Female portion of a percussion drilling tool, drill string rod, and drill bit.

Abstract

THREAD CLEARANCE. The present invention relates to a female portion for forming part of a threaded joint for a percussion drilling tool comprising a mounting sleeve having an axial end, wherein the mounting sleeve surrounds an internal cavity having an axial inner wall at the opposite end of the mounting sleeve compared to the axial end; wherein the mounting sleeve has at least one substantially cylindrical internally threaded section having a length L1, a thread entry towards the axial end and a thread exit towards the axial inner wall; a thread clearance section positioned between the axial inner wall and the thread exit having a length L2 and a diameter D1; a guide section positioned between the thread entry and the axial end of the sleeve having a length L3; characterized in that: 0 mm < L3 - L2 < 12 mm.

Description

THREAD CLEARANCE Technical field

[0001] The present invention relates to a female portion for forming part of a threaded joint for a percussion drilling tool, especially for, though not exclusively for, drill bits and drill rods. Technical overview

[0002] Percussion drilling is used to create a long hole by means of a plurality of elongated drill string rods coupled together end-to-end by interconnected male and female threads. Alternatively, a drill bit can be connected to a single rod. The well-established technique breaks rock by transferring hammer impacts from the rock drill bit to the rock at the bottom of the hole. The rock drill bit is mounted on one end of the drill string via a male thread on the drill string rod, the most extreme being a female thread on the drill bit. 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 rod adapter) to create a stress (or shock) wave that propagates through the drill string to the drill bit.Conventional threaded joints are described in U.S. patents numbers 4,432,502; 4,398,756; 4,687,368 and in German patent number DE 2800887.

[0003] Threaded joints in the percussion drilling tool, such as those between drill string rods and between the drill string rod and the other Petition 870220123102, dated 12 / 28 / 2022, page 5 / 27 2 / 9 extreme and the drill bit are subjected to bending forces during drilling from stress waves propagating in the drill string. These bending moments fatigue the threaded joints and lead to breakage within the threaded portion of the joint. Eventually, the stress will cause the threaded joint to become worn and eventually fail.

[0004] Consequently, it is desirable to reduce stress on the threaded joint to improve the performance of the percussion drilling tool and reduce the risk of failure in the threaded joint. One solution to reduce stress on the threaded joint is to increase the diameter of the male thread; however, the problem with this is that it weakens the female part of the threaded joint, meaning that it is more likely to break. Consequently, the problem to be solved is how to reduce stress on the threaded joint to consequently increase its service life. Summary

[0005] It is an object of the present invention to provide a new and improved design for threaded joints for percussion drilling tools. The object of the present invention is achieved by providing a female portion to form part of a threaded joint for a percussion drilling tool comprising: a mounting sleeve having an axial end, wherein the mounting sleeve surrounds an internal cavity having an axial inner wall at the opposite end of the mounting sleeve compared to the axial end; wherein the mounting sleeve has at least Petition 870220123102, dated 12 / 28 / 2022, page 6 / 27 3 / 9 less a substantially cylindrical internally threaded section having a length Li, a thread entry towards the axial end and a thread exit towards the axial inner wall; a thread clearance section positioned between the axial inner wall and the thread exit having a length L2 and a diameter Di; a guide section positioned between the thread entry and the axial end of the sleeve having a length L3; characterized in that: 0 mm < L3 - L2 < 12 mm. More preferably, 5 mm < L3 - L2 < 11.5 mm, even more preferably 7 mm < L3 - L2 < 11.1 mm.

[0006] Advantageously, this reduces stress on the female portion of the threaded joint, meaning that the risk of breakage in the female portion is decreased. Additionally, if the stress on the female portion is increased, then the diameter of the male threaded part can be increased, which improves the performance of the percussion drilling tool.

[0007] Preferably, L1 is between 25 mm - 56 mm, preferably between 30 mm - 45 mm. Preferably, the total length of the female thread (L1 + L2 + L3) is between 70 mm and 86 mm. Advantageously, this is the most optimized threaded section length for increased performance.

[0008] Preferably, L2 / L1 > 0.01 x D1. Advantageously, increasing the ratio of the thread clearance area length compared to the threaded section length means that the stress in the thread clearance area decreases.

[0009] Preferably, L2 / L1 > 26%, more preferably L2 / L1 > 32%. Advantageously, increasing the ratio of thread clearance area length compared Petition 870220123102, dated 12 / 28 / 2022, page 7 / 27 4 / 9 with the length of the threaded section means that the stress in the thread clearance area decreases.

[0010] Preferably, L2 / L1 < 65%, more preferably L2 / L1 < 50%. Advantageously, this provides sufficient length in the threaded section to achieve a secure threaded connection.

[0011] Preferably, L1 / D1 > 30%, more preferably L1 / D1 > 38%. Advantageously, increasing the ratio of the thread clearance area length compared to the threaded section diameter means that the stress in the thread clearance area decreases. Consequently, the diameter of the thread clearance and female thread can be reduced and consequently the diameter of the male part, which leads to decreased performance of the male part and less risk of skirt (edge) failures in the female part.

[0012] Preferably, L2 / D1 < 65%, more preferably < 50%. Advantageously, this allows for a secure threaded connection.

[0013] In one embodiment, the female portion is a drill bit. In an alternative embodiment, the female portion is a female end of a drill string rod. Brief description of the drawings

[0014] 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:

[0015] Figure 1: Perspective view of a percussion drilling tool having a male end and a female end.

[0016] Figure 2: Perspective view of a Petition 870220123102, dated 12 / 28 / 2022, page 8 / 27 5 / 9 drill shank with two male ends.

[0017] Figure 3: Cross-section of the female end of a drill rod.

[0018] Figure 4: Cross-section of a drill bit.

[0019] Figure 5: Cross-section of an internal profile of the cavity of the female portion to form part of a threaded joint for a percussion drilling tool. Detailed description

[0020] Figure 1 shows a percussion drilling tool (2) whereby a drill rod (4) is threaded coupled to a conventional design drill bit (6). The percussion drilling tool (2) is especially used for butt hammer drilling. Shock waves generated by a surface piston (not shown) are translated through the paired (coupled, combined) surfaces from the drill rod (4) to the drill bit (6). The drill rod (4) comprises a main length section extending axially (8) which is terminated at one end by a male end (10) and at a second opposite end by a female end (12) having a longitudinal geometric axis (14). The drill rod (4) has the capability to be coupled end-to-end with other additional drill rods to form a drill string (not shown) by means of another threaded joint.Figure 2 shows that alternatively the drill bit (6) can be connected to a single drill rod (4) having two ends. Petition 870220123102, dated 12 / 28 / 2022, page 9 / 27 6 / 9 male (10).

[0021] Figure 3 shows a cross-section of the female end (12) of the drill rod (4) having a mounting sleeve (18) and an internal cavity (20), which is a hollow space, for receiving the male end (10) of the drill rod (4).

[0022] Figure 4 shows a cross-section of the drill bit (6) comprising an axially advanced drill head (16) of conventional design (e.g., comprising a rock crushing feature, most typically this is a plurality of wear-resistant cutting bottoms projecting axially forward from the drill head (not shown); a mounting sleeve (18) comprising an axially extending inner cavity (20) for receiving the male end (10) of the drill rod (4).

[0023] The present invention relates to a special design for a female portion (22) that forms part of a threaded joint for a percussion drilling tool (2). The female portion (22) can be either the female end (12) on the drill shank (4) or the drill bit (6).

[0024] Figure 5 shows a cross-section of an internal profile of the cavity (20) of the female portion (22), in other words Figure 5 is an enlargement of the interior of Figure 3 or Figure 4. The cavity (20) has an axial inner wall (24) for support with a male end (10) of a drill shank (4). Additionally, the cavity (20) has at least one substantially cylindrical internally threaded section (26) having a Petition 870220123102, dated 12 / 28 / 2022, page 10 / 27 7 / 9 thread entry (28) at the axially opposite end compared to the axial inner wall (24) and a thread exit (30) closer to the axial inner wall (24). The threaded section (26) has a length, Li, which is defined as the length between the thread entry (28) and the thread exit (30). The cavity (20) of the female portion (22) also has a thread clearance section (32) positioned between the axial inner wall (24) and the thread section (26). The thread clearance section (32) is a concave circumferential recess. The thread clearance section (32) has a length, L2, which is defined as the length between the thread exit (30) and the axial inner wall (24). The thread clearance section has a diameter, D1. There is a guide section (50) on the opposite end of the threaded section (26) compared with the thread clearance section (32) to guide the male end (10) of the rod (4) to the correct position.The guide section (50) has a length, L3, which is defined as the length between the thread entry (28) and an axial end (52) of the sleeve (18). The guide section (50) can either be of a constant diameter throughout the entire guide section (50) or it can optionally be stepped in such a way that it has at least two different diameters.

[0025] Compared with conventional designs, the L2 ratio compared to Li and / or L3 was increased.

[0026] L3 - L2 for female portions (22) in accordance with the present invention is < 12 mm, more preferably < 11.5 mm, even more preferably < 11 mm. L3 - L2 for female portions (22) in accordance with Petition 870220123102, dated 12 / 28 / 2022, page 11 / 27 8 / 9 with the present invention is > 0 mm, more preferably > 5 mm, even more preferably > 7 mm. In a embodiment Li is between 25 mm - 56 mm, more preferably

[0027] between 30 mm - 45 mm. In an embodiment, L2 / L1 > 0.01 x D1.

[0028] In an embodiment, L2 / L1 > 26%, more preferably

[0029] > 32%. In an embodiment, L2 / L1 < 65%, more preferably

[0030] < 50%. In an embodiment, L2 / D1 > 30%, more preferably

[0031] > 38%. In an embodiment, L2 / D1 < 65%, more preferably

[0032] < 50%. Preferably, the female portion (22) is used to form a threaded joint (34) for a percussion drilling tool (2) in which there is a bottom contact, as opposed to a stop contact, between the female portion (22) and the male end (10) of the adjacent (joining) rod. In other words, there is contact between the axial inner wall (24) on the female portion and the male end (10) of the adjacent (joining) rod (4).

[0033] Software simulation programming with added bending force for the female portion (22) of inventive and non-inventive female portions was performed. Table 1 shows a summary of stress measurements for state-of-the-art and inventive female portions (22), it can be clearly seen that the stress in the thread clearance region is lower for the inventive samples. Petition 870220123102, dated 12 / 28 / 2022, page 12 / 27 9 / 9 Example D1 (mm) L3-L2 (mm) Stress (MPa) in the thread clearance region on the female portion of a threaded joint 1 (state of the art) 33.1 12.7 305 2 (present invention) 33.1 11.0 290 3 (state of the art) 36.5 14.3 300 4 (present invention) 36.5 10.5 275 Table 1: Summary of stress measurements.

Claims

CLAIMS 1. A female portion (22) for forming part of a threaded joint (34) for a percussion drilling tool (2) comprising: - a mounting sleeve (18) having an axial end (52), wherein the mounting sleeve (18) encircles an internal cavity (20) having an axial inner wall (24) at the opposite end of the mounting sleeve (18) compared with the axial end (52); - wherein the mounting sleeve (18) has at least one substantially cylindrical internally threaded section (26) having a length L1, a thread entry (28) towards the axial end (52) and a thread exit (30) towards the axial inner wall (24); - a thread clearance section (32) positioned between the axial inner wall (24) and the thread exit (30) having a length L2 and a diameter D1; - a guide section (50) positioned between the thread entry (28) and the axial end (52) of the sleeve (18) having a length, L3;characterized in that: 0 mm < L3 - L2 < 12 mm.

2. The female portion (22) according to claim 1, wherein L1 is between 25 mm — 56 mm.

3. The female portion (22) according to claim 1 or claim 2, wherein L2 / L1 > 0.01 x D1.

4. The female portion (22) according to any of the preceding claims, where L2 / L1 > 26%.

5. The female portion (22) according to any of the preceding claims, where L2 / L1 < 65%.

6. The female portion (22) according to any of the preceding claims, where L2 / L1 > 30%.

7. The female portion (22) according to any of the preceding claims, where L2 / L1 < 65%.

8. The female portion (22) according to any of the preceding claims, wherein the female portion (22) is part of a drill bit (6).

9. The female portion (22) according to any of the preceding claims, wherein the female portion (22) is a female end (12) of a drill string rod (4).

10. A drill string rod comprising a female portion (22) in accordance with any of claims 1 - 7.

11. A drill bit comprising a female portion (22) in accordance with any of claims 1 7.