Elliptical design of the shank adapter

Abstract

A shank adapter forming part of a boring assembly, having a body extending axially between a first end and a second end, a threaded portion on an outer surface, and a non-threaded shank disposed axially intermediate the body and the threaded portion, a male insertion portion provided at the second end, and a radially projecting shoulder disposed axially intermediate the body and the male insertion portion, the shank having a transition portion disposed adjacent to the shoulder at the second end, the transition portion having an outer diameter increasing from the insertion portion toward the shoulder, and a cross-sectional shape profile of an outer surface of the transition portion in a plane of a longitudinal axis having a portion of an ellipse according to an equation (Equation (I)) having an orbital major radius (a), an orbital minor radius (b), and an exponential factor (n), in the shank adapter, a ratio of the orbital major radius to the orbital minor radius (a:b) is within a range of 2b < a < 8b. (Equation (I)) TIFF2024507341000009.tif15170

Description

[Technical Field]

[0001] The present invention relates to rock drilling shank adapters, and particularly, but not exclusively, to shank adapter connections configured to minimize stress concentrations. [Background technology]

[0002] Percussion drilling is used to drill long boreholes via a number of elongated drill string rods joined end to end by interconnected male and female threaded ends. A well-established technique is to fracture the rock by percussive impact delivered from a rock drill bit attached to one end of the drill string to the rock mass at the bottom of the borehole. Typically, the energy required to fracture the rock mass is generated by a hydraulically driven piston which contacts the end of the drill string via a shank adapter, generating stress (or shock) waves which propagate through the drill string and ultimately to the bottom rock level. The shank adapter comprises a body at one end with a threaded male connection for connection to the drill string, and at a second, opposite end, a rigid end portion against which an impact piston integrated into the drilling machine acts. The rigid end portion further includes a set of splines to allow twisting or rotation of the shank adapter and drill string.

[0003] When the threaded male end of a shank adapter is mated to the female threaded end of the most distal drill rod, the connection is typically subjected to bending moments during drilling. These bending moments can fatigue the connection and cause breaks within the threaded portion of the connection. It is usually the threaded male insert that is damaged and determines the operational life of the connection.

[0004] Specifically, the transition between the different diameters of the threaded male spigot and the main length of the shank adapter (or the annular shoulder of the shank adapter in the case of a "shoulder contact" connection) creates an area of ​​potential high stress concentration due to bending moments and tensile loads. Traditionally, the outer diameter of the shank adapter at the transition between the threaded male spigot and the main length or shoulder in the axial direction is flared radially outward with a curved profile having as large a single radius of curvature as can be tolerated between the two regions. However, in a typical threaded connection stressed to 200 MPa in tension, the transition region reaches a stress level of approximately 300 MPa. Therefore, there is a significant risk of fatigue and failure, which can significantly disrupt the boring operation. Therefore, a shank adapter design that addresses these issues is needed. Summary of the Invention

[0005] It is an object of the present invention to provide a shank adapter having an externally threaded connection that is optimized to minimize the potential for stress concentrations in the transition area between the shoulder and spigot of the shank adapter, thereby extending the operational life of the shank adapter and minimizing the risk of fatigue and failure during use. A more specific object is to provide a shank adapter that is compatible with existing boring equipment and methods and has an enhanced ability to withstand large bending moments and tensile loads.

[0006] These objectives are achieved by specially configuring a transition region located at the end of the main length or at the axial boundary of the end of the main length with the annular shoulder. The present invention provides a shank adapter to drill rod connection that, compared to known designs, reduces stress concentrations at the connection of the male spigot with the main length, which stress concentrations arise as a result of likely bending moments or tensile loads.

[0007] According to a first aspect of the present invention, a shank adapter forming part of a boring assembly, comprising a body extending axially between a first end and a second end, a male insertion part provided at the second end having an outer surface with a threaded portion and a non-threaded shank disposed axially intermediate the body and the threaded portion, and a radially projecting shoulder disposed axially intermediate the body and the male insertion part, the shank having a transition portion disposed adjacent to the shoulder at the second end, the transition portion having an outer diameter increasing from the insertion part towards the shoulder, and the cross-sectional shape profile of the outer surface of the transition portion in the plane of the longitudinal axis having an equation with an orbital major radius (a), an orbital minor radius (b), and an exponential factor (n). There is a shank adapter having a portion of an ellipse according to TIFF0007827736000001.tif15170, characterized in that the ratio of the orbital major radius to the orbital minor radius (a:b) is within the range 2b < a < 8b.

[0008] Advantageously, this exhibits enhanced rigidity and creates a male coupling end with higher resistance to bending moments and tensile forces. The transition portion is configured to eliminate or at least minimize stress concentration in the portion where the insertion part axially projects from the shoulder. When the ratio of the length of the orbital major radius to the length of the orbital minor radius is greater or smaller than this, stress concentration increases. As a result, the risk of breakage decreases, and thus the operating life of the shank adapter increases. Optionally, the transition portion may comprise portions where the shape profile is a straight line and / or different curved profiles.

[0009] Optionally, the non-threaded shank is axially divided into a straight portion disposed axially closest to the threaded portion and a curved transition portion disposed axially closest to the side surface. It may be advantageous to increase the distance between the shoulder and the threaded portion. In this case, including the straight portion may also be beneficial.

[0010] Alternatively, the non-threaded shank has only a curved transition portion that extends entirely from the side surface to the threaded portion. When the non-threaded shank is shorter, the presence of only the curved transition portion, i.e., no straight portion, helps to keep the stress concentration as low as possible, which is advantageous.

[0011] Preferably, the ratio (a:b) of the minor radius of the orbit to the major radius of the orbit is within the range 2.5b < a < 6b. Advantageously, within a narrow ratio range, the stress concentration at the portion where the insertion part projects axially from the shoulder is further reduced, which means that the ability to withstand large bending moments and tensile stresses is enhanced.

[0012] Preferably, the minor radius (b) of the orbit is proportional to the diameter of the threaded portion according to the following equation, TIFF0007827736000002.tif13170where Di is the diameter of the threaded portion between opposing valleys, and Dy is the diameter of the threaded portion between opposing helical ridges. It is advantageous that the length of the major radius (b) of the orbit is as long as possible, as this creates an elliptical shape with blunt ends and thus the lowest stress concentration. However, if the length of the major radius (b) of the orbit is too long, there will be substantially no shoulder, and as a result, energy cannot be effectively transmitted between the male and female ends, leading to breakage of the female end of the rod.

[0013] Preferably, the exponential factor (n) is within the range 1 ≦ n ≦ 3. Advantageously, this creates a transition portion with an elliptical profile having the lowest stress concentration.

[0014] Optionally, the apex of the ellipse is arranged on the tangent to the annular side surface of the shoulder. Alternatively, the apex of the ellipse scoops out the base of the annular side surface of the shoulder. Various loading conditions can benefit from various forms of the ellipse.

[0015] Optionally, the x-axis of the ellipse is parallel to the longitudinal axis. Alternatively, the x-axis of the ellipse is inclined with respect to the longitudinal axis. Various loading conditions can benefit from various forms of the ellipse.

[0016] Optionally, the profile of the outer surface of the transition portion in the plane of the longitudinal axis comprises one-quarter of an ellipse. Alternatively, the cross-sectional shape profile of the outer surface of the transition portion in the plane of the longitudinal axis comprises more than one-quarter of an ellipse. Alternatively, the cross-sectional shape profile of the outer surface of the transition portion in the plane of the longitudinal axis comprises less than one-quarter of an ellipse. Different loading conditions may benefit from different configurations of the ellipse.

[0017] Within this specification, references to "curvature" include smooth or gradual changes in surface profile, as well as multiple successive linear increases (or decreases) in diameter that can be considered to collectively form a "curved" shape profile. For example, the term "curvature" includes relatively small linear step changes where the ends or intermediate regions of each step can be considered to collectively form a curve.

[0018] Preferably, the shank adapter includes a shoulder projecting radially from the main length, the outer diameter of the shoulder being larger than the outer diameters of the main length and the transition portion of the shank. Such a configuration allows for a conventional "shoulder contact" connection between the male plug and female sleeve, which shoulder contact is preferable to the alternative "bottom contact" due to the larger diameter and surface area contact between the male and female portions.

[0019] Preferably, the side of the shoulder that meets the transition portion comprises an annular radially outer region aligned substantially perpendicular to the longitudinal axis, and the curved transition portion is therefore not continuous over the entire radial length of the annular side, but rather establishes a flat annular surface for contact with the annular end face of the female sleeve.

[0020] Optionally, the threaded portion includes at least one axially extending helical ridge and groove, and the outer diameter of the shank axially between the threaded portion and the transition portion is substantially equal to the outer diameter of the threaded portion at an axial and radial location corresponding to the ridge of the threaded portion. Optionally, the threaded portion includes multiple threads formed as double or triple helices, etc. Such configurations can be selected to obtain a desired thread profile having desired mechanical and physical properties.

[0021] Optionally, in a plane perpendicular to the longitudinal axis, the cross-sectional area of ​​the shank is at least equal to the cross-sectional area of ​​the main length along the entire axial length of the shank between the threaded portion and the main length or shoulder. Optionally, the diameter of the threaded portion is slightly smaller than the diameter of the main length. Thus, the shank is configured to be robust against bending moments and tensile loads.

[0022] According to a second aspect of the present invention, there is provided a boring assembly comprising a shank adapter as referred to herein.

[0023] Specific implementations 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]

[0024] [Figure 1] FIG. 1 is a perspective view of a shank adapter drill string forming part of a rock drilling rig. [Figure 2] 2 is an external side view of one end of the shank adapter of FIG. 1 in the region of the male coupling in accordance with a particular implementation of the present invention, in which the non-threaded shank is axially divided into a straight section and a curved transition section. [Figure 3] 1 in the region of a male coupling according to another implementation of the present invention, wherein the non-threaded shank has only a curved transition portion. FIG. [Figure 4]FIG. 10 is a close-up view of the shank portion of a male coupling according to one embodiment of the present invention, where the apex of the elliptical profile of the transition portion is tangent to the shoulder. [Figure 5] FIG. 10 is an enlarged view of the shank portion of a male coupling according to another embodiment of the present invention, in which the elliptical profile of the transition portion hollows out the base of the annular side of the shoulder. [Figure 6] FIG. 10 is an enlarged view of the shank portion of a male coupling according to another embodiment of the present invention, in which the elliptical profile of the transition portion is tapered. [Figures 7a-7g] 7A-7G are safety factor images comparing the prior art (FIG. 7a) with various embodiments of the present invention (FIGS. 7b-g). DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 illustrates a shank adapter 100 comprising a body 101 having a forward end 103 and an aft end 104 relative to a longitudinal axis. A plurality of axially parallel, elongated splines 106 project radially outward from an outer surface 102 at a rearward region of the body 101 toward the aft end 104. The splines 106 are configured to be engaged by corresponding splines of a rotary motor (not shown) to rotate the adapter 100 about an axis 109 during a drilling operation. The adapter 100 further comprises a washout hole (or bore) 105 axially disposed between the ends 103, 104 and extending radially through the body 101 from the outer surface 102 to an internal cavity or region extending axially within the adapter 100. The shank adapter 100 is configured to couple to an elongated drill string and to enable the propagation of stress waves to a drilling tool (not shown) located in the deepest region of the borehole to generate a percussion drilling operation. Specifically, the adapter forward end 103 may be coupled to the rear end of an aftmost elongated drill rod 107 that forms part of the drill string. The aftmost adapter end 104 is configured to be compressed by a hydraulically driven piston 108 that generates stress waves within the adapter 100 and the drill string. The forward end 103 includes an annular shoulder 110 from which the male spigot 108 projects axially.

[0026] Figure 2 shows that the insert 108 is divided axially into a distalmost threaded section 107 and an unthreaded shank 109 located axially intermediate the threaded section 107 and a shoulder 110. When the male end of the shank adapter and the female end of the adjacent drill rod are joined, an annular surface 115 at the axially distal end of the rearmost elongated drill rod 107 abuts the shoulder 110 (as shown in Figure 1), and an annular end face 114 of the male insert 108 is fully received within the sleeve (not shown) of the rearmost elongated drill rod 107.

[0027] The tubular body 101 comprises a cylindrical outer surface 200 that flares radially outward toward a shoulder 110 to form an annular concave region 201 that terminates in a cylindrical surface 202 located at the shoulder 110. The diameter and cross-sectional area of ​​the surface 202 in a plane perpendicular to the axis 204 is therefore greater than the corresponding diameter or cross-sectional area (in a parallel plane) of the main length surface 200. The shoulder 110, and more specifically the cylindrical surface 202, terminates on the spigot side by an annular side surface 203 oriented perpendicular to the axis 204. The spigot 108 projects axially from the radially inner region of the surface 203 and is coaxially aligned with the body 101 and the annular shoulder 110. The diameter of the body 101 may be the same as or smaller than the diameter of the male spigot 108. The body 101 may have a constant or varying diameter along its length.

[0028] According to certain implementations, the threaded portion 107 includes a pair of helical turns 209 extending axially from the shank 109 to the spigot end 114. Specifically, a pair of helical ridges 207 and valleys 208 extend the entire axial length of the portion 107. The unthreaded shank 109 can be axially divided into a straight portion 205 located axially closest to the threaded portion 107 and a curved transition portion 206 located closest to the lateral surface 203. The outer surface of the straight portion 205 is substantially parallel to the axis 204, while the outer surface of the transition portion 206 slopes radially outward from the threaded portion 107 toward the tangent point with the annular lateral surface 203. The combined axial length of the straight portion 205 and the transition portion 206 may be the same as, greater than, or less than the axial length of the shoulder surface 202, but may be less than the axial length of the threaded portion 107. Thus, the diameter or cross-sectional area of ​​straight portion 205 is smaller than the diameter or cross-sectional area of ​​transition portion 206. Furthermore, the diameter or cross-sectional area of ​​straight portion 205 is approximately equal to the diameter or cross-sectional area of ​​threaded portion 107 at an axial and radial location corresponding to the radially outermost portion of apex 207.

[0029] 3 shows that alternatively, the non-threaded shank 109 may have only a curved transition portion 206 that extends all the way from the side surface 203 to the threaded portion 107. In other words, the straight length portion 205 may be absent.

[0030] Referring to FIGS. 2 and 3, the transition portion 206 can be considered as a transition region between the insertion portion 108 and the annular shoulder 110. As shown in FIGS. 2 and 3, the diameter and cross-sectional area of the transition portion 206 increase from the threaded portion 107 to the shoulder 110, whereby the outer surface profile of the transition portion 206 in the plane along the axis 204 follows a progressive curve corresponding to, slightly larger than, or slightly smaller than a quarter of the outer periphery of the ellipse 214. The ellipse 214 has an orbital major radius (x) and an orbital minor radius (y). Along the length of the transition portion 206, there is no abrupt change from the first radius to the second radius. Instead, it is preferred that there is a continuous and gradual change in the radius along the length of the transition portion 206. Optionally, the transition portion 206 may further comprise portions where the shape profile is a straight line and / or different curved profiles, and the profiles can be arranged at either end of the elliptical profile or as an interrupted portion in the middle of the elliptical profile.

[0031] The equation of the ellipse is defined by the Lamé curve when n = 2. TIFF0007827736000003.tif14170 wherein, x is the coordinate on the x-axis, y is the coordinate on the y-axis, a is the orbital major radius (x), b is the orbital minor radius (y), n determines the shape of the curve. n = 2 defines a normal ellipse. n < 2 defines a quasi-ellipse, and n > 2 defines a super-ellipse.

[0032] The elliptical profile 214 is shown in the enlarged view of the transition portion 206 in FIG. 4.

[0033] In the present invention, the ratio of the major axis to the minor axis (a:b) is within the range of 2b < a < 8b, preferably 2b < a < 6b, more preferably 2.5b < a < 6b, and even more preferably 2.5b < a < 5.75b.

[0034] Preferably, the minor axis of the orbit (b) is as large as possible. More preferably, the minor axis of the orbit (b) is proportional to the diameter of the threaded portion 107 of the male plug 108 according to the following equation: TIFF0007827736000004.tif13170 (as shown in Figure 4) Di = diameter of threaded portion 107 between opposing valleys 208; Dy=diameter of threaded portion 107 between opposing helical ridges 207.

[0035] Preferably, the exponent factor n is in the range 1≦n≦3, preferably 1.8≦n≦2.2, most preferably 2.

[0036] The equation of the elliptical profile of the transition section 206 can be measured using a profilometer, which traces a stylus across the surface of the transition section 206, and then the device fits various geometric shapes and outputs the equation of the measured shape profile.

[0037] At each endpoint of the semi-major axis (x) is a vertex 215 of the ellipse 214, and at each endpoint of the minor axis (y) is a co-vertex 216 of the ellipse 214. Optionally, the vertices 215 of the ellipse are positioned tangent to the annular side surface 203 of the shoulder 110, as shown in FIG.

[0038] FIG. 5 shows an alternative design in which the apex 215 of the ellipse 214 is hollowed out from the base of the annular side surface 203 of the shoulder 110 .

[0039] Optionally, the x-axis of ellipse 214 is parallel to longitudinal axis 204, as shown in FIG.

[0040] FIG. 6 shows an alternative in which the x-axis of the ellipse 214 is tilted relative to the longitudinal axis 204 .

[0041] It should be understood that the location of the apex 215 can be aligned with any orientation of the x-axis relative to the longitudinal axis 204 described above.

[0042] The profile of transition section 206 exhibits increased stiffness, resulting in a male coupling end that is more resistant to bending moments and tensile forces compared to conventional couplings. Additionally, transition section 206 is configured to eliminate or at least minimize stress concentrations where spigot portion 108 protrudes axially from shoulder 110.

[0043] 7a-g show the safety factor images determined using the Dang van criterion for the various transition section 206 profiles shown in Table 1, with rotating bending as the load case. TIFF0007827736000005.tif78170

[0044] The risk of failure increases as the value of the Dang van criterion decreases. Therefore, the darker the color, the higher the risk of failure. By comparing Figure 7a (prior art) with Figures 7b-g (embodiments of the present invention), it can be seen that the risk of failure is reduced for the profiles of the present invention. The stress images were obtained using an implicit method in LS-Dyna, and the Dang van criterion was derived using nCode software. Table 1 further shows the safety factors derived from this software, with higher safety factors being better and indicating lower stress. The results in Table 1 show that all samples of the present invention have higher safety factors compared to the prior art types.

Claims

1. A shank adapter (100) forming part of a boring assembly, comprising: a body (101) extending axially between a first end (105) and a second end (106); a male plug portion (108) at the second end (106) having an externally threaded threaded portion (107) and a non-threaded shank (109) axially intermediate the body (101) and the threaded portion (107); a radially projecting shoulder (110) located axially intermediate said body (101) and said male plug portion (108); Equipped with the non-threaded shank (109) has a transition portion (206) disposed at the second end (106) adjacent the shoulder (110), the transition portion (206) having an outer diameter that increases from the insert portion (108) toward the shoulder (110); a cross-sectional shape profile of the outer surface of said transition section (206) in the plane of the longitudinal axis (204) having a semi-major axis (a), a semi-minor axis (b), and an exponent factor (n) according to the equation In a shank adapter having a portion of an ellipse (214) according to the ratio of the semimajor axis to the semiminor axis (a:b) is in the range 2b<a<8b; and the exponential factor (n) is in the range 1≦n≦3; Shank adapter.

2. 2. The shank adapter (100) of claim 1, wherein the non-threaded shank (109) is axially divided into a straight portion (205) located axially closest to the threaded portion (107) and a curved transition portion (206) located axially closest to the side surface (203).

3. The shank adapter (100) of claim 1, wherein the non-threaded shank (109) has only a curved transition portion (206) extending entirely from a side surface (203) to the threaded portion (107).

4. The shank adapter (100) of any one of claims 1 to 3, wherein the ratio of the semimajor axis to the semiminor axis (a:b) is in the range 2.5b<a<6b.

5. The minor axis of orbit (b) is proportional to the diameter of the threaded portion (107) according to the following equation:

5. The shank adapter (100) of claim 1, wherein Di is the diameter of the threaded portion (107) between opposing valleys (208) and Dy is the diameter of the threaded portion (107) between opposing helical ridges (207).

6. The shank adapter (100) of any one of claims 1 to 5, wherein an apex (215) of the ellipse (214) is located tangent to the annular side surface (203) of the shoulder (110).

7. The shank adapter (100) of any one of claims 1 to 5, wherein the apex (215) of the ellipse (214) is hollowed out at the base of the annular side surface (203) of the shoulder (110).

8. The shank adapter (100) of any one of claims 1 to 7, wherein the x-axis of the ellipse (214) is parallel to the longitudinal axis (204).

9. The shank adapter (100) of any one of claims 1 to 7, wherein an x-axis of the ellipse (214) is inclined relative to the longitudinal axis (204).

10. 10. The shank adapter (100) of any one of claims 1 to 9, wherein the cross-sectional shape profile of the outer surface of the transition portion (206) in the plane of the longitudinal axis (204) comprises a quarter portion of an ellipse (214).

11. 10. The shank adapter (100) of claim 1, wherein the cross-sectional shape profile of the outer surface of the transition portion (206) in the plane of the longitudinal axis (204) comprises a portion that is greater than one-quarter of an ellipse (214).

12. 10. The shank adapter (100) of any one of claims 1 to 9, wherein the cross-sectional shape profile of the outer surface of the transition portion (206) in the plane of the longitudinal axis (204) comprises less than one-quarter of an ellipse (214).

13. A boring assembly comprising a shank adapter (100) according to any one of claims 1 to 12.

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