JPS60220724A - Preplasticizing apparatus - Google Patents

Abstract

PURPOSE:To prevent foaming gas from abnormal flow-in and shrinking in a preplasticizing apparatus for foam- or defoam- molding by providing a circular choked part for cutting off a resin passage at the back position of an extensible screw. CONSTITUTION:The preplasticizing apparatus 1 is provided with an extensible screw 12 and circular choked parts 15, 16 to cut off the resin passage. As the screw 12 is revolved, foaming gas is pressed in from the opening 13 to plasticize resin, the molten resin forced out to the front end of the heating cylinder 11 is pressed into the front part 24 of the plunger 22 through the nozzle device 3. Then, the screw 12 is put in a free state and backed by the reaction of the resin to position A, the resin passage is cut off by the circular choke parts 15, 16 and troubles due to the pressing of foaming gas are removed. Then, the valve 4 is backed and the plunger 22 is moved forward to position (b) to inject resin. Defoam molding also is executed in the same way as foam molding and shrinkage can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a pre-plasticizing device for a screw pre-plasticizing injection molding machine used for performing foam molding, degassing molding, etc. of synthetic resin.

Conventional technology A normal pre-plasticizing device is constructed by connecting a heating cylinder with a rotatable screw inside to the nozzle part of an injection device with a switching valve, and inside the heating cylinder there is an escape valve installed in the cylinder. The front section is divided into an extrusion section and the rear section is divided into an extrusion section and a plasticization section, with the opening for pressurizing air or gas as the boundary, and by operating the above-mentioned switching valve, the plasticized resin is measured in the injection device and transferred to the mold. It consists of a structure in which injection and filling are repeated in sequence.

Problems to be Solved by the Invention Plasticizing, extruding and stopping the resin in the pre-plasticizing device occur by rotating and stopping the screw. Further, the pressure in the molten resin in the heating cylinder is increased due to the rotation of the screw, and the pressure tends to equalize at the same time as the screw stops.

Therefore, the molten resin in the extrusion section and plasticization section easily flows into the vicinity of the opening, and in the case of foam molding, the foaming gas flows from the opening to the plasticization section, extrusion section, and even the tip of the screw. In the case of degassing molding, abnormal inflow occurs, and conversely, phenomena such as venting up from the opening occur, which not only makes molding unstable, but also makes it impossible to ensure foaming and degassing of the molded product. First, there was a drawback that it was difficult to obtain a molded product with good molding condition.

Means for Solving the Problems This invention attempts to solve the above-mentioned conventional problems by moving the screw forward and backward, and the structure is such that the rotatable screw inside the heating cylinder is further moved forward and backward. In addition, the screw is provided with an annular closing portion that blocks the resin path between the heating cylinder and the screw at two locations, the tip of the extrusion portion and the opening when the screw is in the retracted position.

Function In the pre-plasticizing device having the above configuration, the resin path between the heating cylinder and the screw is brought into communication by the forward movement of the screw, and when the screw is moved backward, the resin path is Tip of extrusion part and opening part 2
The molten resin in the resin path is divided into the extrusion section and the plasticization section and is in a sealed state, and the influence of the resin pressure on the opening where the pressure is lowest is reduced.

Example The present invention will be explained in detail below with reference to illustrated embodiments.

In the figure, 1 is a pre-plasticizing device, 2 is an injection device, 3 is a nozzle device, and the pre-plasticizing device 1 is located at the rear of this nozzle device 3.
Further, the injection devices 2 are connected to the front part at different positions. Further, inside the nozzle device 3, a switching pulp 4 is provided which alternately opens and closes the injection port side and the preliminary plasticizing device side, connected to the piston 6 of the hydraulic cylinder 5 provided at the rear end.

The preliminary plasticizing device 1 includes a heating cylinder 11, a screw 12 inside the heating cylinder 11, and a screw driving device 7 connected to the rear end of the heating cylinder. In addition, the front and rear parts of the heating cylinder 11 are divided into an extrusion part and a plasticizing part in relation to the screw 12, and an opening 13 for degassing or pressurizing foaming gas is provided between them. The inner side of the cylinder of the cylinder tip portion 14 where the portion 13 and the screw tip are located is formed into a recess.

The tip of the screw 12 and the portion located at the opening 14 form annular closing portions 15 and 16 that can separate and block the resin path from the extrusion portion and the plasticization portion. This screw 12 is housed inside the heating cylinder 11 so as to be able to move forward and backward, and its rear end is connected to the ram 8 of the screw drive device 7, and is rotated by a hydraulic or electric motor.
The hydraulically operated ram 8 moves forward and backward within the heating cylinder 11.

Next, the operation will be explained.

In FIG. 1, when injection and filling of molten resin is completed by the injection device 2, the switching pulp 4 of the nozzle device 3 closes the injection port side as shown in FIG. 2 by the operation of the hydraulic cylinder 5, and performs preliminary plasticization. A resin path is formed that connects the device 1 and the injection device 2 and extends between the heating cylinder 11 and the injection cylinder 21 .

Further, in the preplasticizing device 1, the screw drive device 7 is activated, and the ram 8 advances the screw 12 to the position of the position detector A. This forward movement causes the annular closure portions 15, 1
6 also moves, the resin path that was blocked at two locations, the tip 14 of the extrusion part and the opening 13, by the annular blocking parts 15 and 16 as shown in FIG. 1 is restored to the state shown in FIG. 2. Open.

Then, when the screw 12 is rotated by the motor 9, the resin in the material supply port 17 is plasticized by the plasticizing section and transferred to the opening 13. The opening 13 is degassed or a foaming gas is press-fitted, and the resin is further pushed out to the tip of the heating cylinder 11 by rotating the screw 120.

In addition, in the injection device 2, after injection and filling, the hydraulic pressure on the injection syringe n in the injection cylinder 21 is removed, and the injection syringe n moves back together with the injection piston n at the rear end. The extruded molten resin passes through the nozzle device 3, is pumped to the injection syringe B, and is moved backward to the position of the metering detector a, completing metering of the molten resin.

At the same time as this metering is completed, the injection plunger n is stopped, and the screw 12 is left in a free state and continues to rotate.
The screw 12 moves backward to the position detector B while being rotated by the resin pressure pumped to the cylinder tip, and the resin path is again blocked at two places, the extrusion part tip 14 and the opening 13, by the annular blocking parts 15 and 16. and stop.

When the screw 12 stops as described above, the switching pulp 4 of the nozzle device 3 moves backward to open the injection port side,
Close the connection port side with the pre-plasticizing device 1. Then, the injection piston n is operated again to advance the injection sylanger η to the position of the injection completion detector 1, and the molten resin measured in the front tube is injected and filled into the mold from the nozzle device 3.

While this injection filling is being performed, the molten resin on the heating cylinder 11 side is in a sealed state by blocking the resin path, and even if the resin pressure is equalized there, it will be between the extrusion section and the plasticization section. Since the pressure is generated separately, the influence on the opening 13 where the pressure is the lowest is extremely small.

In the example shown in Fig. 3, the screw diameter of the extrusion section is made larger than that of the plasticization section to facilitate degassing and foaming, and the inner diameter of the heating cylinder of the extrusion section is larger than that of the plasticization section. Therefore, since a resin passage is formed on the outer diameter of the closed part at the tip of the plasticizing part when the screw advances, the recess of the heating cylinder 11 can be omitted.

The embodiment shown in FIG. 4 is mainly used for degassing, and is a case in which a backflow ring 15a is used for the annular closing part 15 at the tip of the extrusion part, and in this case, when the screw is stopped, the annular closing part 15 is connected to the tip of the screw. The backflow ring 15a operates depending on the resin pressure balance, but more reliably,
The amount of retraction of the screw 12 is increased somewhat, and Suff 93120
It is preferable to advance the screw 12 slightly by hydraulic pressure after the rotation has stopped.

Effects of the Invention As described above, in this invention, the screw is provided with an annular closing portion, and the resin path between the heating cylinder and the screw can be blocked at two locations, at the tip of the extrusion portion and at the opening, by the backward movement of the screw. With this structure, the resin at the tip of the plasticizing section or the tip of the screw, which is under relatively high pressure during plasticizing extrusion, does not flow into the vicinity of the opening of the extruding section, where the pressure is relatively low. Conversely, the foaming agent injected into the extrusion section from the opening does not abnormally flow into the plasticization section or the screw tip, resulting in stable molding such as plasticization extrusion, and high quality foam molding. Further, even in degassing (venting) molding, there is an advantage that stable molding can be performed without venting up at the opening when stopping.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional plan view of an injection molding machine equipped with a pre-plasticizing device according to the present invention at the time of completion of injection, FIG. FIG. 7 is a partial cross-sectional view of another embodiment of the preplasticizing device. 1...Preliminary plasticizing device 2...Injection device 3...Nozzle device 11...Heating cylinder 12...Screw 13... ... Opening part 14 ... Cylinder tip 15 , 16 ... Annular closure part

Claims (1)

[Claims] It has a heating cylinder connected to the nozzle part of the injection device with a switching valve, and a rotatable screw inside the heating cylinder, and a degassing or foaming gas is provided between the heating cylinder extrusion part and the plasticizing part. In a pre-plasticizing device provided with an opening for injection, the screw is installed inside the heating cylinder so that it can move forward and backward, and when the screw is in the retracted position, the resin path between the heating cylinder and the screw is connected between the tip of the extrusion part and the opening. A pre-plasticizing device in which a screw is provided with an annular closing part that is closed at two places.