Patent Application
20240247553
The invention relates to a threaded bushing, a use of a threaded bushing, a use of a threaded plug and a threaded connection having a threaded bushing and a threaded plug, in particular relating to a rod section for an earth drilling device.
The term “earth drilling device” is understood to mean devices using which drive power from a drive device is transmitted via a rod to a tool that is arranged on a rod, in particular at the end. This includes, in particular, earth drilling devices using which earth bores and in particular horizontal bores are drilled into the ground. In this case, thrust or pressure forces are generally transmitted from the drive device via the rod to the tool designed as a drill head. It is also possible that a rotational movement can be applied to the rod around its longitudinal axis by means of the earth drilling device. Using the earth drilling devices, existing bores in the ground or old pipes that have already been laid can be expanded or pulled out and, if necessary, a new pipe can be pulled in at the same time. The earth drilling devices are often designed in such a way that they can be used both for creating earth bores and for pulling work, i.e., for expanding an existing bore or an old pipe or for pulling in a new pipe. This makes it possible to first create a pilot bore using the same earthwork device, wherein a pilot drill head is pushed through the ground until it reaches a target excavation pit, and the pilot drill head in the target excavation pit is replaced by an expansion head, wherein the pilot bore is expanded when the drill rod is retracted. If necessary, a new pipe attached to the expansion head can be pulled into the expanded borehole at the same time as the expansion head.
The rod of such earthwork devices regularly consists of a plurality of rod sections, which are gradually connected to one another in accordance with the drilling advance. The individual rod sections are connected via coupling elements, wherein screw connections in particular are widely used in addition to plug-in couplings, as described in DE 196 08 980. The essential advantages of screw connections are the low costs associated with their production and the possibility of having the screwing carried out easily in an automated manner. An essential disadvantage of screw connections, however, is that they often represent the largest weak points of the rod, which is to be attributed to the relatively small diameter in the area of the threaded plug of the threaded connection and to the geometrically related high notch effect of the thread itself.
A threaded connection is known from EP 2 334 892 B1, 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 forming the flanks in the form of a section of an ellipse, a constantly changing flank angle is achieved, by which optimized contact between the flanks of the threaded plug and the corresponding flanks of an internal thread of a corresponding threaded bushing can be achieved. The threaded plug and threaded bushing are designed correspondingly.
API threads and round threads in accordance with DIN 20 400 are also known. However, the service life of such thread shapes has proven to be too short in the daily operation of earth drilling devices.
Alternative thread shapes have therefore been developed that are specially designed for the specific loads of the rod that occur in earth drilling devices. DE 198 03 304 A1 discloses a threaded connection using which rod sections of a drill pipe are to be connected, wherein the drill rod is intended to be used in particular for rotary impact drilling. The essential special features of these threaded connections are the asymmetrical shape of the thread having different pitch angles of the load-bearing and non-load-bearing flanks in rotary impact drilling operation, as well as the provision of a threadless insertion section. The non-load-bearing flanks are also to be designed in the shape of a circular arc. The threaded connection known from DE 198 03 304 A1 has also proven to be insufficiently robust in daily operation.
Asymmetrical threaded connections are also known from EP 0 324 442 B1 and U.S. Pat. No. 5,060,740, which were designed for use for connecting rod sections of earth drilling devices. The threaded connections disclosed in these publications are characterized in that the thread base forms a section of an ellipse. This is intended to enable a transition from the thread base into the flat flanks of the thread that is as free from notch effects as possible.
Threaded connections for rods of earth drilling devices are also known from WO 2006/092649 A1, in which the thread base forms a section of an ellipse. The thread shapes disclosed in this publication can be designed both asymmetrically and symmetrically.
Although good results are achievable in particular using the thread shape known from EP 2 334 892 B1, it has been shown that forming and releasing the connection requires more precise handling.
Based on this prior art, the invention was therefore based on the object of creating a threaded connection which in particular facilitates the formation and release of the connection and the service life of which is impaired as little as possible or not at all.
The object is achieved by the subjects of the independent claims. Advantageous embodiments are the subject matter of the respective dependent claims and result from the following description of the invention.
According to the core concept of the invention, the idea of only having to take into consideration a reduction in the notch effect and of wanting to achieve a more homogeneous stress distribution was abandoned, which is why an elliptical shape was previously provided at the thread base, as a result of which the stress maxima occur less in the thread base than in the area of the flanks. Previously, the preferred thread shape was assumed to be a simple elliptical design, as this has a positive effect on the service life of the threaded connection, since there is usually no geometric notch in the area of the flanks and the notch effect in the thread base is thereby reduced. According to the invention, it has now been recognized that it is not only the design in the thread base that is important, the design of which 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 changed in such a way that adjacent flanks of the thread are predetermined by a displacement of an ellipse. This makes it possible to improve the sliding properties when screwing together the screw connection, wherein the advantageous properties of an elliptical shape can be used or retained. Damage to the thread due to shearing or worsened thread guidance, which is colloquially referred to in general as cold welding of the thread flanks, can be counteracted.
At first it seems paradoxical that a screw connection, which has been known for decades and the main function of which is to elastically clamp two parts by means of form fit and frictional locking, is not already known, as proposed here. The acting operating forces and operating torques can be reliably absorbed on the one hand, and on the other hand, a thread shape once “found to be good” in the field can be retained at least partially. Especially for the conical thread, it was recognized according to the invention that a force, which is perceptible as a “pre-tension”, is present, since a gap exists between the threaded bushing and the threaded plug upon the initial screwing together, even though the threads of the threaded bushing and the threaded plug already rest on one another congruently. During further screwing together, a resulting normal force is generated, which increases the frictional force in the thread. This can result in part of the screwing torque being absorbed by the friction. The overlap, which is already present upon the initial screen together, results in sliding of the threaded bushing and the threaded plug in relation to one another, since the “pre-tension” in the axial direction causes a radial movement due to the cone angle. In order that the sliding can take place with as large an area as possible in order to distribute the surface pressure accordingly, it was recognized according to the invention that the shape of the thread is to be enlarged via displacing adjacent thread flanks, which are part of a section of an ellipse, wherein the ellipse shape, which has proven to be advantageous, is maintained with a significant change of an offset of the adjacent flanks.
By offsetting an identical ellipse, a thread that is symmetrical with respect to the flanks is possible, in which a particularly uniform distribution of stress can be achieved under both compressive and tensile loads.
The invention creates 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 designed as sections of two identical ellipses offset from one another.
The term “conical (internal) thread” comprises a design of the thread such that the thread bases and/or the thread tips of the threaded plug or the threaded bushing define a jacket or are arranged on a jacket having a conical shape. This allows the threaded plug to be screwed together quickly and easily with the threaded bushing, wherein both threaded plug and threaded bushing preferably have a conical thread. Preferably, the angle that the jacket on which the thread bases and/or thread tips lie encloses with a parallel to the longitudinal axis of the threaded plug or threaded bushing can be an angle (cone angle), in the range between 2° and 10°, in particular 3° and 8°, more preferably 3° and 7°.
For the purposes of the description, the term “flank” of the thread essentially comprises the section of the thread between the thread base and the thread tip. Since the shape of the flank has a curved course due to its formation as an ellipse section, the assignment of the areas of the “thread base” and the “thread tip” is not necessarily to be reduced to a point, as would be the case, for example, with a thread, the flanks of which are designed as straight lines. In particular, the area from a turning point can be assigned to the thread tip, so that the flank has the section of a pure ellipse shape, wherein the area from the turning point can be made small. Parts of the thread base or the entire thread base can be designed as section(s) of one of the two ellipses or both ellipses. A shape other than an ellipse section can also be provided for the thread base, which adjoins the flank in the direction of the thread base.
In the sense of the description, the flank is formed as a section of an ellipse over a significant height between thread base and thread tip. In particular, the area around the, in particular geometric, center between thread base and thread tip can be designed as a section of the ellipse. At the middle between thread base and thread tip, the section of the ellipse can continue in both directions over a height that is in each case between 0.2 times and 0.5 times the distance from the thread base to the thread tip. The height in which the section of the ellipse can extend between thread base and thread tip can be chosen identically for the thread of the threaded bushing or threaded plug; in a particularly preferred embodiment, the height at which the section of the ellipse can extend between thread base and thread tip is different from one another for the threaded plug and threaded bushing of a rod system. The height at which the section of the ellipse can extend between thread base and thread tip of a threaded plug and a threaded bushing of a rod system can be different for threaded plug and threaded bushing. It can be provided that the height at which the section of the ellipse extends between thread base and thread tip in 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 thread base and thread tip. It can be provided that the height at which the section of the ellipse extends between thread base and thread tip in a threaded plug 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 thread base and thread tip. Since the thread base can also be at least partially formed as part of the ellipse or the ellipse can extend into the thread base, the height at which the section of the ellipse extends from the middle between thread base and thread tip in the direction of the thread base can be up to 0.5 times the distance between the thread base and the thread tip. Since a rounding is preferably provided for the thread tip, the respective height over which the elliptical shape of the thread extends from the middle between thread base and thread tip in the direction of the thread tip can be less than 0.5 times the distance between thread tip and thread base. It can therefore be provided that the height of the extension of the section of the ellipse from the middle between thread base and thread tip in the direction of the thread base is greater than the height of the extension from the middle between thread base and thread tip in the direction of the thread tip, in particular it can be provided that the section of the ellipse for a threaded plug can extend into the thread base.
In the sense of the description, the term “adjacent flanks” comprises the two flanks which are connected by means of exactly one thread base arranged between them. The term “adjacent flanks” can be used synonymously for “two directly consecutive flanks of the thread, which are connected to one another by means of a thread base arranged between the flanks”.
The two adjacent flanks of the thread can be differentiated 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.
If it is described that the flank(s) is/are designed as a section of an ellipse, then in the sense of the description in one preferred embodiment this is understood to mean that the flank has exactly a section of an ellipse and no other shape. The shape of the thread base and the thread tip are independent thereof, such as a rounding in the area of the thread tip and a change in shape in the area of the thread base.
In the sense of the description, the term “ellipse” comprises the closed oval curve, which usually results as a conic section, which has a center and the major and minor axes extending through the center.
The shape of the thread is generally considered in the sense of the description in a sectional view, in which the threaded bushing is cut by a plane of section that intersects the longitudinal axis of the elongated body or is contained in the plane of section.
The term “height” or “thread height” to describe the thread comprises the specification of a length or spacing or distance relative to the plane of section for the consideration of the thread, in one direction essentially perpendicular to the longitudinal axis of the elongated body. The total height can result from a distance between thread base and thread tip. To describe the extension of the thread over the course between thread base and thread tip, it is possible to specify the height over which the section of the ellipse of one of the flanks extends from the middle between thread base and thread tip in the direction of the thread base or the thread tip.
The term “offset” or the adjectivally used term “offset” in relation to the two identical ellipses comprises, in the sense of the description, a spatial displacement of one of the two ellipses in relation to the other, wherein in particular at least a component of the spatial displacement in one direction is present parallel to the longitudinal axis of the elongated body.
A tensioning of the threaded bushing against a shoulder on the threaded plug can be provided. Threaded plug and threaded bushing can be brought into contact with one another using end faces, so that a force screw connection takes place between an end face of the shoulder and the load-bearing flanks, in particular those in the area near the shoulder. The shoulder or the end face on the threaded plug can alternatively or additionally be used as a maximum stop for the screw connection. Axial forces and/or torsional torques can also be transmitted by means of the shoulder or the end face(s). In one preferred embodiment, the end face angle of the end faces of the threaded plug and the threaded bushing, which can come into contact with one another, is in the range of 65° to 85°, particularly preferably in the range of 70° to 80°. Very particularly preferably, the end face angle of the end faces of the threaded plug and the threaded bushing, which can come into contact with one another, can be 75°.
The term “rod section” in the sense of the description includes individual, in particular rigid, rod sections which can be connected directly or indirectly to one another and which can be connected to one another in the longitudinal axial direction to form a drill rod or a drill string. For connection to one another, the rod sections can be screwed together with the mechanical interconnection of an intermediate element or without the interconnection of an intermediate element using a described threaded bushing having a threaded plug. A rod section does not necessarily have to have an element for a screw connection 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 longitudinal end, iii) one threaded bushing at one longitudinal end and a different type of coupling element at the other longitudinal end.
The term “drill string” in the sense of the description comprises multiple interconnected rod sections. Boring can be carried out by means of a boring string, which can have a boring head at its front end and an optionally provided boring head tip, which can be designed as a boring tool (for example as an expansion head).
The term “earth drilling device” in the sense of the description comprises one (and thus any) device which, in particular, can move a drill string having rod sections in a channel, which is already existing or has to be created, in particular in the ground, in order to create or widen a bore, in particular a horizontal bore (HD), or pull pipelines or other long bodies into the ground. The earth drilling device can in particular be an HD device. An earth drilling device can be a device that drives a drill string and that can work in particular by displacing soil. The drill string can be translationally and/or rotationally introduced into the ground in the longitudinal axial direction of the drill string. The drill string can be moved in the ground by applying tension or pressure and possibly also rotationally or by turning. In the sense of the description, the term “drive element” comprises an element arranged on the earth drilling device, which 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. Usually, a rod section to be connected to the drill string is brought into engagement with the drive element in order to then connect the rod section connected to the drive element to the drill string that has already been drilled.
In a preferred embodiment, the ellipses offset from one another are standing ellipses. A simple design can be achieved in which the flank(s) can run out into the area of the thread base in order to reduce the notch effect there.
A “standing ellipse” is defined as an ellipse, the major axis of which (i.e., the longer of the center axes) encloses a larger angle with the center axis of the threaded plug or socket than the minor axis thereof (i.e., the shorter center axis). The angle between the main axis of the ellipse and the center axis of the threaded plug or socket can be “corrected” for a possible inclination of the ellipse, which may be caused by an arrangement of the ellipse on a cone of the threaded plug or threaded bushing, preferably in a standing ellipse between 70° and 110°, preferably between 80° and 100°, and particularly preferably 90°, wherein deviations thereto can occur, e.g., due to tolerances during production.
In a preferred embodiment, a center axis of at least one of the two ellipses, in particular the major axis, is arranged perpendicular to the longitudinal axis of the elongated body. This enables a particularly simple construction. Very particularly preferably, both center axes of the two ellipses, in particular the major axis, are arranged perpendicular to the longitudinal axis of the elongated body.
In a preferred embodiment, at least one of the thread tips of the adjacent flanks is rounded, by which sharp transitions in the thread can be reduced or avoided. Both thread tips are particularly preferably rounded.
In a preferred embodiment, the thread base between the adjacent flanks is designed as an envelope of the two ellipses, which results in a geometry of the thread base that reduces the notch effect and also enables a simple construction.
The term “envelope” is understood in the sense of the description as a curve which results from a continuous connection of the two ellipse sections in the thread base at the intersection of the two ellipses, wherein the envelope end may be rounded in the area of the intersection of the two ellipses. The construction of the thread is simplified, and the notch effect in the thread base is counteracted by the geometric design.
In a preferred embodiment, the offset includes at least one translational displacement in the direction of the longitudinal axis of the threaded bushing, the extent of which is between ⅛ and ¼ of the thread height. It was surprisingly found that the extent of the translational displacement can depend on the extent of the thread height in order to create a screw connection having suitable properties in terms of low notch effect and easy screwing together. Very good results were achieved in the mentioned range.
In a preferred embodiment, the offset includes at least one 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 bases. Particularly preferably, the offset can have at least one 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 bases. It was surprisingly found that the extent of the translational displacement can depend on the amount of the distance between two adjacent thread bases in order to create a screw connection having suitable properties in terms of low notch effect and easy screwing together. Very good results were achieved in the mentioned range.
In a preferred embodiment, the offset includes at least one 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 minor axis of the identical ellipses, wherein the offset preferably includes at least one 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 minor axis of the identical ellipses. It was surprisingly found that the extent of the translational displacement can depend on the value of the quotient of the center axes of the ellipses in order to enable a screw connection having suitable properties in terms of low notch effect and easy screwing together. Very good results were achieved in the mentioned range.
The improvement described in relation to the amount of offset in relation to the value of the thread depth, the distance between two adjacent thread bases, and the quotient of the center axes of the ellipses surprisingly occurs for each of the variables mentioned. However, a combination of the dimensions mentioned can also be taken into account by setting the offset depending on at least two of the dimensions mentioned. This means that a further improvement can be achieved.
In a preferred embodiment, the offset of the two ellipse sections is a pure translation in the direction of the longitudinal axis of the threaded bushing. This allows the construction of the thread to be greatly simplified.
In the sense of the description, the longitudinal axis of the threaded bushing is generally coincident with the longitudinal axis of the elongated body. The terms can be used essentially synonymously with one another, wherein depending on the context the use of one term may be preferred over the other.
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. The invention also creates a use of a threaded bushing on an elongated body for a threaded connection with a threaded plug, wherein the threaded plug has an external thread applied to a core, in which adjacent flanks of a thread 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 designed as sections of two identical ellipses offset from one another.
The invention also creates a use of a threaded plug on an elongated body for a threaded connection with a threaded bushing, wherein the threaded bushing has an internal thread, in which adjacent flanks of the internal thread are designed as sections of two identical ellipses offset from one another, wherein the threaded plug has an external thread applied to a core, in which adjacent flanks of a thread of the threaded plug form sections of the same ellipse.
In a preferred embodiment, the use of 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.
The invention also creates a threaded connection comprising a threaded bushing described in the present description and a threaded plug on an elongated body, wherein the threaded bushing has an internal thread, in which adjacent flanks of the internal thread are designed as sections of two identical ellipses offset from one another.
If the invention is described by means of different embodiments and/or aspects (regarding, for example, a device-related or usage-related design), the descriptions of the individual designs or aspects complement each other. In particular, the statements regarding the threaded bushing can also apply to the aspect of “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 threaded bushing described, there is also 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 of the threaded plug form sections of the same ellipse.
It has been shown that the threaded bushing can also cooperate with other threaded plugs to a certain extent, in which adjacent flanks are not necessarily designed to correspond or complement one another. It was recognized that a design of the threaded plug adapted to the design of the threaded bushing described may be preferred in the design described in the present description. It has surprisingly also been shown that a further improvement of the thread can occur with a design of the threaded plug in which adjacent flanks form a section of the same ellipse.
In a preferred embodiment, the ellipse, which 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 construction of the thread is possible.
In a preferred embodiment, the thread base can also form a section of the ellipse in the threaded plug. This can also reduce a notch effect on the threaded plug.
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.
In a preferred embodiment, the lead angle is between 20° and 30°.
In a preferred embodiment, the lead dimension of the threaded plug is at least 0.5 mm. In a preferred embodiment, the lead dimension of the threaded bushing is at least 1 mm. In a preferred embodiment, the difference between the length dimension of the threaded plug and the threaded bushing is at most 0.5 mm.
In the following, the invention will be explained in greater detail with reference to an exemplary embodiment illustrated in the drawings.
In the drawings:
The right of the two representations in
The elongated body 1 has a longitudinal axis L. The internal thread 3 of the threaded bushing 2 is a conical internal thread. The internal thread 3 of the threaded bushing 2 is shown in an enlarged view in
The thread tip GS is positioned in the middle between two adjacent flanks. The thread base GG is positioned in the middle between two adjacent flanks.
The right of the two representations in
The elongated body 1 has a longitudinal axis L. The external thread 5 of the threaded plug 4 is a conical external thread. The external thread 5 of the threaded plug 4 is shown in an enlarged view in
| Number | Date | Country | Kind |
|---|---|---|---|
| 23 152 004.0 | Jan 2023 | EP | regional |
