Drill bit

Abstract

A percussive drill bit (1) comprising a bit body (10) having a longitudinal axis of rotation (X). The bit body comprises a front face (12) and a skirt (14) extending in a rearward direction from the front face, an internal conduit (16) for supplying pressurized fluid to the front face, at least one flushing port (18) in the front face and arranged in fluid communication with the internal conduit, and at least one evacuation channel (34) extending through the bit body from an evacuation port (36) in the front face to an opening (38) in the skirt.

Description

DRILL BITTechnical Field

[0001] The present disclosure relates to a drill bit for use in mining and construction operations. It relates particularly but not exclusively to a down-the-hole (DTH) drill bit or a top hammer (TH) drill bit, which are specific types of drill bit used with a primarily percussive action.Background

[0002] Various types of drill bits are employed when drilling rock formations in association with, for example, mining and other types of rock breaking activities. One particular type of drill bit is known as a percussion or hammer drill bit. Percussion type drill bits are positioned at the end of a drill string and engage a rock formation while impacting the formation and also rotating relative to the formation.

[0003] The drill bit is mounted on the lower end of a drill string. The hammer, also known as the percussion mechanism, is located directly behind the drill bit in the case of DTH percussive drilling or above ground for TH percussive drilling. Drill pipes connected to the drill string serve to deliver the necessary feed force and rotation to the hammer and bit, along with fluid such as compressed air or water. As the hole gets deeper, additional drill pipes are added successively.

[0004] Percussive drill bits typically comprise a steel body, called bit body, with a front face and a skirt portion which extends in a rearward direction from the front face. A number of inserts of a harder material, usually cemented carbides, are mounted in the front face and optionally on the skirt as cutting elements. The inserts being of a harder material improves the service life of the drill bit as they are more resistant to wear than the steel of the bit body.

[0005] In order to continue penetration of the drill bit through the rock formation, crushed rock and debris, so called drill cuttings, must be removed from the bore hole. This is typically achieved by a pressurized fluid supplied through ports in the front face in fluid communication with an internal bore of the drill bit. Further, the drill bit usually comprisesa number of flutes or scallops formed around the perimeter and skirt to allow passage of the drill cuttings and pressurized fluid.

[0006] The size and number of flutes or scallops dictates the amount of drill cuttings which can be removed per unit time and thus the rate of penetration of the drill bit.Increasing the size and / or number of flutes or scallops reduces the available area for inserts on the drill bit and thereby negatively affects the service life. Vice versa, increasing the number of inserts on the perimeter decreases the available area for the flutes or scallops and negatively affects the rate of penetration. Thus, the design of the drill bit must reconcile two competing characteristics, the service life and rate of penetration, to find an optimal configuration.

[0007] Hence there is a need to develop improved percussive drill bits wherein service life may be increased without negatively affecting the rate of penetration.Summary of Invention

[0008] An objective of the present disclosure is therefore to provide an improved percussive drill bit to solve the problems identified above.

[0009] According to a first aspect of the present disclosure, there is provided a percussive drill bit comprising a bit body having a longitudinal axis of rotation. The bit body comprises a front face and a skirt extending in a rearward direction from the front face, an internal conduit for supplying pressurized fluid to the front face, at least one flushing port in the front face and arranged in fluid communication with the internal conduit, and at least one evacuation channel extending through the bit body from an evacuation port in the front face to an opening in the skirt.

[0010] By means of the evacuation channels, additional pathways for removal of rock drillings from the front face are provided. This allows for either increasing the penetration rate of the drill bit with maintained service life, or alternatively to increase the service life of the drill bit, by increasing the number of wear-resistant inserts, with a maintained penetration rate.

[0011] In one embodiment, the opening may be arranged in a lateral surface of the skirt. Alternatively or additionally, the opening may be arranged in a shoulder of the skirt,the shoulder extending between a rear edge of the skirt and a shank of the drill bit. By arranging the opening at a distance from the front face, congestion of rock drillings across the outer perimeter of the front face is avoided, reducing the wear on the bit body.

[0012] In one embodiment, wherein the number of evacuation channels may be equal to or greater than the number of flushing ports, preferably two times greater. Thus, it is ensured that the flushing fluid and rock drillings have sufficient pathways for removal from the bore hole.

[0013] In one embodiment, the drill bit may further comprise at least one elongate recess arranged in the front face, wherein the at least one elongate recess extends between the at least one evacuation port and an adjacent flushing port. The elongate recess provides space for guiding rock drillings towards the evacuation port to facilitate removal and reduce wear and tear on the bit body.

[0014] In one embodiment, the drill bit may comprise a plurality of evacuation channels with respective evacuation ports arranged in a circular configuration in the front face. The circular configuration may provide a symmetrical distribution of flow across the front face and facilitates manufacturing.

[0015] In one embodiment, wherein the at least one evacuation port may be arranged radially outside the at least one flushing port. Thus, the evacuation ports may be optimally located to receive the flushing fluid introduced through the flushing ports and the rock drillings which tends to move outward from the center when the drill bit is rotated.

[0016] In one embodiment, the drill bit may further comprise a plurality of wearresistant inserts each seated in a correspondingly shaped recess in the front face, wherein at least a portion of the wear-resistant inserts are arranged along an outer perimeter of the bit body.

[0017] In one embodiment, the bit body may further comprise a plurality of scallops along the outer perimeter of the front face, each scallop being arranged between two adjacent wear-resistant inserts.

[0018] In one embodiment, the wear-resistant inserts arranged along the outer perimeter substantially cover at least half the circumference of the front face. This configuration provides an optimal ratio of surface area of the front face being covered by inserts to exposed surface area.

[0019] In one embodiment, the sum of cross-sectional areas of all evacuation ports and scallops may be equal to or greater than the sum of cross-sectional areas of all flushing ports. This ensures that the fluid entering the bore hole to flush away rock drillings has sufficient space to exit.

[0020] The percussive drill bit according to any one of claims -, wherein the wearresistant inserts may comprise cemented carbide and / or polycrystalline diamond (PCD) material.

[0021] In one embodiment, wherein the at least one flushing port may be arranged adjacent to a flushing groove in the front face, the flushing groove extending radially outwards from the flushing port towards an outer perimeter of the bit body. The flushing grooves serve to guide cut rock drillings away from the central portion of the front face towards the outer perimeter.Brief Description of Drawings

[0022] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:Fig. 1 shows a perspective view of a drill bit according to one embodiment of the present disclosure.Fig. 2 shows a side view of a drill bit according to one embodiment of the present disclosure.Fig. 3 shows a top view of a drill bit according to one embodiment of the present disclosure.Fig. 4 shows a cross-sectional view taken along line A- A of Fig. 3.Fig. 5 shows a cross-sectional view taken along line B-B of Fig. 3.Fig. 6 shows a cross-sectional view of an alternative embodiment, corresponding to the view of Fig. 5.Detailed Description

[0023] In the following, a detailed description of a percussive drill bit according to the present disclosure is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of ‘including’, ‘comprising’, or ‘having’ and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms ‘mounted’, ‘connected’, ‘supported’, and ‘coupled’ and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, ‘connected’ and ‘coupled’ are not restricted to physical or mechanical connections or couplings.

[0024] For the sake of simplicity and consistency in this specification, the term ‘axial’ refers to a direction parallel to a central longitudinal axis of a drill bit as illustrated in the drawings. The term ‘radial’ refers to a direction perpendicular to the axis of the drill bit. All elements also have first and second ends which, using the convention of the illustrated embodiment, may be referred to as ‘proximal’ and ‘distal’ ends with respect to the typical operating orientation of a hammer and drill bit in relation to the operator.

[0025] Referring now to Figs. 1-3, there is shown perspective, side and top views of an exemplary percussive drill bit 1 according to the present disclosure. The drill bit 1 is connectable to a percussion mechanism and drill string in a conventional manner. The drill bit 1 comprises a drill bit body 10 having a front face 12 and a skirt 14 extending from the front face 12 in a rearward direction. The bit body 10 is rotationally symmetric and has a generally cylindrical shape. Other shapes wherein the diameter of the skirt 14 varies along the axial direction are also foreseen, such as conical or flared. The diameter of the front face 12 determines the diameter or gauge of the bore hole.

[0026] The front face 12 may be planar (flat or substantially flat) or curved, such as convex or concave, or a combination thereof. For instance, a central portion 12a of the front face 12 may be planar, whereas a peripheral portion 12b may be bevelled in one ormore steps, creating an overall substantially convex shape of the front face 12, as shown in Figs. 4-6. Concave faces are generally considered to be excellent all-round performers, used as a general-purpose bit for most conditions while drilling a very straight hole. Convex faces are used for a combination of speed and service life. Flat faces are best suited for broken or fragmented ground and hard formations.

[0027] The drill bit 1 further comprises an internal conduit 16, as shown in Fig. 4, for supplying flushing fluid to the front face 12, e.g. pressurized air or water indicated by the arrows, for flushing away rock drillings. In the embodiment shown, three flushing ports 18 are provided in the front face 12, each arranged in fluid communication with the internal conduit 16 by means of a flushing channel 20. It is foreseen that any number of flushing ports 18 is encompassed in the present disclosure.

[0028] The front face 12 may comprise a flushing groove 22 associated with each flushing port 18. The flushing groove 22 extends radially outwards from the flushing port 18 towards an outer perimeter 13 of the front face 12. The flushing grooves 22 serve to guide cut rock drillings away from the central portion of the front face 12 towards the outer perimeter 13. Further, the bit body 10 comprises a plurality of flutes or scallops 32 formed around the outer perimeter 13 of the front face 12 and extending in a rearward direction. The scallops 32 may be regularly or irregularly distributed about the circumference of the front face 12. The scallops 32 aid in removing the rock drillings from the bore hole.

[0029] Furthermore, the drill bit 1 comprises a shank 24 including a plurality of splines 26 for connecting to a hammer (not shown). The shank 24 adjoins the drill bit body 10. The drill bit body 10 and shank 24 conventionally comprise steel or an alloy thereof. Both drill bit body 10 and shank 24 are typically cylindrical, but the diameter of the drill bit body may also vary along the axial extension thereof. The outer diameter of the skirt 14 may be in the range 140-200 mm, but any size diameter may be used as required by the drilling operation. The outer diameter of the shank 24 is less than that of the skirt 14 to allow for maneuverability of the drill bit 1. The portion of the bit body 10 extending between the rear edge 17 of the skirt 14 and the shank 24 is referred to as the shoulder 28. The drill bit body 10 has a longitudinal axis of rotation X (best seen in Fig. 2).

[0030] The drill bit 1 further comprises a plurality of wear-resistant inserts 30 in the front face 12, also known as buttons or studs. Each insert 30 is seated in a correspondingly shaped recess in the front face 12. The studs 30 are secured to the bit body 10 using brazing, but alternatively press-fitting, shrink fitting, gluing or any other means of attachment could be used instead.

[0031] In the embodiment shown in Figs. 1-3, a total number of thirty-two inserts 30 are provided on the bit body 10, eighteen peripheral inserts 30 arranged along the outer perimeter 13, and fourteen inserts 30 arranged in the central portion 12a of the front face 12. However, it is foreseen any number of inserts 30 could be used. The inserts 30 can be arranged only in the central portion 12a, only along the outer perimeter 13, or a combination thereof. The inserts 30 may be arranged in a symmetrical or non-symmetrical pattern about the axis of rotation X. As shown in Figs. 1-3, the peripheral inserts 30 may be regularly distributed about the circumference of the front face 12, with a scallop 32 arranged between two adjacent inserts 30. The number of inserts 30 between two adjacent scallops 32 could be one or more, depending on the distance between adjacent scallops 32 which in turn is dependent on the number of scallops 32. In one embodiment, the number of inserts 30 between two adjacent scallops is in the range 2-4. It is also foreseen that the scallops 32 may be unevenly distributed about the outer perimeter 13, resulting in varying distance between adjacent scallops 32, and thus allowing for varying the number of inserts 30 between adjacent scallops 32.

[0032] In the case of an overall substantially convex shape of the front face 12 mentioned above, the wear-resistant inserts 30 along the outer perimeter 13 are slightly outwardly tilted compared to the inserts 30 in the central portion 12a of the front face 12.

[0033] Typically, each insert 30 has a diameter in the range 5-20 mm, with a length of about 5-40 mm. Other diameters may be used, for example, 6-30 mm. The diameter of the inserts 30 used in the central portion 12a may be different to or the same as the diameter of the inserts 30 used along the outer perimeter 13, or a combination thereof.

[0034] The inserts 30 comprise a material that is harder / more wear-resistant than the material of the bit body 10. The inserts 30 preferably comprises cemented carbide or polycrystalline diamond (PCD) material. Other wear-resistant materials are also foreseen.

[0035] The inserts 30 may be spherical, hemi-spherical, or frusto-conical studs and any combination of these shapes may be used. Furthermore, the shape of the inserts 30 located on the central portion 12a may be different to or the same as those located along the outer perimeter 13, or a combination thereof.

[0036] Referring now to Fig. 5, there is shown a cross-sectional view of the drill bit 1 taken along line B-B in Fig. 3. As may be seen, the drill bit 1 comprises one or more evacuation channels 34 which extend through the bit body 10 from an evacuation port 36 in the front face 12 to an opening 38 in the skirt 14. The opening 38 may be located in a lateral surface 15 of the skirt 14. The openings 38 may be located at a distance from the front face 12 which exceeds the axial extension of the scallops 32. In one embodiment, the diameter of the skirt 14 decreases in the axial direction rearwardly from the front face 12, reaching a minimum diameter in a region where the openings 38 are located, before increasing towards the rear edge 17. The reduced diameter in the region of the openings 38 provides space for passage of the rock drillings and flushing fluid exiting the evacuation channels 34.

[0037] Alternatively, as shown in Fig. 6, the opening 38 may be located in the shoulder 28, further away from the front face 12. In embodiments comprising a plurality of evacuation channels 34, the location of the opening 38 may be selected from the lateral surface 15 and / or the shoulder 28 for each evacuation channel 34. Thus, depending on the circumstances, the drill bit may have evacuation channels 34 with openings 38 in the lateral surface of the skirt 14 or in the shoulder 28, or a combination thereof.

[0038] The evacuation channels 34 provide additional pathways for removal of rock drillings and fluid from the front face 12 as indicated by the arrows, thereby enabling an increased penetration rate of the drill bit 1. Alternatively, the provision of one or more evacuation channels 34 allows for reducing the number and / or area of the scallops 32 along the outer perimeter 13 of the front face 12 whilst maintaining the penetration rate in that the total cross-sectional area of the scallops 32 and the evacuation ports 36 remains substantially unchanged. This enables increasing the available area for placement of inserts 30 along the outer perimeter 13. It has been found that inserts having a small diameter contribute to an increased service life of the drill bit 1 compared to larger diameter inserts. This is due to the possibility of fitting a larger number of small inserts 30 per unit surfacearea of the front face 12. Consequently, the portion of surface area of the front face 12 not covered by inserts 30 is reduced. Thus, by increasing the number of inserts 30, the service life of the drill bit 1 can be increased. The optimal diameter of the inserts 30 is found to vary with the diameter of the drill bit 10; a small drill bit diameter gives a smaller optimal insert diameter and vice versa. In one embodiment, the diameter of the inserts may be in the range 10-15 mm, preferably 11-14.5 mm, more preferably 12-12.7 mm, for a drill bit diameter of about 116 mm.

[0039] In one embodiment, the inserts 30 arranged along the outer perimeter 13 substantially may cover at least half of the circumference of the front face 12. The scallops 32 may extend over the remaining parts of the circumference, thus providing an optimal ratio of surface area of the front face 12 being covered by inserts 30 to exposed surface area.

[0040] In one embodiment, the sum of the cross-sectional areas of the scallops 32 and the evacuation ports 36 combined is equal to or greater than the sum of the cross-sectional areas of the flushing ports 18. This ensures that the fluid entering the bore hole to flush away rock drillings has sufficient space to exit.

[0041] The number of evacuation channels 34 may be equal to or greater than the number of flushing channels 20. In one embodiment, there may be twice the number of evacuation channels 34 as flushing channels, thus for each flushing port 18 in the front face 12, there may be provided two evacuation ports 36. The front face 12 may further comprise an elongate recess 40 extending between each evacuation port 26 and the adjacent flushing port 18. The elongate recess 40 provides space for guiding rock drillings towards the evacuation port 36 to facilitate removal and reduce wear and tear on the bit body 10. In one embodiment, the evacuation ports 36 are arranged radially outside the flushing ports 18. This is advantageous as the evacuation ports 36 may be optimally located to receive the flushing fluid introduced through the flushing ports 18 and the rock drillings which tends to move outward from the center when the drill bit 1 is rotated. Either or both of the evacuation ports 36 and the flushing ports 18 may be arranged in a circular configuration in the front face 12. The circular configuration may provide a symmetrical distribution of flow across the front face 12 and facilitates manufacturing.

[0042] Embodiments of a drill bit according to the present disclosure has been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0043] All the described alternative embodiments above or parts of an embodiment can be freely combined without departing from the inventive idea as long as the combination is not contradictory.

Claims

List of Reference Signs1 Drill bit10 Bit body12 Front face12a Central portion12b Peripheral portion13 Outer perimeter14 Skirt15 Lateral surface16 Internal conduit17 Rear edge18 Flushing port20 Flushing channel22 Flushing groove24 Shank26 Splines28 Shoulder30 Wear-resistant inserts32 Scallops34 Evacuation channel36 Evacuation port38 Opening40 Elongate recessX Rotation axisCLAIMS1. A percussive drill bit (1) comprising: a bit body (10) having a longitudinal axis of rotation (X), the bit body comprising a front face (12) and a skirt (14) extending in a rearward direction from the front face, an internal conduit (16) for supplying pressurized fluid to the front face, at least one flushing port (18) in the front face and arranged in fluid communication with the internal conduit, and at least one evacuation channel (34) extending through the bit body from an evacuation port (36) in the front face to an opening (38) in the skirt.

2. The percussive drill bit according to claim 1, wherein the opening is arranged in a lateral surface (15) of the skirt.

3. The percussive drill bit according to claim 1, wherein the opening is arranged in a shoulder (28) of the skirt, the shoulder extending between a rear edge (17) of the skirt and a shank (24) of the drill bit.

4. The percussive drill bit according to any one of the preceding claims, wherein the number of evacuation channels is equal to or greater than the number of flushing ports, preferably two times greater.

5. The percussive drill bit according to any one of the preceding claims, further comprising at least one elongate recess (40) arranged in the front face, wherein the at least one elongate recess extends between the at least one evacuation port and an adjacent flushing port.

6. The percussive drill bit according to any one of the preceding claims, comprising a plurality of evacuation channels with respective evacuation ports arranged in a circular configuration in the front face.

7. The percussive drill bit according to any one of the preceding claims, wherein the at least one evacuation port is arranged radially outside the at least one flushing port.

8. The percussive drill bit according to any one of the preceding claims, further comprising a plurality of wear-resistant inserts (30) each seated in a correspondingly shaped recess in the front face, wherein at least a portion of the wear-resistant inserts are arranged along an outer perimeter (13) of the bit body.

9. The percussive drill bit according to claim 8, wherein the bit body further comprises a plurality of scallops (32) along the outer perimeter of the front face, each scallop being arranged between two adjacent wear-resistant inserts.

10. The percussive drill bit according to claim 9, wherein the wear-resistant inserts arranged along the outer perimeter substantially cover at least half the circumference of the front face.

11. The percussive drill bit according to claim 9 or 10, wherein the sum of cross- sectional areas of all evacuation ports and scallops is equal to or greater than the sum of cross-sectional areas of all flushing ports.

12. The percussive drill bit according to any one of claims 8-11, wherein the wearresistant inserts comprise cemented carbide and / or polycrystalline diamond (PCD) material.

13. The percussive drill bit according to any one of the preceding claims, wherein the at least one flushing port is arranged adjacent to a flushing groove (22) in the front face, the flushing groove extending radially outwards from the flushing port towards an outer perimeter of the bit body.

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