Injection device

Abstract

The present invention relates to an injection device, an injection piston driving screw, an injection hydraulic cylinder driving the injection piston and being partitioned into a first chamber and a second chamber. A first oil discharge port is provided on the injection hydraulic cylinder in such a manner that it is capped by a piston portion of the injection piston when the piston portion advances to a pressure-holding switching position, and discharges hydraulic oil from the second chamber, a second oil discharge port is provided on the injection hydraulic cylinder in such a manner that it can discharge hydraulic oil from the second chamber irrespective of the position of the injection piston, the injection piston includes a first member and a second member, and an engagement portion of the first member and the second member is provided at a position spaced apart from an end portion on the second chamber side of the piston portion by a predetermined distance.

Description

TECHNICAL FIELD

[0001] The present application relates to an injection device, for example, to an injection device for a metal injection molding machine for injection molding of metals such as magnesium alloys and aluminum alloys. BACKGROUND

[0002] Metal injection molding machines are widely used for molding products by filling a cavity in a mold with a molten metal material. As an example of injection molding used in such a metal injection molding machine, an injection device of a metal injection molding machine has been proposed which has a configuration in which the speed of an injection piston is rapidly reduced to switch the process from an injection process to a holding process (Unexamined Japanese Patent Application Publication No. 2007-216285).

[0003] In this injection device, an oil drain port having a large opening and an oil drain port having a small opening are provided in a front chamber, and the oil drain port having the large opening is capped by the injection piston when the injection piston advances to a holding switch position. As a result, the discharge of hydraulic oil is greatly reduced, so that a sudden brake is applied to the injection piston, and the discharge for operation during the holding process can be performed through the oil drain port having the small opening. SUMMARY

[0004] However, in the above-described injection device, there is a problem that an unbalanced load is applied to the injection piston when the injection piston is decelerated. As described above, when the oil drain port having the large opening is capped by the injection piston, the pressure applied to the portion of the side surface exposed from the oil drain port becomes low. On the other hand, there is high-pressure hydraulic oil at the portion of the side surface of the injection piston opposite to the portion exposed from the oil drain port. Therefore, this pressure difference causes a problem that a shear force or an eccentric load as a force applied in a side direction is applied to the injection piston.

[0005] Other challenges and novel features will be set forth in the description and drawings that follow.

[0006] An injection device according to an embodiment is an injection device including: an injection piston configured to drive a screw shaft which is axially movable and rotatable in an axial direction; an injection hydraulic cylinder configured to drive the injection piston in the axial direction and partitioned into a first chamber and a second chamber to which hydraulic oil is supplied; a first oil discharge port configured to discharge the hydraulic oil from the second chamber and capped by a piston portion of the injection piston when the piston portion advances to a pressure-holding switching position; and a second oil discharge port configured to discharge the hydraulic oil from the second chamber regardless of a position of the injection piston, wherein the injection piston includes: a first member on a first chamber side; and a second member on a second chamber side and connected to the first member at a piston portion, an interface between the first member and the second member being provided at a position spaced apart from an end portion of the second member side of the piston portion by a predetermined distance in the axial direction.

[0007] According to an embodiment of the present invention, it is possible to provide an injection device of a metal injection molding machine capable of advantageously protecting an injection piston.

[0008] The above and other objects, features and advantages of the present disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, which are to be considered illustrative only, and not to be considered as restricting the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a diagram showing a schematic configuration of an injection device of a metal injection molding machine according to a first embodiment;

[0010] Figure 2 is an enlarged view of a vicinity of a front chamber of the injection device according to the first embodiment;

[0011] Figure 3 is a diagram schematically showing a configuration of an injection piston according to the first embodiment;

[0012] Figure 4 is a diagram showing a state in which the injection piston according to the first embodiment caps a first oil discharge port;

[0013] Figure 5 is a diagram showing a vicinity of a piston portion displaced by eccentric load in the injection device according to the first embodiment;

[0014] Figure 6 is a diagram showing a schematic configuration of a general injection device of a metal injection molding machine;

[0015] Figure 7is an enlarged view of the vicinity of a front chamber of a general injection device;

[0016] Figure 8 is a view schematically showing a configuration of an injection piston of a general injection device;

[0017] Figure 9 is a view showing a state in which the injection piston of the general injection device covers a first oil discharge port; and

[0018] Figure 10 shows the vicinity of a piston portion displaced by an eccentric load. DETAILED DESCRIPTION

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to the following embodiments. The following description and drawings are appropriately simplified in order to make the explanation clear. Further, the same elements are denoted by the same reference numerals, and redundant description will be omitted.

[0020] First Embodiment

[0021] As a prerequisite for understanding an injection device of a metal injection molding machine according to the present embodiment, a general injection device of a metal injection molding machine according to unexamined Japanese Patent Application Publication No. 2007-216285 will be described. Figure 6 A schematic configuration of the injection device 1000 of the above-described metal injection molding machine is shown. The injection device 1000 includes a heating cylinder 101 and a screw 102 provided in the heating cylinder 101 to be freely driven in the axial and rotational directions. A molding material is charged into the heating cylinder 101 from a hopper 103, and the charged material is melted by frictional heat, shear heat generated due to rotation of the screw 102, and heat applied from a heater 104 provided on the outer periphery of the heating cylinder 101. The melted material is kneaded by rotation of the screw 102 and is sent to the front of the heating cylinder 101. A nozzle 105 is attached to the top end of the heating cylinder 101. When the material is injected, the melted molding material held at the top end of the heating cylinder 101 is injected into a cavity 107 of a closed mold 106 through the nozzle 105.

[0022] The screw 102 is rotationally driven by a motor 108, and is axially driven by an injection piston 110 provided in an injection hydraulic cylinder 109.

[0023] The injection hydraulic cylinder 109 is divided into two chambers by the injection piston 110, a front chamber 111B is provided at the front (-X direction), and a rear chamber 111A is provided at the rear (+X direction). Pressure oil accumulated in an accumulator 113 is supplied to the rear chamber 111A by a hydraulic pump 112 through a flow control valve 114.

[0024] Figure 7is a close-up view of the vicinity of the front chamber 111B of the injection device 100. In the front chamber 111B, the first oil drain port 115A is completely or mostly capped by the injection piston 110 at the desired switchover position of the injection piston 110 for the pressure holding, while the second oil drain port 115B is not capped by the injection piston 110 even at the most forward position of the injection piston 110. The first oil drain port 115A is formed in a side surface portion of the injection hydraulic cylinder 109, and the second oil drain port 115B is formed in an end surface portion of the injection hydraulic cylinder 109.

[0025] The first oil drain port 115A is connected to the oil tank 117 through the flow control valve 116, and has an opening area large enough to drain the hydraulic oil stored in the front chamber 111B to the oil tank 117 during the injection. The second oil drain port 115B is connected to the oil tank 117 through the flow control valve 118, and drains the hydraulic oil in the front chamber 111B to the oil tank 117 during the pressure holding. The opening area of the second oil drain port 115B can be smaller than that of the first oil drain port 115A, as long as the hydraulic oil can flow through the second oil drain port 115B at the flow rate in the pressure holding and at the flow rate for the retreat of the injection piston 110 in the measurement (+X direction).

[0026] The injection molding mainly includes a measurement process, an injection process, and a pressure holding process. In the measurement process, the solid molding material is supplied from the hopper 103 into the heating cylinder 101, and the screw 102 is driven in the axial direction backward (+X direction) by the injection hydraulic cylinder 109 while being rotationally driven by the motor 108. Thus, the material is fed inside the heating cylinder 101 to the front of the heating cylinder 101 (-X direction). In the injection process, when the measurement value reaches a predetermined value, the screw 102 is driven in the axial direction forward (-X direction) by supplying pressure oil to the injection hydraulic cylinder 109, and the measured molten material is injected from the nozzle 105 into the cavity 107 of the mold 106. The pressure holding process is a process of applying pressure to the material in the mold 106 from the material remaining in the heating cylinder 101 to compensate for shrinkage caused by cooling of the material after completion of the material injection. By performing these processes, the material can be molded into the desired shape of the cavity 107.

[0027] However, it has been found that the injection device 1000 has a problem that eccentric load is applied to the injection piston 110 when the injection piston 110 decelerates.

[0028] Figure 8The configuration of the injection piston 110 in the injection device 1000 is schematically shown. The injection piston 110 includes a front member 120 disposed in the front direction (-X direction) and a rear member 130 disposed in the rear direction (+X direction). The front member 120 and the rear member 130 are connected at a piston portion 110A, which has the largest cross-sectional diameter of the injection piston 110 and is closest to or contacts the inner surface of the injection hydraulic cylinder 109 (i.e., the housing 109A). The front member 120 and the rear member 130 are cylindrical members, and a shaft member 140 is inserted into the hollow portion thereof.

[0029] A front piston portion 121 having the largest outer diameter is disposed at the rear side (+X direction) of the front member 120. A cylindrical member 122 extending in the forward (-X direction) with a smaller outer diameter than that of the front piston portion 121 and a fitting member 123 extending in the rearward (+X direction) are connected to the front piston portion 121.

[0030] A rear piston portion 131 having a cylindrical shape extending in the X direction and having the largest outer diameter is disposed at the front (+X direction) end of the rear member 130. A cylindrical member 132 extending in the rearward (+X direction) with an outer diameter smaller than that of the rear piston portion 131 is connected to the rear piston portion 131.

[0031] A holding portion 140A having a larger outer shape is disposed in the middle of the shaft member 140 in the X direction. A flange portion 140B protruding in the radial direction is disposed on the holding portion 140A. An angular contact bearing (angular contact ball bearing) 151 for bearing a radial force (radial load) is disposed between the inner surface of the front piston portion 121 and the fitting member 123 and the holding portion 140A to hold the position of the shaft member 140 in the radial direction. A thrust bearing (thrust roller bearing) 152 is disposed between the front (-X direction) side end of the rear piston portion 131 and the flange portion 140B to bear a force (axial load or thrust load) in the axial direction (X direction). The shaft member 140 is configured to be movable in a predetermined range in the X direction with respect to the front member 120 and the rear member 130, while the movement toward the rear (+X direction) is limited by the thrust bearing 152.

[0032] The outer diameter of the fitting member 123 and the inner diameter of the rear piston portion 131 are sized such that the fitting member 123 can be inserted into the rear piston portion 131. Thus, for example, the injection piston 110 can be configured in such a manner that the shaft member 140 on which the angular contact bearing 151 is mounted is inserted into the rear member 130 on which the thrust bearing 152 is mounted, and then the shaft member 140 is covered with the front member 120, and the fitting member 123 and the rear piston portion 131 are fitted.

[0033] At this time, since the rear piston portion 131 covers the fitting member 123 when viewed in the radial direction (for example, the Y direction or the Z direction), the engaging portion 110B formed on the outer surface of the piston portion 110A is at a position offset to the front (-X direction) of the piston portion 110A.

[0034] To prevent leakage of hydraulic oil, sealing members 119A to 119C such as guide rings and oil seals are provided between the injection piston 110 and the injection hydraulic cylinder 109 (i.e., the housing 109A). The sealing member 119A is a ring-shaped member fitted to the inner surface of the opening on the -X side of the housing 109A, and is provided to seal between the inner surface of the housing 109A and the outer surface of the cylindrical member 122 of the front member 120. The sealing member 119B is a ring-shaped member fitted to the outer surface of the rear piston portion 131 of the rear member 130, and is provided to seal between the inner surface of the housing 109A and the outer surface of the rear piston portion 131. The sealing member 119C is a ring-shaped member fitted to the inner surface of the opening on the +X side of the housing 109A, and is provided to seal between the inner surface of the housing 109A and the outer surface of the cylindrical member 132 of the rear member 130.

[0035] Next, Figure 9 A state in which the injection piston 110 covers the first oil discharge port 115A is shown. In the injection device 1000, hydraulic oil is discharged at a large flow rate from the first oil discharge port 115A, and is discharged at a flow rate smaller than that of the first oil discharge port 115A from the second oil discharge port 115B. When the injection piston 110 advances in the -X direction to cover the first oil discharge port 115A completely or substantially, the pressure applied to the side surface portion S11 (indicated by a thick line) of the side surface of the injection piston 110 decreases rapidly (for example, to atmospheric pressure).

[0036] On the other hand, since the hydraulic oil at a position outside the side surface portion S11 around the injection piston 110 is discharged only through the second oil discharge port 115B having a small flow rate, the pressure of the hydraulic oil becomes high (indicated by a thick hatched line). As a result, the hydraulic oil pressure applied to the side surface portion S12 across the center axis of the injection piston 110 from the side surface portion S11 becomes high. Therefore, an eccentric load F directed from the side surface portion S12 toward the side surface portion S11 is applied to the injection piston 110.

[0037] At this time, the eccentric load F presses the piston portion 110A downward (-Z direction). Therefore, the load is concentrated on the sealing member 119C fitted to the rear piston portion 131, which causes deterioration, for example, uneven wear, of the sealing member 119B. Furthermore, when the uneven wear of the sealing member 119B progresses, the piston portion 110A cannot be held sufficiently, and the piston portion 110A can be displaced downward (-Z direction).

[0038] Figure 10 The vicinity of the piston portion displaced by the eccentric load is shown. At this time, as the displacement of the piston portion increases, the corner portion 121A on the front (-X direction) side of the front piston portion 121 can collide with the opening portion of the first oil discharge port 115A. In Figure 10 In the middle, the profile of the injection piston at the time of no displacement is shown by a dotted line. As described above, since the joint portion 110B is located on the front (-X direction) side of the piston portion 110A, i.e., close to the collision portion, a large force can be applied to the joint portion 110B.

[0039] At the joint portion 110B, the front piston portion 121 and the rear piston portion 131 are connected by a connecting mechanism for connecting the two members. For example, a bolt can be used as the connecting mechanism. In this case, by forming a female screw (not shown) that penetrates the front piston portion 121 and the rear piston portion 131 in the rear (+X direction) from the top surface 121C of the front piston portion 121, and by screwing a bolt (not shown) with a male screw into the female screw, the front member 120 and the rear member 130 are connected. The bolt is one example of the connecting mechanism, and various connecting mechanisms other than the bolt can be used, as described later.

[0040] As described above, when the front member 120 and the rear member 130 are connected by the connecting mechanism, it can be understood that, since the joint portion 110B is located on the front (-X direction) side of the piston portion 110A, i.e., close to the collision portion, a large force can be applied to the connecting mechanism.

[0041] Further, since the collision portion is also close to the connecting portion 121B between the front piston portion 121 and the cylindrical member 122 having different diameters, and the material of the connecting portion is relatively thin, a large force can be applied to the thin portion.

[0042] Hereinafter, an injection device of a metal injection molding machine capable of preventing a large force from being applied to the joint portion of the injection piston will be described.

[0043] Figure 1 is a diagram showing a schematic configuration of an injection device of a metal injection molding machine according to a first embodiment. Figure 1The illustrated injection apparatus 100 includes a heating cylinder 1 and a screw 2 disposed in the heating cylinder 1 to be freely driven in the axial and rotational directions. A molding material is charged into the heating cylinder 1 from a hopper 3, and the charged material is melted by frictional heat, shear heat generated due to rotation of the screw 2, and heat applied from a heater 4 provided on the outer periphery of the heating cylinder 1. The melted material is kneaded by rotation of the screw 2 and is sent to the front (-X direction) of the heating cylinder 1. A nozzle 5 is attached to the top end of the heating cylinder 101. When the injection material is injected, the melted molding material held at the top end of the heating cylinder 1 is injected into a cavity 7 of a closed mold 6 through the nozzle 5.

[0044] The screw 2 is rotationally driven by a motor 8, and is axially driven by an injection piston 10 disposed in an injection hydraulic cylinder 9.

[0045] The injection hydraulic cylinder 9 is divided into two chambers by the injection piston 10, a front chamber 11B (also referred to as a second chamber) is provided at the front (-X direction), and a rear chamber 11A (also referred to as a first chamber) is provided at the rear (+X direction). Pressure oil accumulated in an accumulator 13 is supplied to the rear chamber 11A by a hydraulic pump 12 through a flow control valve 14.

[0046] In Figures 1 to 10 , the direction along the central axis of the injection piston 10 from the front chamber 11B to the rear chamber 11A is defined as the X direction, the direction perpendicular to the plane of the drawing and from the front to the back of the drawing is defined as the Y direction, and the vertical direction from the bottom to the top of the drawing is defined as the Z direction.

[0047] The configuration of the front chamber 11B will be described in detail below. Figure 2 is an enlarged view of the vicinity of the front chamber 11B of the injection apparatus 100. In the front chamber 11B, the first oil drain port 15A is completely or mostly capped by the injection piston 10 at a desired pressure-holding switching position of the injection piston 10, while the second oil drain port 15B is not capped by the injection piston 10 even at the most front position of the injection piston 10.

[0048] The first oil drain port 15A is connected to a tank 17 through a flow control valve 16, and has an opening area large enough to drain hydraulic oil stored in the front chamber 11B to the tank 17 in an injection process to be described later.

[0049] A second oil discharge port 15B is formed on the end surface of the injection hydraulic cylinder 9. The second oil discharge port 15B is connected to the oil tank 17 through a flow control valve 18, and discharges hydraulic oil in the front chamber 11B to the oil tank 17 in a pressure holding process to be described later. The opening area of the second oil discharge port 115B can be smaller than the opening area of the first oil discharge port 15A, as long as hydraulic oil can flow through the second oil discharge port 15B at a flow rate in the pressure holding process and at a flow rate to cause the injection piston 10 to retreat in the +X direction in the measurement process. For example, the opening area of the second oil discharge port 15B can be 1 / 10 or less of the opening area of the first oil discharge port 15A.

[0050] Next, the injection piston 10 will be described in detail. Figure 3 The configuration of the injection piston 10 according to the first embodiment is schematically shown.

[0051] The injection piston 10 includes a front member 20 (also referred to as a second member) provided at the front (-X direction) and a rear member 30 (also referred to as a first member) provided at the rear (+X direction). The front member 20 and the rear member 30 are connected at a piston portion 10A having the largest cross-sectional diameter of the injection piston 10 and closest to or contacting the inner surface of the injection hydraulic cylinder 9 (i.e., the housing 9A). The front member 20 and the rear member 30 are cylindrical members, and a shaft member 40 is inserted into the hollow portions thereof.

[0052] A front piston portion 21 extending in the X direction and having the largest outer diameter is provided at the rear (+X direction) side of the front member 20. A cylindrical member 22 having an outer diameter smaller than that of the front piston portion 21 and extending forward (-X direction) is connected to the front piston portion 121.

[0053] A rear piston portion 31 having the largest outer diameter is provided at the front (-X direction) side of the rear member 30. A cylindrical member 32 having an outer diameter smaller than that of the rear piston portion 31 and extending rearward (+X direction) and a fitting member 33 extending forward (-X direction) are connected to the rear piston portion 31.

[0054] A holding portion 40A having a large outer shape is provided in the middle of the shaft member 40 in the X direction. A flange portion 40B protruding in the radial direction is provided at the holding portion 40A. An angular contact bearing (angular contact ball bearing) 51 for receiving a radial force (radial load) is provided between the inner surface of the front piston portion 21 and the holding portion 40A to hold the position of the shaft member 40 in the radial direction. A thrust bearing (thrust roller bearing) 52 is provided between the front (-X direction) side end portion of the rear piston portion 31 and the flange portion 40B to receive a force (axial load or thrust load) in the axial direction (X direction). The shaft member 40 is configured to be movable with respect to the front member 20 and the rear member 30 in a predetermined range in the X direction, while movement toward the rear (+X direction) is restricted by the thrust bearing 52.

[0055] The outer diameter of the fitting member 33 and the inner diameter of the front piston portion 21 are sized so that the fitting member 33 can be inserted into the front piston portion 21. Thus, for example, the injection piston 10 can be configured in such a manner that the shaft member 40 on which the angular contact bearing 51 is mounted is inserted into the rear member 30 on which the thrust bearing 52 is mounted, and then the front member 20 is placed over the shaft member 40, and the fitting member 33 and the front piston portion 21 are mated.

[0056] The front member 20 and the rear member 30 are connected by forming an internal thread (not shown) that penetrates the rear piston portion 31 and the front piston portion 21 in the forward (-X direction) from the top surface 31A of the rear piston portion 31, and by screwing a bolt 60 having an external thread into the internal thread.

[0057] In this configuration, when viewed in the radial direction (e.g., in the Y direction or the Z direction), the engaging portion 10B formed on the outer surface of the piston portion 10A is at a position that is offset toward the rear (+X direction) of the piston portion 10A due to the front piston portion 21 covering the fitting member 33.

[0058] To prevent leakage of hydraulic oil, sealing members 19A to 19C such as guide rings and oil seals are provided between the injection piston 10 and the injection hydraulic cylinder 9 (i.e., the housing 9A). The sealing member 19A is a ring-shaped member that is fitted to the inner surface of the opening of the -X side of the housing 9A, and is provided to seal between the inner surface of the housing 9A and the outer surface of the cylindrical member 22 of the front member 20. The sealing member 19B is a ring-shaped member that is fitted to the outer surface of the rear piston portion 31 of the rear member 30, and is provided to seal between the inner surface of the housing 9A and the outer surface of the rear piston portion 31. The sealing member 19C is a ring-shaped member that is fitted to the inner surface of the opening of the +X side of the housing 9A, and is provided to seal between the inner surface of the housing 9A and the outer surface of the cylindrical member 32 of the rear member 30.

[0059] Next, injection molding by the injection device 100 will be described. The injection molding mainly includes a measurement process, an injection process, and a holding process. Each process will be described below.

[0060] The measurement process is a process of measuring the material filled into the cavity. In this process, the solid molding material is supplied into the heating cylinder 1 from the hopper 3, and the screw 2 is driven in the axial direction backward (+X direction) by the injection hydraulic cylinder 9 while being rotationally driven by the motor 8. Thus, the material is transported in the heating cylinder 1 in a molten state to the front of the screw 2. By measuring the amount of movement of the screw 2, the material supplied into the heating cylinder 1 can be measured.

[0061] The injection process is a process of filling the cavity 7 with the material. In the injection process, when the measurement value reaches a predetermined value, the screw 2 is driven to advance in the axial direction by supplying pressure oil to the injection hydraulic cylinder 9, and the measured molten material is injected from the nozzle 5 into the cavity 7 of the mold 6. In injection molding of an alloy material, if the molten material is not injected at a relatively high speed, the molten metal rapidly cools, and filling of the cavity 7 becomes insufficient. Thus, in general injection molding for a metal material, the accumulator 13 is used as a pressure oil supply source of the injection hydraulic cylinder 9, and the screw 2 is driven at a high speed (for example, a speed of 1 to 5 m / s) in the axial direction to inject the molten material.

[0062] The holding process is a process of applying pressure to the material filled in the cavity 7 by holding the pressure applied to the material remaining in the heating cylinder 1 after the material is injected, for the purpose of compensating for shrinkage caused by cooling of the material. Thereafter, the material in the cavity 7 is cooled while the held pressure is applied. Thus, the material can form a desired shape of the cavity 7.

[0063] At this time, if the switching from the injection process to the holding process is performed too early, the material filling of the cavity 7 becomes insufficient, resulting in short shots (insufficient filling) and sink marks in the molded product. If the switching from the injection process to the holding process is performed too late, the material excessively fills into the cavity 7, resulting in flash, and the durability of the injection device 100 and the mold 6 deteriorates. Thus, in injection molding, it is required to keep the holding switch position at the end of injection constant.

[0064] The operation at the time of switching from the injection process to the holding process in the present embodiment will be specifically described below. In the present embodiment, when pressure oil is supplied from the accumulator 13 to the rear chamber 11 A of the injection hydraulic cylinder 9 in the injection process, the injection piston 10 advances in the injection direction (-X direction) while hydraulic oil is discharged from the first oil discharge port 15 A of the front chamber 11 B. Thereafter, when the injection piston 10 reaches the holding switch position, the first oil discharge port 15 A is completely or substantially capped by the injection piston 10.

[0065] In this configuration, when the first oil discharge port 15A is capped by the injection piston 10 (when the injection piston 10 reaches the pressure-holding switching position), the discharge of hydraulic oil from the front chamber 1 IB is restricted at any injection speed, and a braking pressure (indicated by a broken line) is immediately generated. Therefore, the injection piston 10 can be rapidly decelerated. The switching position from the injection process to the pressure-holding process (the pressure-holding switching position) can be a fixed position at which the injection piston 10 caps the first oil discharge port 15A.

[0066] Since the pressure-holding switching position is a fixed position, the timing of the pressure-holding switching for the molded article can be controlled by adjusting the measurement completion position.

[0067] Further, by setting the discharge flow rate of the flow rate control valve 18 to a value that enables the pressure to be maintained during the pressure-holding process, after the injection piston 10 is decelerated, hydraulic oil can be discharged from the second oil discharge port 15B at a desired flow rate by the flow rate control valve 18, and therefore, the pressure of the pressure oil supplied to the rear chamber 1 IA can be controlled so as to smoothly switch from the injection process to the pressure-holding process. Instead of using the flow rate control valve 18 described above, by appropriately setting the number of second oil discharge ports 15B and the opening area of the second oil discharge ports 15B, the flow rate of the hydraulic oil discharged from the second oil discharge ports 15B can be adjusted.

[0068] Next, measures to prevent the injection piston 10 from being damaged in this configuration will be described. Figure 4 A state in which the injection piston 10 caps the first oil discharge port 15A is shown. As described above, hydraulic oil is discharged from the first oil discharge port 15A at a large flow rate, and is discharged from the second oil discharge port 15B at a flow rate smaller than that of the first oil discharge port 15A. Therefore, as shown in Figure 4 When the injection piston 10 advances in the -X direction and the first oil discharge port 15A is completely or substantially capped, the pressure applied to the side surface portion S1 (indicated by a thick line, also referred to as a first surface) of the side surface of the injection piston 10 exposed from the first oil discharge port 15A rapidly decreases (for example, to atmospheric pressure).

[0069] On the other hand, since the hydraulic oil around the injection piston 10 at a position other than the side surface portion S1 is discharged only through the second oil discharge port 15B having a small flow rate, the pressure of the hydraulic oil becomes high (indicated by a thick hatched line, also referred to as a second surface). As a result, the pressure of the hydraulic oil applied to the side surface portion S2 of the side surface of the injection piston 10 opposite to the center axis of the injection piston 10 from the side surface portion S1 becomes high. Therefore, an eccentric load F directed from the side surface portion S2 toward the side surface portion S1 is applied to the injection piston 10. In other words, when the axial direction (X direction) of the injection piston 10 is used as a reference, it can be understood that the eccentric load F is a shear force or a force applied in a side direction with respect to the injection piston 10.

[0070] At this time, the eccentric load F presses the piston portion 10A downward (-Z direction). Therefore, the load is concentrated on the sealing member 19B fitted to the rear piston portion 31, and uneven wear of the sealing member 19B can occur. Further, it is conceivable that as the uneven wear of the sealing member 19B progresses, the piston portion 10A cannot be held sufficiently, and the piston portion 10A is displaced downward (-Z direction). Due to the displacement in this case, it can be considered that the injection piston 10 moves in parallel to the Y direction, or the injection piston 10 rotates around a direction orthogonal to the axial direction (X direction), for example, the Y direction, that is, side displacement occurs.

[0071] Figure 5 The vicinity of the piston portion displaced by the eccentric load is shown. As the displacement of the piston portion 10A increases, the corner portion 21A on the front (-X direction) side of the front piston portion 21 can collide with the opening of the first oil discharge port 15A and the inner surface of the housing 9A. In Figure 5 In the embodiment, the profile of the injection piston in the absence of displacement is indicated by a broken line. However, in this configuration, since the joint portion 10B exists on the rear (+X direction) side of the piston portion 10A, that is, at a position away from the collision portion, it is considered that the joint portion 10B is not affected or is affected little even when a force is applied at the time of collision. Therefore, it is possible to prevent the joint portion 10B from being damaged.

[0072] In this configuration, since the joint portion 10B is not exposed from the first oil discharge port 15A, it is possible to prevent the joint portion 10B from being subjected to a load due to a pressure difference. Therefore, from the viewpoint of preventing damage, the joint portion 10B is advantageous.

[0073] As described above, according to this configuration, even when the front piston portion 21 contacts the housing 9A due to uneven wear of the sealing member 19B, it is possible to prevent the injection piston 10 configured by connecting two members from being damaged.

[0074] Other Embodiments

[0075] The present disclosure is not limited to the above-described embodiments, and can be appropriately changed without departing from the scope of the present disclosure. For example, in the above-described embodiments, it has been described that the front member 20 and the rear member 30 are connected by bolting, however, the connection method is not limited thereto. An internal thread can be formed on the inner surface of the front piston portion 21, an external thread can be formed on the outer surface of the fitting member 33, and the fitting member 33 can be screwed into the front piston portion 21 to connect the front member 20 and the rear member 30. Further, the front piston portion 21 and the fitting member 33 can be welded or bonded to each other with an adhesive, thereby connecting the front member 20 and the rear member 30. From the above-described disclosure, it is apparent that the scheme of the present disclosure can be changed in various ways.

[0076] These changes, along with others, should not be viewed as departing from the spirit and scope of the present disclosure, and such modifications are intended to be included in the appended claims.

Claims

1. An injection apparatus comprising: an injection piston connected to a screw rod disposed in a heating cylinder in a manner capable of moving and rotating in an axial direction of the heating cylinder, and configured to drive the screw rod in the axial direction; an injection hydraulic cylinder configured to drive the injection piston in the axial direction by pressure of hydraulic oil, and configured to be partitioned into a first chamber to which hydraulic oil pressurized for driving the injection piston is supplied, and a second chamber from which hydraulic oil is discharged, the first chamber driving the injection piston in the axial direction by hydraulic pressure; a first oil discharge port configured to discharge the hydraulic oil from the second chamber, the first oil discharge port being disposed on the injection hydraulic cylinder in a manner to be capped by a piston portion of the injection piston when the piston portion advances to a pressure-holding switching position; and a second oil discharge port disposed on the injection hydraulic cylinder in a manner capable of discharging hydraulic oil from the second chamber regardless of a position of the injection piston, wherein the injection piston includes: a first member disposed on a first chamber side and extending in the axial direction; and a second member disposed on a second chamber side, the second member being connected to the first member in the piston portion and extending in the axial direction, an engagement portion between the first member and the second member is disposed in the piston portion at a position spaced apart from an end portion of the piston portion on the second chamber side by a predetermined distance in the axial direction, wherein the engagement portion is disposed on the first chamber side with respect to a center of the piston portion in the axial direction.

2. The injection apparatus according to claim 1, wherein when the piston portion of the injection piston advances to the pressure-holding switching position and the first oil discharge port is capped by the piston portion, a pressure applied to a first surface of the piston portion exposed from the first oil discharge port is lower than a pressure applied to a second surface of the piston portion opposite to the first oil discharge port, and an eccentric load generated due to a pressure difference between the pressure applied to the first surface and the pressure applied to the second surface is applied to the piston portion.

3. An injection device according to claim 2, wherein, By the partial load, a gap between the end portion of the piston portion on the second chamber side and the injection hydraulic cylinder becomes smaller than a gap between the end portion of the piston portion on the first chamber side and the injection hydraulic cylinder.

4. The injection device of claim 3, wherein, In a plane perpendicular to the axial direction, a seal member configured to seal a space between the piston portion and an inner surface of the injection hydraulic cylinder is provided on an outer periphery of the piston portion, and a gap between the piston portion on the second chamber side with respect to the seal member and the injection hydraulic cylinder becomes smaller than a gap between the piston portion on the first chamber side with respect to the seal member and the injection hydraulic cylinder.

5. The injection device of claim 1 or 2, wherein, The joint is provided at a position that is not exposed from the first oil discharge port when the piston portion of the injection piston advances to the pressure-holding switching position.

6. The injection device of claim 1 or 2, wherein, The first member and the second member are configured such that the end of one member cooperates with the end of the other member.

7. An injection device according to claim 6, wherein, The first member and the second member are connected by screwing a member having an external thread into an internal thread formed on the first member and the second member.

8. The injection device of claim 6, wherein, The first member and the second member are connected by screwing an external thread formed on one member into an internal thread formed on the other member.

9. The injection device of claim 1 or 2, wherein, The first member and the second member are connected by welding or adhesion.

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