Screw joint, fastening body, and screw member

Abstract

To provide a screw joint which can reduce a large load generated locally to level the load in an axial direction even in a screw which is fastened securely.SOLUTION: A screw joint of the invention is a screw joint 10A in which a male screw 11 and a female screw 15 having threads are engaged. A slit SL is formed from a top surface of a thread M11A toward an axis line C at one side in an axial direction of a first screw which is one of the male screw 11 and the female screw 15. Preferably, in the slit, a depth from the top surface increases gradually or continuously in a direction toward one side in the axial direction of the first screw. Preferably, in the slit, a width in the axial direction increases gradually or continuously in the direction toward the one side in the axial direction of the first screw.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a threaded joint in which a male thread and a female thread are mated together. [Background technology]

[0002] In conventional threaded joints that have been in general use, the concept is that the effective diameter and pitch of the male and female threads that mesh with each other are made equal. In conventional threaded joints, the cross-sectional area of the male thread is generally much smaller than that of the female thread. Therefore, when the male and female threads are tightened and an external force is applied, most of the deformation occurs on the male thread side, and it is known that, for example, 80% of the total thread load is borne within a range of a few threads from the start of engagement between the male and female threads. In other words, the load and stress distribution when the male and female threads are tightened together are concentrated in a small area on the load side. Therefore, statically, the threads break from the beginning of engagement where the stress is high.

[0003] In contrast to this, Patent Documents 1 and 2 employ a method in which, in order to prevent damage to the meshing start portion, the effective diameter is reduced around the meshing start portion and the effective diameter is increased with increasing distance from the meshing start portion.

[0004] Furthermore, Patent Document 3 proposes improving reliability and extending service life by reducing the bending moment generated in the screw shaft of a ball screw as much as possible. This proposal proposes a method of forming a slit groove in the screw shaft that reaches a position deeper than the bottom of the thread groove provided in the screw shaft, and using this slit groove to reduce the bending rigidity of the screw shaft. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-281129 [Patent Document 2] Japanese Patent Application Publication No. 49-30740 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-76791 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Documents 1 and 2, the outer diameter of the male thread is reduced to reduce the effective diameter, resulting in a small amount of thread engagement. Ideally, the mating thread should penetrate deeply into the thread groove between adjacent threads, tightly interlocking both threads and maintaining high thread flexural rigidity. However, if the thread engagement is small and the mating thread penetration is shallow, the resistance to flexural deformation of the threads is weakened, resulting in reduced thread rigidity. This makes the threads more likely to flex and reduces the load generated, but the contact area between the threads is also reduced, meaning the contact stress (surface pressure) between the threads cannot be reduced. Particularly in the case of large-diameter screws with large thread widths (thread thicknesses) and high thread rigidity, the contact area is reduced without significant reduction in rigidity, potentially increasing contact stress. Therefore, the proposals in Patent Documents 1 and 2 pose a risk of adhesive wear.

[0007] Furthermore, the proposal in Patent Document 3 is a technology targeted at general-purpose ball screws, in which the load position cannot be identified within the operating range of the ball screw shaft. Therefore, the proposal reduces the bending stiffness of the screw shaft uniformly (evenly) throughout the entire operating stroke range of the ball screw's screw shaft. This reduces the bending stiffness of the screw shaft not only near the nut nose, where the load point is large, but also in areas away from the nose. While this evenly suppresses the increase in ball load and enables smooth rotation of the screw shaft, it may not be effective enough for bolted fasteners where strong fixation is the top priority. Specifically, bolted fasteners where strong fixation is the top priority cannot release part of the load energy as a moving force (linear force) of the component (nut or shaft). Therefore, it is difficult to sufficiently equalize the load distribution, which differs significantly between the nut nose and areas away from the nose.

[0008] In view of the above, an object of the present invention is to suppress large loads that occur locally and to level out the load in the axial direction even when a screw is firmly fastened and fixed. [Means for solving the problem]

[0009] The present invention relates to a threaded joint in which a male screw having a thread and a female screw are engaged with each other, A slit is formed on one side in the axial direction of the first screw, which is either a male screw or a female screw, from the crest surface of the thread toward the axis.

[0010] In the threaded joint of the present invention, The slits preferably have The depth from the top surface becomes deeper in a stepwise or continuous manner as it approaches one side in the axial direction of the first screw.

[0011] In the threaded joint of the present invention, The slits preferably have The width in the axial direction increases stepwise or continuously as it approaches one side of the first screw in the axial direction.

[0012] In the threaded joint of the present invention, a first surface facing one side and a second surface facing the other side opposite to the first surface, The slits preferably have The closer to one side in the axial direction of the first screw, the shorter the distance to the first surface becomes in a stepwise or continuous manner.

[0013] The present invention provides a fastened body in which at least two members are fastened together using any of the threaded joints described above. In this fastened body, the first screw and the second screw are subjected to loads in opposite directions in the axial direction, or the first screw and the second screw are subjected to loads in opposite directions in the axial direction and a reaction force to the loads.

[0014] The present invention provides a screw element having a multi-threaded external or internal thread. This screw member has a slit formed on one side in the axial direction of the screw from the crest of the thread toward the axis. [Effects of the Invention]

[0015] According to the present invention, even when a screw is firmly fastened and fixed, a large load that occurs locally can be suppressed and leveled. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a vertical cross-sectional view showing a schematic configuration of a mold clamping device according to an embodiment. [Figure 2] 1 is a vertical cross-sectional view showing a main part of a mold clamping device having a screw structure according to an embodiment. [Figure 3] FIG. 2 is a longitudinal cross-sectional view showing a main part of the screw structure according to the first embodiment. [Figure 4] FIG. 10 is a longitudinal cross-sectional view showing a main part of a screw structure according to a second embodiment. [Figure 5] FIG. 10 is a longitudinal cross-sectional view showing a main part of a screw structure according to a third embodiment. [Figure 6] 10A and 10B are a longitudinal sectional view showing the main parts of a screw structure according to a fourth embodiment and a developed view of the threads of a male screw. [Figure 7] 10A and 10B are a longitudinal sectional view showing the main parts of a screw structure according to a fourth embodiment and a developed view of the threads of a male screw. [Figure 8] 1 is a diagram showing an example of a threaded joint to which the present invention is applied. [Figure 9] 8 is a longitudinal sectional view showing the main part of a conventional screw structure and a diagram explaining the positions of the development views in FIGS. 6 and 7.

[0033] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. This embodiment relates to a threaded joint in which a male thread and a female thread are meshed together, and for example, a slit is provided on one side of the axial direction of one of the female threads from the crest of the thread toward the axis of the thread. By providing a slit in the thread, the contact pressure between the threads of the male thread and the female thread is reduced, thereby reducing the load at the start of meshing and making the load distribution on the threads more uniform, even in a threaded joint in which screws are firmly fastened and fixed together.

[0018] Below, we will explain a mold clamping device installed in an injection molding machine as an example of an application of a screw joint, and then we will explain a conventional screw joint and four embodiments of the screw joint according to this embodiment in order. All four embodiments have in common that they reduce the bending stiffness in the axial direction of the thread, but the specific means for reducing the bending stiffness differ.

[0019] [Mold clamping unit: see Figures 1 and 2] The mold clamping device 1 is provided to clamp a pair of molds (a fixed mold and a movable mold) of an injection molding machine, etc. The mold clamping device 1 clamps the fixed mold and the movable mold by applying a mold clamping force between a fixed mold platen that holds the fixed mold and a movable mold platen that holds the movable mold.

[0020] 1 and 2, a clamping unit 1 according to this embodiment includes a base 10, a fixed platen 11 fixed to the base 10, and a movable platen 12 provided on the base 10 so as to be movable toward and away from the fixed platen 11. The clamping unit 1 also includes tie bars 15A, 15B, 15C, and 15D provided across the fixed platen 11 and the movable platen 12, a movable platen moving means 18 that moves the movable platen 12 forward and backward, and a split nut opening / closing unit 20 that engages with the tie bars 15A, 15B, 15C, and 15D during clamping. In the mold clamping device 1, the vertical direction V and the horizontal direction H are defined as shown in Fig. 1, etc. Furthermore, the front (F) and rear (R) are defined as shown in Fig. 2, etc.

[0021] [Fixed mold board 11, movable mold board 12] 1, fixed platen 11 is provided on one end side of base 10 in the horizontal direction H, and movable platen 12 is provided slidably relative to base 10 and facing fixed platen 11. Note that the surfaces of fixed platen 11 and movable platen 12 facing each other are referred to as front surfaces 11A and 12A, and the surfaces facing front surfaces 11A and 12A are referred to as back surfaces 11B and 12B.

[0022] The fixed platen 11 holds a fixed mold 13 on its front surface 11A, and the movable platen 12 holds a movable mold 14 on its front surface 12A. A cavity into which molten material is supplied is formed inside each of the fixed mold 13 and the movable mold 14. The cavity is not shown in the drawing. When the mold clamping device 1 is used in an injection molding machine, the molten material is made of molten resin, and when the mold clamping device 1 is used in a die-casting machine, the molten material is made of molten metal such as an aluminum alloy.

[0023] The fixed platen 11 and the movable platen 12 are connected by a plurality of tie bars, in particular four tie bars 15A, 15B, 15C, and 15D in this embodiment. The four tie bars 15A, 15B, 15C, and 15D are arranged at the four corners when the fixed platen 11 and the movable platen 12 are viewed from the front. Sliding members can be interposed between the tie bars 15A, 15B, 15C, and 15D and the movable platen 12 to reduce friction between them.

[0024] [Tie bars 15A, 15B, 15C, 15D] As shown in FIG. 1 , the tie bars 15A to 15D are provided with piston heads 16 for generating a clamping force at the ends thereof on the fixed platen 11 side. In this embodiment, the tie bars 15A to 15D and the piston heads 16 are connected by threaded joints 30. The tie bars 15A to 15D are also formed with ring-shaped meshing teeth 17 that are continuous in the circumferential direction at the ends thereof on the movable platen 12 side. The meshing teeth 17 mesh with meshing teeth formed on the inner peripheries of the first split nut 21 and the second split nut 22. This allows the tie bars 15A to 15D to be locked to the movable platen 12. Note that some of the meshing teeth formed on the inner peripheries of the first split nut 21 and the second split nut 22 are not shown in the figure. In addition, the base 10 is provided with, for example, an electric or hydraulic movable platen moving means 18, which allows the movable platen 12 to move back and forth relative to the fixed platen 11. Figure 1 shows a mold closing state in which the movable platen moving means 18 has moved the movable platen 12 toward the fixed platen 11 and brought the movable mold 14 into contact with the fixed mold 13.

[0025] As shown in FIG. 2, the screw joint 30 in the mold clamping device 1 is composed of a male screw 31 formed on the tip side of the tie bar 15A (to 15D) and a female screw 35 formed on the piston head 16. When clamping the mold in the mold clamping device 1, as shown in Fig. 2, hydraulic pressure OP is applied to the piston head 16 that constitutes the hydraulic cylinder. Since the tie bar 15A (to 15D) is locked at the rear (R) by the first split nut 21 and the second split nut 22, a reaction force Fr due to the hydraulic pressure OP is generated in the rear (R) direction on the tie bar 15A (to 15D). As a result, loads are applied to the male screw 31 and the female screw 35 in opposite directions along the axis C, and a thread load is generated in the direction of the axis C on each of the threads of the male screw 31 and the female screw 35.

[0026] An example of the distribution of thread loads on the male thread 31 and the female thread 35 is shown in Figure 2. In conventional thread joints, the thread load on the base side (load side) is highest, and the thread load on the base side is considerably larger than that on the base and tip sides. In contrast, the thread joint according to the embodiment not only can keep the thread load on the base side low, but also has a small difference in thread load between the base side and tip side. Note that although there is no part corresponding to the head of a bolt on the rear (R) side of the tie bar 15A, it is referred to as the base side for convenience as an expression for the tip side. In other words, in this embodiment and the present invention, the "neck side" means the side opposite to the tip side of the male screw 31 in the range where the threads of the female screw 35 are provided or the range where the threads of the male screw 31 that mesh with the threads of the female screw 35 are provided, and closer to the end face or cross section of the female screw 35, which is the surface onto which the external force (tensile load Fa) that is the source of tensile stress generated in the shank of the male screw 31 or the support force of the initial tightening load (reaction force of the initial tightening load: tensile load Fb) is directly applied.

[0027] In this embodiment, the tie bar 15A and the piston head 16 are fastened together by the male thread 31 and the female thread 35 to form a fastened assembly. The tie bar 15A and the piston head 16 can also be manufactured by molding the material as a single unit and then performing the necessary processing. In this case, the radial dimensions of the material must correspond to the piston head 16, and the portion corresponding to the tie bar 15A must also be large in diameter. Furthermore, typically, companies capable of performing shaping processes such as forging, cutting, or finishing on large-diameter and long materials each specialize in different processing techniques, and companies specializing in each type of shaping process are rare nationwide and often located far apart. Therefore, if the entity that forms the material and the entity that forms it into the final shape are different entities, the material must be transported long distances. In contrast, if the tie bar 15A and the piston head 16 are manufactured separately and joined using a separate threaded joint 30, material costs and long-distance transportation costs can be reduced.

[0028] [Conventional threaded joint 50: Figure 9] In a conventional threaded joint 50, the thread M51 of the male thread 51 and the thread 55M of the female thread 55 are solid throughout the entire area in the direction of the axis C. Therefore, the thread M51 and the thread 55M have constant bending rigidity in the direction of the axis C, and the thread load on the base side becomes large. The point where the lead of the thread M51 of the male thread 51 and the lead of the thread 55M of the female thread 55 match, and where the thread width and groove width of the thread M51 match, is called the reference line RL of the female thread 35. In the embodiments described below, the thread width and groove width also match, but the thread width in the embodiments does not include the slit for the thread M51 on which a slit is formed.

[0029] In the embodiment described below, the specifications (shape and dimensions) of the female thread are the same as conventional ones, but the specifications of the male thread 51 are adjusted. The region of the male thread where this adjustment is made is called an adjustment region RA, and the other region is called a normal region NA. The threads M51 and M55 are each connected in a spiral shape, and the thread grooves G51 and G55 are also connected in a spiral shape. Although not mentioned in the first to fourth embodiments described below, the threads and thread grooves are connected in a spiral shape. Therefore, in the drawings of the first to fourth embodiments, only one reference symbol is used for the threads and thread grooves, but all slits shown in the cross section are given a reference symbol. The right side of Fig. 9 shows the ridge lines (a1, d1...) and valley lines (b1, c1...) in the cross section of the thread (thread groove). The developed view of the male screw in the fourth embodiment is obtained by linearly developing the ridge lines and valley lines in Fig. 9.

[0030] [First embodiment: see Figure 3] [Configuration of screw joints 10A and 10B] In the threaded joint 10A according to the first embodiment, the leads of the male thread 11A and the female thread 15 are the same. The male thread 11A corresponds to the first thread of the present invention, and the female thread 15 corresponds to the second thread of the present invention. As an example, a slit SL11 is provided in the thread M11A of the male screw 11A from the base to the second thread. By providing the slit SL11 in this manner up to a predetermined range (adjustment region RA) on the base side, the effective thread width of the thread M11A becomes smaller, and therefore the bending rigidity of the thread M11A in the adjustment region RA in the direction of the axis C becomes smaller than that of the thread M11A in the normal region NA. Because the bending rigidity is smaller, the thread M11A in the adjustment region RA is more likely to bend in the direction of the axis C than the thread M11A in the normal region NA. As an example, the depth of the slit SL11 from the top surface of the thread M11A is constant. Hereinafter, when referring to the bending rigidity of a thread, it refers to the bending rigidity in the direction of the axis of the thread. The threads M11A and the slits SL11 are spirally connected in the direction of the axis C, and in order to clarify that the slits SL11 are connected, the slits SL11 are shown for each of the threads M11A and the slits SL11 shown in the cross section.

[0031] [Actions / effects of threaded joint 10A] In the thread joint 10A, a slit SL11 is formed in the thread M11A in the adjustment region RA, reducing the flexural rigidity of the thread M11A compared to the normal region NA where the slit SL11 is not formed. Therefore, if the thread joint 10A did not have a slit, the thread load on the base side would normally be large when the male thread 11A and the female thread 15 are mated. However, the presence of the adjustment region RA, which has low rigidity on the base side, allows the thread M11A corresponding to the base side to easily flex, reducing the thread load. In this case, the load not supported by the thread M11A on the base side shifts to the tip side. However, because the tip side is the normal region NA, the flexural rigidity of the thread M11A is high, allowing the load applied to the thread to be fully supported. This allows the distribution of the thread load in the direction of the axis C of the male thread 11A to be more uniform (leveled).

[0032] The slits SL11 can be provided only in areas where the thread load is particularly large, or can also be provided in the area of the thread M11B near the tip, as in the case of the threaded joint 10B. Even in this case, the effect of making the distribution of the thread load in the direction of the axis C of the male thread 11B more uniform is achieved.

[0033] [Second embodiment: see Figure 4] [Configuration of screw joints 20A and 20B] Next, threaded joints 20A and 20B according to a second embodiment will be described. The threaded joints 20A, 20B differ from the threaded joints 10A, 10B according to the first embodiment in the radial dimension (depth) of the slits. Note that for the threaded joints 20A, 20B, the same components as those of the threaded joints 10A, 10B are given the same reference numerals as those of the threaded joints 10A, 10B, and descriptions thereof may be omitted.

[0034] In the threaded joint 20A, the slits SL21 and SL22 are formed from the neck side to the third thread M21A. Among these, the slits SL21 and SL22 have different depths. The slits SL21 have the same depth D21 from the neck side to the second thread M21A, and the slit SL22 has a depth D22 smaller than that of the slit SL21 from the neck side to the third thread M21A from the neck side. Thus, in the threaded joint 20A, from the region where the slit SL21 with a depth D21 is formed to the region where the slit SL22 with a depth D22 is formed, the slit depth gradually increases from the side with a smaller load to the side with a larger load in the thread load distribution when no slits are formed. If the depths of the slits SL21 and SL22 are D21 and D22, respectively, the relationship D21 > D22 holds.

[0035] In contrast to the above-described thread joint 20A, the thread joint 20B has a slit depth of slit SL21, slit SL22, slit SL23 and slit SL24 in the order of slit SL21 from the neck side to the fourth thread M21B. When the slit depths of the slits SL21, SL22, SL23 and SL24 are D21, D22, D23 and D24, respectively, the relationship D21>D22>D23>D24 holds.

[0036] [Actions / effects of threaded joints 20A and 20B] In both the threaded joint 20A and the threaded joint 20B, the slit depth increases toward the neck, but the greater the slit depth, the smaller the bending rigidity of the threads M21A, 21B. This corresponds to the fact that the thread load increases toward the neck of the threaded joints 20A, 20B. Therefore, with the threaded joints 20A, 20B, the threads bend more toward the neck, where the thread load would be greater if no slits were formed, and more of the load can be released, making it possible to more evenly distribute the thread load in the direction of the axis C of the male threads 21A, 21B. In other words, the bending rigidity is adjusted by the slits, just as with the threaded joints 20A, 20B.

[0037] [Third embodiment: see Figure 5] [Configuration of screw joints 30A and 30B] Next, threaded joints 30A and 30B according to a third embodiment will be described. Like the screw joints 20A and 20B, the screw joints 30A and 30B adjust the magnitude of bending rigidity by using slits, but the means for doing so differs from that of the screw joints 20A and 20B in that the width of the slits is adjusted.

[0038] In the threaded joint 30A, slits SL31 and SL32 are formed from the neck side to the third thread M31A. Among these, slits SL31 and SL32 have different widths. Slits SL31 are formed with the same width W31 from the neck side to the second thread M31A, and slit SL32, with a width W32 smaller than slit SL31, is formed on the third thread M31A from the neck side. Thus, in the threaded joint 30A, the slit width increases stepwise from the region where slit SL31 is formed to the region where slit SL32 is formed, moving from the side with a smaller load to the side with a larger load in the thread load distribution when no slits are formed. If the widths of slits SL31 and SL32 are W31 and W32, respectively, the relationship W31 > W32 holds.

[0039] In contrast to the above-described threaded joint 30A, the slit widths of threaded joint 30B decrease successively from the neck side to the fourth thread M41B in the order of slit SL31, slit SL32, slit SL33, and slit SL34. If the slit widths of slit SL31, slit SL32, slit SL33, and slit SL34 are W31, W32, W33, and W34, respectively, the relationship W31 > W32 > W33 > W34 holds.

[0040] [Actions / effects of threaded joints 30A and 30B] In both the threaded joints 30A and 30B, the slit width increases toward the neck. The wider the slit, the greater the amount of deflection of the thread when a load is applied until the thread with the push side surface PS contacts the thread with the pull side surface TS opposite the slit. Therefore, the flexural rigidity of the thread is low until the thread with the push side surface PS contacts the thread with the pull side surface TS opposite the slit. However, the flexural rigidity of the thread increases after the thread with the push side surface PS contacts the thread with the pull side surface TS opposite the slit. This corresponds to the fact that the thread load increases toward the neck of the threaded joints 30A and 30B. Therefore, with the threaded joints 30A and 30B, the threads flex more toward the neck, where the thread load would be greater if a slit were not formed, allowing for greater load relief. This allows for a more uniform distribution of the thread load in the direction of the axis C of the male thread 31A.

[0041] Here, the pushing side surface PS corresponds to the first surface of the present invention, and the pulling side surface TS corresponds to the second surface of the present invention. The pushing side surface is the surface that supports the external force when it is applied to the screw, that is, the pressing force increases as the external force increases, and the pulling side surface is the surface on one thread opposite the pushing side surface.

[0042] [Fourth embodiment: see Figs. 6 and 7] [Configuration of screw joints 40A and 40B] Next, threaded joints 40A and 40B according to a fourth embodiment will be described. The threaded joints 40A and 40B adjust the bending rigidity by using slits in the same way as the threaded joints 20A and 20B, but the means for doing so differs from that of the threaded joints 20A and 20B in that the position in the direction of the axis C forming the slit is adjusted.

[0043] The screw joint 40A continuously changes the position of the slit from the base end side to the tip end side. Here, the position of the slit refers to the position in the direction of the axis C or the position in the width direction of the thread M41A. In order to continuously change the position of the slit, if the lead of the thread M41A of the screw joint 40A is L1 and the lead of the slit is L2, then L1 < L2. As a result, the slit SL41 on the base end side is formed near the pressing side surface PS of the thread M41A, and the slit SL46 on the tip end side is formed near the pulling side surface TS of the thread M11. And the position of this slit is set so that the position is displaced from the pressing side surface PS to the pulling side surface TS from the base end side to the tip end side. In the developed view of the thread in Fig. 6, the broken line represents the slit. Note that the form of the connecting portion of the slits with different leads L1 and L2 is arbitrary and can be appropriately selected from a straight line, a curve, etc.

[0044] The screw joint 40B, unlike the screw joint 40A, changes the position of the slit stepwise. That is, in the screw joint 40B, the slits SL41 and SL42 are formed up to the third thread M41B from the base end side. Among them, the slit SL41 formed up to the second thread M41B from the base end side has the same position in the thread M11, and the slit SL42 formed on the third thread M41B from the base end side is formed farther from the pressing side surface PS than the slit SL41. Note that the form of the connecting portion of the slits SL41 and SL42 with different distances from the pressing side surface PS is arbitrary and can be appropriately selected from a straight line, a curve, etc.

[0045] Also, it may be a mode in which the feature of continuously changing the position of the slit of the screw joint 40A is combined with the feature of changing the position of the slit of the screw joint 40B stepwise. Specifically, in the screw joint 40A, an example of the slit is shown where when the lead of the screw thread M41A of the screw joint 40A is L1 and the lead of the slit is L2, L1 < L2. Not limited to this example, the lead of the slit may be changed step by step. In this case, when the lead on the tip side is L2 and the lead on the base side is L3, it is preferable to satisfy the relationship L2 > L3 > L1. As an example applied to the screw joint 40A in FIG. 6, the leads L2 can be set for the slits SL31 and SL32, the lead L3 can be set for the slits SL33, SL34, and SL35, and the lead L1 can be set for the slit SL36. In this example, within the ranges of the slits SL31 and SL32, the position of the slit changes continuously, and within the ranges of the slits SL33 to SL35, the position of the slit changes continuously. In addition, the leads L1 and L3 of the slits SL32 and SL33 are different, and the leads L3 and L1 of the slits SL35 and SL36 are different. Therefore, at the connection part between the slits SL32 and SL33 and at the connection part between the slits SL35 and SL36, the degree of change in the position of the slit becomes stepwise. Note that the form of the connection part of the slits with different leads is arbitrary and can be appropriately selected from a straight line, a curve, etc.

[0046] Also, while continuously changing the position of the slit with a small lead in a part of the region, the position of the slit in another part of the region may be set to a certain position closer to the pressing side surface PS or the pulling side surface TS than the position of the slit in the said part of the region. As an example applied to the screw joint 40A in FIG. 6, the lead L4 (> L1) can be set for the slits SL31, SL32, and SL33, the lead L1 can be set for the slits SL34, SL35, and SL36, and the slits SL34 and SL35 can be set to a certain position closer to the pressing side surface PS than the slit SL36 having the same lead L1. Note that the form of the connection part of the slits with different leads is arbitrary and can be appropriately selected from a straight line, a curve, etc. The same also applies to the connection parts of the slits with different distances from the pressing side surface PS.

[0047] When changing the lead of the slit, the change can be in any manner. For example, the lead may be changed so that it continuously decreases from the tip side to the neck side according to a linear function, or it may be changed so that it continuously increases from the tip side to the neck side according to an n-th order function. Note that n is an integer of 2 or more, and the quadratic function includes the equation of a parabola.

[0048] [Actions / effects of threaded joints 40A and 40B] In both the threaded joints 40A and 40B, the closer the slit is to the base, the closer it is to the push surface PS. However, the closer the slit is to the push surface PS, the lower the bending rigidity of the threads M41A, M41B. This corresponds to the fact that the thread load increases toward the base of the threaded joints 40A, 40B. Therefore, with the threaded joints 40A, 40B, the threads flex more toward the base where the thread load is greater, allowing more load to be released, making it possible to more evenly distribute the thread load in the direction of the axis C of the male thread 11A.

[0049] In addition to the above, the configurations given in the above embodiments can be selected or changed as appropriate to other configurations without departing from the spirit of the present invention. For example, it is possible to combine the first and second embodiments. For example, it is possible to combine the second embodiment, in which the depth of the slit is changed, with the third embodiment, in which the width of the slit is changed.

[0050] [Load pattern to which the present invention is applied: see Figure 8] In the first and second forms, when viewed in relation to a bolt B on which a male thread 41 is formed and a nut N on which a female thread 35 is formed, as shown in FIG. 8(a), loads Fb and Fn1 are applied in opposite directions to the bolt B and the nut N, respectively. The load Fb is applied to the nut N from the rear (R). In this case, the load distribution occurring in the nut N increases from the front (F) to the rear (R). Note that the front (F) and rear (R) have relative meanings.

[0051] The present invention is not limited to the load pattern shown in FIG. 8(a), but is also applicable to the load patterns shown in FIGS. 8(b) and 8(c). In the load pattern shown in Figure 8(b), for example, because the nut N is fixed, the reaction force Fn2 of the load Fb applied to the bolt B is applied in the forward direction (F). In this case, the thread load exhibits a distribution in which it is large not only in the rear (R) but also in the front (F). In this case, the adjustment region RA of this embodiment can be applied to the two regions corresponding to this thread load distribution. The load pattern shown in FIG. 8(c) has a nut N with a fastened portion N1 having a thread and a non-fastened portion N2 without a thread. Note that in this case, for convenience, the threaded portion on the base side of the nut N is referred to as the fastened portion N1, and the round hole portion on the bottom side of the hole is referred to as the non-fastened portion N2, in relation to the blind-hole type screw hole provided in the nut N. The nut N is also assumed to be fixed to a member (not shown). When a load Fb is applied to the bolt B, a reaction force Fn3 is generated in the non-fastened portion N2 toward the front (F). In response to this reaction force Fn3, a reaction force Fn4 is generated in the fastened portion N1 toward the rear (R). In this load pattern, the thread load on the fastened portion N1 increases from the rear (R) to the front (F). In this load pattern, the adjustment region RA of this embodiment can be applied only to the front (F) side of the fastened portion N1, i.e., the reaction force support side. In this case, the normal area NA is applied to the rear (R) side of the fastening portion N1, that is, the load side.

[0052] In summary, the load patterns to which the present invention is applicable are as follows: First load pattern: Loads Fb and Fn are applied to the male screw (bolt) and female screw (nut) in opposite directions. Second load pattern: A load Fb (Fn) is applied to one of the male thread (bolt) and the female thread (nut), and a reaction force Fn (Fb) due to the load Fb (Fn) is applied to the other of the male thread (bolt) and the female thread (nut).

[0053] [Screw to which this embodiment is applied] In the first to fourth embodiments, the present invention is applied to a male thread, but the present invention can also be applied to a female thread. Also, in the first to fourth embodiments, the present invention is applied to a helical thread, but the present invention can also be applied to a ring-shaped thread (saw teeth) that continues in the circumferential direction, such as the meshing teeth 17 of the tie bars 15A to 15D.

[0054] [Fastened body to which this embodiment is applied] In the first to fourth embodiments described above, a tie bar and a piston rod are used as an example of a fastened body using a threaded joint, but the fastened body of the present invention is not limited to this. Although the bolt and screw have been described above, the present invention can be applied to various fastened bodies in which a male thread is formed on one member and a female thread that meshes with the male thread of the one member is formed on the other member. In particular, the present invention is suitable for dividing an integrally molded product having elements of different dimensions, such as a tie bar and a piston rod, into two members and fastening them together using a threaded joint. [Explanation of symbols]

[0055] 1 Mold clamping device 10 Foundations 11 Fixed platen 11A, 12A front 11B, 12B back side 12 Movable mold board 13 Fixed mold 14 Movable mold 10A, 10B screw joint 15 female thread 15A, 15B, 15C, 15D tie bars 16 Piston head 17 Interlocking teeth 18 Movable mold platen moving means 20-nut opening and closing device 21 Split nut 22 split nut 20A, 20B screw joint 20B threaded joint 30A, 30B screw joint 31 Male thread 35 female thread 40A, 40B screw joint 50 Threaded joint 51 Male thread 51M,55M screw thread 51G, 55G screw groove 55 female thread M11A,M11B screw thread M21A,M21B screw thread M31A,M31B screw thread M41A,M41B screw thread NA normal area OP hydraulic RA adjustment area RL reference line SL11 Slit SL21, SL22, SL23, SL24 slits SL31, SL32, SL33, SL34 slits SL41, SL42, SL46 slits

Claims

1. A threaded joint in which a male screw having a thread and a female screw are engaged, A threaded joint, wherein a slit is formed from the crest of the thread toward the axis on one side in the axial direction of a first thread, which is either the male thread or the female thread.

2. The slit is the depth from the top surface is gradually or continuously deeper as it approaches one side in the axial direction of the first screw; Threaded joint according to claim 1.

3. The slit is The width in the axial direction is gradually or continuously wider as it approaches one side of the axial direction of the first screw. Threaded joint according to claim 1.

4. The screw thread is a first surface facing one side of the first screw; and a second surface facing the other side opposite the one side, the second surface being on the back side of the first surface; The slit is The closer to the one side, the shorter the distance to the first surface becomes in a stepwise or continuous manner. Threaded joint according to claim 1.

5. A fastened body in which at least two members are fastened by the threaded joint according to any one of claims 1 to 5, A load is applied to the first screw and the second screw, which is the other of the male screw and the female screw, in the axial direction in opposite directions to each other, or A fastener in which the first screw and the second screw are subjected to loads in opposite directions in the axial direction and a reaction force to the loads.

6. A screw member having a male or female screw with a plurality of threads, A screw member, wherein a slit is formed from the top surface of the thread toward the axis on one side of the screw member in the axial direction.

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