WO1992001856A1

WO1992001856A1 - Variable geometry cluster drill

Info

Publication number: WO1992001856A1
Application number: PCT/AU1991/000316
Authority: WO
Inventors: Ian Mckenzie Speer
Original assignee: Norncott Pty Ltd
Priority date: 1990-07-16
Filing date: 1991-07-15
Publication date: 1992-02-06
Also published as: ZA915502B; CA2086758A1

Abstract

A variable geometry cluster drill for rockboring comprising a central support (11) having a longitudinal axis about which the drill is capable of rotating to bore a hole. The drill also comprises a plurality of elongate hammers (14) located about the central support (11), each hammer (14) having a drill bit (16) at one end. At least one hammer (14) is pivotally mounted to the central support (11) so that the drill bit (16) thereof is capable of radial movement away from or towards the central support (11) between an operative position and an inoperative position, the diameter of the rotation path of the drill bit (16) in the operative position being greater than in the inoperative position. The cental support (11) also including means (17, 18, 19, 20) for controlling the radial movement of the drill bit (16) between the operative and inoperative positions.

Description

"VARIABLE GEOMETRY CLUSTER DRILL"

THIS INVENTION relates to a variable geometry cluster drill which is intended for roc boring.

In particular the invention relates to drills which utilise a set of hammers disposed around the central axis of the drill. Such drills are generally used for boring large diameter holes.

A difficulty which has been encountered with such hammers results from the wear of the drill bits of the hammers. As the drill proceeds through the ground, the hole which is being drilled reduces in diameter as the drill progresses due to wear on the lateral portions of the drill bits. When the drill is withdrawn from the hole the drill bits are replaced by sharpened drill bits, or alternatively the drill bits are repositioned such that the unworn portions of each bit are utilised in the drilling. Due to the reduction in diameter, it is not possible for the drill to freely re-enter the hole and recommence drilling at the previous depth. In this respect, the diameter of the hammer as determined by the rotation path of the new drill bits is greater than the diameter of the hammer as determined by the rotation path with the worn drill bits. As a result it is necessary for the new drill bits to remove the tapered portions of the drill hole before drilling can recommence at the previous depth. Not only is this time consuming, but it can be detrimental to the hammer and drill bits, and results in unnecessarily drilling a part of the same hole twice.

Furthermore, such hammers have suffered from difficulty when it becomes necessary to withdraw them from the borehole due to the ^' very close tolerance between the diameter of the hole and the diameter of the rotation path of the drill bits. Difficulties have been encountered as a result of the drill becoming jammed on its withdrawal, and this jamming can usually only be overcome by very careful manipulation.

Of course, since these operations are usually undertaken in underground mining where labour costs are very high, it is of advantage to minimise the degree of down time necessary to replace or reposition the drill and/or the drill bits, and to ensure maximisation of the labour available.

It is an object of this invention to provide a variable geometry cluster drill which can be used in rockboring and _* which will overcome or at least partly alleviate the above difficulties.

The present invention provides a variable geometry cluster drill for rockboring comprising a central support having a longitudinal axis about which the drill is capable of rotating to bore a hole and a plurality of elongate hammers located about the central support, each hammer having a drill bit at one end, wherein at least one hammer is pivotally mounted to the central support so that the drill bit thereof is capable of radial movement away from or towards the central support between an operative position and an inoperative position, the diameter of the rotation path of the drill bit in the operative position being greater than in the inoperative position, the central support including means for controlling the radial movement of the drill bit between the operative and inoperative positions. The central support is preferably an elongate central body having a top end and a bottom end. The body may be adapted at the top end to be mounted to a drill string, and at the bottom end to include a set of roller elements capable of substantially centrally supporting the drill in a borehole by interaction thereof with the walls of the bored hole.

In a preferred form each hammer is pivotally mounted to the central support so that each drill bit is capable of the radial movement described above. In this respect, it will be appreciated that where the drill of this invention comprises only two elongate hammers, either or both may be pivotally mounted, and where the drill comprises three elongate hammers any one or combination of two or all three may be pivotally mounted. Where the drill comprises more than three hammers it would be generally preferred to half at least half of the hammers pivotally mounted. The following description will generally relate to the preferred form of three hammers, each pivotally mounted.

The hammers may be pivotally mounted to the elongate central body so as to be generally adjacent thereto and substantially parallel therewith when the drill bits are in their inoperative position. In this form, the bottom end of each hammer may be pivotally mounted to the body at or near the bottom end thereof, while the top end of each hammer may engage the body at or near the top end thereof. It will be understood that the point of pivotal mounting of the hammers need not always be at the bottom ends of the body and the hammers, but may be at another location, provided that the drill bits of the hammers are capable of pivotal movement between operative and inoperative positions. It will also be understood that in this preferred form of the invention, the drill bits are at the top ends of the hammers.

The engagement of the top end of each hammer with the top end of the body is preferably achieved via the control means. The control means preferably includes a means for actuating the pivotal movement of the hammer. The actuating means is capable of pivotally moving the hammers from the inoperative position, which in this form is substantially parallel to the longitudinal axis of the elongate central body, to an operative position where each hammer is at an angle to that axis. The actuating means may be one actuating device responsible for the pivotal movement of all the hammers, or more preferably may be one actuating device per hammer.

The actuating means are preferably a pneumatically or hydraulically operated cylinder having a piston movable against a hammer as a result of the introduction of air or hydraulic fluid into a piston chamber. The piston is preferably urged away from the hammer by a biasing means so that pneumatic or hydraulic actuation is required to overcome the force of the biasing means to move the hammers to their operative position, while the release of the pneumatic or hydraulic pressure will allow the biasing means to return the hammers to their inoperative position.

The means for pivotally mounting the hammers to the central body is preferably a bracket means which extends beyond the central body to allow the hammer to be mounted adjacent the central body. In a preferred form, the bracket means- includes a pivotally mounted support element which itself receives the hammer and thus allows for the pivotal movement of the hammer. A clamping means may be provided in association with the support element to clampingly and non-rotatably retain the hammers within the support element.

The support element is preferably in the form of a polygonal socket, such as a hexagonally shaped socket, which inter-engages with a correspondingly shaped portion of the bottom of the hammer. The nature of this engagement is preferably such that the hammer can be indexed to a number of positions (in this embodiment, six) around the central axis of the hammer prior to the hammer being clamped into position. This allows the hammer to be repositioned after the drill bits have worn to bring unworn portions thereof into service.

An alternative method of mounting the hammers to the central body to allow for repositioning utilises the combination of an alignment taper and an alignment plate or the like at the top end, with a locking means at the bottom end. The locking means may be in the form of a locking key and a key plate.

In use the drill is introduced into a borehole with the hammers in their inoperative position. The actuating means are then actuated to cause controlled movement of the hammers to the operative position at which time drilling can commence. When it becomes necessary to remove the drill from a borehole the actuating means releases the hammers to allow controlled movement thereof back to their inoperative position at which position the drill bits lie clear of the sides of the borehole. As a result the drill can be readily removed from the borehole.

The radially outermost portions of the drill bits will suffer the greatest wear. In order to maximise the wear of the drill bits, the hammers can be disengaged from the bracket means and indexed in the sockets such that unworn portions of the drill bit can be brought into service. This action is effected without the necessity for any specialised tools and without any significant disassembling of the hammer or drill.

On reintroduσtion of the drill to the hole the hammers are located in their inoperative position and as result the drill bits are maintained clear of the sides of the wall until such time as the drill is in its desired position in the borehole. At that time the hammers can be moved to their operative position.

It will also be appreciated that the drill of the invention is capable of varying its cutting diameter during operation which allows holes of varying diameters to be bored if required. It would thus be possible to operate the drill of the invention to slowly increase the cutting diameter as the drill bits are wearing to compensate for the usual loss in diameter because of that wear, resulting in a hole without the slight taper which is normally present.

It will further be appreciated that .the drill of the invention may be adapted to also include additional fixed hammers which are mounted so as to operate within the diameter of the rotation path of the drill bits of the , pivotally mounted hammers when in the operative position.

In order to assist in arriving at an understanding of the present invention, a preferred embodiment is illustrated in the attached drawings. However, it should be understood that the following description is illustrative only and should not be taken in any way as a restriction on the generality of the invention as described above. Figure 1 is a schematic side elevation of a drill according to the invention showing the hammers in the operative position;

Figure 2 is a schematic side elevation of the hammer showing the hammers in the inoperative position;

Figure 3 is a schematic planned view of the embodiment illustrating the hammers in the operative position;

Figure 4 is a schematic planned view of the embodiment illustrating the hammers in the inoperative position;

Figure 5 is a detailed cross sectional elevation of a portion of the embodiment.

Figures 1 to 4 illustrate a variable geometry cluster drill which can be used in production of large diameter holes. The drill comprises a central support 10 having a substantially elongate body 11 and having a longitudinal axis A about which the drill may rotate when in use. The body 11 is adapted at the top end 12 to be mounted to the end of a drill string. In addition, the body 11 includes a set of rollers 13 which are spaced angularly equidistant around the longitudinal axis of the body 11 and which are located towards the bottom end thereof. The rollers are mounted to the body to substantially centrally locate the support within the borehole 8.

The body 11 has pivotally mounted thereto a set of three hammers which are mounted substantially axially, when in the inoperative position of Figures 2 and 4, with respect to the body ^".' 1 and are pivotably supported from the support 11 through bracket means 15 provided towards the bottom end of the body 11. The .interconnection between the hammers 14 and the bracket means 15 provides for pivotal movement of the hammers about a transverse axis of the hammers such that the top ends thereof (which accommodate drill bits 16) are movable radially towards and away from the body 11 between the operative position of Figures 1 and 3 and the inoperative position of Figures 2 and 4.

Figure 3 illustrates the drill in the operative position and shows the diameter of the rotation path (indicated by circle X) of the drill bits when in that operative position. Figure 4 illustrates the drill in the inoperative position where the diameter of the rotation path (indicated by circle Y) is less than the equivalent diameter in the operative position. It will be noted that in this embodiment the rotation paths of each hammer are the same.

An actuating means in the form a hydraulic or pneumatic cylinder 17 is provided between the body 11 and each hammer 14 to cause the radial movement of the top ends of the hammers 14 between the operative position at which said • drill bits 16 are spaced radially from the body 11 and the inoperative position which said_.drill bit 16 are disposed substantially adjacent the body 11. The actuating means in this embodiment also serves to control and limit the movement of the drill bits.

The body 11 is provided with a support assembly adjacent the top ends of the hammers 14 which serves to limit the degree of outward movement of the hammers with respect to the body 11 when said hammers are moved to their operative position. The actuating means illustrated at Figure 5 comprises a pneumatic cylinder in which a cup-like shaped piston 18 is movable against the hammers as a result of the introduction of air into a chamber 19. The air is introduced into the chamber 19 through a restricted passageway 20. The purpose of the restricted passageway is to provide a substantially constant fluid pressure within the chamber 19 which is not necessarily subject to incidental variations in fluid pressure being applied down the drill string. As an alternative the pneumatic cylinder may be substituted by a hydraulic cylinder whereby a hydraulic accumulator is provided within the body 11 to cause the introduction of hydraulic fluid into the hydraulic cylinder whereby such introduction is effected by the fluid pressure applied through the drill string.

The hammers are mounted in the bracket means 15 through a support element in the form of a polygonal socket (not shown) which is pivotally supported from the bracket means 15 and which is adapted to non-rotatably receive and support the end of the hammers 14. The configuration of the inter-engaging portions of the socket and hammer 14 may be such that the hammer can be indexed to a variety of positions around the central axis of the hammer prior to said hammer being clamped into position.

If desired the bracket means 15 may be located on the body 11 such that the hammers are pivotally supported intermediate of their length rather than at an end thereof and the support element may take the form of a collar or like means. It should be appreciated that the scope of the invention need not be limited to the particular scope of the embodiment described above.

Claims

THE CLAIMS defining the invention are as follows:-

1. A variable geometry cluster drill for rockboring comprising a central support having a longitudinal axis about which the drill is capable of rotating to bore a hole and a plurality of elongate hammers located about the central support, each hammer having a drill bit at one end, wherein at least one hammer is pivotally mounted to the central support so that the drill bit thereof is capable of radial movement away from or towards the central support between an operative position and an inoperative position, the diameter of the rotation path of the drill bit in the operative position being greater than in the inoperative position, the central support including means for controlling the radial movement of the drill bit between the operative and inoperative positions.

2. A drill according to claim 1 wherein the central support is an elongate central body having a top end and a bottom end, being adapted at the top end to be mounted to a drill string and at the bottom end to include a set of roller elements, each of said hammers being pivotally mounted to the body at or towards the bottom end thereof and engaging the body at or towards the top end thereof, so as to be generally adjacent to the body and substantially parallel to the longitudinal axis when in the inoperative position and at an angle to that axis when in the operative position.

3. A drill according to claim 2 wherein the engagement of each hammer with the top end of the body is achieved

-via the control means which includes means for actuating the pivotal movement of the hammer.

4. A drill according to claim 1 wherein each hammer engages with the central support via the control means which includes an actuating means to provide pivotal movement to each hammer.

5. A drill according to claim 3 or claim 4, wherein the actuating means is a single actuating device responsible for the pivotal movement of all of the hammers.

6. A drill according to claim 3 or claim 4, wherein the actuating means is a plurality of actuating devices, there being one actuating device per hammer.

7. A drill according to claim 5 or claim 6 wherein the or each actuating device is a pneumatically or hydraulically operated cylinder having a piston movable against a hammer as a result of the introduction of air or fluid into a piston chamber.

8. A drill according to claim 7 wherein the piston is urged away from the hammer by a biasing means whereby force', is required to be applied by the actuating means to overcome the force of the biasing .means to move the hammers to their operative position.

9. A drill according to any one of claims 1 to 8, wherein the or each pivotally mounted hammer is mounted to the central support by a bracket means which extends beyond the central support to allow the hammer to be mounted adjacent the central support.

10. A drill according to claim 9 wherein the bracket means includes a pivotally mounted support element capable of receiving a hammer, and a clamping means for clampingly and non rotatably retaining the hammer within the support element..

11. A drill according to claim 10 wherein the support element is a socket having a polygonal cross-section suitable for engagement with a correspondingly shaped portion of a hammer, such that the hammer can be indexed to a plurality of positions to allow unworn portions of the drill bit to be rotated into service.

12. A drill according to claim 10 wherein the support element includes a locking means which combines with an alignment taper and plate located away therefrom to together be responsible for mounting a hammer such that it can be indexed to allow unworn portions of the drill bit to be rotated into service.

13. A drill according to claim 12 wherein the locking means is a locking key and a key plate.

14. A drill according to claim 1 substantially as herein described with reference to the accompanying drawings.