JPH0564831A - Back current preventive method and device for injection molding machine - Google Patents

Abstract

PURPOSE:To prevent a back current of molten plastic in an injection stroke, by a method wherein a sealing part of a back current preventive device is stuck beforehand by magnetic force after completion of a plasticization stroke. CONSTITUTION:The title device is constituted of a screw 2 and screw head 3 comprised of a ferromagnetic substance, a press metal 5 comprised of a nonmagnetic material incorporated into a space between the screw 2 and screw head 3, a permanent magnet 6 and a back current preventive ring 4 incorporated between the screw head 3 and press metal 5 so that the same may freely move between the screw head 3 and press metal 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention of an injection molding machine. Even if the screw does not advance by the floating stroke of the backflow prevention ring in the early stage of the injection stroke, the backflow prevention device seals in advance. The purpose is to bring the parts into close contact with each other to prevent backflow of the molten plastic during the injection process.

[0002]

2. Description of the Related Art In a conventional backflow prevention device for an injection molding machine, as shown in FIG. 4, the oscilloscope 5 is made of a single material and has no permanent magnet. In the plasticizing process, the backflow prevention ring 4 is pushed forward by the propulsive force via the molten plastic due to the rotational movement of the screw 2. The backflow prevention ring 4 that has moved forward stops when the claw 4a hits the screw head 3. The molten plastic consists of a cylinder 1, a screw 2, a rod 5,
It is pushed forward through the screw head 3, the backflow prevention ring 4, and the claw 4a. When the injection stroke starts, the screw 2 advances to inject the molten plastic, but the backflow prevention ring 4 has a gap between it and the oscilloscope 5, and at the beginning of the injection stroke, the molten plastic Backflow cannot be prevented. Backflow is prevented when the screw 2 moves forward and the backflow prevention ring 4 and the oscilloscope 5 come into close contact with each other as shown in FIG.

[0003]

However, in the case of such a conventional backflow preventive apparatus for an injection molding machine, in the initial stage of the injection process, the backflow prevention ring 4 and the oscilloscope 5 are melted until they come into close contact with each other. The plastic flows backward, and in the molding operation, the amount of molten plastic to be filled in the mold cavity varies, and in the precision molding, the quality of the molded product varies. The present invention aims to solve such problems.

[0004]

According to the present invention, in the backflow prevention of an injection molding machine, after the plasticizing process is completed, the backflow prevention ring 4 and the oshigane 5 are brought into close contact with each other by a magnetic force. Screw 2 and screw head 3
And an oscilloscope 5 made of a non-magnetic material incorporated between the screw 2 and the screw head 3, a permanent magnet 6 installed in the oscilloscope 5, and floating between the screw head 3 and the oscilloscope 5. The above problem is solved by having the backflow prevention ring 4 made of a ferromagnetic material incorporated as described above.

[0005]

In the backflow prevention device of the present invention, after the plasticizing process is completed, the backflow prevention ring 4 and the oscilloscope 5 are in close contact with each other by the attractive force of the permanent magnet 6, so that the backflow rate of the molten plastic is minimized. Since the amount of molten plastic filled in the mold can always be kept constant, the precision molding stability is improved.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A backflow prevention device for an injection molding machine according to the present invention will be described in detail below with reference to the drawings. 1 and 2 are cross-sectional views showing the structure of the present invention, FIG. 1 showing an injection stroke, and FIG. 2 showing a plasticizing stroke.

As is apparent from this figure, in FIG. 1, the oscilloscope 5 is made of a non-magnetic material so that it can be smoothly removed during the plasticizing process, and protects the permanent magnet 6 made of a brittle material. Cover to do.
The screw 2 and the screw head 3 are integrated with each other by sandwiching the oscilloscope 5 and the permanent magnet 6 therebetween and screwing them together. Screw 2, cylinder 1, screw head 3,
The backflow prevention ring 4 is made of a ferromagnetic material, and as shown in FIG. 3, a magnetic circuit is formed by the parts of the cylinder 1, the screw 2, the screw head 3, the backflow prevention ring 4, the oscilloscope 5, and the permanent magnet 6. There is. In FIG.
When one of the permanent magnets 6 is the N pole, the magnetic flux lines act as shown by the dotted lines, and the backflow prevention ring 4 is attracted by the force f and is brought into close contact with the oscilloscope 5.

Next, the operation of the backflow prevention device of the injection molding machine thus configured will be described. In the plasticizing process, the molten plastic is pushed forward by the rotation of the screw 2 and is pushed forward. Therefore, the molten plastic moves the backflow prevention ring 4 forward by the force of the propulsive force F to form a gap between the molten plastic and the rod 5, and the molten plastic forms a gap between the backflow prevention ring 4 and the screw head 3. Furthermore, the screw head 3 and the claw 4
It is extruded toward the front of the screw head 3 through a space between a and a.

The backflow prevention ring 4 is about to be pressed against the rush 5 by the attraction force of the permanent magnet 6, but F> f
If the attraction force of the permanent magnet 6 is adjusted so that the backflow prevention ring 4 is always pushed forward during the plasticizing process,
A gap is formed between the welded rod 5 and the flow path for the molten plastic, and the molten plastic flow passage is maintained.

When the plasticizing process is completed, the molten plastic does not receive the propulsive force F of the screw 2, and is attracted to the oscilloscope 5 side by the attractive force f of the permanent magnet 6 and closes the flow path.

When the injection process is started from this state, the flow path is already closed, so that the backflow prevention ring 2 is provided as in the conventional case.
Molten plastic does not flow back until
The injection process can be started and the amount of molten plastic filled can be stabilized, which is effective for maintaining precision molding.

[0012]

As is apparent from the above description, the seal portion of the backflow prevention device according to the present invention is closely contacted with a magnetic force in advance to prevent the backflow of the molten plastic in the injection stroke, thereby filling the mold cavity. It is possible to stabilize the quantity, improve the accuracy of the variation in the weight of the molded product, help reduce molding defects, and improve the production.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of the present invention (during an injection process).

FIG. 2 is a sectional view showing the constitution of the present invention (during a plasticizing process).

FIG. 3 is a diagram showing a magnetic circuit.

FIG. 4 is a sectional view showing a conventional configuration.

[Explanation of symbols]

 1 ... ・ Cylinder 2 ・ ・ ・ ・ Screw 3 ・ ・ ・ ・ ・ ・ Screw head 4 ・ ・ ・ ・ Backflow prevention ring 4a ・ ・ ・ Claws 5 ・ ・ ・

Claims (2)

[Claims] 1. A method for preventing backflow of an injection molding machine, comprising the step of closely contacting the backflow prevention ring (4) and an oscilloscope (5) with a magnetic force after the completion of the plasticizing process in the backflow prevention of the injection molding machine. 2. A screw (2) and a screw head (3) made of a ferromagnetic material in a backflow prevention device of an injection molding machine.
And an oscilloscope (5) made of a non-magnetic material incorporated between the screw (2) and the screw head (3),
A permanent magnet (6) installed in the rod (5) and a backflow prevention ring (4) made of a ferromagnetic material incorporated so as to float between the screw head (3) and the rod (5). A backflow prevention device for an injection molding machine characterized by having.