JPH0397517A - Preplastication type injection molding machine - Google Patents

Abstract

PURPOSE:To completely inject a material remaining in an injection chamber therefrom in the subsequent operation of injection by allowing a material newly supplied from a plasticizing chamber into the injection chamber to be flowed in the rear of the material that has remained in the injection chamber at the time of the preceding injection stroke. CONSTITUTION:The injection chamber side opening 35 a passage 33 is opened to a position confronting to a space i.e. a space defined between a material 20a remaining in the top end part of an injection chamber 24 and an injection plunger 23, or to a portion where the packed material becomes sparse, due to the forcibly backward movement of the injection plunger 23. Further, the injection plunger 23 is pushed back by the material 20b the material 20b fed into the space to be moved backward up to a predetermined position, and after the measurement of the supplied material is finished and then a shut-off valve 31 is opened, said material is injected. A kneading screw 3 advances just prior to an injection stroke to close the passage 33 prevents the back-flow of the material.

Description

[Detailed Description of the Invention] <<Industrial Application Field>> The present invention independently comprises a plasticizing chamber equipped with a kneading device such as a screw and an injection chamber equipped with an injection plunger, and the kneading process is performed in the plasticizing chamber. This invention relates to a so-called Pribra type injection molding machine, which has a structure in which the material is transferred to an injection chamber through a passage communicating with the chamber, and the material is injected into a large cavity with an injection plunger.

<<Prior Art>> Injection molding machines are widely used for shaping plastic parts. The injection molding machine currently in use is a so-called in-line screw type in which the plasticizing chamber and the injection chamber are integrated, and its structure is simple and convenient for shaping general resins. However, synthetic resins and composite materials with special properties,
When injection molding materials such as new ceramics, more stable plasticization and higher injection pressure are required depending on the material. With in-line screw type, the plasticizing chamber and injection chamber are shared, so it is necessary to perform both plasticization and injection with one screw, and a check valve is attached to the screw. There were problems such as rapid wear and inability to obtain high injection pressure. Therefore, for such materials, it is convenient to use a blibra type in which the plasticizing chamber and the injection chamber are separated. Bribra type injection molding machines have been known for a long time.
In the conventional pre-plastic injection molding machine, as shown in FIG. 4, an opening 35 on the injection chamber 24 side of a passage 33 that communicates the plasticizing chamber 4 and the injection chamber 24 is connected to the injection plunger 23 when it is at the forward limit. It opens further forward (on the nozzle 27 side) than the position, and a check valve 37 is provided in the opening or in the middle of the passage to prevent the material in the injection chamber 24 from flowing back into the plasticizing chamber 4 during the injection process. are doing.

As is well known, the mechanical energy generated by the rotation of the kneading screw 3 built into the plasticizing chamber 4 and the thermal energy from the band heater 5 wrapped around the casing 2 of the plasticizing chamber flow into the plasticizing chamber from the hopper 6. The material is melted and kneaded in the plasticizing chamber 4, sent forward by the conveying force of the kneading screw 3, and sent to the injection chamber 24 through the passage 33. The injection plunger 23 retreats due to the pressure of the material being fed, so after measuring the material by controlling the stroke of the plunger 23, the injection plunger 23 is moved back by the thrust of the injection cylinder 26 connected to the rear end of the injection plunger 23. is advanced to fill a molding cavity (not shown) with material.

<<Problem to be Solved by the Invention> Even when the injection plunger 23 is at the forward limit position, the material 20a remains at the tip of the injection chamber 24, and it is impossible to reduce this to zero. Even if material remains inside the device,
If all of the remaining material is injected in the next injection process, no problem will occur. However, in conventional devices, as shown in Figure 5, there is a time when a portion of the remaining material 20c remains uninjected for a long time. Problems such as deterioration, deterioration, and gas generation occur. Furthermore, since the previous material 20c remains at the tip of the injection chamber 24 for a long time when changing materials, a problem arises in that a large number of defective products are produced when changing materials.

(Means for Solving the Problems) The Pribula injection molding machine of the present invention has an injection plunger 2
drive means 28, 30 for forcibly retracting the injection plunger 23; and the drive means 28, 30 for forcibly retracting the injection plunger 23 after the injection process ends and before starting the plasticization metering process, so as to slightly retract the injection plunger 23 to create a cavity 36 at its tip. 30, and a control device 29 that gives a drive command to the injection chamber side opening 3 of the passage 33.
Reference numeral 5 denotes the material 20a remaining in the void, that is, the tip of the injection chamber 24 due to the forced retreat of the injection plunger 23.
It opens at a position facing the space formed between the injection plunger 23 and the part where the filling of the material is rough. That is, the opening 35 of the passage 33 on the injection chamber side is connected to the space 36.
The apparatus of the present invention operates in a manner similar to that of a conventional BRIBRA injection molding machine. Similarly, after the injection process has ended and before the transfer of the next material from the plasticizing chamber 4 to the injection chamber 24, the injection plunger 23 is forced, i.e. due to the pressure of the material 20 being fed. The difference is that it is driven by the drive devices 28 and 30 instead of by itself, and performs a slight backward movement.

In the conventional device, the injection chamber side opening 35 of the passage opened further forward than the injection plunger 23 when it was at the forward limit, so as shown in FIG. 5, the injection chamber was newly opened after the injection process. The material 20b fed into the injection chamber 24 is pushed in between the remaining materials 20a, and the material 20c remaining on the side of the injection plunger 23 from this pushing position is not fed out from that part forever, so the tip of the injection chamber 24 However, in the apparatus of the present invention having the above configuration, a new injection chamber 2 is added after the injection process.
The material 20b fed into the remaining material 20a
The material 20a remaining from the previous time is located closer to the nozzle 27 than the newly fed material 20b, so that
The material is completely injected during the next injection, and the material does not remain in the injection chamber 24 for a long time.

《Example》 Figures 1 to 3 are diagrams showing examples of the present invention, which are the most common screw libra type, and show an embodiment in which the injection nozzle is provided with a shunt-off valve. It is a diagram.

In the figure, l is a plasticizing section, which includes a plasticizing casing 2, a kneading screw 3 installed therein, a casing 2 and a screw 3.
It is equipped with a plasticizing chamber 4 partitioned into sections, a band heater 5 wrapped around a casing 2, a hopper 6 for supplying material, and a hydraulic motor 7 for rotating a screw 3. These structures and functions, except for the parts described below,
There is nothing particularly different from the conventional one.

8 is a hydraulic cylinder for advancing and retracting the kneading screw 3, and 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 which is slidably but unrotatably mounted on the guide bin 10 in the axial direction, and the kneading screw 3 is attached to the piston 9 with a bearing 14
, 15 is connected to the output shaft 12 of the hydraulic motor 7 via a connecting shaft l3 supported by the hydraulic motor 7. Therefore, the hydraulic cylinder 8
When pressure oil is supplied from the hydraulic supply port 16 or 17, the kneading screw 3 and the hydraulic motor 7 move forward or backward in the axial direction. Also, when the kneading screw 3 rotates, the connecting shaft 1
3 rotates, but piston 9 does not rotate. 2l is an injection section, which includes an injection casing 22, an injection plunger 23 fitted in the casing, an injection chamber 24 defined by the casing 22 and the plunger 23, and the casing 2.
Band heater 25 and injection plunger 23 wrapped around 2
It is equipped with an injection cylinder 26 for advancing the material, and a nozzle 27 for introducing the material to be injected into a certain type of cavity (not shown). These structures and functions are not particularly different from those of conventional devices except for the points described below.

The injection cylinder 26 is provided with a rond side chamber 28, and by supplying pressure oil to this rond side chamber, the injection plunger 23 can be forced to retreat. Pressure oil is supplied to the rond side chamber 28 via a solenoid valve 30 that is opened and closed according to commands from the control device 29, and the timing for supplying pressure oil to the rond side chamber 28 is determined when the injection process ends and the injection plunger 23 reaches the forward limit,
After the injection plunger 23 waits at its forward limit for a predetermined period of time, that is, maintains pressure, before the kneading screw 3 starts rotating to transfer the next material to the injection chamber 24.

The nozzle 27 is provided with a shaft off valve 31. This shunt-off valve is naturally open during the injection process, and is closed immediately before the injection plunger 23 starts the forcible retraction operation. This closed state is maintained until the injection plunger 23 reaches its retraction limit, that is, until the plasticization metering process for the next injection is completed. This valve 31 prevents the material from flowing back from the nozzle 27 when the injection plunger 23 is forcibly retracted, and such a valve 31 is provided when the fluidity of the material is high. is desirable.

A passage 33 communicates the plasticizing chamber 4 with the injection chamber 24, and the material plasticized and kneaded in the plasticizing chamber 4 is led to the injection chamber 24 through this passage 33.

The opening 34 of this passage 33 on the plasticizing chamber 4 side opens on the axis of the kneading screw 3 at the tip of the plasticizing chamber. A concave conical surface 34a that exactly contacts the convex conical surface 3a at the tip of the kneading screw 3 is formed in this opening. When pressure oil is supplied from the supply port 16 on the hydraulic motor side of the hydraulic cylinder 8, the kneading screw 3 moves forward, and the convex conical surface 3a at the tip thereof is pressed against the concave conical surface 34a at the opening of the passage 33. Passage 33 is closed.

The opening 35 of the passage 33 on the side of the injection chamber 24 is located at a position immediately in front of the tip of the injection plunger 23 when the injection plunger 23 reaches its forward limit, as shown in FIG. The injection plunger 23 is provided at a position where at least a portion of the space 36 created by the retreat is opened (the one in FIG. 3 is an example where the entire space is open). It will be done.

2 and 3 (a) show the state immediately after the injection process, and (b) of the same figure shows the injection plunger 2.
This figure shows the situation immediately after the next plasticizing and metering process has started after No. 3 has been forcibly retreated. When the injection process is completed, the injection plunger 23 is at its forward limit.

Before starting the plasticization metering process, the shaft off valve 3
1 is closed, pressure oil is supplied to the rond side chamber 28 of the injection cylinder 23, and the injection plunger 23 is slightly (several mm) retracted. Since the material 20 such as molten resin has a certain degree of viscosity, the material 20a remaining at the tip of the injection chamber 24 during the previous injection process is retained on the nozzle 27 side of the injection chamber 24.
A cavity 36 is formed at the tip of the injection plunger 23 by the above-described retraction operation. The amount of retreat at this time is small, and the next plasticizing process starts immediately and the material is supplied, so
The effect of negative pressure generation is instantaneous and causes no problems, and air entrainment does not occur at all. In the structure shown in Figure 2, passage 3
3 opens into the injection chamber 24 from the beginning, and in the structure shown in FIG. 3, the passage 33 opens into the injection chamber 24 when the injection plunger 23 is retreated.
When the plasticizing metering process is started after slightly retracting, material is supplied from the plasticizing chamber 4 to the injection chamber 24. This material 2ob newly flowing into the injection chamber 24 enters the cavity 36 formed by the retreating movement of the injection plunger 23. Then, the injection plunger 23 is pushed by the further fed material 20b and retreated to a predetermined position to complete metering of the material, after which the shaft off valve 31 is opened and the material is injected. The kneading screw 3 advances immediately before the injection process to close the passage 33 and prevent backflow of the material. The structure in which the passage 33 is closed by the advance of the shaft 7} off valve 31 and the kneading screw 3 in the above embodiment is unique to the embodiment, and the presence or absence of these does not limit the present invention. For example, if the tip of the nozzle 27 is pressed against a mold (not shown) and the next plasticization is performed after the gate sealing of the bottom-shaped product is completed, there is no need to provide a shutoff valve in the nozzle, and the passage 33 Backflow of material can also be prevented by providing a shaft-off valve or check valve in the passageway. Furthermore, in the above explanation, the most common hydraulically driven screw type was described, but it goes without saying that devices equipped with a plunger type plasticizing device or an electric drive device are also included in the present invention. be.

<<Effects of the Invention>> As explained above, according to the apparatus of the present invention, the material newly supplied from the plasticizing chamber to the injection chamber flows behind the material remaining in the injection chamber during the previous injection process. Therefore, the remaining material is swept away from the injection chamber by the next injection operation, and the problem of material retention in the injection chamber does not occur. Therefore, problems such as hardening and deterioration of the material and generation of gas due to material retention in the heated atmosphere do not occur, and materials can be quickly replaced.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing embodiments of this invention,
FIG. 1 is an overall sectional view, FIG. 2 is a partially enlarged sectional view showing the operation of essential parts, and FIG. 3 is a view similar to FIG. 2 in a different aspect of the apparatus from FIG. 2. 4 and 5 are diagrams showing a conventional device, with FIG. 4 being an overall sectional view and FIG. 5 being a partially enlarged sectional view showing the behavior of materials. In the figure,

Claims (2)

[Claims] (1) A plasticizing chamber (4) equipped with a kneading device (3) and an injection chamber (24) equipped with an injection plunger (23) are provided separately, and the plasticizing chamber (4) is connected to the injection chamber (24) equipped with an injection plunger (23). ) In an injection molding machine equipped with a passageway (33) for transferring material to
Driving means (28), (30) for forcibly retracting the injection plunger (23), and driving means (28), (30) for forcibly retracting the injection plunger (23), and a hollow space ( a control device (29) that gives a drive command to the drive means (28), (30) so as to cause the drive means (28), (36)
), wherein an injection chamber side opening (35) of the passageway (33) opens at a position facing the cavity (36). (2) The injection chamber side opening (35) of the passage (33) is
When the injection plunger (23) is at its forward limit, part or all of the opening (35) is closed to the injection plunger (23).
23) The pre-plastic injection molding machine according to claim 1, characterized in that the opening is in a position that is closed by itself.