Screw pitch

Abstract

A female part forming part of a threaded joint for an impact drilling tool, the female part being a mounting sleeve, the mounting sleeve having a length L 1 and at least one substantially cylindrical internal threaded section having a thread inlet toward an axial end and a thread outlet toward an axial inner wall, the threaded section including a crest, a root, a contact flank, and a non-contact flank, and a pitch length L between two axially adjacent crests. 4 , and the radial inner diameter D between the roots 2 a mounting sleeve having a thread form, the mounting sleeve being positioned between the axially inner wall and the thread outlet, and having a length L 2 and diameter D 1 and a thread clearance section having a length L located between the thread inlet and the axial end of the sleeve. 3 and a guide section having a pitch length L 4 The female part is characterized by being 12.8 to 14.5 mm.

Description

[Technical Field]

[0001] The present invention relates to a female portion forming part of a threaded joint for impact drilling tools, and is particularly for, but not limited to, drill bits and drill rods. [Background technology]

[0002] Using impact drilling, a long borehole is created by multiple elongated drill string rods, each connected end-to-end by interconnected male and female threads. Alternatively, the drill bit may be connected to a single rod. By well-established techniques, the rock is fractured by the impact force transmitted from the rock drill bit to the rock at the bottom of the borehole. The rock drill bit is attached to a female thread on the drill bit at one end of the drill string via a male thread on the outermost drill string rod. Typically, the energy required to fracture the rock is generated by a hydraulically driven piston that contacts the end of the drill string (via a shank adapter) to generate a stress (or shock) wave that propagates through the drill string to the drill bit. Conventional threaded fittings are described in U.S. Patents 4,332,502, 4,398,756, 4,687,368 and German Patent No. 2800887.

[0003] Threaded joints in impact drilling tools, such as those between drill string rods and between the outermost drill string rod and the drill bit, are subjected to bending forces from stress waves propagating through the drill string during drilling. These bending moments fatigue the threaded joints, leading to breakage within the threaded portion of the joint. Ultimately, the stress wears down the threaded joint, eventually causing it to break.

[0004] Therefore, it is desirable to reduce the stress in threaded fittings in order to improve the performance of impact drilling tools and reduce the risk of damage to threaded fittings. One solution to reduce stress in threaded fittings is to increase the diameter of the male thread, but the problem with this is that increasing the diameter of the male thread weakens the female portion of the threaded fitting, making the threaded fitting more prone to breakage. Therefore, the problem to be solved is how to reduce the stress in threaded fittings and extend their lifespan. [Overview of the Initiative]

[0005] The object of the present invention is to provide a novel and improved design for a threaded fitting for a striking drilling tool. This object is achieved by providing a female portion that forms part of a threaded fitting for a striking drilling tool, the female portion being a mounting sleeve having an axial end, the mounting sleeve surrounding an internal cavity having an axial inner wall at the end opposite the mounting sleeve to the axial end, the mounting sleeve having at least one substantially cylindrical internal threaded section having length L1, a thread entry toward the axial end, and a thread exit toward the axial inner wall, the threaded section having a thread shape including a vertex, a root, a contact flank, and a non-contact flank, and a pitch length L4 between two axially adjacent vertices and a radial inner diameter D2 between roots, the mounting sleeve comprising a thread clearance section positioned between the axial inner wall and the thread exit, having length L2 and diameter D1, and a guide section positioned between the thread entry and the axial end of the sleeve, having length L3, wherein the pitch length L4 is 12.8 to 14.5 mm. Preferably, L4 is 13.0 to 13.5 mm.

[0006] Advantageously, this reduces stress in the female portion of the threaded fitting, which means a reduced risk of failure in the female portion. Furthermore, increasing stress in the female portion allows for an increase in the diameter of the male thread portion, thereby improving the performance of the impact drilling tool.

[0007] In one embodiment, the threaded section has a ratio of (L1+L2+D2) / L4 > 6.2. Preferably, the ratio is (L1+L2+D2) / L4 > 6.4. Advantageously, this reduces stress in the female portion of the threaded joint, which means a reduced risk of failure in the female portion.

[0008] In another embodiment, L3-L2 is 0-12 mm. Advantageously, this reduces stress in the female portion of the threaded fitting, which means a reduced risk of failure in the female portion.

[0009] In another embodiment, L1 is 25 to 56 mm. Preferably, L1 is 25 to 56 mm, and more preferably 30 to 45 mm. Preferably, the total length of the female thread (L1 + L2 + L3) is 70 to 86 mm. Advantageously, this is the optimal length for a threaded section with increased performance.

[0010] In one embodiment, L2 / L1 > 0.01 × D1. Advantageously, increasing the ratio of the length of the thread clearance area to the length of the threaded section means that the stress in the thread clearance area is reduced.

[0011] In one embodiment, L2 / L1 > 26%, preferably L2 / L1 > 32%. Advantageously, increasing the ratio of the length of the thread clearance area to the length of the threaded section means that the stress in the thread clearance area is reduced.

[0012] In one embodiment, L2 / L1 < 65%, preferably < 50%. Advantageously, this provides sufficient length in the threaded section to achieve a secure threaded connection.

[0013] In one embodiment, L2 / D1 > 30%, preferably L1 / D1 > 38%. Advantageously, increasing the ratio of the length of the thread clearance area to the diameter of the threaded section means that the stress in the thread clearance area is reduced. Therefore, the thread clearance and the diameter of the female thread can be increased, and consequently, the diameter of the male portion can also be increased, thereby improving the performance of the male portion and reducing the risk of skirt damage in the female portion.

[0014] In one embodiment, L2 / D1 < 65%, preferably < 50%. Advantageously, this allows for a secure screw connection.

[0015] In one embodiment, each thread shape has a contact flank angle α and a non-contact flank angle β inclined with respect to the respective baseline located at the respective inner or outer diameter of the respective thread shape, wherein the non-contact flank angle β is greater than the contact flank angle α, the apex of each thread shape is inclined from the respective contact flank to the respective non-contact flank, the apex of each thread shape defining the respective outer and inner diameters of the respective thread shape is located adjacent to the respective non-contact flank, the root of each thread is a first arc, and each contact flank is connected to the root of each thread by a second arc, wherein the first radius of each first arc is greater than the second radius of each second arc.

[0016] Advantageously, compared to the conventional technology described above, the inclined top of the threaded shape allows the contact flank to enlarge in response to coupling wear. Furthermore, pitting formed in the region adjacent to the contact flank can be removed as a result of wear.

[0017] In one embodiment, the female portion is part of the drill bit.

[0018] In one embodiment, the female portion is the female end of a drill string rod.

[0019] Another aspect of the present invention relates to a drill string rod including a female part as described above or below.

[0020] Another aspect of the present invention relates to a drill bit including a female part as described above or below. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Next, specific embodiments of the present invention will be described by way of example only, with reference to the accompanying drawings. [Figure 1] Perspective view of an impact drilling tool having one male end and one female end. [Figure 2] Perspective view of a drill rod having two male ends. [Figure 3] Cross-sectional view of the female end of a drill rod. [Figure 4] Cross-sectional view of a drill bit. [Figure 5] Cross-sectional view of the internal profile of the cavity of the female part forming a part of the screw joint for an impact drilling tool. [Figure 6] Diagram of a screw form. [Figure 7] Plot of the safety factor of the screw form of the comparative example. [Figure 8] Plot of the safety factor of the screw form of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Figure 1 shows a striking drilling tool 2 in which a drill rod 4 is screw-connected to a conventionally designed drill bit 6. The striking drilling tool 2 is used particularly for top hammer drilling. The shock wave generated by a surface piston (not shown) is transmitted from the drill rod 4 to the drill bit 6 via the mating surface. The drill rod 4 includes a main length section 8 that extends axially, with one end terminated at a male end 10 and the second opposite end terminated at a female end 12, and has a longitudinal axis 14. The drill rod 4 can be end-to-end connected to other further drill rods via another screw coupling to form a drill string (not shown).

[0023] Figure 2 shows that, alternatively, the drill bit 6 may be connected to a single drill rod 4 having two male ends 10.

[0024] Figure 3 shows a cross-section of the female end 12 of the drill rod 4, which has a mounting sleeve 18 and an internal cavity 20 that is a hollow space for receiving the male end 10 of the drill rod 4.

[0025] Figure 4 shows a cross-section of a drill bit 6, which includes, for example, a conventional axially forward drill head 16 including rock-breaking means, most typically a plurality of wear-resistant cutting buttons projecting axially forward from the drill head (not shown), and a mounting sleeve 18 having an axially extending internal cavity 20 for receiving the male end 10 of a drill rod 4.

[0026] The present invention relates to a special design for a female portion 22, and more particularly to a threaded form 54 that forms part of a threaded joint for a striking drilling tool 2. The female portion 22 may be either a female end 12 on a drill rod 4 or a drill bit 6.

[0027] Figure 5 shows a cross-section of the internal profile of the cavity 20 of the female part 22; in other words, Figure 5 is an enlarged view of the interior of Figure 3 or Figure 4. The cavity 20 has an axial inner wall 24 that abuts against the male end 10 of the drill rod 4. Furthermore, the cavity 20 has at least one substantially cylindrical internal threaded section 26 having a thread inlet 28 at the end axially opposite to the axial inner wall 24 and a thread outlet 30 closer to the axial inner wall 24. The threaded section 26 has a length L1 defined as the length between the thread inlet 28 and the thread outlet 30. The threaded section 26 has a thread configuration 54 having a pitch length L4 defined as the length between two axially adjacent vertices 56, including a plurality of vertices 56, roots 58, contact flanks E1 and non-contact flanks E2. The threaded section 26 also has a radial inner diameter D2 between the roots 58.

[0028] The cavity 20 of the female portion 22 also has a thread clearance section 32 positioned between the axial inner wall 24 and the threaded section 26. The thread clearance section 32 is a recessed area in the circumferential direction. The thread clearance section 32 has a length L2 defined as the length between the thread exit 30 and the axial inner wall 24. The thread clearance section has a diameter D1. On the opposite end of the threaded section 26 from the thread clearance section 32 is a guide section 50 for guiding the male end 10 of the rod 4 into the correct position. The guide section 50 has a length L3 defined as the length between the thread entry 28 and the axial end 52 of the sleeve 18. The guide section 50 may have a constant diameter throughout its length, or it may be stepped to have at least two different diameters.

[0029] Preferably, L3-L2 is <12 mm, more preferably <11.5 mm, and even more preferably <11 mm. Preferably, L3-L2 is >0 mm, more preferably >5 mm, and even more preferably >7 mm. In one embodiment, L1 is 25-56 mm, more preferably 30-45 mm.

[0030] In one embodiment, L2 / L1 > 0.01 × D1.

[0031] In one embodiment, L2 / L1 > 26%, more preferably > 32%.

[0032] In one embodiment, L2 / L1 < 65%, more preferably < 50%.

[0033] In one embodiment, L2 / D1 > 30%, more preferably > 38%.

[0034] In one embodiment, L2 / D1 < 65%, more preferably < 50%.

[0035] The female portion 22 is preferably used to form a threaded joint for a striking drilling tool 2 in which the bottom, rather than the shoulder, contacts the female portion 22 and the male end 10 of the adjacent rod. In other words, there is contact between the axial inner wall 24 of the female portion 22 and the male end 10 of the adjacent rod 4.

[0036] Figure 6 shows the screw configurations 54. Each screw configuration 54 is at point X B It may start at and may include a valley bottom A1. Each valley bottom A1 may be a concave arc having a radius R1 and may extend to a second arc A2. Each second arc A2 may be concave and may have a radius R2 and may extend from each first apex A1 to each contact flank E1. The radius R1 of each valley bottom may be greater than the radius R2 of each second, for example, at least 50 percent greater than the second radius. Each contact flank E1 may be a straight line inclined with respect to each baseline BL at each first flank angle α. The baseline BL may be longitudinal and the outer diameter D of each thread configuration 54 J or inner diameter D NIt may be located at. Each first flank angle α may be in the range of 15 to 50 degrees. Each contact flank E1 may extend from each second arc A2 to each third arc A3. Each third arc A3 may be convex and may have each radius R3. Each third arc A3 may extend from each contact flank E1 to each top A4. Each top A4 may have each first height H1 adjacent to each third arc A3 and each second height H2 adjacent to each fifth arc A5. Each height H1, H2 can be measured from each baseline BL. Each top A4 may be inclined from each contact flank E1 to each non-contact flank E2, and each outer diameter D J or inner diameter D N The apex X of each thread form 54 that defines it is positioned adjacent to each non-contact flank. Each thread form 54 can be in the longitudinal direction, and each outer diameter D A or inner diameter D J can have each peak line PL that can be located at. Each diameter D N of each thread form 54 N , D JThe angle may be constant. Due to the inclination of each apex A4, each second height H2 may be greater than each first height H1. Each inclination can be achieved by each apex A4 being a convex arc having its respective radius R4. The radius R4 of each apex may be greater than 10 percent of the outer diameter of the male coupling 1. Each apex A4 may extend from each third arc A3 to each fifth arc A5. Each second height H2 may be 5 to 20 percent greater than each first height H1. Alternatively, each apex A4 may be inclined linearly. Each fifth arc A5 may be convex, may have its respective radius R5, and may extend from each apex A4 to each non-contact flank E2. Each non-contact flank E2 may be a straight line inclined with respect to each baseline BL by its respective second flank angle β. Each second flank angle β may be greater than each first flank angle α, for example, 5 to 30 degrees greater than each first flank angle, thereby obtaining each asymmetric screw configuration 54. Each non-contact flank E2 may extend from each fifth arc A5 to each sixth arc A6. Each sixth arc A6 extends from each non-contact flank E2 to each endpoint X E It may extend to the . Each sixth arc A6 may be concave and may have its own radius R6. Each thread form 54 has its own starting point X B and their respective endpoints X E Each pitch L4 can be defined by the longitudinal distance between them.

[0037] In one embodiment, each contact flank angle α is in the range of 15 to 50 degrees, and each non-contact flank angle β is equal to the respective contact flank angle plus 5 to 30 degrees.

[0038] In one embodiment, the inclination of each top 56 is straight.

[0039] In one embodiment, the height H2 of each top 56 adjacent to each non-contact flank 62 is 5% to 20% greater than the height H1 of each top 56 adjacent to each contact flank 60.

[0040] In one embodiment, the non-contact flanks 62 are connected to their respective tops by their respective arcs A5.

[0041] In one embodiment, each diameter D J , D N It is constant.

[0042] Figures 7 and 8 show plots of safety factors measured along the dotted lines shown in the figures, when a bending force is applied, for a symmetrical thread profile with a pitch L4 of 12.7 mm (comparative sample) and an asymmetrical thread profile with a pitch L4 of 13.2 mm (sample of the present invention). A higher safety factor value indicates a reduced risk of failure. The sample of the present invention, with its increased pitch length, shows a reduced risk of failure along the length of the thread profile.

Claims

1. A female portion (22) that forms part of a threaded joint (34) for a striking drilling tool (2), A mounting sleeve (18) having an axial end (52), wherein the mounting sleeve (18) surrounds an internal cavity (20) having an axial inner wall (24) at the end of the mounting sleeve (18) opposite to the axial end (52), The aforementioned mounting sleeve (18) has a length L １ It has at least one substantially cylindrical internal threaded section (26) having a threaded entrance (28) toward the axial end (52) and a threaded exit (30) toward the axial inner wall (24), The threaded section (26) has a top (56), a root (58), and a contact flank (E １ ), and contactless flank (E ２ ) including the pitch length L between two axially adjacent vertices (56). ４ and the radial inner diameter D between the valley bottom portions (58) ２ A mounting sleeve (18) having a screw shape (54) and Length L ２ and diameter D １ A thread clearance section (32) is located between the axial inner wall (24) and the thread exit (30), and A length L is positioned between the screw entry (28) and the axial end (52) of the mounting sleeve (18). ３ A guide section (50) having, The length L of the pitch ４ is 12.8 to 14.5 mm, and the threaded section (26) is (the length L １ + the length L ２ + the inner diameter D ２ ) / the length L of the pitch ４ has a ratio of > 6.2, and is characterized by the female part (22).

2. The length L ３ - The aforementioned length L ２ The female portion (22) according to claim 1 is 0 to 12 mm in length.

3. The length L １ The female portion (22) according to claim 1 is 25 to 56 mm in length.

4. The length L ２ / The aforementioned length L １ >0.01 × the diameter D １ The female portion (22) according to claim 1.

5. The length L ２ / The aforementioned length L １ The female portion (22) according to claim 1, which is 26%.

6. The length L ２ / The aforementioned length L １ The female portion (22) according to claim 1, which is 65%.

7. The length L ２ / The diameter D １ The female portion (22) according to claim 1, which is 30%.

8. The length L ２ / The diameter D １ The female portion (22) according to claim 1, which is 65%.

9. Each screw shape (54) has an inner diameter (D Ｎ ) or outer diameter (D Ｊ Each of the baselines (BL) located at ) has a contact flank angle (α) and a non-contact flank angle (β) that are inclined with respect to each of the contact flank angles (α), and each of the non-contact flank angles (β) is greater than each of the contact flank angles (α), and the top portion (56) of each of the screw forms (54) is the contact flank (E １ ) from each of the aforementioned non-contact flanks (E ２ ) is inclined to the extent of each of the aforementioned screw shapes (54) and the respective outer diameter (D Ｊ ) and the inner diameter (D Ｎ The vertices (X) of each of the aforementioned screw shapes (54) that define the Ａ ) is each of the aforementioned non-contact flanks (E ２ ) is located adjacent to each valley bottom (58), and each of the contact flanks (E １ ) are each second arc (A ２ ) are connected to each of the aforementioned valley bottoms (58) by the first radius (R) of each first arc １ ) is each of the aforementioned second arcs (A ２ The second radius (R) of ) ２ The female portion (22) according to any one of claims 1 to 8, which is larger than ).

10. The female portion (22) is part of the drill bit (6), as described in any one of claims 1 to 8.

11. The female portion (22) is the female end (12) of the drill string rod (4), as described in any one of claims 1 to 8.

12. A drill string rod comprising a female portion (22) according to any one of claims 1 to 8.

13. A drill bit comprising the female portion (22) according to any one of claims 1 to 8.

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