Hydraulic cylinder unit and clamping device

Abstract

To provide a hydraulic cylinder unit that, in addition to suppressing sealing failures between the piston and the tie bar, can suppress the bias in the relative position of the central axes of the piston and the tie bar in a clamping device employing a cantilever structure of the tie bar. [Solution] The hydraulic cylinder unit comprises a cylinder tube having an oil chamber inside, a piston positioned in the oil chamber, and a piston rod fastened to the piston. The piston comprises a pressure-receiving portion that receives hydraulic pressure from the hydraulic fluid in the oil chamber, an intermediate portion connected to the pressure-receiving portion, and a fastening portion connected to the intermediate portion that is involved in fastening to the piston rod. The intermediate portion comprises a piston recess that is recessed radially outward from the pressure-receiving portion and the fastening portion.

Description

Technical Field

[0003] ,

[0001] The present invention relates to a clamping device applied to an injection molding machine or the like.

Background Art

[0002] In a clamping device, a piston head and a rod (tie bar) having a screw joint structure are well known. This is to facilitate acquisition by making the piston head and the rod (tie bar) separately and reducing the outer diameter or length of each material. For example, Patent Document 1 discloses a structure that can efficiently perform on-site assembly work in a clamping device in which a piston head and a tie bar have a screw joint structure. In this clamping device, a clamping cylinder mechanism (28) is provided on the side of the fixed platen (14). This clamping cylinder mechanism (28) includes a ring nut (38) screwed to the end of the tie bar (22), a clamping cylinder (32) formed on the back surface of the fixed platen (14) opposite to the mold mounting surface, and a clamping piston (30) penetrating the clamping cylinder (32). After mold alignment, the clamping cylinder mechanism (28) supplies hydraulic oil to the hydraulic chamber (34) formed between the clamping piston (30) and the clamping cylinder (32), thereby pulling the movable platen (16) toward the fixed platen (14) via the tie bar (22) to generate a clamping force.

[0003] In the clamping device of Patent Document 1, one end of the tie bar is supported and fixed by the movable platen, and after the other end of the tie bar is inserted into the clamping piston of the clamping cylinder built into the fixed platen, the tie bar and the clamping piston are fixed. That is, the tie bar in the clamping device of Patent Document 1 is a part that does not have a ring groove for engaging with the half nut mechanism at one end, and includes a part for supporting one end of the tie bar by the movable platen. Thus, even when the movable platen is separated from the fixed platen to the mechanical stroke limit when replacing the mold, etc., the tie bar has a structure that does not come out of the movable platen, so the tie bar is supported at both ends by the movable platen and the fixed platen. <00​ [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2006-321204 [Patent Document 2] Japanese Patent Application Publication No. 49-30740 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] It is envisioned that the clamping cylinder mechanism of Patent Document 1 will be applied to a clamping device with a structure in which the tie bars are cantilevered and supported only by the fixed platen, with the aim of eliminating the bushings (sliding materials) and lubrication of the bushings necessary for supporting the tie bars of the movable platen. Alternatively, it is envisioned that the clamping device will be applied to a clamping device with a structure in which the overall length of the clamping device will be shortened to save space in the installation of the machine, and the tie bars will detach from the movable platen and be cantilevered and supported only by the fixed platen when the movable platen is separated from the fixed platen even during normal molding operation. In these cantilevered cases, under all or some molding conditions, the tie bars will detach from the movable platen and be cantilevered in each molding cycle. In this state, the tie bars will bend downward due to their own weight as they move away from the support point. At this time, the clamping piston fixed to the tie bars will also tilt. As a result, the sleeve constituting the clamping piston will also be pushed down and pressed against the fixed platen, and there is a risk that the sleeve will undergo plastic deformation due to the reaction force from the fixed platen.

[0006] Since the space between the sleeve and the fixed mold plate forms a seal, plastic deformation of the sleeve means that the seal will also undergo plastic deformation. This can lead to seal failure during mold clamping and pressure increase, potentially resulting in oil leakage or pressure increase failure.

[0007] Furthermore, in Patent Document 1, a ring nut is interposed between the clamping piston and the tie bar. Therefore, there are fitting gaps at two locations between the clamping piston and the tie bar: at the boundary between the clamping piston and the ring nut, and at the boundary between the ring nut and the tie bar. As a result, an imbalance is likely to occur in the relative position between the central axis of the tie bar and the central axis of the clamping piston. Therefore, if the tie bar is supported in a cantilevered structure, the gap between the tie bar and the sleeve will also be uneven, and there is a risk that the tie bar will be more likely to hit the sleeve due to its own weight.

[0008] Therefore, the present invention aims to provide a hydraulic cylinder unit that employs a cantilever structure for the tie bar, which can suppress sealing defects between the piston and the tie bar, as well as suppress the bias in the relative position of the central axes of the piston and the tie bar. [Means for solving the problem]

[0009] The hydraulic cylinder unit of the present invention is A cylinder tube with an oil chamber inside, The piston is positioned in the oil chamber, It comprises a piston and a piston rod that is fastened to it. The piston is A pressure receiving section that receives hydraulic pressure from the hydraulic fluid in the oil chamber, The fastening part involved in fastening with the piston rod, An intermediate section is provided between the pressure-receiving section and the fastening section, and these are connected along the central axis. The intermediate section is provided with a piston recess that is recessed radially outward from the pressure-receiving section and the fastening section.

[0010] Preferably, the inner diameter DB in the intermediate section is larger than the inner diameter DA in the pressure-receiving section and the inner diameter DC in the fastening section.

[0011] In the piston rod, preferably, It comprises a pressure-receiving part corresponding to a pressure-receiving part, an intermediate part connected to the pressure-receiving part and corresponding to an intermediate part, and a fastening part connected to the intermediate part and corresponding to a fastening part, The intermediate corresponding section is provided with a rod recess that is recessed radially inward from the pressure-receiving corresponding section and the fastening corresponding section. The piston recess and rod recess provide a hollow region spanning between the intermediate and corresponding intermediate sections in the radial direction.

[0012] Preferably, the hollow region in the piston is It extends radially outward from the fastening portion, beyond the boundary between the intermediate portion and the fastening portion, and into the fastening portion.

[0013] In the fastening portion, preferably, the diameter on the side closer to the central axis C in the extended hollow region has a tapered sleeve shape, where the diameter increases as it moves away from the intermediate portion.

[0014] Preferably, a first packing is provided between the pressure receiving part and the pressure receiving corresponding part. A second packing is provided between the pressure-receiving section and the cylinder tube.

[0015] The clamping device of the present invention is A fixed mold plate that supports the fixed mold, A movable mold plate, which supports the movable mold, is positioned opposite the fixed mold plate, Multiple tie bars connecting the fixed panel and the movable panel, The system includes one of the following hydraulic cylinder units, which applies clamping force between a fixed mold plate and a movable mold plate, and uses a tie bar as a piston rod.

[0016] The fixed panel preferably has a front surface facing the movable panel and a back surface opposite the front surface. The cylinder tube housing the piston is positioned on the underside of the movable mold plate, detachably from the fixed mold plate. [Effects of the Invention]

[0017] According to the hydraulic cylinder unit of the present invention, the intermediate portion includes a piston recess that is recessed radially outward from the pressure receiving portion and the fastening portion. Thus, according to the present invention, in addition to suppressing seal failure between the piston and the tie bar, it is possible to suppress deviation in the relative position of the central axes of the piston and the tie bar.

Brief Description of the Drawings

[0018] [Figure 1] It is a side view showing a schematic configuration of an injection molding machine according to an embodiment. [Figure 2] It is a cross-sectional view showing a configuration of a mold clamping cylinder unit according to an embodiment. [Figure 3] It is a partially enlarged view of FIG. 2. [Figure 4] It is a cross-sectional view showing the behavior of the piston during mold clamping pressure increase. [Figure 5] It is a cross-sectional view showing a configuration of a mold clamping cylinder unit according to a modification. [Figure 6] It is a cross-sectional view showing a configuration of a mold clamping cylinder unit according to another modification.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described by taking an injection molding machine 1 as an example while referring to the accompanying drawings. In the embodiment, a tie bar 33 and a piston 53 constituting a hydraulic cylinder unit 50 are fastened. In addition, the hydraulic cylinder unit 50 is provided outside with a cylinder tube 51 on the side of the fixed platen 25 and on the back surface 25B of the fixed platen 25, and is separable from the fixed platen 25.

[0020] 〔Overall Configuration: Refer to FIG. 1〕 As shown in FIG. 1, an injection molding machine 1 according to an embodiment includes a plasticizing unit 10 and a molding unit 20. In the injection molding machine 1, for convenience of explanation, the front (F) and the rear (R) are defined as shown in FIG. 1 and the like. This definition is relative.

[0021] [Plasticizing Unit 10: Refer to FIG. 1] The plasticizing unit 10 comprises a heating cylinder 11 and a discharge nozzle 13 provided at the front end of the heating cylinder 11. The plasticizing unit 10 also includes a screw rotatably mounted inside the heating cylinder 11 and a heater wrapped around the heating cylinder 11, although these are not shown in the figures. The pelletized raw material resin is supplied into the heating cylinder 11 via a raw material input hopper 15 provided in the heating cylinder 11. The screw is capable of moving forward and backward, as well as rotating in both forward and reverse directions, within the fixed position of the heating cylinder 11. The plasticizing unit 10 includes a drive source 17 for moving the screw forward or backward, and a drive source 18 for rotating the screw in both forward and reverse directions. The injection molding machine 1 performs resin injection molding by combining the forward or backward movement and forward or reverse rotation of the screw.

[0022] [Molded section 20: See Figure 1] The molding unit 20 includes a fixed mold 21 whose position is fixed and a movable mold 23 which can move forward and backward relative to the fixed mold 21. In the mold clamping state where the fixed mold 21 and the movable mold 23 are abutted together, a mold cavity is formed between the fixed mold 21 and the movable mold 23. The resin plasticized in the plasticizing unit 10 is injected and filled into the mold cavity of the molding unit 20 to obtain a resin molded body. Note that in Figure 1, the fixed mold 21 and the movable mold 23 are shown removed from the fixed mold plate 25 and the movable mold plate 27, respectively. The fixed mold 21 is attached to the fixed mold platen 25, and the movable mold 23 is attached to the movable mold platen 27. Multiple tie bars 33, for example four, are provided between the fixed mold platen 25 and the movable mold platen 27 to connect them, and the pressure from the hydraulic cylinder unit 50 is applied between the fixed mold platen 25 and the movable mold platen 27 via the tie bars 33 and split nuts 35 to perform mold clamping or mold opening. In addition, although not shown in the figures, a mold opening and closing mechanism is provided to move the movable mold platen 27 a large distance away from the fixed mold platen 25, and the molding section 20 is provided with ejector pins, etc., to eject the injection molded product out of the mold in the open state. The clamping device is comprised of a fixed mold plate 25, a movable mold plate 27, a tie bar 33, a split nut 35, and a hydraulic cylinder unit 50.

[0023] [Fixed panel 25, movable panel 27: See Figure 1] The fixed mold plate 25 supports the fixed mold 21 in a fixed position on the base plate 2. The fixed mold plate 25 comprises a front surface 25A that supports the fixed mold 21 and a back surface 25B on the opposite side of the front surface 25A. Support holes 37 are formed in each of the four corners of the fixed mold plate 25 through which tie bars 33 are inserted, and the support holes 37 penetrate the front surface 25A and the back surface 25B.

[0024] The movable mold platen 27 is positioned on the base platen 2 to move back and forth relative to the fixed mold platen 25 while supporting the movable mold 23. The movable mold platen 27 has a front surface 27A that supports the movable mold 23 and a back surface 27B on the opposite side of the front surface 27A. Support holes 39 are formed in each of the four corners of the movable mold platen 27, through which tie bars 33 are inserted, and the support holes 39 penetrate the front surface 27A and the back surface 27B. Split nuts 35 are provided on the back surface 27B of the movable mold platen 27, facing each of the support holes 39 at the four corners, and grip the ends of the tie bars 33 that penetrate the back surface 27B.

[0025] [Hydraulic cylinder unit 50: See Figures 1, 2, and 3] The hydraulic cylinder unit 50 is installed across the fixed mold plate 25 and the movable mold plate 27, and clamps the fixed mold 21 and the movable mold 23 by applying a clamping force between the fixed mold plate 25 and the movable mold plate 27. In this embodiment, the hydraulic cylinder unit 50 is provided separately from the fixed mold plate 25, that is, a separate hydraulic cylinder unit 50 is used. Integrated hydraulic cylinders (e.g., built-in fixed mold plate type) that give the fixed mold plate the function of a hydraulic cylinder are well known, but this embodiment adopts a separate type that is detachably assembled to the fixed mold plate 25. By using a separate hydraulic cylinder unit 50, the overall height and width of the mold plate can be reduced compared to a fixed mold plate 25 that has hydraulic cylinders built into, for example, the four corners, so in addition to making the mold plate lighter and smaller in size, the lighter and smaller size is also extremely advantageous in terms of transportation. In this embodiment, the hydraulic cylinder unit 50 is shown as being assembled to a fixed mold plate 25. However, the hydraulic cylinder unit 50 can be assembled to a movable mold plate 27 instead of a fixed mold plate 25. In this case, the same benefits as when the hydraulic cylinder unit 50 is assembled to a fixed mold plate 25 can be obtained, such as weight reduction, size reduction, and transportation advantages for the mold plate.

[0026] The hydraulic cylinder unit 50 comprises a cylinder tube 51 in which an oil chamber 52 is formed, a piston 53 arranged to be able to reciprocate in the front-rear direction inside the oil chamber 52, and a piston rod 55 connected to the piston 53. In this embodiment, the tie bar 33 functions as the piston rod 55.

[0027] As an example, the cylinder tube 51 includes a cylindrical housing 51A with one end closed and a lid 51B that closes the open end of the housing 51A, as shown in Figure 2. An oil chamber 52 is formed inside the cylinder tube 51 into which the housing 51A and the lid 51B are assembled.

[0028] The oil chamber 52 comprises a first oil chamber 52A located in front of (F) the piston 53 and a second oil chamber 52B located behind (R) the piston 53. A first oil passage 54A is connected to the first oil chamber 52A, passing through the housing 51A, and a second oil passage 54B is connected to the second oil chamber 52B, also passing through the housing 51A. When clamping the mold, hydraulic fluid from a hydraulic source (not shown) is supplied to the first oil chamber 52A, and when opening the mold, hydraulic fluid is supplied to the second oil chamber 52B.

[0029] The piston 53 is attached to the rear (R) end of the piston rod 55 and is fastened to its outer circumference. The piston 53 is a cylindrical, integrally molded member comprising a pressure-receiving portion 53A positioned at the front (F) when mounted on the piston rod 55, a fastening portion 53C positioned at the rear (R), and an intermediate portion 53B provided between the pressure-receiving portion 53A and the fastening portion 53C. The pressure-receiving portion 53A, the intermediate portion 53B, and the fastening portion 53C are arranged in sequence in the direction of the central axis C to constitute the piston 53. By providing the intermediate portion 53B between the pressure-receiving portion 53A and the fastening portion 53C, when the pressure-receiving portion 53A receives pressure from the hydraulic fluid in the direction of the central axis C, the pressure-receiving portion 53A and the intermediate portion 53B can bend toward the central axis C.

[0030] As shown in Figure 3, the pressure receiving section 53A directly receives hydraulic pressure OP towards the rear (R) from the hydraulic fluid supplied to the first oil chamber 52A during mold clamping. The intermediate section 53B is provided with a piston recess 53D whose wall thickness in the radial direction RD is thinner than that of the pressure-receiving section 53A and the fastening section 53C. The piston recess 53D is recessed toward the outside in the radial direction RD. As a result, the pressure-receiving section 53A and the intermediate section 53B connected to the pressure-receiving section 53A have a cantilever structure supported at the rear (R) of the intermediate section 53B. When the pressure-receiving section 53A receives hydraulic pressure, the pressure-receiving section 53A and the intermediate section 53B connected to the pressure-receiving section 53A flex toward the central axis C. The behavior of this flexing will be described in detail later. The fastening portion 53C is equipped with a female thread 53S that engages with a male thread 55S of the fastening corresponding portion 55C formed at the rear (R) end of the piston rod 55. While it is effective in increasing the fastening strength between the female thread 53S and the male thread 55S if their lengths in the direction of the central axis C are the same, they do not have to be the same. In other words, for example, it is not a problem if the male thread 55S is longer than the female thread 53S or shorter than the female thread 53S.

[0031] In the piston 53, the outer diameters of the outer surfaces 53OS of the pressure-receiving portion 53A, the intermediate portion 53B, and the fastening portion 53C are the same, but the inner diameters of the inner surfaces 53IS are different. That is, the inner diameter DA of the pressure-receiving portion 53A, the inner diameter DB of the intermediate portion 53B, and the inner diameter DC of the fastening portion 53C have the following relationship: equation (1) or equation (2). In other words, the piston recess 53D of the intermediate portion 53B is recessed outward in the radial direction RD compared to the pressure-receiving portion 53A and the fastening portion 53C. In this embodiment, for simplicity, the length of the inner surface 53IS of the pressure-receiving portion 53A in the direction of the central axis C and the length of the pressure-receiving corresponding portion 55A corresponding to the pressure-receiving portion 53A in the direction of the central axis C are shown to be the same. However, in the present invention, it is not a problem if the length of the inner surface 53IS of the pressure-receiving portion 53A in the direction of the central axis C and the length of the pressure-receiving corresponding portion 55A corresponding to the pressure-receiving portion 53A in the direction of the central axis C are not the same. DB > DA > DC …(1) DB > DC > DA …(2)

[0032] The piston rod 55 includes a pressure-receiving portion 55A corresponding to the pressure-receiving portion 53A, an intermediate portion 55B connected to the pressure-receiving portion 55A and corresponding to the intermediate portion 53B, and a fastening portion 55C connected to the intermediate portion 55B and corresponding to the fastening portion 53C. Here, "corresponding" means that the arrangement or order of the connected parts along the central axis C is the same. There is a fitting clearance between the outer circumferential surface 55OS of the pressure-receiving portion 55A and the inner circumferential surface 53IS of the pressure-receiving portion 53A. However, since this fitting clearance portion is a hydraulic seal and the size of the fitting clearance is precise, the outer circumferential surface 55OS has substantially the same outer diameter as the inner circumferential surface 53IS of the pressure-receiving portion 53A. However, the fitting clearance between the outer circumferential surface 55OS and the inner circumferential surface 53IS of the pressure-receiving portion 53A can allow for a deflection amount that brings it closer to the central axis C of the pressure-receiving portion 53A and the intermediate portion 53B connected to the pressure-receiving portion 53A. A hollow, annular region VA centered on the central axis C is provided between the outer circumferential surface 55OS of the intermediate section 55B and the inner circumferential surface 53IS of the intermediate section 53B. The inner circumferential surface 53IS of the piston 53 is shown as a collective term for the inner circumferential surfaces of the pressure receiving section 53A, the intermediate section 53B, and the fastening section 53C, and the outer circumferential surface 55OS of the piston rod 55 is shown as a collective term for the outer circumferential surfaces of the pressure receiving section 55A, the intermediate section 55B, and the fastening section 55C.

[0033] In the hydraulic cylinder unit 50, the fastening portion 53C and the corresponding fastening portion 55C are interlocked and fixed to each other in the direction of the central axis C. In addition, the hydraulic cylinder unit 50 has the rear (R) ends of the piston 53 and piston rod 55 flush with each other, and is equipped with a connecting plate 57 that connects and fixes the piston 53 and piston rod 55 to each other in the radial direction RD. The connecting plate 57 is fixed to each of the piston 53 and piston rod 55 at multiple points in the circumferential direction by fasteners such as screws and bolts. Note that the rear (R) ends of the piston 53 and piston rod 55 are not limited to being flush with each other and in even contact with the connecting plate 57. In other words, it is sufficient that one of the rear (R) ends of the piston 53 or piston rod 55 is in contact with the connecting plate 57, and there may be a gap between the rear (R) end of the piston 53 or piston rod 55 and the connecting plate 57.

[0034] [Packing: See Figure 3] The hydraulic cylinder unit 50 is equipped with a first packing P1 between the pressure-receiving portion 53A of the piston 53 and the piston rod 55. The first packing P1 is provided to prevent hydraulic fluid from entering the meshing portion of the female thread 53S and the male thread 55S when the mold clamping pressure is increased. The hydraulic cylinder unit 50 is equipped with a second packing P2 and a third packing P3 between the piston 53 and the cylinder tube 51. The second packing P2 and the third packing P3 are provided to prevent hydraulic fluid from leaking from the first oil chamber 52A to the second oil chamber 52B during mold clamping pressure increase, which would otherwise cause mold clamping pressure increase failure.

[0035] [Operation of hydraulic cylinder unit 50 (first effect): See Figure 4] In the hydraulic cylinder unit 50, when hydraulic pressure OP for clamping is applied, the portion of the piston 53 forward (F) from the intermediate portion 53B flexes toward the central axis C. This allows for highly precise alignment of the piston 53 and the piston rod 55, as well as ensuring sealing performance between the piston 53 and the piston rod 55. A more detailed explanation follows with reference to Figure 4.

[0036] When hydraulic fluid is supplied to the first oil chamber 52A during mold clamping, hydraulic pressure OP is applied to the pressure-receiving surface 53a of the pressure-receiving portion 53A of the piston 53. As a result, since there is a hollow region VA inside the intermediate portion 53B and no part to support the thrust caused by the hydraulic pressure OP applied to the pressure-receiving surface 53a, the portion of the pressure-receiving portion 53A, particularly the part corresponding to the hollow region VA, is pushed backward (R). This causes the pressure-receiving portion 53A and the intermediate portion 53B to bend inward, i.e., toward the central axis C, axially symmetric with respect to the central axis C. Along with this bending, the outer circumferential surfaces 53OS corresponding to the pressure-receiving portion 53A and the intermediate portion 53B are displaced inward, widening the gap between the outer circumferential surface 53OS of the piston 53 and the inner circumferential surface 51IS of the cylinder tube 51. As a result, the increased thickness of the oil film in this gap allows a stable hydraulic pressure OP to push the piston 53 toward the central axis C, axially symmetric with respect to the central axis C. In this way, the hydraulic pressure OP directed from the outer circumferential surface 53OS of the pressure-receiving section 53A and the intermediate section 53B toward the central axis C in an axially symmetric manner with respect to the central axis C is stabilized, resulting in a high centering force that aligns the central axis of the piston 53 with the central axis of the piston rod 55. This allows the gap between the outer circumferential surface 53OS of the piston 53 and the inner circumferential surface 51IS of the cylinder tube 51, and the gap between the outer circumferential surface 55OS of the piston rod 55 and the inner circumferential surface of the cylinder tube 51, which are sealing areas, to be stably and uniformly maintained in the circumferential direction. This maintains the sealing performance of these areas and prevents oil leakage and pressure increase failures due to sealing defects during mold clamping and pressure increase. Furthermore, as the pressure-receiving section 53A of the piston 53 flexes toward the inner diameter, the gap between the piston 53, particularly the pressure-receiving section 53A, and the piston rod 55 (tie bar 33) is reduced, increasing the sealing surface pressure of the first packing P1, thereby more reliably preventing the inflow of high-pressure oil into the screw fastening portion between the piston 53 and the piston rod 55. Furthermore, if the piston 53 does not have a hollow region VA, and the gap between the outer surface 53OS of the piston 53 and the inner surface 51IS of the cylinder tube 51 does not widen, the hydraulic fluid film will become thinner. In cases where low-cost, low-viscosity hydraulic fluid is used, the oil film may break easily and become unstable, which can lead to unstable hydraulic pressure.

[0037] [Second effect of the hydraulic cylinder unit 50: Figure 1] The hydraulic cylinder unit 50 is configured to be separable from the fixed mold plate 25. This allows the clamping device to be assembled by pre-assembling components such as the cylinder tube 51, piston 53, and piston rod 55, and then inserting the piston rod 55 into the support hole 37 of the fixed mold plate 25. As a result, the packings, which are prone to damage or wear, are pre-sealed and assembled within the hydraulic cylinder unit 50. Therefore, the packings do not need to be assembled during on-site assembly work where the injection molding machine 1 is installed, ensuring that the packings remain intact and are not damaged during assembly. Furthermore, since the packings are sealed and assembled within the hydraulic cylinder unit 50 during transport to the site, the packings do not need to be assembled during transport, allowing for efficient on-site assembly work. Furthermore, if the vertical and horizontal dimensions of the fixed mold 21 and the movable mold 23 are greater than the spacing of the tie bars 33, it is necessary to remove at least the tie bars to secure a route for loading the molds into the mold plate when mounting the molds to the mold plate. However, when pulling the hydraulic cylinder unit 50 out of the fixed mold plate 25 in the opposite direction to the movable mold plate 27, the packings provided on the clamping cylinders can be exposed and removed without having to remove them, and the hydraulic cylinder unit 50 can be removed from the fixed mold plate 25 while the packings remain built into the hydraulic cylinder unit 50.

[0038] [Variations, etc.] Although preferred embodiments of the present invention have been described above, modifications can be made to these embodiments. [Expansion of the hollow region VA: See Figure 5] In the hydraulic cylinder unit 50 described above, an example is shown in which the hollow region VA is formed in an annular shape. However, as shown in Figure 5, the hollow region VA can extend beyond the boundary between the intermediate portion 53B and the fastening portion 53C to the fastening portion 53C, outside the radial RD of the female thread 53S, thereby providing an extended portion EX. Although the hollow region VA extends to the fastening portion 53C, the length in the direction of the central axis C of the female thread 53S of the fastening portion 53C and the male thread 55S of the corresponding fastening portion 55C is maintained. As described above, by extending the hollow region VA outside the radial RD beyond the female thread 53S, the rigidity of the radial RD of the fastening portion 53C that cantilever-supports the pressure-receiving portion 53A and the intermediate portion 53B is reduced, making it easier to obtain deflection of the pressure-receiving portion 53A and the intermediate portion 53B due to the hydraulic OP during mold clamping. Furthermore, while maintaining the fastening length between the piston 53 and the piston rod 55 and ensuring fastening force, the piston 53 can be made lighter by reducing its thickness through the expansion of the hollow region VA, thereby facilitating the transportation of the hydraulic cylinder unit 50.

[0039] [Formation of tapered sleeve 53E: See Figure 5] Next, as the hollow region VA on the outside of the female thread 53S extends, a tapered sleeve 53E is formed in the fastening portion 53C that protrudes forward (F). This tapered sleeve 53E allows the front (F) side of the female thread 53S, which has a small cross-sectional area and low rigidity, to easily deform in the direction of the central axis C and radially RD, thereby reducing the load generated on the threads of the female thread 53S. In screw fastening structures between tie bars (rods) and pistons, which are commonly used in single-rod cylinders including clamping cylinders, it is generally known that when hydraulic pressure is applied to the rod side, the load on the threads of the screw fastening portion is greater on the side opposite to the load-bearing end of the tie bar (the side receiving the clamping hydraulic pressure) in the axial direction of the tie bar, and the load on the threads decreases as you move towards the tie bar shaft end, which is on the opposite side of the load-bearing side (for example, Patent Document 2). This occurs because minute deformation due to the load causes the male thread to stretch and the screw pitch spacing to widen, while the female thread to compress and the screw pitch spacing to narrow. In response to this, a tapered sleeve 53E is provided on the side closer to the pressure-receiving surface 53a that receives the hydraulic OP, where the thread load is large, and which protrudes toward the movable platen 27. This reduces the cross-sectional area of ​​the tip side of the male screw 53S where the maximum stress occurs, making it easier to deform, and thus the load can be relieved by deformation, reducing the load generated on the threads.

[0040] [Length L of piston recess 53D: See Figures 5 and 6] When the pressure-receiving portion 53A of the piston 53 bends and contacts the outer circumferential surface 55OS of the piston rod 55, no further bending occurs. The degree of this bending is the distance between the two end faces of the opposing hollow region VA in the direction of the central axis C, and is influenced by the dimension L of the piston recess 53D in the direction of the central axis C. In other words, the longer the dimension L, the easier it is for the two end faces of the hollow region VA to contact due to bending. Also, because the pressure-receiving portion 53A and the intermediate corresponding portion 55B of the piston 53 are compressed in the direction of the central axis C by the clamping hydraulic pressure applied to the pressure-receiving surface 53a, the hollow region VA shrinks in the direction of the central axis C. At the same time, because the tie bar 33 is pulled toward the movable mold plate 27 by the clamping force, the male screw 55S that grips the tie bar 33 is stretched toward the movable mold plate 27, and this also shrinks the hollow region VA in the direction of the central axis C. Therefore, it is preferable that dimension L is of sufficient length so that the two opposing walls of the hollow region VA do not come into contact in the direction of the central axis C, so that there is still spatial margin that allows for deflection even when affected not only by the deflection of the piston 53 but also by the reduction of the hollow region VA due to the compression of the piston 53 and the stretching of the male screw 55S.

[0041] [Arrangement of packings P1 to P3: See Figure 6] In the present invention, the position of the first packing P1, which is provided between the piston 53 and the piston rod 55, in the direction of the central axis C is preferably near the pressure receiving surface 53a, but it is any position that can prevent hydraulic fluid from flowing into the fastening portion between the female thread 53S and the male thread 55S. Furthermore, the positions of the second packing P2 and the third packing P3, which are provided between the piston 53 and the cylinder tube 51, in the direction of the central axis C are also arbitrary. In this embodiment, in order to more reliably prevent hydraulic fluid leakage from the first oil chamber 52A to the second oil chamber 52B and subsequent mold clamping pressure increase failure, the second packing P2 and the third packing P3 are provided redundantly. However, if the sealing performance of the packing is high, the second packing P2 alone will suffice. Conversely, if the sealing performance of the two packings, the second packing P2 and the third packing P3, is insufficient, a fourth packing P4 can also be provided.

[0042] Here, the tie bar 33 connected to the piston 53 is supported by a fixed plate 25 and a movable plate 27, but its own weight causes the front (F) to tilt downward, and consequently the piston 53 also tilts, resulting in eccentricity with respect to the central axis C. This amount of eccentricity geometrically increases as it approaches the rear (R) end of the piston 53 and decreases as it approaches the front (F) end of the piston 53. From the viewpoint of sealing performance and packing damage, it is preferable to place the packing between the piston 53 and the cylinder tube 51 in a location with minimal eccentricity. Therefore, it is preferable that at least the second packing P2 closest to the pressure-receiving surface 53a be placed forward (F) of the center in the direction of the central axis C on the outer circumferential surface 53OS. Furthermore, even when the pressure-receiving section 53A and the intermediate section 53B bend towards the central axis C, it is preferable that at least the second packing P2 closest to the pressure-receiving surface 53a be positioned forward (F) of the intermediate section 53B so that hydraulic fluid does not leak from the first oil chamber 52A to the second oil chamber 52B during mold clamping pressure increase, thus preventing mold clamping pressure increase failure. In this case, when the pressure-receiving section 53A and the intermediate section 53B bend towards the central axis C, the second packing P2 recovers due to its own elasticity and maintains the seal between the piston 53 and the cylinder tube 51.

[0043] In this embodiment, it is assumed that the outer circumferential surface 53OS of the piston 53 has a constant radial dimension RD. However, considering that the pressure-receiving portion 53A flexes to introduce hydraulic fluid between the piston 53 and the cylinder tube 51, the outer circumferential surface 53OS of the pressure-receiving portion 53A can be tilted forward (F) in the direction of the central axis C, that is, the outer diameter of the outer circumferential surface 53OS near the pressure-receiving surface 53a can be gradually reduced (reduced in diameter) from the rear (R) toward the pressure-receiving surface 53a, thereby expanding the gap between the piston 53 and the cylinder tube 51 near the pressure-receiving surface 53a. This allows hydraulic fluid to be introduced into the gap even before the pressure-receiving portion 53A is tilted, making it easier to cause flexing. However, in order to prevent leakage of hydraulic fluid toward the rear (R), it is preferable to tilt within a limited range from the front (F) of the pressure-receiving portion 53A, for example, in the range in front (F) of the second packing P2.

[0044] The hydraulic cylinder unit 50 shown in this embodiment includes a rod recess 55D connected to a male thread 55S. The rod recess 55D contributes to forming a tapered shape on the threads closer to the pressure-receiving surface 53a, which receives the hydraulic pressure OP and where the thread load is large. As a specific example of the tapered shape, the inner diameter or effective diameter of the female thread 53S can be gradually increased, or the outer diameter or effective diameter of the male thread 55S can be gradually decreased, as shown in Patent Document 2. This reduces the thread engagement on the threads where the maximum stress occurs closer to the pressure-receiving surface 53a, thereby reducing the load generated on the threads. The shape, which includes a rod recess 55D connected to the male thread 55S, allows the rod recess 55D to act as a relief groove when machining a tapered shape on the outer diameter of the male thread 55S. This makes it easy to machine a tapered shape on the threads of the male thread 55S that are close to the pressure-receiving surface 53a, which receives hydraulic pressure OP and where the thread load is large. However, if a tapered sleeve 53E that protrudes forward (F) on the radially outer side RD of the female thread 53S, which provides a similar thread load reduction effect, is already provided, then it is not necessary to provide a tapered shape on the threads that are close to the pressure-receiving surface 53a.

[0045] Furthermore, when a tapered sleeve 53E is used on the outside of the female thread 53S, there is a risk that the load on the threads on the side closer to the pressure-receiving surface 53a, which receives the hydraulic OP and has a large thread load, may be excessively reduced. This could lead to an excessive increase in the thread load on other parts, but if the tapered shape of the tapered sleeve 53E and the threads can be designed in a balanced manner, it may be possible to find the optimal tapered shape of the tapered sleeve 53E and threads for load reduction.

[0046] Furthermore, during mold clamping, the mold plate bends with the mold mounting side concave, but the tie bar 33 tightens the movable mold plate 27 and the fixed mold 21, and the movable mold 23 and the fixed mold plate 25, so it is pulled in the mold clamping direction (mold opening and closing direction). For this reason, the piston rod 55 extends parallel to the central axis C so as to follow the shortest distance between the fixed mold plate 25 and the movable mold plate 27. In contrast, the cylinder tube 51 in which the piston 53 is housed is fixed to the fixed mold plate 25, so the central axis of the cylinder tube 51 is tilted to intersect the central axis C. At this time, since the piston 53 is fixed to the end of the piston rod 55, the central axis of the piston 53 also tries to become parallel to the central axis C, but because the piston 53 is precisely housed in the cylinder tube 51, when the piston rod 55 bends, the piston 53 comes into contact with the inner wall of the cylinder tube 51 and receives resistance, generating bending stress in the male screw 55S. In this configuration, the shape includes a rod recess 55D connected to the male thread 55S. This allows the bending stress generated in the male thread 55S and its vicinity to be absorbed by the deformation of the intermediate corresponding section 55B, which has the rod recess 55D and lower bending rigidity than other parts, thereby reducing the stress generated in the male thread 55S. This suppresses the tilting of the central axis of the piston 53 relative to the central axis of the cylinder tube 51, thus suppressing the tilting more than the gap between the piston 53 and the cylinder tube 51, maintaining the sealing performance of that section and effectively preventing oil leakage and pressure increase failures due to sealing failures during mold clamping and pressure increase.

[0047] Furthermore, for the fastening portion between the female thread 53S and the male thread 55S to withstand the clamping force, it is effective for the male thread 55S to engage with the entire length of the female thread 53S. However, since the rod recess 55D does not participate in the deflection of the pressure-receiving portion 53A, the dimension of its central axis C does not need to be the same as that of the piston recess 53D.

[0048] [Application of hydraulic cylinder unit 50] In this embodiment, the hydraulic cylinder unit 50 is shown as an example of being applied to the clamping device of an injection molding machine 1, but the application of the hydraulic cylinder unit 50 in this invention is arbitrary. For example, it can be applied to a die-casting apparatus equipped with a similar clamping device. Furthermore, it can be broadly applied to any apparatus other than a clamping device that requires a strong clamping force to be applied between two members. [Explanation of Symbols]

[0049] 1 injection molding machine 2 Surface plate 10 Plasticizing part 11 Heating tube 13 Discharge nozzle 15 Raw material input hopper 17,18 Power source 20 Molding section 21 Fixed mold 23. Movable mold 25 Fixed board 25A Front side 25B Reverse side 27 Movable mold board 27A Front side 27B Reverse side 31 Hydraulic Cylinder 33 Tie Bar 35 split nuts 37,39 Support hole 50 Hydraulic Cylinder Units 51 Cylinder tube 51A enclosure 51B Lid 51IS Inner surface 52 Oil room 52A 1st oil room 52B 2nd oil room 53 Pistons 53A Pressure receiving section 53a Pressure-receiving surface 53B Middle part 53C Fastening section 53D Piston recess 53E Tapered Sleeve 53OS outer surface 53IS Inner surface 54A No. 1 oilway 54B 2nd oilway 55 Piston Rod 55OS outer surface 55A Pressure-receiving section 55B Intermediate Response Section 55C fastening compatible section 57 Connecting plate P1 First packing P2 Second packing P3 Third packing P4 4th packing VA hollow area F forward R rear RD radial direction C center axis

Claims

1. A cylinder tube with an oil chamber inside, A piston arranged in the oil chamber, The piston rod is fastened to the piston, The aforementioned piston is The oil chamber includes a pressure receiving section that receives hydraulic pressure from the hydraulic fluid, A fastening portion involved in fastening with the piston rod, The pressure-receiving portion and the fastening portion are connected along the central axis, The intermediate portion is a hydraulic cylinder unit having a piston recess that is recessed radially outward from the pressure-receiving portion and the fastening portion.

2. The inner diameter DB in the intermediate portion is larger than the inner diameter DA in the pressure-receiving portion and the inner diameter DC in the fastening portion. The hydraulic cylinder unit according to claim 1.

3. The aforementioned piston rod is It comprises a pressure-receiving part corresponding to the pressure-receiving part, an intermediate part connected to the pressure-receiving part and corresponding to the intermediate part, and a fastening part connected to the intermediate part and corresponding to the fastening part, The intermediate corresponding portion is provided with a rod recess that is recessed radially inward from the pressure-receiving corresponding portion and the fastening corresponding portion. The piston recess and the rod recess provide a hollow region spanning between the intermediate portion and the corresponding intermediate portion in the radial direction. The hydraulic cylinder unit according to claim 1.

4. The hollow region in the piston is Outer radially from the fastening portion, extending beyond the boundary between the intermediate portion and the fastening portion to the fastening portion, The hydraulic cylinder unit according to claim 3.

5. In the fastening portion, the diameter of the extended hollow region on the side closer to the central axis C has a tapered sleeve shape, which increases as it moves away from the intermediate portion. The hydraulic cylinder unit according to claim 4.

6. A first packing is provided between the pressure receiving portion and the pressure receiving corresponding portion. A second packing is provided between the pressure receiving part and the cylinder tube. The hydraulic cylinder unit according to claim 3.

7. A fixed mold plate that supports the fixed mold, A movable mold plate, which supports the movable mold, is positioned opposite the fixed mold plate, Multiple tie bars connecting the fixed panel and the movable panel, A clamping device comprising a hydraulic cylinder unit according to any one of claims 1 to 6, wherein a clamping force is applied between the fixed mold plate and the movable mold plate, and the tie bar is the piston rod.

8. The fixed mold plate has a front surface facing the movable mold plate and a back surface opposite to the front surface. The cylinder tube housing the piston is positioned on the back side of the movable mold plate, detachably from the fixed mold plate. The clamping device according to claim 7.

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