Tilted ellipse thread bottom

Abstract

A percussive drill component (2) having a longitudinal central axis (14) comprising at least one threaded part (4); wherein threaded part comprises a plurality of thread profiles (16); wherein each thread profile includes a crest (6), a root (8), a contact flank (10); a non-contact flank (12); a contact flank transition section (22) extending between the root and the contact flank; and a non-contact flank transition section (24) extending between the root and the non-contact flank; characterised in that: at least one of the contact flank transition section and the non-contact flank transition section has a curvature defined by a portion of an ellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: wherein the semi-major axis (a) and the semi-minor axis (b) are non- parallel with the longitudinal central axis wherein the ratio of the semi-major axes (a :b) is within the range 10:1 to 1.5:1 and the major axis (a) of the ellipse extends in a substantially longitudinal direction.

Description

[0001] Tilted ellipse thread bottom

[0002] Field of invention

[0003] The present disclosure generally relates to a thread profile for stronger connections, fewer abrupt failures and reduced stress for use in percussion drilling.

[0004] Background art

[0005] Percussion drilling is used to create a long borehole via a plurality of elongate drill string rods coupled together end-to-end by interconnected male and female threads. The well- established technique breaks rock by hammering impacts transferred from the rock drill bit, mounted at one end of the drill string, to the rock at the bottom of the borehole. Typically, the energy required to break the rock is generated by a hydraulically driven piston that contacts the end of the drill string (via a shank adaptor) to create a stress (or shock) wave that propagates through the drill string and ultimately to the base rock level.

[0006] Percussive drilling components are typically coupling together via threaded parts.

[0007] Typically, there is a single radius in the transition regions between the roots and flanks in the thread profile. Stress is generated in these sharp transitions leading to increased wear and therefore reducing the lifetime of the components. Therefore, the problem to be solved is how to reduce stress generated in the threaded couplings in order to increase their wear resistance and improve the lifetime of the components.

[0008] Summary of the Invention

[0009] It is an objective of the present invention to provide a percussive drill component having a longitudinal central axis comprising at least one threaded part; wherein the threaded part comprises a plurality of thread profiles; wherein each thread profile includes a crest, a root, a contact flank; a non-contact flank; a contact flank transition section extending between the root and the contact flank; and a non-contact flank transition section extending between the root and the non-contact flank; wherein at least one portion of at least one of the contact flank transition section and the non-contact flank transition section has a curvature defined by a portion of an ellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: wherein the semi-major axis (a) and the semi-minor axis (b) are non-parallel with the longitudinal central axis.

[0010] Advantageously, this enables the largest possible radius of the ellipse to be positioned in the region of the transition section between the root and the flank having the smallest cross section. Consequently, less steel needs to be removed to form the threaded profile without needing to change the length of the contact and / or non-contact flanks. By tilting the ellipse, it is possible to position it tangent to both the flanks and the root of the thread in an advantageous way. The tilting also allows for the major and minor radii of the ellipse to be increased therefore achieving a smoother transition. Overall, the stress level in the threaded part is reduced making it less prone to wear or premature breakage, thus the lifetime of the threaded coupling is increased.

[0011] In some example embodiments, both the contact flank transition section and the noncontact flank transition section have curvatures defined by a portion of an ellipse wherein the semi-major axis (a) and semi-minor axis (b) are non-parallel with the longitudinal central axis. Advantageously, the stress in the thread profile is further reduced.

[0012] In some example embodiments there is an angle (y) between the semi-major axis (a) of the elliptical profile of the transition section and the longitudinal central axis and wherein y is between 1-89°. Advantageously, this range results in the lowest levels of stress in thread profile.

[0013] In some example embodiments the cross-sectional shape profile of the outer surface of the transition section(s) comprises between a 5 - 50% segment of an ellipse. Advantageously, this range results in reduced stress whilst still being able to geometrically fit into the thread profile to enable good contact with the corresponding thread from the adjoining component.

[0014] In some example embodiments the ratio of the semi-major axis to semi-minor axes (a: b) is within the range 10: 1 to 1.5: 1. Advantageously, this range results in reduced stress whilst still being able to geometrically fit into the thread profile to enable good contact with the corresponding thread from an adjoining component.

[0015] In some example embodiments the exponential factor (n) is in the range 1.1 < n < 8. Advantageously, this produces smooth transition sections which results in increased stress reduction.

[0016] In some example embodiments the major axis (a) of the ellipse extends in a substantially longitudinal direction. Advantageously, this produces smooth transition sections which results in increased stress reduction.

[0017] In some example embodiments the root in the thread profile has a straight section that is inclined relative to the longitudinal central axis of the component. Advantageously, by tilting the root of the thread it is possible to enlarge the radii at a transition between the root and the contact flank which will reduce stress levels in the root of the thread without increasing stress levels at the transition between the root and the non-contact flank. By tilting the root of the thread, the cross-sectional area is increased, meaning that there is an increased volume of steel which reduces the level of stress and makes the thread stiffer to the non-contact radii, thus making it possible to reduce the radii to the non-contact flank without increasing stress in this region. Furthermore, the small radius to the non-contact flank is advantageous for aiding unthreading. Consequently, the overall level of stress in the thread is reduced making it less prone to wear and premature breakage and thus the lifetime of the threaded coupling is increased.

[0018] In some example embodiments the crests and the roots of the thread profile are cambered along the length of the threaded part. Advantageously, this improves the stiffness of the coupling when subjected to bending loads. The cambered threads distribute the bending load more evenly across the length due to the curvature thereof aligning better with a curvature of the bending. Furthermore, coupling and uncoupling times are reduced.

[0019] Brief description of drawings

[0020] 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:

[0021] Figure l is a schematic drawing of a drilling component.

[0022] Figure 2 is a schematic drawing of the thread profile showing the tilted thread bottom.

[0023] Figure 3a is a schematic drawing of a thread profile illustrating the tilted elliptical transition section wherein the ellipse is positioned in only one of the transition sections.

[0024] Figure 3b is a schematic drawing of a thread profile illustrating the tilted elliptical transition section wherein the contact flank transition section, the non-contact flank transition section and the root all have a curvature defined by a portion of the same ellipse.

[0025] Figure 4 is a schematic drawing of a thread profile illustrating y.

[0026] Figure 5 is schematic drawing of a thread profile having a tilted root.

[0027] Detailed description

[0028] Figure 1 shows a percussive drill component 2 having a longitudinal central axis 14 comprising at least one threaded part 4. There are typically three or more thread profiles on the threaded part 4. The threaded part 4 could be a male or female. The component 2 may have one male threaded part; or one female threaded part; or two male threaded parts; or two female threaded parts; or one male threaded part and one female threaded part. The threaded part(s) may have any suitable thread form, for example but not limited to trapezoidal. The threaded part(s) could be a single, double or triple thread. The percussive drilling component could for example be, but not limited to, a rod, tube, shank adapter, drill bit, thread adapter or coupling sleeve. The drill component could be configured for either a shoulder contact or bottom contact coupling. A single thread profile 16 is considered to be between the midpoint of one crest 6 to the midpoint of the adjacent crest 6.

[0029] Figure 2 shows a schematic drawing of a thread profile of the threaded part 4. The threaded part(s) 4 comprises a thread profile 16; wherein the thread profile 16 includes a crest 6 (otherwise known as a thread top), a root 8 (otherwise known as a thread bottom), a contact flank 10; a non-contact flank 12; a contact flank transition section 22 between the root 8 and the contact flank 10 and a non-contact flank transition section 24 between the root 8 and the non-contact flank 12. The crests may have any suitable form, for example flat, curved, straight or inclined. The roots 8 are defined as the section that includes the lowest part of the thread profile 16, they could either be straight or curved. If the roots are curved, they may have a curvature defined by a single radius, multiple radii or a portion of an ellipse. Typically, the contact flanks 10 and the non-contact flanks 12 are straight.

[0030] Figure 3a shows a thread profile (not to scale) illustrating that at least one portion of at least one of the contact flank transition section 22 and the non-contact flank transition section 24 has a curvature defined by a portion of an ellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: wherein the semi-major axis (a) and the semi-minor axis (b) are non-parallel with the longitudinal central axis 14.

[0031] “x” represents the horizontal co-ordinate point on the ellipse.

[0032] “y” represents the vertical co-ordinate point on the ellipse. “a” represents the semi-major axis, i.e., half the length of the major axis, where the major axis is the longest diameter of the ellipse passing through the centre.

[0033] “b” represents the semi-minor axis, i.e., half the length of the minor axis, where the minor axis is the shortest diameter of the ellipse passing through the centre. The minor axis is perpendicular to the major axis.

[0034] “n” is the exponential factor.

[0035] In other words, the semi-major axis and semi-minor axes are tilted relative to the longitudinal axis 14 of the component. The semi-minor and semi-major axes are also nonperpendicular to the longitudinal axis 14 of the component 2.

[0036] In some example embodiments both the contact flank transition section 22 and the noncontact flank transition section 24 have a curvature defined by a portion of an ellipse wherein the semi-major axis (a) and semi-minor axis (b) are non-parallel with the longitudinal central axis (14). The transition sections 22, 24 could have the same or different elliptical profiles.

[0037] Alternatively, the second of the transition sections 22, 24 could have an alternative curvature, for example, but not limited to a radius, a portion of a non-tilted ellipse (i.e., such that the semi-major axis (a) is parallel with the longitudinal axis 14 or any other suitable form of curvature.

[0038] In some example embodiments, the whole of at least one of the transition sections 22, 24 has a curvature defined by a portion of an ellipse. In other example embodiments, only part of at least of the transition sections 22, 24 has a curvature defined by a portion of an ellipse, the transition sections 22, 24 may also have straight sections and / or curved sections having a single radius or multiple radii.

[0039] Figure 3b shows that in some example embodiments, the contact flank transition section 22 and the non-contact flank transition section 24 and the root 8 have curvatures defined by a portion of the same ellipse, i.e. one ellipse (with the same equation) extending between contact flank 10 and non-contact flank 12. Figure 4 is a schematic drawing of thread profile (not to scale) showing that there is an angle (y) between the semi-major axis (a) of the elliptical profile of the transition section 22, 24 and the longitudinal central axis 14. In some example embodiments, y is between 1- 89°. For example, y is between 1-45°, for example y is between 5-15°

[0040] In some example embodiments the cross-sectional shape profile of the outer surface of the transition section(s) 22, 24 comprises between a 5 - 50% segment of an ellipse. For example, between a 5 - 20% segment of an ellipse. For example, between a 5 - 15 % segment of an ellipse, for example between a 10 - 15% segment of an ellipse. For example, between a 30 - 50 % segment of an ellipse. For example, between a 35 - 45 % segment of an ellipse.

[0041] In some example embodiments the ratio of the semi-major axis to semi-minor axes (a:b) is within the range 15: 1 to 1 : 1. For example, the ratio a:b is in the range 10: 1 to 1.5 - 1. For example, the ratio of a:b is between 15: 1 - 5: 1. For example the ratio of a:b is between 12: 1 - 8:1. For example, the ratio of a:b is in the range 5: 1 - 2:1.

[0042] In some example embodiments, the exponential factor (n) is in the range 1.1 - 8. For example, n is in the range 1.5 - 4. For example, n is in the range 1.5 - 2.5. In some example embodiments n is 2. The value of n determines the shape of the curve, when n=2 this forms an ordinary ellipse, when n<2 this forms a hypoellipse and when n>2 this forms a hyperellipse.

[0043] The size of the ellipse, proportion of a:b, exponential factor n and % segment of ellipse can be varied in different ways to achieve similar or the same curvature in the transitional sections 22, 24.

[0044] In some examples embodiments the semi-major axis (a) of the ellipse extends in a substantially longitudinal direction. In some example embodiments, the semi-minor axis (b) of the ellipse extents in a substantially radial direction. Figure 5 is a schematic drawing of a thread profile (not to scale) showing that in some example embodiments the root 8 in the thread profile 16 has a straight section that is inclined relative to the longitudinal central axis 14. In other words, the root 8 of the thread profile 16 is non-parallel with the longitudinal central axis 14. In some example embodiments, there is an angle (a) between the longitudinal axis 14 and the root 8. In some example embodiments a is between 0.1 - 20°. For example, a is between 1 - 15°. For example, a is between 2 - 10°. The contact flank transition section 22 has a first axially innermost end 18 and the non-contact flank transition section 24 has a second axially innermost end 20; a first length (Li) is measured between the first axially innermost end 18 and the longitudinal central axis 14; a second length L2 is measured between the second axially innermost end 20 and the longitudinal central axis 14. In some example embodiments within in the same thread profile 16 L2>LI. The axially innermost ends 18, 20 are considered to be where the curvature of the transition sections 22, 24 end and the start of the root 8 begins.

[0045] In some example embodiments, the crests 6 and the roots 8 of the thread profile 16 are cambered along the length of the threaded part 4. Further details of cambered thread profiles are described in EP 3536894.

[0046] 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

Claims1. A percussive drill component (2) having a longitudinal central axis (14) comprising at least one threaded part (4); wherein threaded part (4) comprises a plurality of thread profiles (16); wherein each thread profile (16) includes a crest (6), a root (8), a contact flank (10); and a non-contact flank (12); wherein there is a contact flank transition section (22) extending between the root (8) and the contact flank (10) and a non-contact flank transition section (24) extending between the root (8) and the non-contact flank (12); characterised in that: at least one portion of at least one of the contact flank transition section (22) and the noncontact flank transition section (24) has a curvature defined by a portion of an ellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation:wherein the semi-major axis (a) and the semi-minor axis (b) are non-parallel with the longitudinal central axis (14) wherein the ratio of the semi-major axis to semi-minor axes (a:b) is within the range 10: 1 to 1.5: 1 and the major axis (a) of the ellipse extends in a substantially longitudinal direction.

2. The component (2) according to any of the previous claims wherein both the contact flank transition section (22) and the non-contact flank transition section (24) have a curvature defined by a portion of an ellipse wherein the semi-major axis (a) and semiminor axis (b) are non-parallel with the longitudinal central axis (14).

3. The component (2) according to any of the previous claims wherein an angle (y) between the semi-major axis (a) of the elliptical profile of the transition section (22, 24) and the longitudinal central axis (14) is between 1-89°.

4. The component (2) according to any of the previous claims wherein the cross-sectional shape profile of the outer surface of the transition section(s) (22, 24) comprises between a 5 - 50% segment of an ellipse.

5. The component (2) according to any of the previous claims wherein the ratio of the semi-major axis to semi-minor axes (a:b) is within the range 5: 1 to 2: 1.

6. The component (2) according to any of the previous claims wherein the exponential factor (n) is in the range 1.1 < n < 8.

7. The component (2) according to any of the previous claims wherein the contact flank transition section (22), the non-contact flank transition section (24) and the root (8) have a curvature defined by a portion of the same ellipse.

8. The component (2) according to any of claims 1-6 wherein the root (8) in each thread profile (16) has a straight section that is inclined relative to the longitudinal central axis (14).

9. The component (2) according to any of the previous claims wherein the crests (6) and the roots (8) of the thread profile (16) are cambered along the length of the threaded part (4).