THREADED CONNECTION

Description

[0001] The invention relates to a threaded bushing, a use of a threaded bushing, a use of a threaded plug and a threaded connection with a threaded bushing and a threaded plug, in particular relating to a rod section for an earth drilling device.

[0002] The term "earth drilling device" refers to devices with which the drive power of a drive device is transmitted via a rod assembly to a tool arranged on a rod assembly, particularly at the end. This includes, in particular, earth drilling devices used to drill holes in the ground, particularly horizontal bores. The drive device generally transmits thrust or pressure forces via the rod assembly to the tool designed as a drill head. It is also possible for the earth drilling device to impart a rotary movement to the rod assembly around its longitudinal axis. Using earth drilling devices, existing bores in the ground or previously laid old pipes can be widened or extracted, and if necessary, a new pipe can be pulled in simultaneously.Earth drilling rigs are often designed to be used both for drilling holes in the ground and for pulling operations, i.e., for enlarging an existing borehole or old pipeline, or for pulling in a new pipe. This allows the same earthworking rig to first create a pilot bore. A pilot drill head is pushed through the ground until it reaches a target excavation pit. The pilot drill head is replaced in the target excavation pit by an expander head. The pilot bore is expanded as the drill rod is retracted. If necessary, a new pipe attached to the expander head can be pulled into the expanded borehole at the same time as the expander head.

[0003] The rod assembly of such earthwork equipment usually consists of several rod sections that are gradually connected to one another as the drilling progresses. The individual rod sections are connected using coupling elements; in addition to plug-in couplings, as described in DE 196 08 980, screw connections are particularly widespread. The key advantages of screw connections are the low costs associated with their production and the ability to easily automate the screwing process. A significant disadvantage of screw connections, however, is that they often represent the greatest weak points in the rod assembly. This is due to the relatively small diameter in the area of ​​the threaded plug of the threaded connection and the geometrically high stress concentration of the thread itself.

[0004] EP 2 334 892 B1 discloses a threaded connection in which the external thread of a threaded plug is designed such that flanks of this external thread form a section of an ellipse. By designing the flanks in the shape of a section of an ellipse, a continuously changing flank angle is achieved, which allows for optimized contact between the flanks of the threaded plug and the corresponding flanks of an internal thread of a corresponding threaded bushing. The threaded plug and threaded bushing are designed correspondingly.

[0005] API threads and round threads according to DIN 20 400 are also known. However, the service life of such thread forms has proven to be too short in the daily operation of earth drilling devices.

[0006] Alternative thread shapes have therefore been developed that are specifically designed for the specific loads on the rods that occur in earth drilling devices. DE 198 03 304 A1 discloses a threaded connection intended to connect rod sections of a drill rod, whereby the drill rod is intended to be used in particular for rotary percussion drilling. Key features of these threaded connections are the asymmetrical shape of the thread with different pitch angles of the load-bearing and non-load-bearing flanks during rotary percussion drilling, as well as the provision of a threadless insertion section. The non-load-bearing flanks are also intended to be circularly arc-shaped. The threaded connection known from DE 198 03 304 A1 has also proven to be insufficiently robust in daily operation.

[0007] EP 0 324 442 B1 and US Patent 5,060,740 also disclose asymmetric threaded connections designed for use in connecting rod sections of earth drilling devices. The threaded connections disclosed in these publications are characterized by the fact that the thread root forms a section of an ellipse. This is intended to enable a transition from the thread root to the flat flanks of the thread with as little stress as possible.

[0008] WO 2006 / 092649 A1 also discloses threaded connections for rods of earth drilling devices, in which the thread root forms a section of an ellipse. The thread shapes disclosed in this document can be both asymmetrical and symmetrical.

[0009] Although good results can be achieved, particularly with the thread form known from EP 2 334 892 B1, it has been shown that the formation and release of the connection requires more precise handling.

[0010] Based on this prior art, the object of the invention was therefore to create a threaded connection which particularly facilitates the formation and release of the connection and whose service life is impaired as little as possible or not at all.

[0011] This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the respective dependent patent claims and will become apparent from the following description of the invention.

[0012] The core of the invention is based on the idea that only a reduction in the notch effect had to be taken into account and the desire to achieve a more homogeneous stress distribution was abandoned. This is why an elliptical shape was previously provided at the thread root, whereby the stress maxima occur less in the thread root than in the flank area. Previously, the preferred thread form was assumed to be a simple elliptical design, as this has a positive effect on the service life of the threaded connection, as there is usually no geometric notch in the flank area and the notch effect in the thread root is therefore reduced. The invention has now recognized that it is not only the design in the thread root that is important - this design has previously been extended to the flanks - but in particular an adaptation of the geometry of the threaded bushing is required.According to the invention, the geometry of the threaded bushing was modified such that adjacent flanks of the thread are defined by a displacement of an ellipse. This makes it possible to improve the sliding properties when screwing the screw connection, while utilizing or retaining the advantageous properties of an elliptical shape. Damage to the thread caused by shearing or impaired thread guidance, which is commonly referred to as cold welding of the thread flanks, can be counteracted.

[0013] At first, it seems paradoxical that a screw connection, known for decades, whose primary function is to elastically clamp two parts together using positive and frictional engagement, is not already known in the way proposed here. On the one hand, the operating forces and torques acting can be reliably absorbed, and on the other hand, a thread form once deemed "good" can be at least partially retained in the field.

[0014] Especially for the conical thread, the invention recognized that a force perceivable as "preload" exists because a gap exists between the threaded bushing and the threaded plug during the initial screwing, even though the threads of the threaded bushing and the threaded plug are already congruent. Upon further screwing, a resulting normal force is generated, which increases the frictional force in the thread. This can lead to part of the screwing torque being absorbed by friction. The overlap already present during the initial screwing leads to the threaded bushing and the threaded plug sliding relative to each other, because the "preload" in the axial direction causes a radial movement due to the cone angle.In order to ensure that the sliding action can take place over as large a surface as possible in order to distribute the surface pressure accordingly, it was recognized according to the invention that the shape of the thread can be enlarged by shifting adjacent thread flanks which are part of a section of an ellipse, wherein the elliptical shape which has proven to be advantageous is maintained with a significant change in an offset of the adjacent flanks.

[0015] By offsetting an identical ellipse, a thread that is symmetrical with respect to the flanks is possible, in which a particularly uniform stress distribution can be achieved under both compressive and tensile loads.

[0016] The invention provides a threaded bushing on an elongated body for a threaded connection with a threaded plug, wherein the threaded bushing has a conical internal thread in which adjacent flanks of the internal thread are formed as sections of two mutually offset identical ellipses.

[0017] The term "conical (internal) thread" encompasses a thread configuration such that the thread roots and / or thread crests of the threaded plug or threaded bushing define a shell or are arranged on a shell that has a conical shape. This allows for simple and quick screwing of the threaded plug to the threaded bushing, whereby preferably both the threaded plug and the threaded bushing have a conical thread. The angle that the shell, on which the thread roots and / or thread crests lie, forms with a line parallel to the longitudinal axis of the threaded plug or threaded bushing (cone angle) can preferably be in the range between 2° and 10°, in particular 3° and 8°, more preferably 3° and 7°.

[0018] For the purposes of this description, the term "flank" of a thread essentially encompasses the section of the thread between the root and crest. Since the shape of the flank has a curved profile due to its elliptical configuration, the assignment of the "root" and "crescent" regions is not necessarily reduced to a single point, as would be the case, for example, with a thread whose flanks are designed as straight lines. In particular, the region from an inflection point onward can be assigned to the crest, so that the flank has a section of a pure elliptical shape, whereby the region from the inflection point onward can be small. Parts of the root or the entire root of the thread can be designed as a section(s) of one or both ellipses. The root of the thread can also have a shape other than an elliptical section, which adjoins the flank in the direction of the root of the thread.

[0019] The formation of the flank as a section of an ellipse occurs, as described, over a significant height between the thread root and the thread crest. In particular, the area around the, in particular geometric, center between the thread root and the thread crest can be designed as a section of the ellipse. At the center between the thread root and the thread crest, the section of the ellipse can continue in both directions over a height that is between 0.2 times and 0.5 times the distance from the thread root to the thread crest. The height over which the section of the ellipse can extend between the thread root and the thread crest can be for the thread of the threaded bushing or.of the threaded plug can be selected to be identical; in a particularly preferred embodiment, the height at which the section of the ellipse can extend between the thread root and the thread crest is different for the threaded plug and the threaded bushing of a rod assembly system. The height at which the section of the ellipse can extend between the thread root and the thread crest of a threaded plug and a threaded bushing of a rod assembly system can be different for the threaded plug and the threaded bushing. It can be provided that the height at which the section of the ellipse extends between the thread root and the thread crest in the case of a threaded plug is in the range from 0.5 to 0.9, preferably in the range from 0.6 to 0.9, preferably in the range from 0.7 to 0.9, very particularly preferably in the range from 0.75 to 0.85, of the distance between the thread root and the thread crest.It can be provided that the height at which the section of the ellipse extends between the thread root and the thread crest in a threaded bushing is in the range from 0.5 to 0.8, preferably in the range from 0.6 to 0.7, very particularly preferably in the range from 0.63 to 0.68, of the distance between the thread root and the thread crest. Since the thread root can also be formed at least partially as part of the ellipse or the ellipse can extend into the thread root, the height at which the section of the ellipse extends from the center between the thread root and the thread crest in the direction of the thread root can be up to 0.5 times the distance between the thread root and the thread crest.Since a rounding is preferably provided for the thread crest, the respective height over which the elliptical shape of the thread extends from the center between the thread root and the thread crest in the direction of the thread crest can be less than 0.5 times the distance between the thread crest and the thread root. It can therefore be provided that the height of the extension of the section of the ellipse from the center between the thread root and the thread crest in the direction of the thread root is greater than the height of the extension from the center between the thread root and the thread crest in the direction of the thread crest. In particular, it can be provided that the section of the ellipse for a threaded plug can extend into the thread root.

[0020] For the purposes of this description, the term "adjacent flanks" refers to two flanks that are connected by exactly one thread root located between them. The term "adjacent flanks" can be used synonymously for "two directly consecutive flanks of the thread that are connected by a thread root located between the flanks."

[0021] The two adjacent flanks of the thread can be divided into a load-bearing flank and a non-load-bearing flank. The load-bearing flank is responsible for transmitting force from the threaded plug to the threaded bushing.

[0022] If it is described that the flank(s) is / are formed as a section of an ellipse, this is understood in a preferred embodiment for the purposes of the description to mean that the flank has exactly a section of an ellipse and no further shape. The shape of the thread root and the thread crest are independent of this, such as, for example, a rounding in the area of ​​the thread crest and a change in shape in the area of ​​the thread root.

[0023] The term "ellipse" in the sense of the description includes the closed oval curve, usually resulting from a conic section, which has a center point and the major and minor axes passing through the center point.

[0024] As described, the shape of the thread is usually viewed in a sectional view, in which the threaded bushing is cut by a cutting plane that intersects the longitudinal axis of the elongated body or is contained in the cutting plane.

[0025] The term "height" or "thread height" used to describe a thread includes the specification of a length or distance relative to the sectional plane for viewing the thread, in a direction essentially perpendicular to the longitudinal axis of the elongated body. The total height can be determined from the distance between the thread root and the thread crest. To describe the extension of the thread over the course between the thread root and the thread crest, the height over which the section of the ellipse of one of the flanks extends from the center between the thread root and the thread crest toward the thread root or the thread crest can be specified.

[0026] The term "offset" or the adjectivally used term "offset" with regard to the two identical ellipses comprises, in the sense of the description, a spatial displacement of one of the two ellipses with respect to the other, wherein in particular at least a portion of the spatial displacement is present in a direction parallel to the longitudinal axis of the elongated body.

[0027] The threaded bushing can be clamped against a shoulder on the threaded plug. The threaded plug and threaded bushing can be brought into contact with each other with their end faces, creating a force-tight connection between an end face of the shoulder and the supporting flanks, particularly those near the shoulder. The shoulder or end face on the threaded plug can alternatively or additionally serve as the maximum stop for the screw connection. Axial forces and / or torsional moments can also be transmitted via the shoulder or end face(s).

[0028] In a preferred embodiment, the end face angle of the end faces of the threaded plug and the threaded bushing, which can come into contact with each other, is in the range of 65° to 85°, particularly preferably in the range of 70° to 80°. Most preferably, the end face angle of the end faces of the threaded plug and the threaded bushing, which can come into contact with each other, can be 75°.

[0029] The term "rod section" as used in this description encompasses individual, particularly rigid, directly or indirectly connectable rod sections that can be connected to one another in the longitudinal axial direction to form a drill rod or a drill string. The rod sections can be screwed together with a threaded plug using a threaded bushing or a threaded bushing, either mechanically interposed or without the interposition of an intermediate element. A rod section does not necessarily have to have a screwing element at both longitudinal ends, so it is possible for the rod section to have i) a threaded bushing at one longitudinal end and a threaded plug at the other longitudinal end, ii) a threaded bushing at each of the longitudinal ends, iii) a threaded bushing at one longitudinal end and a different type of coupling element at the other longitudinal end.

[0030] The term "drill string" as used in this description refers to several interconnected rod sections. A drill string, which may have a drill head at its front end and, if present, a drill tip configured as a drilling tool (e.g., an expander head), can be used to drill a hole.

[0031] The term "earth drilling device" as used herein encompasses a (and thus any) device that can move, in particular, a drill string comprising rod sections in an existing or future channel, particularly in the ground, in order to create or widen a bore, particularly a horizontal bore (HD), or to pull pipelines or other long bodies into the ground. The earth drilling device can, in particular, be a HD device. An earth drilling device can be a device that drives a drill string and can, in particular, displace soil. The drill string can be inserted into the ground translationally and / or rotationally in the longitudinal axial direction of the drill string. The drill string can be moved in the ground by tensile or compressive loading and, if necessary, also rotationally or rotatingly.

[0032] The term "drive element" as used herein refers to an element arranged on the earth drilling device that is designed to be connected to a drill string or a rod section of the drill string in order to exert a translational and / or rotational force on the drill string. Typically, a rod section to be connected to the drill string is engaged with the drive element, and the rod section connected to the drive element is then connected to the already drilled drill string.

[0033] In a preferred embodiment, the offset ellipses are vertical ellipses. A simple design can be achieved in which the flank(s) can taper into the area of ​​the thread root to reduce the notch effect there.

[0034] For the purposes of this description, a "vertical ellipse" is understood to mean an ellipse whose major axis (i.e., the longer of the central axes) forms a larger angle with the central axis of the threaded plug or threaded bushing than its minor axis (i.e., the shorter central axis). The angle between the major axis of the ellipse and the central axis of the threaded plug or threaded bushing can be "corrected" for a possible inclination of the ellipse, which may be caused by the arrangement of the ellipse on a cone of the threaded plug or threaded bushing, preferably between 70° and 110° for a vertical ellipse, preferably between 80° and 100°, and particularly preferably 90°. Deviations from this may arise, for example, due to manufacturing tolerances.

[0035] In a preferred embodiment, a central axis of at least one of the two ellipses, in particular the main axis, is arranged perpendicular to the longitudinal axis of the elongated body. This enables a particularly simple construction. Most preferably, both central axes of the two ellipses, in particular the main axis in each case, are arranged perpendicular to the longitudinal axis of the elongated body.

[0036] In a preferred embodiment, at least one of the thread crests of the adjacent flanks is rounded, which can reduce or eliminate sharp transitions in the thread. Most preferably, both thread crests are rounded.

[0037] In a preferred embodiment, the thread root between the adjacent flanks is formed as an envelope of the two ellipses, resulting in a geometry of the thread root that reduces the notch effect and also enables a simple construction.

[0038] For the purposes of this description, the term "envelope" refers to a curve resulting from a continuous connection of the two elliptical segments in the thread root at the intersection point of the two ellipses. The envelope may be rounded in the area of ​​the intersection point. This simplifies the thread design, and the geometric design also counteracts the stress concentration in the thread root.

[0039] In a preferred embodiment, the offset includes at least a translational displacement in the direction of the longitudinal axis of the threaded bushing, the extent of which is between 1 / 8 and 1 / 4 of the thread height. It was surprisingly discovered that the extent of the translational displacement can be dependent on the thread height to create a screw connection with suitable properties with regard to low stress concentration and easy screwing. Very good results were achieved in this range.

[0040] In a preferred embodiment, the offset includes at least a translational displacement in the direction of the longitudinal axis of the threaded bushing, the extent of which is between 1 / 10 and 3 / 10 of the distance between two adjacent thread roots. Particularly preferably, the offset can have at least a translational displacement in the direction of the longitudinal axis of the threaded bushing, the extent of which is between 17 / 100 and 25 / 100 of the distance between two adjacent thread roots. It has surprisingly been found that the extent of the translational displacement can be dependent on the distance between two adjacent thread roots in order to enable a screw connection with suitable properties with regard to low notch effect and easy screwing. Very good results have been achieved in this range.

[0041] In a preferred embodiment, the offset includes at least a translational displacement in the direction of the longitudinal axis of the threaded bushing, the extent of which is between 1 / 10 and 2 / 10 of the quotient of the major axis and the minor axis of the identical ellipses, wherein the offset preferably includes at least a translational displacement in the direction of the longitudinal axis of the threaded bushing, the extent of which is between 12 / 100 and 15 / 100 of the quotient of the major axis and the minor axis of the identical ellipses. It has surprisingly been found that the extent of the translational displacement can be dependent on the value of the quotient of the central axes of the ellipses in order to enable a screw connection with suitable properties with regard to low notch effect and easy screwing. Very good results have been achieved in this range.

[0042] The described improvement in the offset value compared to the thread depth, the distance between two adjacent thread roots, and the quotient of the center axes of the ellipses is surprisingly evident for each of the mentioned variables individually. However, a combination of the mentioned variables can also be considered by adjusting the offset depending on at least two of the mentioned variables. This can again result in an improvement.

[0043] In a preferred embodiment, the offset of the two elliptical sections is purely a translation along the longitudinal axis of the threaded bushing. This greatly simplifies the design of the thread.

[0044] For the purposes of this description, the longitudinal axis of the threaded bushing is generally coincident with the longitudinal axis of the elongated body. The terms can essentially be used synonymously, although depending on the context, one term may be preferred over the other.

[0045] In a preferred embodiment, the elongated body is a rod section of a drill string for an earth drilling device or a drive element for a rod section of a drill string of an earth drilling device.

[0046] The use of a threaded bushing on an elongated body for a threaded connection with a threaded plug is also described, wherein the threaded plug has an external thread applied to a core, in which adjacent flanks of a thread turn of the threaded plug form sections of the same ellipse, wherein a thread is used as the internal thread of the threaded bushing in which adjacent flanks of the internal thread are formed as sections of two mutually offset identical ellipses.

[0047] The invention also provides a use of a threaded plug on an elongated body for a threaded connection with a threaded bushing, wherein the threaded bushing has a conical internal thread in which adjacent flanks of the internal thread are formed as sections of two mutually offset identical ellipses, wherein the threaded plug has an external thread applied to a core in which adjacent flanks of a thread turn of the threaded plug form sections of the same ellipse.

[0048] In a preferred embodiment, the elongated body can also be a rod section of a drill string for an earth drilling device or a drive element for a rod section of a drill string of an earth drilling device.

[0049] The invention also provides a threaded connection comprising a threaded bushing as described in the present description and a threaded plug on an elongated body, wherein the threaded plug has an external thread applied to a core, in which adjacent flanks of a thread turn of the threaded plug form sections of the same ellipse.

[0050] If the invention is described by means of different embodiments and / or aspects (e.g., concerning a device-related or application-related configuration), the descriptions of the individual embodiments or aspects complement each other. In particular, the statements regarding the threaded bushing can also apply to the aspect of a "use." The statements regarding the geometry of the thread, the elongated body connected thereto, a rod section, and the like also apply to the aspect of a threaded connection in which, in addition to the described threaded bushing, a threaded plug is also present on an elongated body. The threaded plug has an external thread applied to a core, in which adjacent flanks of a thread pitch of the threaded plug form sections of the same ellipse.

[0051] It has been shown that the threaded bushing can, to a certain extent, also interact with other threaded plugs in which adjacent flanks are not necessarily designed to correspond or complement each other. It has been recognized that a design of the threaded plug adapted to the design of the described threaded bushing may be preferred in the configuration described in the present description. Surprisingly, it has also been shown that a design of the threaded plug in which adjacent flanks form a section of one and the same ellipse can lead to a further improvement of the thread.

[0052] In a preferred embodiment, the ellipse that forms adjacent flanks of the thread of the threaded plug, at least in sections, is identical to the two ellipses of the threaded bushing. A simple thread design is possible.

[0053] In a preferred embodiment, the thread root of the threaded plug can also form a portion of the ellipse. This can also reduce the notch effect of the threaded plug.

[0054] In a preferred embodiment, the thread pitch of the threaded bushing and / or the threaded plug is between 5 mm and 9 mm, preferably 7 mm.

[0055] In a preferred embodiment, the cutting angle is between 20° and 30°.

[0056] In a preferred embodiment, the cutting dimension of the threaded plug is at least 0.5 mm.

[0057] In a preferred embodiment, the chamfer dimension of the threaded bushing is at least 1 mm.

[0058] In a preferred embodiment, the difference between the length of the threaded plug and the threaded bushing is at most 0.5 mm.

[0059] The invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0060] In the drawings shows: Fig. 1 a threaded bushing; Fig. 2 an enlarged section of the Figure 1 , in which additional geometric data are shown; Fig. 3 one to the threaded bushing of the Figure 1 in one embodiment, corresponding threaded plug; and Fig. 4 an enlarged section of the Figure 3 , with the specification of further geometric data.

[0061] Figure 1The right-hand side of the two views shows a section of an elongated body 1 with a threaded bushing 4 having an internal thread 5 in a sectional view. The threaded bushing 4 is located at the end of the elongated body 1, which is designed as a rod section of a drill string for an earth drilling device or a drive element for a rod section of a drill string of an earth drilling device.

[0062] The right of the two representations of the Figure 1 is a sectional view of the left representation of the Figure 1 along AA. The left of the two representations of the Figure 1 shows a view of the threaded bushing 4 of the elongated body 1 in the longitudinal direction of the elongated body 1.

[0063] The elongated body 1 has a longitudinal axis L. The internal thread 5 of the threaded bushing 4 is a conical internal thread. The internal thread 5 of the threaded bushing 4 is shown in an enlarged view in the Figure 2 shown.

[0064] Figure 2 shows the internal thread 5 of the Figure 1 in an enlarged view. The adjacent flanks between two thread crests GS are formed as sections of two offset identical ellipses E1, E2. There is an offset VS between the two ellipses E1, E2.

[0065] The Figure 2 shows the thread height designated GH between the thread crest GS and the thread root GG.

[0066] The thread crest (GS) is positioned centrally between two adjacent flanks. The thread root (GG) is positioned centrally between two adjacent flanks.

[0067] Figure 3The right-hand side of the two views shows a section of an elongated body 1 with a threaded plug 2 having an external thread 3 in a sectional view. The threaded plug 2 is located at the end of the elongated body 1, which is designed as a rod section of a drill string for an earth drilling device or a drive element for a rod section of a drill string of an earth drilling device.

[0068] The right of the two representations of the Figure 3 is a sectional view of the left representation of the Figure 3 along AA. The left of the two representations of the Figure 3 shows a view of the threaded plug 2 of the elongated body 1 in the longitudinal direction of the elongated body 1.

[0069] The elongated body 1 has a longitudinal axis L. The external thread 3 of the threaded plug 2 is a conical external thread. The external thread 3 of the threaded plug 2 is shown in an enlarged view in the Figure 4 shown.

[0070] Figure 4 shows the external thread 3 of the Figure 3 in an enlarged view. The adjacent flanks between two thread crests GS are formed as a section of an ellipse E3.

Claims

1. Threaded bushing (4) on an elongated body (1) for a threaded connection with a threaded connector (2), wherein the threaded bushing (4) has a conical inner thread (5), characterised in that adjacent flanks of the inner thread (5) are formed as sections of two identical ellipses (E1, E2) offset from one another.

2. Threaded bushing (4) according to claim 1, wherein the two ellipses (E1, E2) are standing ellipses.

3. Threaded bushing (4) according to claim 1 or 2, wherein a central axis of at least one of the two ellipses is arranged at an angle of 70° to 110°, preferably 80° to 100°, to the longitudinal axis of the elongated body.

4. Threaded bushing (4) according to one of claims 1 to 3, wherein the thread root (GG) between the adjacent flanks is formed as an envelope of the two ellipses (E1, E2).

5. Threaded bushing (4) according to one of claims 1 to 4, wherein the offset (VS) includes at least one translational displacement in the direction of the longitudinal axis (L) of the threaded bushing (4), the extent of which is between 1 / 6 and 1 / 8 of the thread height (GH).

6. Threaded bushing (4) according to one of claims 1 to 5, wherein the offset (VS) includes at least one translational displacement in the direction of the longitudinal axis (L) of the threaded bushing (4), the extent of which is between 1 / 37 and 1 / 27 of the distance between two adjacent thread roots (GG).

7. Threaded bushing (4) according to one of claims 1 to 6, wherein the offset (VS) includes at least one translational displacement in the direction of the longitudinal axis (L) of the threaded bushing (4), the extent of which is between 1 / 10 and 2 / 10 of the quotient of the main axis and the secondary axis of the identical ellipses (E1, E2).

8. Threaded bushing (4) according to one of claims 1 to 7, wherein the offset (VS) of the two ellipses (E1, E2) is a pure translation in the direction of the longitudinal axis (L) of the threaded bushing.

9. Threaded bushing (4) according to one of claims 1 to 8, wherein the elongated body (1) is a string section of a drill string for an earth drilling device or a drive element for a string section of a drill string of an earth drilling device.

10. Use of a threaded connector (2) on an elongated body (1) for a threaded connection with a threaded bushing (4), wherein the threaded bushing (4) has a conical inner thread (5), characterised in that adjacent flanks of the inner thread (5) are formed as sections of two identical ellipses (E1, E2) offset from one another, wherein the threaded connector (2) has an outer thread (3) applied to a core, wherein adjacent flanks of a thread turn of the threaded connector (2) form sections of the same ellipse (E3).

11. Use according to claim 10, wherein the elongated body (1) is a string section of a drill string for an earth drilling device or a drive element for a string section of a drill string of an earth drilling device.

12. Threaded connection comprising a threaded bushing (4) according to one of claims 1 to 9 and a threaded connector (2) on an elongated body (1), wherein the threaded connector (2) has an outer thread (3) applied to a core, wherein adjacent flanks of a thread turn of the threaded connector (2) form sections of the same ellipse (E3).

13. Threaded connection according to claim 12, wherein the ellipse (E3) is identical to the two ellipses (E1, E2) of the threaded bushing (2).

14. Threaded connection according to claim 12 or 13, wherein the thread root (GG) also forms a section of the ellipse (E3).