JPH11165333A - Preplasticating type injecting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply prevent a backflow of a molten resin from an injecting unit to a plasticizing unit without using a mechanism such as a check valve or the like. SOLUTION: A discharge passage 30 of a plasticized molten resin is formed at an end of a screw 24. A discharge port 30a of the passage 30 is formed so as to be opened with an outer periphery from a central side of a shaft of the screw 24 toward a radial direction. A resin passage 26 for introducing the resin to an injecting cylinder 25 intermittently communicates with the port 30a as the screw 24 is rotated. Then, the screw 24 is stopped at a position for closing the port 30a to prevent a backflow of the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-plastic injection apparatus, and more particularly, to an apparatus for preventing a back flow of a molten resin from an injection section to a plasticizing section and eliminating the stagnation of the molten resin in an injection chamber. The present invention relates to a pre-plastic injection device.

[0002]

2. Description of the Related Art Injection devices of an injection molding machine are roughly classified into an in-line type injection device and a pre-plastic type injection device. The in-line injection device melts a resin material with a screw, and the screw advances to inject the molten resin. In the plastic injection device, a plasticizing section for melting the resin and an injection section are provided independently, so that the resin melted in the plasticizing section is sent to an injection chamber of the injection section and injected by an injection plunger. Has become.

[0003] The pre-plastic injection device can change the diameter and stroke of the plunger separately from the screw, and thus has an advantage that the injection capacity and injection pressure can be increased as compared with the in-line injection device. On the other hand,
The in-line type, in which the melting and injection of the resin can be carried out coaxially in the heating cylinder, has little resin retention, whereas the pre-plasticizer type, in which the plasticizing section and injection section are separate, has a structurally Easy to occur. For this reason, in the pre-plastic injection device, various improvements have been made to reduce the retention of the molten resin. FIG. 7 shows an injection section in a conventional pre-plastic injection apparatus described in Japanese Patent Application Laid-Open No. 6-23796. The injection unit 2 has an injection cylinder 10 into which a plunger 12 is inserted. The injection chamber 14 is formed in the injection cylinder 10 in front of the plunger 12. The molten resin melted in the plasticizing section is supplied to the injection chamber 14 through the resin passage 15. Further, an injection passage 16 is opened in front of the injection chamber 14. In the injection chamber 14, the molten resin is stored while the injection plunger 12 is retracted in the measuring step (FIG. 7B). In the injection step, the injection plunger 12 advances to inject the molten resin stored in the injection chamber 14. Passage 1
6, and is injected into a mold via an injection nozzle (not shown) (FIG. 7A).

In such a pre-plastic injection apparatus, the molten resin flows from the resin passage 15 into the injection chamber 14 as shown by an arrow in FIG. Therefore, a portion A of the corner opposite to the opening of the resin passage 15 with the injection passage 16 therebetween.
Is easy for resin to stay. In the injection step of FIG. 7A, even if the injection plunger 12 advances, the resin in the corner portion A tends to remain without being injected.

[0005]

When dynamically focusing on the molten resin in the injection chamber 14 in relation to the stagnation, the resin passage 15
Is opened in front of the injection chamber 14,
In terms of time before and after the resin accumulated in the injection plunger 12, the farther from the injection plunger 12, the more the resin has flowed in later. Therefore, when the injection plunger 12 moves forward, the molten resin that has entered the injection chamber 14 later is injected into the mold first.

[0006] The homogeneity of the molten resin in injection molding includes:
It is known that the history from the plasticization of the molten resin to the injection thereof (hereinafter, referred to as heat history) influences. In order for the molten resin to be always injected uniformly in each injection step, it is necessary that the thermal history of the molten resin accumulated in the injection chamber 14 as a whole does not vary and becomes the same.

However, as described above, the injection chamber 14
The new molten resin that has entered is injected first (that is, the thermal history of this portion of the resin is small), and the oldest molten resin is injected last (the thermal history of this portion is large). In this way, a molten resin having a constantly varying thermal history is injected.

[0008] The variation in the thermal history means that the resin having a larger thermal history has a longer time in the injection chamber 14. In other words, the distribution of the thermal history in which the molten resin is liable to stay is inherent.

In addition, in the injection step, it is necessary to separately provide a backflow prevention mechanism such as a check valve so that the molten resin does not flow backward from the resin passage 15 to the plasticizing portion (not shown).

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to make it possible to sequentially inject the molten resin that has entered the injection chamber first, so that the heat history becomes uniform as a whole. Accordingly, it is an object of the present invention to provide a prepra-type injection apparatus which prevents the molten resin from staying in the injection chamber and also simultaneously prevents backflow to the plasticizing section.

[0011]

In order to achieve the above object, the present invention provides a plasticizing section for rotating a screw in a heating cylinder to plasticize a resin material, and a plasticizing section in an injection cylinder in front of an injection plunger. A molten plastic sent from the plasticizing section is stored in an injection chamber to be formed, and a molten plastic is provided in an injection section for independently injecting the molten resin from a nozzle into a mold by advancing the injection plunger. A discharge passage for the plasticized molten resin is formed at the tip of the screw, and a discharge port of the discharge passage is formed so as to open radially from an axial center side of the screw to an outer peripheral surface, and the injection cylinder And a resin passage for guiding the molten resin to the discharge port intermittently with the rotation of the screw.

According to the present invention, by stopping the screw at the position where the discharge port of the discharge passage is closed, it is possible to prevent the molten resin in the injection chamber from flowing back into the heating cylinder in the injection step.

According to a preferred embodiment of the present invention, the inner diameter of the heating cylinder corresponding to the discharge port opened on the outer peripheral surface of the tip of the screw is partially different around the inlet of the resin passage. It is configured to have a larger diameter than the part. In the injection step, the screw is stopped at a rotational angle position where the discharge port and the resin passage do not communicate with each other, and the discharge port is closed.

Further, according to the present invention, in the above construction, a long groove communicating with the resin passage is formed in the inner peripheral portion of the injection cylinder in an axial direction, and the injection plunger has a molten resin accumulated at a tip end thereof. A chamber is formed, and a cylindrical portion having a passage hole overlapping the long groove is provided from the completion of the injection process to the completion of the metering process, and a shaft portion slidably fitted in the cylindrical portion is provided on the nozzle. .

According to the present invention, the position of the injection plunger is guided to the injection chamber from the passage hole which moves backward as the injection plunger retreats. As a result of the movement of the passage hole, the heat history of the molten resin accumulated in the injection chamber gradually decreases from the nozzle side toward the injection plunger, so that the resin that has entered first is injected into the mold first. You.

It is preferable that the passage hole is formed at a position coinciding with the front end of the long groove at the start of the measuring step and at the rear end of the cylindrical portion.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of a pre-plastic injection apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a configuration of a pre-plastic injection device according to the present embodiment. Reference numeral 20 denotes an entire plasticizing section for plasticizing the resin raw material, and reference numeral 22 denotes an entire injection section for injecting the molten resin into a mold (not shown).

A screw 24 is inserted into a heating cylinder 23 provided in the plasticizing section 20. The screw 24 rotates to plasticize the resin raw material charged into the heating cylinder 23 from a hopper (not shown). The connecting portion 23a at the tip of the heating cylinder 23 is
Is joined to the side surface of the injection cylinder 25 provided in the main body.
Inside the connecting portion between the plasticizing section 20 and the injection section 22,
A resin passage 26 is formed.

On the other hand, at the tip of the screw 24, a cylindrical portion 28 is formed ahead of a narrowed portion 27 having a narrow outer diameter. The outer peripheral surface of the constricted portion 27 and the inner peripheral surface of the heating cylinder 23 form a resin pool portion 29 in which the molten resin plasticized by the screw 24 accumulates. The molten resin is discharged from the resin reservoir 29 through the discharge passage 30 to the resin passage 26. The discharge port 30a of the discharge passage 30
Is opened radially outward from the axial center line of the screw 24. In this embodiment, the discharge passage 30 is bent radially outward in the middle thereof,
Thereby, an opening is formed on the outer peripheral surface of the cylindrical portion 28.

FIG. 4 is a view showing the positional relationship between the discharge port 30a of the discharge passage 30 and the inlet 26a of the resin passage 26. FIG. 4 (a) is a sectional view taken along the line AA in FIG. (B)
FIG. 4 is a diagram showing a cross section taken along the line BB in FIG. 3. In the vicinity of the inlet portion 26a of the resin passage 26, the inner diameter of the heating cylinder 23 is larger than other portions, so that the inlet portion 26a has an arc shape with the cylindrical portion 28 of the screw 24. Heating cylinder 2 as an eccentric space
3 is opened to a part of the inner peripheral surface. When the screw 24 rotates, the discharge port 30a and the inlet 26a of the resin passage 26 can overlap with each other within a predetermined rotation angle range.

Downstream of the resin passage 26, a resin supply port 32 is formed at a side portion of the injection cylinder 25 through a ring-shaped groove 31.
It is open as. The molten resin is supplied into the injection cylinder 25 through the resin supply port 32 of the resin passage 26 as the screw 24 rotates. By adopting a structure in which the molten resin is supplied to the injection cylinder 25 from the side portion in this manner, the accessibility between the plasticizing portion 20 and the mold is improved, and the structure is less likely to interfere.

Next, the configuration of the injection section 22 will be described. An injection plunger 34 is inserted into the injection cylinder 25 of the injection section 22 so as to be able to advance and retreat. The injection plunger 34 moves forward and backward in the injection cylinder 25 by using an injection servomotor (not shown) as a drive source. The torque of the servomotor is transmitted to the ball screw shaft 35 via a transmission mechanism (not shown) including a timing belt and a pulley. A nut 36 is screwed onto the ball screw shaft 35, and the rotational movement of the ball screw shaft 35
Is converted into a linear motion of the injection plunger 34 via the control unit. The nut 36 is connected to the end of the rod 39 of the injection plunger 34 via a coupling 37 and a load cell 38. During the weighing process,
The back pressure applied to the retreating injection plunger 34 is detected by the load cell 38, and the magnitude of the rotational torque of the servomotor is controlled so that the back pressure becomes a set value.

At the front end of the injection cylinder 25, a nozzle 4
The nozzle 40 comes in contact with a mold (not shown) when the entire injection section 22 moves forward for nozzle touch. On the injection plunger 34 side of the nozzle 40, a shaft portion 41 has an integral structure and extends coaxially. The injection passage 42 of the nozzle 40 is formed concentrically through the shaft portion 41. The shaft portion 41 has an outer diameter smaller than the inner diameter of the injection cylinder 25, and when inserted into the injection cylinder 25, has a predetermined size between the inner peripheral surface of the injection cylinder 25 and the outer peripheral surface of the shaft portion 41. Are formed.

FIG. 5 shows a state in which the injection plunger 34 is fitted to the shaft 41 of the nozzle 40. At the front end of the injection plunger 34, a cylindrical portion 43 having the same diameter is integrally formed. This cylindrical portion 43 is used for the injection plunger 3.
4 forms an injection chamber 44 in which the molten resin to be injected is stored. The outer diameter of the cylindrical portion 43 corresponds to the inner diameter of the injection cylinder 25, and the inner diameter corresponds to the outer diameter of the shaft portion 41 of the nozzle 40. Therefore,
The injection plunger 34 including the cylindrical portion 43 slides on the injection cylinder 25 and slidably fits on the shaft portion 41.

Next, a passage for guiding the molten resin to the injection chamber 44 will be described. A plurality of long grooves 45 are formed in the inner peripheral portion of the injection cylinder 25. In this embodiment, two long grooves 45 are formed symmetrically with respect to the center of the injection cylinder 25. The long groove 45 has a predetermined length along the axial direction of the injection cylinder 25, and the length substantially corresponds to the stroke of the injection plunger 34. The rear end of the long groove 45 is provided at a position overlapping with the resin supply port 32.

On the other hand, in the injection plunger 34, at the rear end of the cylindrical portion 43, two passage holes 46 are provided symmetrically with respect to the center. As shown in FIG. 6, each of the passage holes 46 has a long groove 45 even when the injection plunger 34 moves.
The phases are adjusted so as to overlap and communicate.

As shown in FIG. 1, the passage hole 46 has a long groove 45 when the injection plunger 34 is at the injection step completion position.
And is overlapped with the front end of the head. Further, as shown in FIG. 2, when the injection plunger 34 is at the position where the measuring step is completed, the passage hole 46 coincides with and overlaps the rear end of the long groove 45. Therefore,
During the measuring step, the molten resin introduced from the resin passage 26 is guided through the long groove 45 and the passage hole 46 as a flow path, and is led out to the injection chamber 44 inside the cylindrical portion 43.

In this embodiment, a tapered surface 47 whose diameter decreases toward the injection passage 42 is formed on the end surface of the shaft portion 41 defining the injection chamber 44, and the bottom of the cylindrical portion 43 opposed to the tapered surface 47. Is formed with a conical portion 48. Thus, the injection chamber 44 is designed to have a shape in which the molten resin does not easily stay.

The pre-plastic injection device according to the present embodiment
The configuration is as described above. Next, the operation will be described. The metering process starts when the injection plunger 34 is at the position shown in FIG. 1 and the injection process is completed. The molten resin is plasticized by the screw 24 rotating in the plasticizing section 20. Also, while the screw 24 rotates,
When the discharge port 30a and the inlet 26a of the resin passage 26 overlap as shown in FIG. 4A, the discharge passage 30 and the resin passage 26 intermittently communicate with each other. After passing through the resin passage 26, the resin flows from the resin supply port 32 through the long groove 45 and the passage hole 46 and is introduced into the injection chamber 44. When the molten resin fills the injection chamber 44,
The resin pressure rises and acts as a force to retract the injection plunger 34. During the weighing process, the injection plunger 3 is set so that a slight rotational torque in the forward direction is generated in a servo motor (not shown) that drives the ball screw shaft 35.
4 retreats while applying back pressure to the molten resin. The molten resin is injected into the injection chamber 4 as the injection plunger 34 retreats.
4 and weighed.

FIG. 2 shows a state in which the injection plunger 34 has retracted to the set metering completion position. 1 to 2, the molten resin is guided to the injection chamber 44 from a passage hole 46 whose position moves backward as the injection plunger 34 retreats. As a result of the movement of the passage hole 46, the thermal history of the molten resin accumulated in the injection chamber 44 gradually decreases from the nozzle 40 side toward the injection plunger 34 side.

When the injection plunger 34 is retracted to the metering completion position, the rotation of the screw 24 is stopped and the metering process ends. FIG. 3 shows a state when the injection process is started. Simultaneously with the completion of the weighing process, the screw 24 stops at the rotation angle position shown in FIGS. 3 and 4B and is fixed at this position. In this position, the discharge port 30a is closed by the inner peripheral surface of the heating cylinder 23. Therefore,
In the injection step, the communication between the long groove 45 and the resin supply passage 26 and the discharge passage 30 is reliably shut off so that the molten resin in the injection chamber 44 does not flow back into the heating cylinder 23. When the injection plunger 34 moves forward, the molten resin in the injection chamber 44 becomes a resin having a large heat history, that is, a mold (not shown) that first touches the nozzle 40 from the resin that has entered first.
It is injected inside. Therefore, it is difficult for the resin having a large heat history to stay in the injection chamber 44.

As described above, the molten resin that has entered the injection chamber 44 first is injected first, and the molten resin that has entered the injection chamber 44 later is injected later. There is no variation in the heat history until the whole is injected. In other words, a part of the molten resin does not stay for a long time, there is no variation in the time that the molten resin stays in the injection chamber 44, and the molten resin as a whole having a uniform temperature and other conditions can be injected into the mold. it can.

Further, by merely stopping the screw 24 at the position where the discharge port 30a is closed, the backflow of the molten resin from the injection chamber 44 to the plasticizing section 20 can be easily and reliably achieved. Can be.

[0034]

As is apparent from the above description, according to the present invention, the screw is stopped at the position where the discharge port provided in the screw is closed, thereby preventing the molten resin from flowing back to the plasticizing section. It can be easily achieved.

Further, the molten resin that has entered the injection chamber first can be sequentially injected into the mold so that the heat history becomes uniform as a whole, thereby preventing the molten resin from staying in the injection chamber. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of a pre-plastic injection apparatus according to the present invention, showing a state in which an injection plunger is at a measurement process start position.

FIG. 2 is a cross-sectional view of one embodiment of a pre-plastic injection apparatus according to the present invention, showing a state where an injection plunger is at a position where a measuring step is completed.

FIG. 3 shows a state where the screw is stopped at a position where the screw closes a discharge port at a position where the measuring step is completed.

FIG. 4 shows a cross section of a plasticized portion, and FIG.
FIG. 4B is a sectional view taken along the arrow BB in FIG. 3.

FIG. 5 is a sectional view in which an injection plunger and a nozzle are combined.

FIG. 6 is a sectional view taken along the line CC of FIG. 1;

FIG. 7 is a sectional view showing an injection chamber of a conventional pre-plastic injection apparatus.

[Explanation of symbols]

 Reference Signs List 20 plasticizing part 22 injection part 23 heating cylinder 24 screw 25 injection cylinder 26 resin passage 28 cylindrical part 29 resin accumulation part 30 discharge passage 30a discharge port 34 injection plunger 35 ball screw shaft 36 nut 40 nozzle 41 shaft part 43 cylindrical part 44 injection Chamber 45 Long groove 46 Passage hole

Claims (5)

[Claims] 1. A plasticizing part for plasticizing a resin material by rotating a screw in a heating cylinder and a molten resin sent from the plasticizing part in an injection chamber formed in front of an injection plunger in an injection cylinder. In a pre-plastic injection device in which an injection section for injecting the molten resin from a nozzle into a mold by advancing the injection plunger is provided independently, a discharge passage for plasticized molten resin is formed at a tip end of the screw. The discharge port of the discharge passage is formed so as to open radially outward from the shaft center side of the screw on the outer peripheral surface, and the resin passage for guiding the molten resin to the injection cylinder intermittently with the rotation of the screw. A pre-plastic injection device characterized in that it communicates with the discharge port. 2. The heating cylinder according to claim 2, wherein the inner diameter of the heating cylinder corresponding to the discharge port opened on the outer peripheral surface of the tip end of the screw is partially larger than the other portion around the inlet of the resin passage. The pre-plastic injection device according to claim 1, wherein: 3. The injection step according to claim 1, wherein in the injection step, the screw is stopped at a rotational angle position where the discharge port and the resin passage do not communicate with each other, and the discharge port is closed. Pre-plastic injection device. 4. A long groove communicating with the resin passage is formed in an inner peripheral portion of the injection cylinder in an axial direction, an injection chamber for storing molten resin is formed at a tip end of the injection plunger, and measurement is performed from completion of the injection process. 4. The nozzle according to claim 1, wherein a cylindrical portion having a passage hole overlapping with the long groove is provided over a time when the process is completed, and a shaft portion slidably fitted in the cylindrical portion is provided on the nozzle. 4. A pre-plastic injection device according to item 1. 5. The pre-plasticizing method according to claim 4, wherein said passage hole is formed at a position coinciding with a front end of said elongated groove at the start of the measuring step and at a rear end of said cylindrical portion. Injection device.