JP7805809B2 - Backflow prevention device, screw, and injection molding machine - Google Patents

Description

The present invention relates to a backflow prevention device installed in the screw of an injection molding machine, a screw equipped with a backflow prevention device, and an injection molding machine.

As described in Patent Document 1, the screw of an injection molding machine is equipped with a backflow prevention device at its tip. The backflow prevention device consists of a presser foot 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 consists 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 able to slide freely between the head portion and the presser foot.

A gap is formed between the backflow prevention ring and the shank, through which the injection material can flow, and the head also has a groove on its outer surface through which the injection material can flow. Therefore, when the screw is rotated to send molten injection material forward, the backflow prevention ring is pushed forward by the injection material, and part of its end face comes into contact with the rear end face of the head, i.e., the contact surface. The injection material is sent forward through the gap between the backflow prevention ring and the shank and the groove in the head. In other words, 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 flow path for the injection material. This prevents the injection material from flowing back, allowing it to be injected into the mold.

Backflow prevention devices come in two types: so-called co-rotating types, in which the backflow prevention ring rotates integrally with the screw when the screw is rotated to measure, and so-called non-co-rotating types, in which the backflow prevention ring does not rotate integrally with the screw. With non-co-rotating types, the backflow prevention ring rotates and slides 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.

Japanese Patent Application Laid-Open No. 2003-62879

Non-corotating backflow prevention devices have a smooth contact surface on the screw head, which reduces wear on the backflow prevention ring. However, this can sometimes result in unstable injection volume. In other words, there can be variations in the screw position at the end of injection and pressure holding for each molding cycle.

This disclosure provides a non-corotating backflow prevention device that can suppress variations in injection volume, a screw equipped with such a backflow prevention device, and an injection molding machine.

Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

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 these multiple contact surfaces to release ringing that occurs when the contact surface and the end face come into close contact with each other. The head has multiple grooves formed on its outer periphery to form multiple blades, and the contact surfaces are formed at the ends of the blades facing the presser foot.

This disclosure can reduce variations in the injection amount.

1 is a front view showing an injection molding machine according to an embodiment of the present invention; 1 is a front cross-sectional view showing a backflow prevention device and a part of an injection device according to the present embodiment. 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. 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. 3 is a side cross-sectional view of the backflow prevention device according to the present embodiment, taken along the YY cross section in FIG. 2. FIG. 10 is an enlarged front cross-sectional view showing a portion of a backflow prevention device according to a second embodiment. FIG. FIG. 10 is an enlarged front cross-sectional view showing a portion of a backflow prevention device according to a third embodiment. FIG. 10 is an enlarged side cross-sectional view showing a portion of a backflow prevention device according to a fourth embodiment. FIG. 10 is an enlarged side cross-sectional view showing a portion of a backflow prevention device according to a fifth embodiment. FIG. 10 is a front cross-sectional view showing the screw head and the backflow prevention ring, illustrating the experimental method. 10 is a photograph of a screw head and a backflow prevention ring showing the experimental results.

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, 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 have been omitted as necessary. In addition, hatching has been omitted in some areas to avoid cluttering the drawings.

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

<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.

<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 injection material is supplied from the hopper 20 and the heating cylinder 16 is heated and the screw 17 is rotated by the screw drive device 18, the injection material is melted and metered. 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.

<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.

The outer surface of the backflow prevention ring 30 slides against the bore of the heating cylinder 16 with a small gap, preventing leakage of injection material from this area. 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 foot 27 side. When the backflow prevention ring 30 seats on the presser foot 27, the closed end face 35 comes into contact with the presser foot 27, closing the flow path for the injection material. In other words, backflow of the injection material is prevented.

The head portion 32 has multiple grooves 37, 37, ... formed on its outer circumferential surface, which form multiple blades 38, 38, .... A side view of the head portion 32 is shown in Figure 3C. In this embodiment, there are four grooves 37, 37, ... and four blades 38, 38, .... As shown in Figure 2, the blades 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, making them less susceptible to wear.

As shown in Figure 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 this contact surface 42 and is formed at an angle θ different from that of the contact surface 42. When the screw 17 (see Figure 2) is rotated to measure the injection material, the end face 34 of the backflow prevention ring 30 contacts the contact surface 42 as shown in Figure 3B, and rotates relative to the contact surface 42 while sliding against it. In other words, the backflow prevention device 25 of 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.

However, with this type of non-corotating backflow prevention device 25, the injection amount can sometimes become unstable during injection. In other words, the backflow prevention device 25 may not function properly, causing the injected material to backflow. The inventors have discovered that the cause of this phenomenon is 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. In other words, they found that 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.

The inventors therefore 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 face 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 face 34. As 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 has a ringing release structure. As a result, there is no delay in the timing at which the backflow prevention ring 30 separates from the head portion 32 during injection. This means that the injection amount 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.

In this embodiment, as shown in FIG. 2, the head portion 32 and shank portion 28 are formed as a single integral part, the 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 threads into the female thread 48, attaching the screw head 45 to the screw 17. Note that the head portion 32 and shank portion 28 do not need 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.

<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. Therefore, ringing between the end face 34A and the contact face 42A is easily released.

<Backflow prevention device according to the third embodiment>
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.

<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 surface 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 surface 34 and the groove 51. The injected material enters this gap, increasing the pressure and easily releasing the ringing between the end surface 34 and the contact surface 42.

<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. That is, although there are a total of four contact surfaces 42, the ringing release structure is formed on only two of the four contact surfaces 42. The ringing release structure is made up of inclined surfaces 43D formed at a different angle from the contact surfaces 42. The positions at which the inclined surfaces 43D are formed differ from those in the first embodiment. That is, the inclined surfaces 43D are formed on both sides of the contact surfaces 42. In this fifth embodiment, the ringing is also easily released by the action of these inclined surfaces 43D.

<Other Modifications>
Other modifications are possible to this embodiment and the second to fifth embodiments. For example, although the head portion 32 has been described as being provided with the reinforcing tip 40, 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 head portion 32 has been described as having four blade portions 38, 38, the number may be two, three, or five or more.

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

Experimental content:
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.

The screw heads 45', 45 of Comparative Example Z and Example A were placed upright on the floor. Komyotan 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 did not fall on the left screw head 45', but did fall on the right screw head 45, as shown in Figure 9.

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.

Injection molding was actually performed using a screw 17 equipped with the backflow prevention device 25 of Example A (see Figure 2) and a screw 17 equipped with the backflow prevention device 25 of Comparative Example Z, and an experiment was conducted to confirm whether variations in the injection amount occurred.

Experimental content:
Using the screws 17, 17 equipped with the backflow prevention devices 25, 25 of Example A and Comparative Example Z, the injection process of injecting the injection material into the molds 13, 14 (see FIG. 1) was carried out 30 times each. 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.

Experimental 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.

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, but 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 an 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.

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 embodiments already described, 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.

REFERENCE SIGNS LIST 1 injection molding machine 2 mold clamping device 3 injection device 5 fixed platen 7 movable platen 6 mold clamping housing 9 tie bar 11 mold 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 presser die 28 shaft portion 30 backflow prevention ring 32 head portion 34 end face 35 closed end face 37 groove 38 blade portion 40 reinforcing tip 42 contact surface 43 inclined surface 45 screw head 46 male thread 48 female thread 50 step portion 51 groove

Claims (16)

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 . The backflow prevention device of claim 1, wherein the multiple contact surfaces are smooth. A backflow prevention device as described in claim 1 or 2, wherein the head portion and the shaft portion are integrally formed as a screw head. 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. 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. 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. 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. 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. 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 . The screw according to claim 9 , wherein the contact surfaces of the plurality of surfaces are smooth surfaces. 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. 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. 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. 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. 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. 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 .