fastener

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 screw joint in which a male screw and a female screw are engaged with each other.

Background Art

[0002] In a screw joint that has been generally used conventionally, the male screw and the female screw that mesh with each other are based on the concept of making the effective diameters and pitches of both screws equal. In this conventional screw joint, generally, the cross-sectional area of the male screw is overwhelmingly smaller than that of the female screw. Therefore, deformation in a state where the male screw and the female screw are tightened and an external force is applied occurs almost entirely on the male screw side, and it is known that, within a range of several threads counted from the starting portion of the engagement between the male screw and the female screw, about 80% of the total thread load is borne. That is, the load and stress distribution in the tightened state of the male screw and the female screw are concentrated in a small part on the load side. Therefore, statically, it breaks from the starting portion of the engagement of the screw with high stress.

[0003] On the other hand, in Patent Document 1 and Patent Document 2, in order to prevent breakage at the starting portion of engagement, a method is adopted in which the effective diameter around the starting portion of engagement is reduced and the effective diameter is enlarged as the distance from the starting portion of engagement increases.

[0004] Further, in Patent Document 3, a proposal is made regarding a split nut portion for gripping tie rods provided at the four corners of a mold plate of a mold clamping device such as an injection molding machine or a die casting machine and clamping a mold provided on the mold plate. This proposal suggests a method of reducing the load at the starting portion of engagement and equalizing the load distribution generated over the entire area of the serrated teeth by making the pitches of the independent ring-shaped screw threads (serrated teeth) at the engagement portion between the tie rod and the split nut unequal.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, Patent Documents 1 and 2 reduce the outer diameter of the male screw in order to reduce the effective diameter, resulting in less thread engagement. Ideally, the threads of the mating thread should deeply engage in the groove between adjacent threads, ensuring a tight meshing and maintaining high thread rigidity. However, if the thread engagement is small and the mating thread does not engage deeply, the restraint on the bending deformation of the threads weakens, reducing the thread rigidity. As a result, the threads become more prone to bending, and the generated load itself decreases, but because the contact area between the threads is also reduced, the contact stress (surface pressure) between the threads cannot be reduced. In particular, in the case of large-diameter screws with a large thread width (thickness) and high thread rigidity, the contact area decreases while the reduction in rigidity is minimal, potentially leading to an increase in contact stress. Therefore, the proposals in Patent Documents 1 and 2 carry the risk of adhesive wear. Furthermore, the proposal in Patent Document 3 is only applicable to screws having annular sawtooth teeth and cannot be applied to screws having ordinary helical threads.

[0007] Therefore, the present invention aims to suppress large localized loads even in screws having a helical thread shape. [Means for solving the problem]

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

[0009] It is preferable that the thread widths of the multiple threads on one side are either uniform or uneven.

[0010] The first thread of the first screw is It comprises a first surface facing one side and a second surface that is the reverse side of the first surface and faces 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 screw, and In the first screw, It is preferable that the thread root width is larger and the thread width is smaller closer to one side.

[0011] The first thread of the first screw is It is preferable that the thread width decreases gradually or continuously as you approach one side.

[0012] In the first screw, preferably, The thread width differs from one side to the other.

[0013] The first thread of the first screw is It comprises a first surface facing one side and a second surface that is the reverse side of the first surface and faces 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 screw, The thread width on one side in the axial direction is smaller than the thread width on the other side excluding that side in the axial direction, and It is preferable that the thread width on the other side is uniform.

[0015] There is provided a fastening body in which at least two members are fastened by any one of the above-mentioned screw joints. This fastening body is configured such that a load in which the first screw and the second screw are opposite to each other in the axial direction is applied, or a load in which the first screw and the second screw are opposite to each other in the axial direction and a reaction force of the load are applied.

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

[0017] The present invention provides a screw member having a male screw or a female screw with a plurality of threads. 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.

Advantages of the Invention

[0018] According to the present invention, even a screw having a helical thread shape can suppress a large locally generated load.

Brief Description of the Drawings

[0019] [Figure 1] It is a longitudinal section showing a schematic configuration of a mold clamping device according to an embodiment. [Figure 2] It is a longitudinal section showing a main part of a mold clamping device having a screw joint according to an embodiment. [Figure 3] It is a longitudinal sectional view showing a main part of a screw joint according to the first A form. [Figure 4] It is a longitudinal sectional view showing a main part of a screw joint according to the first B form. [Figure 5] It is a longitudinal sectional view showing a main part of a screw joint according to the second form. [Figure 6] It is a developed view of the thread of the male screw in each of the screw joint according to the first A form, the screw joint according to the first B form, and the screw joint according to the second form. [Figure 7]This diagram illustrates the positions of the key parts of a conventional screw joint, specifically the longitudinal cross-sectional view and the unfolded view shown in Figure 6. [Figure 8] This figure shows an example of a screw fitting to which the present invention is applied. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described below with reference to the attached drawings. This embodiment relates to a screw joint in which a male screw and a female screw mesh together. 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, the contact pressure between the threads of the male and female screws is reduced. This reduces the load at the beginning of the meshing on one side, even in a screw joint between screws with helical threads, and makes the load distribution of the threads more uniform.

[0021] The following describes a clamping device installed in an injection molding machine as an example of a fastening body using screw joints, and then describes conventional screw joints and three embodiments of the screw joint according to this embodiment (1A form, 1B form, and 2nd form) in order.

[0022] [Clamping device: See Figures 1 and 2] The mold clamping device 1 is provided for clamping a pair of molds (a fixed mold and a movable mold) in an injection molding machine or the like. The mold clamping device 1 clamps the fixed mold and the movable mold by applying a clamping force between the fixed mold plate that holds the fixed mold and the movable mold plate that holds the movable mold.

[0023] As shown in Figures 1 and 2, the mold clamping device 1 according to this embodiment comprises 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 relative to the fixed mold plate 11. The mold clamping device 1 also comprises tie bars 15A, 15B, 15C, and 15D provided across the fixed mold plate 11 and the movable mold plate 12, a movable mold plate moving means 18 for moving the movable mold plate 12 forward and backward, and a split nut opening and closing device 20 that engages with the tie bars 15A, 15B, 15C, and 15D when clamping the mold. In the clamping device 1, the vertical direction V and the horizontal direction H are defined as shown in Figures 1 and 2. Furthermore, the front (F) and rear (R) directions are defined as shown in Figures 1 and 2.

[0024] [Fixed mold board 11, movable mold board 12] As shown in Figures 1 and 2, the fixed platen 11 is provided on one end of the base 10 in the horizontal direction H, and the movable platen 12 is provided so as to be slidable relative to the base 10 and facing the fixed platen 11. In the fixed platen 11 and the movable platen 12, the faces that face each other are called the front faces 11A and 12A, and the faces that face the front faces 11A and 12A are called the back faces 11B and 12B.

[0025] The fixed mold plate 11 holds the fixed mold 13 on its front surface 11A, and the movable mold plate 12 holds the movable mold 14 on its front surface 12A. Cavities into which molten material is supplied are formed inside both the fixed mold 13 and the movable mold 14. The cavities are not shown in the illustration. When the clamping device 1 is used in an injection molding machine, the molten material consists of molten resin, and when the clamping device 1 is used in a die-casting machine, the molten material consists of molten metal such as aluminum alloy.

[0026] The fixed platen 11 and the movable platen 12 are connected by multiple tie bars, specifically four tie bars 15A, 15B, 15C, and 15D in this embodiment. When viewed from the front, the four tie bars 15A, 15B, 15C, and 15D are positioned at the four corners of the fixed platen 11 and the movable platen 12. A sliding material can be interposed between the tie bars 15A, 15B, 15C, and 15D and the movable platen 12 to reduce friction between them.

[0027] [Tie bar 15A, 15B, 15C, 15D] As shown in Figure 1, the tie bars 15A to 15D are provided with piston heads 16 for generating clamping force at the ends facing the fixed mold plate 11. In this embodiment, the tie bars 15A to 15D and the piston heads 16 are connected by screw couplings 30. In addition, the tie bars 15A to 15D have ring-shaped meshing teeth 17 that are arranged in a circumferential direction at the ends facing the movable mold plate 12. The meshing teeth 17 engage with the meshing teeth formed on the inner circumference of the first split nut 21 and the second split nut 22. As a result, the tie bars 15A to 15D are locked to the movable mold plate 12. Note that some of the meshing teeth formed on the inner circumference of the first split nut 21 and the second split nut 22 are not shown in the figure. Furthermore, the base 10 is provided with, for example, an electrically operated or hydraulically operated movable mold platen moving mechanism 18, which allows the movable mold platen 12 to reciprocate relative to the fixed mold platen 11. Figure 1 shows the mold closed state in which the movable mold platen 12 is moved toward the fixed mold platen 11 by the movable mold platen moving mechanism 18, and the movable mold 14 is in contact with the fixed mold 13.

[0028] As shown in Figure 2, the screw joint 30 in the clamping device 1 is composed of a male thread 31 formed on the tip side of the tie bar 15A (~15D) and a female thread 35 formed on the piston head 16. When clamping the mold in the clamping device 1, hydraulic pressure OP is applied to the piston head 16 that constitutes the hydraulic cylinder, as shown in Figure 2. Since the tie bar 15A (~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 on the tie bar 15A (~15D) towards the rear (R). As a result, the male screw 31 and the female screw 35 are subjected to loads in opposite directions along the axis C. Consequently, thread loads are generated on the threads of the male screw 31 and the female screw 35 in the direction of the axis C.

[0029] Figure 2 shows an example of the thread load distribution in the male thread 31 and female thread 35. In conventional screw joints, the thread load is highest on the neck side (load side), and the thread load on the neck side is considerably larger than that on the tip side. In contrast, the screw joint according to this embodiment can keep the thread load on the neck side low, and the difference in thread load between the neck side and the tip side is small. Note that there is no part on the rear (R) side of the tie bar 15A that corresponds to the head of a bolt, but for convenience, it is referred to as the neck side in relation to the tip side. In other words, in this embodiment and the present invention, the neck side refers to the side of the female screw 35 that is opposite to the tip side of the male screw 31 and is closer to the end face or cross-section of the female screw 35, which is the surface to which the external force (tensile load Fa) that is the source of 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) is directly applied.

[0030] In this embodiment, the tie bar 15A and the piston head 16 are fastened together by a male screw 31 and a female screw 35. The tie bar 15A and the piston head 16 can also be manufactured by forming the material as a single unit and then performing the necessary processing. In this case, the radial dimensions of the material must correspond to those of the piston head 16, and the portion corresponding to the tie bar 15A must also be large in diameter. Furthermore, generally, companies capable of forming large-diameter and long materials, such as forging, cutting, or finishing, each have different areas of expertise, and companies specializing in each type of forming process are rare nationwide and are often located far apart. Therefore, when the entity that forms the material and the entity that forms the final shape are different, the material needs to be transported over long distances. In contrast, by joining the tie bar 15A and the piston head 16, which are manufactured separately, with a separate screw joint 30, material costs and long-distance transportation costs can be reduced.

[0031] [Conventional screw fitting 50: Figure 7] In a conventional screw joint 50, the lead of the thread 53 of the male screw 51 and the lead of the thread 57 of the female screw 55 are equal at L1. In addition, throughout the entire area where the thread is formed, the width of the thread 53 of the male screw 51 and the groove width of the thread groove 54 are equal, and the width of the thread 53 is uniform, as is the groove width of the thread 53. Furthermore, throughout the entire area where the thread is formed, the width of the thread 57 of the female screw 55 and the groove width of the thread groove 58 are equal, and the width of the thread 57 is uniform, as is the groove width of the thread groove 58. The point where the thread width and groove width are equal is referred to as the reference line RL, and the reference line RL shown in the embodiments described below indicates the point where the thread width and groove width are equal in a conventional screw joint 50.

[0032] In the first A form, first B form, and second form described below, the specifications (shape, dimensions) of the female thread remain the same as before, while the specifications of the male thread 51 are adjusted. The area of ​​the male thread in which this adjustment is made is called the adjustment area RA, and the other area is called the normal area NA. The screw threads 53 and 57 are connected in a helical pattern, and the screw grooves 54 and 58 are also connected in a helical pattern. In the first A form, first B form, and second form described below, the screw threads and screw grooves are connected in a helical pattern. Note that the right-hand diagram in Figure 7 shows the ridges (a1, d1…) and valleys (b1, c1…) in the cross-section of the screw thread (screw groove). The unfolded diagrams of the male screw in the 1A, 1B, and 2 forms are obtained by unfolding the ridges and valleys in Figure 7 in a straight line.

[0033] [Form 1A: See Figures 3 and 6] [Configuration of threaded fitting 30A] In the screw joint 30A according to the first A form, the leads of the male thread 31A and the female thread 35 are equal at L1. However, the lead of the female thread 35 is equal to the lead of the male thread 31A on the pull side TS.

[0034] The threads of the male screw 31A are designated M11, M12, M13, M14, M15, and M16, respectively, from the neck end to the tip end. Similarly, the grooves of the male screw 31A are designated G11, G12, G13, G14, G15, and G16, respectively, from the neck end to the tip end. Of these, threads M11 and M12 and groove G11 are included in the adjustment region RA, while the remaining threads M13 to M16 and grooves G12 to G16 are included in the normal region NA. Their respective dimensions are described below. Note that although the threads are continuous in the direction of axis C, they are designated as M11, etc., to distinguish each thread as shown in the cross-section. The same applies to the grooves.

[0035] The threads of the female screw 35 are designated as M51, M52, M53, M54, M55, and M56, respectively, from the neck end to the tip end. The screw grooves of the female screw 35 are designated as G51, G52, G53, G54, G55, and G56, respectively, from the neck end to the tip end. For screw threads M51-M56 and screw grooves G51-G56, the same specifications as for screw threads M13-M16 and screw grooves G12-G16 in the normal NA range apply.

[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 screw 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 screw 35. LM2 < LG2 … Formula (1)

[0037] A gap is shown between the thread M11 of the male screw 31A and the thread M51 of the female screw 35 located on the base side and facing the thread M11, and between the thread M12 of the male screw 31A and the thread M52 of the female screw 35 located on the base side and facing the thread M12. This gap is for clarifying that the formula (1) is satisfied in the adjustment region RA, and 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, throughout the adjustment region RA and the normal region NA, the lead on the pull side TS of the male screw 31A is constant at L1, and this lead L1 is equal to the lead L1 of the female screw 35. Also, although the thread width LM2 on the push side PS of the male screw 31A is smaller than the thread width LM1, the lead on the push side PS of the male screw 31A in the adjustment region RA is equal to the lead in the normal region NA. The push side PS corresponds to the first surface of the present invention, and the pull side TS corresponds to the second surface of the present invention. In this embodiment, the push side is the surface that supports the external force when an external force is applied to the screw, that is, the surface on which the pressing force increases as the external force increases, and the pull side is the surface opposite the push side in a single screw thread.

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

[0041] Although not shown in the illustration, the thread width and groove width of the female thread 35 are equal to the normal region NA of the male thread 31A, with LM1 and LG1 being the same.

[0042] Refer to the unfolded view of the screw joint 30A (male thread 31A) shown in Figure 6. By displacing the valley line c1 and ridge line d1 so that they are separated from the ridge line a1 and valley line b1 with respect to the bending point BA, the relationship in equation (3) can be satisfied.

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

[0044] [The function / effect of screw fitting 30A] The screw fitting 30A is provided with an adjustment region RA that satisfies equation (1). Therefore, a minute gap is provided between the thread M11 of the male screw 31A and the thread M51 of the female screw 35 located opposite to thread M11 on the neck side in the adjustment region RA, and between the thread M12 of the male screw 31A and the thread M52 of the female screw 35 located opposite to thread M12 on the neck side, or even if the threads are in contact with each other, the pressure due to contact can be made minute. This allows for a reduction in the contact pressure between threads in the adjustment region RA when, for example, the male thread 31A receives a tensile load Fa on one side in the direction of axis C, and the female thread 35 receives a tensile load Fb (reaction force of the tensile load Fa) on the other side in the direction of axis C. As a result, the screw joint 30A can equalize the load generated across the entire thread. 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 threads of the female thread 35 can be made the same for all threads, thereby reducing the surface pressure generated.

[0045] Furthermore, in the male screw 31A, by reducing the thread width on the neck side, which is closer to the area where the tensile load Fa is applied and where a strong thread load occurs, the bending rigidity of the thread is reduced, making deformation easier. This deformation absorbs high stress, further promoting the reduction of the load generated on the neck side. Furthermore, by providing a normal region NA, particularly at the tip, where the thread width is not reduced, even with relatively small loads, sufficient thread engagement (screw support) can be achieved at the tip, preventing looseness in the screw and ensuring sufficient fastening force (screw fixing force).

[0046] Furthermore, the thread width LM1 of the male screw 31A in the normal region NA is equal to or approximates the thread width M51, M52… of the female screw 35. This allows the axis C of one screw to be aligned with the axis C of the other screw when the male screw 31A and the female screw 35 are engaged. As a result, in the adjustment region RA where the thread width of the male screw 31A is small, the minute gap between the threads of the male screw 31A and the threads of the female screw 35 can be made approximately uniform in the circumferential direction without variation. This prevents localized or uneven contact between threads in the adjustment region RA, and the effects of this embodiment can be obtained effectively and without variation.

[0047] Furthermore, in conventional screw joints 50, increasing the number of threads that distribute the load and lengthening the thread engagement length can reduce concentrated load at the neck end. In contrast, according to the first A form, the concentration of load on the threads belonging to the adjustment region RA is suppressed, and the load can be distributed evenly across the threads, so there is no need to increase the number of threads. As a result, according to the first A form, the thread engagement length can be shortened, which reduces the dimension of the screw member in the direction of the axis C, enabling space saving and cost reduction.

[0048] [Form 1B: See Figures 4 and 6] Next, the threaded joint 30B relating to the first B form will be described with reference to Figure 4. In the threaded joint 30B, elements that are the same as those in the threaded joint 30A may be given the same reference numerals as in Figure 3 and their explanation may be omitted.

[0049] Screw fitting 30B extends the adjustment range RA towards the tip compared to screw fitting 30A. In other words, screw fitting 30B also has adjusted specifications for the screw groove G12 and screw thread M13. The groove width LG3 of screw groove G12 and the thread width LM3 of screw thread M13 satisfy the following relationship in equation (4). As is clear from equation (4), in the screw fitting 30B, the thread width of the male screw 31B decreases in stages from the normal region NA to the adjustment region RA, as LM1, LM3, and LM2. Also, since the lead L1 of the pull side TS is constant, the groove width of the screw groove sandwiched between the push side PS of the thread located on the tip side of the male screw 31B and the pull side TS of the thread located on the neck side increases in stages. In particular, in the adjustment region RA, the thread width of the male screw 31B decreases in two stages. LM2 <LM3<LM1=LG1=1 / 2·L1<LG3<LG2 …(4)

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

[0051] In addition to providing the same effects as screw fitting 30A, screw fitting 30B also provides the following effects. Specifically, in screw fitting 30B, the thread width of the male screw 31B decreases in stages in accordance with the generated load distribution from the normal region NA to the adjustment region RA, so the distribution of thread load can be smoothed out more than with screw fitting 30A.

[0052] [Second form: See Figures 5 and 6] Next, the screw joint 40 according to the second embodiment will be described with reference to Figures 5 and 6. The screw fitting 40 according to the second embodiment continuously changes the thread width and groove width over the entire area from the tip to the neck. To this end, the screw fitting 40 employs different leads in the male thread 41 for the pushing side PS and the pulling side TS of the thread. Specifically, the lead L2 on the pushing side PS of each thread M11 to M16 is made smaller than the lead L1 on the pulling side TS of each thread M11 to M16. In other words, the male thread 41 of the screw fitting 40 satisfies the relationship in equation (5) below. The female thread 45 of the screw fitting 40 has a constant lead L1, similar to the female thread 35 of the screw fittings 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 they approach 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 they approach 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 load 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 and discard the configurations exemplified in the above embodiments or appropriately change them to other configurations. For example, a combination of the first and second forms may be used. Specifically, in the first B form, an example was shown in which the thread width of the male screw 31B decreases in stages, with the lead L1 remaining constant for each of the valley line c1 and ridge line d1, as LM1, LM3, and LM2. Not limited to this example, the leads may also be set to L2 and L3, which are smaller than lead L1, as in the second form, for each of the valley line c1 and ridge line d1, and the leads may be changed in stages for each of the valley line c1 and ridge line d1. In this case, it is preferable that the relationship L2 > L3 is satisfied when the lead on the tip side is L2 and the lead on the neck side is L3. Instead of changing the leads in stages, the leads may also be continuously changed in a parabolic shape from the tip side to the neck side.

[0057] Furthermore, in this embodiment, an example was shown in which the thread widths LM2 and LM3 are made smaller than LM1 by bringing the valley line c1 and ridge line d1 closer to the valley line b1 and ridge line a1 so that there is a gap between the pressing surface PS of the male screw 41 and the female screw 45, and between the pressing surface PS of the male screw 41 and the female screw 45. Not limited to this example, the thread widths LM2 and LM3 may also be made smaller than LM1 by bringing the valley line b1 and ridge line a1 closer to the valley line c1 and ridge line d1 while keeping the positions of the valley line c1 and ridge line d1 in a position where there is no gap between the pressing surface PS of the male screw 41 and the female screw 45, and between the pressing surface PS of the male screw 41 and the female screw 45. In this case, since no gap is generated between the pressing surface PS of the male screw 41 and the female screw 45, and between the pressing surface PS of the male screw 41 and the female screw 45, the stress reduction effect for large loads is slightly inferior compared to when such a gap is generated. However, by reducing the thread width and thus the rigidity of the screw threads, it is expected that the generated stress will be reduced under medium loads.

[0058] [Applicable load patterns of the present invention: See Figure 8] Regarding the first and second embodiments, when comparing the bolt B on which the male thread 41 is formed and the nut N on which the female thread 35 is formed, as shown in Figure 8(a), loads Fa and Fb1 are applied to the bolt B and nut N, respectively, in opposite directions. Load Fa is applied to the nut N from the rear (R). In this case, the load distribution on the nut N increases from the front (F) to the rear (R). Note that front (F) and rear (R) have relative meanings.

[0059] The present invention is applicable not only to the load pattern shown in Figure 8(a), but also to the load patterns shown in Figures 8(b) and (c). The load pattern shown in Figure 8(b) is such that, for example, because the nut N is fixed, the reaction force Fb2 of the load Fa applied to the bolt B is applied forward (F). In this case, the thread load shows a distribution in which it is large not only backward (R) but also forward (F). In this case, the adjustment region RA in this embodiment can be applied in the two regions corresponding to this thread load distribution. The load pattern shown in Figure 8(c) has a fastening portion N1 with threads and a non-fastening portion N2 without threads in the nut N. Note that in a blind-hole type screw hole provided in the nut N, the threaded portion at the opening and the round hole at the bottom of the hole are conveniently represented as the fastening portion N1 and the round hole at the bottom as the non-fastening portion N2. Furthermore, the nut N is 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-fastening portion N2 toward the front (F), and a reaction force Fb4 is generated in the fastening portion N1 toward the rear (R) in response to this reaction force Fb3. In this load pattern, the thread load on the fastening portion N1 increases from the rear (R) toward the front (F). In this load pattern, the adjustment region RA in this embodiment can be applied only to the front (F) side of the fastening portion N1, i.e., the reaction force support side. In this case, the rear (R) side of the fastening portion N1, i.e., the load side, is normally the area NA.

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

[0061] [Screws to which this embodiment applies] In the above-described first A, first B, and second embodiments, examples of applying the present invention to male threads (31, 41) were shown. However, the present invention is not limited to these and can also be applied to female threads (35, 45).

[0062] [Fasteners to which this embodiment applies] In the above-described first A, first B, and second embodiments, tie bars and piston rods were given as examples of fasteners using screw joints, but the fasteners of the present invention are not limited to these. Although bolts and screws have been described above, the present invention can be applied to various fasteners in which a male thread is formed on one member and a female thread that engages with the male thread on the other member is formed on the other member. In particular, the present invention is suitable for fastening a one-piece molded product having elements of different dimensions, such as tie bars and piston rods, by dividing it into two members and fastening them together with screw joints.

[0063] [Location of the gap] In the above-described first A, first B, and second embodiments, 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 between the pressing surface PS of the male screw 41 and the female screw 45, but the present invention is not limited thereto. 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 symbols]

[0064] 1 Mold clamping device 10 bases 11 Fixed platen 12 Movable mold board 11A, 12A Front side 11B, 12B Reverse side 13 Fixed mold 14. Movable mold 15A, 15B, 15C, 15D Tie Bar 16 Piston Head 17. Opposing teeth 18 Movable mold platen moving means 20-part nut opening and closing device 21. First split nut 22. Second split nut 30, 30A, 30B threaded fittings 31A, 31B Male screw 35 Female thread 40 Screw fittings 41 Male screw 45 Female thread 50 Screw fittings 51 Male screw 53 Screw threads 54 Screw grooves 55 Female thread 57 Screw threads 58 Screw grooves M11, M12, M13, M14, M15, M16 screw threads M51, M52, M53, M54, M55, M56 screw threads LM1,LM2,LM3 Mountain width G11, G12, G13, G14, G15, G16 screw threads G51, G52, G53, G54, G55, G56 screw grooves LG1,LG2,LG3,LG4,LG5,LG6 Groove width RA adjustment area NA normal area PS push side TS pull side a1,a2,a3,d1,d2 ridgeline b1,b2,b3,c1,c2 valley line BA, BA1, BA2 bending part N1 fastening part N2 Non-fastened part OP Hydraulic RL reference line V Vertical direction H horizontal direction B bolt C-axis

Claims

1. A fastening body fastened by a screw joint in which male and female threads, each having multiple helical threads, interlock, The aforementioned screw fitting is, The thread width on one side in the axial direction of the first screw, which is either the male screw or the female screw, is smaller than the thread width on the other side excluding the one side in the axial direction. The other of the male screw and the female screw, the thread width of the second screw that meshes with the first screw is uniform, The first screw and the second screw are subjected to loads in opposite directions in the axial direction, or An axial load is applied to one of the first screw and the second screw, and a reaction force in the opposite direction due to the said load is generated on the other of the first screw and the second screw. The first screw is a bolt, A fastening body in which one side in the axial direction corresponds to the neck side of the bolt, and the other side in the axial direction, excluding the one side, corresponds to the tip side of the bolt.

2. The thread widths of the multiple threads on one side are either uniform or uneven. The fastener according to claim 1.

3. The first thread of the first screw is It comprises a first surface facing one side and a second surface that is the back side of the first surface and faces the other side, The first lead of the first thread on the second surface is equal to the lead of the second thread of the second screw, and In the first screw, The closer to one side, the larger the thread root width and the smaller the thread width. The fastener according to claim 2.

4. In the first screw, The thread width differs from one side to the other side. The fastener according to claim 2.

5. The first thread of the first screw is It comprises a first surface facing one side and a second surface that is the back side of the first surface and faces the other side, The first lead on the first surface is smaller than the second lead on the second surface. The fastener according to claim 4.

6. The first thread of the first screw is As you approach the aforementioned one side, the thread width decreases in stages or continuously. The fastener according to claim 5.

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

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