WO1994023172A1

WO1994023172A1 - Rotary percussive core drill bit

Info

Publication number: WO1994023172A1
Application number: PCT/AU1994/000164
Authority: WO
Inventors: Roger Arthur Crocker; Frederick Graham Moir
Original assignee: Sds Pty. Ltd.
Priority date: 1993-04-05
Filing date: 1994-04-05
Publication date: 1994-10-13
Also published as: CA2159903A1

Abstract

A drill bit for a drill system using a down-the-hole reverse circulation percussive hammer with at least one aperture (5a) in a cutting face of the drill bit, the aperture communicating with a return conduit (4), with a part only of the aperture being located and shaped so as to coincide with an axial centre (8) of the drill but such that as the drill bit is rotated about the central axis, the aperture in the drill bit will define an un-cut area (5) which is coaxial with the central axis of the drill bit, and a clearance space (6) offset from the un-cut area.

Description

ROTARY PERCUSSIVE CORE DRILL BIT

TECHNICAL FIELD

This invention relates to a drilling arrangement and a method wherein there is included a reciprocating piston hammer adapted to effect a hammering against a drill bit in a down-the-hole location.

BACKGROUND ART

Conventionally such an arrangement uses air at pressure which is used to drive the reciprocating hammer and which is also directed across the face of the bit to collect cuttings and to then transport these back up the hole.

In a reverse circulation arrangement, air is directed to an external periphery of the bit from whence it is directed from the outside of the working face of the bit to an inner collecting conduit in the face of the bit.

In some instances, the fluid can be a liquid such as water.

The problem to which this invention is directed is an attempt to achieve larger pieces of recoverable target rock than has hitherto been able to be achieved.

Such larger pieces are more valuable for geological interpretation of the target material and if it was possible to obtain full core pieces, that would be even better. DISCLOSURE OF THE INVENTION

In one form of the invention, there is proposed a drill bit for a drill system using an down-the-hole reverse circulation percussive hammer adapted to use fluid pressure to both drive a percussion hammer and clear cuttings, the drill bit having at least one aperture in a cutting face of the drill bit, the aperture communicating with a return conduit , the drill bit being characterised in that a part of the at least one aperture is located and shaped so as to coincide with an axial centre of the drill bit such that as the drill bit is rotated about the central axis, the aperture in the drill bit will define an un-cut area in the face being cut, the un-cut area being coaxial with the central axis of the drill bit, and the rotation of the drill bit further defining a clearance space offset from the un¬ cut area. Using this arrangement, as the drill bit is rotated and driven by the reciprocating hammer, there will be therefore the tendency to leave in the centre of the drill bit an un-cut portion of the cut face which can be subsequently broken off to provide a sufficiently large sample of rock or cutting to satisfy the needs of testing.

As the drill bit is driven through the rock face, there will be some tendency for a protruding part of the rock face to exist in the form of an un-cut portion which can then be subjected to a fracturing force either by reason of incidental sideways vibration of the bit under its hammer stresses or by reason of the shape of the conduit into which the un-cut portion is being directed.

In preference, the shape of the aperture in a central part of the drill bit comprises a shape which is circular in cross section and which has a central axis which is inclined to the central axis of the drill bit and connects with a clearing conduit through a remainder of the drill bit which has a substantially equivalent cross sectional area.

In preference, such an arrangement further includes one or more cutting elements which are specifically located in the adjacent vicinity of the central aperture so as to be adapted to effect a cutting of a rock face around a centrally located un-cut portion.

Conveniently the aperture in the drill bit is cylindrical. The advantage of having a cylindrical aperture passing through the drill face simply at an inclined angle is that this can be cut very readily with conventional machine tools so that the manufacture of such a drill bit is relatively straightforward.

The advantages of having one or more cutting elements located on the periphery of such an aperture is that this then helps to cut and define a central un-cut portion more effectively as it develops and saves undue wearing of the supporting material of the drill face as the core is effected.

In a further form the invention may comprise a drill bit for a down-the-hole reverse circulation percussive drilling using fluid under pressure to effect clearing of cut chips, having a collecting aperture through a cutting face of the drill bit, the shape and location of the aperture being such that as the drill bit is used and rotated around an elongate axis thereof, the cutting face will define and leave substantially an un-cut central core part while having at least one further part which will be left open and clear from any core to assist separate passage of the fluid by passing the un-cut central core.

For a better understanding of the invention it will now be described with relation to a preferred embodiment which shall be described with the assistance of drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a drill bit constructed according to the embodiment;

FIG. 2 is a cross sectional view through the lines A-A of FIG. 1 ;

FIG. 3 is a cross sectional through the lines B-B of FIG. 1 , and FIG. 4 is a cross sectional through the lines C-C of FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Shown in the drawings is a drill bit which is to be used in a down-the-hole, reverse flow, percussive drill arrangement.

The drill bit is designed for air and fe arranged such that air will flow from the outside periphery of the bit across the face and then return carrying such chips as might be gathered, through a central return conduit.

Referring now to the drawings, the drill bit 1 has substantially U-shaped channels or flutes 2 formed in a conventional manner around outer edges of the drill bit 1 for supply of air from around the outside of the drill bit 1. The air directed across the cutting face of the drill bit 1 and travels along channels 3 formed in the cutting face of the drill bit 1 to a return conduit 4. The return conduit 4 is positioned generally centrally within the drill bit 1 and extends along an elongate axis thereof.

The drill bit 1 has an aperture 5a located in a cutting face thereof. The aperture 5a is in fluid communication with the return conduit 4. As can be seen from Figs 2 and 4 the aperture 5a is coincident to some degree with the return conduit 4. This coincident area defines an un-cut portion of the rock face shown at 5 as a hatched notional circle. This area will not be either subject to any cutting effect for any cutting tips or otherwise intercepted with metal so that there will be allowed some development an un-cut column of rock in this vicinity.

In order to allow for return air however, the aperture 5a is offset from the return conduit 4.

This has the effect of creating a space shown at 6 as the drill bit 1 is rotated around a central axis thereof. Conveniently, the space 6 is chosen so as to be big enough to allow for sufficient return of air and appropriate cuttings from the remainder of the cutting tips and the cutting face to be directed there through.

There is some advantage in making sure that the aperture size of the return conduit 4 is smaller at the entrance than subsequently so that whatever gets through including perhaps big columnar pieces of target rock, will not thereafter be stopped from proceeding under the fluid pressure.

A technique which is both effective from a manufacturing point of view and from an application point of view to achieve the shape and position of the aperture 5a conduit is shown more particularly at FIG. 2 in which there is a first portion shown at 7 which is drilled so that its axis is at an inclined relationship with the central axis shown at 8 of the drill.

In the embodiment describes herein the first portion 7 is inclined 10° to the return conduit 4.

The length is approximately the same as the diameter so that the offset extent is as is shown in FIG. 1 which is calculated to be appropriate for the purposes described.

However, different positions and different calculations can result in different answers and it is not intended that this particular solution should be the only one that is useful.

However, the advantage of having a circular shape is that this can always be cut very easily with appropriate drills and therefore manufacturing is both economical and convenient.

Alternatives such as ovuloid shapes can also be cut but of course add to complications in cutting and therefore costs.

In order to effect most efficient cutting effect cutting tips or buttons these are conventionally located except that in this particular case there are located two cutting buttons 10 and 11 which lie relatively close to the closest part of the aperture 5a to the central axis of the drill bit 8. To the extent that the cutting buttons 10,11 are relatively close to the aperture 5a and in fact slightly overhang across the aperture, they, therefore, effectively define and cut out the columnar shape of the rock.

What has been found in experimental trials so far is that the substantial vibration being created by the hammering, creates a sideways vibrational thrust which breaks up the target rock material so that whereas previously it had been thought useful to have some means of breaking up the columnar shape, this has not been found to be specifically necessary as it happens inevitably because of the total dynamics of the arrangement.

It is to be particularly noted that the inlet passage 7 is non-circular, and by drilling the passage at the above described angle, the inlet passage is elliptical and it is due to this shape which produces the un-cut portion which fractures into larger pieces.

Also, alternate airways 12 shown in FIG. 3 are provided. Thus if the drill face encounters a material such as clay, the passages 3 may become blocked. The air will then pass through the alternate passage so that the material in the passage 4 will continue to be carried upwardly.

It is to be noted in the drawings that the cross section through the cutting buttons or their profile has not been included in FIGS. 2 and 3 simply for sake of convenience.

In experimental trials with the apparatus described thus far, cuttings have been significantly larger in mass than would be obtained by an equivalent drill bit without the feature described in equivalent target material.

Such additional size of chips has been found useful for geological interpretation so far so that the use of this feature is regarded as an improvement of the previous devices and therefore significant economic value in the industry.

Throughout the specification the purpose has been to illustrate the invention and not to limit this.

Claims

1. A drill bit for a drill system using an down-the-hole reverse circulation percussive hammer adapted to use fluid pressure to both drive a percussion hammer and clear cuttings, the drill bit having at least one aperture in a cutting face of the drill bit, the aperture communicating with a return conduit , the drill bit being characterised in that a part of the at least one aperture is located and shaped so as to coincide with an axial centre of the drill bit such that as the drill bit is rotated about the central axis, the aperture in the drill bit will define an un-cut area in the face being cut, the un-cut area being coaxial with the central axis of the drill bit, and the rotation of the drill bit further defining a clearance space offset from the un-cut area.

2. A drill bit according to claim 1 , further characterised in that there is at least one cutting tip associated with each at least one aperture, each at least one cutting tip being positioned so as to be adjoining a periphery of a respective aperture, each at least one cutting tip being adapted to effect a cutting in a target face around the un-cut area.

3. A drill bit according to claim 2, further characterised in that there are at least two cutting tips which are each positioned so as to be adjoining the periphery of a respective aperture, the cutting tips being adapted to effect a cutting in a target face around the un-cut area..

4. A drill bit as according to any one of the preceding claims, further characterised in that the un-cut area is elliptical in shape.

5. A drill bit according to any one of claims 1 to 3, further characterised in that the un-cut area is circular in shape.

6. A drill bit according to any one of the preceding claims, characterised in that the fluid is air.

7. A drill bit according to any one of the preceding claims, further characterised in that there are at least two cutting tips each of which is positioned so as to be adjoining the periphery of the said un-cut area, the cutting tips being adapted to effect a cutting in a target face around the un-cut area.

8. A drill bit for down-the-hole reverse circulation percussive drilling using fluid under pressure to effect clearing of cut chips, having a collecting aperture through a cutting face of the drill bit, the shape and location of the aperture being such that as the drill bit is used and rotated around an elongate axis thereof, the cutting face will define and leave substantially an un-cut central core part while having at least one further part which will be left open and clear from any core to assist separate passage of the fluid by passing the un¬ cut central core.

9. A drill bit according to claim 8, further characterised in that the drill bit includes a return conduit, the return conduit including means to fracture the core periodically so that the fractured piece or pieces can be further removed by the fluid passing thereby.

10. A drill bit according to claim 9, further characterised in that the means for fracturing the core includes the orientation of the return conduit.

11. A method of drilling using a down-the-hole reverse circulation percussive hammer adapted to use fluid pressure to both drive a percussion hammer and clear cuttings comprising using as a bit the drill bit as characterised in any one of the preceding claims and using it so that the un¬ cut area in the aperture is caused to rotate about its coaxis with the central elongate axis of the drill bit.

12. A method of drilling using a down-the-hole reverse circulation percussive hammer using fluid under pressure to both drive a percussion hammer and clear cuttings, having a collecting aperture through its bit cutting face the shape and location of which is such that as the bit is used and rotated it will define and leave substantially uncut a central core part while having at least one further part which will be left open and clear from any core to assist separate passage of fluid bypassing uncut core.