Backflow prevention device and injection device provided with same

Abstract

Provided is a backflow prevention device in which a piston ring does not easily enter a gap between a backflow prevention ring and a cylinder. A backflow prevention device (4) of an injection device (3) includes a backflow prevention ring (41) having an annular groove (42) facing an inner surface of a cylinder (32) of the injection device (3), and a piston ring (51) fitted into the annular groove (42). The piston ring (51) has a housing part (56) housed in the annular groove (42), and an outer peripheral surface (53) positioned further outward in the radial direction than the annular groove (42). A rear end part (53A) of the outer peripheral surface (53) in the injection direction is positioned forward in the injection direction than a rearmost end part (55) of the housing part (56) in the injection direction.

Description

TECHNICAL FIELD

[0001] This application is based on Japanese Application No. 2023-108729 filed on June 30, 2023, and claims priority based on this application.

[0002] The entire contents of the application are hereby incorporated by reference in this application.

[0003] The present application relates to a backflow prevention device and an injection device provided with the backflow prevention device. BACKGROUND

[0004] An injection device of an injection molding machine is provided with a backflow prevention device that prevents backflow of an injection material at the time of injection. Japanese Patent Application Publication No. H7-314510 describes an injection device having a screw housed in a cylinder, a presser attached to the screw, and a backflow prevention device provided between a screw head of the screw and the presser. At the time of injection, if the screw advances, the backflow prevention device is pressed by the presser, and injection of the material to the rear of the presser is prevented. The backflow prevention device has a backflow prevention ring and a piston ring that is inserted into the backflow prevention ring. SUMMARY

[0005] The piston ring is provided to improve the sealability of the backflow prevention device and the cylinder. However, since the screw operates at high speed at the time of injection, there is a possibility that the piston ring deforms and enters the gap between the backflow prevention ring and the cylinder. In this case, not only the wear of the piston ring is accelerated, but there is also a possibility that the piston ring that has entered the gap between the backflow prevention ring and the cylinder damages the cylinder.

[0006] An object of the present application is to provide a backflow prevention device in which it is difficult for the piston ring to enter the gap between the backflow prevention ring and the cylinder.

[0007] The backflow prevention device of the present application includes a backflow prevention ring having a ring-shaped groove and a piston ring that is inserted into the ring-shaped groove. The piston ring has a housing portion that is housed in the ring-shaped groove and an outer peripheral surface that is located radially outward of the ring-shaped groove, and a rear end portion of the outer peripheral surface in the injection direction is located forward of a rear end portion of the housing portion in the injection direction.

[0008] According to the present application, it is possible to provide a backflow prevention device in which it is difficult for the piston ring to enter the gap between the backflow prevention ring and the cylinder. The above and other objects, features and advantages of the present application will become more apparent from the following description when taken in conjunction with the accompanying drawings, which illustrate preferred embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is a schematic front view of an injection molding machine of Embodiment 1.

[0010] Figure 2 is an enlarged view of A portion of Figure 1 ​

[0011] Figure 3 is Figure 2 an enlarged view of B portion of

[0012] Figure 4 is a sectional view taken along line 4-4 of Figure 3

[0013] Figure 5 is an enlarged view of a portion corresponding to B portion of Figure 2 in the second embodiment.

[0014] Figure 6 is an enlarged view of a portion corresponding to B portion of Figure 2 in the third embodiment.

[0015] Figure 7 is an enlarged view of a portion corresponding to B portion of Figure 2 in the fourth embodiment.

[0016] Figure 8 is an enlarged view of a portion corresponding to B portion of Figure 2 in the fifth embodiment.

[0017] Figure 9 is an enlarged view of a portion corresponding to B portion of Figure 2 in the sixth embodiment.

[0018] Figure 10 is an enlarged view of a portion corresponding to B portion of Figure 2 in the seventh embodiment.

[0019] Figure 11 is an enlarged view of a portion corresponding to B portion of Figure 2 in the eighth embodiment.

[0020] Figure 12 is an enlarged view of a portion corresponding to B portion of Figure 2 in the ninth embodiment.

[0021] Figure 13A is an enlarged view of a portion corresponding to B portion of Figure 2 in the comparative example.

[0022] Figure 13B is a diagram showing a problem of the comparative example. DETAILED DESCRIPTION

[0023] ​Several embodiments of the present application will be described below with reference to the drawings. The present application can be applied to a metal injection molding machine, particularly 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 refers to the axial direction of the cylinder 32, and the direction of injection is referred to as the +X direction, and the opposite direction of the direction of injection is referred to as the -X direction. The terms "front", "rear", "front portion", "rear portion", and the like are defined with reference to the direction of injection. In addition, the "radial direction" is defined with reference to the center axis CL of the cylinder 32.

[0024] (First Embodiment)

[0025] <Overall Configuration of Injection Molding Machine>

[0026] Figure 1 A schematic front view of the injection molding machine 1 of the first embodiment is shown. 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 mold clamping device 2 that performs mold clamping, and an injection device 3 that performs heating and melting of the injected metal material and injection.

[0027] <Mold Clamping Device 2>

[0028] The mold clamping device 2 includes a fixed disk 21 that is fixed to a base (not shown) and on which a fixed mold Ml is installed, and a movable disk 22 that is slidable on the base and on which a movable mold M2 is installed. Opposite the movable disk 22, on the opposite side of the fixed disk 21, a mold clamping housing (not shown) that is slidable on the base is provided, and the fixed disk 21 and the mold clamping housing are linked by a plurality of tie rods 23. A link mechanism (not shown) for performing mold opening and closing is provided between the movable disk 22 and the mold clamping housing. The link mechanism is driven by a ball screw of an electric type. A hydraulic mold clamping cylinder can be provided instead of the link mechanism. A chamber M3 that is filled with a molten metal is formed between the fixed mold Ml and the movable mold M2.

[0029] <Injection Device 3>

[0030] The injection device 3 is provided on a base (not shown). The injection device 3 includes a hollow cylindrical cylinder 32 that heats and melts the injected metal material, a screw 33 that is housed in the cylinder 32, and a drive mechanism 34 that drives the screw 33. The screw 33 is coaxial with the cylinder 32. The screw 33 is rotationally driven by the drive mechanism 34 and is driven in the +X and -X directions. A heater 38 that heats and melts the metal material is provided on the outer periphery of the cylinder 32.

[0031] The cylinder 32 is roughly divided from the rear to the front into a supply section P1, a compression section P2, and a metering section P3. A hopper 36 is provided in the supply section P1, and a granular metal material is supplied thereto. The metal material is transported 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 a molten state and is carried to the metering section P3. The metering section P3 meters the molten metal to be injected in one injection cycle (injection). The screw 33 has a screw head 35 at the front end in the X direction. An injection nozzle 37 that supplies the molten metal to the chamber M3 is attached to the front end of the cylinder 32.

[0032] <Anti-backflow device 4>

[0033] Figure 2 A partial detailed view of the front portion of the cylinder 32 Figure 1 is shown. For convenience, in Figure 2 , the upper portion of the cylinder 32 shows the state at the time of injection of the anti-backflow device 4, and the lower portion shows the state at the time of metering of the anti-backflow device 4. Figure 3 is a B portion enlarged view of Figure 2 , showing the positional relationship between the annular groove 42 and the piston ring 51. That is, Figure 3 shows the state at the time of injection Figure 2 of the anti-backflow ring 41 shown in the upper portion of Figure 4 is a cross-sectional view along the 4-4 line of Figure 3 .

[0034] As shown in Figure 2 , an anti-backflow device 4 that prevents backflow of the injected metal material is provided in the metering section P3 of the cylinder 32 of the injection device 3. The anti-backflow device 4 has an anti-backflow ring 41 made of a hollow cylindrical member, and the anti-backflow ring 41 has an annular groove 42 that opposes the inner surface of the cylinder 32 of the injection device 3. The anti-backflow device 4 has a piston ring 51 that is fitted in the annular groove 42 of the anti-backflow ring 41. The anti-backflow ring 41, the annular groove 42, and the piston ring 51 are coaxial with the cylinder 32. The annular groove 42 is annular around the outer periphery of the anti-backflow ring 41, and has the same cross section at each angular position around the center axis CL of the cylinder 32.

[0035] In the present embodiment, the anti-backflow ring 41 has two annular grooves 42, and one piston ring 51 is fitted in each annular groove 42, but there can be at least one annular groove 42 and at least one piston ring 51.

[0036] The piston ring 51 is a circular ring-shaped sealing member that is fitted in the annular groove 42 of the anti-backflow ring 41, and separates the front and the rear of the anti-backflow ring 41. The piston ring 51 is made of metal. As Figure 4As shown, the piston ring 51 has stepped both end portions 63, and is installed in the annular groove 42 in a manner that the steps of the both end portions 63 coincide in the circumferential direction. Therefore, in correspondence with the pressure applied to the inner peripheral surface 52 and the outer peripheral surface 53 of the piston ring 51, the steps of the both end portions 63 are shifted in the circumferential direction, whereby 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 block 32 except the vicinity of the both end portions 63.

[0037] As shown in Figure 2 , a presser 39 composed of a circular plate provided with a central hole for the screw head 35 to pass through is fixed to the screw 33. The reverse flow prevention ring 41 is inserted in the screw 33 between the screw head 35 in front of the injection direction and the presser 39 behind the injection direction. The outer diameter of the screw head 35 and the presser 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 of the screw head 35 and the presser 39 in the X-direction. Therefore, the reverse flow prevention ring 41 can move in the X-direction while being restricted by the screw head 35 and the presser 39.

[0038] As shown in Figure 2 B and Figure 3 , 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 presser 39, and prevents the metered molten metal in front of the screw 33 from leaking backward at the time of injection (when the screw 33 advances). As shown in Figure 2 C, when the molten metal is metered, 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, and the molten metal behind the presser 39 is supplied to the space in front of the screw head 35 through the flow path 35A inside the screw head 35. In this way, the reverse flow prevention ring 41 is functionally a kind of valve.

[0039] In the injection direction, the annular groove 42 in front is connected with the through hole 46 that penetrates the reverse flow prevention ring 41 in the radial direction. The high-pressure molten metal flows into the through hole 46, and the piston ring 51 is applied with pressure from the radial outside. The piston ring 51 is pressed against the inner wall of the cylinder block 32 due to the pressure, and the sealing property of the piston ring 51 is improved. The annular groove 42 behind is not connected with the through hole 46. However, a part of the molten metal applies pressure to the inner peripheral surface 52 of the piston ring 51 behind through the gap between the piston ring 51 in front and the cylinder block 32, the gap between the reverse flow prevention ring 41 and the cylinder block 32, and the annular groove 42 behind. Therefore, both the piston rings 51 in front and behind contribute to the improvement of the sealing property.

[0040] The sealability is improved by providing the through hole 46, but since the piston ring 51 is subjected to a large pressure, the wear of the piston ring 51 is liable to be accelerated. Whether or not to provide the through hole 46 is appropriately determined in consideration of the sealability and the wear inhibition of the piston ring 51. The through hole 46 can be provided in both of the annular grooves 42, can be provided only in the rear annular groove 42, or can not be provided in all of the annular grooves 42. However, by providing the through hole 46 only in the front annular groove 42, it is easy to equalize the wear amounts of the front piston ring 51 and the rear piston ring 51.

[0041] The front annular groove 42 and the rear annular groove 42 have the same configuration except for whether or not they are connected to the through hole 46. The two piston rings 51 have the same configuration. Therefore, in the following description, the front annular groove 42 and the piston ring 51 embedded in the front annular groove 42 will mainly be described.

[0042] <Anti-backflow device 104 of comparative example>

[0043] Here, the anti-backflow device 104 of the comparative example will be described. Figure 13A is a magnified view of a portion corresponding to the B portion of Figure 2 The annular groove 142 and the piston ring 151 have a rectangular cross section. As described above, since the piston ring 151 is subjected to a pressure on the radially outer side, the piston ring 151 is pressed against the inner wall of the cylinder 32. Further, at the time of injection, the molten metal flows in the gap between the backflow prevention ring 141 and the cylinder 32 in the -X direction to flow into the annular groove 142, and thus 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 of the annular groove 142 (not shown), but since the speed of the screw 33 is higher at the time of injection, 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.

[0044] Figure 13B A case where the piston ring 151 is deformed is shown. The piston ring 151 is formed of a relatively soft metal. Therefore, when the piston ring 151 is pressed in the radially outer direction and the -X direction, the piston ring 151 is deformed, and a portion thereof sometimes enters the gap G in the -X direction between the backflow prevention ring 141 and the cylinder 32. If such a state occurs, not only the wear of the piston ring 151 is accelerated, but also the portion of the piston ring 151 that enters the gap G between the backflow prevention ring 141 and the cylinder 32 can damage the cylinder 32.

[0045] <Shapes of annular groove 42 and piston ring 51>

[0046] Reference will be made mainly to Figure 3The shape of the annular groove 42 and the piston ring 51 of the present embodiment will be described in more detail. The annular groove 42 has a front side 43, a rear side 44, and a bottom surface 45. The bottom surface 45 is located at the deepest part of the annular groove 42, separating the front side 43 from the rear side 44. The front side 43 is a plane orthogonal to the center axis CL of the cylinder block 32. The bottom surface 45 is connected to the through-hole 46.

[0047] The piston ring 51 has an inner peripheral surface 52, an outer peripheral surface 53, a front side 54, and a rear side 55. The inner peripheral surface 52 separates the front side 54 from the rear side 55. The inner peripheral surface 52 is opposite the bottom surface 45 of the annular groove 42. The front side 54 is a plane orthogonal to the center axis CL of the cylinder block 32, and is opposite the front side 43 of the annular groove 42. The rear side 55 is a plane orthogonal to the center axis CL of the cylinder block 32, and is opposite the rear side 44 of the annular groove 42.

[0048] The piston ring 51 has a receiving portion 56 received 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 in the injection direction with respect to the rear end portion (rear side 55) of the receiving portion 56 in the injection direction. The rear portion in the injection direction is smaller than the front portion in the injection direction in terms of the outer diameter of the piston ring 51. The radially outermost portion 58 of the rear end portion of the receiving portion 56 is located at substantially the same position in the radial direction as the opening 59 of the annular groove 42. As described above, the piston ring 51 easily enters the gap G on the -X direction side between the reverse flow prevention ring 41 and the cylinder block 32. However, in the present embodiment, since there is no protruding portion 57 in the vicinity of the gap G, the piston ring 51 does not easily enter the gap G.

[0049] The surface connecting the rear end portion 53A of the outer peripheral surface 53 and the radially outermost portion 58 of the rear end portion of the receiving portion 56 has a cylindrical surface 60 having the center axis CL of the cylinder block 32 as a center axis, and an inclined surface 61 connecting the cylindrical surface 60 and the rear end portion 53A of the outer peripheral surface 53 and inclined with respect to the center axis CL of the cylinder block 32. Thus, the piston ring 51 is easily distanced from the gap G, and the piston ring 51 does not easily enter the gap G. The diameter of the cylindrical surface 60 is constant in the X direction, but can also increase as it approaches the +X direction.

[0050] Other embodiments of the present application will be described below. In the embodiments shown below, the configurations and effects that are omitted are the same as those of the first embodiment.

[0051] (Second Embodiment)

[0052] Figure 5 is a view showing the second embodiment of the reverse flow prevention ring 41 and the piston ring 51. Figure 2is an enlarged view of a portion corresponding to B part of Fig. 6. In the present embodiment, the outermost portion 58 of the rear end portion of the accommodation portion 56 is located inside the annular groove 42 in the radial direction, and is otherwise the same as the first embodiment. The piston ring 51 is worn by use, and thus the thickness of the protruding portion 57 is gradually reduced, and the cylindrical surface 60 can eventually come into contact with the cylinder block 32. However, since the cylindrical surface 60 is located inside the annular groove 42, even if the piston ring 51 is thinned by wear, it takes a longer time until the cylindrical surface 60 comes into contact with the cylinder block 32. In the present embodiment, the life of the piston ring 51 can be extended, and the frequency of replacement of the piston ring 51 can be reduced.

[0053] (Third Embodiment)

[0054] Figure 6 is an enlarged view of a portion corresponding to B part of Fig. 6. In the present embodiment, the outermost portion 58 of the rear end portion of the accommodation portion 56 is located inside the annular groove 42 in the radial direction, and is otherwise the same as the first embodiment. The piston ring 51 is worn by use, and thus the thickness of the protruding portion 57 is gradually reduced, and the cylindrical surface 60 can eventually come into contact with the cylinder block 32. However, since the cylindrical surface 60 is located inside the annular groove 42, even if the piston ring 51 is thinned by wear, it takes a longer time until the cylindrical surface 60 comes into contact with the cylinder block 32. In the present embodiment, the life of the piston ring 51 can be extended, and the frequency of replacement of the piston ring 51 can be reduced. Figure 2

[0055] (Fourth Embodiment)

[0056] Figure 7 is an enlarged view of a portion corresponding to B part of Fig. 6. In the present embodiment, the outermost portion 58 of the rear end portion of the accommodation portion 56 is located inside the annular groove 42 in the radial direction, and is otherwise the same as the first embodiment. The piston ring 51 is worn by use, and thus the thickness of the protruding portion 57 is gradually reduced, and the cylindrical surface 60 can eventually come into contact with the cylinder block 32. However, since the cylindrical surface 60 is located inside the annular groove 42, even if the piston ring 51 is thinned by wear, it takes a longer time until the cylindrical surface 60 comes into contact with the cylinder block 32. In the present embodiment, the life of the piston ring 51 can be extended, and the frequency of replacement of the piston ring 51 can be reduced. Figure 2 (Fifth Embodiment)

[0057]

[0058] Figure 8 is an enlarged view of a portion corresponding to B part of Fig. 6. In the present embodiment, the outermost portion 58 of the rear end portion of the accommodation portion 56 is located inside the annular groove 42 in the radial direction, and is otherwise the same as the first embodiment. The piston ring 51 is worn by use, and thus the thickness of the protruding portion 57 is gradually reduced, and the cylindrical surface 60 can eventually come into contact with the cylinder block 32. However, since the cylindrical surface 60 is located inside the annular groove 42, even if the piston ring 51 is thinned by wear, it takes a longer time until the cylindrical surface 60 comes into contact with the cylinder block 32. In the present embodiment, the life of the piston ring 51 can be extended, and the frequency of replacement of the piston ring 51 can be reduced. Figure 2 ​​A magnified view of a portion of the B portion of FIG. 6. The piston ring 51 has a receiving portion 56 received 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 in the injection direction with respect to the rear end portion of the receiving portion 56 (the radially inner portion 55B of the rear surface 55). The rear portion in the injection direction is smaller than the front portion in the injection direction in terms of the outer diameter of the piston ring 51. As described above, the piston ring 51 easily enters the gap G on the -X direction side between the reverse flow prevention ring 41 and the cylinder block 32. However, in the present embodiment, since there is no protruding portion 57 in the vicinity of the gap G, the piston ring 51 hardly enters the gap G.

[0059] The rear surface 55 of the piston ring 51 has a step portion 55C. The rear surface 55 of the piston ring 51 has a radially outer portion 55A and a radially inner portion 55B separated by the step portion 55C. The radially outer portion 55A and the radially inner portion 55B are opposite to the rear surface 44 of the annular groove 42. The front surface 54 is a plane orthogonal to the center axis CL of the cylinder block 32 and is opposite to the front surface 43 of the annular groove 42.

[0060] The step portion 55C is provided only to the piston ring 51, and the rear surface 44 of the annular groove 42 is a plane orthogonal to the center axis CL of the cylinder block 32. The radially outer portion 55A of the rear surface 55 of the piston ring 51 is located forward in the injection direction with respect to the radially inner portion 55B. At the time of injection, the piston ring 51 relatively moves in the -X direction with respect to the annular groove 42, and the radially inner portion 55B of the rear surface 55 of the piston ring 51 comes into contact with the rear surface 44 of the annular groove 42. At this time, the radially outer portion 55A of the rear surface 55 of the piston ring 51 cannot come into contact with the rear surface 44 of the annular groove 42. Therefore, a portion of the piston ring 51 hardly enters the gap G on the -X side between the reverse flow prevention ring 41 and the cylinder block 32.

[0061] As described above, a pressure is applied to the radially outer portion of the piston ring 51, but in the present embodiment, the adjustment of the pressure is easy. 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. If the pressure applied to the inner peripheral surface 52 of the piston ring 51 is set as P1, 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 W1, and the width of the outer peripheral surface 53 of the piston ring 51 is set as W2, then P2 = (W1 / W2) x P1. The pressure with which the piston ring 51 presses the cylinder block 32 can be easily adjusted by the ratio of the width W1 of the inner peripheral surface 52 of the piston ring 51 to the width W2 of the outer peripheral surface 53.

[0062] (6th Embodiment)

[0063] Figure 9 is an enlarged view of a portion corresponding to B part of Figure 2 The rear side 44 of the annular groove 42 has a radially outer portion 44A, a radially inner portion 44B, and a step portion 44C, which separates the radially outer portion 44A and the radially inner portion 44B. In terms of the inner diameter of the piston ring 51, the rear portion in the injection direction is larger than the front portion in the injection direction. At the time of injection, when the piston ring 51 relatively moves in the -X direction with respect to the annular groove 42, 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.

[0064] In addition, the rear end portion 53A of the outer peripheral surface 53 in the injection direction is located in front of the last end portion (the radially outer portion 55A of the rear side 55) of the housing portion 56 in the injection direction. In terms of the outer diameter of the piston ring 51, the rear portion in the injection direction is smaller than the front portion in the injection direction. Since the piston ring 51 is distanced from the gap G, the piston ring 51 is more difficult to enter the gap G.

[0065] (7th Embodiment)

[0066] Figure 10 is an enlarged view of a portion corresponding to B part of Figure 2 In the present embodiment, the radially outermost portion 58 of the rear end portion of the housing portion 56 is located inside the annular groove 42, and is otherwise the same as the 6th embodiment. The piston ring 51 is worn due to use, and thus the thickness of the protruding portion 57 gradually decreases, and there is a possibility that the cylindrical surface 60 eventually comes into contact with the cylinder block 32. However, since the cylindrical surface 60 is located inside the annular groove 42, even if the piston ring 51 is thinned by wear, it takes a longer time until the cylindrical surface 60 comes into contact with the cylinder block 32. In the present embodiment, it is possible to extend the life of the piston ring 51, and it is possible to reduce the frequency of replacement of the piston ring 51. In addition, since the piston ring 51 is distanced from the gap G, the piston ring 51 is more difficult to enter the gap G.

[0067] (8th Embodiment)

[0068] Figure 11 is an enlarged view of a portion corresponding to B part of Figure 2An enlarged view of a portion corresponding to B part of FIG. 8. The face 62 connecting the rear end portion 53A of the outer peripheral surface 53 and the outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is inclined as a whole with respect to the center axis CL of the cylinder 32. The other aspects are the same as those of the 6th embodiment. The outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is located at substantially the same position in the radial direction as the opening 59 of the annular groove 42. The present embodiment has substantially the same effects as those of the 6th embodiment, but since the shape of the face 62 connecting the rear end portion 53A of the outer peripheral surface 53 and the outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is simple, the machining of the piston ring 51 is easy.

[0069] (9th Embodiment)

[0070] Figure 12 is an enlarged view of a portion corresponding to B part of FIG. 8. The face 62 connecting the rear end portion 53A of the outer peripheral surface 53 and the outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is inclined as a whole with respect to the center axis CL of the cylinder 32. The other aspects are the same as those of the 6th embodiment. The outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is located at substantially the same position in the radial direction as the opening 59 of the annular groove 42. The present embodiment has substantially the same effects as those of the 6th embodiment, but since the shape of the face 62 connecting the rear end portion 53A of the outer peripheral surface 53 and the outermost portion 58 in the radial direction of the rear end portion of the housing portion 56 is simple, the machining of the piston ring 51 is easy. Figure 2

[0071] Several preferred embodiments of the present application are shown and described in detail, but it should be understood that various changes and modifications can be made without departing from the spirit or scope of the appended claims. Explanation of Reference Numerals

[0072] 3 Injection device

[0073] 4 Backflow prevention device

[0074] 32 Cylinder

[0075] 33 Screw

[0076] 41 Backflow prevention ring

[0077] 42 Annular groove

[0078] 44 Rear side of annular groove

[0079] 44A Radially outer portion of rear side of annular groove

[0080] 44B Radially inner portion of rear side of annular groove

[0081] 46 Through hole

[0082] 51 Piston ring

[0083] 53 Outer peripheral surface

[0084] 53A Rear end portion of outer peripheral surface

[0085] 55 Rear side of piston ring​

[0086] 55A radially outer portion of the rear side of the piston ring

[0087] 55B radially inner portion of the rear side of the piston ring

[0088] 56 housing portion

Claims

1. A backflow prevention device for an injection apparatus, wherein, include: A backflow prevention ring having at least one annular groove opposite to the inner surface of the cylinder of the injection device; as well as At least one piston ring, which is embedded in the at least one annular groove. The at least one piston ring has a receiving portion housed in the at least one annular groove and an outer peripheral surface located radially outward compared to the at least one annular groove, wherein the rear end of the outer peripheral surface in the injection direction is located in front of the last end of the receiving portion in the injection direction in the injection direction.

2. The anti-backflow device of the injection apparatus according to claim 1, wherein, The surface connecting the rear end of the outer peripheral surface to the rear end of the receiving portion has: A cylindrical surface, with the central axis of the cylinder as its central axis; as well as An inclined surface, which connects the front end of the cylindrical surface in the injection direction to the rear end of the outer peripheral surface, is inclined relative to the central axis of the cylinder.

3. The anti-backflow device of the injection apparatus according to claim 1, wherein, The surface connecting the rear end of the outer peripheral surface to the rear end of the receiving portion is inclined integrally relative to the central axis of the cylinder.

4. The anti-backflow device of the injection apparatus according to claim 2 or 3, wherein, The outermost radial portion of the rear end of the receiving portion is located at approximately the same position as the opening of the annular groove.

5. The anti-backflow device of the injection apparatus according to claim 2 or 3, wherein, The outermost radial portion of the rear end of the receiving part is located inside the annular groove.

6. The anti-backflow device of the injection apparatus according to any one of claims 1 to 5, wherein, The at least one annular groove and the at least one piston ring each have a rear side portion in the injection direction. The rear side of the at least one annular groove and the rear side of the at least one piston ring can contact each other only on their respective radially inner sides.

7. The anti-backflow device according to 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. The anti-backflow device according to claim 7, wherein, The radially inner portion of the rear side of the at least one annular groove and the radially inner portion of the rear side of the at least one piston ring are planes orthogonal to the central axis of the cylinder.

9. The anti-backflow device according to claim 6, wherein, The radially outer portion of the rear side of the at least one piston ring is located in front of the radially inner portion of the rear side of the at least one piston ring in the injection direction.

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

11. The anti-backflow device according to any one of claims 1 to 10, wherein, Regarding the outer diameter of the piston ring, the rear portion in the injection direction is smaller than the front portion in the injection direction.

12. An injection device, wherein, have: The anti-backflow device according to any one of claims 1 to 11; The cylinder block; The screw housed in the cylinder; and An injection nozzle is installed at the front end of the cylinder.

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