Method for design respective manufacture of threads in a threaded member, a threaded member manufactured according to the method, and a bolted joint including such a member
The invention relates to a method in the formation of threads of a thread-provided element intended to be included as one of two thread-provided parts in a bolted joint. The bolted joint comprises a part (2) having an internal thread and a part (1) having an external thread, and the threads of the respective parts are initially formed according to the ISO and/or Unified basic profile having an initial play in both the radial and axial direction, when said parts are tightened together. The invention is characterized in that the threads of said thread-provided element are formed so that an additional play (ΔSa) between said two thread-provided parts is obtained in the axial direction, at the same time as said initial play in radial direction remains substantially unaltered, the part of the bolted joint which consists of the thread-provided element no longer having ISO/Unified basic profile. The invention also relates to a method for the manufacture of threads, as well as corresponding thread-provided element and bolted joint.
The present invention relates to a method in the formation of threads of a thread-provided element intended to be included as one of two thread-provided parts in a bolted joint, which bolted joint comprises a part having an internal thread and a part having an external thread, and where the threads of the respective parts initially are formed according to the ISO and/or Unified basic profile having an initial play in both the radial and axial direction, when said parts are tightened together. The invention also relates to a thread-provided element formed according to the method as well as a bolted joint where at least one of the thread-provided parts of the joint consists of such a thread-provided element.
The invention furthermore relates to a method for the manufacture of threads of a thread-provided element intended to be included as one of two thread-provided parts of a bolted joint, a thread-provided element manufactured according to the method as well as a bolted joint where at least one of the thread-provided parts of the joint consists of such a thread-provided element.
Thus, the thread-provided element in question according to the invention may be either a screw or a nut, and said screws or nuts provided with threads formed according to the invention may either be used together with each other or together with screws and nuts formed according to standard.
According to the ISO standard (ISO/68) for metric threads, as well as for threads according to the American Unified standard (ANSI/ASME B1.1 which refers to ISO/68), a so-called basic profile is used which is illustrated in
Theoretically, the mean diameters for screw and nut, respectively, coincide with each other according to the basic profile. However, in practice, there has to be a play between screw and nut in order to be assemblable.
By using standardized manufacturing tolerances, a play is obtained which gives replaceability between screw and nut from different manufacturers. The play is provided by displacing the mean diameter of the screw inwards, or the mean diameter of the nut outwards. Thereby, both a radial and an axial play is obtained, see
According to Hooke's law, a body is extended proportional to the force that is applied on it. Such an extension may also be brought about by heating. To a screw, an extension means that the thread pitch increases. If the extension of the screw within the height of the nut becomes greater than the axial play between the flanks of the threads, interference will arise, which involves that the nut get locked.
This problem is particularly noticeably at high prestressing forces, as is the case at hydraulic prestress of high-strength screw in dimension M18 and upwards, with thread tolerances according to standard, and nut greater height than standard. During the prestress, the nut is, in the end of the screw where the prestressing tool pulls, unloaded while the prestressing tool pulls the screw with an axial tensile force. High-strength screw is characterized by the force obtained at prestress near the yield point in tension being significantly greater than for ordinary screws, and that it thereby requires more threads to distribute the force among so that the stress per thread does not become too high, which results in a greater nut height than standard, e.g. of the order of 100%. The axial extension of the screw that is obtained within the greater nut height has, however, still to be housed within the axial play of the nut in order to avoid interference. Thus, use of high-strength screw implies an increased risk of locking when thread tolerances according to standard do not give enough axial play. Thus, the size of the play sets a limit for how much the screw may be prestressed. In
The prevalent method to bring about an axial play is, according to the above, to give the screw a smaller mean diameter than the nut. It is, however, inappropriate, and occasionally even impossible, to additionally increase the difference in mean diameter between screw and nut so as to thereby obtain a sufficient axial play, since this decreases the thread coverage and implies higher surface pressure between the threads, as has been explained above.
The object of the invention is to overcome the above-mentioned disadvantages and find a solution to the problems mentioned above. This takes place by the method for the formation of the threads of a thread-provided element, such as a screw or a nut, which has the new features defined in the characterizing part of claim 1, as well as the method for the manufacture of threads of a thread-provided element intended to be included as one of two thread-provided parts in a bolted joint, which has the new features defined in claim 11.
Thus, the method for the formation of the threads, according to the invention, is characterized in that the threads of the thread-provided element are formed so that an additional play between said two thread-provided parts is obtained in the axial direction, at the same time as said initial play in radial direction remains substantially unaltered, the part of the bolted joint which consists of the thread-provided element no longer having ISO/Unified basic profile. In this way, the advantage is obtained that the thread coverage may be maintained and the largest feasible abutment between the two parts is obtained, which gives an opportunity to a maximum transfer of forces. This enables a high prestressing force of a screw, which is particularly advantageous for screws in high-strength material. However, the invention is not limited to the application for high-strength screw but may advantageously be used also in other applications.
According to an advantageous embodiment, the invention is characterized in that the part having an external thread is intended to be prestressed, that the thread-provided element consists of the part having an internal thread the threads of which are formed so that said additional axial play together with the initial axial play equals at least the maximal elongation which the part having external thread is expected undergo, at the prestress, within the area where said parts co-operates.
According to another advantageous embodiment, the invention is characterized in that the thread-provided element consists of the part having external thread and that said part is intended to be prestressed, that the threads of the part having external thread is formed so that said additional axial play together with the initial axial play corresponds at least the maximal elongation which the part having external thread is expected undergo, at the prestress, within the area where said part having external thread co-operates with the part having internal thread.
According to an advantageous aspect, the width of the thread ridge of the thread-provided element is decreased by a measure corresponding to the desired additional axial play. This may be effected either by the decrease of the width of the thread ridge only occurs on one flank thereof, or is distributed on the two flanks thereof.
Furthermore, the present invention provides a thread-provided element formed according to the method of formation, as well as a bolted joint comprising at least one such thread-provided element.
The method in the manufacture of threads, according to the present invention, is characterized in that the threads are manufactured in two step, viz. a first step wherein the threads are manufactured by means of a cutting tool in the same way as in the manufacture of threads according to the ISO standard or Unified standard with the appurtenant initial axial and radial play, and a second step where the cutting tool only is advanced axially an additional distance in order to bring about an additional axial play decided beforehand, which distance equals said play, as well as with an unaltered radial position. The advantages that are attained have already been described previously, but additional advantages are obtained by elements having the new thread of the invention that gives additional axial play simply may be manufactured starting from the manufacturing method applying to elements having usual standard threads, with the same equipment and with a very small changing in the control. The two steps may follow directly one after the other, non-stop. The invention also relates to a thread-provided element manufactured according to said method, as well as a bolted joint comprising at least one such thread-provided element.
The invention will now be disclosed in detail reference being made to the accompanying drawing figures, which illustrate prior art and the problems therewith, as well as show embodiment example of the present invention, and in which:
As already has been mentioned in the introduction of the description,
In
In
In
Finally, an embodiment example is shown in
It should be added that in all illustrated cases, the bottoms of the threads are somewhat rounded, according to standard, but this has not has been shown in the drawings for reasons of clarity.
In the shown examples, the nut has been illustrated as the part that has been formed with a thread that gives an additional play according to the present invention, but it may of course as well be the screw that is formed in this way, or alternatively both parts, if this is considered convenient.
The present invention should not be regarded as limited by the embodiments which have been disclosed, in terms of examples only, but may be modified and varied in a of multiple of ways, as is realized by a person skilled in the art, within the scope of the accompanying claims.
Claims
1. Method for forming threads of a thread-provided part which is intended to be one of two thread-provided parts in a bolted joint, the method comprising:
- providing a first part having an internal thread and a second part having an external thread wherein the first and second parts are screwed together with the second part is intended to be inside the first part, and wherein the second part having the external thread intended to be prestressed with an axial tensile force, the threads of the respective parts initially being formed according to a basic profile which provides an initial play in both radial and axial directions, when the parts are screwed together and are unstressed,
- further forming the threads of at least one of the thread-provided parts such that an additional play ΔSa between the two thread-provided parts is obtained in the axial direction, while the initial play in the radial direction remains substantially unaltered, and the at least one of parts of the bolted joint which is formed to provide the additional play, no longer having the basic profile.
2. Method according to claim 1, wherein the at least one thread-provided part is the first part having the internal thread which includes threads formed so that the additional axial play together with the initial axial play corresponds to at least a maximum elongation which the second part having the external thread is expected to undergo, at the prestress, within an area where the parts cooperate.
3. Method according to claim 1, wherein the at least one thread-provided part is the second part having the external thread, and the external thread being formed so that the additional axial play together with the initial axial play corresponds to at least a maximum elongation which the second part having the external thread is expected to undergo, at the prestress, within an area where the second part having the external thread co-operates with the first part having the internal thread.
4. Method according to claim 1, further comprising increasing the axial play with maintained thread coverage.
5. Method according to claim 1, wherein the threads of the parts have respective thread ridges, of an initial width, the method further comprising decreasing the width of the thread ridge of the at least one thread-provided part by a measure corresponding to the desired additional axial play.
6. Method according to claim 5, wherein the thread ridges have opposite flanks, and the decreasing of the width of the thread ridge occurs on one of the flanks of the ridge.
7. Method according to claim 5, wherein the decreasing of the width of the thread ridge is distributed on both opposite flanks thereof.
8. A thread-provided part produced according to the method of claim 1.
9. A bolted joint comprising a first part having an internal thread and a second part having an external thread, and the parts are two thread-provided parts which are tightened together with each other for forming the joint, wherein at least one of the thread-provided parts is produced according to the method of claim 1.
10. A method for producing of threads of a thread-provided part to be included as one of two thread-provided parts of a bolted joint, wherein the bolted joint comprises a first part having an internal thread and a second part having an external thread, the thread producing method comprising manufacturing the threads using a cutting tool in the threads according to a standard with appurtenant initial axial and radial play, and then axially advancing the cutting tool only an additional distance, while retaining with unaltered radial position, for achieving an additional selected axial play ΔSa, the additional distance corresponding to the additional axial play.
11. A thread-provided part produced according to the method of claim 10.
12. A bolted joint comprising two thread provided parts, with one part screwed into the other part, at least one of the thread-provided parts being produced according to the method of claim 10.
13. The method according to claim 1, wherein the basic profile with which the threads of the respective parts are formed according to at least one of the ISO and Unified basic profile.
14. The method according to claim 10, wherein the threads are manufactured according to at least one of the ISO and Unified basic profile.
Type: Application
Filed: May 21, 2003
Publication Date: Jun 16, 2005
Inventor: Mats Webjorn (Spanga)
Application Number: 10/515,030