Thread Clearance

Abstract

A female part forming a part of a screw joint for an impact piercing tool, the female part being a mounting sleeve having an axial end, the mounting sleeve surrounding an internal cavity having an axial inner wall at an end opposite to the axial end of the mounting sleeve, the mounting sleeve having at least one substantially cylindrical female thread portion having a length L1, a thread inlet towards the axial end, and a thread outlet towards the axial inner wall, a thread clearance portion disposed between the axial inner wall and the thread outlet and having a length L2 and a diameter D1, and a guide portion disposed between the thread inlet and the axial end of the sleeve and having a length L3, wherein the female part is characterized in that 0 mm < L3 - L2 < 12 mm.

Description

[Technical Field]

[0001] The present invention relates to a percussive drilling tool, in particular a female part forming part of a threaded joint for, but not limited to, drill bits and drill rods. [Background technology]

[0002] Percussion drilling is used to create long boreholes via multiple elongated drill string rods connected end-to-end by interconnected external and internal threads. Alternatively, the drill bit may be connected to a single rod. An established technique involves breaking rock by driving an impact transmitted from a rock drill bit into the rock at the bottom of the borehole. The rock drill bit is attached at one end of the drill string via an external thread on the endmost drill string rod and an internal 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 shank adapter) and generates a stress (or shock) wave that propagates through the drill string to the drill bit. Conventional threaded joints are described in U.S. Pat. No. 4,332,502, U.S. Pat. No. 4,398,756, U.S. Pat. No. 4,687,368, and DE 2800887.

[0003] Threaded joints in percussive drilling tools, such as those between drill string rods and between the most distal drill string rod and the drill bit, are subjected to bending forces during drilling from stress waves propagating through the drill string. These bending moments can fatigue the threaded joints and lead to fractures within the threaded portion of the joint. Ultimately, the stresses cause the threaded joints to wear and ultimately fail.

[0004] Therefore, in order to improve the performance of the percussion piercing tool and reduce the risk of failure of the screw joint, it is desirable to reduce the stress on the screw joint. One solution to reduce the stress on the screw joint is to increase the diameter of the male thread, but the problem associated with this is that the female part of the screw joint becomes weaker, which means that it is more likely to break. Therefore, the problem to be solved is how to reduce the stress on the screw joints and thus extend their lifespan.

Summary of the Invention

[0005] The object of the present invention is to provide a novel and improved design of a screw joint for a percussion piercing tool. This object is achieved by providing a female part that forms part of the screw joint for the percussion piercing tool, which female part is a mounting sleeve having axial ends, the mounting sleeve surrounding an internal cavity having an axial inner wall at an end opposite the axial ends of the mounting sleeve, the mounting sleeve having at least one substantially cylindrical female thread portion having a length L1, a thread inlet leading towards the axial ends, and a thread outlet leading towards the axial inner wall, a mounting sleeve, a thread clearance portion disposed between the axial inner wall and the thread outlet and having a length L2 and a diameter D1, and a guide portion disposed between the thread inlet and the axial ends of the sleeve and 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 means that the stress on the female part of the screw joint is reduced and the risk of damage to the female part is decreased. Further, when the stress on the female part increases, the diameter of the male thread part can be increased, improving the performance of the percussion piercing tool.

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

[0008] Preferably, L2 / L1>0.01*D1. Advantageously, increasing the ratio of the length of the thread clearance area compared to the length of the thread means that the stresses in the thread clearance area are reduced.

[0009] Preferably, L2 / L1 > 26%, more preferably L2 / L1 > 32%. Advantageously, increasing the ratio of the length of the thread clearance area compared to the length of the thread means that the stresses in the thread clearance area are reduced.

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

[0011] Preferably, L2 / D1 > 30%, more preferably L1 / D1 > 38%. Advantageously, increasing the ratio of the length of the thread clearance area compared to the diameter of the thread 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, which in turn allows for a larger diameter of the male part, improving the performance of the male part and reducing the risk of skirt failure on 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 the female end of a drill string rod.

[0014] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0015] [Figure 1]FIG. 1 is a perspective view of a hammer drilling tool having one male end and one female end. [Figure 2] FIG. 1 is a perspective view of a drill rod having two male ends. [Figure 3] FIG. 1 is a cross-sectional view of the female end of the drill rod. [Figure 4] FIG. 1 is a cross-sectional view of a drill bit. [Figure 5] 10 is a cross-sectional view of the internal profile of a cavity in a female part that forms part of a threaded joint for a percussion drilling tool. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 illustrates a percussive drilling tool 2 in which a drill rod 4 is threadedly coupled to a drill bit 6 of conventional design. The percussive drilling tool 2 is particularly used for tophammer drilling. A shock wave generated by a surface piston (not shown) travels from the drill rod 4 to the drill bit 6 through a mating surface. The drill rod 4 includes an axially extending main length section 8 terminated at one end by a male end 10 and at a second, opposite end by a female end 12 having a longitudinal axis 14. The drill rod 4 can be connected end-to-end with other additional drill rods to form a drill string (not shown) via another threaded joint. FIG. 2 illustrates that, alternatively, the drill bit 6 can be connected to a single drill rod 4 having two male ends 10.

[0017] FIG. 3 shows a cross section of the female end 12 of a 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.

[0018] FIG. 4 shows a cross section of a drill bit 6 comprising an axially forward drill head 16 of conventional design, for example provided with 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.

[0019] The present invention relates to a special design of a female part 22 forming part of a threaded joint for a percussion drilling tool 2. The female part 22 can be either the female end 12 of the drill rod 4 or the drill bit 6.

[0020] FIG. 5 shows a cross section of the internal profile of the cavity 20 of the female portion 22; in other words, FIG. 5 is an enlarged view of the interior of FIG. 3 or 4. The cavity 20 has an axial inner wall 24 for abutting against the male end 10 of the drill rod 4. Furthermore, the cavity 20 has at least one substantially cylindrical female threaded portion 26 having a threaded inlet 28 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 portion 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 thread clearance portion 32 disposed between the axial inner wall 24 and the threaded portion 26. The thread clearance portion 32 is a circumferentially recessed recess. The thread clearance portion 32 has a length L2 defined as the length between the threaded outlet 30 and the axial inner wall 24. The thread clearance portion has a diameter D1. To guide the male end 10 of the rod 4 into the correct position, there is a guide portion 50 at the opposite end of the threaded portion 26 compared to the thread clearance portion 32. The guide portion 50 has a length L3 defined as the length between the threaded entry 28 and the axial end 52 of the sleeve 18. The guide portion 50 may be of a constant diameter throughout the guide portion 50, or may optionally be stepped to have at least two different diameters.

[0021] Compared to conventional designs, the ratio of L2 compared to L1 and / or L3 is increased.

[0022] L3-L2 of the female part 22 according to the present invention is <12 mm, more preferably <11.5 mm, even more preferably <11 mm. L3-L2 of the female part 22 according to the present invention is >0 mm, more preferably >5 mm, even more preferably >7 mm. In one embodiment, L1 is 25-56 mm, more preferably 30-45 mm.

[0023] In one embodiment, L2 / L1>0.01×D1.

[0024] In one embodiment, L2 / L1 > 26%, more preferably > 32%.

[0025] In one embodiment, L2 / L1<65%, more preferably <50%.

[0026] In one embodiment, L2 / D1 > 30%, more preferably > 38%.

[0027] In one embodiment, L2 / D1<65%, more preferably <50%.

[0028] Preferably, the female portion 22 is used to form the threaded joint 34 for the percussion drilling tool 2, and there is bottom contact, as opposed to shoulder contact, between 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 and the male end 10 of the adjacent rod 4.

[0029] A software simulation was performed in which bending forces were applied to the female portion 22 of the present invention and to a female portion other than the present invention. Table 1 summarizes the stress measurements for the prior art and the female portion 22 of the present invention, clearly showing that the stress in the area of ​​the thread clearance is lower for the sample of the present invention. TIFF0007733683000001.tif45170

Claims

1. A female part (22) forming part of a threaded joint (34) for a percussion drilling tool (2), a mounting sleeve (18) having an axial end (52), said mounting sleeve (18) enclosing an internal cavity (20) having an axial inner wall (24) at an opposite end of said mounting sleeve (18) compared to said axial end (52); The mounting sleeve (18) has a length L １ a threaded entrance (28) toward said axial end (52), and a threaded exit (30) toward said axial inner wall (24), a mounting sleeve (18); A length L ２ and diameter D １ a thread clearance portion (32) having A screw thread (28) is disposed between the threaded inlet (28) and the axial end (52) of the sleeve (18), and has a length L ３ and a guide portion (50) having L 1 is 25 to 56 mm, and the total length of L 1 + L 2 + L 3 is 70 to 86 mm; 0 mm < L ３ -L ２ < 12 mm, Female part (22).

2. L ２ / L １ >0.01 x D １ 2. The female part (22) according to claim 1,

3. L ２ / L １ 3. The female part (22) according to claim 1 or 2, wherein the thickness is >26%.

4. L ２ / L １ 4. The female part (22) according to any one of claims 1 to 3, wherein the thickness is < 65%.

5. L ２ / D １ The female part (22) according to any one of claims 1 to 4, wherein the thickness is >30%.

6. L ２ / D １ 6. The female part (22) according to any one of claims 1 to 5, wherein the thickness is < 65%.

7. A female part (22) according to any one of claims 1 to 6, which is part of a drill bit (6).

8. A female section (22) according to any one of claims 1 to 7, which is a female end (12) of a drill string rod (4).

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

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

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