Backflow prevention device and injection device

Abstract

To provide a backflow prevention device that suppresses the backflow of molten resin while preventing galling of a check ring.SOLUTION: A backflow prevention device of the present invention comprises: a check head fixed to the tip of the screw; a check ring fitted onto the check head so as to be slidable between a forward limit that allows the passage of molten resin and a backward limit that prevents the passage of molten resin; and a check sheet fixed by extrapolation to the check head at a position where it abuts against the check ring at the backward limit. The check ring has a cylindrical portion with a communication passage formed between itself and the check head for passing molten resin, and a locking claw that protrudes from the cylindrical portion in the axial direction of the screw and is locked to the check head. The axial length of the cylindrical portion is shorter than that of the check sheet.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a backflow prevention device that prevents the backflow of molten resin, and to an injection device equipped with the same. [Background technology]

[0002] Conventionally, in an injection molding machine that injects molten resin into the cavity of a clamped mold, a backflow prevention device that is attached to the tip of the screw to prevent the molten resin from backflowing inside the heating cylinder has been known (see, for example, Patent Documents 1 to 3).

[0003] The backflow prevention device has, for example, a check ring that can move back and forth between the check seat and the head portion of the check head fixed to the tip of the screw. When the pressure behind the check ring becomes higher than the pressure in front of it, the check ring moves forward to allow the molten resin to pass. On the other hand, when the pressure in front of the check ring becomes higher than the pressure in front of it, the check ring moves backward to prevent the molten resin from flowing back. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-160792 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-254726 [Patent Document 3] Japanese Utility Model Application Publication No. 59-194924 Summary of the Invention [Problem to be solved by the invention]

[0005] If the pressure loss when the molten resin passes through the check ring is large, the timing of the check ring's backward movement when the molten resin is injected may be delayed, causing a portion of the measured molten resin to flow back, resulting in a problem of variation in the amount of molten resin injected into the cavity.

[0006] Furthermore, if the melting state of the resin passing through the check ring becomes uneven in the circumferential direction, stress will be generated in a direction that tilts the check ring. If the check ring slides in this state, it may become damaged as it moves back and forth inside the heating cylinder.

[0007] The present invention has been made to solve the problems of the prior art, and its purpose is to provide a backflow prevention device that can prevent the backflow of molten resin and prevent the check ring from being scuffed. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a backflow prevention device attached to the tip of a screw of an injection molding machine, comprising: a check head fixed to the tip of the screw; a check ring extrapolated to the check head so as to be slidable between a forward limit that allows the passage of molten resin and a backward limit that prevents the passage of molten resin; and a check sheet extrapolated and fixed to the check head at a position where it abuts the check ring at the backward limit, wherein the check ring comprises a cylindrical portion having a communicating passage formed between it and the check head to allow the passage of molten resin, and a locking claw that protrudes from the cylindrical portion in the axial direction of the screw and is locked to the check head, and the axial length of the cylindrical portion is shorter than that of the check sheet. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain a backflow prevention device that can prevent backflow of molten resin and also prevent the check ring from being scuffed. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a side view of an injection molding machine according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded perspective view of the backflow prevention device according to the present embodiment. [Figure 3] 1A and 1B are cross-sectional views of a check ring and a check sheet according to the present embodiment. [Figure 4] 1 is a cross-sectional view of a backflow prevention device according to an embodiment of the present invention. [Figure 5] FIG. 1 is a cross-sectional view of a conventional backflow prevention device. DETAILED DESCRIPTION OF THE INVENTION

[0011] An injection molding machine 10 according to the present invention will be described below with reference to the drawings. The injection molding machine 10 is a device that injects a measured amount of molten resin into a mold to form an injection-molded product (hereinafter referred to as "injection molding").

[0012] [Configuration of injection molding machine 10] 1 is a side view of an injection molding machine 10 according to this embodiment. As shown in FIG. 1, the injection molding machine 10 mainly includes a mold clamping device 20 and an injection device 30.

[0013] The mold clamping device 20 opens, closes, and clamps the mold 21. Specifically, the mold clamping device 20 mainly includes a fixed die plate 23 that supports a fixed-side mold 22, and a movable die plate 25 that supports a movable-side mold 24. The fixed-side mold 22 and the movable-side mold 24 are supported so as to face each other in the left-right direction (horizontal direction) of the injection molding machine 10.

[0014] The movable die plate 25 moves left and right along tie bars 27 by transmitting the driving force of a die opening / closing motor (not shown) through a toggle link mechanism 26. When the movable die plate 25 moves leftward, the fixed-side die 22 and the movable-side die 24 move apart. On the other hand, when the movable die plate 25 moves rightward, the fixed-side die 22 and the movable-side die 24 come into contact with each other, forming a cavity (internal space) inside the die 21. Then, when pressure is further applied in a direction that moves the movable die plate 25 rightward, the fixed-side die 22 and the movable-side die 24 are clamped.

[0015] The injection device 30 plasticizes, measures, and injects the molten resin. The injection device 30 according to this embodiment is disposed horizontally apart from the mold clamping device 20 (to the right of the mold clamping device 20). The injection device 30 mainly includes a heating cylinder 31, a screw 32, a hopper 33, and a hopper block 34.

[0016] The heating cylinder 31 is a cylindrical member extending in the left-right direction of the injection molding machine 10. The heating cylinder 31 mainly includes a resin passage 35 and a nozzle 36. A band heater (not shown) for heating the heating cylinder 31 is attached to the outer circumferential surface of the heating cylinder 31.

[0017] The resin passage 35 is a cylindrical space extending in the axial direction (longitudinal direction) inside the heating cylinder 31. The resin passage 35 communicates with the outside of the heating cylinder 31 (the cavity of the mold 21) through a nozzle 36 provided at the tip (front end) of the heating cylinder 31. In other words, the resin passage 35 is a space extending from the nozzle 36 along the axial direction.

[0018] The screw 32 is a cylindrical member. A spiral groove is formed on the outer circumferential surface of the screw 32. The screw 32 is housed in the internal space of the heating cylinder 31 in a state in which it can move left and right (hereinafter referred to as "forward and backward") and rotate in the injection molding machine 10. The screw 32 moves forward and backward when a driving force from an injection motor (not shown) is transmitted thereto, and rotates when a driving force from a metering motor (not shown) is transmitted thereto.

[0019] More specifically, when the injection motor is rotated forward, the screw 32 moves (advances) toward the tip of the heating cylinder 31 (i.e., the nozzle 36). On the other hand, when the injection motor is rotated backward, the screw 32 moves (retreats) toward the base end of the heating cylinder 31 (i.e., the side opposite the nozzle 36). Hereinafter, within the range that the tip position of the screw 32 can reach within the heating cylinder 31, the position closest to the nozzle 36 will be referred to as the "forward limit," and the position farthest from the nozzle 36 will be referred to as the "rear limit." Furthermore, the terms "forward rotation" and "reverse rotation" of the injection motor do not specify an absolute direction of rotation, but merely specify a relative relationship (i.e., forward rotation and reverse rotation are rotations in opposite directions).

[0020] The hopper 33 is a funnel-shaped member that stores the raw resin material. The hopper block 34 is a member that supports the heating cylinder 31 and the hopper 33. The hopper 33 is connected to a resin passage 35 through the hopper block 34 on the base end side of the tip of the heating cylinder 31. The resin material stored in the hopper 33 is supplied to the resin passage 35 of the heating cylinder 31 through an opening provided at the bottom end. The resin material used in this injection molding machine 10 is, for example, so-called "pellets" molded into a cylindrical shape.

[0021] In the injection device 30, the screw 32 moves backward while rotating by rotating the injection motor in the reverse direction and rotating the metering motor. As a result, pellets supplied through the hopper 33 are plasticized and filled (metered) into the resin passage 35 ahead of the screw 32. In addition, in the injection device 30, the screw 32 moves forward by rotating the injection motor in the forward direction. As a result, the plasticized molten resin ahead of the screw 32 is injected into the cavity of the mold 21 through the nozzle 36.

[0022] [Configuration of backflow prevention device 40] Fig. 2 is an exploded perspective view of the backflow prevention device 40 according to this embodiment. Fig. 3 is a cross-sectional view of the check ring 42 (A) and check sheet 43 (B) according to this embodiment. Fig. 4 is a cross-sectional view of the backflow prevention device 40 according to this embodiment. Fig. 5 is a cross-sectional view of a conventional backflow prevention device 60. Hereinafter, the extension direction of the screw 32 may be referred to as the "axial direction", the forward direction of the screw 32 may be referred to as the "forward", and the backward direction of the screw 32 may be referred to as the "rearward".

[0023] The injection molding machine 10 is equipped with a backflow prevention device 40 shown in Figures 2 to 4. The backflow prevention device 40 is attached to the tip of the screw 32. As shown in Figures 2 to 4, the backflow prevention device 40 mainly includes, for example, a check head 41, a check ring 42, and a check sheet 43.

[0024] The backflow prevention device 40 is a device that prevents the molten resin from flowing backward inside the heating cylinder 31. More specifically, the backflow prevention device 40 allows the plasticized molten resin to pass through the backflow prevention device 40 (more specifically, the check ring 42) from the rear side to the front side when the molten resin is metered (i.e., when the screw 32 rotates backward). On the other hand, the backflow prevention device 40 prevents the metered molten resin from passing through the backflow prevention device 40 (more specifically, the check ring 42) from the front side to the rear side (i.e., backflow) when the molten resin is injected (i.e., when the screw 32 rotates forward).

[0025] The check head 41 is fixed to the tip of the screw 32 and supports the check ring 42 and the check seat 43. The check head 41 is, for example, a long rod-shaped member composed of a tip portion 44, an intermediate portion 45, and a base end portion 46.

[0026] The tip portion 44 is the tip of the check head 41 (the end farther from the screw 32). The tip portion 44 has a tapered shape toward the front. In addition, grooves 47 extending in the axial direction are formed in the tip portion 44 at a plurality of positions (four positions in this embodiment) spaced apart in the circumferential direction. These grooves 47 allow the molten resin to pass through in the axial direction and receive locking claws 51, which will be described later.

[0027] The intermediate portion 45 is located between the tip portion 44 and the base portion 46 in the axial direction. The diameter of the intermediate portion 45 is cylindrical and smaller than the maximum diameter of the tip portion 44 but larger than the maximum diameter of the base portion 46. The intermediate portion 45 supports the check ring 42 so that it can slide in the axial direction. A flange portion 48 is provided at the base end of the intermediate portion 45 (the portion that contacts the base portion 46).

[0028] The flange portion 48 is a portion that protrudes radially from the intermediate portion 45 and continues circumferentially. The front surface of the flange portion 48 (the surface on the intermediate portion 45 side) is an inclined surface whose diameter gradually decreases toward the front. On the other hand, the rear surface of the flange portion 48 (the surface on the base end portion 46 side) is a vertical surface that is perpendicular to the axial direction. The vertical surface of the flange portion 48 functions as a reference surface for positioning the check sheet 43.

[0029] The base end 46 is the base end (the end on the screw 32 side) of the check head 41. The check sheet 43 is fitted onto the base end 46. A male thread 49 is formed on the outer circumferential surface of the base end 46 and is threaded into the screw hole 39 provided at the tip of the screw 32. When the male thread 49 is threaded into the screw hole 39, the check sheet 43 is positioned and fixed between the tip of the screw 32 and the vertical surface of the flange portion 48, as shown in FIG.

[0030] The check ring 42 is fitted onto an intermediate portion 45 of the check head 41. The check ring 42 is supported by the check head 41 so as to be slidable in the axial direction. The check ring 42 rotates integrally with the check head 41 (screw 32). The check ring 42 is composed of, for example, a cylindrical portion 50 and a plurality of (two in this embodiment) locking claws 51.

[0031] The cylindrical portion 50 is a cylindrical portion that is extrapolated onto the intermediate portion 45 of the check head 41. A small gap is formed between the outer dimensions of the cylindrical portion 50 and the inner diameter of the heating cylinder 31. That is, the check ring 42 slides in the axial direction with the outer peripheral surface of the cylindrical portion 50 facing the inner peripheral surface of the heating cylinder 31. As a result, when the check ring 42 slides, resistance is generated whose magnitude depends on the facing area between the inner peripheral surface of the heating cylinder 31 and the cylindrical portion 50. In addition, a plurality of communication passages 52 that allow molten resin to pass in the axial direction are formed on the inner peripheral surface of the cylindrical portion 50.

[0032] The communicating passages 52 are formed at a plurality of positions (four positions in this embodiment) spaced apart in the circumferential direction. The communicating passages 52 are open at both ends of the cylindrical portion 50 in the thickness direction (i.e., the axial direction). The communicating passages 52 are recessed radially outward from the inner circumferential surface of the cylindrical portion 50. That is, the communicating passages 52 are spaces surrounded by the recesses in the inner circumferential surface of the cylindrical portion 50 and the outer circumferential surface of the intermediate portion 45. Meanwhile, an imaginary circle connecting the portions of the inner circumferential surface of the cylindrical portion 50 that are different from the communicating passages 52 is a perfect circle that matches the outer dimensions of the intermediate portion 45. That is, the check ring 42 slides over the portions of the inner circumferential surface of the cylindrical portion 50 that are different from the communicating passages 52, with the outer circumferential surface of the intermediate portion 45 facing each other.

[0033] The locking claws 51 are formed at a plurality of positions (two positions in this embodiment) spaced apart in the circumferential direction of the cylindrical portion 50. The locking claws 51 protrude axially forward from the end face of the cylindrical portion 50. The diameter of an imaginary circle connecting the outer circumferential surfaces of the locking claws 51 is slightly smaller than the inner diameter of the heating cylinder 31. That is, when the check ring 42 slides, the outer circumferential surface of the locking claws 51 does not slide against the inner circumferential surface of the heating cylinder 31. The locking claws 51 enter the grooves 47. When the check ring 42 slides, the locking claws 51 move axially in the grooves 47. When the screw 32 (check head 41) rotates, the locking claws 51 are locked to the circumferential wall surfaces of the grooves 47, and the check ring 42 rotates together with the locking claws 51.

[0034] The check sheet 43 has a ring-shaped outer shape. The check sheet 43 is fitted onto and fixed to the check head 41 (more specifically, the base end 46). The outer dimensions of the check sheet 43 are smaller than the inner diameter of the heating cylinder 31 and match the diameter of the shaft of the screw 32 (the outer dimensions of the spiral groove portion). That is, the molten resin plasticized by the screw 32 passes through the space between the inner circumferential surface of the heating cylinder 31 and the outer circumferential surface of the check sheet 43 and enters the communicating passage 52. The check sheet 43 is positioned between the tip of the screw 32 and the vertical surface of the flange portion 48. As shown in FIG. 4(B), the check sheet 43 abuts against the check ring 42 at the retraction limit.

[0035] 3 and 4, the axial length L1 of the cylindrical portion 50, the axial length L2 of the locking claw 51, and the axial length L3 of the check sheet 43 have the following relationship: First, the axial length L1 of the cylindrical portion 50 is shorter than the axial length L3 of the check sheet 43. Also, the axial length (L1 + L2) of the check ring 42 is longer than the axial length L3 of the check sheet 43.

[0036] 4, the sliding range L4 of the cylindrical portion 50 in the axial direction is shorter than the diameter D1 of the cylindrical portion 50. More specifically, the sliding range L4 is set to a range of 50% to 60% (most preferably 55%) of the diameter D1. The sliding range L4 corresponds to the axial distance between the base end of the tip portion 44 (the end that contacts the intermediate portion 45) and the vertical surface of the flange portion 48. The diameter D1 of the cylindrical portion 50 corresponds to the inner diameter dimension of the heating cylinder 31 and the maximum diameter of the screw 32.

[0037] The check ring 42 slides in the axial direction between a forward limit shown in FIG. 4(A) and a backward limit shown in FIG. 4(B). The forward limit is the position of the front end of the sliding range L4 of the check ring 42. The backward limit is the position of the rear end of the sliding range L4 of the check ring 42. The check ring 42 at the forward limit moves away from the check seat 43 and opens the rear end of the communicating passage 52. On the other hand, the check ring 42 at the backward limit abuts against the check seat 43 and closes the rear end of the communicating passage 52. On the other hand, the front end of the communicating passage 52 is always open. In other words, the check ring 42 at the forward limit allows the molten resin to pass through the communicating passage 52. On the other hand, the check ring 42 at the backward limit prevents the molten resin from passing through the communicating passage 52.

[0038] More specifically, when the screw 32 rotates backward during metering of the molten resin, the pressure behind the check ring 42 inside the heating cylinder 31 becomes higher than the pressure in front of it. This causes the check ring 42 to slide forward inside the heating cylinder 31 and reach its limit of forward movement. As a result, the molten resin plasticized by the screw 32 passes through the space between the inner circumferential surface of the heating cylinder 31 and the outer circumferential surface of the check sheet 43, and further passes through the opened communicating passage 52, to be metered (filled) into the space in front of the check head 41 of the heating cylinder 31.

[0039] On the other hand, when the screw 32 moves forward during injection of the molten resin, the pressure in front of the check ring 42 becomes higher than the pressure behind the check ring 42 inside the heating cylinder 31. This causes the check ring 42 to slide rearward inside the heating cylinder 31 and reach its limit of retraction. As a result, the metered molten resin is injected into the cavity of the mold 21 through the nozzle 36 without flowing back behind the check ring 42 through the closed communicating passage 52.

[0040] [Effects of the above embodiment] As in the above embodiment, by shortening the axial length L1 of the cylindrical portion 50, the axial length of the communicating passage 52 is shortened. As a result, the pressure loss of the molten resin when passing through the communicating passage 52 can be reduced. In addition, the opposing area between the inner circumferential surface of the heating cylinder 31 and the outer circumferential surface of the cylindrical portion 50 is reduced, so the resistance when the check ring 42 slides can be reduced. This allows the check ring 42 to slide smoothly when the molten resin is injected. As a result, there is no delay in the retraction of the check ring 42 during injection, and backflow of the molten resin is prevented.

[0041] Furthermore, as in the above embodiment, by increasing the axial length L3 of the check sheet 43, the time (distance) required for the molten resin to pass through the tip of the screw 32 and flow into the communicating passage 52 is increased. This makes the molten state of the molten resin uniform as it passes between the inner circumferential surface of the heating cylinder 31 and the outer circumferential surface of the check sheet 43. As a result, the generation of stress in a direction that tilts the check ring 42 is suppressed, thereby preventing the check ring 42 facing the inner circumferential surface of the heating cylinder 31 from being galled.

[0042] Furthermore, according to the above embodiment, the length L2 of the locking claws 51 can be ensured by making the length (L1 + L2) of the check ring 42 longer than the length L3 of the check seat 43. In this way, by selectively shortening the axial length L1 of the cylindrical portion 50 rather than reducing the overall size of the check ring 42 in the axial direction, the above-mentioned effects can be obtained while maintaining the locking force of the check ring 42 with respect to the check head 41.

[0043] As shown in Figure 5, in a conventional backflow prevention device 60, the axial length L5 of the check ring 62 is longer than the axial length L6 of the check sheet 63. Until now, no one had considered focusing on the dimensional relationship between lengths L5 and L6 in order to solve the technical problem of suppressing the backflow of molten resin and preventing the check ring from galling. In contrast, the present invention focuses for the first time on the relationship between lengths L1 and L3, thereby solving the above technical problem.

[0044] 5, in the conventional backflow prevention device 60, the sliding range L7 was set to be the same as the diameter D2 of the check ring 62. In contrast, in the above embodiment, the sliding range L4 is set to be shorter than the diameter D1 of the cylindrical portion 50. This makes it possible to further reduce pressure loss and sliding resistance, and also increases the degree of freedom in selecting various dimensions compared to the conventional backflow prevention device 60.

[0045] Here, it is desirable to make the length (L4+L3) in Figure 4 the same as the length (L7+L6) in Figure 5. Also, as the sliding range L4 (i.e., the axial length of the intermediate portion 45) is shortened relative to the diameter D1 of the cylindrical portion 50, it is desirable to lengthen the length of the base end portion 46 so that the overall lengths of the check heads 41, 61 are the same. This ensures that the overall dimensional relationship between the backflow prevention devices 40, 60 is consistent, thereby maintaining the interchangeability of the backflow prevention devices 40, 60.

[0046] The above-described embodiments are merely illustrative examples of the present invention, and are not intended to limit the scope of the present invention to these embodiments. Those skilled in the art can implement the present invention in various other forms without departing from the spirit of the present invention. [Explanation of symbols]

[0047] 10... injection molding machine, 20... mold clamping device, 21... mold, 22... fixed side mold, 23... fixed die plate, 24... movable side mold, 25... movable die plate, 26... toggle link mechanism, 27... tie bar, 30... injection unit, 31... heating cylinder, 32... screw, 33... hopper, 34... hopper block, 35... resin passage, 36... nozzle, 39... screw hole, 40, 60... backflow prevention device, 41, 61... check head, 42, 62... check ring, 43, 63... check sheet, 44... tip portion, 45... middle portion, 46... base end portion, 47... groove, 48... flange portion, 49... male thread, 50... cylindrical portion, 51... locking claw, 52... communicating passage

Claims

1. A backflow prevention device attached to the tip of the screw of an injection molding machine, a check head fixed to the tip of the screw; a check ring fitted onto the check head so as to be slidable between a forward limit that allows passage of the molten resin and a backward limit that prevents passage of the molten resin; a check sheet fixed to the check head at a position where it abuts against the check ring at the rearmost position, The check ring is a cylindrical portion having a communication passage formed between the cylindrical portion and the check head for passing molten resin; a locking claw that protrudes from the cylindrical portion in the axial direction of the screw and is locked to the check head, A backflow prevention device, characterized in that the axial length of the cylindrical portion is shorter than that of the check sheet.

2. 2. The backflow prevention device according to claim 1, A backflow prevention device, characterized in that the axial length of the check ring is longer than that of the check sheet.

3. 2. The backflow prevention device according to claim 1, A backflow prevention device, characterized in that the sliding range of the cylindrical portion is shorter than the diameter of the cylindrical portion.

4. In an injection device that injects molten resin into a cavity of a clamped mold, a heating cylinder filled with molten resin; a screw that moves backward inside the heating cylinder to measure the molten resin and moves forward inside the heating cylinder to inject the molten resin into the cavity; An injection device comprising the backflow prevention device according to claim 1 attached to the tip of the screw.

Images