Backflow prevention device and injection device having same

Abstract

Provided is a backflow prevention device in which a piston ring is less likely to enter a gap between a backflow prevention ring and a cylinder. A backflow prevention device (4) of an injection device (3) is provided with: a backflow prevention ring (41) having an annular groove (42) facing the inner surface of a cylinder (32) of the injection device (3); and a piston ring (51) fitted into the annular groove (42). The annular groove (42) and the piston ring (51) have rear side surfaces (44, 55) in the injection direction of the injection device (3), respectively, and the rear side surface (44) of the annular groove (42) and the rear side surface (55) of the piston ring (51) can contact each other only at respective radially inner portions (44B, 55B).

Description

TECHNICAL FIELD

[0001] The present application is based on Japanese Application No. 2023-108728 filed on June 30, 2023, and claims priority based on the application. The entire contents of the application are hereby incorporated by reference. The present application relates to a backflow preventing device and an injection device having the same. BACKGROUND

[0002] An injection device of an injection molding machine has a backflow preventing device that prevents backflow of a material injected at the time of injection. In Japanese Patent Application Publication No. H7-314510, an injection device is described that has a screw housed in a cylinder, a pusher mounted to the screw, and a backflow preventing device provided between a screw head of the screw and the pusher. If the screw advances at the time of injection, the backflow preventing device is pressed against the pusher, preventing the injected material from returning to the rear of the pusher. The backflow preventing device has a backflow preventing ring and a piston ring that is embedded in the backflow preventing ring. SUMMARY

[0003] The piston ring is provided for the purpose of improving the sealing performance between the backflow preventing device and the cylinder. However, the screw moves at high speed at the time of injection, and thus there is a possibility that the piston ring deforms and intrudes into the gap between the backflow preventing ring and the cylinder. In this case, not only does the wear of the piston ring progress, but there is also a possibility that the piston ring that has intruded into the gap between the backflow preventing ring and the cylinder damages the cylinder.

[0004] An object of the present application is to provide a backflow preventing device in which a piston ring is less likely to intrude into a gap between a backflow preventing ring and a cylinder.

[0005] The backflow preventing device of the present application has a backflow preventing ring having an annular groove, and a piston ring embedded in the annular groove. The rear side of the annular groove in the injection direction and the rear side of the piston ring in the injection direction can only contact each other on the inside of the respective radial directions.

[0006] According to the present application, a backflow preventing device in which a piston ring is less likely to intrude into a gap between a backflow preventing ring and a cylinder can be provided. The above and other objects, features, and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a schematic front view of an injection molding machine of Embodiment 1. Figure 2 is an enlarged view of A portion of Figure 1 Figure 3A is an enlarged view of B portion of Figure 2 Figure 3B Figure 2 ​​​An enlarged view of the C portion of FIG. 1. Figure 4 is along Figure 3A A cross-sectional view of the 4-4 line of FIG. 1. Figure 5 is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the second embodiment. Figure 2 Figure 6 is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the third embodiment. Figure 2 Figure 7 is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the fourth embodiment. Figure 2 Figure 8 is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the fifth embodiment. Figure 2 Figure 9 is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the sixth embodiment. Figure 2 Figure 10 is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the seventh embodiment. Figure 2 Figure 11A is an enlarged view of the portion corresponding to the B portion of FIG. 1 in the comparative example. Figure 2 Figure 11B is a diagram showing the problem of the comparative example. DETAILED DESCRIPTION

[0008] Hereinafter, several embodiments of the present application will be described with reference to the drawings. The present application can be preferably applied to a metal injection molding machine, and in particular, to a metal injection molding machine that injects a metal having a low viscosity at the time of injection. However, the present application can also be applied to an injection molding machine that injects a resin. In the following description, the X direction is referred to as the axial direction of the cylinder 32, the injection direction is referred to as the +X direction, and the direction opposite to the injection direction is referred to as the -X direction. The terms "front", "rear", "front portion", "rear portion", and the like are defined with the injection direction as a reference. In addition, the "radial direction" is defined with the center axis CL of the cylinder 32 as a reference.

[0009] (First Embodiment) <Overall Configuration of Injection Molding Machine> Figure 1 shows a schematic front view of the injection molding machine 1 of the first embodiment. The injection molding machine 1 is a horizontal metal injection molding machine that injects a molten metal such as a magnesium alloy or an aluminum alloy. The injection molding machine 1 is generally composed of a clamping device 2 that clamps a mold, and an injection device 3 that heats and melts a metal material to be injected and injects it.

[0010] <Clamping Device 2>​​​​​​​ The mold clamping device 2 has a fixed platen 21 fixed to a machine base (not shown) for mounting a fixed mold M1, and a movable platen 22 slidable on the machine base for mounting a movable mold M2. A mold clamping housing (not shown) slidable on the machine base is provided on the side of the movable platen 22 opposite to the fixed platen 21. The fixed platen 21 and the mold clamping housing are connected by multiple connecting rods 23. A linkage mechanism (not shown) for opening and closing the mold is provided between the movable platen 22 and the mold clamping housing. The linkage mechanism is driven by an electrically operated ball screw. Alternatively, a hydraulic mold clamping cylinder can be used instead of the linkage mechanism. A cavity M3 for filling molten metal is formed between the fixed mold M1 and the movable mold M2.

[0011] <Injection Device 3> The injection device 3 is mounted on a base (not shown). The injection device 3 includes a hollow cylindrical cylinder 32 for heating and melting the injected metal material, a screw 33 housed within the cylinder 32, and a drive mechanism 34 for driving the screw 33. The screw 33 is coaxial with the cylinder 32. The screw 33 is driven to rotate by the drive mechanism 34 and is driven in both the +X and -X directions. A heater 38 for heating and melting the metal material is provided on the outer periphery of the cylinder 32.

[0012] The cylinder body 32 is roughly divided into a supply section P1, a compression section P2, and a metering section P3 from rear to front. The supply section P1 has a hopper 36 for supplying granular metal material. The metal material is fed into the compression section P2 while being heated by the heater 38. The metal material is compressed, heated, and mixed in the compression section P2 until it becomes molten, and then conveyed to the metering section P3. The metering section P3 meters the molten metal injected in one injection cycle (shot). The screw 33 has a screw head 35 at its tip in the X direction. An injection nozzle 37 for supplying molten metal to the cavity M3 is installed at the tip of the cylinder body 32.

[0013] <Backflow Prevention Device 4> Figure 2 A detailed view of the front portion of cylinder block 32. Figure 1 (Enlarged view of part A). Figure 2 For convenience, compared with the central axis CL of cylinder 32, the upper side represents the state of backflow prevention device 4 during injection, and the lower side represents the state of backflow prevention device 4 during metering. Figure 3A yes Figure 2 Enlarged view of part B, Figure 3B yes Figure 2 The enlarged view of section C shows the positional relationship between the annular groove 42 and the piston ring 51. That is to say, Figure 3A Indicates the state at the time of injection ( Figure 2 The state of the backflow prevention ring 41 shown on the upper side). Figure 3Bindicates the state at the time of metering Figure 2 the state of the reverse flow prevention ring 41 shown on the lower side of the reverse flow prevention ring 41). Figure 4 is a cross-sectional view along the 4-4 line of Figure 3A

[0014] As shown in Figure 2 , at the metering portion P3 of the cylinder 32 of the injection device 3, a reverse flow prevention device 4 that prevents reverse flow of the injected metal material is provided. The reverse flow prevention device 4 has a reverse flow prevention ring 41 that is composed of a hollow cylindrical member made of metal, and the reverse flow prevention ring 41 has an annular groove 42 that opposes the inner surface of the cylinder 32 of the injection device 3. The reverse flow prevention device 4 has a piston ring 51 that is embedded in the annular groove 42 of the reverse flow prevention ring 41. The reverse flow prevention ring 41, the annular groove 42, and the piston ring 51 are coaxial with the cylinder 32. The annular groove 42 is circumferentially provided along the outer periphery of the reverse flow prevention ring 41, and has the same cross section at each angular position around the center axis CL of the cylinder 32.

[0015] In the present embodiment, the reverse flow prevention ring 41 has two annular grooves 42, and one piston ring 51 is embedded in each annular groove 42, but the annular groove 42 and the piston ring 51 can each have at least one.

[0016] The piston ring 51 is a circular ring-shaped sealing member that is embedded in the annular groove 42 of the reverse flow prevention ring 41, and divides the front and the rear of the reverse flow prevention ring 41. The piston ring 51 is made of metal. As shown in Figure 4 , the piston ring 51 has stepped both end portions 63, and is installed in the annular groove 42 in such a manner that the steps of the both end portions 63 coincide in the circumferential direction. Therefore, the steps of the both end portions 63 are shifted in the circumferential direction in accordance with the pressure applied to the inner peripheral surface 52 and the outer peripheral surface 53 of the piston ring 51, and thus the diameter of the piston ring 51 changes. The piston ring 51 has the same cross section at each angular position around the center axis CL of the cylinder 32, except in the vicinity of the both end portions 63.

[0017] As shown in Figure 2 , a push member 39 composed of an annular plate is inserted into the screw head 35. The reverse flow prevention ring 41 is inserted into the screw 33 between the screw head 35 in front in the injection direction and the push member 39 in back in the injection direction. The outer diameter of the screw head 35 and the push member 39 is larger than the inner diameter of the reverse flow prevention ring 41, and the X-direction length of the reverse flow prevention ring 41 is smaller than the separation distance in the X-direction between the screw head 35 and the push member 39. Therefore, the reverse flow prevention ring 41 can move in the X-direction while being restricted by the screw head 35 and the push member 39.

[0018] As shown in Figure 2 , B, and Figure 3A ​As shown, when the molten metal is injected, the screw 33 advances in the +X direction, and the reverse flow prevention ring 41 relatively retreats in the -X direction with respect to the screw 33. The reverse flow prevention ring 41 abuts against the push member 39, and prevents the measured molten metal in front of the screw 33 from leaking backward when it is injected (when the screw 33 advances). As shown in Figure 2 C, and Figure 3B As shown, when the molten metal is measured, the screw 33 retreats in the -X direction, and the reverse flow prevention ring 41 relatively advances in the +X direction with respect to the screw 33. The reverse flow prevention ring 41 abuts against the screw head 35, but the molten metal in the rear of the push member 39 passes through the flow path 35A inside the screw head 35, and is supplied to the space in front of the screw head 35. In this way, the reverse flow prevention ring 41 is functionally a kind of valve.

[0019] The through hole 46 that penetrates the reverse flow prevention ring 41 in the radial direction is connected to the annular groove 42 in front in the injection direction. The high-pressure molten metal flows into the through hole 46 and exerts pressure on the outer side in the radial direction of the piston ring 51. The piston ring 51 is pressed against the inner wall of the cylinder 32 by this pressure, and the sealability of the piston ring 51 is improved. The annular groove 42 in the rear is not connected to the through hole 46. However, a part of the molten metal passes through the gap between the piston ring 51 in the front and the cylinder 32, the gap between the reverse flow prevention ring 41 and the cylinder 32, and the annular groove 42 in the rear, and exerts pressure on the inner circumferential surface 52 of the piston ring 51 in the rear. Therefore, both the piston ring 51 in the front and the piston ring 51 in the rear contribute to the improvement of the sealability.

[0020] The sealability is improved by providing the through hole 46, but since large pressure is exerted on the piston ring 51, the wear of the piston ring 51 easily progresses. Whether or not to provide the through hole 46 is appropriately decided in consideration of the sealability and the suppression of the wear of the piston ring 51. The through hole 46 can be provided in both annular grooves 42, or can be provided only in the annular groove 42 in the rear, or can not be provided in any of the annular grooves 42. However, by providing the through hole 46 only in the annular groove 42 in the front, it becomes easy to equalize the amount of wear of the piston ring 51 in the front and the piston ring 51 in the rear, and the like.

[0021] The annular groove 42 in the front and the annular groove 42 in the rear have the same configuration except whether or not the through hole 46 is connected. The two piston rings 51 have the same configuration. Therefore, in the following description, mainly the annular groove 42 in the front and the piston ring 51 that is embedded in the annular groove 42 in the front are described.

[0022] <Comparative Reverse Flow Prevention Device 104> Here, the comparative reverse flow prevention device 104 is described. Figure 11A is equivalent to Figure 2An enlarged view of the portion of the B portion of the piston ring 151. The annular groove 142 and the piston ring 151 have rectangular cross sections. As described above, the radial outer side pressure is applied to the piston ring 151, and thus the piston ring 151 is pressed against the inner wall of the cylinder 32. In addition, when the molten metal flows in the -X direction in the gap between the reverse flow prevention ring 141 and the cylinder 32 at the time of injection to flow into the annular groove 142, the piston ring 151 is pressed against the rear side surface 144 of the annular groove 142. At the time of metering, the piston ring 151 is pressed against the front side surface 143 (not shown in the drawing) of the annular groove 142, but the speed of the screw 33 is high at the time of injection, and thus the pressure with which the piston ring 151 is pressed against the side surface of the annular groove 142 is greater at the time of injection.

[0023] Figure 11B An illustration showing the deformation of the piston ring 151. The piston ring 151 is made of a relatively soft metal. Thus, if the piston ring 151 is pressed in the radial outer side and -X direction, the piston ring 151 deforms and sometimes a portion thereof intrudes into the -X direction gap G between the reverse flow prevention ring 141 and the cylinder 32. If such a state occurs, not only does the wear of the piston ring 151 progress, but also the portion of the piston ring 151 that has intruded into the gap G between the reverse flow prevention ring 141 and the cylinder 32 has the potential to damage the cylinder 32.

[0024] <Shape of the annular groove 42 and the piston ring 51> The shape of the annular groove 42 and the piston ring 51 of the present embodiment will be described in more detail with reference to Figure 3A The annular groove 42 has a front side surface 43, a rear side surface 44, and a bottom surface 45. The bottom surface 45 is the deepest portion of the annular groove 42, and divides the front side surface 43 and the rear side surface 44. The rear side surface 44 has a step portion 44C. The rear side surface 44 has a radial outer side portion 44A and a radial inner side portion 44B divided by the step portion 44C. The front side surface 43 is a plane orthogonal to the center axis CL of the cylinder 32. The through hole 46 is connected to the bottom surface 45.

[0025] The piston ring 51 has an inner peripheral surface 52, an outer peripheral surface 53, a front side surface 54, and a rear side surface 55. The inner peripheral surface 52 is the deepest portion of the annular groove 42, and divides the front side surface 54 and the rear side surface 55. The inner peripheral surface 52 opposes the bottom surface 45 of the annular groove 42. The rear side surface 55 of the piston ring 51 has a step portion 55C. The rear side surface 55 of the piston ring 51 has a radial outer side portion 55A and a radial inner side portion 55B divided by the step portion 55C. The radial outer side portion 55A, the radial inner side portion 55B, and the step portion 55C respectively oppose the radial outer side portion 44A, the radial inner side portion 44B, and the step portion 44C of the rear side surface 44 of the annular groove 42. The front side surface 54 is a plane orthogonal to the center axis CL of the cylinder 32, and opposes the front side surface 43 of the annular groove 42.

[0026] The radially outer portion 44A of the rear side 44 of the annular groove 42 is located rearward in the injection direction with respect to the radially inner portion 44B, and the radially outer portion 55A of the rear side 55 of the piston ring 51 projects rearward in the injection direction (-X direction) with respect to the radially inner portion 55B. The inner diameter of the rear portion of the piston ring 51 in the injection direction is larger than the inner diameter of the front portion of the piston ring 51 in the injection direction. The distance Dl in the X direction between the radially outer portion 44A and the radially inner portion 44B of the rear side 44 of the annular groove 42 is larger than the distance D2 in the X direction between the radially outer portion 55A and the radially inner portion 55B of the rear side 55 of the piston ring 51.

[0027] Therefore, when the piston ring 51 relatively moves in the -X direction with respect to the annular groove 42 at the time of injection, the radially inner portion 55B of the rear side 55 of the piston ring 51 can come into contact with the radially inner portion 44B of the rear side 44 of the annular groove 42, whereas the radially outer portion 55A of the rear side 55 of the piston ring 51 cannot come into contact with the radially outer portion 44A of the rear side 44 of the annular groove 42. That is, when the radially inner portion 55B of the rear side 55 of the piston ring 51 comes into contact with the radially inner portion 44B of the rear side 44 of the annular groove 42, a gap S equal to the distance Dl - D2 is formed between the radially outer portion 55A of the rear side 55 of the piston ring 51 and the radially outer portion 44A of the rear side 44 of the annular groove 42.

[0028] In this way, the rear side 44 of the annular groove 42 and the rear side 55 of the piston ring 51 can come into contact with each other only at the respective radially inner portions 44B, 55B. In the present embodiment, the shapes of the annular groove 42 and the piston ring 51 are changed from those of the comparative example, whereby a portion of the piston ring 51 becomes difficult to intrude into the -X side gap G between the reverse flow prevention ring 41 and the cylinder block 32.

[0029] As described above, the pressure is applied to the radially outer portion of the piston ring 51, but in the present embodiment, the pressure is easily reduced or adjusted. The pressure with which the piston ring 51 presses the inner surface of the cylinder block 32 is generated by the pressure applied to the inner peripheral surface 52 of the piston ring 51. When the pressure applied to the inner peripheral surface 52 of the piston ring 51 is set as Pl, the pressure with which the piston ring 51 presses the cylinder block 32 is set as P2, the width of the inner peripheral surface 52 of the piston ring 51 is set as Wl, and the width of the outer peripheral surface 53 of the piston ring 51 is set as W2, P2 = (Wl / W2) x Pl. Since P2 < Pl, the abrasion of the piston ring 51 can be suppressed. Furthermore, the pressure P2 can be adjusted by Wl / W2, whereby the balance between the sealing performance and the suppression of the abrasion of the piston ring 51 can be achieved.

[0030] Hereinafter, other embodiments of the present application will be described. In the embodiments shown below, the configurations and effects of the description are the same as those of the first embodiment.

[0031] (Second Implementation) Figure 5 This indicates the equivalent of the second embodiment. Figure 2 An enlarged view of part B. In this embodiment, a stepped portion 43C of the annular groove 42 and a stepped portion 54C of the piston ring 51 are also formed in front of the injection direction. The front side surface 43 of the annular groove 42 has a radially outer portion 43A and a radially inner portion 43B divided by the stepped portion 43C. The front side surface 54 of the piston ring 51 has a radially inner portion 54A and a radially inner portion 54B divided by the stepped portion 54C.

[0032] The radially outer portion 43A of the front side surface 43 of the annular groove 42 is positioned in front of the radially inner portion 43B in the injection direction, and the radially outer portion 54A of the front side surface 54 of the piston ring 51 protrudes in the injection direction (X direction) relative to the radially inner portion 54B. The distance D3 in the X direction between the radially outer portion 43A and the radially inner portion 43B of the front side surface 43 of the annular groove 42 is greater than the distance D4 in the X direction between the radially outer portion 54A and the radially inner portion 54B of the front side surface 54 of the piston ring 51. Therefore, Figure 5 As shown by the dashed line, when the piston ring 51 moves relative to the annular groove 42 in the X direction during metering, the radially inner side 54B of the front side 54 of the piston ring 51 can contact the radially inner side 43B of the front side 43 of the annular groove 42. On the other hand, the radially outer side 54A of the front side 54 of the piston ring 51 cannot contact the radially outer side 43A of the front side 43 of the annular groove 42.

[0033] Therefore, the front side 43 of the annular groove 42 and the front side 54 of the piston ring 51 can only contact each other at their respective radially inner sides 43B and 54B. As described above, the screw 33 moves slowly during metering, thus reducing the likelihood of the piston ring 51 intruding into the +X side gap G1 between the backflow prevention ring 41 and the cylinder 32. However, according to this embodiment, this possibility can be further reduced.

[0034] (Third implementation) Figure 6 This indicates the equivalent of the third embodiment. Figure 2An enlarged view of part B. The radially inner portion 44B of the rear side surface 44 of the annular groove 42 and the radially inner portion 55B of the rear side surface 55 of the piston ring 51 are inclined at the same angle relative to the central axis CL of the cylinder body 32. The radially inner portion 44B of the annular groove 42 forms an obtuse angle with the bottom surface 45, and the radially inner portion 55B of the piston ring 51 forms an obtuse angle with the inner circumferential surface 52. Therefore, during injection, the radially inner portion 55B of the rear side surface 55 of the piston ring 51 and the radially inner portion 44B of the rear side surface 44 of the annular groove 42 are in uniform contact. The radially outer portion 44A of the rear side surface 44 of the annular groove 42 and the radially outer portion 55A of the rear side surface 55 of the piston ring 51 are orthogonal to the central axis CL of the cylinder body 32. In this embodiment, the pressure P3 applied to the piston ring 51 in the -X direction is converted into a pressure P4 towards the radially outward direction, thereby improving the sealing performance.

[0035] (Fourth implementation) Figure 7 This indicates the equivalent of the fourth embodiment. Figure 2 An enlarged view of part B. The rear side surface 44 of the annular groove 42 has a radially outer portion 44A, a radially inner portion 44B, and a stepped portion 44C, with the radially outer portion 44A and the radially inner portion 44B divided by the stepped portion 44C. The inner diameter of the rear portion of the piston ring 51 in the injection direction is larger than the inner diameter of the front portion of the piston ring 51 in the injection direction. When the piston ring 51 moves relative to the annular groove 42 in the -X direction during injection, the radially inner portion 55B of the rear side surface 55 of the piston ring 51 can contact the radially inner portion 44B of the rear side surface 44 of the annular groove 42, while the radially outer portion 55A of the rear side surface 55 of the piston ring 51 cannot contact the radially outer portion 44A of the rear side surface 44 of the annular groove 42.

[0036] The piston ring 51 has a receiving portion 56 accommodated in the annular groove 42 and a protrusion 57 located outside the annular groove 42. The outer peripheral surface 53 of the piston ring 51 is located radially outside the annular groove 42. The rear end portion 53A of the outer peripheral surface 53 in the injection direction is located in front of the receiving portion 56 in the injection direction (radially outer portion 55A of the rear side surface 55) in the injection direction, and the outer diameter of the rear portion of the piston ring 51 in the injection direction is smaller than the outer diameter of the front portion of the piston ring 51 in the injection direction. Compared with the first embodiment, in this embodiment, the piston ring 51 moves away from the gap G, thereby making it more difficult for the piston ring 51 to invade the gap G.

[0037] The surface connecting the rear end portion 53A of the outer peripheral surface 53 and the outermost radially outermost portion 58 of the rear end portion of the receiving portion 56 has: a cylindrical surface 60 with the central axis CL of the cylinder body 32 as its central axis; and an inclined surface 61 that connects the cylindrical surface 60 to the rear end portion 53A of the outer peripheral surface 53 and is inclined relative to the central axis CL of the cylinder body 32. Therefore, it is easy for the piston ring 51 to leave the gap G, and it becomes difficult for the piston ring 51 to invade the gap G. The diameter of the cylindrical surface 60 is constant in the X direction, but it can also be increased in the +X direction.

[0038] (Fifth implementation) Figure 8 This indicates the equivalent of the fifth embodiment. Figure 2 An enlarged view of part B. In this embodiment, the outermost radial part 58 of the rear end portion of the receiving portion 56 is located inside the annular groove 42, and other points are the same as in the fourth embodiment. This embodiment achieves the effects of the fourth embodiment. In addition, compared with the first and fourth embodiments, the piston ring 51 is further away from the gap G in this embodiment, thereby making it more difficult for the piston ring 51 to invade the gap G.

[0039] As piston ring 51 wears down with use, the thickness of the protrusion 57 gradually decreases, eventually making it possible for the cylindrical surface 60 to contact the cylinder block 32. However, since the cylindrical surface 60 is located inside the annular groove 42, even if the piston ring 51 becomes thinner due to wear, it will take a long time for the cylindrical surface 60 to contact the cylinder block 32. In this embodiment, the lifespan of the piston ring 51 can be extended, and the replacement frequency of the piston ring 51 can be reduced.

[0040] (Sixth implementation) Figure 9 This indicates the equivalent of the sixth embodiment. Figure 2 An enlarged view of part B. The surface 62 connecting the rear end 53A of the outer peripheral surface 53 and the outermost radially outermost part 58 of the rear end portion of the receiving portion 56 is generally inclined relative to the central axis CL of the cylinder block 32. Other points are the same as in the fourth embodiment. The outermost radially outermost part 58 of the rear end portion of the receiving portion 56 is located radially at approximately the same position as the opening 59 of the annular groove 42. This embodiment achieves almost the same effect as the fourth embodiment, but the shape of the surface 62 connecting the rear end 53A of the outer peripheral surface 53 and the outermost radially outermost part 58 of the rear end portion of the receiving portion 56 is simple, thereby facilitating the machining of the piston ring 51.

[0041] (Seventh implementation) Figure 10 This indicates the equivalent of the 7th embodiment. Figure 2An enlarged view of a portion of the B portion of the piston ring 51. In this embodiment, the outermost portion 58 in the radial direction of the rear end portion of the accommodation portion 56 is located inside the annular groove 42, and the other points are the same as in the sixth embodiment. This embodiment has the same effect as the fifth embodiment. That is, the outermost portion 58 is located inside the annular groove 42, and thus even if the piston ring 51 is thinned by abrasion, it takes a longer time for the outermost portion 58 to come into contact with the cylinder block 32. In this embodiment, the life of the piston ring 51 can be extended, and the replacement frequency of the piston ring 51 can be reduced. In addition, in this embodiment, the piston ring 51 is away from the gap G, and thus the piston ring 51 is less likely to intrude into the gap G, as compared with the first embodiment.

[0042] Several preferred embodiments of the present application have been shown and described in detail, but it is to be understood that various changes and modifications can be made without departing from the true spirit or scope of the appended technical solutions. Explanation of Reference Numerals

[0043] 3 injection device 4 backflow prevention device 32 cylinder block 33 screw 41 backflow prevention ring 42 annular groove 44 rear portion side surface of annular groove 44A radially outer portion of rear portion side surface of annular groove 44B radially inner portion of rear portion side surface of annular groove 46 through hole 51 piston ring 53 outer peripheral surface 53A rear end portion of outer peripheral surface 55 rear portion side surface of piston ring 55A radially outer portion of rear portion side surface of piston ring 55B radially inner portion of rear portion side surface of piston ring 56 accommodation portion

Claims

1. A backflow preventing device of an injection device, wherein the backflow preventing device has: a backflow preventing ring having at least one annular groove facing an inner surface of a cylinder of the injection device; and at least one piston ring embedded in the at least one annular groove, the at least one annular groove and the at least one piston ring each have a rear side in an injection direction of the injection device, the rear side of the at least one annular groove and the rear side of the at least one piston ring are capable of contacting each other only at a respective radially inner side.

2. The backflow preventing device of an injection device according to claim 1, wherein when the radially inner side of the rear side of the at least one piston ring contacts the radially inner side of the rear side of the at least one annular groove, a gap is formed between a radially outer side of the rear side of the at least one piston ring and a radially outer side of the rear side of the at least one annular groove.

3. The backflow preventing device according to claim 2, wherein the radially outer side of the rear side of the at least one annular groove is located rearward in the injection direction with respect to the radially inner side of the rear side of the at least one annular groove, the radially outer side of the rear side of the at least one piston ring protrudes rearward in the injection direction with respect to the radially inner side of the rear side of the at least one piston ring.

4. The backflow preventing device according to claim 3, wherein the radially inner side of the rear side of the at least one annular groove and the radially inner side of the rear side of the at least one piston ring are planes orthogonal to a central axis of the cylinder.

5. The backflow preventing device according to claim 4, wherein a distance between the radially outer side and the radially inner side of the rear side of the at least one annular groove is greater than a distance between the radially outer side and the radially inner side of the rear side of the at least one piston ring.

6. The backflow preventing device according to claim 3, wherein the radially inner side of the rear side of the at least one annular groove and the radially inner side of the rear side of the at least one piston ring are inclined with respect to a central axis of the cylinder.

7. The backflow preventing device according to any one of claims 1 to 6, wherein the at least one piston ring has a housing portion housed in the at least one annular groove and an outer peripheral surface located radially outward of the at least one annular groove, a rear end portion of the outer peripheral surface in the injection direction is located forward in the injection direction with respect to a rear end portion of the housing portion in the injection direction.

8. The backflow preventing device of an injection device according to claim 7, wherein a surface connecting the rear end portion of the outer peripheral surface and the rear end portion of the housing portion has: a cylindrical surface having a central axis that is the central axis of the cylinder; and an inclined surface connecting a front end portion of the cylindrical surface in the injection direction and the rear end portion of the outer peripheral surface and inclined with respect to the central axis of the cylinder. ​ 9. The backflow preventing device of the injection apparatus according to claim 7, wherein a surface connecting the rear end portion of the outer peripheral surface and the rear end portion of the accommodation portion is inclined as a whole with respect to the center axis of the cylinder.

10. The backflow preventing device of the injection apparatus according to claim 8 or 9, wherein the outermost portion of the rear end portion of the accommodation portion in the radial direction is located at substantially the same position as the opening of the annular groove in the radial direction.

11. The backflow preventing device of the injection apparatus according to claim 8 or 9, wherein the outermost portion of the rear end portion of the accommodation portion in the radial direction is located inside the annular groove.

12. The backflow preventing device according to any one of claims 1 to 11, wherein the at least one annular groove and the at least one piston ring each have a front side in the injection direction, the front side of the at least one annular groove and the front side of the at least one piston ring are capable of contacting each other only at an inner side portion in the respective radial direction.

13. The backflow preventing device according to any one of claims 1 to 12, wherein an inner diameter of a rear portion of the piston ring in the injection direction is larger than an inner diameter of a front portion of the piston ring in the injection direction.

14. An injection device, wherein, having: the backflow preventing device according to any one of claims 1 to 13; the cylinder; a screw rod accommodated in the cylinder; and an injection nozzle mounted to a top end of the cylinder.

Images