WO2014030139A1

WO2014030139A1 - A stemming device

Info

Publication number: WO2014030139A1
Application number: PCT/IB2013/056813
Authority: WO
Inventors: John Hofmeyr Godsiff
Original assignee: Fowlds 3 Limited; Non-Detonating Solutions (Pty) Limited
Priority date: 2012-08-22
Filing date: 2013-08-22
Publication date: 2014-02-27

Abstract

A stemming device (10) for use with a charge (44) containing a gas producing material in a borehole (46) is provided. The stemming device (10) has a piston (14) movable from a rest position to an operative position relative to a complementary static member (12) to cause radial expansion of the stemming device (10). The piston (14) has a leading end (36) which operatively faces the charge (44) in the borehole (46) and provides a sliding fit within the borehole (46) and which is configured to move under action from the charge (44) or gas produced by the charge (44). The device (10) is further configured to accommodate an actuating tube or cable (20) extending from the charge (44) externally of the borehole (46) and the static member (12) includes formations (24) to engage the sides of the borehole (46).

Description

A STEMMING DEVICE

FIELD OF THE INVENTION This invention relates to rock breaking and, more particularly, it relates to a device for stemming a charge of a gas producing material used in rock breaking.

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 or 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 associated 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 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 that surrounds 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 rock typically associated with detonating explosives.

Non-detonating explosives are used by drilling boreholes into the rock, inserting a non-detonating explosive cartridge containing a gas generating compound, commonly a propellant, into the boreholes and igniting the cartridge. Prior to ignition of the cartridge, the borehole must be stemmed by either packing particulate material or a stemming device into the borehole after insertion of the cartridge. The stemming of the borehole 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, thus causing the rock to fracture.

It is time consuming to use particulate matter, such as sand, as stemming as the hole must be filled and the sand tamped down during filling of the borehole to create an effective seal. It is also difficult to fill holes which are inclined downwardly with particulate material. For this reason, stemming devices have been proposed in the prior art. These typically rely on some form of wedging action to secure the device in position in the hole. Although numerous stemming devices have been proposed in the prior art, these are typically intended for use with detonating explosives. As such, they must be secured in position, that is, expanded in the hole after insertion and before initiation of the explosive. The shock wave produced after detonation cannot be harnessed to activate or expand the stemming device. As far as the applicant is aware, no prior art stemming devices are particularly effective and the use thereof remains limited, thus the use of particulate material for stemming remains widespread.

One reason for prior art stemming devices not being effective may be that it is not possible for the stemming device to manually produce sufficient force, through wedging or similar action, against the side of the borehole. It also appears to the applicant that the rapidity of the shock wave produced by detonating explosives may somehow obviate the need for a locking fit of the stemming device in the borehole. However, with non-detonating explosives it has been found that unless a strong, pressure resistant seal is formed by the stemming device in the hole, the cartridge and stemming device are simply ejected from the hole. This is because gas pressure alone is used to fracture the rock and unless the gas can be contained within the hole it simply escapes without creating any fractures.

A further issue with prior art stemming devices is that once they have been placed in the hole and expanded they become difficult or impossible to remove. This poses a problem with misfires as it then becomes impossible to remove the cartridge from the borehole. As a result, further adjacent holes must be drilled and charged. This is not only time consuming but also dangerous to the operator as the misfired cartridge always has the potential to ignite during the operation.

In this specification, "gas producing material" shall have its widest meaning and include any material which produces gas in a suitably vigorous manner to be useful in breaking rock.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a stemming device comprising a piston movable from a rest position to an operative position relative to a complementary static member to cause radial expansion of the device and wherein the piston has a leading end which operatively faces a charge in a borehole and the piston is configured to move under action from the charge or gas produced by the charge, and wherein part of the piston, preferably the leading end, provides a sliding fit within the borehole and the stemming device includes a passage to accommodate an actuating tube or cable extending from the charge externally of the borehole. Further features of the invention provide for the passage to extend substantially centrally through the stemming device; for a detent to be associated with the passage to operatively prevent withdrawal of the actuating tube or cable therefrom; and for a pressure resistant seal or grommet to be provided within the passage operatively over the actuating tube or cable.

Still further features of the invention provide for formations to be provided on the static member to engage the sides of the borehole.

Yet further features of the invention provide for the leading end of the piston to include a radially extending flange; for the flange to have an outwardly inclined circumferential skirt; and for the skirt to be resiliency flexible. Further features of the invention provide for the piston to have a tapered end that extends within a passage in the static member; and for the passage in the static member to have a taper complementary to the tapered end of the piston. In one embodiment of the invention the static member has a plurality of circumferentially spaced longitudinal slots or lines of weakness; for the slots or lines of weakness to extend from a trailing end toward the leading end of the static member; and for each slot or line of weakness to extend approximately half way along the length of the static member.

In an alternative embodiment of the invention the static member has a tubular body with a number of ports therein and an anchor member associated with each port; for each anchor member to have a lug which extends centrally from one side of a panel; for each lug to provide a complementary fit within a port and the panels to be configured to extend over a part of the outer surface of the body; for the end of each lug opposite the panel to have a complementary taper to the piston; and for the tapered end of the piston to engage the lugs to cause radially outward displacement of each anchor member from the body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only with reference to the accompanying representations in which: illustrates a partial longitudinal section of a first embodiment of a stemming device in accordance with the invention. illustrates a three-dimensional view of the stemming device illustrated in Figure 1 ; illustrates a three-dimensional end view of the stemming device illustrated in Figure 1 ; illustrates a partial longitudinal section of the stemming device illustrated in Figure 1 in use with a cartridge in a borehole; illustrates a three-dimensional view of a skirt for a stemming device; illustrates a sectional side view of the skirt in Figure 5 in use;

Figure 7 illustrates a longitudinal section of a second embodiment of a stemming device in accordance with the invention; illustrates a three-dimensional view of a third embodiment of a stemming device in accordance with the invention; illustrates a longitudinal section of the static member of the stemming device illustrated in Figure 8; illustrates an end view if the static member illustrated in Figures 7; and illustrates a longitudinal section of the stemming device illustrated in Figure 6 in use with a cartridge in a borehole.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

The invention provides a stemming device for use with a cartridge containing a gas producing substance, such as propellant, commonly referred to as non- detonating explosives. The stemming device comprises a static member and a piston, wherein the piston is able to move from a rest position to an operative position relative to the static member so as to cause radial expansion of the stemming device. To accommodate efficient stemming, the static member includes formations for engaging the sides of a borehole.

The piston has a leading end which, in use, faces the cartridge in a borehole and part of the piston, preferably the leading end, provides a sliding fit within the borehole. Ignition of the cartridge causes gas to form resulting in pressure being exerted on the leading end of the piston. The pressure causes the piston to move from its rest position to its operative position to thereby cause radial expansion of the device and effect stemming within the borehole. Figures 1 to 4 illustrate a first embodiment of a stemming device (10) in accordance with the invention. The stemming device (10) includes a static member (12) and a piston (14) which moves relative thereto. The static member (12) is provided by a cylindrical body (16), preferably moulded from a suitable plastics material, with a passage (18) extending axially therethrough. The passage (18) is shaped to receive a shock tube (20) therein, as best illustrated in Figures 3 and 4. Part way along its length, the passage (18) tapers outwardly toward a leading end (22) of the static member (18).

The static member (12) further includes three circumferential grooves (24) spaced apart from a trailing end (26) of the static member, and two longitudinal slots (28) that extend normally to each other, diametrically through the static member (12) from the trailing end (26) approximately half way along the length of the static member (12).

The piston (14) has a tapered end (30) which provides a complementary fit within the tapered portion of the passage (18) of the static member (12). An inwardly extending lip (31 ) about the end of the passage (18) provides a snap fit over the tapered end (3) of the piston (14) and prevents its withdrawal from the passage (18).

A stem (32) extends centrally between the tapered end (30) and a radially extending flange (34) or disc which forms the leading end (36) of the piston (14). An outwardly inclined resiliency flexible skirt (38) extends integrally from the leading end (40) of the flange (34). The flange (34) and the outwardly inclined resiliency flexible skirt (38) provide a sliding fit within a borehole (46), the advantage of which will become apparent from the description further below. A passage (42) extends centrally through the piston (14) and corresponds to the passage (18) in the static member (12) so that the shock tube (20) may be fed through both passages (18, 42) into a cartridge (44) within the borehole (46), as best illustrated in Figures 3 and 4.

A detent (48) is provided at the trailing end (26) of the static member (12) and includes a plate (50) which extends hingedly from a base (52) which is secured to the static member (12). The plate (50) and base (52) are preferably made from a resiliency flexible metal and are formed so that the plate (50) is inclined away from the trailing end (26) of the static member (12) adjacent the opening to the passage (18). An aperture (54) is provided in the plate (50) having the same diameter as that of the passage (18) so as to allow the shock tube (20) to be fed through the aperture (54) and into the passage (18). The plate (50) can be pushed into contact with the trailing end (26) of the static member (12) and when in contact, the aperture (54) is coaxial with the passage (18).

The detent (48) acts to permit the shock tube (20) to be inserted into the passage (18) from the trailing end (26) as friction between the plate (50) and the shock tube (20) moves the plate (50) against its bias towards the trailing end (26) so that the aperture (54) aligns with the passage (18). However, when the shock tube (20) is withdrawn from the passage (18), the plate (50) moves away from the trailing end (26) so that the aperture (54) moves out of alignment with the passage (18). This movement causes the periphery (56) of the aperture (54) distal from the base (52) to bite into the shock tube (20) and prevent further movement and withdrawal thereof.

It will be appreciated that in order to better ensure that the periphery (56) of the aperture (54) bites into the shock tube (20), the periphery may be provided with teeth that are inclined toward the trailing end (26) of the static member (12), and which enable the shock tube (20) to be fed through the aperture (54), but at the same time preventing its withdrawal therefrom. The benefit of the detent (48) will become apparent from the further description below, and it should be noted that the shock tube (20) may be withdrawn from the passage (18) by manually pressing the plate (50) against the trailing end (26) of the static member (12).

Figure 4 illustrates the stemming device (10) of Figures 1 to 3 in use with a charge, in this embodiment a non-explosive cartridge (44) in a borehole (46). Once the cartridge (44) has been inserted into the borehole (46), the stemming device (10) is inserted into the borehole (46) with the shock tube (20) extending therethrough. An igniter (47) or detonator is secured to the end of the shock tube (20) in conventional fashion and located within the cartridge (44) to cause ignition thereof. The igniter (47) is typically crimped over the shock tube (20) and has a diameter only slightly larger than that of the shock tube (20). The passages (18, 42) are typically of sufficient diameter to accommodate the igniter (47), but may also be sized to only accept the shock tube (20), in which case the igniter (47) will be fitted after inserting the shock tube (20) through the stemming device (10). The stemming device (10) is inserted into the borehole (46) with the skirt (38) adjacent the cartridge (44). The radially extending flange (34) has a circumference of approximately that of the borehole (46) to ensure a sliding fit within the borehole (46), while the skirt (38) has a circumference slightly larger than that of the borehole (46) so that when the stemming device (10) is inserted into the borehole (46), the skirt (38) deforms slightly inwardly, thereby ensuring a sealing fit against the sides (58) of the borehole (46).

Insertion of the stemming device (10) into the borehole (46) after the cartridge (44) causes the skirt (38) to engage with the sides (58) of the borehole (46), as well as the leading end (38) of the piston (14) to engage the cartridge (44). Once the cartridge (44) abuts the end (59) of the borehole (46), further movement of the stemming device (10) against the cartridge (44), for example by pushing it with a stick or rod (not shown), causes the piston (14) to move from its rest position deeper into the passage (18) in the static member (12). This causes partial expansion of the static member (12) and is continued until the static member (12) engages the sides (58) of the borehole (46) creating resistance to further movement. In this condition the stemming device (10) is lightly wedged into the borehole (46).

Ignition of the cartridge (44) causes the production of gas, which then attempts to escape from the borehole (46). However, the flange (34) and skirt (38) effectively prevent the gas from escaping. The pressure created in the confined space by the rapidly expanding gas acts on the flange (34) and causes the piston (14) to rapidly move further into the passage (18) of the static member (12) causing complete radial expansion thereof and stemming of the borehole (46). The pressure from the gas acting on the inner surface (60) of the skirt (38) forces the skirt (38) outwardly and thus into more intimate contact with the sides (58) of the borehole (46), thereby preventing any gas from escaping between the sides (58) of the borehole (46) and the flange (34). The high pressure of the gas forces the piston (14) much more firmly into the static member (12) than can be achieved by using manual force by an operator. This results in the stemming device (10) becoming locked in position in the borehole (46) and trapping the gas in the borehole (46). This, in turn, leads to the rock being fractured by the gas.

It will be appreciated that the sliding fit provided by the flange (34) and the skirt (38) effectively ensures that no gas can escape along the sides of the stemming device (10), thereby ensuring that the piston (14) is moved into the static member (12) and that stemming occurs. If gas were allowed to escape along the sides of the stemming device (10), the pressure formed by the expanding gas would not cause stemming to occur, thereby causing the stemming device (10) to simply be shot out of the borehole (46) with no fracture of the rock taking place as the gas would not be confined within the borehole (26).

The slots (28) provided in the static member (12) permit rapid expansion thereof, and similar slots may be provided from the leading end (22) of the static member (12) should this be required. Alternatively, lines of weakness can be provided instead of, or in addition to, slots. These can take the form of sulcations, score lines, grooves, perforations and the like. In the event of a misfire of the cartridge (44), it is preferred to remove the cartridge (44) from the borehole (46) and replace it with a new one. The stemming device (10) of the present invention allows for easy removal of the stemming device (10) and cartridge (44) through the detent (48) provided at the trailing end (26) of the static member (12). Pulling on the shock tube (20) causes the detent (48) to bite into the shock tube (20) and prevent it from being withdrawn from the stemming device (10), enabling the stemming device (10) to be simply withdrawn from the borehole (46). Withdrawal is facilitated by the skirt (38) on the leading end (40) of the piston (14) providing a tight fit within the borehole (46) as the pulling force exerted on the shock tube (20) causes the static member (12) to disengage from the piston (14) and return to its un-expanded condition.

If the igniter (47) is secured within the cartridge (44), it can be withdrawn together with the stemming device (10). Alternatively, a further cartridge (not shown) is inserted into the borehole (46) and the stemming procedure simply repeated.

In cases where an electrical operating cable (not shown) is used to ignite the cartridge (44), such cable may typically provide insufficient strength to permit withdrawal of the stemming device (10) and cartridge (44) as described above. It is envisaged that in such cases, the stemming device (10) will be supplied with a suitably reinforced length of cable already in place, to which the electrical operating cable may be connected, so that, should a misfire occur, it will be possible to remove the stemming device (10) and cartridge (44) from the borehole (46) and replace the cartridge (44) with a new one. Alternatively, a hook or similar structure could be provided on the static member about which the cable could be looped or knotted to enable later withdrawal. Further alternatively, a hook or loop or similar structure could be provide on the static member which permits the stemming device to be fished out of the borehole using a stick with a hook on its end. As illustrated and described above, the stemming device (10) in accordance with the invention is simple to construct, easy to insert into a borehole (46) and highly effective in operation. Furthermore, the stemming device (10) can easily be withdrawn from a borehole (44) should the need arise, which most stemming devices disclosed in the prior art do not allow.

It will be appreciated, however, that many other embodiments of a stemming device exist which fall within the scope of the invention particularly as regards the shape and configuration thereof. For example, as shown in Figures 5 and 6, the skirt (70) can extend from a web (72) which is adhesively secured to the leading end (74) of the flange (34). The web (72) includes an aperture (76) that is slightly smaller than the circumference of the shock tube (20) so that when the shock tube (20) is fed through the aperture (76), the material of the web (72) extends about the shock tube (20) away from the flange (34) and toward the cartridge (44). The pressure created by the expanding gas acts on the material of the web (72) and forces the material into a more intimate contact with the shock tube (20), again preventing the escape of gas between the web (72) and the circumference of the shock tube (20).

It will be appreciated that although the seal formed by the skirt (70) and the web (72) is only effective for a very short period of time, it will be sufficient for the gas pressure to move the piston (14) from its rest position to its operative position in which the flange (70) abuts the leading end (22) of the static member (12) with the result that complete radial expansion of the stemming device (10) occurs.

Also, the piston (80) need not have a conical surface engaging the static member (82) but could have any suitable shape, including a rounded shape as shown in Figure 7. The static member (82) could have any suitable shape which co-operates with the piston to result in radial expansion of the device.

Figures 8 to 1 1 illustrate yet a further embodiment of a stemming device (90) in accordance with the invention. In this embodiment, the piston (92) is identical to the piston (14) illustrated in Figures 1 to 4 with the static member (94) having a different configuration. Figures 9 to 10 illustrate different views of only the static member (94), while Figure 1 1 illustrates the whole stemming device (90) in use.

The static member (94) has three elongate, longitudinally extending, circumferentially spaced ports (96) near its trailing end (98) and an anchor member (100) is associated with each port (96). Each anchor member (100) has a lug (102) which extends centrally from one side of a panel (104). Each lug (102) provides a complementary, sliding fit within a port (96) with each panel (104) providing a complementary fit over part of the outer surface of the static member (94). The panels (104) each have a number of longitudinally spaced grooves (106) on their outer surface. The anchor members (100) are held in place by a loop of thin wire (108) wrapped about the static member (94) and which rests within one of the groves (106). Any other suitable means could be used, for example, elastic or rubber band, adhesive tape or a tube of a plastics film.

The end (1 10) of each lug (102) opposite the panel (104) abuts the piston (92) and has a taper complementary thereto. In use, as illustrated in Figure 9, when the cartridge (1 12) is ignited, the pressure created by the rapidly expanding gas acts on the radially extending flange (1 14) of the piston (92) and causes the piston (92) move into the passage (1 16) of the static member (94). This movement causes the tapered end (1 18) of the piston (92) to engage the lugs (102) of the anchor members (100), thereby displacing the anchor members (100) outwardly from the static member (94) and resulting in radial expansion of the stemming device (90).

Any suitable materials can be used for the stemming device of the present invention and the shock tube or operating cord can be accommodated in any suitable manner. It is, for example, not required to have a central passage through the stemming device and a passage could instead be provided extending along the outer surface of the device. Also, any suitable detent could be used including, for example, inclined teeth within the passage in which the shock tube or operating cord is accommodated. Furthermore, the stemming devices and cartridges could be configured to be securable to each other and any suitable method can be used for preventing separation of the piston and static member of the stemming device. Also, it is not necessary for the leading end to provide a sliding fit in the borehole, but rather a flange or similar structure could be provided partway along the piston. It is merely required that a surface be provided on which gas will act and which prevents substantial egress of gas therearound which has the ability to act directly on the static member and potentially cause it to be ejected from he borehole.

Claims

CLAIMS:

A stemming device (10, 90) which includes a piston (14, 80, 92) movable from a rest position to an operative position relative to a complementary static member (12, 82, 94) to cause radial expansion of the stemming device (10, 90) and wherein the piston (14, 80, 92) has a leading end (36) which operatively faces a charge (44, 1 12) in a borehole (46), and wherein the piston (14, 80, 92) is configured to move under action from the charge (44, 1 12) or gas produced by the charge (44, 1 12), characterised in that part of the piston (14, 80, 92) provides a sliding fit within the borehole (46) and the stemming device (1 0, 90) includes a passage (1 8, 1 16) to accommodate an actuating tube or cable (20) extending from the charge (44, 1 12) externally of the borehole (46).

2. A stemming device (10, 90) as claimed in claim 1 in which the leading end (36) of the piston (14, 80, 92) provides a sliding fit within the borehole (46).

3. A stemming device (1 0, 90) as claimed in claim 1 or 2 in which the passage (18, 1 16) extends substantially centrally through the stemming device (10, 90).

4. A stemming device (10, 90) as claimed in any one of the preceding claims in which a detent (48) is associated with the passage (18, 1 1 6) to operatively prevent withdrawal of the actuating tube or cable (20) therefrom.

5. A stemming device (10, 90) as claimed in any one of the preceding claims in which the leading end (36) of the piston (14, 92) is provided by a radially extending flange (34, 1 14).

6. A stemming device (10, 90) as claimed in any one of the preceding claims in which the leading end (36) of the piston (14, 92) includes a resiliently flexible outwardly inclined circumferential skirt (38).

7. A stemming device (10, 90) as claimed in any one of the preceding claims in which a pressure resistant seal (72) is provided within the passage (18, 1 16) operatively over the actuating tube or cable (20).

8. A stemming device (10, 90) as claimed in any one of the preceding claims in which the static member (12, 94) includes formations (24, 1 16) to engage the sides of the borehole (46).

9. A stemming device (10, 90) as claimed in any one of the preceding claims in which the piston (14, 92) has a tapered end (30, 1 1 8) which extends within the passage (18, 1 1 6) in the static member (12, 94).

1 0. A stemming device (1 0) as claimed in claim 9 in which the passage (18) has a complementary taper to the tapered end (30) of the piston (14) and the static member (12) has a plurality of circumferentially spaced longitudinal slots (28) or lines of weakness, each slot or line of weakness extending approximately half way along the length of the static member (12).

1 1 . A stemming device (90) as claimed in any one of claims 1 to 9 in which the static member (94) has a tubular body with a number of ports (96) therein and an anchor member (100) associated with each port (96) such that movement of the piston (92) causes radially outward displacement of each anchor member (100).

12. A stemming device (90) as claimed in claim 1 1 in which each anchor member (100) has a lug (102) which extends centrally from one side of a panel (1 04), each lug (102) providing a complementary fit within a port (96) and wherein the tapered end (1 18) of the piston (92) engages the lugs (102).

13. A stemming device (90) as claimed in claim 12 in which the end (100) of each lug (1 02) opposite the panel (104) has a taper complementary to that of the piston (92).

14. A stemming device (90) as claimed in claim 12 or claim 13 in which the panels (1 04) extend over a part of the outer surface of the body.