EP4650562A1

EP4650562A1 - Camber threaded percussive drill component for bottom contact couplings

Info

Publication number: EP4650562A1
Application number: EP24175919.0A
Authority: EP
Inventors: Tomas Jansson; Anders Nordberg; Martin Larsson
Original assignee: Sandvik Mining and Construction Tools AB
Current assignee: Sandvik Mining and Construction Tools AB
Priority date: 2024-05-15
Filing date: 2024-05-15
Publication date: 2025-11-19

Abstract

A percussive drill component for a bottom contact coupling comprising at least one of a female coupling part with a female thread formed its inner surface and a radially extending axially positioned inner wall for abutment with a male coupling part; and a male coupling part with a male thread formed on its an outer surface and a non-threaded axially endmost section for abutment with a female coupling part; wherein at least one of the threads has a thread-form including a crest, a root, and a pair of flanks; wherein the crests and the roots are each cambered about a respective first and second camber radius (R_b, R_b-T) along the entire length of the thread-form.

Description

Field of invention

The present invention relates to a cambered threaded percussive drill component for a bottom contact coupling.

Background art

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.
Adjacent drill components in the drill string can be coupled together either using a "shoulder contact" or a "bottom contact" coupling. The present invention is related to "bottom contact" couplings wherein a male coupling part is screwed into the female coupling part until the axially endmost section of the male coupling part abuts the radially projecting, axially positioned inner wall of the female coupling part where the transfer of energy between adjacent drill components takes place. One issue with shoulder driven couplings is that design of the flushing house diameter is limited. To resolve this issue bottom driven couplings are used which are more versatile from a design perspective and are able to be used on a wider range of rock drills.
The problem with bottom contact couplings is that higher stress levels in the thread release (the non-threaded section adjacent to the abutment surface) of the female coupling part are generated and the last thread revolution is commonly the main point of failure. This has the issue of premature breakage of the male and female coupling components as well as excessive wear on the threads thus making it difficult to thread and unthread the coupling.
Furthermore, bottom contact couplings are more sensitive to bending. Therefore, the problem to be solved is how to reduce stress in bottom contact couplings for percussive drilling, make them more resilient against bending in order to increase the lifetime of the drill components and the improve the integrity of the coupling.

Summary of the Invention

It is an objective of the present invention is to provide a percussive drill component for a bottom contact coupling comprising at least one of: a female coupling part comprising a mounting sleeve with a female thread formed its inner surface and a radially extending axially positioned inner wall for abutment with a male coupling part; and a male coupling part with a male thread formed on its an outer surface and a non-threaded axially endmost section for abutment with a female coupling part; wherein at least one of the threads has a thread-form including a crest, a root, and a pair of flanks; wherein the crest and the root are each cambered about a respective first and second camber radius along the entire length of the thread-form.
Advantageously, using the cambered thread design on components used for a bottom contact couplings provides additional steel in the threaded section compared to conventional straight threads. The presence of the additional steel reduces the stress generated in the thread release section and reduces sensitivity to bending. The cambered threads exhibit improved coupling characteristics and sometimes improved stiffness when subject to bending loads. Additionally, the cambered threads reduce coupling and uncoupling time. 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. The cambered threads also exhibit superior wear resistance due to the direction of the contact forces being more perpendicular, thereby reducing the sliding forces. Furthermore, using cambered threads the diameter of the cavity in the female coupling at its axially innermost end can be reduced. A smaller diameter at the end of the internal part lowers the stresses observed there. Using the cambered thread on the bottom contact couplings also enables the contact pressure to be more evenly spread out and located in the correct places.
In some example embodiments the component comprises a female coupling part having an inner diameter between 20 - 120 mm.
In some example embodiments the component comprises a female coupling part having an inner diameter between 20 - 60 mm.
In some example embodiments the component comprises a female coupling part having an inner diameter between 30 - 50 mm. Advantageously, the cambered thread profile is especially beneficial for components having a smaller diameter as the additional steel volume gained is even more valuable for reducing stress levels in the threads.
In some example embodiments the component comprises a male coupling part having an outer diameter between 19 - 119 mm.
In some example embodiments the component comprises a male coupling part having an outer diameter between 19 - 59 mm.
In some example embodiments the component comprises a male coupling part having an outer diameter 29 - 49 mm. Advantageously, the cambered thread profile is especially beneficial for components having a smaller diameter as additional steel volume gained is even more valuable for reducing stress levels in the threads.
In some example embodiments each camber radius is between 500 - 2000 mm. Advantageously, this achieves the lowest possible average stress along the length of the thread. If the camber radius is too large, then the thread acts like a straight thread and will therefore not have enough technical benefit over a straight thread. If the camber radius is too small the stresses will be hard to balance and will also increase the stresses as a result of this. Consequently, the wear along the length of the thread occurs more evenly due to an even distribution of contact pressure while bending so that premature failures are less likely. This provides a threaded coupling wherein the stress is reduced as low as possible as an average along the length of the thread. Consequently, the wear along the length of the thread occurs more evenly due to an even distribution of contact pressure while bending so that premature failures are less likely and the lifetime of the parts are therefore increased.
In some example embodiments both the male thread and the female thread are cambered and wherein the male thread has a camber radius (R_bm) and the female thread has a camber radius (R_bf) and the ratio of the male thread camber radius to the female thread camber radius (R_bm/ R_bf) is ≤1. Advantageously, this ratio provides an optimised spread and balance of contact between the threads and therefore reduces stress in the coupling.
In some example embodiments the thread(s) is a single entry. Advantageously, this type of thread provides an increased wear volume and offers more design freedom in the thread profile.
In some example embodiments the thread(s) is / are a double entry. Advantageously, this type of thread enables quicker coupling and de-coupling; higher contact area and a more balanced bending resistance.

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 1a illustrates a drill rod having a male coupling and a female coupling for a bottom contact coupling, each coupling including a cambered thread, according to one embodiment of the present disclosure.
Figure 1b illustrates a shank adapter having a male coupling for a bottom contact coupling, each coupling including a cambered thread, according to one embodiment of the present disclosure.
Figures 2A illustrates a cambered helix for designing the cambered threads. Figure 2B illustrates parameters of the cambered threads.
Figures 3A-3G illustrate formulas for the cambered helix.
Figure 4 illustrates the relationship of the male and female camber radii.
Figure 5 illustrates a profile of the male cambered thread.
Figures 6A and 6B are enlargements of portions of Figure 5.
Figure 7 illustrates a profile of the female cambered thread.
Figures 8A and 8B are enlargements of portions of Figure 7.
Figure 9 illustrates the male and female couplings screwed together.

Detailed description

The present invention relates to a percussive drill component 8 for a bottom contact coupling comprising at least one of a female coupling part 2 comprising a mounting sleeve 10 with a female thread 2t formed its inner surface and a radially extending axially positioned inner wall 12 for abutment with a male coupling part of an adjacent drill component 2; and a male coupling part 4 with a male thread 4t formed on its an outer surface and a non-threaded axially endmost section 14 for abutment with a female coupling part 2 of an adjacent female coupling part 2. The male coupling part 4 is absent of a radially projecting shoulder. The non-threaded endmost part 14 could be straight, tapered or stepped. The non-threaded endmost part 14 is the section that transfers the stress wave to the inner wall 12 on the female coupling part 2. The male coupling part has an inner diameter (D₂) measured between the crests of the thread 4t as the widest point. The percussive drilling component 8 could for example be, but not limited to, a rod, tube, shank adapter, drill bit, thread adapter or coupling sleeve.
Figure 1a illustrates a drill component 8 in the form of the drill rod, having a female coupling 2 and a male coupling 4, each coupling including a respective cambered thread 2t, 4t, according to one embodiment of the present disclosure. The drill component 8 may be made from a metal or alloy, such as steel. The drill component 8 may also be case hardened, such as by carburization. Each coupling 2, 4 may be attached, such as welded, to an intermediate rod body 3 so as to form longitudinal ends of the drill rod. Each weld may be seamless, such as a friction weld. The drill component 8 may have a flow bore formed therethrough. The drill component 8 may have a length of 6 meters. Figure 1b illustrates a drill component 8 in the form of a shank adapter having a male coupling 4 with a male thread 4t.
A drill string (not shown) may be formed by screwing together a plurality of drill rods together (coupling shown in Figure 9) along with a drill bit at one end and a shank adapter at the other end. The drill bit and shank adapter may also have either of the cambered threads 2t, 4t. The drill string may be used for percussive rock drilling with a top hammer (not shown) or downhole hammer (not shown). If a downhole hammer is used, the hammer may have each of the cambered threads 2t, 4t for assembly as part of the drill string.
Alternatively, the cambered threads 2t, 4t may be used to connect other types of drill components (downhole tubulars), such as oilfield drill pipe, oilfield casing or liner, oilfield production tubing, or oilfield sucker rod.
The female coupling part 2 may have mounting sleeve 10 and a lower portion for connection to an upper end of the rod body 3. The female coupling part 2 may have the internal female thread 2t formed in an inner surface thereof adj acent to the flow bore thereof. The flow bore may be sized to receive the reduced diameter lower portion of the male coupling part 4 of another drill rod (Figure 9). The flow bore of the female coupling part 2 may include a diffuser located adjacent to a lower end of the female thread 2t. The female coupling part 2 has an inner diameter (D₃) measured between the roots of the thread 2t at its widest point.
Alternatively, the male coupling part 4 may be connected to an upper end of the rod body 3 and the female coupling part 2 may be connected to a lower end of the rod body. In this alternative, the nozzle of the male coupling part 4 would be a diffuser and the diffuser of the female coupling part 2 would be a nozzle.
Figures 2A illustrates a cambered helix 6 for designing the cambered threads 2t, 4t. Figure 2B illustrates parameters of the cambered threads 2t, 4t. Figures 3A-3H illustrate formulas for the cambered helix 6. To design the cambered threads 2t, 4t, one or more thread parameters, such as a start diameter D₀, an end diameter D₁, and a (linear) length L, may be specified utilizing dimensions of the drill component 8. Once the thread parameters have been specified, a camber radius R_b may be calculated utilizing the formula of Figure 3A. The camber radius R_b may extend from a CenterPoint C_P and may define crests of the male thread 4t and roots of the female thread 2t. The thread parameters may be specified such that the camber radius R_b is greater than, such as 5 or 10 times greater than D₂ or D₃.
Once the camber radius R_b has been calculated, a sweep angle γ may be calculated utilizing the formula of Figure 3B. The sweep angle γ may range between one and ten degrees. Once the sweep angle γ has been calculated, the cambered helix 6 may be generated using the parametric formulas of Figures 3C-3G. The cambered helix 6 may be used to define an outline of the cambered threads 2t, 4t. In the parametric formulas, R(t) may be a radial coordinate of the cambered helix about a longitudinal axis G_L of the drill component 8. The convention of the formulas of Figures 3E-3G may be negative (shown) for a left-handed thread and positive for a right-handed thread.
The female 2t and male 4t threads may be complementary such that the male thread of one drill component 8 may be screwed into the female thread of drill component 8 (Figure 9). To facilitate screwing and unscrewing of the threads 2t, 4t, the male 4t and female 2t threads may be similar but not be identical mirror images of each other. The above discussed design process may be performed once for the female thread 2t and again for the male thread 4t.
In some example embodiments D₂ is between 19 - 119 mm. For example, D₂ is between 27 - 89 mm. For example, D₂ is between 34 - 69 mm. For example, D₂ is between 29 - 49 mm. For example, D₂ is between 33 - 46 mm. For example, D₂ is between 31 - 39 mm.
In some example embodiments, D₃ is between 20 - 120 mm. For example, D₃ is between 20 - 60 mm. For example, D₃ is between 28 - 90 mm. For example, D₃ is between 35 - 70 mm. For example, D₃ is between 30 - 50 mm. For example, D₃ is between 34 - 47 mm. For example, D₃ is between 32 - 40 mm.
Each of the female 2t and male 4t threads may be single threads, double threads or triple threads i.e., single entry, double entry or triple entry.
In some example embodiments, to avoid stress concentrations in localised regions of the thread the ratio of the camber radius on the male thread R_bm to the camber radius on the female thread R_bf should be between ≤1. For example, R_bm/ R_bf is < 1. For example, R_bm/ R_bf is between 0. 9 - 0.99. For example, R_bm/ R_bf is between 0.97 - 0.99.
Figure 4 illustrates an example when the ratio of the male and female camber radii is within the preferred range.
Drill components 8 having a female coupling part 2 with D₃ in the range 30 - 50, for example in the range 34 - 47 mm, for example in the range 32 - 40 mm and / or a male coupling part 4 with D₂ in the range 29 - 49 mm, for example in the range 33 -46 mm, for example in the range 31 - 39 mm may be used in a shoulder contact coupling, i.e. where the male coupling part 4 comprises a shoulder and the transfer of energy between adjacent components occurs through the shoulder contact. When shoulder contact couplings are combined with D₃ and / or D₂ in the ranges as disclosed above it is beneficial to have the Rbm/ Rbf ≤ 1.
Preferably, each camber radius (R_b, R_b-T) is between 500 - 2000 mm. For example, each camber radius (R_b, R_b-T) is between 700 - 1825 mm. For example, each camber radius (R_b, R_b-T) is between 900 - 1650 mm.
Alternatively, the cambered threads 2t, 4t may be right-handed threads.
Figure 5 illustrates a profile 7m of the male cambered thread 4t. Figures 6A and 6B are enlargements of portions of Figure 5. Once the outline of the male thread 4t has been generated, the profile 7m may be determined. The profile 7m may end at a point where the crest of the profile intersects an axis G₁ parallel to the longitudinal axis G_L and offset to the end diameter D₁. The sweep angle γ may define the arcuate extent of the profile 7m from start to end and may range between one and 10 degrees.
Referring specifically to Figure 6A, a thread-form of the profile 7m may include a first crest A₁. The thread-form may have a trapezoidal shape. The first crest A₁ may be an arc with the (outer) camber radius R_b and may extend to a second arc A₂. The centerline C_L may be inclined relative to the offset axis G₁ at an acute and nearly perpendicular first angle δ₀. The second arc A₂ may have a radius less than one percent of the outer camber radius R_b. The second arc A₂ may extend from the first crest A₁ to a non-contact flank E₁. The second arc A₂ may be tangential to the first crest A₁ and the non-contact flank E₁.
The non-contact flank E₁ may be a straight line inclined at a first flank angle α relative to the centerline C_L. The first flank angle α may range between 35 and 55 degrees or the first flank angle may be less than 45 degrees. The non-contact flank E₁ may extend from the second arc A₂ to a third arc A₃. The third arc A₃ may have a radius less than one percent of the outer camber radius R_b. The third arc A₃ may extend from the non-contact flank E₁ to a first root A₄. The third arc A₃ may be tangential to the non-contact flank E₁ and the first root A₄. The thread-form may have a height T between the first root A₄ and a second crest A₇. The first root A₄ may be an arc with an inner camber radius R_b-T and may extend from the third arc A₃ to a fifth arc A₅. The height T may be less than one percent of the outer camber radius R_b such that the inner camber radius R_b-T is also greater than the outer diameter of the male coupling part 4, as discussed above for the camber radius. The first root A₄ may be concentric with the first crest A₁. The centerline C_L may be perpendicular to an arc of each camber radius R_b, R_b-T.
The fifth arc A₅ may have a radius less than one percent of the camber radius R_b. The fifth arc A₅ may extend from the first root A₄ to a contact flank E₂. The fifth arc A₅ may be tangential to the first root A₄ and the contact flank E₂. The contact flank E₂ may be a straight line inclined at a second flank angle β relative to the centerline C_L. The second flank angle β may range between 40 and 45 degrees. The first flank angle α may be less than the second flank angle β, thereby resulting in an asymmetric thread-form. The contact flank E₂ may extend from the fifth arc A₅ to a sixth arc A₆. The sixth arc A₆ may extend from the contact flank E₂ to the second crest A₇. The sixth arc A₆ may be tangential to the contact flank E₂ and the second crest A₇. The second crest A₇ may be an arc with the outer camber radius R_b.
The thread-form may have an (arc length) pitch P between a start of the profile 7m and a centre of the second crest A₇. The first crest A₁ may have an arc length X₁ which may also be equal to one-half the arc-length of the second crest A₇. The first root A₄ may also have an arc length equal to twice that of the arc length X₁.
Alternatively, the crests and roots may have different arc lengths. Alternatively, the second flank angle may be less than 45 degrees.
Referring specifically to Figure 6B, due to the camber of the profile 7m about each camber radius R_b, R_b-T, the centerline C_L of the thread-form adjacent to the end of the profile 7m may be inclined relative to the offset axis G₁ at a second acute angle δ₁ which is less than the first angle δ₀.
Figure 7 illustrates a profile 7f of the female cambered thread 2t. Figures 8A and 8B are enlargements of portions of Figure 7. Once the outline of the female thread 2t has been generated, the profile 7f may be determined. The profile 7f may end at a point where the root of the profile intersects an axis G₁ parallel to the longitudinal axis G_L and offset to the end diameter D₁. The standoff distance X₀ of the female profile 7f may differ slightly from the standoff distance of the male profile 7m. The sweep angle γ may define the arcuate extent of the profile 7f from start to end and may range between one and 10 degrees.
Referring specifically to Figure 8A, a thread-form of the profile 7f may include a first root A₁. The thread-form may have a trapezoidal shape. The first root A₁ may be an arc with the outer camber radius R_b and may extend to a second arc A₂. The outer camber radius R_b of the female profile 7f may differ slightly from the outer camber radius of the male profile 7m. The centerline C_L may be inclined relative to the offset axis G₁ at an acute and nearly perpendicular first angle δ₀. The second arc A₂ may have a radius less than one percent of the outer camber radius R_b. The second arc A₂ may extend from the first root A₁ to a non-contact flank E₁. The second arc A₂ may be tangential to the first root A₁ and the non-contact flank E₁. The non-contact flank E₁ may be a straight line inclined at a first flank angle α relative to the centerline C_L. The first flank angle α may range between 35 and 55 degrees.
The non-contact flank E₁ may extend from the second arc A₂ to a third arc A₃. The third arc A₃ may have a radius less than one percent of the outer camber radius R_b. The third arc A₃ may extend from the non-contact flank E₁ to a first crest A₄. The third arc A₃ may be tangential to the non-contact flank E₁ and the first crest A₄. The thread-form may have a height T between the first crest A₄ and a second root A₇. The first crest A₄ may be an arc with an inner camber radius R_b-T and may extend from the third arc A₃ to a fifth arc A₅. The inner camber radius R_b-T of the female profile 7f may differ slightly from the inner camber radius of the male profile 7m. As shown by the pair of phantom lines extending from endpoints of the first crest A₄, the centerline C_L may extend through a midpoint of the first crest A₄. The centerline C_L may be perpendicular to an arc of each camber radius R_b, R_b-T. The height T may be less than one percent of the outer camber radius R_b such that the inner camber radius R_b-T is also greater than the outer diameter of the female coupling 2 as discussed above for the camber radius.
The fifth arc A₅ may have a radius less than one percent of the outer camber radius R_b. The fifth arc A₅ may extend from the first crest A₄ to a contact flank E₂. The fifth arc A₅ may be tangential to the first crest A₄ and the contact flank E₂. The contact flank E2 may be a straight line inclined at a second flank angle β relative to the centerline C_L. The second flank angle β may range between 40 and 45 degrees. The first flank angle α may be less than the second flank angle β, thereby resulting in an asymmetric thread-form. The asymmetric thread-form is further illustrated by projections of the flanks E₁, E₂ intersecting at a point offset from the centerline C_L. The second flank angle β of the female profile 7f may differ slightly from the second flank angle of the male profile 7m. The contact flank E₂ may extend from the fifth arc A₅ to a sixth arc A₆. The sixth arc A₆ may extend from the contact flank E₂ to the second root A₇. The sixth arc A₆ may be tangential to the contact flank E₂ and the second root A₇. The second root A₇ may be an arc with the outer camber radius R_b.
The thread-form may have an (arc length) pitch P between a start of the profile 7m and a center of the second root A₇. The first root A₁ may have an arc length X₁ which may also be equal to one-half the arc-length of the second root A₇. The arc length X₁ of the female profile 7f may differ from the arc length of the male profile 7m. The first crest A₄ may also have an arc length less than twice that of the arc length X₁.
Alternatively, the roots and crests may have the same arc lengths.
Referring specifically to Figure 8B, due to the camber of the profile 7m about each camber radius R_b, R_b-T, the centerline C_L of the thread-form adjacent to the end of the profile 7m may be inclined relative to the offset axis G₁ at a second acute angle δ₁ which is less than the first angle δ₀.
Reference to the contact flanks E₂ and the non-contact flanks E₁ is for the context of drilling when the drill string is in compression. When tripping the drill string from the drilled hole and unscrewing the drill rods, the drill string is in tension and the contact flanks E₂ become the non-contact flanks and the non-contact flanks E₁ become the contact flanks, as shown in Figure 9.
Figure 9 illustrates the male 4 and female 2 coupling parts screwed together. Once the thread profiles 7m,f have been generated, each profile may be adapted to create the geometry of the respective cambered thread 4t, 2t, such as by truncation thereof. The cambered curvature of each thread 2t, 4t along the longitudinal axis G_L may result in an frusto-ogive shape.
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 drill component (8) for a bottom contact coupling comprising at least one of:
a female coupling part (2) comprising a mounting sleeve (10) with a female thread (2t) formed its inner surface and a radially extending axially positioned inner wall (12) for abutment with a male coupling part; and

a male coupling part (4) with a male thread (4t) formed on its outer surface and a non-threaded axially endmost section (14) for abutment with a female coupling part;

wherein at least one of the threads (2t, 4t) has a thread-form including a crest (A₁, A₄, A₇), a root (A₁, A₄, A₇), and a pair of flanks (E₁, E₂);

wherein the crest (A₁, A₄, A₇) and the root (A₁, A₄, A₇) are each cambered about a respective first and second camber radius (R_b, R_b-T) along the entire length of the thread-form.
The drill component (8) according to claim 1 wherein the component (8) comprises a female coupling part (2) having an inner diameter (D₃) between 20 - 120 mm.
The drill component (8) according to claim 2 wherein the component (8) comprises a female coupling part (2) having an inner diameter (D₃) between 20 - 60 mm.
The drill component (8) according to claim 2 or 3 wherein the female coupling part (2) has an inner diameter (D₃) between 30 - 50 mm.
The drill component (8) according to any of the previous claims wherein the component (8) comprises a male coupling part (4) having an outer diameter (D₂) between 19 - 119 mm.
The drill component (8) according to claim 5 wherein the male coupling part (4) has an outer diameter (D₂) between 19 - 59 mm.
The drill component (8) according to claim 5 or 6 wherein the male coupling part (4) has an outer diameter (D₂) between 29 - 49 mm.
The drill component (8) according to any of the previous claims wherein each camber radius (R_b, R_b-T) is between 500 - 2000 mm.
The drill component (8) according to any of the previous claims wherein the male thread (4t) has a camber radius (R_bm) and the female thread (2t) has a camber radius (R_bf) and the ratio of the male thread camber radius to the female thread camber radius (R_bm/ R_bf) is ≤1.
The drill component (8) according to any of the previous claims wherein the thread(s) (2t, 4t) is / are single entry.
The coupling according to any of claims 1-7 wherein the thread(s) (2t, 4t) is / are double entry.