Thread 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 part forming part of a threaded joint for percussion drilling tools, in particular but not exclusively for drill bits and drill rods. [Background technology]

[0002] Using percussion drilling, long boreholes are produced by multiple elongated drill string rods joined end to end by interconnected male and female threads. Alternatively, the drill bit may be connected to a single rod. By well-established techniques, rock is broken by percussive impact transmitted from the rock drill bit to the rock at the bottom of the borehole. The rock drill bit is attached at one end of the drill string via male threads on the endmost drill string rod to female threads 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) to generate stress (or shock) waves that propagate through the drill string to the drill bit. Conventional threaded joints are described in U.S. Pat. Nos. 4,332,502, 4,398,756, 4,687,368 and German Patent No. 2 800 887.

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

[0004] Therefore, it is desirable to reduce the stress in threaded joints to improve the performance of the percussion tool and reduce the risk of damage in the threaded joint. One solution to reduce the stress in threaded joints is to increase the diameter of the male thread, but the problem with this is that by increasing the diameter of the male thread, the female part of the threaded joint is weakened and the threaded joint becomes more susceptible to failure. Therefore, the problem to be solved is how to reduce the stress in threaded joints to extend their life. Summary of the Invention

[0005] It is an object of the present invention to provide a new and improved design of a threaded joint for an impact drilling tool. This object is achieved by providing a female part forming part of a threaded joint for an impact drilling tool, the female part being characterized in that it comprises a mounting sleeve having an axial end, the mounting sleeve enclosing an internal cavity having an axial inner wall at an opposite end of the mounting sleeve relative to the axial end, the mounting sleeve having at least one substantially cylindrical internal threaded section having a length L1, a thread entry towards the axial end, and a thread exit towards the axial inner wall, the threaded section including a crest, a root, a contact flank, and a non-contact flank, the threaded section having a thread form having a pitch length L4 between two axially adjacent crests and a radial inner diameter D2 between the roots, a thread clearance section located between the axial inner wall and the thread exit and having a length L2 and a diameter D1, and a guide section located between the thread entry and the axial end of the sleeve and having a length L3, the pitch length L4 being 12.8-14.5 mm. Preferably, L4 is 13.0 to 13.5 mm.

[0006] Advantageously, this reduces the stress in the female part of the threaded joint, which means that the risk of fracture in the female part is reduced. Furthermore, the increased stress in the female part allows the diameter of the male threaded part to be increased, which improves 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 of (L1+L2+D2) / L4>6.4. Advantageously, this reduces the stress in the female part of the threaded joint, which means that the risk of fracture in the female part is reduced.

[0008] In another embodiment, L3-L2 is 0-12 mm. Advantageously, this reduces the stress in the female part of the threaded joint, which means that the risk of breakage in the female part is reduced.

[0009] In another embodiment, L1 is between 25 and 56 mm. Preferably, L1 is between 25 and 56 mm, more preferably between 30 and 45 mm. Preferably, the total length of the female thread (L1+L2+L3) is between 70 and 86 mm. Advantageously, this is the optimum length of the 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 stresses in the thread clearance area are 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 stresses in the thread clearance area are reduced.

[0012] In one embodiment L2 / L1<65%, preferably <50%. Advantageously, this provides sufficient length in the threaded section to achieve a reliable 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 stresses in the thread clearance area are reduced. Thus, the thread clearance and the diameter of the female thread can be increased, and as a result, the diameter of the male part can also be increased, which improves the performance of the male part and reduces the risk of skirt damage in the female part.

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

[0015] In one embodiment, the respective thread forms have contact flank angles α and non-contact flank angles β inclined relative to a respective baseline located on a respective minor or major diameter of the respective thread form, the respective non-contact flank angles β being greater than the respective contact flank angles α, the respective thread form apexes inclined from the respective contact flanks to the respective non-contact flanks defining the respective major and minor diameters of the respective thread forms, the respective thread form apexes being located adjacent the respective non-contact flanks, the respective roots being a first arc, the respective contact flanks being connected to the respective roots by a respective second arc, and the first radius of the respective first arc being greater than the second radius of the respective second arc.

[0016] Advantageously, in comparison with the above-mentioned prior art, the inclined crest of the thread form allows the contact flank to be enlarged in response to wear of the coupling, and furthermore, pitting formed in the area adjacent to the contact flank can be removed as a result of wear.

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

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

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

[0020] Another aspect of the invention relates to a drill bit including a female portion as described above or below. [Brief description of the drawings]

[0021] Specific embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a perspective view of a strike drilling tool having one male end and one female end. [Diagram 2] FIG. 1 is a perspective view of a drill rod having two male ends. [Diagram 3] FIG. 2 is a cross-sectional view of the female end of the drill rod. [Figure 4] FIG. 2 is a cross-sectional view of a drill bit. [Diagram 5] FIG. 13 is a cross-sectional view of the internal profile of a cavity in a female part forming part of a threaded joint for an impact drilling tool. [Figure 6] FIG. 1 is a diagram of a screw configuration. [Figure 7] 13 is a plot of the safety factor of comparative example thread forms. [Figure 8] 1 is a plot of the safety factor of the thread form of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] FIG. 1 shows an impact drilling tool 2 in which a drill rod 4 is threadedly connected to a drill bit 6 of conventional design. The impact drilling tool 2 is used in particular 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 via a mating surface. The drill rod 4 includes an axially extending main length section 8 terminating at one end in a male end 10 and at a second, opposite end in a female end 12, and having a longitudinal axis 14. The drill rod 4 can be connected end-to-end with other further drill rods via further threaded joints to form a drill string (not shown).

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

[0024] FIG. 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 .

[0025] FIG. 4 shows, for example, a cross-section of a drill bit 6 including an axially forward most drill head 16 of conventional design 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 with 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 the female part 22, and in particular to a thread form 54 which forms part of a threaded joint for the 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.

[0027] FIG. 5 shows a cross section of the internal profile of the cavity 20 of the female part 22, in other words, FIG. 5 is an enlarged view of the inside of FIG. 3 or FIG. 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 an axially opposite end 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 form 54 including a plurality of crests 56, roots 58, contact flanks E1 and non-contact flanks E2, and has a pitch length L4 defined as the length between two axially adjacent crests 56. The threaded section 26 also has a radial inner diameter D2 between the roots 58.

[0028] The cavity 20 of the female part 22 also has a thread clearance section 32 located between the axial inner wall 24 and the threaded section 26. The thread clearance section 32 is a circumferentially recessed recess. The thread clearance section 32 has a length L2 defined as the length between the thread outlet 30 and the axial inner wall 24. The thread clearance section has a diameter D1. At the opposite end of the threaded section 26 to the thread clearance section 32 is a guide section 50 for guiding the male end 10 of the rod 4 into position. The guide section 50 has a length L3 defined as the length between the thread inlet 28 and the axial end 52 of the sleeve 18. The guide section 50 may be of constant diameter throughout the guide section 50 or may be optionally stepped to have at least two different diameters.

[0029] Preferably, L3-L2 is <12 mm, more preferably <11.5 mm, even more preferably <11 mm. Preferably, L3-L2 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.

[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 part 22 is preferably used to form a threaded joint for the percussion drilling tool 2 that has bottom contact rather than shoulder contact between the female part 22 and the male end 10 of the adjacent rod 4. In other words, there is contact between the inner axial wall 24 of the female part 22 and the male end 10 of the adjacent rod 4.

[0036] FIG. 6 shows thread forms 54. Each thread form 54 is connected to a point X B Each of the thread forms 54 may start at a first apex A1 and may include a root A1. Each of the roots A1 may be a concave arc having a respective radius R1 and may extend to a respective second arc A2. Each of the second arcs A2 may be concave, have a respective radius R2 and may extend from a respective first apex A1 to a respective contact flank E1. Each of the roots R1 may be greater than each of the second radii R2, for example at least 50 percent greater than each of the second radii. Each of the contact flanks E1 may be a straight line inclined at a respective first flank angle α relative to a respective baseline BL. The baseline BL may be longitudinal and may be in a direction perpendicular to a respective major diameter D of the respective thread form 54. J Or inner diameter D NThe respective first flank angle α may be in the range of 15 to 50 degrees. The respective contact flank E1 may extend from the respective second arc A2 to a respective third arc A3. The respective third arc A3 may be convex and may have a respective radius R3. The respective third arc A3 may extend from the respective contact flank E1 to a respective apex A4. The respective apex A4 may have a respective first height H1 adjacent the respective third arc A3 and a respective second height H2 adjacent the respective fifth arc A5. The respective heights H1, H2 may be measured from a respective baseline BL. The respective apex A4 may be inclined from the respective contact flank E1 to the respective non-contact flank E2 and may have a respective outer diameter D J Or inner diameter D N Each vertex X of each thread form 54 defines A Each thread form 54 may be longitudinal, with a respective outer diameter D of each thread form 54 being located adjacent the respective non-contact flank. J Or inner diameter D N Each of the thread forms 54 may have a respective peak line PL that may be located at a respective diameter D N , D Jmay be constant. Due to the inclination of each apex A4, each second height H2 may be greater than each first height H1. The inclination may be achieved by each apex A4 being a convex arc having a respective radius R4. Each apex radius R4 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 a respective 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 linearly inclined. Each fifth arc A5 may be convex, have a respective radius R5, and extend from each apex A4 to a respective non-contact flank E2. Each non-contact flank E2 may be linearly inclined at a respective second flank angle β with respect to a respective baseline BL. 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 resulting in each asymmetric thread form 54. Each non-contacting flank E2 may extend from a respective fifth arc A5 to a respective sixth arc A6. Each sixth arc A6 may extend from a respective non-contacting flank E2 to a respective end point X E Each sixth arc A6 may be concave and may have a respective radius R6. Each thread form 54 may extend from a respective start point X B and each end point X E and each of the first and second electrodes may have a respective pitch L4 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 slope of each apex 56 is linear.

[0039] In one embodiment, the height H2 of each apex 56 adjacent the respective non-contacting flank 62 is between 5% and 20% greater than the height H1 of each apex 56 adjacent the respective contacting flank 60.

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

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

[0042] Figures 7 and 8 show plots of the factor of safety for a symmetric thread profile with a pitch L4 of 12.7 mm (comparative sample) and an asymmetric thread profile with a pitch L4 of 13.2 mm (inventive sample), respectively, measured along the dotted line shown in the figures, when a bending force is applied. Higher factor of safety values ​​indicate a reduced risk of failure. It can be seen that the inventive sample, with its increased pitch length, reduces the risk of failure along the length of the thread profile.

Claims

1. A female part (22) forming part of a threaded joint (34) for a percussion drilling tool (2), comprising: a mounting sleeve (17) having an axial end (52), said mounting sleeve (17) enclosing an internal cavity (20) having an axial inner wall (24) at an opposite end of said mounting sleeve (17) relative to said axial end (52); The mounting sleeve (17) has a length L １ a threaded inlet (27) towards said axial end (52) and a threaded outlet (30) towards said axial inner wall (24), The threaded section (26) has a crest (56), a root (57), a contact flank (E １ ), and non-contact flank (E ２ ) and the pitch length L between two axially adjacent apexes (56) ４ and the radial inner diameter D between the valley bottoms (57) ２ a mounting sleeve (17) having a thread form (54) having Length L ２ and diameter D １ a thread clearance section (32) positioned between the axial inner wall (24) and the thread outlet (30), A length L positioned between the threaded inlet (27) and the axial end (52) of the sleeve (17). ３ and a guide section (50) having The pitch length L ４ is 12.7 to 14.5 mm, and the threaded section (26) is (L １ +L ２ +D ２ ) / L ４ A female part (22) characterized by having a ratio of >6.

2.

2. L ３ -L ２ The female part (22) according to claim 1, wherein the length is between 0 and 12 mm.

3. L １ The female part (22) according to claim 1, wherein the length is between 25 and 56 mm.

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

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

6. L ２ / L １ 2. The female part (22) according to claim 1, wherein the thickness is < 65%.

7. L ２ / D １ 2. The female part (22) according to claim 1, wherein the thickness is >30%.

8. L ２ / D １ 2. The female part (22) according to claim 1, wherein the thickness is < 65%.

9. Each thread form (54) has a respective minor diameter (D Ｎ ) or outer diameter (D Ｊ ) and a non-contact flank angle (β) inclined relative to a respective baseline (BL) located at the apex (56) of each thread form (54), each non-contact flank angle (β) being greater than the respective contact flank angle (α), and １ ) to each of the non-contact flanks (E ２ ) to each of the major diameters (D ) of each of the thread forms (54). Ｊ ) and the inner diameter (D Ｎ ) of each of said thread forms (54) defining an apex (X Ａ ) is the distance between each of said non-contact flanks (E ２ ) and each root (57) is a first arc and each contact flank (E １ ) is the second arc (A ２ ) connected to each of said roots (57), and a first radius (R １ ) is the second arc (A ２ ) the second radius (R ２ 9. The female part (22) according to any one of claims 1 to 8, wherein the female part (22) is larger than the first part (22).

10. The female part (22) according to any one of claims 1 to 8, wherein the female part (22) is part of a drill bit (6).

11. The female part (22) according to any one of claims 1 to 8, wherein the female part (22) is a female end (12) of a drill string rod (4).

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

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

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