AU722007B2 - Method and apparatus for blasthole stemming - Google Patents

Description

P:\OPER\PHH726J0-96.rs.doc-4A)0/00 -1- METHOD AND APPARATUS FOR BLASTHOLE STEMMING The present invention relates to a method and apparatus for use in charging blastholes, and is particularly concerned with a device for plugging a blasthole and with methods of use of the device.

In mining operations the main objective of blasting is to break rock and shift material in a useful way. When an explosive charge explodes there is a powerful force exerted in all directions and any earth surrounding the explosive charge will break along the line of least resistance. In order to achieve an optimal result in blasting, the location and degree of confinement of an explosive charge must be carefully designed. In mining applications this generally consists of locating explosive charges in blastholes drilled in ore, rock, coal or the like. Factors such as the diameter, length, angle and spacing of the blastholes are critical to the success of a blast.

Charging a newly drilled blasthole with explosives generally involves careful placement of an initiation device such as a detonator, a primer and bulk and/or packaged explosives. Detonators are small, compact high energy explosives which can initiate a larger body of explosive such as a primer which in turn may detonate with enough force to S: :initiate bulk or packaged explosives. The nature, quantity and arrangement of the initiation :I device, primer and bulk or packaged explosives in a blasthole has a large influence on the results of a blast.

°Often the blasthole is not completely filled with explosive charges. Often there is a gap between the top of the column of explosive charge and the collar of the blasthole which is either left open or filled with non-explosive material called stemming,. The column itself may not necessarily be continuous; sometimes the column comprises several charges or short columns separated by inert material or devices referred to as decks.

Decking tends to lower the explosion pressure in a blasthole and provide a more even distribution of energy than can be achieved in the absence of decking.

In the past many attempts have been made to provide a plugging device which can perform the function of air decking and/or stemming. For example attempts have been made to stem blastholes using polymeric containers filled with water and sealed closed at Seach end. One end is well rounded for easy insertion of the containers into the blasthole P:\OPER\PHH72690V-96.-d.d4c/t -2where they are secured in place by driving a wedge made of wood or plastic material between the container and the blasthole wall. This type of stemming is inconvenient to use because of the difficulty of manually forcing a water filled container into a blasthole and then driving in wedges while avoiding rupturing the container,. These containers are particularly difficult to place into upholes.

Australian Patent Application No. 41907/93 describes an inflatable plugging device for stemming blastholes, This particular device comprises a resilient inflatable body member which is contained within a substantially non-resilient container. Inflation of the flexible member causes the container to engage the walls of a blasthole to keep the device in place and maintain suspension of the stemming.

Blastholes are commonly charged with bulk explosives by pumping or pneumatically conveying the bulk explosive through a loading hose into the blasthole. One of the drawbacks of most of the plugging devices of the prior art is that when such devices are used for decking, it is necessary to interrupt the charging of the blasthole with explosive in order to put the plugging device in place. When charging a deep blasthole full of emulsion explosive it is very inconvenient and inefficient to have to cease pumping or pneumatically conveying the emulsion and remove the loading hose in order to insert a plugging device. This method of operation is particularly inconvenient when charging upholes where the bulk emulsion already in the blasthole starts to slowly flow out of the 20 hole under the influence of gravity before the plugging device is pushed into place.

According to the present invention there is provided a device for plugging a blasthole which device comprises an inner member comprising a conduit for the passage of fluid bulk explosives material and having an inlet port and an outlet port, the conduit including a valve means adapted to allow passage of the explosives material through the conduit in only the direction from said inlet port to said outlet port, and the conduit being .adapted for attachment of the device to an end of an explosives' loading hose and an outer member adapted to engage the walls of the blasthole.

The inner member essentially comprises a conduit or passage, with an opening or inlet port at one end and an opening or outlet port at the other end, through which fluid bulk explosive may be passed. A valve prevents back flow of fluid bulk explosive.

P:\OPERPHH\72690-96.-doc-O405/OO -3- The outer member performs the function of bracing the plugging device against the walls of a blasthole such that the device forms a good seal with the blasthole walls and is prevented from slipping out of the blasthole. Clearly it is preferably that the outer member substantially confirms to the general shape of the blasthole.

The outer member may be constructed of a deformable material which provides good contact between the device and the walls of the blasthole. Suitable materials include natural polymeric materials such as rubber, synthetic polymers such as expanded polyurethanes or expanded polystyrenes, neoprene and the like.

The outer member may be inflatable so that the plugging device can be easily pushed into place along a blasthole and then the outer member inflated so as to provide good contact with the blasthole walls. The outer member may be inflated by a source of fluid material located externally such as a cylinder of gas or liquid which is kept under pressure or a reservoir of liquid which may be pumped into the outer member. Depending on the fluid used it may be possible to pressurise the outer member. The outer member may comprising a filling means such as a non-return valve, bleed valve, needle valve or any other convenient means for controlling fluid flow.

The fluid material for inflating the outer member may be any convenient matter and 0: includes liquids, gases or finely divided particulate matter. Water and air are particularly T inexpensive and convenient fluid materials.

In a preferred embodiment of the plugging device of the present invention the outer member and the inner member comprise separate detachable elements which are assembled to give the plugging device of the present invention.

0.•0 In such a preferred embodiment, preferably the outer member defines an openended passage therethrough, for example a flexible container or bag in the shape of a toroid.

The inner member of such a preferred embodiment of the present invention may be tubular and be adapted to fit into the passage in the outer member. Such an inner member may be conveniently referred to as a "liner" as it in effect "lines" the passage in the outer member when the inner and outer members are assembled to form the plugging device.

In this preferred embodiment the tubular inner member is formed in two parts ,A 7 which are adapted to be received in the open-ended passage from opposite ends of the P:\OPER\PHl 72690-96.-.dc-044/0500 -4outer member. The two parts of the tubular inner member are conveniently joined by an interference fit. A seal is advantageously provided at the join of the two parts of the inner member.

One end of the liner may define the inlet port, while the other end of the liner may define the outlet port. The inlet port may be adapted for attachment of the end of the explosives' loading hose to the device. Alternatively, the inlet port may be adapted to receive the hose therethrough with a seat for the end of the hose being provided part-way through the conduit.

Preferably the valve means of the device of the present invention is located at the end of the conduit nearest the outlet port. The valve means is most advantageously in the form of a ball valve. Preferably, when the valve means is in a condition in which passage of the explosives material through the conduit in said direction is allowed the ball is held in the outlet port. The movement of the ball may be limited by means such as tapered fins protruding from the wall of the inner member defining the conduit or a cage or the like.

Such movement limiting means may be integral with the inner member, and the inner member may be constructed of any convenient material, such as a polymeric material.

The valve means of the device of the current invention permits fluid bulk explosive 0000 to be pumped through the conduit of the plugging device into the blasthole but prevents o#000i any fluid bulk explosive flow in the opposite direction by sealing off the passage. Where 20 the plugging device is being used in upholes, the hydrostatic head should be sufficient to o* •cause the valve to close off the passage.

In general, the plugging device of the current invention is located in place in a blasthole and fluid bulk explosive is pumped or pneumatically conveyed into the blasthole.

Initially the bulk explosive passes through the plugging device to fill the space between the end of the blasthole and the plugging device. As this happens, air is displaced and it may S-be necessary to provide means such as a bleed tube by which the air can vent from the blasthole. In a preferred embodiment the device of the current invention is provided with a channel for a bleed tube. It will be apparent to those skilled in the art that an air bleed tube will not be required in broken ground or in open holes from which displaced air can readily escape.

P: \PER\PHH\72690.96.res.doc-04A)5/ The invention also provides a method of charging a blasthole using the device of the invention. In a first aspect the method comprising the steps of: placing initiating explosives and optionally a bleed tube in a blasthole; inserting the end of an explosives' loading hose into the plugging device; locating the plugging device in place in the blasthole; pumping fluid bulk explosive from the hose through the conduit in the inner member of the device into the blasthole; and removing the loading hose.

The plugging device may be pushed into place into the blasthole using the end of the loading hose.

The plugging device of the invention can be used at any position within a blasthole or for any convenient purpose. For example, the plugging device can be used instead of stemming material or to hold stemming material in place. The stemming device can also be used in a decked blasthole between charges of explosives or between stemming material and explosives charges.

Where the plugging device is used to stem the blasthole in the first aspect of the method of the invention. The plugging device may be located in place at or near the collar of the blasthole.

Where the plugging device of the invention is used in a decked blasthole to S 20 separate charges of explosives from each other or separate explosive charges from inert material, the invention provides in a second aspect a method of charging a blasthole comprising the steps of: placing initiating explosives and optionally a bleed tube in a blasthole; part charging the blasthole with explosives material or inert material; 25 before or after step locating the plugging device in place in the *6 blasthole; and repeating steps and until the blasthole is filled.

Commonly in the second aspect of the method of charging a blasthole the explosives composition would be pneumatically conveyed or pumped into the blasthole through a loading hose but it may be tipped or augered into the blasthole. The inert M7 material may be any suitable non-explosive material known in the explosives filed such as P:\OPER\PHH\7269-96.r-.dc-04Ai5A0 -6raw soil, gravel, sand and the like. The inert material may be charged into the blasthole by any convenient means including pneumatic conveying or pumping.

In a preferred embodiment of the second aspect of the method, the end of an explosives loading hose or stem material loading hose is inserted into the plugging device before the plugging device is located in place in the blasthole and explosives composition or stemming material is pumped through the plugging device.

One embodiment of the method and device of the invention will now be further described by way of example only with reference to the drawings. Figure la is a side view of the embodiment of the plugging device, Figures lb and c are end views of the device of Figure 1 a, taken from an outlet port end and an inlet port end, respectively, Figure 2 is a sectional view of the inner member of the plugging device of Figure la, dismantled to show its constituent members, Figure 3 is a sectional view of the assembled plugging device of Figure 1 a, and Figure 4 illustrates the device of Figure 1 a (shown in schematic section) in one method of use.

Referring to the drawings, the plugging device illustrated comprises an outer member 1 and an inner member 7. The outer member 1 is generally cylindrical in overall shape and inflatable but has an open-ended passage 15 therethrough to receive the inner member 7 (see Figure The cross-section of the outer member 7 is therefore toroidal. An inlet port 2 and an outlet port 3 are provided in the pugging device and are defined by the 20 inner member 7. A conduit 4extends through the inner member between the inlet and outlet ports. A channel 5 in the outer member 1 is adapted to accommodate a bleed tube. as shown schematically in Figure 4. A needle valve 6 is provided for inflation of the outer oo member.

As may be seen from Figure 2, the inner member is generally tubular in shape, comprising two body members 7a, 7b which are held together by interference fit to define the conduit 4 therethrough. The body members 7a and 7b are introduced into the passage of the outer member 1 from opposite ends and are fitted together in the passage. Flared end portions defining the inlet port 2 and outlet port 3 locate the outer member 1 on the inner member, as shown in Figure 3. Also shown in Figure 3 is an O-ring seal 10 received in an annular groove between the body members 7a and b.

P:\OPERPHH\72690-96.res..doc-44/05/00 -7- The inlet port 2 may be fitted with an inlet seal 8. A ball 9 is received in the conduit 4 of the inner member near the outlet port 3 and is displaceable longitudinally in the conduit between tapered fins 3a, which prevent the ball escaping through the outlet port 3, and a valve seat 16. As may be seen from Figure 3 the conduit 4 tapers in diameter from the outlet port towards the seat 16. In use, as fluid bulk explosive is pumped through the conduit 4 towards the outlet port 3, the ball 9 moves towards the outlet port but is prevented from escaping the conduit by the fins 3a. The bulk explosive flows around the ball 9 as the conduit near the outlet port is of greater diameter than the ball. As the blasthole fills with bulk explosive, the hydrostatic head of bulk explosive forces the ball 9 away from the outlet port 3, towards the valve seat 16 where the ball lodges, blocking the conduit 4 and preventing back flow of bulk explosive out of the plugging device through the inlet port 2.

In use, the end of an explosives' loading hose 13 (not shown in Figures 1 to 3) is introduced into the conduit 4 through the inlet port 2 until it engages a seat 17. The hose passes through the O-ring seal 10 which helps to seal around the hose. A larger hose may only fit up to the sea 18 which partly defines the groove for the O-ring seal 10, as shown in Figure 4. An even larger hose may only be received by the inlet port 2.

Figure 4 depicts the plugging device of Figures 1 to 3 in place in an uphole. In practice, after a blasthole is drilled, a detonator attached to a length of signal tube 12 (or 20 alternatively leg wires) is inserted into a primer 11. The primer is then located in position in a blasthole, preferably using a STOPEPRIME primer locater. (STOPEPRIME is a trade mark of Orica Australia Proprietary Limited). A bleed tube 14 is then positioned in the m. blasthole.

S..Next, the end of the explosive loading hose 13 is inserted into the plugging device and used to push the plugging device into position in the blasthole bear the collar of the blasthole. The outer member 1 is then inflated using compressed air. Care is taken that the bleed tube 14 passes along the channel 5 in the outer member of the plugging device. It may be convenient (but not mandatory) that the single tube 12 also passes along the channel Fluid bulk explosive is then pumped through the plugging device into the blasthole.

S As the blasthole fills with explosive emulsion, air is displaced from the blasthole and p:\OPER\PHH7269( -96.s.d)c4A/00 -8escapes through the bleed tube. By the time the column of bulk explosive has risen from the collar area of the blasthole to the toe, the hydrostatic head of the column is sufficient to push the ball 9 of the ball valve away from the outlet port 3 towards the valve seat 16 to seal off the conduit 4 through the plugging device. The loading hose is subsequently removed and the blasthole is ready for detonation.

The plugging device can be used as the sole means of plugging a blasthole or may be used in conjunction with other plugging or stemming means such as drill cuttings or the like and/or with further plugging devices for decking. In some mining applications it may occur that the blasthole is open at both ends or that the two of the blasthole is likely to break through the surrounding structure into a fissure, void, old tunnel or the like. In this situation it may be advisable to locate one plugging device at the toe and another at the collar of the blasthole.

While the invention has been explained in relation to its preferred embodiments it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the oo appended claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and 20 "comprising", will be understood to imply the inclusion of a stated integer or step or group .o of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

o° .o

OVO..

o• o*

Claims (19)

1. A device for plugging a blasthole which device comprises: an inner member comprising a conduit for the passage of fluid bulk explosives material and having an inlet port and an outlet port, the conduit including a valve means adapted to allow passage of the explosives material through the conduit in only the direction from said inlet port to said outlet port, and the conduit being adapted for attachment of the device to an end of an explosives' loading hose; and (ii) an outer member adapted to engage the walls of the blasthole.

2. A device according to claim 1 wherein the outer member comprises a deformable material.

3. A device according to claim 1 or claim 2 wherein the outer member is inflatable.

4. A device according to any one of claims 1 to 3 wherein the outer member and inner member comprises separate detachable elements. V* a a 20

5. A device according to claim 4 wherein the outer member defines an open-ended passage therethrough and the inner member is tubular and received in the passage in the outer member. a a*a

6. A device according to claim 5 wherein the tubular inner member is formed in two parts which are adapted to be received in the open-ended passage from opposite *ends of the outer member. S•

7. A device according to claim 6 wherein the two parts of the inner member are joined in the open-ended passage by an interference fit. P:\OPER\PHH\72690-96.res.doc-04/05/00

8. A device according to claim 6 or 7 wherein a seal is provided at the join of the two parts of the inner member.

9. A device according to any one of the preceding claims wherein the inlet port is adapted for attachment of the end of the explosives' loading hose to the device.

A device according to any one of claims 1 to 8 wherein the inlet port is adapted to receive the explosives' loading hose therethrough and a seat for the end of the hose is provided part-way through the conduit.

11. A device according to claim 10 wherein a seal for the hose is provided in the conduit.

12. A device according to any one of the preceding claims wherein the inlet port is provided with a removable inlet seal. °e

13. A device according to any one of the preceding claims wherein the valve means comprises a ball valve. S 20

14. A device according to claim 13 wherein when the valve means is in a condition in which passage of the explosives material through the conduit in said direction is allowed the ball is held in the outlet port. *oo*

15. A device for plugging a blasthole substantially as herein described with reference to the drawings.

16. A method of charging a blasthole comprising the steps of: placing initiating explosives and optionally a bleed tube in a blasthole; inserting the end of an explosives' loading hose into a plugging device according to any of the preceding claims; S(c) locating the plugging device in place in the blasthole; P:\OPER\PHH\72690-96.res.doc.4-4A1)5 11 pumping fluid bulk explosive from the hose through the conduit in the inner member of the device into the blasthole; and removing the loading hose.

17. A method according to claim 16 wherein the plugging device is located in place at or near the collar of the blasthole.

18. A method of charging a blasthole comprising the steps of: placing initiating explosives and optionally a bleed tube in a blasthole; part charging the blasthole with explosives material or inert material; before or after step locating a plugging device according to any one of claims 1 to 15 in place in the blasthole; and repeating steps and until the blasthole is filled.

19. A method according to claim 18 which includes inserting the end of a material loading hose into the plugging device before the plugging device is located in place in the blasthole and part charging the blasthole with the material from the hose through the conduit in the inner member of the device. DATED this 4 th day of May, 2000 ORICA AUSTRALIA PTY LTD By Its Patent Attorneys DAVIES COLLISON CAVE