Backflow prevention device, screw, and injection molding machine

Abstract

To provide a non-cooperative backflow prevention device that suppresses variation in injection volume.SOLUTION: A backflow prevention device (25) in which a backflow prevention ring (30) rotates relative to a head (32) during metering includes: a push metal (27); a shaft (28) protruding from the push metal; the backflow prevention ring (30) penetrated through the shaft (28); and the head (32) provided at a tip of the shaft (28). The head (32) includes a plurality of contact surfaces (42) that contact an end surface (34) of the backflow prevention ring (30). A ringing release structure (43) is formed near these contact surfaces (42) to release ringing caused by the contact surface (42) and the end surface (34) coming into close contact.SELECTED DRAWING: Figure 3A

Description

[Technical Field]

[0001] The present invention relates to a backflow prevention device provided in a screw of an injection molding machine, a screw provided with a backflow prevention device, and an injection molding machine. [Background technology]

[0002] As described in Patent Document 1, the screw of an injection molding machine is provided with a backflow prevention device at its tip. The backflow prevention device is composed of a presser die attached to the tip of the screw, a screw head also attached to the tip of the screw, and a backflow prevention ring. The screw head is composed of a head portion at the tip and a small-diameter shank portion, and the shank portion is connected to the end of the screw. The backflow prevention ring passes through this shank portion and is slidable between the head portion and the presser die.

[0003] A gap is formed between the backflow prevention ring and the shank, allowing the injection material to flow, and the head also has a groove formed on its outer periphery through which the injection material can flow. Therefore, when the screw rotates to feed the molten injection material forward, the backflow prevention ring is pushed forward by the injection material, causing part of its end face to come into contact with the rear end face of the head, i.e., the contact surface. The injection material is then sent forward through the gap between the backflow prevention ring and the shank and the groove in the head, i.e., it is metered. Meanwhile, when the screw is driven forward, the pressure of the injection material acts on the end face of the backflow prevention ring. The opposite end face of the backflow prevention ring is pressed against the presser die, closing the injection material flow path. This prevents the injection material from flowing back, allowing the injection material to be injected into the mold.

[0004] There are two types of backflow prevention devices: a so-called co-rotating type in which the backflow prevention ring rotates integrally with the screw when the screw is rotated to measure, and a so-called non-co-rotating type in which the backflow prevention ring does not rotate integrally with the screw. In the non-co-rotating type, the backflow prevention ring rotates while sliding with its end face in contact with the contact surface of the head of the screw head during metering. Therefore, to prevent wear on the end face of the backflow prevention ring due to sliding, the contact surface of the head is machined to a smooth surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-62879 Summary of the Invention [Problem to be solved by the invention]

[0006] In non-corotating backflow prevention devices, the contact surface of the screw head is formed as a smooth surface, which can reduce wear on the backflow prevention ring. However, there are cases where the injection volume is unstable. In other words, there is variation in the screw position at the end of injection and pressure holding for each molding cycle.

[0007] The present disclosure provides a non-corotating backflow prevention device capable of suppressing variations in injection amount, a screw equipped with such a backflow prevention device, and an injection molding machine.

[0008] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0009] The present disclosure relates to a backflow prevention device comprising a presser foot, a shaft protruding from the presser foot, a backflow prevention ring penetrated by the shaft, and a head attached to the tip of the shaft, wherein the backflow prevention ring rotates relative to the head during metering. The head has multiple contact surfaces that come into contact with the end face of the backflow prevention ring. A ringing release structure is formed near one or more of the multiple contact surfaces to release the ringing that occurs when the contact surface and the end face come into close contact with each other. The head portion has a plurality of grooves formed on its outer circumferential surface to form a plurality of blade portions, and the contact surface is formed at the end of the blade portion on the presser foot side. [Effects of the Invention]

[0010] The present disclosure can suppress variations in the ejection amount. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a front view showing an injection molding machine according to an embodiment of the present invention; [Figure 2] 1 is a front cross-sectional view showing a backflow prevention device and a part of an injection device according to the present embodiment. [Figure 3A] 3 is an enlarged front cross-sectional view of a portion of the backflow prevention device according to the present embodiment, designated by the symbol X in FIG. 2. FIG. [Figure 3B] 3 is an enlarged front cross-sectional view of a portion of the backflow prevention device according to the present embodiment, designated by the symbol X in FIG. 2. FIG. [Figure 3C] 3 is a side cross-sectional view of the backflow prevention device according to the present embodiment, taken along the line YY in FIG. 2. FIG. [Figure 4] FIG. 6 is an enlarged front cross-sectional view showing a portion of a backflow prevention device according to a second embodiment. [Figure 5] FIG. 10 is an enlarged front cross-sectional view showing a portion of a backflow prevention device according to a third embodiment. [Figure 6] FIG. 10 is an enlarged side cross-sectional view showing a portion of a backflow prevention device according to a fourth embodiment. [Figure 7] FIG. 10 is an enlarged side cross-sectional view showing a portion of a backflow prevention device according to a fifth embodiment. [Figure 8]FIG. 10 is a front cross-sectional view showing the screw head and the backflow prevention ring, illustrating the experimental method. [Figure 9] 10 is a photograph of a screw head and a backflow prevention ring showing the experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0012] Specific embodiments will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. For clarity of explanation, the following description and drawings have been simplified as appropriate. In each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary. Furthermore, hatching has been omitted in some areas to avoid cluttering the drawings.

[0013] The present embodiment will be described. <Injection molding machine> As shown in FIG. 1, the injection molding machine 1 according to this embodiment includes a toggle-type mold clamping device 2 and an injection device 3.

[0014] <Mold clamping device> The mold clamping device 2 includes a fixed platen 5 fixed to a bed B, a movable platen 7 slidably provided on the bed B, and a mold clamping housing 6. The fixed platen 5 and the mold clamping housing 6 are connected by a plurality of tie bars 9, 9, ..., and the movable platen 7 is slidably provided between the fixed platen 5 and the mold clamping housing 6. A mold clamping mechanism 11 is provided between the mold clamping housing 6 and the movable platen 7. In this embodiment, the mold clamping mechanism 11 is made up of a toggle mechanism 11. A fixed-side mold 13 and a movable-side mold 14 are provided on the fixed platen 5 and the movable platen 7, respectively. Therefore, when the toggle mechanism 11 is driven, the molds 13 and 14 are opened and closed.

[0015] <Injection device> The injection device 3 includes a heating cylinder 16, a screw 17 provided in the heating cylinder 16, and a screw drive device 18. The heating cylinder 16 is supported by the screw drive device 18, and the screw 17 is driven in the rotational direction and axial direction by the screw drive device 18. The heating cylinder 16 is provided with a hopper 20 and an injection nozzle 22. When the injection material is supplied from the hopper 20, the heating cylinder 16 is heated, and the screw 17 is rotated by the screw drive device 18, the injection material is melted and measured. When the screw 17 is driven in the axial direction by the screw drive device 18, the injection material can be injected into the molds 13, 14.

[0016] <Backflow prevention device according to this embodiment> 2, a backflow prevention device 25 according to this embodiment is provided at the tip of the screw 17. The backflow prevention device 25 is composed of a presser foot 27 provided at the tip of the screw 17, a small-diameter shaft portion 28 protruding forward from the presser foot 27, a backflow prevention ring 30 inserted into the shaft portion 28, and a head portion 32 provided at the tip of the shaft portion 28.

[0017] The outer circumferential surface of the backflow prevention ring 30 slides against the bore of the heating cylinder 16 with a small gap, preventing leakage of the injection material. The inner diameter of the backflow prevention ring 30 is sufficiently larger than the outer diameter of the shaft 28, allowing the gap between the shaft 28 and the backflow prevention ring 30 to form a flow path for the injection material. The backflow prevention ring 30 has an end face 34 on the head 32 side and a closed end face 35 on the presser die 27 side. When the backflow prevention ring 30 is seated on the presser die 27, the closed end face 35 comes into contact with the presser die 27, closing the flow path for the injection material. In other words, backflow of the injection material is prevented.

[0018] The head portion 32 has a plurality of grooves 37, 37, ... formed on its outer circumferential surface, thereby forming a plurality of blade portions 38, 38, .... A side view of the head portion 32 is shown in Figure 3C, and in this embodiment, the number of grooves 37, 37, ... is four, and the number of blade portions 38, 38, ... is four. As shown in Figure 2, the blade portions 38, 38, ... are provided with reinforcing tips 40, 40, ... on the presser foot 27 side or the backflow prevention ring 30 side. The reinforcing tips 40, 40, ... are made of a metal material that is harder than the metal material forming the head portion 32, and are therefore less susceptible to wear.

[0019] As shown in FIG. 3A, each of the reinforcing tips 40, 40, ... has two surfaces: a contact surface 42 that contacts the end face 34 of the backflow prevention ring 30, and an inclined surface 43 that is in contact with the contact surface 42 and is formed at an angle θ different from the contact surface 42. When the screw 17 (see FIG. 2) is rotated to measure the injected material, the end face 34 of the backflow prevention ring 30 contacts the contact surface 42 as shown in FIG. 3B, and rotates relative to the contact surface 42 while sliding against it. In other words, the backflow prevention device 25 according to this embodiment is a non-corotating type. Therefore, the contact surface 42 is smooth to prevent wear on the end face 34 of the backflow prevention ring 30.

[0020] However, with this type of non-corotating backflow prevention device 25, the injection amount can become unstable during injection. In other words, the backflow prevention device 25 may not function properly, causing the injection material to backflow. The inventors discovered that this phenomenon is caused by so-called ringing, in which the contact surface 42 of the head portion 32 and the end face 34 of the backflow prevention ring 30 come into close contact with each other. In other words, because the contact surface 42 is formed as a smooth surface, it tightly adheres to the end face 34, which can cause a delay in the timing at which the backflow prevention ring 30 separates from the head portion 32 during injection.

[0021] Therefore, the inventors formed an inclined surface 43 adjacent to the contact surface 42 on the head portion 32. Figure 3B shows the state in which the end surface 34 of the backflow prevention ring 30 is firmly attached to the contact surface 42 of the head portion 32. At this time, a wedge-shaped gap is formed between the inclined surface 43 and the end surface 34. When the injected material enters this gap, the pressure of the injected material increases in the gap, easily releasing the ringing. In other words, in this embodiment, the inclined surface 43 provides a ringing release structure. This eliminates delays in the timing at which the backflow prevention ring 30 separates from the head portion 32 during injection. This means that the injection volume is stable. In this embodiment, the ringing release structure, i.e., the inclined surfaces 43, 43, ..., are formed adjacent to all four surfaces, i.e., all contact surfaces 42, 42, ..., as shown in Figure 3C.

[0022] In this embodiment, as shown in Fig. 2, the head portion 32 and the shank portion 28 are formed as a single integral part, that is, a screw head 45. The screw head 45 has a male thread 46 formed continuous with the shank portion 28. The screw 17 has a female thread 48, and the male thread 46 threadably engages with the female thread 48, thereby attaching the screw head 45 to the screw 17. The head portion 32 and the shank portion 28 do not have to be formed as a single part; for example, the shank portion 28 and the presser foot 27 can be formed as a single part. In this case, the head portion 32 is fixed to the shank portion 28 by a fixing means such as a screw.

[0023] <Backflow prevention device according to the second embodiment> The backflow prevention device 25 according to this embodiment can be modified in various ways. Figure 4 shows a modified backflow prevention device 25A according to a second embodiment. In this second embodiment, the end face 34A of the backflow prevention ring 30A is tapered. The contact face 42A formed on the reinforcing tip 40 of the head portion 32 is also tapered at the same angle. In this embodiment, the inclined face 43A, which serves as a ringing release structure, is tapered by an angle θ' from the contact face 42A. In the backflow prevention device 25A according to the second embodiment, when the end face 34A of the backflow prevention ring 30A and the contact face 42A of the head portion 32 are in contact with each other, a wedge-shaped gap is formed between the end face 34A and the inclined face 43A. This allows for easy release of ringing between the end face 34A and the contact face 42A.

[0024] <Backflow prevention device according to the third embodiment> FIG. 5 shows a backflow prevention device 25B according to a third embodiment. The backflow prevention device 25B according to the third embodiment differs from the first and second embodiments in the ringing release structure formed adjacent to the contact surface 42. In this embodiment, the ringing release structure is a step 50. The step 50 is a shallowly cut portion of the contact surface 42. In the backflow prevention device 25B according to the third embodiment, when the end face 34 of the backflow prevention ring 30 comes into contact with the contact surface 42 of the head portion 32, a gap is formed between the end face 34 and the step 50. The injected material enters this gap, increasing the pressure and easily releasing the ringing between the end face 34 and the contact surface 42.

[0025] <Backflow prevention device according to the fourth embodiment> 6 shows a backflow prevention device 25C according to a fourth embodiment. In this embodiment, the ringing release structure consists of shallow grooves 51 formed in the contact surfaces 42, 42, traversing the contact surfaces 42. In the backflow prevention device 25C according to the fourth embodiment, when the end face 34 of the backflow prevention ring 30 comes into contact with the contact surface 42 of the head portion 32, a gap is formed between the end face 34 and the groove 51. The injected material enters this gap, increasing the pressure and easily releasing the ringing between the end face 34 and the contact surface 42.

[0026] <Backflow prevention device according to the fifth embodiment> FIG. 7 shows a backflow prevention device 25D according to a fifth embodiment. In this embodiment, the ringing release structure is formed only on some of the contact surfaces 42, 42. That is, although there are a total of four contact surfaces 42, 42, the ringing release structure is formed on only two of the four contact surfaces 42, 42. The ringing release structure is made up of inclined surfaces 43D, 43D, 43D formed at a different angle from the contact surfaces 42, 42. The positions at which the inclined surfaces 43D, 43D, 43D, 43D are formed differ from those in the first embodiment. That is, inclined surfaces 43D, 43D are formed on both sides of the contact surfaces 42, 42. In this fifth embodiment, the ringing is also easily released by the action of these inclined surfaces 43D, 43D, 43D, 43D.

[0027] <Other variations> Other modifications are possible to this embodiment and the second to fifth embodiments. For example, although the reinforcing tip 40 has been described as being provided on the head portion 32, the reinforcing tip 40 is not essential. If the reinforcing tip 40 is not provided, the contact surface 42, inclined surface 43, etc. may be formed directly on the head portion 32. Furthermore, although the number of blade portions 38, 38 on the head portion 32 has been described as being four, the number may be two, three, or five or more. [Example]

[0028] An experiment was conducted to confirm that backflow prevention device 25 according to this embodiment (see FIG. 3A) is less likely to cause ringing between end face 34 of backflow prevention ring 30 and contact surface 42 of head portion 32. If ringing is properly released, backflow prevention ring 30 quickly separates from head portion 32 during injection and seats on presser foot 27, preventing backflow of the injected material and stabilizing the injection amount. The details of the experiment will now be described.

[0029] Test Contents: As shown in Figure 8, two screw heads 45z, 45 (see Figures 2 and 3A) and two backflow prevention rings 30, 30 were prepared. The left screw head 45z does not have an inclined surface 43 formed in the head portion 32. In other words, only the contact surface 42 is formed, and it differs from the backflow prevention device 25 according to this embodiment. Hereinafter, this will be referred to as Comparative Example Z. On the other hand, the right screw head 45 has an inclined surface 43 formed adjacent to the contact surface 42 in the head portion 32. In other words, it is the screw head 45 of the backflow prevention device 25 according to this embodiment. Hereinafter, this will be referred to as Example A.

[0030] The screw heads 45', 45 of Comparative Example Z and Example A were placed upright on the floor. Polishing red lacquer was applied to the end faces 34, 34 of the backflow prevention rings 30, 30, respectively, and the backflow prevention rings 30, 30 were then lifted and pressed against the head portions 32, 32. When the backflow prevention rings 30, 30 were slowly released, the backflow prevention ring 30 of the left screw head 45' did not fall, but the backflow prevention ring 30 of the right screw head 45 did fall, as shown in Figure 9.

[0031] This experiment confirmed that in the backflow prevention device 25 according to this embodiment, which has a ringing release structure, i.e., an inclined surface 43, formed adjacent to the contact surface 42, the backflow prevention ring 30 can be easily separated from the head portion 32. In other words, it was confirmed that ringing is less likely to occur. [Example]

[0032] An experiment was conducted to confirm whether variations in the injection amount occurred by actually performing injection molding using a screw 17 (see Figure 2) equipped with a backflow prevention device 25 of Example A and a screw 17 equipped with a backflow prevention device 25 of Comparative Example Z.

[0033] Test Contents: The screws 17, 17 equipped with the backflow prevention devices 25, 25 of Example A and Comparative Example Z were used to carry out 30 injection processes to inject the injection material into the molds 13, 14 (see FIG. 1). The screw position of the screw 17, i.e., the cushion amount, at the completion of each injection process was detected, and the variation therein was investigated.

[0034] Test Results: In the screw 17 provided with the backflow prevention device 25 of Example A, the maximum cushion amount was 3.56 mm, the minimum was 3.48 mm, and the magnitude of 3σ, which is three times the standard deviation, was 0.069 mm. On the other hand, in the screw 17 provided with the backflow prevention device 25 of Comparative Example Z, the maximum cushion amount was 3.39 mm, the minimum was 1.56 mm, and the magnitude of 3σ was 1.595 mm.

[0035] The variation in cushion amount indicates the frequency of backflow of injection material in the backflow prevention device 25. In other words, if the cushion amount is constant, backflow is not occurring, and if the cushion amount varies, backflow is occurring. The experimental results showed that the variation in cushion amount was smaller in Example A than in Comparative Example Z. In other words, it was confirmed that the backflow prevention device 25 of this embodiment, which is equipped with the inclined surface 43, which is a ringing release structure, in the head portion 32, is less likely to cause backflow of injection material. This ensures a stable injection amount.

[0036] The invention made by the inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments and various modifications are possible without departing from the spirit of the invention. The multiple examples described above can also be implemented in appropriate combinations. [Explanation of symbols]

[0037] 1 Injection molding machine 2 Mold clamping device 3 Injection device 5 Fixed plate 7 Movable platen 6 Clamping housing 9 Tie bar 11 Clamping mechanism 13 Fixed side mold 14 Movable side mold 16 Heating cylinder 17 Screw 18 screw drive device 20 hopper 22 Injection nozzle 25 Backflow prevention device 27 Pressing plate 28 Shank 30 Backflow prevention ring 32 Head 34 End face 35 Closed end face 37 Groove 38 Blade 40 Reinforced tip 42 Contact surface 43 Inclined surface 45 Screw head 46 Male thread 48 Female thread 50 Step 51 Groove

Claims

1. a presser die that is provided at the tip of the screw of the injection device; a shaft portion provided so as to protrude from the presser die; a backflow prevention ring penetrated by the shaft portion; a head portion provided at the tip of the shaft portion, The backflow prevention ring rotates relative to the head portion during metering, the head portion has a plurality of contact surfaces that come into contact with the end surface of the backflow prevention ring, and a ringing release structure is formed near one or more of the contact surfaces to release ringing that occurs when the contact surface and the end surface come into close contact with each other; A backflow prevention device in which the head portion has multiple blade portions formed by multiple grooves formed on its outer surface, and the contact surface is formed at the end of the blade portion on the pressing plate side.

2. The backflow prevention device of claim 1 , wherein the plurality of contact surfaces are smooth.

3. 3. The backflow prevention device according to claim 1, wherein the head portion and the shaft portion are integrally formed as a screw head.

4. a reinforcing tip made of a metal material harder than the metal material forming the head portion is provided at an end of each of the plurality of blade portions on the pressing plate side; The backflow prevention device according to claim 1 or 2, wherein the contact surface is formed on the reinforcing tip.

5. 5. The backflow prevention device according to claim 1, wherein the ringing release structure is formed in the vicinity of all of the plurality of contact surfaces.

6. A backflow prevention device as described in any one of claims 1 to 5, wherein the ringing release structure consists of an inclined surface that is continuous with the contact surface and is formed at a different angle from the contact surface, and when the contact surface and the end surface are in close contact with each other, a wedge-shaped gap is formed between the inclined surface and the end surface.

7. A backflow prevention device as described in any one of claims 1 to 5, wherein the ringing release structure consists of a step formed adjacent to the contact surface, and when the contact surface and the end face are in close contact, a gap is formed between the step and the end face.

8. 6. The backflow prevention device according to claim 1, wherein the ringing release structure comprises a groove formed in the contact surface so as to traverse the contact surface.

9. A screw contained in a heated cylinder of an injection device, The screw includes a screw body and It consists of a backflow prevention device, The backflow prevention device includes a presser foot provided at the tip of the screw body, a shaft portion provided so as to protrude from the presser die; a backflow prevention ring penetrated by the shaft portion; a head portion provided at the tip of the shaft portion, The backflow prevention ring rotates relative to the head portion during metering, the head portion has a plurality of contact surfaces that come into contact with the end surface of the backflow prevention ring, and a ringing release structure is formed near one or more of the contact surfaces to release ringing that occurs when the contact surface and the end surface come into close contact with each other; The head portion has a plurality of blade portions formed by a plurality of grooves formed on its outer surface, and the contact surface is formed at the end of the blade portion on the pressing plate side.

10. The screw according to claim 9, wherein the contact surfaces of the plurality of surfaces are smooth surfaces.

11. a reinforcing tip made of a metal material harder than the metal material forming the head portion is provided at an end of each of the plurality of blade portions on the pressing plate side; The screw according to claim 9 or 10, wherein the contact surface is formed on the reinforcing tip.

12. The screw according to any one of claims 9 to 11, wherein the ringing release structure is formed in the vicinity of all of the plurality of contact surfaces.

13. The screw according to any one of claims 9 to 12, wherein the ringing release structure comprises an inclined surface formed continuously with the contact surface at an angle different from that of the contact surface, and when the contact surface and the end surface are in close contact with each other, a wedge-shaped gap is formed between the inclined surface and the end surface.

14. The screw according to any one of claims 9 to 12, wherein the ringing release structure comprises a step portion formed adjacent to the contact surface, and a gap is formed between the step portion and the end face when the contact surface and the end face are in close contact with each other.

15. The screw according to any one of claims 9 to 12, wherein the ringing release structure is a groove formed in the contact surface so as to cross the contact surface.

16. an injection device that injects an injection material; a mold clamping device that clamps the mold, the injection device comprises a heating cylinder; a screw contained in the heating cylinder; The screw includes a screw body and It consists of a backflow prevention device, The backflow prevention device includes a presser foot provided at the tip of the screw body, a shaft portion provided so as to protrude from the presser die; a backflow prevention ring penetrated by the shaft portion; a head portion provided at the tip of the shaft portion, The backflow prevention ring rotates relative to the head portion during metering, the head portion has a plurality of contact surfaces that come into contact with the end surface of the backflow prevention ring, and a ringing release structure is formed near one or more of the contact surfaces to release ringing that occurs when the contact surface and the end surface come into close contact with each other; An injection molding machine in which the head portion has a plurality of blade portions formed by a plurality of grooves formed on its outer surface, and the contact surface is formed at the end of the blade portion on the presser foot side.

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