JP2004154990A - Injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the backflow and ejection of a molten resin from a hot runner even when an injection nozzle is separated from the inlet part of the hot runner when continuous molding is stopped temporarily. <P>SOLUTION: In an injection molding machine, the injection nozzles 31 of an injection unit 11 are brought into close contact with the inlet parts of the hot runners 18b, 18c, and 20b communicating with the cavity 15 of a molding mold 10, and the molten resin ejected from the injection nozzles 31 is packed in the cavity 15 through the hot runners 18b, 18c, and 20b and cooled and solidified. An opening/closing apparatus 22 for closing the inlet parts of the hot runners 18b, 18c, and 20b when the injection nozzles 31 are separated from the inlet parts of the hot runners 18b, 18c, and 20b is provided. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an injection molding apparatus for producing a molded product by injecting a molten resin into a cavity of a molding die, and relates to a sealed configuration of a hot runner portion for guiding the molten resin from an injection nozzle portion into the cavity.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in this type of injection molding apparatus, an injection nozzle at the tip of an injection cylinder of an injection unit is brought into close contact with an inlet of a hot runner of a molding die at a high pressure. This seals the inlet of the hot runner to seal the hot runner. Various such injection molding apparatuses have been conventionally proposed (for example, see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Publication No. 6-94144
[Problems to be solved by the invention]
By the way, usually, the injection nozzle portion is configured to continuously mold a molded product while maintaining a state in which the injection nozzle portion is in close contact with an inlet portion of a hot runner of a molding die. However, there is a case where the continuous molding is temporarily stopped due to some trouble of the molding die or a break in the molding operation.
[0005]
In this case, it is desirable to separate the injection nozzle from the inlet of the hot runner for the following reasons. In other words, when the molding is temporarily stopped for reasons such as a reduction in the power for bringing the injection nozzle into close contact with the inlet of the hot runner of the molding die at a high pressure, or an extension of the durability life of the injection nozzle or the hot runner. It is desirable to separate the nozzle from the inlet of the hot runner.
[0006]
However, when the injection nozzle is separated from the inlet of the hot runner, the hermetically sealed state of the inlet of the hot runner is opened, so that the high-pressure molten resin in the hot runner flows back from the inlet to the outside and is ejected. Failure occurs.
[0007]
In particular, in order to reduce the weight of molded products or to prevent deformation during molding and shrinkage, foam molding is performed by dispersing a foam material in the molten resin before injection and foaming the foam material in the cavity of the molding die. In this case, when the inlet of the hot runner is opened, the pressure in the cavity is reduced, the degree of foaming is increased, and the volume of the molten resin is increased.
[0008]
In view of the above, it is an object of the present invention to prevent the molten resin from flowing back and being ejected from the hot runner even when the injection nozzle is separated from the inlet of the hot runner when the continuous molding is temporarily stopped.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, an injection unit (11) is provided at an inlet of a hot runner (18b, 18c, 20b) communicating with a cavity (15) of a molding die (10). The molten resin injected from the injection nozzle (31) is filled into the cavity (15) through the hot runners (18b, 18c, 20b) and solidified by cooling and solidifying the molten resin. In an injection molding apparatus for manufacturing a molded article, an opening and closing for closing the inlet of the hot runner (18b, 18c, 20b) when the injection nozzle (31) is separated from the inlet of the hot runner (18b, 18c, 20b). It is characterized by comprising means (22).
[0010]
According to this, even when the injection nozzle (31) is separated from the inlet of the hot runner (18b, 18c, 20b) during the temporary stop of the continuous molding, the molten resin flows backward and jets out of the hot runner (18b, 18c, 20b). Can be reliably prevented by the opening / closing means (22). In particular, in the case of performing foam molding for foaming a foam material, the backflow and ejection of the molten resin become more remarkable as the foaming degree of the foam material increases, but the hot runner (18b, 18b, It is possible to reliably prevent the backflow and ejection of the molten resin by maintaining the sealed state of 18c, 20b). Therefore, even in the case of performing foam molding, the operation of separating the injection nozzle (31) from the inlet of the hot runner (18b, 18c, 20b) can be performed without any trouble when the continuous molding is temporarily stopped.
[0011]
As in the second aspect of the invention, the opening / closing means can be specifically constituted by an opening / closing device (22) of a fluid pressure drive type, and this opening / closing device (22) is capable of injecting the molten resin and maintaining the molten resin. During the pressurizing step, the open state is maintained, and the operation is performed so as to be in the closed state almost in conjunction with the end of the pressure maintaining step.
[0012]
According to the third aspect of the present invention, the opening / closing means may be constituted by a check valve device that opens only when the molten resin flows from the hot runner (18b, 18c, 20b) toward the cavity (15). Good.
[0013]
In addition, the code | symbol in the parenthesis of each said means shows the correspondence with the concrete means described in embodiment mentioned later.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an outline of a main part of an injection molding apparatus according to the present embodiment, and FIG. 2 is an enlarged sectional view of a molding die part of FIG.
[0015]
As shown in FIG. 1, the injection molding apparatus according to the present embodiment includes a molding die 10 and an injection unit 11 for injecting a molten resin into the molding die 10. The molding die 10 has a movable mold 12 and a fixed mold 13, and the movable mold 12 is attached to a movable mold mounting plate 14. The movable mold 12 moves in the left-right direction integrally with the movable mold mounting plate 14, clamps the mold with respect to the fixed mold 13, and opens the mold. 1 and 2 show a state where the movable mold 12 is clamped to the fixed mold 13.
[0016]
A cavity 15 is formed between the movable mold 12 and the fixed mold 13 so as to form a cavity for forming a product of a molded product. The fixed die 13 is attached to a fixed die mounting plate 17 via a ring-shaped member 16, and a hot runner block 18 is arranged in a circular inner space of the ring-shaped member 16.
[0017]
The hot runner block 18 has a disk shape, and a sprue portion 18a that projects cylindrically toward the fixed mounting plate 17 is formed at the center of the disk shape. , The central portion of the hot runner block 18 is fixed to the central portion of the fixed mounting plate 17. The hot runner block 18 is formed with hot runners 18b and 18c which form a resin passage from the sprue portion 18a to the disk-shaped portion.
[0018]
Further, a plurality of holes 19 are provided in a portion of the fixed die 13 which communicates with the cavity 15, and gate bushes 20 are arranged and fixed in the plurality of holes 19 respectively. Each of the gate bushes 20 has a gate 20a (FIG. 2) for injecting the molten resin into the cavity 15 and a secondary hot runner 20b.
[0019]
The secondary hot runner 20b connects the end on the radially outer side of the hot runner 18c to the gate 20a. An electric heater (not shown) for heating the molten resin and maintaining the molten state of the resin is provided around the hot runners 18b and 18c and the secondary hot runner 20b. The gate 20a has a hole shape having a smaller cross-sectional area than the upstream secondary hot runner 20b, and narrows the flow of the molten resin from the secondary hot runner 20b to increase the flow velocity and inject the molten resin into the cavity 15. .
[0020]
Further, a plurality of gate opening / closing devices 21 are arranged and fixed between the disk-shaped portion of the hot runner block 18 and the fixed mounting plate 17. The plurality of gate opening / closing devices 21 have a piston 21a that moves forward and backward by a fluid pressure drive mechanism such as a hydraulic pressure (not shown), and a valve body 21b that is elongated in a shaft shape is integrally connected to the piston 21a. The valve element 21b penetrates through the hot runner block 18 and is inserted into the secondary hot runner 20b of the gate bush 20, and the tapered end of the valve element 21b is disposed to face the gate 20a to open and close the gate 20a.
[0021]
Further, the piston of the hot runner opening / closing device 22 is disposed on the fixed die 13. The hot runner opening / closing device 22 opens and closes the entrances of the hot runners 18b, 18c, 20b (the right end of the sprue portion 18a), and has the same configuration as the gate opening / closing device 21. That is, the hot runner opening / closing device 22 is provided with a piston 22a that moves forward and backward by a fluid pressure such as a hydraulic pressure, and a valve body 22b that is elongated in a shaft shape is integrally connected to the piston 22a.
[0022]
By inserting the tapered end of the valve element 22b into a small-diameter hole 18d formed at the inlet of the hot runner 18b, the inlet of the hot runner 18b is closed.
[0023]
FIG. 3 exemplifies a drive mechanism of a piston 22a of the hot runner opening / closing device 22. The piston 22a is reciprocally housed in a hydraulic cylinder 22c, and is formed on both front and back sides of the piston 22a inside the hydraulic cylinder 22c. The hydraulic switching mechanism 23 is connected to the first chamber 22d and the second chamber 22e via hydraulic pipes 22f and 22g, respectively.
[0024]
The hydraulic switching mechanism 23 incorporates an electric passage switching valve (not shown) controlled by the control device 24, and the electric passage switching valve controls the hydraulic pressure to the first chamber 22d and the second chamber 22e. Is switched to move the piston 22a forward or backward. The drive mechanism of the piston 22a of the hot runner opening / closing device 22 may be configured using a fluid pressure other than the hydraulic pressure.
[0025]
Next, the injection unit 11 will be described with reference to FIG. 1. The injection cylinder 25 is a cylindrical member that is elongated in the horizontal direction, and a hydraulic cylinder 26 is disposed at one end (the right end in FIG. 1) of the injection cylinder 25. ing. A piston 27 is accommodated in the hydraulic cylinder 26 so as to be able to reciprocate. Like the pistons 21a and 22a, the piston 27 also moves forward and backward by a hydraulic drive mechanism such as a hydraulic pressure (not shown).
[0026]
Further, a screw member 28 is integrally connected to the piston 27. A spiral portion 28a is formed on the outer peripheral surface of the screw member 28. The rotation of a hydraulic motor (not shown) or the like is transmitted to the connection structure between the screw member 28 and the piston 27, whereby the connection structure rotates integrally.
[0027]
Further, a hopper-shaped material tank 29 is disposed above the injection cylinder 25 in the vicinity of the hydraulic cylinder 26. Inside the material tank 29, a solid molding resin material is stored in a granular form (pellet form). By connecting the bottom opening of the material tank 29 to the upper part of the internal space of the injection cylinder 25, the solid molding resin material in the material tank 29 is dropped by gravity onto the upper surface near the right end of the screw member 28. It has become.
[0028]
The solid molding resin material is fed into the injection cylinder 25 from the vicinity of the right end to the left end by rotation of the screw member 28. An electric heater 30 is disposed on the outer peripheral surface of the injection cylinder 25 as a heating means for the resin. The solid molding resin material is heated and melted (plasticized) by the electric heater 30 while moving from the right side to the left side of the injection cylinder 25.
[0029]
At the other end (left end) of the injection cylinder 25, an injection nozzle 31 having a throttle passage 31a whose passage area is significantly reduced as compared with the internal space of the injection cylinder 25 is formed. The tip of the injection nozzle 31 is formed in a spherical shape, and is inserted into the through hole 17 a of the fixed mounting plate 17. Then, the spherical tip of the injection nozzle 31 is brought into contact with the spherical seating surface 18e of the tip of the sprue portion 18a of the hot runner block 18, and the tips of the two 31, 31a are brought into close contact with each other. Thus, the throttle passage 31a of the injection nozzle 31 communicates with the inlet of the hot runner 18b of the sprue portion 18a.
[0030]
The entire injection unit 11 is supported on a support table (not shown) so as to be movable in the left-right direction of FIG. FIG. 1 shows a state in which the entire injection unit 11 is advanced most by a driving mechanism (not shown). By retracting the entire injection unit 11 from the position shown in FIG. 1, the spherical tip of the injection nozzle 31 can be separated from the spherical seating surface 18e of the sprue portion 18a of the hot runner block 18.
[0031]
Next, an injection molding method using the injection molding apparatus will be described.
[0032]
(1) Mold Closing and Clamping Step At the end of the previous molding cycle, the movable mold 12 is in the mold open state, and the movable mold 12 moves to the left from FIGS. ing. Therefore, first, the movable mold 12 is moved to the right from the position of the mold open state to contact the fixed mold 13 and the mold is closed. Next, the movable mold 12 and the fixed mold 13 are tightened with a predetermined high pressure. FIG. 1 and FIG. 2 show a state where the mold clamping is completed.
[0033]
After completion of the mold clamping, a step (nozzle touching step) of moving the entire injection unit 11 forward to abut the spherical tip of the injection nozzle 31 against the spherical seating surface 18e of the sprue portion 18a of the hot runner block 18 is performed. However, in the present embodiment, a method is employed in which the spherical tip of the injection nozzle 31 is constantly brought into contact with the spherical seating surface 18e of the sprue portion 18a of the hot runner block 18.
[0034]
(2) Injection Step After completion of the mold clamping, the piston 27 in the hydraulic cylinder 26 of the injection unit 11 is advanced, and the screw member 28 is advanced in the injection cylinder 25. At the same time, the gate opening / closing device 21 is operated to the opening position of the gate 20a, and the hot runner opening / closing device 22 is operated to the opening position of the hot runner 18b entrance of the sprue portion 18a. That is, both opening and closing devices 21 and 22 are opened in conjunction with the advance of the screw member 28 (start of the injection process).
[0035]
As the screw member 28 advances, the molten resin filled in the injection cylinder 25 is pushed out to the throttle passage 31a side of the injection nozzle 31, and the molten resin is further discharged from the sprue portion 18a of the hot runner block 18 through the throttle passage 31a. It is extruded (injected) into the runner 18b. Then, the molten resin reaches the gate 20a via a route of the hot runner 18b → the hot runner 18c → the secondary hot runner 20b of the gate bush 20, and the molten resin is injected from the gate 20a into the cavity 15 at a predetermined high pressure. .
[0036]
(3) Holding Pressure (Secondary Pressure) Step It is possible to determine that the injection of the molten resin into the cavity 15 has been completed by detecting that the advance position of the screw member 28 has reached a predetermined position. After the injection is completed, the forward position of the screw member 28 is maintained at a predetermined pressure (holding pressure or secondary pressure) for a predetermined time to maintain a state of applying pressure to the injection resin in the cavity 15. .
[0037]
(4) After the injection of the cooling / plasticizing step (after the start of the pressure-holding step), when a predetermined time has elapsed, the gate opening / closing device 21 is operated to the closing position of the gate 20a, and the hot runner opening / closing device 22 is moved to the sprue portion. The operator operates the hot runner 18b at the closed position at the entrance of the hot runner 18b. Further, the connection structure of the screw member 28 and the piston 27 is rotationally driven by a hydraulic motor (not shown) or the like, so that the screw member 28 is retracted while rotating. Here, when the rotation of the screw member 28 starts, the pressure-holding step ends.
[0038]
At the same time, the bottom opening of the material tank 29 is communicated with the upper part of the internal space of the injection cylinder 25, and the granular molding resin material in the material tank 29 is dropped on the upper surface of the screw member 28 by gravity. The granular molding resin material dropped on the upper surface is extruded toward the injection nozzle 31 by the rotation of the spiral portion 28 a on the outer peripheral surface of the screw member 28.
[0039]
During this extrusion, the granular molding resin material is heated by the electric heater 30 and melted (plasticized). Therefore, the molten resin is stored in the space on the injection nozzle 31 side in the internal space of the injection cylinder 25. This molten resin is prepared in advance for the next molding.
[0040]
On the other hand, when the pressure holding step is completed, the injected resin in the cavity 15 is cooled by the molding die 10 and solidified. Therefore, the step of cooling the injected resin in the cavity 15 and the step of plasticizing for the next molding are performed concurrently.
[0041]
The resin in the hot runners 18b, 18c and the secondary hot runner 20b is also heated in the cooling step by the heating action of an electric heater (not shown) provided around the hot runners 18b and 18c and the secondary hot runner 20b. Maintain the molten state.
[0042]
(5) Mold Opening Step When the cooling step of the injected resin and the plasticizing step in the injection unit 11 are completed, the movable mold 12 is moved to the left from the mold clamping position shown in FIGS. Open the mold.
[0043]
(6) Molded article removal step After the mold opening, the ejector pins (not shown) provided on the mold 10 are pushed out to eject the molded article from the mold 10 and taken out of the mold 10.
[0044]
By repeating the above steps (1) to (6), it is possible to continuously form a molded product. However, as described above, occurrence of some trouble in a molding die, break of molding operation, etc. For this reason, continuous molding may be temporarily stopped.
[0045]
When the molding is temporarily stopped, for example, after the end of the molded product removal process, the injection cylinder 25 of the injection unit 11 is retracted, and the injection nozzle portion 31 at the tip of the injection cylinder 25 is moved to the hot runners 18b and 18c of the molding die 10. Keep away from entrance. Thereby, the power for bringing the injection nozzle 31 into close contact with the inlets of the hot runners 18b and 18c of the molding die 10 at high pressure can be reduced. In addition, it is possible to prevent the durability of the injection nozzle 31 and the hot runner block 18 from being shortened due to the continuation of the high pressure application state.
[0046]
Moreover, according to the present embodiment, after the injection is completed (after the start of the pressure-holding step), when the pressure-holding step is completed after a predetermined time has elapsed, the hot runner opening / closing device 22 is operated to open the hot runners 18b and 18c. Even if the injection nozzle 31 is separated from the inlets of the hot runners 18b and 18c of the molding die 10 due to the obstruction, the high-pressure molten resin in the hot runners 18b and 18c flows backward to the outside and is ejected. It can be reliably prevented.
[0047]
In particular, when foaming is performed by dispersing the foaming material in the molten resin before injection and foaming the foaming material in the cavity 15 of the molding die 10, the inlet portions of the hot runners 18b and 18c are opened. The degree of foaming increases and the volume of the molten resin increases, and the backflow and ejection of the molten resin become more remarkable. In the present embodiment, however, the hot runner opening / closing device 22 closes the inlets of the hot runners 18b and 18c. Since the state can be maintained, remarkable backflow and ejection of the molten resin during foam molding can be reliably prevented.
[0048]
In addition, as a foaming material, any of a physical foaming material using a gas such as CO ₂ and N ₂ or a chemical foaming material may be used.
[0049]
(Other embodiments)
In the above-described embodiment, after the injection is completed (after the start of the pressure-holding step), when the pressure-holding step ends after a predetermined time, the hot runner opening / closing device 22 is operated to operate the hot runners 18b and 18c. Has been described, but the timing for closing the hot runner opening / closing device 22 can be determined by various methods as follows. For example, the time from the start of the injection step may be measured by a timer to determine the end time of the pressure holding step, and thereby the closing time of the hot runner opening / closing device 22 may be determined.
[0050]
In addition, the position sensor detects that the advance position of the screw member 28 in the internal space of the injection cylinder 25 has reached a predetermined position, thereby determining the end time of the pressure-holding step, and closing the hot runner opening / closing device 22. The timing may be determined. In short, the closing time of the hot runner opening / closing device 22 may be determined by substantially determining the end time of the pressure holding step.
[0051]
Further, in the above-described embodiment, the opening / closing means for opening / closing the inlets of the hot runners 18b and 18c is a fluid pressure driving type opening / closing device 22 which drives the valve body 22b by a piston 22a which reciprocates by hydraulic pressure such as hydraulic pressure. However, a check valve device may be used instead of the fluid pressure drive type opening / closing device 22. That is, the valve is opened only by the flow of the molten resin in one direction from the inlets of the hot runners 18b and 18c to the gate portion 20a, and is always kept closed when there is no flow of the molten resin in one direction. A valve device may be used.
[0052]
Even when this check valve device is used, when the injection nozzle portion 31 is separated from the inlets of the hot runners 18b and 18c of the molding die 10, the check valve device maintains the closed state. Similarly, it is possible to reliably prevent the molten resin from flowing backward from the inlet of the hot runner to the outside and to be ejected.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an injection molding apparatus according to an embodiment of the present invention.
FIG. 2 is an enlarged sectional view of a molding die part of FIG.
FIG. 3 is a system diagram showing a drive mechanism of the hot runner opening / closing device shown in FIGS. 1 and 2;
[Explanation of symbols]
10: Mold, 11: Injection unit, 15: Cavity,
18b, 18c, 20b: hot runner, 31: injection nozzle,
22 ... Opening / closing device (opening / closing means).

Claims (3)

The injection nozzle (31) of the injection unit (11) is brought into close contact with the inlet of the hot runner (18b, 18c, 20b) communicating with the cavity (15) of the molding die (10), and is brought into close contact therewith. ) Is filled into the cavity (15) through the hot runners (18b, 18c, 20b), and the molten resin is cooled and solidified to produce a molded product.
An opening / closing means (22) for closing the inlet of the hot runner (18b, 18c, 20b) when the injection nozzle (31) separates from the inlet of the hot runner (18b, 18c, 20b). An injection molding apparatus characterized by the above-mentioned. The opening / closing means is a fluid pressure driven opening / closing device (22), and the opening / closing device (22) maintains an open state during the molten resin injection step and the molten resin pressure holding step, and 2. The injection molding apparatus according to claim 1, wherein the injection molding apparatus is closed in substantially interlocking with the end of the pressure step. 2. The check valve device according to claim 1, wherein the opening / closing means is a check valve device that opens only when the molten resin flows from the hot runner (18b, 18c, 20b) toward the cavity (15). Injection molding equipment.

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