Screw joint, fastener, and screw member

Abstract

To suppress a large load generated locally even in a screw having a spiral thread shape.SOLUTION: The present invention provides a screw joint in which a male screw (31, 41) and a female screw (35, 45), each having a plurality of spiral threads, mesh with each other. in the screw joint, a thread width (LM2) on one side of an axial direction of a first screw, which is either the male screw (31, 41) or the female screw (35, 45), is smaller than a thread width (LM1) on the other side excluding the one side in the axial direction, and a thread width (LM) of a second screw, which is either the male screw (31, 41) or the female screw (35, 45), is uniform.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 as the distance from the meshing start portion increases.

[0004] Furthermore, Patent Document 3 proposes a split nut portion for clamping tie rods provided at the four corners of the mold platen of a mold clamping device, particularly in an injection molding machine, die-casting machine, etc., to clamp a mold provided on the mold platen. This proposal proposes a method of reducing the load at the start of engagement and leveling the load distribution generated across the entire area of the saw teeth by making the pitches of the independent ring-shaped threads (saw teeth) at the engagement portion between the tie rod and split nut unequal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 10-281129 [Patent Document 2] Japanese Patent Application Laid-Open No. 49-30740 [Patent Document 3] Japanese Utility Model Application Laid-Open No. 2-40112 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, in Patent Documents 1 and 2, since the outer diameter of the male thread is reduced to reduce the effective diameter, the amount of thread engagement is small. Originally, the thread of the mating part should deeply penetrate into the thread groove between adjacent threads so that both threads mesh firmly and maintain a high flexural rigidity of the threads. However, if the amount of thread engagement is small and the penetration of the mating thread is shallow, the suppression of the flexural deformation of the mutual threads becomes weak and the thread rigidity becomes small. For this reason, although the threads are easily bent and the generated load itself becomes small, since the contact area between the mutual threads is also reduced, the contact stress (surface pressure) between the threads cannot be reduced. In particular, in the case of a large-diameter screw with a large thread width (thread thickness) and a large thread rigidity, only the contact area becomes small in a state where the reduction in rigidity is small, and there is a risk that the contact stress increases. Therefore, in the proposals in Patent Documents 1 and 2, there is a risk of seizure wear. In addition, the proposal of Patent Document 3 can be applied only to screws having annular serrations and cannot be applied to screws having ordinary helical threads.

[0007] As described above, an object of the present invention is to suppress a large load locally generated even in a screw having a shape of a helical thread. [Means for Solving the Problems]

[0008] The present invention relates to a screw joint in which a male screw and a female screw each having a plurality of threads are engaged with each other. The screw joint is The thread width on one side in the axial direction of the first thread, which is either a male thread or a female thread, is smaller than the thread width on the other side excluding the one side in the axial direction. The thread width of the second thread, which is either a male thread or a female thread and meshes with the first thread, is uniform.

[0009] It is preferable that the thread widths of a plurality of threads on one side are uniform or non-uniform.

[0010] The first thread of the first thread has a first surface facing one side and a second surface on the back side of the first surface and facing the other side. The first lead of the first thread on the second surface is equal to the lead of the second thread on the second thread, and in the first thread, it is preferable that the thread valley width is larger and the thread width is smaller as it is closer to one side.

[0011] The first thread of the first thread has It is preferable that the thread width gradually or continuously decreases as it approaches one side.

[0012] In the first thread, preferably, the thread width is different from one side to the other side.

[0013] The first thread of the first thread has a first surface facing one side and a second surface on the back side of the first surface and facing the other side. It is preferable that the first lead on the first surface is smaller than the second lead on the second surface.

[0014] In the first thread, the thread width on one side in the axial direction is smaller than the thread width on the other side excluding the one side in the axial direction, and it is preferable that the thread width on the other side is uniform.

[0015] There is provided a fastened body in which at least two members are fastened together using any of the above-described threaded joints. This fastener is 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 and reaction forces in opposite directions in the axial direction.

[0016] The first screw is a bolt, One side can correspond to the neck side of the bolt, and the other side can correspond to the tip side of the bolt.

[0017] The present invention provides a screw element having a multi-threaded external or internal thread. In this screw member, the thread width on one side in the axial direction is smaller than the thread width on the other side excluding the one side in the axial direction. [Effects of the Invention]

[0018] According to the present invention, even for screws having a helical thread shape, it is possible to suppress large loads that occur locally. [Brief explanation of the drawings]

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings This embodiment relates to a screw joint in which a male screw and a female screw are engaged. For example, while the thread width of the female screw is uniform, the thread width of the male screw is locally reduced. As an example, by making the thread width on one side in the axial direction smaller than the other side excluding the one side, the contact pressure between the threads of the male screw and the female screw is suppressed, so that even in a screw joint between screws having spiral threads, the load at the start of engagement on one side can be reduced, and the load distribution of the threads can be made closer to being uniform.

[0021] Hereinafter, as an example of a fastening body by a screw joint, a mold clamping device provided in an injection molding machine will be described, and then three embodiments (First A Form, First B Form, Second Form) of a conventional screw joint and the screw joint according to this embodiment will be described in order.

[0022] 〔Mold Clamping Device: Refer to FIGS. 1 and 2〕 The mold clamping device 1 is provided for clamping a pair of molds (a fixed mold and a movable mold) such as an injection molding machine. The mold clamping device 1 clamps the fixed mold and the movable mold by applying a clamping force between a fixed mold plate that holds the fixed mold and a movable mold plate that holds the movable mold.

[0023] As shown in FIGS. 1 and 2, the mold clamping device 1 according to this embodiment includes a base 10, a fixed mold plate 11 fixed to the base 10, and a movable mold plate 12 provided on the base 10 so as to be movable forward and backward with respect to the fixed mold plate 11. Further, the mold clamping device 1 includes tie bars 15A, 15B, 15C, 15D provided across the fixed mold plate 11 and the movable mold plate 12, movable mold plate moving means 18 for moving the movable mold plate 12 forward and backward, and a split nut opening / closing device 20 engaged with the tie bars 15A, 15B, 15C, 15D when clamping the mold. In the mold clamping device 1, it is assumed that the vertical direction V and the horizontal direction H are defined as shown in FIGS. 1 and 2. Further, the front (F) and the rear (R) are defined as shown in FIGS. 1 and 2.

[0024] [Fixed mold plate 11, movable mold plate 12] As shown in FIGS. 1 and 2, the fixed mold plate 11 is provided on one end side of the base 10 in the horizontal direction H, and the movable mold plate 12 is slidable with respect to the base 10 and is provided facing the fixed mold plate 11. In the fixed mold plate 11 and the movable mold plate 12, the surfaces facing each other are referred to as front surfaces 11A, 12A, and the surfaces facing the front surfaces 11A, 12A are referred to as back surfaces 11B, 12B.

[0025] The fixed mold plate 11 holds a fixed mold 13 on the front surface 11A, and the movable mold plate 12 holds a movable mold 14 on the front surface 12A. Cavities for supplying molten material are formed inside the fixed mold 13 and the movable mold 14, respectively. The illustration of the cavities is omitted. 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 device, the molten material is made of molten metal such as an aluminum alloy.

[0026] The fixed platen 11 and the movable platen 12 are connected by a plurality of, particularly four tie bars 15A, 15B, 15C, 15D in this embodiment. The four tie bars 15A, 15B, 15C, 15D are arranged at the four corners when the fixed platen 11 and the movable platen 12 are viewed from the front. A sliding material for suppressing the friction between them can be interposed between the tie bars 15A, 15B, 15C, 15D and the movable platen 12.

[0027] [Tie bars 15A, 15B, 15C, 15D] As shown in FIG. 1, piston heads 16 for generating clamping force are provided at the ends on the fixed platen 11 side of the tie bars 15A to 15D. In this embodiment, the tie bars 15A to 15D and the piston heads 16 are connected by screw joints 30. In addition, ring-shaped meshing teeth 17 continuous in the circumferential direction are formed at the ends on the movable platen 12 side of the tie bars 15A to 15D. The meshing teeth 17 are meshed with the meshing teeth formed on the inner circumferences of the first split nut 21 and the second split nut 22. Thereby, the tie bars 15A to 15D are locked to the movable platen 12. Note that the meshing teeth formed on the inner circumferences of the first split nut 21 and the second split nut 22 are partially omitted from the illustration. Further, the base 10 is provided with, for example, an electric or hydraulic movable platen moving means 18, and the movable platen 12 can be reciprocally moved with respect to the fixed platen 11. FIG. 1 shows a mold closing state in which the movable platen 12 is moved in the direction of the fixed platen 11 by the movable platen moving means 18 and the movable mold 14 is brought into contact with the fixed mold 13.

[0028] As shown in FIG. 2, the screw joint 30 in the mold clamping device 1 is composed of a male screw 31 formed at the tip side of the tie bar 15A (~ 15D) and a female screw 35 formed on the piston head 16. When clamping in the clamping device 1, as shown in Fig. 2, a hydraulic pressure OP is applied to the piston head 16 constituting the hydraulic cylinder. Since the tie bars 15A to 15D are locked by the first split nut 21 and the second split nut 22 at the rear (R), a reaction force Fr due to the hydraulic pressure OP is generated in the tie bars 15A to 15D toward the rear (R). As a result, loads in opposite directions to each other are applied to the male screw 31 and the female screw 35 along the axis C. Thereby, a thread load is generated in the thread of each of the male screw 31 and the female screw 35 in the direction of the axis C.

[0029] An example of the distribution of the thread loads in the male screw 31 and the female screw 35 is shown in Fig. 2. In the conventional screw joint, the thread load at the base end side (load side) is the highest, and the thread load at the base end side is considerably larger compared to the tip side. On the other hand, the screw joint according to the embodiment can suppress the thread load at the base end side to a low level, and in addition, the difference in the thread loads between the base end side and the tip side is small. Although there is no portion corresponding to the head of the bolt on the rear (R) side of the tie bar 15A, for the sake of convenience in the expression for the tip side, it is referred to as the base end side. That is, in the present embodiment and the present invention, the base end side means the range where the thread of the female screw 35 is provided or the range where the thread of the male screw 31 meshing with the thread of the female screw 35 is provided, in the direction opposite to the tip side of the male screw 31, and is the end face or the side close to the cross section of the female screw 35, which is the surface directly loaded with the external force (tensile load Fa) that is the source of the tensile stress generated in the shaft portion of the male screw 31 or the supporting force of the initial tightening load (reaction force of the initial tightening load: tensile load Fb).

[0030] In the present embodiment, a fastening body is configured in which the tie bar 15A and the piston head 16 are fastened by a male screw 31 and a female screw 35. It is also possible to integrally form the material of the tie bar 15A and the piston head 16 and then perform necessary processing. In this case, the diameter dimension of the material in the radial direction needs to correspond to the piston head 16, and the portion corresponding to the tie bar 15A also has to have a large diameter as the material. Also, generally, the contractors who can perform forming processes such as forging, cutting, or finishing on large-diameter and long materials have different processing techniques they are good at, and the contractors who are good at each forming process are rare nationwide and are often located far apart. For this reason, when the entity that forms the material is different from the entity that forms the final shape, it is necessary to transport the material over a long distance. On the other hand, if the separately manufactured tie bar 15A and piston head 16 are joined by a screw joint 30 of separate members, the material cost and the long-distance transportation cost can be reduced.

[0031] 〔Conventional screw joint 50: FIG. 7〕 In the conventional screw joint 50, the lead of the thread 53 of the male screw 51 is equal to the lead of the thread 57 of the female screw 55 at L1. In addition, over the entire area where the screw is formed, the width of the thread 53 of the male screw 51 is equal to the width of the thread groove 54, and the width of the thread 53 is uniform, and the width of the thread groove 54 is also uniform. Also, over the entire area where the screw is formed, the width of the thread 57 of the female screw 55 is equal to the width of the thread groove 58, and the width of the thread 57 is uniform, and the width of the thread groove 58 is also uniform. Note that the place where the thread width and the groove width are equal is referred to as the reference line RL, and the reference line RL shown in the embodiment described below indicates the place where the thread width and the groove width are equal in the conventional screw joint 50.

[0032] In the 1A form, 1B form, and 2 form described below, the specifications (shape, dimensions) of the female screw are the same as those of the conventional one, while the specifications of the male screw 51 are adjusted. The region in the male screw in which this adjustment is achieved is called the adjustment region RA, and the other regions are called the normal regions NA. The screw threads 53 and 57 are each connected in a spiral shape, and the screw grooves 54 and 58 are also connected in a spiral shape. Although not mentioned in the first A, first B, and second embodiments described below, the screw threads and screw grooves are connected in a spiral shape. The right-hand diagram in Fig. 7 shows the ridge lines (a1, d1...) and valley lines (b1, c1...) in the cross section of the thread (thread groove). The developed views of the male threads in Form 1A, Form 1B, and Form 2 are obtained by linearly developing the ridge lines and valley lines in Fig. 7.

[0033] [Type 1A: See Figures 3 and 6] [Configuration of screw joint 30A] In a threaded joint 30A according to the 1Ath embodiment, the male thread 31A and the female thread 35 have the same lead L1. However, the lead of the female thread 35 is equal to the lead of the male thread 31A on the pull surface TS.

[0034] The threads of the male screw 31A are designated M11, M12, M13, M14, M15, and M16 in order from the base to the tip. The grooves of the male screw 31A are designated G11, G12, G13, G14, G15, and G16 in order from the base to the tip. The threads M11 and M12 and the groove G11 are included in the adjustment region RA, while the other threads M13 to M16 and grooves G12 to G16 are included in the normal region NA. The dimensions of each are as described below. Although the threads are connected in the direction of the axis C, they are designated M11 and so on to distinguish between the threads shown in the cross section. The same applies to the grooves.

[0035] The threads of the female screw 35 are designated M51, M52, M53, M54, M55, and M56 in order from the base to the tip. The grooves of the female screw 35 are designated G51, G52, G53, G54, G55, and G56 in order from the base to the tip. The same specifications as those for the threads M13 to M16 and thread grooves G12 to G16 in the normal region NA are applied to the threads M51 to M56 and thread grooves G51 to G56.

[0036] In the adjustment region RA, the thread widths of both the thread M11 and the thread M12 are equal to LM2. Also, in the adjustment region RA, if the groove width of the thread groove G1 between the thread M11 and the thread M12 is LG2, the thread width LM2 is smaller than the groove width LG2. That is, the adjustment region RA satisfies the following formula (1). Similarly, the thread width LM2 is smaller than the groove widths in the thread grooves G51 and G52 of the female thread 35. Here, the thread width and the groove width refer to the dimensions in the direction of the axis C on the reference line RL of the female thread 35. LM2 < LG2 … Formula (1)

[0037] A gap is shown between the thread M11 of the male thread 31A and the thread M51 of the female thread 35 located on the base side facing the thread M11, and between the thread M12 of the male thread 31A and the thread M52 of the female thread 35 located on the base side facing the thread M12. This gap is for clarifying that the formula (1) is satisfied in the adjustment region RA, and it does not mean that the dimension of the shown gap (the size ratio of the thread width and the groove width) is reflected in the actual screw joint 30A.

[0038] Next, in the normal region NA, the thread widths of the threads M13, M14, M15, and M16 are equal to LM1. Also, the groove widths of the thread grooves G12, G13, G14, and G15 are equal to LG1. And the thread width LM1 and the groove width LG1 are equal and equal to 1 / 2 of the lead L1. That is, the normal region NA satisfies the following formula (2). LG1 = LM1 = 1 / 2·L1 … Formula (2)

[0039] Here, through the adjustment region RA and the normal region NA, the lead on the trailing side surface TS of the male screw 31A is constant at L1, and this lead L1 is equal to the lead of the female screw 35. Also, although the lead on the pressing side surface PS of the male screw 31A has a crest width LM2 smaller than the crest width LM1, the lead on the pressing side surface PS of the adjustment region RA of the male screw 31A is equal to the lead of the normal region NA. The pressing side surface PS corresponds to the first surface of the present invention, and the trailing side surface TS corresponds to the second surface of the present invention. Note that the pressing side surface in the present embodiment is the surface that supports the external force when an external force is applied to the screw, that is, the surface where the pressing force increases as the external force increases, and the trailing side surface indicates the surface on the opposite side of the pressing side surface in one thread crest.

[0040] Furthermore, since the lead L1 is constant and the crest width LM2 is smaller than the crest width LM1, the groove width LG2 sandwiched between the pressing side surface PS of the thread crest M12 and the trailing side surface TS of the thread crest M11 is larger than the groove width LG1 sandwiched between the pressing side surface PS of the thread crest M13 and the trailing side surface TS of the thread crest M12. When organizing this relationship and equations (1) and (2), the adjustment region RA and the normal region NA satisfy the following relationship of equation (3). LM2 < LM1 = LG1 = 1 / 2·L1 < LG2 …(3)

[0041] Regarding the female screw 35, although the illustration is omitted, the crest width of the thread crest and the groove width of the thread groove are equal to the same LM1 and LG1 as the normal region NA of the male screw 31A.

[0042] Referring to the developed view of the screw joint 30A (male screw 31A) shown in FIG. 6, by displacing the ridge line c1 and the valley line d1 away from the ridge line a1 and the valley line b1 with the bending site BA as the boundary, the relationship of equation (3) can be satisfied.

[0043] As described above, the screw joint 30A has the following configuration. The thread width of the male thread 31A, which is the first screw, is locally reduced, and the thread width of the female thread 35, which is the second screw, is uniform. In particular, for the male thread 31A, the thread width LM2 in the adjustment region RA on one side in the direction of the axis C is smaller than the thread width LM1 in the normal region NA on the other side in the direction of the axis C. In addition, the threads M11 and M12 in the adjustment region RA have a uniform thread width LM2.

[0044] [Function / Effect of the Screw Joint 30A] The screw joint 30A provides an adjustment region RA that satisfies equation (1). Therefore, a minute gap is provided between the thread M11 of the male thread 31A in the adjustment region RA and the thread M51 of the female thread 35 located on the head side facing the thread M11, and between the thread M12 of the male thread 31A and the thread M52 of the female thread 35 located on the head side facing the thread M12, or even if the threads are in contact, the pressure due to the contact can be made minute. As a result, for example, when the male thread 31A receives a tensile load Fa on one side in the direction of the axis C and the female thread 35 receives a tensile load Fb (the reaction force of the tensile load Fa) on the other side in the direction of the axis C, the contact pressure between the threads in the adjustment region RA can be reduced. Thus, according to the screw joint 30A, the load generated on the entire thread can be leveled. In particular, since the outer diameter ΦD of the male thread 31A is the same in the adjustment region RA and the normal region NA, the contact area with the thread of the female thread 35 can be made the same for all threads, so that the generated surface pressure can be reduced.

[0045] Also, in the male thread 31A, the closer to the head side where a strong thread load is generated, which is located closer to the part where the tensile load Fa is applied, the smaller the thread width is, so that the bending rigidity of the thread decreases and deformation becomes easier. Since a high stress is absorbed by this deformation, it is possible to further promote the reduction of the load generated on the head side. Furthermore, by providing a normal region NA where the thread width is not reduced, particularly at the tip end of the normal region NA, sufficient screw engagement (screw support) is possible at the tip end even when the load is relatively small, preventing the screw from rattling and ensuring sufficient screw tightening force (screw fixing force).

[0046] Furthermore, the thread width LM1 of the male thread 31A in the normal region NA is equal to or close to the thread width of the threads M51, M52... of the female thread 35. This makes it possible to align the axis C of one thread with the axis C of the other thread when the male thread 31A and the female thread 35 are engaged. This makes it possible to make the minute gap between the threads of the male thread 31A and the threads of the female thread 35 approximately uniform and without variation in the circumferential direction in the adjustment region RA where the thread width of the male thread 31A is small. This prevents the threads from locally or unevenly contacting each other in the adjustment region RA, making it possible to effectively obtain the effects of this embodiment without variation.

[0047] Furthermore, in conventional threaded joints 50, if the number of threads that share the load is increased and the thread engagement length is lengthened, the concentrated load on the base side can be reduced. In contrast, with Form 1A, the load is prevented from concentrating on the threads that belong to the adjustment region RA, and the load can be distributed evenly to the threads, so there is no need to increase the number of threads. As a result, with Form 1A, the thread engagement length can be shortened, which shortens the dimension of the screw member in the direction of the axis C, thereby saving space and reducing costs.

[0048] [Type 1B: See Figures 4 and 6] Next, a threaded joint 30B according to Mode 1B will be described with reference to Fig. 4. In the threaded joint 30B, the same elements as those in the threaded joint 30A will be given the same reference numerals as in Fig. 3, and the description thereof may be omitted.

[0049] The thread joint 30B has an adjustment range RA that is wider toward the tip side than the thread joint 30A. That is, the specifications of the thread groove G12 and the thread M13 of the thread joint 30B are also adjusted. The groove width LG3 of the thread groove G12 and the thread width LM3 of the thread M13 satisfy the relationship of the following formula (4). As is clear from formula (4), in the screw joint 30B, from the normal region NA to the adjustment region RA, the thread width of the male thread 31B gradually decreases, such as LM1, LM3, and LM2. Further, since the lead L1 of the trailing side surface TS is constant, the groove width of the thread groove sandwiched between the pressing side surface PS of the thread located on the tip side of the male thread 31B and the trailing side surface TS of the thread located on the base side gradually increases. In particular, in the adjustment region RA, the thread width of the male thread 31B decreases in two steps. LM2 < LM3 < LM1 = LG1 = 1 / 2·L1 < LG3 < LG2 …(4)

[0050] Refer to the developed view of the screw joint 30B (male thread 31B) shown in FIG. 6. By providing two bending portions BA1 and BA2 for each of the valley line c1 and the ridge line d1, the relationship of formula (4) can be satisfied.

[0051] In addition to having the same effect as the screw joint 30A, the screw joint 30B has the following effect. That is, from the normal region NA to the adjustment region RA of the screw joint 30B, the thread width of the male thread 31B gradually decreases corresponding to the generated load distribution, so that the distribution of the thread load can be made more uniform than that of the screw joint 30A.

[0052] 〔Second form: Refer to FIGS. 5 and 6〕 Next, the screw joint 40 according to the second form will be described with reference to FIGS. 5 and 6. The screw joint 40 according to the second form continuously changes the thread width and the groove width over the entire region from the tip side to the base side. For this purpose, the screw joint 40 employs different leads on the pressing side surface PS and the trailing side surface TS of the thread in the male thread 41. Specifically, the lead L2 on the pressing side surface PS of each of the threads M11 to M16 is made smaller than the lead L1 on the trailing side surface TS of each of the threads M11 to M16. That is, the male thread 41 of the screw joint 40 satisfies the relationship of the following formula (5). The female thread 45 of the screw joint 40 has a constant lead L1, similar to the female threads 35 of the screw joints 30A and 30B. L1 > L2 … Equation (5)

[0053] As a result, for example, as the distances between the ridge line d1 and the ridge line a2 and between the valley line c1 and the valley line b2 in the direction of the axis C gradually decrease continuously as approaching the base side, the thread widths LM1 to LM6 of the male thread 41 satisfying Equation (5) satisfy the relationship of the following Equation (6). Conversely, for example, as the distances between the ridge line d1 and the ridge line a1 and between the valley line c1 and the valley line b1 in the direction of the axis C gradually increase continuously as approaching the base side, the thread grooves G11 to G16 satisfy the relationship of the following Equation (7).

[0054] LM1 < LM2 < LM3 < LM4 < LM5 < LM6 < ~ ≦ 1 / 2·L1 … Equation (6) LG1 > LG2 > LG3 > LG4 > LG5 > LG6 > ~ ≧ 1 / 2·L1 … Equation (7)

[0055] According to the screw joint 40, by satisfying Equation (6) and Equation (7), the thread width can be continuously gradually decreased from the tip side toward the base side, and the thread width can be continuously gradually increased from the tip side toward the base side. Therefore, according to the screw joint 40, the thread loads generated in the entire region where the threads of the male thread 41 and the female thread 35 are formed can be smoothly leveled.

[0056] As described above, the preferred embodiments of the present invention have been described. However, in addition to the above, as long as the gist of the present invention is not deviated from, it is possible to select the configurations exemplified in the above embodiments or to appropriately change them to other configurations. For example, a mode combining the first form and the second form may be adopted. Specifically, in the first B form, an example is shown in which, for each of the valley line c1 and the ridge line d1, while the lead L1 remains constant, the thread width of the male thread 31B gradually decreases as LM1, LM3, and LM2. Not limited to this example, for each of the valley line c1 and the ridge line d1, the leads may be changed stepwise as L2 and L3 smaller than the lead L1 as in the second form. 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. Instead of changing the lead stepwise, the lead may be continuously and gradually decreased in a parabolic shape from the tip side toward the base side.

[0057] Also, in this embodiment, an example is shown in which the valley line c1 and the ridge line d1 are brought closer to the valley line b1 and the ridge line a1 so that a gap is formed between the pressing side surface PS of the male screw 41 and the female screw 45 and between the pressing side surface PS of the male screw 41 and the female screw 45, thereby making the thread widths LM2 and LM3 smaller than LM1. Not limited to this example, with the positions of the valley line c1 and the ridge line d1 remaining such that no gap is formed between the pressing side surface PS of the male screw 41 and the female screw 45 and between the pressing side surface PS of the male screw 41 and the female screw 45, the valley line b1 and the ridge line a1 may be brought closer to the valley line c1 and the ridge line d1 to make the thread widths LM2 and LM3 smaller than LM1. In this case, since no gap is generated between the pressing side surface PS of the male screw 41 and the female screw 45 and between the pressing side surface PS of the male screw 41 and the female screw 45, the stress reduction effect for a large load is slightly inferior compared to when the gap is formed, but by reducing the thread width to decrease the rigidity of the thread, it is expected that the generated stress can be reduced under a medium load.

[0058] [Load pattern to which the present invention is applied: See FIG. 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, loads Fa and Fb1 are applied in opposite directions to the bolt B and the nut N, respectively, as shown in FIG. 8(a). The load Fa 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.

[0059] 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 Fb2 of the load Fa 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 Fa is applied to the bolt B, a reaction force Fb3 is generated in the non-fastened portion N2 toward the front (F). In response to this reaction force Fb3, a reaction force Fb4 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.

[0060] In summary, the load patterns to which the present invention is applicable are as follows: First load pattern: Loads Fa and Fb are applied in opposite directions to each other between the male screw (bolt) and the female screw (nut). Second load pattern: A load Fa (Fb) is applied to one of the male screw (bolt) and the female screw (nut), and a reaction force Fb (Fa) due to the load Fa (Fb) is applied to the other of the male screw (bolt) and the female screw (nut).

[0061] [Screw to which this embodiment is applied] In the above first A form, first B form, and second form, examples of applying the present invention to the male screw (31, 41) were shown. However, the present invention is not limited to this, and the present invention can be applied to the female screw (35, 45).

[0062] [Fastener to which this embodiment is applied] In the above first A form, first B form, and second form, a tie bar and a piston rod were exemplified as fasteners by a screw joint. However, the fastener of the present invention is not limited to this. Although bolts and screws have been described above, the present invention can be applied to various fasteners in which a male screw is formed on one member and a female screw that meshes with the male screw of the one member is formed on the other member. In particular, the present invention is suitable for splitting an integrally formed product having different dimensions into two members and fastening them by a screw joint, such as a tie bar and a piston rod.

[0063] [Position of gap] In the above first A form, first B form, and second form, examples are shown in which a gap is provided between the pressing surface PS of the male screw 31 and the female screw 35 and a gap is provided between the pressing surface PS of the male screw 41 and the female screw 45. However, the present invention is not limited to this. A gap may be provided between the pulling surface TS and the female screw 35, and a gap may be provided between the pulling surface TS and the female screw 45.

Explanation of reference numerals

[0064] 1 Type tightening device 10 Base 11 Fixed mold plate 12 Movable mold plate 11A, 12A Front surface 11B, 12B Rear surface 13 Fixed Mold 14 Movable Mold 15A, 15B, 15C, 15D Tie Bars 16 Piston Head 17 Engaging Teeth 18 Movable Mold Plate Movement Means 20 Split Nut Opening / Closing Device 21 First Split Nut 22 Second Split Nut 30, 30A, 30B Threaded Joints 31A, 31B Male Threads 35 Female Thread 40 Threaded Joint 41 Male Thread 45 Female Thread 50 Threaded Joint 51 Male Thread 53 Thread Pitch 54 Thread Groove 55 Female Thread 57 Thread Pitch 58 Thread Groove M11, M12, M13, M14, M15, M16 Thread Pitches M51, M52, M53, M54, M55, M56 Thread Pitches LM1, LM2, LM3 Flank Width G11, G12, G13, G14, G15, G16 Thread Grooves G51, G52, G53, G54, G55, G56 Thread Grooves LG1, LG2, LG3, LG4, LG5, LG6 Groove Width RA Adjustment Region NA Normal Region PS Pressing Side Surface TS Pulling Side Surface a1, a2, a3, d1, d2 Ridge Lines b1, b2, b3, c1, c2 Valley Lines BA, BA1, BA2 Bending Parts N1 Fastening Part N2 Non - fastening Part OP Hydraulic Pressure RL Reference Line V Vertical Direction H Horizontal Direction B Bolt C-axis

Claims

1. A screw joint in which a male screw and a female screw each having a plurality of helical threads are engaged with each other, wherein a thread width on one side in the axial direction of a first screw, which is either the male screw or the female screw, is smaller than a thread width on the other side excluding the one side in the axial direction, and the screw joint, wherein the other screw, which is either the male screw or the female screw and is engaged with the first screw, has a uniform thread width.

2. The thread widths of the plurality of threads on the one side are uniform or non-uniform, The screw joint according to Claim 1.

3. The first thread of the first screw comprises a first surface facing the one side and a second surface on the back side of the first surface and facing the other side, wherein a first lead of the first thread on the second surface is equal to a lead of a second thread on the second screw, and in the first screw, the closer to the one side, the larger the thread groove width and the smaller the thread width, The screw joint according to Claim 2.

4. In the first screw, the thread width varies from the one side toward the other side, The screw joint according to Claim 2.

5. The first thread of the first screw comprises a first surface facing the one side and a second surface on the back side of the first surface and facing the other side, wherein a first lead on the first surface is smaller than a second lead on the second surface, The screw joint according to Claim 4.

6. The first thread of the first screw is such that the thread width gradually or continuously decreases as it approaches the one side, The screw joint according to Claim 5.

7. In the first screw, the thread width on the other side is uniform, The screw joint according to Claim 1.

8. A fastening body in which at least two members are fastened by the screw joint according to any one of Claims 1 to 7, wherein either a load in the axial direction opposite to each other is applied to the first screw and the second screw, or a load in the axial direction opposite to each other and a reaction force of the load are applied to the first screw and the second screw.

9. The first screw is a bolt, wherein the one side in the axial direction corresponds to the neck side of the bolt, and the other side excluding the one side in the axial direction corresponds to the tip side of the bolt, The fastening body according to Claim 8.

10. A screw member having a male screw or a female screw with a plurality of threads, A screw member in which a thread width on one side in the axial direction is smaller than a thread width on the other side excluding the one side in the axial direction.

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