Screw with backflow prevention mechanism, injection molding apparatus equipped therewith, and backflow prevention ring

Abstract

To provide a screw with an excellent backflow prevention mechanism.SOLUTION: A screw with a backflow prevention mechanism according to one embodiment includes: a screw body part; a pressing metal fixed to a tip of the screw body part; a screw head provided on a tip side away from the pressing metal; a connection shaft connecting the pressing metal and the screw head; and a cylindrical backflow prevention ring provided between the pressing metal and the screw head to cover the connection shaft and to be slidable in an axial direction. One or more chamfers extending at least partially in the axial direction are formed on an outer peripheral surface of the backflow prevention ring.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a screw with a backflow prevention mechanism, an injection molding apparatus provided with the same, and a backflow prevention ring.

Background Art

[0002] An injection molding apparatus provided with a screw with a backflow prevention mechanism is known. For example, Patent Document 1 discloses a screw with a backflow prevention mechanism in which a backflow prevention ring is slidably provided between a retainer integrally provided on a screw main body portion and a screw head.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventor has found various problems in the development of a screw with a backflow prevention mechanism and an injection molding apparatus provided with the same. Other problems and novel features will become apparent from the description of this specification and the accompanying drawings.

Means for Solving the Problems

[0005] The screw with a backflow prevention mechanism according to one embodiment includes: a screw main body portion; a retainer fixed to the tip of the screw main body portion; a screw head provided on the tip side at a distance from the retainer; a connecting shaft that connects the retainer and the screw head; a cylindrical backflow prevention ring that covers the connecting shaft and is provided slidably in the axial direction between the retainer and the screw head. One or more chamfered portions, at least partially extending in the axial direction, are formed on the outer circumferential surface of the backflow prevention ring.

[0006] An injection molding apparatus according to one embodiment, An injection machine that injects molten resin using a screw with a backflow prevention mechanism housed in a cylinder, An injection molding apparatus comprising a mold for molding the molten resin injected from the injection machine, The screw with the backflow prevention mechanism is, The screw body and A push pin fixed to the tip of the screw body, A screw head is provided at the tip side, spaced apart from the aforementioned push pin, A connecting shaft that connects the aforementioned push pin and the aforementioned screw head, Between the push pin and the screw head, a cylindrical backflow prevention ring is provided that covers the connecting shaft and is slidable in the axial direction, A chamfered portion, at least partially extending in the axial direction, is formed on the outer circumferential surface of the backflow prevention ring.

[0007] A backflow prevention ring according to one embodiment is: A cylindrical backflow prevention ring that is attached to the screw of an injection molding machine, One or more chamfered portions are formed on the outer circumferential surface, each extending at least partially in the axial direction. [Effects of the Invention]

[0008] According to one embodiment, a screw with an excellent backflow prevention mechanism can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing the overall configuration of a screw with a backflow prevention mechanism and an injection molding apparatus equipped therewith according to the first embodiment. [Figure 2] This is a schematic cross-sectional view showing the overall configuration of a screw with a backflow prevention mechanism and an injection molding apparatus equipped therewith according to the first embodiment. [Figure 3] It is a schematic cross-sectional view showing the overall configuration of a screw with a backflow prevention mechanism according to the first embodiment and an injection molding apparatus including the same. [Figure 4] It is a diagram for explaining the movement of the screw during injection. [Figure 5] It is a diagram for explaining the movement of the screw during plasticization and metering. [Figure 6] It is a diagram showing the screw head and the backflow prevention ring. [Figure 7] It is a cross-sectional view showing the relationship between the screw head and the backflow prevention ring during injection. [Figure 8] It is a cross-sectional view showing the relationship between the screw head and the backflow prevention ring during plasticization (metering). [Figure 9] It is a perspective view showing the detailed configuration of the backflow prevention ring 250 according to the comparative example. [Figure 10] It is a schematic cross-sectional view showing the relationship between the backflow prevention ring 250 and the cylinder 10. [Figure 11] It is a graph showing the measurement results of the displacement during the rotation of the backflow prevention ring. [Figure 12] It is a perspective view showing the detailed configuration of the backflow prevention ring 25 according to the first embodiment. [Figure 13] It is a cross-sectional view for explaining the R processing method for the backflow prevention ring 25 according to the first embodiment. [Figure 14] It is a cross-sectional view of the backflow prevention ring 25 according to the first embodiment after R processing. [Figure 15] It is a cross-sectional view for explaining the R processing method for the backflow prevention ring 25 according to the first embodiment. [Figure 16] It is a perspective view showing the detailed configuration of the backflow prevention ring according to another embodiment. [Figure 17] It is a perspective view showing the detailed configuration of the backflow prevention ring according to still another embodiment. [Figure 18] It is a side view for explaining the chamfered portion partially formed as shown in FIG. 17. [Figure 19] It is a front view of the backflow prevention ring as viewed from the screw head side in the axial direction. [Figure 20] This graph shows the amount of screw advance relative to the outer dimensions of the backflow prevention ring. [Figure 21] This figure shows the results of comparing the amount of runout when a thermoplastic elastomer is used as the resin. [Figure 22] This figure shows the results of comparing the amount of vibration when polyethylene is used as the resin. [Figure 23] This figure shows the results of comparing the amount of runout when acrylic resin is used as the resin. [Modes for carrying out the invention]

[0010] The following describes specific embodiments in detail with reference to the drawings. However, the embodiments are not limited to those described below. Also, for clarity, the following descriptions and drawings have been simplified as appropriate.

[0011] (First Embodiment) <Overall configuration of injection molding equipment> First, with reference to Figures 1 to 3, the overall configuration of the screw with a backflow prevention mechanism and the injection molding apparatus equipped therewith according to the first embodiment will be described. Figures 1 to 3 are schematic cross-sectional views showing the overall configuration of the screw with a backflow prevention mechanism and the injection molding apparatus equipped therewith according to the first embodiment. Note that the right-handed xyz Cartesian coordinate system shown in Figures 1 to 3, and the other drawings described below, is for convenience in explaining the positional relationships of the components. Typically, the positive z-axis is vertically upward, and the xy-plane is the horizontal plane, and this is common across all drawings.

[0012] An injection molding apparatus can uniformly melt resin to an appropriate viscosity, measure a fixed amount of molten resin, and fill the mold with the molten resin. As shown in Figures 1 to 3, the injection molding apparatus according to this embodiment comprises an injection machine 100, a fixed mold D1, and a movable mold D2. Here, the injection machine 100 comprises a cylinder 10, a screw 20, a hopper 30, and an annular heater 40.

[0013] Figure 1 shows the state of an injection molding machine just before molten resin R2 is injected into the cavity C of the mold (fixed mold D1 and movable mold D2). Figure 2 shows the injection of molten resin R2 into the mold cavity C in an injection molding machine. Figure 3 shows the resin molded product R3 being removed from the mold in an injection molding machine.

[0014] As shown in Figures 1 to 3, the cylinder 10 of the injection machine 100 is a cylindrical member extending in the x-axis direction. The tip of the cylinder 10 (the end on the negative x-axis side) is tapered in stages, forming a nozzle. In the illustrated example, the tip of the cylinder 10 is tapered in two stages, and the tip of the cylinder 10, which has an injection hole, is fitted into a recess provided in the fixed mold D1 and fixed to the fixed mold D1.

[0015] As shown in Figures 1 to 3, the screw 20 extends in the x-axis direction and is rotatably housed in the cylinder 10. That is, the axis of rotation of the screw 20 is parallel to the x-axis. The screw 20 is a screw with a backflow prevention mechanism according to this embodiment, and comprises a screw body 21, a thrust pin 22, a screw head 23, a connecting shaft 24, and a backflow prevention ring 25.

[0016] Furthermore, the base of the screw 20, that is, the base of the screw body 21 (the end on the positive x-axis side), is connected to the motor MT, which is the rotational drive source, via the piston 20a. Since the piston 20a can be moved in the x-axis direction by an actuator (not shown), the screw 20 can also move in the x-axis direction. As shown in Figure 2, as the screw 20 moves forward in the negative x-axis direction, the molten resin R2 is injected from the leading edge of the cylinder 10 into the molds (fixed mold D1 and movable mold D2). The negative x-axis direction is also called the downstream side.

[0017] The screw body 21 is the main body of the screw 20. The screw body 21 comprises a screw shaft extending in the x-axis direction from the base to the tip of the screw 20, and screw blades helically provided on the outer circumferential surface of the screw shaft. The push pin 22 is a disc-shaped member fixed to the tip of the screw body 21. The diameter of the push pin 22 is larger than the diameter of the screw shaft of the screw body 21.

[0018] The screw head 23 is a conical member located at the tip side (negative x-axis direction side) away from the thrust pin 22. The central part of the main surface at the tip side of the thrust pin 22 and the central part of the bottom surface of the screw head 23 are connected by a connecting shaft 24 that is coaxial with the screw axis of the screw body 21. That is, the screw head 23 rotates together with the screw body 21 and moves together with the screw body 21 in the x-axis direction. As shown in Figure 1, the molten resin R2 stored at the tip of the cylinder 10 is pushed out by the side (i.e., front) of the conical screw head 23, as shown in Figure 2.

[0019] The backflow prevention ring 25 is a cylindrical member that covers the connecting shaft 24 and slides axially between the plunger 22 and the screw head 23. As will be described in detail later, the backflow prevention ring 25 is provided to prevent molten resin R2 from flowing back from the screw head 23 side to the screw body 21 side during injection as shown in Figure 2. For this reason, the outer diameter of the backflow prevention ring 25 is about the same as the inner diameter of the cylinder 10. On the other hand, the inner diameter of the backflow prevention ring 25 is larger than the outer diameter of the connecting shaft 24, providing a gap through which the molten resin R2 can pass.

[0020] Furthermore, since it is impossible to eliminate the gap between the backflow prevention ring 25 and the cylinder 10, it is not possible to completely prevent the backflow of molten resin R2 through this gap. The gap between the backflow prevention ring 25 and the cylinder 10 is, for example, about 50 or 60 μm. The detailed configuration of the backflow prevention ring 25 will be described later.

[0021] Here, with reference to Figures 1 to 3, the operation of the backflow prevention mechanism, including the backflow prevention ring 25, will be explained. As shown in Figures 1 and 2, the molten resin R2 is injected as the screw 20 moves forward. At this time, the backflow prevention ring 25 is in close contact with the push pin 22, preventing the molten resin R2 from flowing back from the screw head 23 to the screw body 21. Although not particularly limited, the rotation of the screw 20 is stopped when the screw 20 moves forward to inject the molten resin R2.

[0022] On the other hand, as shown in Figure 3, as the screw 20 retracts, the molten resin R2 for injection is metered and stored at the tip of the cylinder 10. At this time, the backflow prevention ring 25 moves toward the screw head 23, creating a gap between the backflow prevention ring 25 and the plunger 22. As a result, the molten resin R2 flows from the screw body 21 to the screw head 23 through the gap between the backflow prevention ring 25 and the connecting shaft 24 and the gap between the backflow prevention ring 25 and the screw head 23.

[0023] The hopper 30 is a cylindrical member for feeding resin pellets R1, which are the raw material for the molten resin R2 shown in Figures 1 to 3, into the cylinder 10. The hopper 30 is located above the end of the cylinder 10 in the positive x-axis direction. The positive x-axis direction is also called the upstream side.

[0024] The annular heaters 40 are arranged along the axial direction (x-axis direction) of the cylinder 10 so as to cover the outer circumferential surface of the cylinder 10. In the example shown in Figures 1 to 3, nine annular heaters 40 are provided on the tip side (negative x-axis direction side) of the hopper 30. Each of the multiple annular heaters 40 is individually controlled, for example, by a control unit (not shown). The number and installation range of the annular heaters 40 are not particularly limited and can be determined as appropriate.

[0025] In the injection machine 100 according to the first embodiment, granular resin pellets R1 supplied from the hopper 30 are heated by an annular heater 40 inside the cylinder 10 and stirred by a rotating screw 20. The heating temperature by the annular heater 40 is, for example, about 200 to 300°C. As the resin pellets R1 are heated, they are compressed by being pushed out from the base to the tip of the screw 20 (in the negative x-axis direction) and transformed into molten resin R2.

[0026] The fixed mold D1 is a mold fixed to the tip of the injection machine 100. On the other hand, the movable mold D2 is a mold that is driven by a drive source (not shown) and can slide in the x-axis direction. When the movable mold D2 moves in the positive x-axis direction and comes into contact with the fixed mold D1, a cavity C is formed between the fixed mold D1 and the movable mold D2, according to the shape of the resin molded product R3 (see Figure 3) to be manufactured, as shown in Figure 1.

[0027] Next, as shown in Figure 2, the screw 20 is advanced in the negative x-axis direction, filling the inside of the mold (fixed mold D1 and movable mold D2), i.e., the cavity C, with molten resin R2. The molten resin R2 is cooled and hardened by the mold (fixed mold D1 and movable mold D2), thereby forming the resin molded product R3. The temperature of the mold (fixed mold D1 and movable mold D2) is, for example, around 40 to 100°C. Then, as shown in Figure 3, the screw 20 retracts in the positive x-axis direction, and the movable mold D2 moves in the negative x-axis direction, releasing it from the fixed mold D1, thereby removing the resin molded product R3.

[0028] Figure 4 illustrates the movement of the screw during injection. During injection, when molten resin is injected into the mold under pressure, the screw 20 moves forward downstream within the cylinder 10, as indicated by the arrow.

[0029] Figure 5 illustrates the movement of the screw during plasticization metering. During plasticizing metering, when mixing and melting the molten resin, the screw 20 moves backward towards the upstream side within the cylinder 10. Note that the thrust pin is not shown in Figures 4 and 5 for simplification.

[0030] As described above, the injection molding apparatus can uniformly melt the resin to an appropriate viscosity, measure a fixed amount of molten resin, and fill the mold with the molten resin.

[0031] Figure 6 shows the screw head and the backflow prevention ring. The conical screw head 23 has a recess 231a on the side of the backflow prevention ring 25. On the other hand, the backflow prevention ring 25 has a claw portion 252a that engages with the recess 231a of the screw head 23. As a result, the backflow prevention ring 25 can rotate along with the rotation of the screw head 23. The backflow prevention ring 25 is in contact with a plunger 22 provided on the screw body side.

[0032] Next, with reference to Figures 7 and 8, the function of the backflow prevention ring during injection and plasticization metering will be explained. Figure 7 is a cross-sectional view showing the relationship between the screw head and the backflow prevention ring during injection. The arrows in Figures 7 and 8 indicate the direction of resin flow. During injection, it is necessary to inject more molten resin to replenish the volume contraction of the solid resin within the mold. The pressure required to replenish the molten resin at this time is called holding pressure. In Figure 7, the pressure from injection causes the backflow prevention ring 25 to move upstream and come into contact with the plunger 22. This prevents backflow of resin from the downstream side to the upstream side and maintains the necessary holding pressure.

[0033] Figure 8 is a cross-sectional view showing the relationship between the screw head and the backflow prevention ring during plasticization metering. In Figure 8, the pressure of the resin flowing from upstream to downstream causes the backflow prevention ring 25 to move downstream (i.e., towards the screw head 23). A gap is created between the plunger 22 and the backflow prevention ring 25, and the resin flows into the screw head through this gap. The resin that flows in is then injected into the mold on the downstream side.

[0034] Thus, the backflow prevention ring 25 prevents the resin from flowing back to the upstream side during injection. Below, the detailed configuration and problems of a typical backflow prevention ring related to a comparative example are described.

[0035] <Detailed configuration of the backflow prevention ring 250 in the comparative example> Referring to Figure 9, the detailed configuration of the backflow prevention ring 250 according to the comparative example will be described. Figure 9 is a perspective view showing the detailed configuration of the backflow prevention ring 250 according to the comparative example. As shown in Figure 9, the backflow prevention ring 250 in the comparative example comprises a ring body portion 251 and claw portions 252a and 252b.

[0036] The ring body portion 251 is the main body portion of the backflow prevention ring 250 and has a cylindrical shape. The claw portions 252a and 252b protrude from the end face of the ring body portion 251 on the screw head 23 side (negative x-axis direction side) and are integrally provided with the ring body portion 251. In other words, a recess (notch) is provided between adjacent claw portions 252a and 252b. Because the claw portions 252a and 252b engage with a recess formed in the screw head 23 (231a in Figure 6), the backflow prevention ring 250 can rotate together with the screw head 23. The large claw portion 252a and the small claw portion 252b are provided alternately, spaced apart from each other.

[0037] In the example shown in Figure 9, a pair of claw portions 252a are provided axially symmetrically so as to face each other. Additionally, a pair of claw portions 252b are provided axially symmetrically in the central part between the pair of claw portions 252a so as to face each other. Furthermore, the height (length in the rotation axis direction) of the claw portion 252a is greater than the height of the claw portion 252b, and the width (length in the circumferential direction) of the claw portion 252a is greater than the width of the claw portion 252b. Furthermore, the inner circumferential surfaces of the claw portions 252a and 252b are flush with the inner circumferential surface of the ring body portion 251. On the other hand, the outer circumferential surfaces of the claw portions 252a and 252b are inclined in the direction of the rotation axis as they move toward the screw head 23.

[0038] Here, Figure 10 is a schematic cross-sectional view showing the relationship between the backflow prevention ring 250 and the cylinder 10. As mentioned above, the outer diameter of the backflow prevention ring 250 and the inner diameter of the cylinder 10 are approximately the same, but Figure 10 Therefore, the gap between the backflow prevention ring 250 and the cylinder 10 is depicted in an exaggerated manner.

[0039] As shown in Figure 10, the backflow prevention ring 250 rotates within the cylinder 10 around its central axis O1, while revolving around the central axis O2 of the cylinder 10. This revolving motion of the backflow prevention ring 250 is called whirring.

[0040] Here, the rotational speed ω1 of the backflow prevention ring 250 is the same as the rotational speed of the screw 20. As shown in Figure 10, the inventors investigated the orbital speed ω2 of the backflow prevention ring 250 by measuring the periodic change in the gap between the backflow prevention ring 250 and the cylinder 10. The displacement measurement method involved inserting a displacement sensor into the cylinder 10 and measuring the distance between the inner surface of the cylinder (sensor) and the backflow prevention ring.

[0041] Figure 11 is a graph showing the measurement results of the displacement of the anti-backflow ring during rotation. As shown in Figure 11, the screw rotation speed is 182 rpm, 0.33 s / revolution, and the anti-backflow ring's orbital speed is approximately 91 rpm, 0.66 s / revolution. Since the anti-backflow ring rotates in engagement with the claw portion of the screw head, it rotates at the same speed as the screw rotation speed of 182 rpm while orbiting at half that period (approximately 91 rpm). In other words, it was found that the ratio of the orbital speed ω2 to the rotational speed ω1 of the anti-backflow ring 250, ω2 / ω1, is 1 / 2 (i.e., 0.5).

[0042] The phenomenon in which the ratio of the orbital speed ω2 to the rotational speed ω1 of the backflow prevention ring 250, ω2 / ω1, becomes 1 / 2, is presumed to be similar to the "half-speed whirl" phenomenon observed in journal bearings. Thus, in the backflow prevention ring 250 of the comparative example, the ratio of the orbital speed ω2 to the rotational speed ω1, ω2 / ω1, becomes 1 / 2, which presents a problem in that galling wear is likely to occur between the cylinder 10 and the backflow prevention ring 250. As a result, metal fragments generated by galling friction may be mixed into the molded product, or insufficient holding pressure may be applied due to wear on the outer surface of the ring, resulting in defective molded products. Therefore, in order to solve these problems, we propose the following configuration of a backflow prevention ring.

[0043] <Detailed configuration of the backflow prevention ring 25 according to the first embodiment> Next, with reference to Figure 12, the detailed configuration of the backflow prevention ring 25 according to the first embodiment will be described. Figure 12 is a perspective view showing the detailed configuration of the backflow prevention ring 25 according to the first embodiment.

[0044] As shown in Figure 12, the backflow prevention ring 25 according to this embodiment includes a chamfered portion 253b in addition to the ring body portion 251 and the large claw portion 252a and small claw portion 252b shown in Figure 9. Here, the configuration of the ring body portion 251 and the claw portions 252a and 252b is the same as that of the backflow prevention ring 250 in the comparative example shown in Figure 9, so the explanation is omitted.

[0045] As shown in Figure 12, the chamfered portion 253b is a chamfered surface extending axially on the outer circumferential surface of the ring body portion 251. The chamfered portion 253b is formed, for example, by machining. The chamfered portion is provided to widen the gap between the backflow prevention ring and the inner surface of the cylinder, and can solve the problem of the backflow prevention ring's wobble described above. It is thought that a pressure difference is created between the chamfered portion and the unchamfered portion, thereby preventing wobble.

[0046] In the example shown in Figure 12, two chamfered portions 253b extend over the entire axial direction (x-axis direction) of the ring body portion 251 and are provided at equal intervals in the circumferential direction, i.e., axially symmetrically at 180° intervals. In the example in Figure 12, a pair of chamfered portions 253b are formed axially symmetrically. That is, on the outer circumferential surface of the ring body portion 251, the normal outer circumferential portion 253a and the chamfered portion 253b are formed alternately such that the chamfered and unchamfered portions form a striped pattern.

[0047] The chamfered portion 253b is provided in a position corresponding to the claw portion 252a. The circumferential length of the chamfered portion 253b is shorter than the circumferential length of the claw portion 252a. The claw portion 252a is not chamfered, and it protrudes slightly from the chamfered portion 253b. This makes it possible to prevent backflow of resin by the claw portion 252a and to prevent galling friction due to the runout of the backflow prevention ring by the chamfered portion 253b.

[0048] The number of chamfered portions 253b can be determined as appropriate and may be singular. If there are multiple chamfered portions 253, the spacing between adjacent chamfered portions 253 does not have to be equal. Furthermore, the chamfered portions 253 may be formed on a part of the axial direction of the ring body 251, as long as they extend in the axial direction (x-axis direction) of the ring body 251. In addition, the chamfered portions 253 may be curved, flat, or grooved. Furthermore, the chamfered portions 253 may extend spirally along the axial direction of the ring body 251. From the viewpoint of uniformity of pressure, etc., it may be preferable to perform chamfering at equal intervals by R processing.

[0049] Next, the chamfered portion created by R-machining will be explained with reference to Figures 13 to 15. Figure 13 is a cross-sectional view illustrating the R-processing method for the backflow prevention ring 25 according to the first embodiment. Figure 14 is a cross-sectional view of the backflow prevention ring 25 after R-processing according to the first embodiment. Figure 15 is a cross-sectional view illustrating the R-processing method for the backflow prevention ring 25 according to the first embodiment.

[0050] Figure 13 illustrates an example of performing R-machining on an annular backflow prevention ring 25 with a diameter of 35 mm. R-machining is performed on the chamfered portion so that the diameter is reduced by 0.1 mm (i.e., the diameter after R-machining becomes 34.9 mm). Consider the case of performing R-machining with a radius of 18 mm on the desired outer surface area of ​​the backflow prevention ring. Radius 18 mm × 2 = diameter 36 mm, 36 mm - 34.9 mm = 1.1 mm, 1.1 mm / 2 = 0.55 mm. Therefore, the R-machining should be performed by shifting the center of the circle by 0.55 mm. That is, the center of the R-machining is set at a position 0.55 mm away from the chamfered portion (i.e., the machined surface) from the center of the circle with a diameter of 35 mm. When forming two opposing chamfered portions at 180° intervals, as shown in Figure 13, the centers of the R-machining are set at positions away from the opposing desired outer surface areas.

[0051] Figure 14 is a cross-sectional view showing an example of R-machining applied to the chamfered portion centered on the position set in Figure 13. In this way, a pair of chamfered portions 253b are formed axially symmetrically on the outer surface of the backflow prevention ring 25 by R-machining. That is, the cross-sectional view of the backflow prevention ring shown in Figure 14 is not a perfect circle. Note that these diameter and radius values ​​are merely examples and can be set arbitrarily.

[0052] Figure 15 illustrates an example of determining the dimensions of R-shaped machining. The outer diameter D0 of the standard backflow prevention ring is defined as the outer diameter D of the backflow prevention ring after R-processing. R Let's assume that D0-D R =C (C≦0.20)[mm] R dimension = D0 / 2 + A [mm], and the range of A is (0 <A<D0 / 2) The axis of the R-shaped part is offset radially by B [mm] from the axis of the backflow prevention ring, and B is (0 <B<D0)かつ(A<B) Let 2*(BA) = C, and the outer diameter D after R machining. R is D R =D0-2*(BA)[mm] (0 <D R <D0)

[0053] As described above, the outer diameter dimension of the R-shaped section can be determined arbitrarily. In some embodiments, chamfering may be performed so that the cross-section becomes elliptical, but the embodiment in which the axis is shifted and chamfered as described above can provide better effects in preventing runout and backflow.

[0054] Figure 16 is a perspective view of a backflow prevention ring according to another embodiment. In the backflow prevention ring 25 shown in Figure 16, unlike the first embodiment, four chamfered portions 253b are formed along the axial direction over the entire ring body 251, offset by 90° each. The pair of chamfered portions 253b are provided in accordance with the positions of a pair of opposing large claw portions 252a. The circumferential length of the chamfered portions 253b is shorter than the circumferential length of the large claw portions 252a.

[0055] On the other hand, the pair of chamfered portions 253b are provided in accordance with the positions of the pair of smaller claw portions 252b that face each other. The circumferential length of the chamfered portion 253b is greater than the circumferential length of the smaller claw portions 252b.

[0056] The backflow prevention ring according to this embodiment can also achieve both the prevention of resin backflow and the prevention of galling friction caused by the backflow prevention ring's movement.

[0057] Figure 17 is a perspective view of a backflow prevention ring according to yet another embodiment. In the backflow prevention ring 25 shown in Figure 17, unlike the example in Figure 16, four chamfered portions 253b are partially formed along the axial direction, offset by 90° each. Specifically, the chamfered portions 253b corresponding to the large claw portion 252a are formed only on the claw portion 252a side of the ring body portion 251. The chamfered portions 253b corresponding to the small claw portion 252b are formed only on the side of the ring body portion 251 opposite to the claw portion 252a.

[0058] The first chamfered portion 253b is partially provided on the ring body portion 251 of the backflow prevention ring 25 from the screw head side end to the axial center. The second chamfered portion 253b is also partially provided on the ring body portion 251 of the backflow prevention ring 25 from the screw body side end to the axial center. The first chamfered portion and the second chamfered portion are alternately provided on the circumferential direction of the backflow prevention ring 25.

[0059] Figure 18 is a side view illustrating the partially formed chamfered portion shown in Figure 17. As shown in Figure 18, the chamfered portion 253b corresponding to the large claw portion 252a is formed to be partially nested in the circumferential direction, spaced apart from the chamfered portion 253b corresponding to the small claw portion 252b. This creates a pressure difference and repulsive force around the backflow prevention ring, suppressing wobble and preventing contact between the backflow prevention ring 25 and the inner surface of the cylinder.

[0060] Figure 19 is a front view of the backflow prevention ring as seen from the screw head side in the axial direction. In the backflow prevention ring 25, a pair of large claw portions 252a are provided facing each other via an axis. Similarly, a pair of large claw portions 252b are provided facing each other via an axis. Note that Figure 19 is similar in other embodiments as well.

[0061] Figure 20 is a graph showing the screw advance (mm) relative to the external dimensions after R-machining. The vertical axis shows the screw advance (mm) during injection holding pressure. The standard dimensions refer to the backflow prevention ring 250 in the comparative example shown in Figure 9. On the other hand, the values ​​for the external dimensions with R-machining on the horizontal axis represent an example where the same amount (e.g., 0.10 mm) of chamfering was applied to the entire outer surface of the backflow prevention ring of the standard dimensions.

[0062] In Figure 20, each value represents the same pressure applied when pushing the screw. It can be seen that as the outer diameter of the backflow prevention ring is gradually reduced by chamfering compared to the standard size outer diameter of the backflow prevention ring, the amount of screw advancement increases. In other words, it can be shown that the backflow rate during holding pressure increases in proportion to the amount of chamfering. In particular, when the diameter is reduced by more than 0.2 mm from the standard diameter, the backflow rate clearly increases. That is, the backflow prevention function no longer works sufficiently. The backflow rate changes depending on the standard outer diameter, material viscosity, and holding pressure. Therefore, from the viewpoint of preventing runout and preventing backflow, it is desirable to chamfer the outer surface of the backflow prevention ring by 0.10 mm or less. It is also desirable to perform R-processing to reduce the diameter by 0.20 mm or less. In the case where a pair of opposing chamfered sections are provided as in the embodiment described above, it is desirable that the total chamfering depth of both sections be 0.2 mm or less at most.

[0063] The above example shows the case where the same amount of chamfering is applied to the entire outer surface of a standard-sized backflow prevention ring. Therefore, the above embodiment, in which chamfering is applied partially at equal intervals in the circumferential direction, yields better results. Furthermore, as shown in Figure 12, by making the circumferential length of the chamfered portion 253b shorter than the circumferential length of the claw portion 252a, better results can be obtained than those in Figure 20. Moreover, as shown in Figure 17, by partially forming the chamfered portion 253b along the axial direction, and as shown in Figure 18, by forming adjacent chamfered portions 253b to be staggered and partially nested, better results can be obtained. As described above, it is desirable that the maximum difference between the chamfered surface and the unchamfered outer surface be 0.1 mm or less.

[0064] Referring to Figures 21 to 23, the effect of preventing backflow from swinging out of the anti-backflow ring according to embodiments of various resin types will be explained. The backflow prevention ring shown in Figure 9, a comparative example, and the backflow prevention ring shown in Figure 12, according to the embodiment (i.e., a backflow prevention ring having two opposing chamfered portions due to R-processing), were compared. The runout and displacement were measured by inserting a displacement sensor into the cylinder 10 and measuring the distance between the inner surface of the cylinder (sensor) and the backflow prevention ring. These comparison results demonstrate the effectiveness of preventing runout according to various types of resins with different melt viscosities.

[0065] Figure 21 shows a comparison of runout amounts when thermoplastic elastomer (TPE) is used as the resin. The backflow prevention ring according to the embodiment was able to reduce the runout amount to approximately 0.3 compared to the comparative example, with the runout amount of the comparative example set to 1. Figure 22 shows the results of comparing the amount of runout when polyethylene (PE) is used as the resin. The backflow prevention ring according to the embodiment was able to reduce the amount of runout to about 0.7 compared to the comparative example, with the runout of the comparative example set to 1. Figure 23 shows a comparison of the amount of runout when acrylic resin (Poly Methyl Methacrylate / PMMA) is used as the resin. The backflow prevention ring according to the embodiment was able to reduce the amount of runout to approximately 0.05 compared to the comparative example, with the runout of the comparative example set to 1.

[0066] As described above, the backflow prevention ring according to the embodiment can reduce the amount of runout while maintaining the backflow prevention function. As a result, the above-mentioned galling friction can be suppressed.

[0067] Although the present invention has been specifically described above based on embodiments, it goes without saying that the present invention is not limited to the embodiments already described, and various modifications are possible without departing from the spirit of the invention. Furthermore, some embodiments may be used in various combinations. [Explanation of Symbols]

[0068] 10 cylinders 20 Screw 20a Piston 21 Screw body 22 Oshigane 23 Screwhead 24 Connecting shaft 25 Anti-backflow ring 30 Hoppers 40 Ring Heater 100 injection machine 251 Ring body 252a, 252b Claw part 253, 253a outer periphery 253b Chamfered section C Cavity D1 Fixed type D2 Movable type MT Motor R1 Resin Pellets R2 molten resin R3 Resin molded product

Claims

1. The screw body and A push pin fixed to the tip of the screw body, A screw head is provided at the tip side, spaced apart from the aforementioned push pin, A connecting shaft that connects the aforementioned push pin and the aforementioned screw head, Between the push pin and the screw head, a cylindrical backflow prevention ring is provided that covers the connecting shaft and is slidable in the axial direction, One or more chamfered portions extending at least partially in the axial direction are formed on the outer circumferential surface of the backflow prevention ring. In the chamfered portion, the outer surface of the backflow prevention ring is chamfered by 0.10 mm or less. Screw with backflow prevention mechanism for injection molding equipment.

2. The screw with a backflow prevention mechanism according to claim 1, wherein the chamfering process is performed by R-processing.

3. The screw with a backflow prevention mechanism according to claim 2, wherein the R machining is performed around a position offset from the axis of the backflow prevention ring.

4. The screw with a backflow prevention mechanism according to claim 3, wherein the R machining is performed at a center offset from the axis of the backflow prevention ring and at a radius different from the radius of the backflow prevention ring.

5. The aforementioned backflow prevention ring is The ring body and The ring body portion has a claw portion that protrudes from the end face on the screw head side and engages with a recess in the screw head, The screw with a backflow prevention mechanism according to any one of claims 1 to 4, wherein the chamfered portion extends at least partially in the axial direction along the claw portion.

6. The screw with a backflow prevention mechanism according to claim 5, wherein the circumferential length of the chamfered portion is shorter than the circumferential length of the claw portion.

7. The screw with a backflow prevention mechanism according to any one of claims 1 to 6, wherein the multiple chamfered portions are provided at equal intervals in the circumferential direction of the backflow prevention ring.

8. The chamfered portion is provided over the entire axial area of ​​the ring body portion of the backflow prevention ring. A screw with a backflow prevention mechanism according to any one of claims 1 to 7.

9. The chamfered portion is, The first chamfered portion of the ring body of the backflow prevention ring is partially provided from the end on the screw head side to the axial center, The backflow prevention ring includes a second chamfered portion that is partially provided on the ring body portion from the end on the screw body portion side to the axial center portion, The first chamfered portion and the second chamfered portion are alternately provided in the circumferential direction of the backflow prevention ring. A screw with a backflow prevention mechanism according to any one of claims 1 to 8.

10. The first chamfered portion and the second chamfered portion are spaced apart from each other and are arranged to be partially nested in the circumferential direction. A screw with a backflow prevention mechanism as described in claim 9.

11. An injection machine that injects molten resin using a screw with a backflow prevention mechanism housed in a cylinder, An injection molding apparatus comprising a mold for molding the molten resin injected from the injection machine, The screw with the backflow prevention mechanism is, The screw body and A push pin fixed to the tip of the screw body, A screw head is provided at the tip side, spaced apart from the aforementioned push pin, A connecting shaft that connects the aforementioned push pin and the aforementioned screw head, Between the push pin and the screw head, a cylindrical backflow prevention ring is provided that covers the connecting shaft and is slidable in the axial direction, The outer circumferential surface of the backflow prevention ring has a chamfered portion that extends at least partially in the axial direction. In the chamfered portion, the outer surface of the backflow prevention ring is chamfered by 0.10 mm or less. Injection molding equipment.

12. The injection molding apparatus according to claim 11, wherein the chamfering process is performed by R-processing.

13. The aforementioned backflow prevention ring is The ring body and The ring body portion has a claw portion that protrudes from the end face on the screw head side and engages with a recess in the screw head, The chamfered portion extends at least partially in the axial direction along the claw portion. The injection molding apparatus according to claim 11.

14. A cylindrical backflow prevention ring that is attached to the screw of an injection molding machine, One or more chamfered portions are formed on the outer surface, at least partially extending in the axial direction. A backflow prevention ring in which the outer surface of the backflow prevention ring is chamfered by 0.10 mm or less at the chamfered portion.

15. The backflow prevention ring according to claim 14, wherein the chamfering process is performed by R-processing.

16. The ring body and The ring has a claw portion that protrudes from the end face of the ring body and engages with a recess in the screw head, The chamfered portion extends at least partially in the axial direction along the claw portion. The backflow prevention ring according to claim 14.

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