Backflow prevention device and injection device including the same

Abstract

To provide a backflow prevention device which prevents a piston ring from entering into a gap between a backflow prevention ring and a cylinder.SOLUTION: A backflow prevention device 4 of an injection device 3 has a backflow prevention ring 41 having an annular groove 42 facing an inner face of a cylinder 32 of the injection device 3, and a piston ring 51 fit into the annular groove 42. The piston ring 51 has a storage part 56 stored in the annular groove 42, and an outer peripheral surface 53 positioned radially outside the annular groove 42, and a rear end 53A in an injection direction of the outer peripheral surface 53 exists ahead in an injection direction of the storage part 56, with respect to a rearmost end 55 in the injection direction.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a backflow prevention device and an injection device equipped with the same. [Background technology]

[0002] The injection device of an injection molding machine is equipped with a backflow prevention device that prevents the backflow of the material injected during injection. Patent Document 1 describes an injection device having a screw housed in a cylinder, a presser attached to the screw, and a backflow prevention device provided between the screw head of the screw and the presser. When the screw moves forward during injection, the backflow prevention device is pressed against the presser, preventing the injected material from flowing behind the presser. The backflow prevention device has a backflow prevention ring and a piston ring fitted into the backflow prevention ring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-314510 Summary of the Invention [Problem to be solved by the invention]

[0004] The piston rings are provided to improve the sealing performance between the backflow prevention device and the cylinder. However, because the screw moves at high speed during injection, the piston rings may deform and enter the gap between the backflow prevention ring and the cylinder. In this case, not only will the piston rings wear out, but the piston rings that enter the gap between the backflow prevention ring and the cylinder may damage the cylinder.

[0005] An object of the present invention is to provide a backflow prevention device that prevents piston rings from entering the gap between the backflow prevention ring and the cylinder. [Means for solving the problem]

[0006] The backflow prevention device of the present invention includes a backflow prevention ring having an annular groove, and a piston ring fitted in the annular groove. The piston ring has a housing portion housed in the annular groove and an outer peripheral surface located radially outward from the annular groove, and a rear end portion in the injection direction of the outer peripheral surface is forward in the injection direction of the rear end portion in the injection direction of the housing portion. Effect of the Invention

[0007] According to the present invention, it is possible to provide a backflow prevention device in which the piston ring is less likely to enter the gap between the backflow prevention ring and the cylinder. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic front view of an injection molding machine according to a first embodiment. [Diagram 2] FIG. 2 is an enlarged view of part A in FIG. [Diagram 3] FIG. 3 is an enlarged view of part B in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. [Diagram 5] 3 is an enlarged view of a portion corresponding to part B in FIG. 2 in the second embodiment. [Figure 6] 10 is an enlarged view of a portion corresponding to part B in FIG. 2 in the third embodiment. [Figure 7] 10 is an enlarged view of a portion corresponding to part B in FIG. 2 in the fourth embodiment. [Figure 8] 10 is an enlarged view of a portion corresponding to part B in FIG. 2 in the fifth embodiment. [Figure 9] 13 is an enlarged view of a portion corresponding to part B in FIG. 2 in the sixth embodiment. [Figure 10] 13 is an enlarged view of a portion corresponding to part B in FIG. 2 in the seventh embodiment. [Figure 11] 13 is an enlarged view of a portion corresponding to part B in FIG. 2 in the eighth embodiment. FIG. [Figure 12] 13 is an enlarged view of a portion corresponding to part B in FIG. 2 in the ninth embodiment. [Figure 13A] 3 is an enlarged view of a portion corresponding to part B in FIG. 2 in a comparative example. [Figure 13B] FIG. 13 is a diagram showing a problem in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, several embodiments of the present invention will be described with reference to the drawings. The present invention can be suitably applied to a metal injection molding machine, particularly to a metal injection molding machine that injects a metal with low viscosity when molten. However, the present invention can also be applied to an injection molding machine that injects a resin. In the following description, the X direction refers to the axial direction of the cylinder 32, the injection direction is called the +X direction, and the direction opposite to the injection direction is called the -X direction. Terms such as "front", "rear", "front part", and "rear part" are defined based on the injection direction. In addition, the "radial direction" is defined based on the central axis CL of the cylinder 32.

[0010] (First embodiment) <Overall configuration of injection molding machine> 1 shows a schematic front view of an injection molding machine 1 according to a first embodiment. The injection molding machine 1 is a horizontal metal injection molding machine that injects molten metal such as a magnesium alloy or an aluminum alloy. The injection molding machine 1 is generally composed of a mold clamping device 2 that clamps a mold, and an injection device 3 that heats, melts, and injects the metal material to be injected.

[0011] <Mold clamping device 2> The mold clamping device 2 includes a fixed platen 21 fixed on a bed (not shown) to which a fixed mold M1 is attached, and a movable platen 22 slidable on the bed to which a movable mold M2 is attached. A mold clamping housing (not shown) slidable on the bed is provided on the opposite side of the fixed platen 21 with respect to the movable platen 22, and the fixed platen 21 and the mold clamping housing are connected by a plurality of tie bars 23. A link mechanism (not shown) for opening and closing the mold is provided between the movable platen 22 and the mold clamping housing. The link mechanism is driven by an electric ball screw. Instead of the link mechanism, a hydraulic mold clamping cylinder may be provided. A cavity M3 is formed between the fixed mold M1 and the movable mold M2 and is filled with molten metal.

[0012] <Injection device 3> The injection device 3 is provided on a base (not shown). The injection device 3 includes a hollow cylindrical cylinder 32 for heating and melting the metal material to be injected, a screw 33 housed in 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 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.

[0013] The cylinder 32 is roughly divided into a supply section P1, a compression section P2, and a metering section P3 from the rear to the front. A hopper 36 is provided in the supply section P1, and a pellet-shaped metal material is supplied to the supply section P1. The metal material is sent to the compression section P2 while being heated by a heater 38. The metal material is compressed, heated, and kneaded in the compression section P2 to become molten, and is then transported to the metering section P3. The metering section P3 measures the molten metal to be injected in one injection cycle (shot). The screw 33 is provided with a screw head 35 at its tip in the X direction. An injection nozzle 37 is attached to the tip of the cylinder 32 to supply molten metal to the cavity M3.

[0014] <Backflow prevention device 4> FIG. 2 shows a partial detailed view of the front portion of the cylinder 32 (an enlarged view of part A in FIG. 1). For the sake of convenience, in FIG. 2, the upper side of the central axis CL of the cylinder 32 shows the state of the backflow prevention device 4 at the time of injection, and the lower side shows the state of the backflow prevention device 4 at the time of metering. FIG. 3 is an enlarged view of part B in FIG. 2, and shows the positional relationship between the annular groove 42 and the piston ring 51. That is, FIG. 3 shows the state at the time of injection (the state of the backflow prevention ring 41 shown in the upper part of FIG. 2). FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. 3.

[0015] As shown in Fig. 2, the metering section P3 of the cylinder 32 of the injection device 3 is provided with a backflow prevention device 4 for preventing the backflow of the injected metal material. The backflow prevention device 4 has a backflow prevention ring 41 made of a hollow cylindrical metal member, and the backflow prevention ring 41 has an annular groove 42 that faces the inner surface of the cylinder 32 of the injection device 3. The backflow prevention device 4 has a piston ring 51 fitted in the annular groove 42 of the backflow prevention ring 41. The backflow prevention ring 41, the annular groove 42, and the piston ring 51 are coaxial with the cylinder 32. The annular groove 42 runs around the outer periphery of the backflow prevention ring 41 and has the same cross section at each angular position around the central axis CL of the cylinder 32.

[0016] In this embodiment, the backflow prevention ring 41 has two annular grooves 42, and one piston ring 51 is fitted in each annular groove 42, but it is sufficient to have at least one annular groove 42 and at least one piston ring 51.

[0017] The piston ring 51 is an annular sealing part fitted in the annular groove 42 of the backflow prevention ring 41, and separates the front and rear of the backflow prevention ring 41. The piston ring 51 is made of metal. As shown in FIG. 4, the piston ring 51 has stepped end portions 63, and is fitted into the annular groove 42 so that the steps of the end portions 63 overlap in the circumferential direction. Therefore, the steps of the end portions 63 shift in the circumferential direction depending on the pressure applied to the inner circumferential surface 52 and the outer circumferential surface 53 of the piston ring 51, thereby changing the diameter of the piston ring 51. The piston ring 51 has the same cross section at each angular position around the central axis CL of the cylinder 32, except for the vicinity of the end portions 63.

[0018] As shown in Fig. 2, a presser plate 39 consisting of a disk with a central hole for passing the screw head 35 is fixed to the screw 33. The backflow prevention ring 41 is inserted into the screw 33 between the screw head 35 at the front in the injection direction and the presser plate 39 at the rear in the injection direction. The outer diameters of the screw head 35 and the presser plate 39 are larger than the inner diameter of the backflow prevention ring 41, and the length of the backflow prevention ring 41 in the X direction is smaller than the distance between the screw head 35 and the presser plate 39 in the X direction. Therefore, the backflow prevention ring 41 is movable in the X direction while being restricted by the screw head 35 and the presser plate 39.

[0019] As shown in part B of FIG. 2 and part 3, when the molten metal is injected, the screw 33 advances in the +X direction, and the backflow prevention ring 41 retreats in the -X direction relative to the screw 33. The backflow prevention ring 41 abuts against the presser 39, and prevents the molten metal measured in front of the screw 33 from leaking backward during injection (when the screw 33 advances). As shown in part C of FIG. 2, when the molten metal is metered, the screw 33 retreats in the -X direction, and the backflow prevention ring 41 advances in the +X direction relative to the screw 33. The backflow prevention ring 41 abuts against the screw head 35, but the molten metal behind the presser 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 backflow prevention ring 41 is functionally a kind of valve.

[0020] A through hole 46 that penetrates the backflow prevention ring 41 in the radial direction is connected to the front annular groove 42 in the injection direction. High-pressure molten metal flows into the through hole 46 and applies radially outward pressure to the piston ring 51. This pressure presses the piston ring 51 against the inner wall of the cylinder 32, improving the sealing performance of the piston ring 51. The through hole 46 is not connected to the rear annular groove 42. However, some of the molten metal passes through the gap between the front piston ring 51 and the cylinder 32, the gap between the backflow prevention ring 41 and the cylinder 32, and the rear annular groove 42 and exerts pressure on the inner circumferential surface 52 of the rear piston ring 51. Therefore, both the front and rear piston rings 51 contribute to improving the sealing performance.

[0021] Providing the through holes 46 improves sealing performance, but since a large pressure is applied to the piston ring 51, wear of the piston ring 51 is likely to progress. Whether or not to provide the through holes 46 is appropriately determined in consideration of sealing performance and suppression of wear of the piston ring 51. The through holes 46 may be provided in both annular grooves 42, the through holes 46 may be provided only in the rear annular groove 42, or none of the annular grooves 42 may have the through holes 46. However, by providing the through holes 46 only in the front annular groove 42, it becomes easier to equalize the amount of wear of the front piston ring 51 and the rear piston ring 51.

[0022] The front annular groove 42 and the rear annular groove 42 have the same configuration except for whether the through holes 46 are connected or not. The two piston rings 51 have the same configuration. Therefore, the following description will mainly focus on the front annular groove 42 and the piston ring 51 fitted in the front annular groove 42.

[0023] <Comparative Example Backflow Prevention Device 104> Here, the backflow prevention device 104 of the comparative example will be described. Fig. 13A is an enlarged view of a portion corresponding to part B in Fig. 2. The annular groove 142 and the piston ring 151 have a rectangular cross section. As described above, the piston ring 151 is subjected to radially outward pressure, so that the piston ring 151 is pressed against the inner wall of the cylinder 32. Also, during injection, the molten metal flows through the gap between the backflow prevention ring 141 and the cylinder 32 in the -X direction and flows into the annular groove 142, so that the piston ring 151 is pressed against the rear side surface 144 of the annular groove 142. During metering, the piston ring 151 is pressed against the front side surface 143 of the annular groove 142 (not shown), but since the speed of the screw 33 is higher during injection, the pressure with which the piston ring 151 is pressed against the side surface of the annular groove 142 is greater during injection.

[0024] 13B shows the state of the piston ring 151 after it has been deformed. The piston ring 151 is made of a relatively soft metal. Therefore, when the piston ring 151 is pressed radially outward and in the -X direction, it may deform and part of it may enter the gap G in the -X direction between the backflow prevention ring 141 and the cylinder 32. When this situation occurs, not only will the piston ring 151 wear further, but the part of the piston ring 151 that has entered the gap G between the backflow prevention ring 141 and the cylinder 32 may damage the cylinder 32.

[0025] <Shapes of the annular groove 42 and the piston ring 51> The shapes of the annular groove 42 and the piston ring 51 of this embodiment will be described in more detail, mainly with reference to Fig. 3. 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 located at the deepest part of the annular groove 42 and separates the front side surface 43 and the rear side surface 44. The front side surface 43 is a plane perpendicular to the central axis CL of the cylinder 32. A through hole 46 is connected to the bottom surface 45.

[0026] The piston ring 51 has an inner circumferential surface 52, an outer circumferential surface 53, a front side surface 54, and a rear side surface 55. The inner circumferential surface 52 separates the front side surface 54 from the rear side surface 55. The inner circumferential surface 52 faces the bottom surface 45 of the annular groove 42. The front side surface 54 is a plane perpendicular to the central axis CL of the cylinder 32, and faces the front side surface 43 of the annular groove 42. The rear side surface 55 is a plane perpendicular to the central axis CL of the cylinder 32, and faces the rear side surface 44 of the annular groove 42.

[0027] The piston ring 51 has a housing portion 56 housed in the annular groove 42 and a protruding portion 57 outside the annular groove 42. The outer peripheral surface 53 of the piston ring 51 is located radially outside the annular groove 42. A rear end portion 53A of the outer peripheral surface 53 in the injection direction is located forward of the rear end portion (rear side surface 55) of the housing portion 56 in the injection direction. The rear portion of the piston ring 51 in the injection direction has an outer diameter smaller than that of the front portion in the injection direction. The outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is located at approximately the same position as the opening 59 of the annular groove 42 in the radial direction. As described above, the piston ring 51 is likely to enter the gap G on the −X direction side between the backflow prevention ring 41 and the cylinder 32. However, in this embodiment, the protruding portion 57 is not located near the gap G, so the piston ring 51 is unlikely to enter the gap G.

[0028] The surface connecting the rear end 53A of the outer circumferential surface 53 and the outermost portion 58 in the radial direction of the rear end of the housing portion 56 has a cylindrical surface 60 whose central axis is the central axis CL of the cylinder 32, and an inclined surface 61 that connects the cylindrical surface 60 and the rear end 53A of the outer circumferential surface 53 and is inclined with respect to the central axis CL of the cylinder 32. This makes it easy to move the piston ring 51 away from the gap G, and makes it difficult for the piston ring 51 to enter the gap G. The diameter of the cylindrical surface 60 is constant in the X direction, but may increase in the +X direction.

[0029] Other embodiments of the present invention will be described below. In the embodiments described below, configurations and effects that are not described are the same as those of the first embodiment.

[0030] Second embodiment FIG. 5 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the second embodiment. In this embodiment, the outermost part 58 in the radial direction of the rear end of the housing part 56 is inside the annular groove 42, and the other points are the same as those of the first embodiment. Since the piston ring 51 wears with use, the thickness of the protruding part 57 gradually decreases, and there is a possibility that the cylindrical surface 60 will eventually come into contact with the cylinder 32. However, since the cylindrical surface 60 is inside the annular groove 42, it takes a longer time for the cylindrical surface 60 to come into contact with the cylinder 32 even if the piston ring 51 wears and is reduced in thickness. In this embodiment, the life of the piston ring 51 can be extended, and the frequency of replacing the piston ring 51 can be reduced.

[0031] (Third embodiment) 6 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the third embodiment. A surface 62 connecting the rear end 53A of the outer circumferential surface 53 and the outermost portion 58 in the radial direction of the rear end of the accommodating portion 56 is generally inclined with respect to the central axis CL of the cylinder 32. The other points are the same as those of the first embodiment. The outermost portion 58 in the radial direction of the rear end of the accommodating portion 56 is located at approximately the same position in the radial direction as the opening 59 of the annular groove 42. This embodiment has substantially the same effects as the first embodiment, but since the shape of the surface 62 connecting the rear end 53A of the outer circumferential surface 53 and the outermost portion 58 in the radial direction of the rear end of the accommodating portion 56 is simple, the piston ring 51 can be easily machined.

[0032] (Fourth embodiment) 7 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the fourth embodiment. The outermost part 58 in the radial direction of the rear end of the housing part 56 is inside the annular groove 42, and the other points are the same as those of the third embodiment. This embodiment has the same effect as the second embodiment. That is, since the outermost part 58 is inside the annular groove 42, it takes a longer time for the outermost part 58 to come into contact with the cylinder 32 even if the piston ring 51 wears and is reduced in thickness. In this embodiment, the life of the piston ring 51 can be extended, and the frequency of replacing the piston ring 51 can be reduced.

[0033] Fifth embodiment FIG. 8 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the fifth embodiment. The piston ring 51 has a housing portion 56 housed in the annular groove 42 and a protruding portion 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 forward of the rearmost end portion of the housing portion 56 in the injection direction (the radially inner portion 55B of the rear side surface 55). The outer diameter of the piston ring 51 is smaller at the rear portion in the injection direction than at the front portion in the injection direction. As described above, the piston ring 51 is likely to enter the gap G on the -X direction side between the backflow prevention ring 41 and the cylinder 32. However, in this embodiment, the protruding portion 57 is not located near the gap G, so the piston ring 51 is unlikely to enter the gap G.

[0034] 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 portion 55A and a radial inner portion 55B that are separated by the step portion 55C. The radial outer portion 55A and the radial inner portion 55B face the rear side surface 44 of the annular groove 42. The front side surface 54 is a plane perpendicular to the central axis CL of the cylinder 32, and faces the front side surface 43 of the annular groove 42.

[0035] The step portion 55C is provided only on the piston ring 51, and the rear side surface 44 of the annular groove 42 is a plane perpendicular to the central axis CL of the cylinder 32. The radial outer portion 55A of the rear side surface 55 of the piston ring 51 is located forward of the radial inner portion 55B in the injection direction. During injection, the piston ring 51 moves relative to the annular groove 42 in the -X direction, and the radial inner portion 55B of the rear side surface 55 of the piston ring 51 comes into contact with the rear side surface 44 of the annular groove 42. At this time, the radial outer portion 55A of the rear side surface 55 of the piston ring 51 cannot come into contact with the rear side surface 44 of the annular groove 42. For this reason, it is difficult for a part of the piston ring 51 to enter the gap G on the -X side between the backflow prevention ring 41 and the cylinder 32.

[0036] As described above, the piston ring 51 is subjected to radially outward pressure, but in this embodiment, this pressure can be easily adjusted. The pressure with which the piston ring 51 presses against the inner surface of the cylinder 32 is generated by the pressure applied to the inner circumferential surface 52 of the piston ring 51. If the pressure applied to the inner circumferential surface 52 of the piston ring 51 is P1, the pressure with which the piston ring 51 presses against the cylinder 32 is P2, the width of the inner circumferential surface 52 of the piston ring 51 is W1, and the width of the outer circumferential surface 53 of the piston ring 51 is W2, then P2 = (W1 / W2) x P1. The pressure with which the piston ring 51 presses against the cylinder 32 can be easily adjusted by the ratio of the width W1 of the inner circumferential surface 52 of the piston ring 51 to the width W2 of the outer circumferential surface 53.

[0037] Sixth embodiment 9 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the sixth embodiment. The rear side surface 44 of the annular groove 42 has a radial outer portion 44A, a radial inner portion 44B, and a step portion 44C, and the radial outer portion 44A and the radial inner portion 44B are partitioned by the step portion 44C. The inner diameter of the piston ring 51 is larger at the rear portion in the injection direction than at the front portion in the injection direction. When the piston ring 51 moves relative to the annular groove 42 in the −X direction during injection, the radial inner portion 55B of the rear side surface 55 of the piston ring 51 can come into contact with the radial inner portion 44B of the rear side surface 44 of the annular groove 42, while the radial outer portion 55A of the rear side surface 55 of the piston ring 51 cannot come into contact with the radial outer portion 44A of the rear side surface 44 of the annular groove 42.

[0038] In addition, rear end 53A of outer peripheral surface 53 in the injection direction is located forward in the injection direction with respect to the rearmost end of housing portion 56 in the injection direction (radially outer portion 55A of rear side surface 55). The outer diameter of piston ring 51 is smaller at its rear portion in the injection direction than at its front portion in the injection direction. Since piston ring 51 is away from gap G, piston ring 51 is even less likely to enter gap G.

[0039] Seventh embodiment FIG. 10 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the seventh embodiment. In this embodiment, the outermost part 58 in the radial direction of the rear end of the housing part 56 is inside the annular groove 42, and the other points are the same as those of the sixth embodiment. Since the piston ring 51 wears with use, the thickness of the protruding part 57 gradually decreases, and there is a possibility that the cylindrical surface 60 will eventually come into contact with the cylinder 32. However, since the cylindrical surface 60 is inside the annular groove 42, it takes a longer time for the cylindrical surface 60 to come into contact with the cylinder 32 even if the piston ring 51 wears and loses thickness. In this embodiment, the life of the piston ring 51 can be extended, and the frequency of replacing the piston ring 51 can be reduced. In addition, since the piston ring 51 is away from the gap G, the piston ring 51 is less likely to enter the gap G.

[0040] Eighth embodiment 11 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the eighth embodiment. A surface 62 connecting the rear end 53A of the outer peripheral surface 53 and the outermost portion 58 in the radial direction of the rear end of the accommodating portion 56 is generally inclined with respect to the central axis CL of the cylinder 32. The other points are the same as those of the sixth embodiment. The outermost portion 58 in the radial direction of the rear end of the accommodating portion 56 is located at approximately the same position in the radial direction as the opening 59 of the annular groove 42. This embodiment has substantially the same effects as the sixth embodiment, but since the shape of the surface 62 connecting the rear end 53A of the outer peripheral surface 53 and the outermost portion 58 in the radial direction of the rear end of the accommodating portion 56 is simple, the piston ring 51 can be easily machined.

[0041] Ninth embodiment 12 is an enlarged view of a portion corresponding to part B in FIG. 2, showing the ninth embodiment. This embodiment is a combination of the fourth and eighth embodiments. Therefore, this embodiment has the effects of the fourth and eighth embodiments. In addition, in this embodiment, the piston ring 51 is further away from the gap G than in the fourth embodiment, so that the piston ring 51 is even less likely to enter the gap G.

[0042] (Additional Note) This specification includes the following disclosure. [Configuration 1] a backflow prevention ring having at least one annular groove facing an inner surface of the cylinder of the injection device; At least one piston ring is fitted in the at least one annular groove, a piston ring configured to receive the piston from the piston and configured to receive the piston in the injection direction; a piston ring configured to receive the piston in the injection direction; a piston ring configured to receive the piston in the injection direction; [Configuration 2] A surface connecting the rear end of the outer circumferential surface and the rear end of the storage portion is A cylindrical surface having a central axis along the central axis of the cylinder; an inclined surface that connects a front end of the cylindrical surface in the injection direction and a rear end of the outer circumferential surface and is inclined with respect to a central axis of the cylinder; 2. The backflow prevention device of the injection device according to claim 1, [Configuration 3] 2. The backflow prevention device for the injection device according to claim 1, wherein a surface connecting the rear end of the outer circumferential surface and the rear end of the storage portion is generally inclined with respect to a central axis of the cylinder. [Configuration 4] 4. The backflow prevention device of the injection device according to configuration 2 or 3, wherein a radially outermost portion of the rear end portion of the accommodation portion is located at approximately the same position in the radial direction as an opening of the annular groove. [Configuration 5] 4. The backflow prevention device of the injection device according to configuration 2 or 3, wherein a radially outermost portion of the rear end portion of the accommodation portion is inside the annular groove. [Configuration 6] the at least one annular groove and the at least one piston ring each have a rear side in the injection direction; The backflow prevention device of the injection device described in any one of configurations 1 to 5, wherein the rear side surface of the at least one annular groove and the rear side surface of the at least one piston ring are capable of contacting each other only at their respective radially inner portions. [Configuration 7] 7. The backflow prevention device of claim 6, wherein a gap is formed between a radial outer portion of the rear side of the at least one piston ring and a radial outer portion of the rear side of the at least one annular groove when the radial inner portion of the rear side of the at least one piston ring contacts the radial inner portion of the rear side of the at least one annular groove. [Configuration 8] 8. The backflow prevention device of claim 7, wherein the radially inner portion of the rear side surface of the at least one annular groove and the radially inner portion of the rear side surface of the at least one piston ring are planes perpendicular to a central axis of the cylinder. [Configuration 9] 7. The backflow prevention device of claim 6, wherein a radially outer portion of the rear side of the at least one piston ring is forward in the injection direction relative to a radially inner portion of the rear side of the at least one piston ring. [Configuration 10] 10. The backflow prevention device of claim 9, wherein the rear side of the at least one annular groove is a plane perpendicular to a central axis of the cylinder. [Configuration 11] 11. The backflow prevention device according to any one of configurations 1 to 10, wherein the outer diameter of the piston ring is smaller at a rear portion in the injection direction than at a front portion in the injection direction. [Configuration 12] A backflow prevention device according to any one of configurations 1 to 11, The cylinder; A screw housed in the cylinder; and an injection nozzle attached to the tip of the cylinder. [Explanation of symbols]

[0043] 3 Injection device 4 Backflow prevention device 32 cylinders 33 Screw 41 Backflow prevention ring 42 Annular groove 44 Rear side of annular groove 44A Radially outer portion of rear side of annular groove 44B: radially inner portion of rear side of annular groove 46 Through hole 51 Piston ring 53 Outer surface 53A Rear end of outer periphery 55 Rear side of piston ring 55A Radial outer part of rear side of piston ring 55B Radial inner part of rear side of piston ring 56 Storage unit

Claims

1. a backflow prevention ring having at least one annular groove facing an inner surface of the cylinder of the injection device; At least one piston ring fitted in the at least one annular groove, a piston ring configured to receive the piston from the piston and configured to receive the piston in the injection direction; a piston ring configured to receive the piston in the injection direction; a piston ring configured to receive the piston in the injection direction;

2. A surface connecting the rear end of the outer circumferential surface and the rear end of the storage portion is A cylindrical surface having a central axis along the central axis of the cylinder; an inclined surface that connects a front end of the cylindrical surface in the injection direction and a rear end of the outer circumferential surface and is inclined with respect to a central axis of the cylinder; The backflow prevention device of claim 1 , further comprising:

3. 2. The backflow prevention device for an injection apparatus according to claim 1, wherein a surface connecting the rear end of the outer circumferential surface and the rear end of the housing portion is generally inclined with respect to a central axis of the cylinder.

4. 4. The backflow prevention device of the injection device according to claim 2, wherein a radially outermost portion of the rear end portion of the housing portion is located at substantially the same position in the radial direction as an opening of the annular groove.

5. 4. The backflow prevention device for an injection apparatus according to claim 2, wherein a radially outermost portion of said rear end portion of said housing portion is located inside said annular groove.

6. the at least one annular groove and the at least one piston ring each have a rear side in the injection direction; 2. The backflow prevention device of the injection apparatus according to claim 1, wherein the rear side surface of the at least one annular groove and the rear side surface of the at least one piston ring are capable of contacting each other only at their respective radially inner portions.

7. 7. The backflow prevention device of claim 6, wherein when the radially inner portion of the rear side surface of the at least one piston ring contacts the radially inner portion of the rear side surface of the at least one annular groove, a gap is formed between the radially outer portion of the rear side surface of the at least one piston ring and the radially outer portion of the rear side surface of the at least one annular groove.

8. 8. The backflow prevention device of claim 7, wherein the radially inner portion of the rear side surface of the at least one annular groove and the radially inner portion of the rear side surface of the at least one piston ring are planes perpendicular to a central axis of the cylinder.

9. 7. The backflow prevention device of claim 6, wherein a radially outer portion of the rear side of the at least one piston ring is forward in the injection direction relative to the radially inner portion of the rear side of the at least one piston ring.

10. 10. The backflow prevention device of claim 9, wherein the rear side of the at least one annular groove is a plane perpendicular to a central axis of the cylinder.

11. 2. The backflow prevention device according to claim 1, wherein an outer diameter of the piston ring is smaller at a rear portion in the injection direction than at a front portion in the injection direction.

12. A backflow prevention device according to claim 1 ; The cylinder; A screw housed in the cylinder; and an injection nozzle attached to the tip of the cylinder.

Images