WO2002090873A1

WO2002090873A1 - Split stemming bar and split stemming bar system incorporating same

Info

Publication number: WO2002090873A1
Application number: PCT/AU2002/000579
Authority: WO
Inventors: Jeffrey William Branson; Kenneth David Raph; Chris Woolford
Original assignee: Rocktek Limited
Priority date: 2001-05-09
Filing date: 2002-05-09
Publication date: 2002-11-14
Also published as: ZA200106194B

Abstract

Split stemming bar (10) includes first and second wedge members (12a,12b) having respective wedge contact surfaces (14a) and (14b). The wedge members (12a) and (12b) have a transverse profile or section in the general shape of a semi-circle so that with the services of the members (12a) and (12b) in mutual contact and the members (12a) and (12b) overlying each other, the stemming bar (10) has a circular cross section. The surfaces (14a) and (14b) are inclined in opposite directions so that the outer diameter of the split stemming bar (10) can be varied by sliding the members (12a) and (12b) relative to each other. The wedge members (12a) and (12b) are also each provided with protrusions (12a) and (12b) for mutual abutment with each other when the wedge members (12a) and (12b) are slid relative to each other in a direction which reduces the outer diameter of the stemming bar (10). By virtue of the mutual engagement of the protrusions (24a) and (24b) pulling wedge member (12a) out of the hole also drags out wedge member (12b).

Description

Split Stemming Bar and Split Stemming Bar System Incorporating Same

Field of the Invention

The present invention relates to a split stemming bar for use in fracturing hard materials and to an associated split stemming bar system.

Background of the Invention

Stemming bars are often used either by themselves or in conjunction with other stemming materials to stem holes when explosives or propellants are used for breaking rock or other hard material. In its simplest form, a stemming bar is an elongated solid cylindrical metal bar. When breaking or fracturing a hard material using an energetic material such as an explosive or propellant, a hole is first drilled in the material. The hole is then charged with a quantity of energetic material either in free form or contained within a cartridge. Optionally, a particulate stemming material (e.g. crushed aggregate) or a fluid stemming (e.g. water or gel) is deposited in the hole. When used in conjunction with a stemming bar, the particulate or liquid stemming material does not completely fill the hole but leaves a length free for the insertion of the stemming bar. Next the stemming bar, having an outer diameter marginally less than the inner diameter of the hole, is inserted into the hole.

The stemming bar may be mounted on a boom of a jumbo or alternately may be a free bar which may otherwise be mechanically held in the hole. This can be achieved for example by abutting the bucket of an excavator onto a free end of the stemming bar.

While this type of stemming bar and method of use is often adequate, it can lead to problems from time to time. For example, because the stemming bar must be of a diameter less than that of the hole in order to allow insertion into the hole, a gap necessarily exists between the outer surface of the stemming bar and the inner surface of the hole. This can provide a path for escape of gases generated upon initiation of the energetic material thereby reducing the efficiency of the rock breaking process. In addition, the escape of these gases can cause fracture of the hard material near the collar of the hole generating fly rock which is hazardous to personnel and can damage equipment in the vicinity of the hole. Further, at times, the stemming bar can become wedged tight in the hole and therefore be difficult to remove.

As an alternate to stemming bars, it is also known to use wedges. Wedges are used in pairs to form a plug in a hole. In order to minimise the risk of the wedges turning into projectiles, it is often desirable for them to be disposed below the collar of the hole. However this can make retrieval of the wedges very difficult.

Summary of the Invention

It is an object of the present invention to provide a split stemming bar and an associated split stemming bar system which attempts to overcome one or more of the deficiencies in the above described prior art.

According to a first aspect of the present invention there is provided a split stemming bar including at least: first and second elongated wedge members, each elongated wedge member having a respective wedge contact surface, said split stemming bar being formed by placing the wedge contact surface of one of said elongated wedge members in contact with the wedge contact surface for at least a portion of the length of the other elongated wedge member, said split stemming bar having an outer diameter which decreases to a minimum diameter when said first elongated wedge member is moved in a first direction relative to said second elongated wedge member and increases when said first elongated wedge member is moved in a second opposite direction relative to said second elongated wedge member; said first and second elongated wedge members provided with first and second engaging means respectively, said engaging means located relative to each other so as to come into mutual engagement when said first elongated wedge member is moved in said first direction relative to said second elongated wedge member to an extent that said outer diameter of said split stemming bar reaches said minimum diameter, wherein after upon continued movement of said first elongated wedge member in said first direction said second elongated member moves with and in the same direction as said first elongated wedge member.

Preferably said first and second engaging means includes a protrusion extending from a corresponding respective wedge contact surface.

Preferably said first and second wedge contact surfaces include respective longitudinally extending groove for receiving the protrusion formed on the other wedge contact surface.

Preferably said split stemming bar further includes bias means for biasing said wedge contact surfaces into mutual contact.

In one embodiment, it is envisaged that the elongated wedge members would be made from metal. However in alternate embodiments, it may be preferred for the elongated wedge members to be made from an elastic material. The elastic material may be one of or include an elastomer; an epoxy; or moulded plastics materials. In this embodiment, the wedge contact surfaces are preferably formed of, or coated with, a layer of a low friction material such as, but not limited to nylon.

According to a further aspect of the present invention there is provided a split stemming bar including at least: a first elongated wedge member having a first end and an opposite second end and a wedge contact surface extending between said first and second ends thereof; a second elongated wedge member having a first end and a second end and a wedge contact surface extending between the first and second ends thereof, said first elongated wedge member having substantially the same length as said second elongated wedge member; said split stemming bar formed by juxtaposing said first and second elongated wedge members relative to each other so that said first and second wedge contact surfaces are in mutual contact and, where said split stemming bar has an intermediate outer diameter when the first end of said first elongated wedge member is adjacent the second end of said second elongated wedge member; first engaging means on said first wedge contact surface located at a distance less than one half the length of said first elongated wedge member from the second end of said first elongated wedge member; second engaging means on said wedge contact surface located at a distance less than one half of the length of said second elongated wedge member from the second end of said second elongated wedge member, so that when said first and second elongated wedge members are disposed to provide said split stemming bar with said intermediate outer diameter, said first and second engaging means are spaced apart by a predetermined distance; whereby, when sliding said first elongated member in a first direction which reduces said outer diameter of said split stemming bar and by a distance equal to said predetermined distance, said first engaging means engages a second engaging means whereby, upon further sliding of said first elongated wedge member in said first direction, said second elongated wedge member slides with said first elongated wedge member.

According to a further aspect of the present invention there is provided a split stemming bar system including at least: a split stemming bar according to said first or second aspect of the present invention, wherein said first elongated wedge member further includes first coupling means at one end; and, a retrieval tool having a second coupling means at a first end thereof for coupling with said coupling means to facilitate a transfer of force on said first elongated wedge member in a direction to cause said first elongated wedge member to move in said first direction.

Preferably said retrieval tool includes an elongated bar extending from said first end of said retrieval tool to a stop provided at an opposite end of said retrieval tool, and a mass slidably mounted on said bar. Preferably said split stemming bar system further includes an insertion tool provided at one end with a stepped face for selectively abutting an end of said first and second elongated wedge members.

Brief Description of the Drawings

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings in which:

Figure 1 is an exploded perspective view of a first embodiment of the split stemming bar; Figure 2 is a side view of the split stemming bar in a reduced outer diameter configuration;

Figure 3 is a section view of a split stemming bar system incorporating the split stemming bar depicted in Figures 1 and 2;

Figure 4 is a side view of a split stemming bar retrieval tool incorporated in the system depicted in Figure 3;

Figure 5 is a side view of a cartridge retrieval tool incorporated in the system depicted in

Figure 3;

Figure 6 is a plan view of a member of a second embodiment of the split stemming bar;

Figure 7 is a side elevation view of the member depicted in Figure 6; Figure 8 is an end elevation view of the member shown in Figures 6 and 7;

Figure 9 is a isometric view of the member depicted in Figures 6-8; and,

Figure 10 is a side elevation of a further embodiment of the split stemming bar.

Detailed Description of Preferred Embodiments

Referring in particular to Figures 1 and 2, it can be seen that the split stemming bar 10 includes first and second elongated wedge members 12a and 12b (hereinafter referred to in general as "elongated wedge members 12"). The elongated wedge members 12a and 12b have respective wedge contact surfaces 14a and 14b (hereinafter referred to in general as "surfaces 14"), which are generally planar. The elongated wedge members 12 have a transverse profile or section in the general shape of a semi circle comprising an arc closed by a diameter. The surfaces 14 extend in a plane containing the diameter of the semi circle. The outside arc surfaces of members 12a and 12b constitute an outer peripheral hole contacting surface 16a and 16b respectively (hereinafter referred to in general as "hole contacting surfaces 16"). As shown in Figure 3, when the split stemming bar 10 is assembled and disposed within a hole 18, the hole contacting surfaces 16 are adjacent and/or in contact with the inner circumferential surface of the hole 18.

The first elongated wedge member 12a is provided with first and second opposite ends 20a and 22a respectively. Likewise the second elongated wedge member is provided with a first end 20b and an opposite end 22b. The surface 14a is inclined from the first end 20a to the second end 22a in a direction so that the transverse width of the member 12a reduces the first end 20a to the second end 22a.

The surface 14b is also inclined from the first end 20b to the second end 22b in a direction so that the transverse width of the member 12b reduces from the first end 20b to the second end 22b.

As a result of the inclination of the surfaces 14, the outer diameter of the split stemming bar 10 can be varied by sliding the members 12 relative to each other. The split stemming bar 10 has an intermediate outer diameter when the surfaces 14a and 14b are in contact with each other and the end 20a is adjacent the end 22b. From this configuration, the outer diameter of the split stemming bar can be decreased by sliding the first member 12a in a first direction D relative to the member 12b which results in a reduction in a distance between the second ends 22a and 22b. Alternately, the outer diameter of the split stemming bar 10 can be increased by sliding the first member 12a in a direction I relative to the second member 12b which reduces the distance between the first ends 20a and 20b. The outer diameter of the split stemming bar at any particular juxtaposition of the wedge members 12 is the outer diameter of the proportion of the stemming bar where the surfaces 14 are in mutual contact.

The elongated wedge member 12a is provided with a engaging means in the form of a protrusion 24a which extends along the surface 14a from the second end 22a. The protrusion 24a is of rectangular section and is provided with an abutment face 26a at an end opposite the end 22a. The abutment face 26a is located at a position less than one half of the length of the member 12a from the second end 22a.

Similarly, a second engaging means in the form of protrusion 24b extends from the surface 14b of the member 12b from the second end 22b. The protrusion 24b is of rectangular cross section and is provided with an abutment face 26b which is located at a position less than one half of the length of the member 12b from the end 22b.

Due to the relative positioning of the abutment faces 26a and 26b, they are spaced apart when the split stemming bar 10 is configured to have its intermediate outer diameter, which occurs when the first end 20a is adjacent the second end 22b (as depicted in Figure 3).

The abutment faces 26a and 26b are in axial alignment to enable them to come into face to face contact. Additionally, the abutment faces 26a and 26b are inclined by complimentary angles. The inclination of the surfaces 26a and 26b is arranged so that when in mutual abutment the abutment face 26a undercuts the abutment face 26b. This is depicted most clearly in Figure 2.

The elongated wedge members 12a and 12 b are provided with respective longitudinal grooves 28a and 28b (hereinafter referred to in general as "grooves 28"). The grooves extend from the first ends 20 of the respective members 12 to the corresponding abutment faces 26. With the split stemming bar 10 in the assembled state, the protrusions 24 of respective members 12 are seated within the grooves 28 of the other members 12. This assists in gliding the sliding motion of the members 12 relative to each other.

To assist in holding the surfaces 14 in mutual contact, the split stemming bar 10 can also include a bias means in the form of an O-ring 30 which is disposed about both of the members 12a and 12b, as shown in Figure 2. To facilitate retrieval of the split stemming bar 10 from the hole 18 the member 12a is provided, at end 20a, with a coupling means in the form of a retrieval spigot 32 (depicted in Figures 2 and 3).

A split stemming bar retrieval tool 34, shown in Figure 4, is attached to the spigot 32 of the first member 12a to retrieve the stemming bar 10 from the hole. The tool 34 includes a coupling 36 at one end which can be inserted into and locked with the retrieval spigot 32. The tool 34 further includes an elongated bar 38 having a stop 40 attached near an end of a bar 38 distant the coupling 36. A mass in the form of a sliding hammer piston 42 is coupled with and slidable along the bar 38 between the coupling 36 and stop 40.

By sliding the hammer piston 42 along the bar 38 to impact with the stop 40, the tool 34 imparts a force on the first member 12a causing it to move in the direction D which results in a reduction in the outer diameter of the split stemming bar 10. The member 12a is able to slide relative to the member 12b in the direction D until the abutment faces 26a and 26b, to mutual abutment. Thereafter, if the member 12a is moved further in the direction D, it pulls or drags with it the member 12b thereby effectively withdrawing the stemming bar 10 from the hole 18.

Figures 6-9 illustrate a second embodiment of the first member 12a depicted in these figures as member 12a'. The member 12a' is provided with an inclined wedge contact surface 14a', protrusion 24a', and longitudinal groove 20a' of the same configuration as the member 12a depicted in Figures 1-3. The member 12a' differs from the member 12a in terms of the coupling means for coupling to a retrieval tool. In this embodiment, the coupling means 32' is in the form of a U-shaped loop extending from end 20a'. As a result of the coupling being in the form of the loop 32', the retrieval tool 34 is also modified by replacing the coupling 36 depicted in Figure 4 with a simple hook (not shown) for engaging the loop 32'. In all other aspects, the tool 34 for retrieving a stemming bar which incorporates the first member 12a' as depicted in Figures 6-9 is the same as that depicted in Figure 4. Figure 3 depicts an insertion tool 44 incorporated in the split stemming bar system 45 for inserting the split stemming bar 10. In a typical use scenario, the hole 18 is drilled from a free face 46 of a body of rock. A cartridge 48 containing energetic material is loaded into the hole 18 and forced toward the toe 50 of the hole. The hole 18 is then stemmed with a particulate stemming material 52 and the split stemming bar 10 pushed into the hole 18. When inserted into the hole, the stemming bar 10 may be in the configuration depicted in Figure 2 where the abutment faces 26a and 26b are in mutual contact. This ensures sufficient clearance to allow the stemming bar 10 to be inserted without the exertion of any significant force. The bar is inserted until end 20b of the elongated wedge member 12b initially abuts the stemming 52. Next, the elongated wedge member 12a is slid along the member 12b thereby increasing the outer diameter of the stemming bar. It is envisaged that the member 12a can be pushed by hand up to a distance where the end 22a is close to the end 20b. For the purposes of tamping the stemming material 52 and firmly wedging the split stemming bar 10 into the hole 18, the insertion tool 44 is used to alternately hammer on the end 22b of member 12b and the end 20a of member 12a.

To this end, the insertion tool 44 is provided with a step 53 at end 54 which is configured to allow the force of a hammer 56 to be selectively applied to the members 12a and 12b by simple rotation of the tool 44 abuts its longitudinal axis. The insertion tool 44 is the form of a solid cylindrical metal bar with a cut out at end 54 to provide the step 53.

In the event of a misfire of the cartridge 48, the system 45 may also include a cartridge retrieval tool 58 as shown clearly in Figure 5. The tool 58 comprises an elongated through rod 60 provided at one end with a jaw or coupling 62 which can grip an end 64 of the cartridge 48 facing the collar of the hole 18. Many different types of interaction or coupling between the tool 58 and cartridge 48 can be achieved depending on the specific structure of the cartridge 48 itself. When the cartridge 48 is provided with a tapered end 64, the jaw or coupling 62 can be provided with two or more inwardly directed teeth 66 for gripping the end 64. The gripping can be either by way of puncturing of the end 64 or by forming the jaw 62 in a manner so that it can be opened or closed, for example, by provision of a drawstring or wire passing through the rod 60. Alternately, the cartridge 48 can be configured for specific use with a system 45 by the inclusion of recesses or slots that enable engagement of the jaw or coupling 62 with the cartridge 48. Indeed in this regard, the cartridge 48 can be provided with a spigot similar to spigot 32 provided in the split stemming bar 10 and the jaw or coupling 62 modified to do be the same form as the coupling 36 of the tool 34.

Now that the embodiment of the present invention has been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the split stemming bar 10 is depicted as being formed from two elongated wedge members 12a and 12b, however the same effects and functionality can be obtained by forming the split stemming bar from three or more elongated wedge members. Also, the split stemming bar may be made of, say, wedge members where one wedge member extends for the length of the stemming bar and having two wedge contact surfaces which meet at the mid point of that member and are tapered downwards towards the ends of the member; and two shorter wedge members, one for each of the contact surfaces. Such an arrangement is depicted in Figure 10. Figure 10 depicts a split stemming bar 10" having wedge member 12a", 12b" and 12c". The wedge member 12a" is twice the length of the members 12b" and 12c" and has a wedge contact surface 14a" having two oppositely inclined lengths Ha," and Ma . The lengths 14a," and Haj" meet at the mid point of the length of wedge member 12a" and taper downwardly in the direction toward the opposite ends of the member 12a". (Although in a further variation the lengths 14a," and 14a₂" may not meet but rather stop short of the mid point of wedge member 12a"). Otherwise the salient features of wedge members 12a", 12b" and 12c" are in essence the same as for the embodiment depicted in Figure 1. The outer diameter of bar 10" is at a maximum when either one or both of wedge members 12b" and 12c" have their ends 20b" and 20c" in alignment with ends 20a," and 20a₂" respectively. When retrieving the bar 10" wedge members 12b" and 12c" slide in away from each other down surfaces 14a," and Ma/ respectively to reduce the outer diameter of the bar 10". In addition, the elongated protrusions 24 which form the engaging means can be made considerably shorter than depicted in Figure 1 by commencing inboard of the end 22 of the respective members 12. Further, the specific and physical form of the coupling between the stemming bar retrieval tool 38 and elongated wedge member 12a, facilitated in the illustrated embodiment by the spigot 32 and coupling 36, in Figures 2-4 or the loop 32' of Figures 6-9 and corresponding hook (not shown) is not critical and can take any form which achieves the same effect of allowing reasonable coupling of the two elements together.

The split stemming bar 10 and wedge members 12 can be made from a variety of materials, including metals, wood, plastics materials, rubbers and epoxies. In addition, the split stemming bar 10/wedge members 12 can be made from either rigid or elastic materials. For example, the stemming bar 10/wedge members 12 can be made from elastic materials such as elastomers (i.e. natural or synthetic rubbers) or epoxies. It is preferable for the outer surface of the stemming bar 10/wedge members 12 to be made from a relatively high friction material which may be an inherent characteristic of the elastic materials used for the construction. Alternately, a high friction or rough coating can be applied to the surfaces of the split stemming bar 10/wedge member 12 that contact the surface of the hole 18. This could be achieved by adhering particles of high friction material (rubber crumbs) or abrasives (eg gravel or fines) to the outer surfaces. On the other hand, it may be advantageous for the wedge contact surfaces 14 to be formed from or coated with a layer of a low friction material such as, but not limited to, nylon.

All such modifications and variations together with others that would be obvious to a person of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description.

Claims

The claims defining the invention are as follows:

1. A split stemming bar including at least: first and second elongated wedge members, each elongated wedge member having a respective wedge contact surface, said split stemming bar being formed by placing the wedge contact surface of one of said elongated wedge members in contact with the wedge contact surface for at least a portion of the length of the other elongated wedge member, said split stemming bar having an outer diameter which decreases to a minimum diameter when said first elongated wedge member is moved in a first direction relative to said second elongated wedge member and increases when said first elongated wedge member is moved in a second opposite direction relative to said second elongated wedge member; said first and second elongated wedge members provided with first and second engaging means respectively, said engaging means located relative to each other so as to come into mutual engagement when said first elongated wedge member is moved in said first direction relative to said second elongated wedge member to an extent that said outer diameter of said split stemming bar reaches said minimum diameter, wherein after upon continued movement of said first elongated wedge member in said first direction said second elongated member moves with and in the same direction as said first elongated wedge member.

2. The split stemming bar according to claim 1 wherein said first and second engaging means includes a protrusion extending from a corresponding respective wedge contact surface.

3. The split stemming bar according to claim 2 wherein said first and second wedge contact surfaces include respective longitudinally extending groove for receiving the protrusion formed on the other wedge contact surface.

4. The split stemming bar according to any one of claims 1-3 further including bias means for biasing said wedge contact surfaces into mutual contact.

5. The split stemming bar according to any one of claims 104 wherein said wedge members are made of an elastomeric material.

6. The split stemming bar according to any one of claims 1-5 wherein the wedge contact surfaces are preferably formed of, or coated with, a layer of a low friction material.

7. The split stemming bar according to any one of claims 1-6 wherein an outer surface of said stemming bar is made of, or coated wit, a high friction material or an abrasive material .

8. A split stemming bar including: a first elongated wedge member having a first end and an opposite second end and a wedge contact surface extending between said first and second ends thereof; a second elongated wedge member having a first end and a second end and a wedge contact surface extending between the first and second ends thereof, said first elongated wedge member having substantially the same length as said second elongated wedge member; said split stemming bar formed by juxtaposing said first and second elongated wedge members relative to each other so that said first and second wedge contact surfaces are in mutual contact and, where said split stemming bar has an intermediate outer diameter when the first end of said first elongated wedge member is adjacent the second end of said second elongated wedge member; first engaging means on said first wedge contact surface located at a distance less than one half the length of said first elongated wedge member from the second end of said first elongated wedge member; second engaging means on said wedge contact surface located at a distance less than one half of the length of said second elongated wedge member from the second end of said second elongated wedge member, so that when said first and second elongated wedge members are disposed to provide said split stemming bar with said intermediate outer diameter, said first and second engaging means are spaced apart by a predetermined distance; whereby, when sliding said first elongated member in a first direction which reduces said outer diameter of said split stemming bar and by a distance equal to said predetermined distance, said first engaging means engages a second engaging means whereby, upon further sliding of said first elongated wedge member in said first direction, said second elongated wedge member slides with said first elongated wedge member.

9. The split stemming bar according to claim 8 wherein said first and second engaging means includes a protrusion extending from a corresponding respective wedge contact surface.

10. The split stemming bar according to claim 9 wherein said first and second wedge contact surfaces include respective longitudinally extending groove for receiving the protrusion formed on the other wedge contact surface.

11. The split stemming bar according to any one of claims 8-10 wherein bias means for biasing said wedge contact surfaces into mutual contact.

12. The split stemming bar according to any one of claims 8-11 wherein said wedge members are made of an elastomeric material.

13. The split stemming bar according to any of claims 8-12 wherein the wedge contact surfaces are preferably formed of, or coated with, a layer of a low friction material.

14. The split stemming bar according to any one of claims 8-13 wherein an outer surface of said stemming bar is made of, or coated, with a high friction material or an abrasive material.

15. A split stemming bar system including at least: a split stemming bar according to any one of claims 1-14 wherein said first elongated wedge member further includes first coupling means at one end and a retrieval tool having a second coupling means at a first end thereof for coupling with said coupling means to facilitate a transfer of force on said first elongated wedge member in a direction to cause said first elongated wedge member to move in said first direction.

16. The system according to claim 15 wherein said retrieval tool includes an elongated bar extending from said first end of said retrieval tool to a stop provided at an opposite end of said retrieval tool, and a mass slidably mounted on said bar.

17. The system according to claim 16 further including an insertion tool provided at one end with a stepped face for selectively abutting an end of said first and second elongated wedge members.