JPH0815752B2 - Pre-plastic injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is provided with a plasticizing chamber having a kneading device such as a screw and an injection chamber having an injection plunger independently, and kneading in the plasticizing chamber. The present invention relates to a so-called pre-plastic injection molding machine having a structure in which the material is transferred to an injection chamber through a passage that communicates both chambers and the material is injected into a mold cavity by an injection plunger.

<< Prior Art >> Injection molding machines are widely used for molding synthetic resin parts. Most of the injection molding machines currently used are of the so-called in-line screw type in which the plasticizing chamber and the injection chamber are integrated, and the structure is simple and convenient for molding general synthetic resins. However, when injection molding a material such as a synthetic resin, a composite material, or a new ceramics having a special property, more stable plasticization and high injection pressure are required depending on the material. In the men-line screw type, since the plasticizing chamber and the injection chamber are shared, it is necessary to perform both plasticizing and injection with one screw, and the check valve of the screw is attached. However, there has been a problem that the valve portion of the check valve wears quickly, and therefore a high injection pressure cannot be applied.

Therefore, for such a material, it is convenient to use a pre-plastic type in which the plasticizing chamber and the injection chamber are separated. The pre-plastic type injection molding machine has been known for a long time. In the conventional pre-plastic type injection molding machine, as shown in FIG. 4, the injection chamber of the passage 33 connecting the plasticizing chamber 4 and the injection chamber 24 is communicated.
The opening 35 on the 24 side is the injection plunger when it is in the forward limit.
It opens to the front (nozzle 27 side) further than the position of 23,
A check valve 37 is provided in the middle of the opening or passage to prevent the material in the injection chamber 24 from flowing back into the plasticizing chamber 4 during the injection process.

As is well known, the mechanical energy generated by the rotation of the kneading screw 3 contained in the plasticizing chamber 4 and the thermal energy from the band heater 5 wound around the casing 2 of the plasticizing chamber flow in from the hopper 6. The material is melted and kneaded in the plasticizing chamber 4, and the melted material is sent forward by the carrying force of the screw 3 and sent to the injection chamber 24 through the passage 33. Since the injection plunger 23 retracts due to the pressure of the inflowing material, the material is measured by detecting the stroke of the plunger 23, and then the injection cylinder 26 is thrust by the injection cylinder 26 connected to the rear end of the injection plunger 23. The plunger 23 is advanced to fill the material into a mold cavity (not shown). That is, the four steps of plasticizing measurement, injection (filling), and holding pressure have a series of inseparable relations, and these four steps are collectively called an injection step.

<< Problems to be Solved by the Invention >> When the injection process is completed and the injection plunger 23 is at the forward limit position, the molten resin necessary for performing the pressure holding process is
It remains at the tip of 24 and cannot be zero. Even if the material remains in the apparatus, if the material remaining in the next injection step is preferentially injected, no problem will occur. However, in the conventional apparatus, as shown in FIG. 5, a part 20c of the remaining material tends to stay without being ejected forever, and depending on the material, the material may be hardened or transformed by a long stay in a heating environment. However, problems such as deterioration (aging) and gas generation occur.

Further, when the material is changed, the previous material 20c remains at the tip of the injection chamber 24 for a long time, which causes a problem that many defective products are generated immediately after the material is changed.

Further, since the molten resin is pressed and injected by the front surface of the injection plunger 23, the resin is closely adhered to the front surface of the plunger 23, the adhered resin is measured without being peeled off, and the injection process is continued. As a result, the cause of the defect was latent along with the retention.

An object of the present invention is to eliminate the cause of defects caused by the material stagnation in the injection chamber of such a pre-plastic injection molding machine, and to prevent the screw 3 and the plunger 23 in the injection process.
Control the movement of.

<< Means for Solving the Problem >> The pre-plastic injection molding machine according to the present invention inserts the plasticizing chamber 4 having the kneading device 3 and the injection plunger 23 into the injection plunger 23, and melts the molten resin in front of the injection plunger 23. In a pre-plastic injection molding machine equipped with an injection chamber 24 for accumulating and weighing separately,
Rotating means 7 for rotationally driving the screw 3 inserted into the plasticizing chamber 4, a drive device 8 for advancing the screw 3 in the axial direction, and a plunger 23 opened at the center of the front wall of the injection chamber 24. The nozzle 27 having a nozzle hole for injecting the molten material in the injection chamber toward the cavity by the operation of, and the plasticizing chamber side opening 34 that opens at the one end of the plasticizing chamber 4 on the axis of the screw 3 And a passage 33 that directly communicates these openings with a smooth hole having a substantially constant diameter, and drive means 26 for driving the plunger 23 slidably movable in the injection chamber 24, 30 and the drive means 26,
With a control device 29 for giving a command to 30, during the plasticizing process,
At the position where the screw 3 is retracted, the rotating means is driven to transfer the molten material from the plasticizing chamber side opening 34 to the passage.
It flows through the injection chamber 33 into the injection chamber 24, and during the injection process, the driving device is operated with the rotating means stopped to advance the screw 3 to close the plasticizing chamber side opening 34. The driving means 26 and 30 are operated immediately before the plasticizing step is started again to slightly retract the plunger 23.

Then, the control device 29 gives a command to the drive means 26, 30 to control the drive means 26 and 30, and also controls the rotation means 7 and the drive device 8.

<< Operation >> The operation of the device of the present invention is similar to that of the conventional pre-plastic injection molding machine, but after the injection process is completed and before the next material is transferred from the plasticizing chamber 4 to the injection chamber 24. The difference is that the injection plunger 23 is driven by the drive devices 28, 30 forcibly, i.e. not due to the pressure of the material 20 being fed in, and makes a slight retraction movement.

That is, during the injection process and the pressure maintaining process, the screw 3 advances and the convex conical surface 3a closely contacts the concave conical surface 34a to close the opening 34, and the shut-off valve 31 of the nozzle 27 is used only during the injection process. Since it is open and normally closed, passage 33
Also, the nozzle hole is closed, and a slight amount of molten material remains in the injection chamber 23, and the molten material is sealed in front of the injection plunger 23. In this state, the injection plunger
Since 23 is slightly retracted, a force acts to peel off the molten resin adhering to the front surface of the plunger 23, and the residual resin forms a rare layer 36 on the front surface side of the plunger 23. Then, the thin layer 36 pulls the resin material remaining in the passage 33 and the nozzle hole so as to suck the resin material as well, but immediately after that, the rotation of the screw 3 is started, so that the low pressure which starts melting in the plasticizing chamber 4 is started. Since the above material is pulled in at a high pressure, the urged molten material flows at a high pressure from the start of its melting with respect to the front surface of the plunger 23 and pushes down the plunger 23 while cleaning. Therefore, the remaining previous molten material is pushed to the front of the injection chamber 24 by the new material and is replaced with the new material on the front side of the plunger 23.

<< Embodiment >> FIGS. 1 to 3 are views showing an embodiment of the present invention, showing the most common screw pre-plastic type, in which an injection nozzle is provided with a shut-off valve. It is a figure.

In the figure, reference numeral 1 is a plasticizing section, which is a plasticizing casing 2, a kneading screw 3 installed therein, a casing 2 and a screw 3.
It is provided with a plasticizing chamber 4, which is partitioned and formed by the above, a band heater 5 wound around the casing 2, a hopper 6 for supplying a material, and a hydraulic motor 7 for rotating the screw 3. These structures and functions are not particularly different from the conventional ones except for the parts described later.

Reference numeral 8 denotes a hydraulic cylinder for advancing and retracting the kneading screw 3, which is provided at the base end of the plasticizing casing 2. The piston 9 of this hydraulic cylinder is fixed to a motor mounting plate 11 mounted axially slidably and non-rotatably by a guide pin 10, and the kneading screw 3 is supported on the piston 9 by bearings 14 and 15. It is connected to an output shaft 12 of the hydraulic motor 7 via a connecting shaft 13. Therefore, the hydraulic pressure supply port 16 of the hydraulic cylinder 8
When the pressure oil is supplied to, the kneading screw 3 and the hydraulic motor 7 move forward in the axial direction. Further, the hydraulic pressure supply port 17 is normally open to the atmosphere, and when the kneading screw 3 starts to rotate and the supply of the pressure oil from the hydraulic pressure supply port 16 is stopped as described later, the screw 3 of the screw 3 is stopped. The screw 3 retreats by the melting pressure of the material due to the rotation, and the contact between the convex conical surface 3a and the concave conical surface 34a is released, so that the molten resin flows into the passage 33. Further, when the kneading screw 3 rotates, the connecting shaft 13 rotates but the piston 9 does not rotate.

Reference numeral 21 denotes an injection part, which includes an injection casing 22, an injection plunger 23 fitted in the casing, a casing 22 and a plunger.
An injection chamber 24 defined by 23, a band heater 25 wound around the casing 22, an injection cylinder 26 for advancing the injection plunger 23, and a nozzle 27 for guiding the injected material to a mold cavity (not shown) are provided. These structures and functions are not particularly different from those of the conventional device except for the points described later.

A rod side chamber 28A and a rear chamber 28B are formed in the injection cylinder 26, and the injection plunger 23 can be forcibly retracted by supplying pressure oil to the rod side chamber 28A. Further, by supplying pressure oil to the rear chamber 28B and releasing the pressure oil from the rod side chamber 28A, the injection plunger 23 is forcibly advanced and the measured material can be extruded and injected. Supply / stop (discharging) of the pressure oil to the rod side chamber 28A and the rear chamber 28B is performed via the electromagnetic flow control valve 30 which is opened / closed by a command from the control device 29 to supply the pressure oil to the rod side chamber 28A. When the injection process is completed and the injection plunger 23 reaches the forward limit, the injection plunger 23 waits at the forward limit for a predetermined time (pressure-holding process).
That is, after the pressure is maintained, before the kneading screw 3 starts to rotate in order to transfer the next material to the injection chamber 24.

The nozzle 27 is provided with a shutoff valve 31. The shut-off valve is naturally opened during the injection process, and is closed immediately before the injection plunger 23 starts the forced retreat operation. This closed state is maintained when the injection plunger 23 reaches the retreat limit, that is, until the plasticizing and metering process for the next injection is completed. The shut-off valve 31 prevents the material from flowing backward from the nozzle 27 when the injection plunger 23 is forcedly retracted, and such a valve 31 is provided when the fluidity of the material is high. Is desirable.

Reference numeral 33 denotes a passage that connects the plasticizing chamber 4 and the injection chamber 24, and the molten material plasticized and kneaded in the plasticizing chamber 4 is guided to the injection chamber 24 through the passage 33.

An opening 34 of the passage 33 on the plasticizing chamber 4 side is opened on the axis of the kneading screw 3 at the tip of the plasticizing chamber. The convex conical surface 3a at the tip of the kneading screw 3 is formed in the opening 34 so that it can contact the concave conical surface 34a. When pressure oil is supplied from the supply port 16 of the hydraulic cylinder 8, the kneading screw 3 advances, the convex conical surface 3a at the tip thereof is pressed against the concave conical surface 34a of the opening 34 of the passage 33, and the passage 33 becomes Is blocked.

As shown in FIG. 2, the opening 35 of the passage 33 on the injection chamber 24 side is located immediately before the tip of the injection plunger 23 when the injection plunger 23 reaches the forward limit, or as shown in FIG. As described above, at least a part of the front surface of the plunger 23 is opened when the injection plunger 23 is forcibly retracted (FIG. 3 (b) is an example in which it is fully opened). .

FIGS. 2 (a) and 3 (a) show the state immediately after the injection step, and FIGS. 2 (b) and 3 (b) show that the injection plunger 23 is forced to operate. The figure shows the state immediately after the next plasticization metering process is started after being retracted, and 36 indicates the book layer.

When the injection process is completed, that is, when the pressure holding process is completed,
The injection plunger 23 is in the forward limit. Before the material is plasticized and the metering process is started, the shutoff valve 31 is closed, pressure oil is supplied to the rod side chamber 28A of the injection cylinder 26, and the injection plunger 23 is retracted slightly (about several mm). The material left behind for the last pressure-holding step is the injection cylinder 26.
In front of the molten resin material 20, since the molten resin material 20 has a viscosity peculiar to the resin, a force acts to peel off the molten resin adhered to the front surface of the injection plunger 23 from the front surface of the plunger 23, and the front surface is 36 parts of rare books will be formed,
The material 20a remaining at the tip of the injection chamber 24, and in particular, the material 20a also remaining in the passages 33 and nozzle holes are pulled. At this time, the amount of retreat of the injection plunger 23 is small, and the next plasticization starts immediately and the material is supplied. Therefore, at the start of the plasticization, the rotation of the screw 3 has not reached the constant speed, Although the molten resin plasticized by the rotation of 3 has a low pressure, the resin in the passage 33 is subjected to a tensile force, so that the pressure is increased and the resin flows from the opening 35 toward the front surface of the plunger 23. Come on. Since the front surface of the plunger 23 is located close to the opening 35, the plunger 23 is washed by the new material 20b flowing and entering the front surface of the injection chamber 24.
Push off the previous material 20a to the tip side,
Is retracted by the pressure of the material 20 and accumulated and measured in the injection chamber 24. In the structure of FIG. 2, the passage 33 is opened to the injection chamber 24 from the beginning, and in the structure of FIG. 3, the passage 33 is opened to the injection chamber 24 when the injection plunger 23 is retracted. Therefore, as described above, the material 20a whose front surface of the injection plunger 23 has been cleaned is pushed to the front end side of the injection chamber 24, and the rare book layer 36 is also eliminated. And the material that is sent further 20
The injection plunger 23 is pushed by b and is retracted to a predetermined position to complete the material measuring process, and then the shutoff valve 31 is opened and then the injection process is started. Kneading screw 3
Moves forward just before the injection process to close the passage 33 and prevent backflow of material.

The structure for opening and closing the nozzle hole by providing the shut-off valve 31 of the above embodiment is peculiar to the embodiment, and the presence or absence of these does not limit the present invention.
For example, when the next plasticization is performed after the completion of the gate seal of the molded product while the tip of the nozzle 27 is pressed against the mold (not shown), it is not necessary to provide the nozzle with a shut-off valve, and the material of the passage 33 is not required. The backflow of (1) prevents the backflow completely by closing the passage 33 by advancing the kneading screw 3, and does not affect the plasticizing chamber 4. Further, in the above description, the screw type of the most general hydraulic drive was described, but it goes without saying that a plunger type plasticizing device or an electric drive device is also included in the present invention. is there.

Further, the control device 29 in this device controls the supply of hydraulic pressure from the pump P to the rod side chamber 29A and the rear chamber 28B through the electromagnetic flow control valve 30, but the hydraulic cylinder 8 that advances the hydraulic motor 7 and the kneading screw 3 is used. Since the pipes are branched from the pump P to supply the hydraulic pressure, the control device 29 also controls the solenoid valves in these pipes to coordinate their operation, although not shown.

<< Effects of the Invention >> As described above, according to the device of the present invention, since the material newly supplied from the plasticizing chamber to the injection chamber has the front surface of the injection plunger positioned immediately before the opened passage, Since the remaining material is being pulled and urged by the retreat of the motor, the rotation of the motor does not immediately reach a constant speed when plasticization begins, and while it starts rotating at a low rotation, it instantaneously melts and starts delivery. The material flows into the front surface of the injection plunger from the passage at a high pressure, and the material that has adhered to the front surface of the injection plunger is separated and washed by the new molten material, and further, the remaining material can be pushed away to the tip side of the injection chamber. The material remaining by the next injection operation is swept away from the injection chamber with the highest priority, and the problem of material retention in the injection chamber does not occur. Therefore, it is possible to improve the molding quality of the pre-plastic injection molding machine without causing problems such as hardening and deterioration of the material due to the retention of the material in the heating atmosphere and generation of gas.

[Brief description of drawings]

1 to 3 are views showing an embodiment of the present invention,
1 is an overall cross-sectional view, FIG. 2 is a partially enlarged cross-sectional view showing an operation of a main part, and FIG. 3 is a view similar to FIG. 2 in an apparatus of a mode different from FIG. 4 and 5 are views showing a conventional device, FIG. 4 is an overall cross-sectional view, and FIG. 5 is a partially enlarged cross-sectional view showing the behavior of the material. In the figure, 3: screw (kneading device), 4: plasticizing chamber, 7: hydraulic motor (rotating means) 23: (injection) plunger, 24: injection chamber, 26: (injection) cylinder 27: nozzle, 29: Control device, 30: Electromagnetic flow control valve 33: Passage, 34: (Plasticization chamber side) opening 35: (Injection chamber side) opening

Claims (2)

[Claims] 1. A plasticizing chamber (4) equipped with a kneading device (3).
And an injection chamber (2) in which the injection plunger (23) is fitted and the molten resin is accumulated and measured in front of the injection plunger (23).
In a pre-plastic injection molding machine equipped with 4) and
Rotating means (7) for rotationally driving the screw (3) inserted into the plasticizing chamber (4), a drive device (8) for axially advancing the screw (3), and the injection chamber (24). (27) having a nozzle hole that opens in the center of the front wall of the injection chamber and injects the molten material in the injection chamber toward the cavity by the operation of the plunger (23), and the plasticizing chamber (4) at one end
An injection chamber side opening (35) having a plasticizing chamber side opening (34) that opens on the axis of the screw (3) at the tip and an opening at the front end of the injection chamber (24) at the other end. And a passage (33) that directly communicates these openings with a smooth hole having a substantially constant diameter, and the injection chamber (2
Driving means (26), (30) for driving a plunger (23) slidably movable to 4) and the driving means (26), (30)
And a control device (29) for giving a command to the rotating means for driving the rotating means at a position where the screw (3) is retracted during the plasticizing step to melt the molten material into the plasticizing chamber side opening (34).
Through the passageway (33) into the injection chamber (24), and during the injection process, the drive device is operated with the rotating means stopped to advance the screw (3) to move the plasticizer. A pre-plasticizer characterized in that the opening (34) on the side of the oxidization chamber is closed, and the plungers (23) are slightly retracted by actuating the driving means (26), (30) immediately before starting the plasticizing step again. Injection molding machine. 2. The control device (29) comprises the drive means (2).
6. The pre-plastic injection molding machine according to claim 1, wherein the rotating means (7) and the driving device (8) are controlled while commands 6) and (30) are given and controlled.