleeve (18) adjacent the free end (34) is formed with circumferentially extending, axially spaced ribs (42) between which there are grooves (44). Internally the sleeve (18) has a bore (46) which is cylindrical in shape over a portion of its length and tapering in shape over the remainder. The bore (46) decreases in cross-sectional area in the direction away from its cylindrical part from the securing end to the free end. The slits (38) extend the full length of the tapering bore of the sleeve and part way along the length of the sleeve which has the cylindrical bore.

The piston (20), in this embodiment, is formed by two parts (48). Turning now to FIGS. 8, 9 and 10, the part (48) illustrated constitutes one half of the piston (20). The part (48) has a flat surface (50) from which two pins (52) protrude and in which there are two sockets (54). A groove (56) extends along the centre line of the surface (50). At the larger end the groove (56) enters a central recess (58) in the surface (50).

The cartridge is assembled by placing the tube (12) in a jig in an upright position. The propellant (14) is then poured into the tube (12) and tamped down.

A small quantity of material which produces a flame when ignited, for example black powder, is then placed in the cavity or socket formed by the adjacent recesses (58) of the parts (48) of the piston (20) which are placed face-to-face with the pins (52) in the sockets (54). The longitudinal axis of the cone is in the plane of the flat faces of the parts (48) that are in contact. The material can be in particulate form or moulded into the form of a sleeve as shown at (60) in FIG. 2.

An igniter (62) is also placed in the socket. A foil cover (64) is adhered to the piston (20) to close the cavity. An operating cord, in this embodiment a fuse wire (66), attached to the igniter runs along the bore formed by the registering grooves (56). A thin layer of adhesive can be applied to the surfaces (50) if desired before they are pressed together.

The outer surface of one end of the piston is cylindrical and is stepped so as to form a spigot which slides into the tube (12) when the piston is pressed down onto the open end of the tube (12). A shoulder at the end of the spigot limits the depth of penetration of the piston into the tube (12). The opposite end is conical and forms a complementary fit within the tapering portion of the sleeve (18).

The free end of the fuse wire (66) is threaded through the sleeve (18) (from left to right as viewed in the drawings) and the piston (20) inserted into the tube (12) until it is in the position shown in FIG. 2.

The securing end (32) of the sleeve (18) is then pushed over the open end (24) of the tube (12) until the rib (26) snaps into the groove (40) which locks the tube (12) to the sleeve (18).

The cartridge (10) is now fully assembled and ready for use by pushing it, domed end (22) leading, into a drilled borehole in the rock. If the borehole is horizontal then, using a stick of suitable length, the cartridge is pushed as far along the borehole as is required. If the borehole is vertical the cartridge is just dropped in.

When the igniter (62) is operated, the material in the socket or chamber ignites, producing a flame and bursting the foil (64) so that a flame reaches the propellant (14). Ignition of the material in the socket raises the pressure sufficiently to exert some force on the piston (20) to start the stemming procedure. When the propellant (14) ignites, gas is generated which also forces the piston (20) to move relative to the sleeve (18). Movement of the piston (20) within the sleeve (18) causes radial expansion of the sleeve (18) forcing the ribs (42) outwardly into contact with the surface of the borehole. Whilst there is some gas leakage through the slits (38), it is insignificant and the bulk of gas generated is retained in the container provided by the tube (12) and stemming device (16). This eventually causes the tube (12) to burst releasing the gas into the borehole. The grip between the ribs (42) in the expanded condition of the sleeve (18) and the rough surface of the drilled borehole prevents the cartridge (10) from moving along the borehole and traps the gas within the borehole causing the rock to fracture as a result of the high pressure created by the gas.

The cartridge has been found to be highly effective in breaking rock without the need for any additional stemming material. It thus completely eliminates the need for the time-consuming and costly procedure of using stemming material.

The stemming device (16) remains attached to the tube (12) during stemming as the sliding fit between the sleeve and borehole prevents sufficient radial expansion for the sleeve (18) to disengage from the rib (26). Also, the portion of the sleeve (18) which surrounds the end of the tube (12) provides circumferential reinforcement which assists in preventing radial expansion of the tube in that area and the consequent escape of gas between the piston and tube. It is thus preferable that the sleeve extend over the tube to at least the depth of the piston in the tube, preferably further. Alternatively, some form of circumferential reinforcement, such as a thickening of the sides wall can be provided to assist in preventing radial expansion of the tube about the piston.

The cylindrical end of the piston acts to keep the piston aligned within the sleeve during its travel. This helps ensure proper expansion of the stemming device and avoids potential misalignment which may occur with a purely conical piston moving within a tapered bore. Misalignment can result in incomplete stemming and also in gaps being formed between the piston and sleeve which permit gas to escape therethrough. Both of these situations would have an negative effect on the performance of the cartridge.

It will be appreciated that many embodiments of a cartridge exist which fall within the scope of the invention, particularly regarding the configuration and operation of the stemming devices, the method by which it is secured to the receptacle and the configuration of the receptacle.

For example, as shown in FIGS. 11 and 12, the piston (70) can be of one-piece construction and have a cylindrical body (68) with a first end (71) and a second end (72). A nozzle (74) extends axially from the first end (71) and is provided by a radially inwardly stepped projection. The second end (72) is inwardly tapered from a radially outwardly stepped shoulder (76). A bore (78) extends axially through the piston (70) and is radially enlarged adjacent the first end (71) to form a chamber (80). Flame producing material, for example black powder, is placed into the chamber (80) at the first end (71) of the piston (70) as described above.

This piston configuration has been found to be particularly effective. The additional flame producing material produces a sustained, high temperature flame. This permits a standard igniter to be used in the cartridge. Such igniters have been found to produce erratic propellant ignition when used on their own, particularly with relatively large propellant volumes. Furthermore, although the precise mechanism is not fully understood, the nozzle appears to assist in creating a flame jet which is highly effective in initiating and maintaining propellant ignition.

FIG. 13 illustrates a second embodiment of a cartridge according to the invention. In this embodiment buttons (90) are provided on the surface of the tube (12.1). Each button has an inclined camming surface and a locking surface which intersects the camming surface. The sleeve (18.1) has complementary holes (92) for receiving the buttons (90). As the end (94) of the sleeve (18.1) is pressed onto the tube (12.1) it rides up over the camming surfaces until the holes (92) are reached. With the holes (92) properly aligned, the buttons (90) snap into the holes (92). The locking surfaces of the buttons (90) engage the peripheries of the respective holes (92) to prevent the sleeve (18.1) from being pulled back off the tube (12.1).

Alternatively, as shown in FIGS. 14 and 15, the sleeve (18.2) can have holes (92.2) for receiving buttons (90.2) with corresponding slits (96) extending from the end (98) of the sleeve (18.2) centrally into each hole (92.2). With the piston (70) in position in the open end (24.2) of the tube (12.2), the end (98) of the sleeve (18.2) is forced over the closed, rounded end (22.2) of the tube (12.2) until the buttons (90.2) locate within the respective holes (92.2). No further movement of the sleeve in the direction of the open end of the tube is permitted by this arrangement.

This configuration has been found to work particularly well as it facilitates assembly of the cartridge and eliminates the potential of the sleeve being separated from the tube during expansion of the stemming device.

FIGS. 16 to 20 illustrate a cartridge according to a further embodiment of the invention. In this embodiment a screw thread (100) at the open end of the tube (12.3) cooperates with a complementary thread (102) provided internally of the sleeve (18.3) to secure the sleeve to the tube.

The sleeve (18.3) has three elongate, longitudinally extending, circumferentially spaced ports (104) at its free end (106) and an anchor member (108) is associated with each port (104). Each anchor member (108) has a lug (110) which extends centrally from one side of a panel (112). On the opposite side, the panels each having axially spaced ribs (42.2) between which there are grooves (44.2). Each lug (110) provides a complementary, sliding fit within a port (104) with each panel (112) providing a complementary fit over part of the outer surface of the sleeve (18.3).

The free end (114) of each lug (110) abuts the piston (70.2) and has a taper complementary thereto. When the cartridge is ignited, the piston (70.2) moves towards the sleeve (18.3), causing the tapered end of the piston (70.2) to engage the lugs (110) of the anchor members (108). This displaces the anchor members (108) outwardly from the sleeve (18.3) resulting in radial expansion of the stemming device.

It will be appreciated that the stemming device may be varied in design to allow for the radial expansion and engagement with the walls of the borehole. For example, the sleeve (18) need not have slits to permit expansion, but could have lines of weakness or any other suitable configuration. In particular, it is not required that both the static member (18) and piston (20, 70) have tapered or inclined bearing surfaces. It is simply required that radial expansion occurs upon relative movement of the piston (20, 70) and static member (18).

For example, as shown in FIG. 21, the piston (120) could have a radiused bearing surface (122) which moves within the tapered cavity (124) of the sleeve (126) to cause radial expansion of the sleeve (126).

Referring to FIG. 22, the piston (130) can provide a sliding fit over the end of the tube (12) and within the static member (132) which is in turn secured to the tube (12).

As shown in FIG. 23, the static member (140) could be secured to a post (142) extending centrally within the tube (12) and integral therewith. The static member (140), in this embodiment, has a bearing surface (144) which tapers outwardly from the post (142) and cooperates with a complementary bearing surface (146) on the piston (148), a cylindrical body which slides within the tube (12) over the post (142). Ignition of the propellant causes the piston (148) to move against the static member (140) with a resultant radially outward expansion of the piston (148).

It is also possible for rotational movement to be achieved and employed by the stemming device. For example, as shown in FIG. 24, the piston (200) has one end (202) which is a sliding fit within the tube (12). The opposite end (204) has a smaller diameter which is tapered. Intermediate the ends (202, 204) the piston is radially thickened (206) and provided with a course screw thread which cooperates with a complementary thread (208) provided internally of the static member (210) which has a sleeve-like configuration and fits over the tube (12) in a manner analogous to that described with reference to FIGS. 1 and 2. The thread (208) runs from about the end of the tube (12) to an inward thickening (212) which provides, at one end (214), a bearing surface complementary to, and abutting, the end (204) of the piston (200). The opposite end (216) of the thickened portion (212) is similarly, outwardly tapered from the centre. A shaft (218) extends centrally from the end (204) of the piston (200), through a passage (220) in the thickened portion (212). The end (222) of the shaft is screw threaded and has a complementarily threaded nut (224) secured thereto. The nut (224) has a lug (226) extending from one side which registers in a longitudinally extending groove (not shown) in the end (228) of the static member (210) to prevent rotation thereof. The internal end (230) of the nut (224) abuts the end (216) of the thickened portion (212) and is complementarily tapered to provide a conical surface.

In use, gas produced by the propellant forces the piston (200) towards the static member (210) causing it to rotate through engagement with the screw thread. Rotation of the piston (200) also results in rotation of the shaft (218) which is threaded to cause the nut (224) to be drawn inwardly towards the piston (200) and static member (210). This also applies an axial force to the opposite end (216) of the thickened portion (212) which results in its radially outward displacement. The thickened portion (212) is thus subject to compression between the piston (200) and nut (224) and undergoes rapid and effective radial expansion. To effect radial expansion the thickened portion may be segmented.

Clearly, other configurations exist which make use of a rotating piston. For example, the piston could be made to rotate on a post extending from the tube, similarly to that illustrated in FIG. 23, and to drive into the static member with a screwing action to cause radial expansion.

A very important benefit of the cartridge of the invention, in large part a result of the two-piece construction, is that it can be provided with a stemming device (16) at opposite ends of a receptacle (300), as illustrated in FIG. 25. Of course the receptacle (300) would, in this embodiment, be tubular and open at both ends. A removable membrane, or one that can easily be ruptured can be provide over one or both ends to retain the propellant in the tube until the stemming devices have been fitted. Such a cartridge finds application in relatively thin structures, such as walls, where the end of the borehole may not provide sufficient resistance to the expanding gas of the propellant for effective blasting to occur.

Any suitable stemming device, or combination of stemming devices, including those described above, can be used in such a cartridge. An igniter can be associated with each stemming device if desired, but only one igniter will often be sufficient. In such cases, the stemming device which does not have an igniter or operating cord associated with it will either have no passage or socket for these or will have these plugged. Once again, the configuration of the stemming device, that of a static member and piston, means that it is a simple matter to provide different pistons with the same static member.

Clearly, expansion of the stemming device can be achieved in many other ways and many other embodiments of a cartridge which fall within the scope of the invention will be apparent to those skilled in the art.

Claims

1. A cartridge comprising a receptacle for holding a propellant therein and which has an open end, and a stemming device operable to result in radial expansion thereof having a piston movable relative to a static member, wherein the stemming device is secured to the open end of the receptacle to form a substantially closed container, with the static member secured to the receptacle and the piston movable at least partially within the container such that ignition of the propellant causes movement of the piston to operate the stemming device and cause radial expansion thereof before the receptacle ruptures.

2. A cartridge as claimed in claim 1 wherein the cartridge has an igniter secured within the stemming device with an operating cord extending therethrough.

3. A cartridge as claimed in claim 2 wherein the igniter is located in a socket in the piston.

4. A cartridge as claimed in claim 1 wherein the piston is partly located within the receptacle.

5. A cartridge as claimed in claim 4 wherein a nozzle extends from the end of the piston located within the receptacle.

6. A cartridge as claimed in claim 1 wherein the static member is secured over the open end of the receptacle.

7. A cartridge as claimed in claim 6 wherein the static member has a plurality of holes therein for receiving buttons on the receptacle.

8. A cartridge as claimed in claim 1 wherein the piston and static member have cooperating bearing surfaces, at least one of which is tapered such that relative movement causes radially outward expansion of either the static member or the piston.

9. A cartridge as claimed in claim 8 wherein the static member has a tapered bore and at least one longitudinal slit to permit radial expansion thereof.

10. A cartridge as claimed in claim 9 wherein the static member has a plurality of circumferentially spaced slits, each slit extending substantially the length of the tapered bore.

11. A cartridge as claimed in claim 1 wherein the static member of the stemming device has a tubular body with a number of ports therein and an anchor member associated with each port such that movement of the piston causes radially outward displacement of each anchor member.

12. A cartridge as claimed in claim 11 wherein each anchor member has a lug which extends centrally from one side of a panel, each lug providing a complementary fit within a port and the panels configured to extend over a part of the outer surface of the body, for the end of the piston engaging the lugs to be tapered, and for the free end of each lug to have a complementary taper to the piston.

13. A cartridge as claimed in claim 1 wherein a stemming device is secured to opposite ends of a tubular receptacle.

14. A piston for a cartridge as claimed in claim 1, wherein the piston has a cylindrical section providing a sliding fit within a tubular receptacle and a tapered section which is movable within an expansion sleeve to cause radial expansion thereof, with a bore extending substantially axially through the piston and a nozzle extending from the end of the piston locatable within the receptacle.

Patent History
Publication number: 20150053106
Type: Application
Filed: Apr 3, 2013
Publication Date: Feb 26, 2015
Inventor: John Hofmeyr Godsiff (Tortola)
Application Number: 14/390,676
Classifications
Current U.S. Class: Having A Rupturable Or Expandable Casing (102/323)
International Classification: F42D 3/04 (20060101); F42B 3/00 (20060101);