DRILL BIT WITH CURVED SLUDGE GROOVES

Abstract

A percussive drill bit includes a head and an axially rearward skirt. A plurality of ribs project radially outward at the skirt and define lengthwise extending channels. The ribs and channels, in the lengthwise direction are curved or angled to deviate from a longitudinal axis of the drill bit to facilitate rearward transport of fines and flushing fluid.

Claims

1. A drill bit comprising: a head having cutting elements arranged to abrade rock by rotation of the drill bit about its longitudinal axis; a skirt extending axially rearward from the head; and a plurality of ribs projecting radially outward and extending axially along the skirt to define axially extending channels, the rib and channels each having a length extending axially in a lengthwise direction between the head and an axially rearward end of the skirt, wherein in the lengthwise direction at least a part of the ribs and channels are bent or curved such that a lengthwise part of the ribs or channels is oblique to the longitudinal axis.

2. The drill bit as claimed in claim 1, wherein the lengthwise part of the ribs and channels that are oblique to the longitudinal axis are positioned at an axially rearward part of the skirt.

3. The drill bit as claimed in claim 2, wherein an axially forward part of the ribs and channels is aligned generally parallel to the longitudinal axis.

4. The drill bit as claimed in claim 2, wherein said axially rearward part extends up to 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the length of the skirt between an axially rearwardmost region of the head and the axially rearward end of the skirt.

5. The drill bit as claimed in claim 1, wherein the lengthwise part of the ribs and channels extend at least partly helical around the axis.

6. The drill bit as claimed in claim 1, wherein each rib includes a leading face and a trailing face separated by a radially outward facing land face, the leading and trailing faces at least partial defining the channels.

7. The drill bit as claimed in claim 6, wherein in the lengthwise direction both the leading and trailing faces of the ribs are bent or curved in the same circumferential direction around the axis so as to be aligned oblique to the axis.

8. The drill bit as claimed in claim 6, wherein in the lengthwise direction, at least a part of a leading edge and a trailing edge of the ribs at a junction between the land face and the respective leading face and trailing face is bent or curved so as to be aligned oblique to the axis.

9. The drill bit as claimed in claim 8, wherein the part of the leading edge and the trailing edge that are oblique to the axis are positioned at an axially rearward part of the skirt.

10. The drill bit as claimed in claim 6, wherein at a cross sectional plane perpendicular to the longitudinal axis, the leading face is aligned generally normal to the rotational direction of the bit about the axis.

11. The drill bit as claimed in claim 10, wherein in the cross sectional plane perpendicular to the axis, the trailing face is aligned transverse to the rotational direction of the bit and/or oblique to the leading face.

12. The drill bit as claimed in claim 1 wherein an angle by which the ribs are bent or curved such that their length deviates in a circumferential direction is in the range of 1 to 20° relative to the axis.

13. The drill bit as claimed in claim 12 wherein the range is 3 to 10°, 3 to 8° or 4 to 6°.

14. The drill bit as claimed in claim 1, further comprising an internal bore and passageways extending axially from a forward end of the bore arranged to emerge as openings at a forward cutting face of the head, at least some of the channels extending axially along the head in communication with the openings.

15. The drill bit as claimed in claim 1, wherein the cutting elements include cutting buttons embedded into the head.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0022] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0023] FIG. 1 is a perspective view from above of a percussive drill bit according to a specific implementation of the present invention;

[0024] FIG. 2 is a side perspective view of the drill bit of FIG. 1;

[0025] FIG. 3 is a perspective view from below of the drill bit of FIG. 2;

[0026] FIG. 4 is a rear end perspective view of the drill bit of FIG. 3; and

[0027] FIG. 5 is a cross sectional perspective view of the drill bit of FIG. 3;

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0028] Referring to FIGS. 1 to 3, a percussive drill bit 10 comprises a cutting head 11 from which extends axially rearward an elongate skirt 12. Head 11 comprises a forward facing cutting face 13 that, according to the specific implementation is domed in a forward cutting direction. A plurality of superhard cutting buttons are embedded into cutting face 13 and include radially outer gauge buttons 14a and inner buttons 14b as will be appreciated. Head 11 is provided with a raised annular shoulder 16 the axially forward region of which mounts gauge buttons 14a.

[0029] Referring to FIG. 5, skirt 12 is hollow and comprises an internal bore 26 centred on a longitudinal axis 19 of bit 10. A set of flushing fluid passageways 27 extend axially forward from a forward end 28 of bore 26 to emerge at cutting face 13 as openings 15. According to the specific implementation, three fluid passageways are provided in communication with bore 26 to emerge at cutting face 13. A respective groove or channel 18a projects radially outward from each opening 15 in a direction from axis 19 to head shoulder 16. Channels 18a are recessed into cutting face 13 and also shoulder 16 to extend axially rearward from head 11 along the full axial length of skirt 12. Bit 10 comprises two types of flushing groove including a first channel 18a in fluid communication with each respective passageway 27 (and opening 15) and a second channel 18b that terminates at its axially forward end at neck 12d and does not extend over a medial region of face 13 towards axis 19.

[0030] Referring to FIGS. 1 and 3, the skirt 12 comprises an axial length, centred on axis 19 and extending between a neck 12d (representing an axially rearwardmost region of shoulder 16) and an axially rearwardmost end 12e of skirt 12. Along its length, skirt 12 may be considered to be divided into a number of axial sections defined by the maximum external diameter of the skirt 12 (within each section). A first section 12a immediately axially rearward of neck 12d, comprises a smallest diameter; a second middle section 12b is radially enlarged relative to first section 12a and an axially rearwardmost third section 12c is radially enlarged relative to the first and second sections 12a, 12b. Respective annular step regions 29 provide a transition between the different diameter sections 12a, 12b, 12c.

[0031] Each of the channels 12a, 12b along the length of skirt 12 between neck 12d and rearward end 12e are defined (i.e., flanked) by axially extending ribs indicated generally by reference 17. That is, ribs 17 extend the full length of skirt 12 from head 11 to skirt rearward end 12e. A thickness in the circumferential direction of each rib 17 is non-uniform and changes in a direction of axis 19 between neck 12d and skirt rearward end 12e. Moreover, each rib 17 is curved (alternatively termed angled or bent) in its lengthwise direction between neck 12d and skirt rearward end 12e so as to deviate or deflect in the circumferential direction. According to the specific implementation, each of the ribs 17 is bent within the rearward second and third sections 12b, 12c but are substantially linear within the axially forward section 12a immediately behind head 11. Accordingly, channels 18a, 18b are also bent (alternatively termed angled or curved) so as to deviate in the circumferential direction within the second and third sections 12b, 12c. As such, at least a portion of the axial length of ribs 17 and channels 18a, 18b (within sections 12b, 12c) are aligned oblique to axis 19. According to the specific implementation, ribs 17 and channels 18a, 18b (within sections 12b, 12c) follow a part helical path around axis 19 between a rearward end of first section 12a and skirt rearward end 12e.

[0032] Referring to FIG. 2, an angle θ by which each rib 17 is bent or deflected in its lengthwise direction from axis 19 (so as to be oblique/non-parallel to axis 19) may be in the range 1 to 20°, 3 to 10° or 3 to 8°. Such deviation refers to the general lengthwise path of ribs 17 within the second and third sections 12b, 12c. As illustrated in FIG. 2, the combined rearward sections 12b, 12c represents a majority of the length of skirt 12 as each section 12a, 12b, 12c represents generally a respective third of the length of skirt 12. An axial length over which the ribs 17 (and channels 18a, 18b) are oblique relative to axis 19 may be in the range 20-100%, 30-90%, 40-80% or 50-70%.

[0033] Referring to FIGS. 2 to 4, each rib 17 and channel 18a, 18b may be defined further to include a radially innermost trough 22 which in the lengthwise direction is flanked at a first side by a leading face 20 and an opposite side by a trailing face 25. Faces 20, 25 are so named with reference to the rotational direction R (FIG. 4). Each rib 17 comprises a land face 23 representing a radially outermost region of skirt 12 within each section 12a, 12b, 12c. The land face 23 is terminated at each side (in a circumferential direction around axis 19) by a leading edge 21 at the junction with leading face 20 and a trailing edge 24 at the junction with trailing face 25.

[0034] The angle θ by which each rib 17 and channel 18a, 18b extends oblique to axis 19 may be defined relative to the general lengthwise pathway of the ribs 17 and channels 18a, 18b or with reference to the relative orientation of trough 22, leading faces 20, leading edge 21, land face 23, trailing edge 24 and/or trailing face 25. According to the specific implementation, trailing edge 24 is bent at a greater angle relative to leading edge 21 such that a thickness in the circumferential direction of each rib 17 decreases in the axially rearward direction towards skirt rearward end 12e over second and third sections 12b, 12c. Accordingly, a width in the circumferential direction of each channel 18a, 18b increases in the axially rearward direction over sections 12b, 12c. Where the leading and/or trailing edges 21, 24 are curved along their length, a radius of the leading edge 21 may be greater than a corresponding radius of trailing edge 24 so as to provide a corresponding non-parallel alignment of leading face 20 and trailing face 25.

[0035] Referring to FIG. 4, leading face 20 comprises at least a radially outer portion that is aligned on a radial spoke 30 and normal to the rotational direction R so as to be aligned perpendicular to a tangent of an imaginary circle centred on axis 19. Trailing face 25 is aligned transverse to spoke 30 and leading face 20 so as to be declined radially inward from land face 23.

[0036] The non-linear lengthwise path of each of the ribs 17 and channels 18a, 18b at least within the second and third sections 12b, 12c is advantageous to facilitate axially rearward transport of cuttings mixed with the flushing fluid that is typically represented as a sludge. That is, the angled or curved lengthwise orientation of ribs 17 and channels 18a, 18b, facilitate the rearward passage of the sludge from the cutting region at head 11 and axially rearward along the as-formed bore. Additionally, the oblique alignment of ribs 17 and channels 18a, 18b facilitate axially rearward extraction of the drill bit 10 that is also rotated in direction R during extraction. Removing cut debris and flushing fluid from around the external region of the skirt 12 and at the head 11 reduces the risk of the drill bit 10 getting stuck within the bore during extraction in addition to minimising possible bore collapse during extraction.

[0037] According to further embodiments, the curved or angled lengthwise deviation of ribs 17 and channels 18a, 18b may extend the full axial length of skirt 12 between neck 12d and rearward end 12e. The angle by which each rib 17 is aligned relative to axis 19 may the same for all ribs 17 and at all regions of each rib 17 or the angle of deviation may be different for different ribs 17 and at different regions of each rib 17. Accordingly, a width of each channel 18a, 18b may be the same between neck 12d and skirt rearward end 12e or may vary in a lengthwise direction.