Thread clearance

Abstract

A female portion for forming part of a threaded connector for an impact drilling tool, the female portion comprising: a mounting sleeve having an axial end, wherein the mounting sleeve surrounds an internal cavity having an axial inner wall at an end of the mounting sleeve opposite to the axial end; wherein the mounting sleeve has at least one substantially cylindrical internal threaded section, a threaded inlet toward the axial end, and a threaded outlet toward the axial inner wall, the internal threaded section having a length L1; a threaded clearance section positioned between the axial inner wall and the threaded outlet, having a length L2 and a diameter D1; and a guide section positioned between the threaded inlet and the axial end of the sleeve, having a length L3; characterized in that: 0 mm <L3‑L2<12mm。

Description

Technical Field

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

[0002] Percussion drilling is used to form long boreholes by multiple elongated drill strings joined end-to-end by interconnected male and female threads. Alternatively, the drill bit can be attached to a single string. Established technology involves breaking rock through hammering impacts transmitted from the rock bit to the bottom of the borehole. The rock bit is mounted at one end of the drill string via a male thread on the outermost drill string and 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 aforementioned 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 connections are described in US 4,332,502, US 4,398,756, US 4,687,368, and DE2800887.

[0003] Threaded joints in impact drilling tools (such as the threaded joints between drill strings and between the final drill string and the drill bit) are subjected to bending forces during drilling from stress waves propagating through the drill string. These bending moments cause fatigue in the threaded joints and lead to fracture within the threaded portion of the joint. Ultimately, the stress will cause the threaded joint to wear and eventually fail.

[0004] Therefore, the goal is to reduce stress in threaded joints to improve the performance of impact drilling tools and reduce the risk of joint failure. One solution to reduce stress in threaded joints is to increase the diameter of the male thread; however, this weakens the female portion of the joint, making it more prone to breakage. Therefore, the challenge is to reduce stress in threaded joints to increase their lifespan. Summary of the Invention

[0005] The object of the present invention is to provide a novel and improved design for a threaded joint for an impact drilling tool. This object is achieved by providing a female part for forming a part of the threaded joint for an impact drilling tool, the female part 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 internal thread section, a thread inlet facing the axial end and a thread outlet facing the axial inner wall, the internal thread section having a length L1; a thread clearance section located between the axial inner wall and the thread outlet, having a length L2 and a diameter D1; a guiding section located between the thread inlet 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, and even more preferably, 7 mm < L3 - L2 < 11.1 mm.

[0006] Advantageously, this reduces the stress in the female part of the threaded joint, which means that the risk of fracture of the female part is reduced. In addition, if the stress in the female part increases, then the diameter of the male thread part can be increased, which improves the performance of the impact drilling tool.

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

[0008] Preferably, L2 / L1 > 0.01×D1. Advantageously, increasing the ratio of the length of the thread clearance area to the length of the thread section means that the stress in the thread clearance area is reduced.

[0009] Preferably, L2 / L1 > 26%, more preferably L2 / L1 > 32%. Advantageously, increasing the ratio of the length of the thread clearance area to the length of the thread section means that the stress in the thread clearance area is reduced. <W000021>

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

[0011] Preferably, L2 / D1 > 30%, more preferably L1 / D1 > 38%. Advantageously, increasing the ratio of the length of the thread clearance area to the diameter of the thread 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 thus the diameter of the male part can also be increased, which results in an increase in the performance of the male part and a reduction in the risk of skirt failure of the female part.

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

[0013] In one embodiment, the female portion is the drill bit. In an alternative embodiment, the female portion is the female end of the drill string. Attached Figure Description

[0014] Specific embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings:

[0015] Figure 1 : A perspective view of an impact drilling tool with a male end and a female end.

[0016] Figure 2 : A three-dimensional view of a drill pipe with two male ends.

[0017] Figure 3 : The cross-section of the female end of the drill pipe.

[0018] Figure 4 : The cross-section of the drill bit.

[0019] Figure 5 : The cross-section of the internal contour of the cavity of the female part used to form part of the threaded joint for impact drilling tools. Detailed Implementation

[0020] Figure 1 An impact drilling tool 2 is shown, in which a drill rod 4 is threadedly connected to a drill bit 6 having a conventional design. The impact drilling tool 2 is particularly used for top hammer drilling. Shock waves generated by a surface piston (not shown) are transmitted from the drill rod 4 to the drill bit 6 through mating surfaces. The drill rod 4 includes an axially extending main length section 8, which terminates at one end in a male end 10 and at the opposite second end in a female end 12 having a longitudinal axis 14. The drill rod 4 can be connected end-to-end with other additional drill rods via another threaded joint to form a drill string (not shown). Figure 2 It is shown that, alternatively, the drill bit 6 can be connected to a single drill rod 4 having two male ends 10.

[0021] Figure 3 A cross-section of the female end 12 of the drill pipe 4 is shown. The female end 12 has a mounting sleeve 18 and an internal cavity 20, which is a hollow space for receiving the male end 10 of the drill pipe.

[0022] Figure 4A cross-section of a drill bit 6 is shown, which includes an axially foremost drill head 16 with a conventional design, such as a rock breaking device, most typically a plurality of wear-resistant cutting ball teeth (not shown) projecting axially forward from the drill head; and a mounting sleeve 18, which includes an axially extending internal cavity 20 for receiving the male end 10 of the drill rod 4.

[0023] This invention relates to a specific design of a female portion 22 that forms part of a threaded joint for an impact drilling tool 2. The female portion 22 may be a female end 12 on a drill rod 4 or a drill bit 6.

[0024] Figure 5 A cross-section of the internal contour of the cavity 20 of the female portion 22 is shown; in other words, Figure 5 yes Figure 3 or Figure 4 An enlarged view of the interior of the cavity 20. The cavity 20 has an axial inner wall 24 for abutting the male end 10 of the drill pipe 4. Furthermore, the cavity 20 has at least one substantially cylindrical internally threaded section 26, which has a threaded inlet 28 located at an axially opposite end compared to the axial inner wall 24 and a threaded outlet 30 closer to the axial inner wall 24. The threaded section 26 has a length L1, defined as the length between the threaded inlet 28 and the threaded outlet 30. The cavity 20 of the female portion 22 also has a threaded clearance section 32 positioned between the axial inner wall 24 and the threaded section 26. The threaded clearance section 32 is a circumferentially concave recess. The threaded clearance section 32 has a length L2, defined as the length between the threaded outlet 30 and the axial inner wall 24. The threaded clearance section has a diameter D1. At the opposite end of the threaded section 26 compared to the threaded clearance section 32, there is a guide section 50 for guiding the male end 10 of the drill pipe 4 into the correct position. The guide section 50 has a length L3, which is defined as the length between the threaded inlet 28 and the axial end 52 of the sleeve 18. The guide section 50 may have a constant diameter throughout the guide section 50, or alternatively, the guide section 50 may be stepped, thus the guide section 50 having at least two different diameters.

[0025] Compared to conventional designs, the ratio of L2 to L1 and / or L3 is increased.

[0026] According to the invention, the L3-L2 of the female portion 22 is <12mm, more preferably <11.5mm, and even more preferably <11mm. According to the invention, the L3-L2 of the female portion 22 is >0mm, more preferably >5mm, and even more preferably >7mm. In one embodiment, L1 is between 25-56mm, more preferably between 30-45mm.

[0027] In one embodiment, L2 / L1 > 0.01 × D1.

[0028] In one implementation, L2 / L1 > 26%, more preferably > 32%.

[0029] In one implementation, L2 / L1 < 65%, more preferably < 50%.

[0030] In one embodiment, L2 / D1 > 30%, more preferably > 38%.

[0031] In one implementation, L2 / D1 < 65%, more preferably < 50%.

[0032] Preferably, the female portion 22 is used to form the threaded joint 34 of the impact drilling tool 2, wherein there is bottom contact, rather than shoulder contact, between the female portion 22 and the adjacent male end 10 of the rod. In other words, there is contact between the axial inner wall 24 on the female portion and the adjacent male end 10 of the rod 4.

[0033] Software simulation programming was performed using bending forces applied to the female portion 22 of the present invention and to the female portions of the non-present invention. Table 1 shows a summary of stress measurements for the female portion 22 of the prior art and the present invention. It can be clearly seen that the stress in the thread gap region is lower for the sample of the present invention.

[0034]

[0035] Table 1: Summary of Stress Measurement

Claims

1. A female portion (22) for forming part of a threaded joint (34) for a bottom contact impact drilling tool (2), the female portion (22) comprising: 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 opposite end of the mounting sleeve (18) compared to the axial end (52). The mounting sleeve (18) has at least one substantially cylindrical internal threaded section (26), a threaded inlet (28) toward the axial end (52) and a threaded outlet (30) toward the axial inner wall (24), the internal threaded section (26) having a length L1; A thread clearance section (32) is located between the axial inner wall (24) and the thread outlet (30) and has a length L2 and a diameter D1; A guide section (50) is positioned between the threaded inlet (28) and the axial end (52) of the sleeve (18) and has a length L3; Where L1 is between 25-56mm, and the total length of L1+L2+L3 is between 70-86mm. Its characteristic is that 0mm < L3-L2 < 12mm.

2. The negative portion (22) according to claim 1, wherein L2 / L1>0.01×D1.

3. The negative portion (22) according to any one of the preceding claims, wherein L2 / L1 > 26%.

4. The negative portion (22) according to any one of the preceding claims, wherein L2 / L1 < 65%.

5. The negative portion (22) according to any one of the preceding claims, wherein L2 / D1 > 30%.

6. The female portion (22) according to any one of the preceding claims, wherein L2 / D1 < 65%.

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

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

9. A drill string comprising a female portion (22) according to any one of claims 1-6.

10. A drill bit comprising a female portion (22) according to any one of claims 1-6.

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