EP4603674A1

EP4603674A1 - Percussive rock drill bit with planar front face sections

Info

Publication number: EP4603674A1
Application number: EP24157773.3A
Authority: EP
Inventors: Conny Kraft
Original assignee: Sandvik Mining and Construction Tools AB
Current assignee: Sandvik Mining and Construction Tools AB
Priority date: 2024-02-15
Filing date: 2024-02-15
Publication date: 2025-08-20
Also published as: WO2025172444A1

Abstract

A percussive rock drill bit comprising an axially raised front face surrounded by at least one gauge surface wherein the front face has a plurality of front face sections wherein each front face section has a planar front surface; wherein the normal perpendicular to each of the planar front surfaces is non-parallel to the longitudinal axis and each of the planar front surfaces projects in different directions from the longitudinal axis; and wherein there is at least one front insert mounted on each of the front face sections.

Description

Field of invention

The present invention relates to a percussive drill bit and particularly, although not exclusively to, to a drill bit having a plurality of planar front face sections.

Background art

Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes. For the latter application, drill strings are typically used in which a plurality of rods are interconnected to advance the drill bit and increase the depth of the hole. In 'top hammer drilling' a terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes. In 'down the hole' drilling the impact is delivered not through the upper end of the string, but by a hammer directly connected to the drill bit within the hole.
Known drill bits having a raised front face surface have a curved axisymmetric front face surface. Consequently, this means that when inserts are mounted into holes in the front face surface the protrusion height of the inserts from the lowest exposed point to the tip of the insert will vary around their circumference. The problem with this uneven protrusion is that the interference between the insert and the hole will vary and consequently the areas where there is less interference will suffer from increased steel wear. Increased steel wear is undesirable as it will reduce the service life of the drill bit. Therefore, the problem to be solved is how to reduce steel wear around the inserts in order to improve the service lifetime of the percussive drill bit.

Summary of the Invention

It is an objective of the present invention to provide a percussive rock drill bit comprising: an elongate shank having a bit longitudinal axis with a head provided at an axially forward end of shank; the head having a front face surrounded by at least one gauge surface wherein the front face is raised axially further forward compared to the gauge surface(s); a plurality of front inserts are mounted on the front face and a plurality of gauge inserts are mounted on the gauge surface(s); the front face has a plurality of front face sections wherein each front face section has a planar front surface; wherein a normal perpendicular to each of the planar front surfaces is non-parallel to the bit longitudinal axis and the normal perpendicular to each of the planar front surfaces projects in a different direction from the bit longitudinal axis; and wherein there is at least one front insert mounted on each of the front face sections. Advantageously, this means that each of the front face inserts protrudes evenly from the planar surface of the front face sections around the circumference of the insert. This will result in even interference between the hole in the front face and the front inserts around their circumference, making them more capable of withstanding abrasive and / or erosive-steel wear. Consequently, the front inserts are less likely to become detached and therefore the lifetime of the drill bit is increased.
In some example embodiments there are between 2 and 5 front face sections. The number of front face sections is selected to suit the diameter of the drill bit.
In some example embodiments a first angle (α) between the normal perpendicular to the planar front surface and the bit longitudinal axis for each of the front face sections is between 1-25°. This provides a balance between drilling efficiency and structural integrity of the drill bit.
In some example embodiments α is the same for all front face sections. Advantageously, this results in reduced wear and therefore increase the lifetime of the drill bit.
In some example embodiments a front insert axial projection height (hi) is measured between a front insert lowest front insert exposed point and a front insert tip on the front face inserts and wherein there is less than 4 % difference in hi around the circumference of all the front face inserts. Advantageously, if there is low variation in the axial projection height of the inserts then the interference between the front inserts and the hole into which the front face of the drill bit that the insert is pressed into will be very similar / equal. This will result in even wear around the front inserts which means it is less likely that the front inserts become detached and therefore the lifetime of the drill bit is increased.
In some example embodiments each of the front face inserts has a front insert longitudinal axis and wherein the normal perpendicular to the planar front surface for each of the front face sections is parallel to the insert longitudinal axis of all of the front face inserts located on that front face section.
In some example embodiments the gauge surface(s) have multiple gauge sections wherein each gauge section has a planar gauge surface; wherein the normal perpendicular to the planar gauge surface of each gauge section is non-parallel to the bit longitudinal axis and each project in different directions from the bit longitudinal axis; and wherein there is at least one gauge insert mounted on each of the gauge sections. Advantageously, this means that each of the gauge inserts protrudes evenly from the planar surface of the gauge section around the circumference of the gauge insert. This will result in even interference between the hole in the gauge and the gauge insert making them more capable of withstanding abrasive and / or erosive-steel wear. Consequently, the gauge inserts are less likely to become detached and therefore the lifetime of the drill bit is increased.
In some example embodiments there are between 3 and 15 gauge sections on each gauge surface. The number of front face sections is selected to suit the diameter of the drill bit.
In some example embodiments a second angle (β) between the normal perpendicular to the planar gauge surface and the bit longitudinal axis for each of the gauge sections is between 20 - 45°. Advantageously, the lowest levels of insert damage and premature bit failure occur within this range.
In some example embodiments β is the same for all gauge sections on the same gauge surface. Advantageously, this results in lower wear.
In some example embodiments a gauge insert axial projection height (h₂) is measured between a gauge insert lowest gauge insert exposed point and a gauge insert tip for each of the gauge inserts and wherein there is less than 4 % difference around the circumference of all the gauge inserts in h₂. Advantageously, if there is low variation in the axial projection height of the inserts then the interference between the gauge inserts and the hole in the gauge into which the gauge inserts are pressed is very similar / equal. This will result in even wear around the gauge inserts which means it is less likely that the gauge inserts become detached and therefore the lifetime of the drill bit is increased.
In some example embodiments each of the gauge inserts has a gauge insert longitudinal axis and wherein the normal perpendicular to the planar gauge surface for each of the gauge sections is parallel to the gauge insert longitudinal axis for all of the gauge inserts located on that gauge section.
In some example embodiments one or more flushing ports are located radially outward of the front face. Advantageously, this prevents the flushing holes getting blocked with debris. Furthermore, it enables the front inserts to be positioned radially nearer the bit longitudinal axis, which prevents steel and rock contact in the centre of the bit, which would be detrimental to the lifetime of the bit.
In some example embodiments adjacent front face sections are directly connected to each other. Advantageously, this prevents the flushing holes getting blocked with debris. Furthermore, it enables the front inserts to be positioned radially nearer the bit longitudinal axis, which prevents steel and rock contact in the centre of the bit that would be detrimental to the lifetime of the bit.
In some example embodiments the extension of the normal taken at a radial centre of the front face insert perpendicular to the front face sections intercepts the bit longitudinal axis.
According to another aspect of the present invention is a method of producing the percussive rock drill bit as described hereinbefore or hereinafter wherein the planar front surface(s) and the planar gauge surface(s) are produced by milling. Advantageously, milling is a quick, inexpensive method that enables high precision machining.

Brief description of drawings

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:

Figure 1 is a perspective view of the drill bit.
Figure 2 is top-down of the drill bit.
Figure 3 is a cross-sectioned view of the drill bit sectioned along the line A-A.
Figure 4 is a cross sectioned view of the drill bit sectioned along the line B-B and includes an enlargement of the section around the front face insert.
Figure 5 is a cross-sectioned view of the drill bit sectioned along the line C-C.
Figure 6 is a cross-sectioned view of the drill bit sectioned along the line D-D and includes an enlargement of the section around the front face insert.

Detailed description

Figure 1 shows a percussive rock drill bit 2, which is normally made of steel, comprising an elongate shank 4 having a bit longitudinal axis 6 with a head 8 provided at axially forward-most end of shank 4. The drill bit 2 having a base 44 at the rearward-most end of the shank 4. The head 8 has a front face 10 surrounded by at least one gauge surface 12, i.e., the front face 8 is radially closest to the bit longitudinal axis 6 and radially closer to the bit longitudinal axis 6 compared to the gauges surface(s) 12. The front face 10 is raised axially further forward compared to the gauge surface(s) 12. A plurality of holes are provided in the front face 10 and in the gauge surface(s) 12. A plurality of front inserts 14 are mounted into the holes on the front face 10 and a plurality of gauge inserts 16 are mounted into the holes on the gauge surface(s) 12. The inserts 14, 16 are normally fixed in place by interference fitting, such as press fitting or shrink fitting, or by brazing. Inserts are also known as buttons. The inserts could comprise polycrystalline diamond (PCD). Alternatively, the inserts could comprise cemented carbide or any other suitable hard material suitable for mining or rock cutting applications. The inserts 14, 16 typically have a generally domed shape, but could also have a rounded, conical, ballistic, semi- spherical, flat, or pointed geometry.
The drill bit 2 also comprises an internal bore (not shown) that is centred on the longitudinal axis 6, from which a plurality of flushing fluid passageways (not shown) extend, emerging from the head 8 via one or more flushing ports 38.
Figure 2 shows that the front face 10 has a plurality of front face sections 18 and each front face section 18 has a planar front surface 20. In other words, the front face sections 18 have flat, non-curved surfaces. A normal perpendicular to each of the planar front surfaces 20 is non-parallel to the bit longitudinal axis 6 and the normal perpendicular to each of the planar front surfaces 20 projects in different directions from the bit longitudinal axis 6. There is at least one front insert 14 mounted on each of the front face sections 18. The normal could be taken from any point on the front face surface 20, for example the normal could be taken at a radial centre point of the front insert 14 positioned on that front face surface 20.
In some example embodiments, there is exactly one front insert 14 on each front face section 18. Alternatively, there could be multiple front inserts 14 per front face section 18, for example 2 or 3 front inserts 14 per front face section 18. In some example embodiments, there are the same number of front face inserts 14 on each of the front face sections 18. Alternatively, there could be more front face inserts 14 on some front face sections 18 compared to other front face sections 18.
The gauge surface 12 could comprise just one surface. Alternatively, the gauge surface 12 could comprise multiple surfaces, for example there could be an inner gauge surface and an outer gauge surface which project at different angles from the bit longitudinal axis 6. There could also be further rows of inserts between the gauge surface(s) 12 and the front face 10.
In some example embodiments, the diameter of the drill bit 2 is between 28 - 254 mm, for example between 30 - 150 mm, for example between 40 - 110 mm.
In some example embodiments there are between 2 and 5 front face sections 18. For example, there could be 2, 3, 4 or 5 front face sections 18.
Figure 3 is a cross section of the drill bit 2 along the line A-A, it shows that there is a first angle (α) between the normal perpendicular to the planar front surface 20 and the bit longitudinal axis 6 for each of the front face sections 18. In some example embodiments α is between 1-25°, for example between 3-15°. In some example embodiments α is the same for all front face sections 18. Alternatively, in other example embodiments α is different for different front face sections 18.
Figure 4 is a cross section of the drill bit 2 along the line B-B, also showing an enlargement around the front insert 14. It shows that there is a front insert axial projection height (hi) measured between a front insert lowest exposed point 24, which is considered to be the lowest point on the front insert 14 that is exposed from the steel body of the front face 10, and a front insert tip 26, which is the point furthest from the front face 10, on the front inserts 14. In some example embodiments, there is less than 4%, for example less than 3%, for example less than 2% difference in hi around the circumference of all the front inserts 14.
In some example embodiments, the front inserts 14 have a front insert longitudinal axis 30 and wherein the normal perpendicular to the planar front surface 20 for each of the front face sections 18 is parallel to the front insert longitudinal axis 30 for all of the front face inserts 14 located on that front face section 18. In some example embodiments, the extension of the normal taken from the radial centre point of the front face insert, perpendicular to the front face sections 18 intercepts the bit longitudinal axis 6. In some example embodiments, the circumferential outermost edges 40 of the front face sections 18 (i.e., either side of the insert 14) are axially equal in height relative to the drill bit base 44. In some embodiments, there is a first imaginary circle (Ci) that crosses a radial centre point of all the front face inserts 14 and two regions of each front face section 18 (i.e., one region either side of the insert) and wherein the height of the two regions where Ci crosses the front face section 18 relative to the drill bit base 44 are equal. In other words, the front face sections 18 are not inclined in a circumferential direction.
In some example embodiments, as shown in figure 2, the gauge surface(s) 12 have multiple gauge sections 22 wherein each gauge section 22 has a planar gauge surface 28; wherein the normal perpendicular to the planar gauge surface 28 of each gauge section 22 are non-parallel to the bit longitudinal axis 6 and each project in a different direction from the bit longitudinal axis 6. There is at least one gauge insert 16 mounted on each of the gauge sections 22.
In some example embodiments, there are between 3 and 15 gauge sections 22 on each gauge surface 12. For example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 gauge sections 22 on each gauge surface 12.
If there are multiple gauge surfaces 12, in some example embodiments all the gauge surfaces 12 are split into gauge sections 22. In alternative embodiments, some of the gauge surfaces 12 are split into gauge sections 22 and some of the gauge surfaces 12 are not split into gauge sections 22.
If there are multiple gauge surfaces 12, in some example embodiments all the gauge surfaces 12 are split into the same number of gauge sections 22. In alternative embodiments the different gauge surfaces 12 are split into a different number of the gauge sections 22.
Figure 5 is a cross section of the drill bit 2 sectioned across the line C-C and it shows that there is a second angle (β) between the normal perpendicular to the planar gauge surface 28 and the bit longitudinal axis 6 for each of the gauge sections 22 is between 20-45°, for example between 25 - 40°.
In some example embodiment β is the same for all gauge sections 22 in the same gauge surface 12. In other example embodiments β is different for some gauge sections 22 compared to others in the same gauge surface 12.
If there are multiple gauge surfaces 12, for example an inner gauge surface and an outer gauge surface, β will be different for the gauge surfaces 12, for example β will be larger for the outer gauge surface compared to β for the inner gauge surface.
Figure 6 is a cross section of the drill bit 2 along the line D-D, including an enlargement of the section around the gauge insert 16 and it shows that there is a gauge insert axial projection height (h₂) measured between a gauge insert lowest exposed point 34, which is considered to be the lowest point on the gauge insert 16 that is exposed from the steel body of the gauge surface 12, and a gauge insert tip 36, which is the point of the insert furthest from the from the gauge surface 12, for each of the gauge inserts 16. In some example embodiments, there is less than 4 % difference in h₂ around the circumference of all the gauge inserts 16, for example less than 3% difference, for example less than 2% difference.
In some example embodiments, the gauge inserts 14 have a gauge insert longitudinal axis 32 and wherein the normal perpendicular to the planar gauge surface 28 for each of the gauge sections 22 is parallel to the gauge insert longitudinal axis 32 of all of the gauge inserts 16 located on that gauge section 22. In some example embodiments, the extension of the normal taken from the radial centre point of the gauge insert 16 perpendicular to the gauge sections 22 intercepts the bit longitudinal axis 6. In some example embodiments, the circumferential outermost edges 42 of the gauge sections 22, i.e., either side of the insert 16, are axially equal in height relative to the base 44. In some embodiments, there is a second imaginary circle (C₂) that crosses a radial centre point of all the gauge inserts 16 and two regions of each gauge section 22 (i.e., one region either side of the insert 16) and wherein the height of the two regions where C₂ crosses gauge section 22 relative to the drill bit base 44 are equal. In other words, the gauge sections 22 are not inclined in a circumferential direction.
In some example embodiments, the one or more flushing ports 38 are located radially outward of the between the front face 10. In some example embodiments the one or more flushing ports 38 are located radially inward of the gauge surface(s) 12. In some example embodiments, the one or more flushing ports 38 are located radially between the front face 10 and the and the gauge surface(s) 12. In some example embodiments, adjacent front face sections 10 are directly connected to each other, in other words the front face sections 10 are all continuously connected to each other, meaning that there is no flushing channel or any other sort of recess separating the front face sections 10.
In some example embodiments, the planar front surface(s) 20 and the planar gauge surface(s) 28 are produced by milling. Alternatively, the planar front surface(s) 20 and the planar gauge surface(s) 28 could be produced by grinding or any other suitable method to produce a flat surface.
References in the description to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature or a particular combination of features (e.g., component(s), element(s), integer(s), structure(s), operation(s), and/or step(s)), but every embodiment may not necessarily include the particular feature or the particular combination of features. Such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, or a particular combination of features, is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, or combination of features, in connection with other embodiments whether or not explicitly described.

Claims

A percussive rock drill bit (2) comprising:
an elongate shank (4) having a bit longitudinal axis (6) with a head (8) provided at axially forward-most end of shank (4);

the head (8) having a front face (10) surrounded by at least one gauge surface (12) wherein the front face (10) is raised axially further forward compared to the gauge surface(s) (12);

a plurality of front inserts (14) mounted on the front face (10) and a plurality of gauge inserts (16) mounted on the gauge surface(s) (12);

characterised in that:
the front face (10) has a plurality of front face sections (18) wherein each front face section (18) has a planar front surface (20); wherein a normal perpendicular to each of the planar front surfaces (20) is non-parallel to the bit longitudinal axis (6) and the normal perpendicular to each of the planar front surfaces (20) projects in different directions from the bit longitudinal axis (6); and wherein there is at least one front insert (14) mounted on each of the front face sections (18).
The percussive rock drill bit (2) according to claim 1 wherein there are between 2 and 5 front face sections (18).
The percussive rock drill bit (2) according to claim 1 or 2 wherein a first angle (α) between a normal perpendicular to the planar front surface (20) and the bit longitudinal axis (6) for each of the front face sections (18) is between 1-25°.
The percussive rock drill bit (2) according to claim 3 wherein α is the same for all front face sections (18).
The percussive rock drill bit (2) according to any of the previous claims wherein a front insert axial projection height (hi) is measured between a front insert lowest exposed point (24) and a front insert tip (26) on the front face inserts (14) and wherein there is less than 4% difference around the circumference of all the front face inserts (14) in hi.
The percussive rock drill bit (2) according to any of the previous claims wherein each of the front face inserts (14) has a front insert longitudinal axis (30) and wherein the normal perpendicular to the planar front surface (20) for each of the front face sections (18) is parallel to the front insert longitudinal axis (30) for all of the front face inserts (14) located on that front face section (18).
The percussive rock drill bit (2) according to any of the previous claims wherein the gauge surface(s) (12) have multiple gauge sections (22) wherein each gauge section (22) has a planar gauge surface (28); wherein the normal perpendicular to the planar gauge surface (28) of each gauge section (22) is non-parallel to the bit longitudinal axis (6) and each project in a different direction from the bit longitudinal axis (6); and wherein there is at least one gauge insert (16) mounted on each of the gauge sections (22).
The percussive drill bit (2) according to claim 7 there are between 3 and 15 gauge sections (22) on each gauge surface (12).
The percussive rock drill bit (2) according to claim 7 or 8 wherein a second angle (β) between the normal perpendicular to the planar gauge surface (28) and the longitudinal axis (6) for each of the gauge sections (22) is between 20 - 45°.
The percussive rock drill bit (2) according to claim 9 wherein β is the same for all gauge sections (22) in the same gauge surface (12).
The percussive rock drill bit (2) according to any of claims 7- 10 wherein a gauge insert axial projection height (h₂) is measured between a gauge insert lowest exposed point (34) and a gauge insert tip (36) for each of the gauge inserts (16) and wherein there is less than 4 % difference around the circumference of all the gauge inserts (16) in the axial projection height h₂.
The percussive rock drill bit (2) according to any of claims 7-11 wherein each of the gauge inserts (14) has a gauge insert longitudinal axis (32) and wherein the normal perpendicular to the planar gauge surface (28) for each of the gauge sections (22) is parallel to the gauge insert longitudinal axis (32) for all of the gauge inserts (16) located on that gauge section (22).
The percussive rock drill bit (2) according to any of the previous claims wherein at least one flushing port (38) is located radially outward of the front face (10).
The percussive rock drill bit (2) according to any of the previous claims wherein adjacent front face sections (10) are directly connected to each other.
The percussive rock drill bit (2) according to any of the previous claims wherein the extension of the normal taken at a radial centre of the front face insert (14) perpendicular to the front face sections (18) intercepts the bit longitudinal axis (6).
A method of producing the percussive rock drill bit according to any of the previous claims wherein the planar front surface(s) (20) and the planar gauge surface(s) (28) are produced by milling.