JPH10663A - Reverse flow preventing apparatus for preplasticating injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent reverse flow of molten resin from an injection cylinder side to a plasticizing cylinder side in a preplasticating injection molding machine. SOLUTION: A valve chamber 16 is provided between a connecting passage 7a of a plasticizing cylinder side and a connecting passage 7b of an injection cylinder side. A sphere 12 is placed in the chamber 16. A push bar 13 is disposed oppositely to the sphere 12 to urge it to a seat 23 surface. A base end side of the bar 13 is extended out of the chamber 16, and urged toward the seat 23 surface by a spring 22. A guide 17 for receiving the sphere 12 is provided at an end of the bar 13, and a release hole 18 for preventing sealing of resin is provided. The sphere 12 is attachably and detachably supported by the bar 13 constituted in this manner. Thus, the sphere 12 is extremely stably and effectively operated according to the flow and pressure of molten resin to effectively prevent its reverse flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-plasticization type injection molding machine in which a plasticizing cylinder and an injection cylinder are connected via a backflow prevention device. To a device for preventing backflow.

[0002]

2. Description of the Related Art In a pre-plastic injection molding machine, a molten resin plasticized by a plasticizing cylinder is stored in an injection cylinder, and when a predetermined amount of molten resin has been stored, the molten resin is injected from the injection cylinder into a mold. However, during this injection, the molten resin flows back from the injection cylinder side to the plasticizing cylinder side,
A slide or rotary on-off valve and a check valve using a sphere such as a steel ball are interposed in the middle of the connection path connecting the plasticizing cylinder and the injection cylinder.

[0003]

However, a slide or rotary on-off valve is inferior in sealability to a check valve using a sphere such as a steel ball and requires a drive device for opening and closing. However, there is a disadvantage that the device configuration becomes complicated. In addition, the conventional check valve is either simply rolling the sphere or pressing the sphere against the seat surface by a spring disposed in the molten resin, that is, in the connection path, so that the sphere is simply rolled. If only the injection speed is low, especially when the injection speed is low, a backflow occurs at the initial stage of injection, and the one provided with a spring in the connection path has a defect of causing malfunction due to the influence of the resin.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backflow prevention device for a pre-plastic injection molding machine for more reliably preventing the backflow of molten resin as described above.

[0005]

According to the present invention, there is provided a backflow prevention device for a pre-plastic injection molding machine in which a plasticizing cylinder and an injection cylinder are connected via a backflow prevention device. A valve chamber provided in the middle of a connection path for guiding the molten resin plasticized by the cylinder to the injection cylinder, a sphere placed in the valve chamber, and the valve chamber and the plasticizing cylinder forming a pair with the sphere. A seat surface formed between the sphere and the connection path on the side of the valve body, and the front end is located outside the valve chamber, with the sphere interposed therebetween such that the tip is in the valve chamber and the sphere is pressed against the seat surface. And a push rod movably provided in a direction of pressing the sphere toward the seat surface, and a spring disposed outside the valve chamber and pressing the push rod toward the seat surface, wherein the push rod comprises: Receiving the sphere at the tip It is those having a guide portion and relief hole or relief groove for enclosing prevention of resin.

[0006] With this configuration, in a state before the start of metering where the molten resin is not supplied from the plasticizing cylinder and the pressure in the injection cylinder is low, the sphere is held by the guide portion of the push rod. When the molten resin flows into the injection cylinder from the plasticizing cylinder by the start of the measurement, the sphere is separated from the sheet surface while being held by the guide portion at the tip of the push rod when the molten resin flows into the injection cylinder by the start of the measurement. When the resin is allowed to flow and the measurement is completed and the flow of the resin is stopped, the sphere is pressed again against the sheet surface by the push rod while being held by the guide portion.
The sphere is pressed against the sheet surface as it is by the resin flowing backward from the injection cylinder side to the plasticizing cylinder side. Therefore, reliable backflow prevention is performed. At the time of this injection, the push rod is pushed to the original end side by the pressure of the resin which is going to flow backward, and separates from the sphere. And wait for resumption of weighing. In this way, the sphere is operated stably and accurately by the push rod.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 shows a pre-plastic injection molding machine to which the present invention is applied, 1 is a plasticizing cylinder,
2 is a plasticizing screw, 3 is a hopper, 4 is an injection cylinder,
5 is an injection plunger, 6 is a nozzle, 7a and 7b are connection paths, and 8 is a heater, which plasticizes the raw resin P1 taken in from the hopper 3 in the plasticization cylinder 1 and connects the plasticized molten resin P2 to the connection path 7a. , 7b to the injection cylinder 4, and when a predetermined amount of the molten resin P2 is stored in the injection cylinder 4, the injection plunger 5 injects the molten resin P2 from the nozzle 6 into a mold (not shown). A backflow prevention device 10 according to the present invention is provided between the connection paths 7a and 7b.

FIG. 2 is an enlarged view of the backflow prevention device 10 according to the present invention. The device main body 9 provided between the plasticizing cylinder 1 and the injection cylinder 4 has a front end of a connection path 7a on the plasticizing cylinder side. Extend from left to right in FIG. On the extension of the connection path 7a, a valve chamber 1 described later is provided.
A hole 11 forming 6 is provided. The hole 11 has a circular cross section having a diameter larger than the inner diameter of the connection path 7a, and a sphere 12 made of a steel ball or the like is placed in the hole 11. In FIG. 2, a distal end of a push rod 13 is inserted into the hole 11 from the right side, and a large diameter portion 14 slidably engaged with the inner peripheral surface of the hole 11 is inserted into the distal end of the push rod 13. Provided, large diameter part 1
4, a valve chamber 16 is formed on the left side.

A small-diameter projection 15 is provided at the tip of the large-diameter portion 14, and a concave-spherical guide 17 for receiving the sphere 12 is formed at the tip of the projection 15. The guide portion 17 has an escape hole 18 extending from the center thereof to the peripheral surface of the small-diameter projection 15. This escape hole 18
This is for releasing the resin between the sphere 12 when the sphere 12 enters the guide portion 17 and for guiding the resin between the sphere 12 when the sphere 12 separates from the guide portion 17. The clearance hole 18 may be a clearance groove provided along the concave spherical surface of the guide portion 17 and opened on the outer peripheral portion.

A rod portion 19 on the base end side of the push rod 13 is slidably engaged with a cap 20 attached to the apparatus main body 9, and a front end surface of the cap 20 receives a rear end surface of the large diameter portion 14. With this, the retreat limit position of the push rod 13 is determined. A spring receiver 21 is provided at the base end of the rod portion 19, and a spring 22 for pressing the push rod 13 leftward in FIG.

The connection between the connection path 7a and the valve chamber 16 includes:
A seat surface 23 for receiving the sphere 12 is formed, and a connection path 7b on the injection cylinder side extends from the valve chamber 16 at a substantially right angle to the connection path 7a on the plasticizing cylinder side.

Next, the operation of the present apparatus will be described. Before the start of the metering, the plasticizing screw 2 has stopped rotating, the molten resin P2 is not sent out to the connection path 7a, and the force for moving the injection plunger 5 is zero or a small value for the metering. . Therefore, in the state before the start of the weighing, the pressures in the connection paths 7a and 7b and the valve chamber 16 are all low, and the sphere 12 and the push rod 13 are pushed out to the seat surface 23 side by the spring 22 as shown in FIG. Then, the sphere 12 is placed in close contact with the sealing surface 23.

In this state, the plasticizing screw 2 is rotated, and when the measuring process is started, the plasticizing cylinder 1 is connected to the connecting passage 7.
The molten resin P2 is sent out to a. The molten resin P2 sent out to the connection path 7a is converted into a sphere 1 by the sending pressure.
As shown in FIG. 3, the push rod 2 and the push rod 13 are retracted against the spring 22 and flow into the valve chamber 16. The molten resin that has flowed into the valve chamber 16 is sent from the connection path 7 b to the injection cylinder 4 and stored in the injection cylinder 4.

When the injection plunger 5 retreats by a predetermined amount due to the inflow of the molten resin P2 into the injection cylinder 4, and the metering process is completed, the rotation of the plasticizing screw 2 is stopped. At this time, since the force for advancing the injection plunger 5 is still small, the push rod 13 is pushed out by the spring 22 and
The sphere 12 held by the guide portion 17 is pressed against the sealing surface 23 again.

Next, the injection plunger 5 is advanced to inject the molten resin P2 stored in the injection cylinder 4 from the nozzle 6 into a mold (not shown). In this injection step, the pressure of the molten resin P2 in the injection cylinder 4 increases due to the advance of the injection plunger 5, and the resin P2 tends to flow back to the plasticizing cylinder 1 via the connection path 7b, the valve chamber 16 and the connection path 7a. At this time, since the sphere 12 is pressed against the sheet surface 23 by the push rod 13 as described above, the backflow is reliably prevented.

The push rod 13 retreats to the retreat limit position due to a rise in the pressure in the valve chamber 16, as shown in FIG. At this time, since the molten resin in the valve chamber 16 flows through the escape hole 18 between the sphere 12 and the guide portion 17, the sphere 12 and the guide portion 17 are separated very easily, and the push rod 13 is smoothly retracted. The retraction of the push rod 13 causes the large diameter portion 14 to pass through the gap between the outer periphery of the large diameter portion 14 and the inner surface of the hole 11 shown in FIG.
The molten resin that has entered the rear chamber 24 is returned to the valve chamber 16 through the same gap, and thereafter, the rear end face of the large diameter portion 14 is pressed against the tip of the cap 20 by the injection pressure acting on the valve chamber 16. This prevents the molten resin from flowing out of the gap between the cap 20 and the rod portion 19 of the push rod 13.

When the injection step and the subsequent pressure-holding step are completed and the force for advancing the injection plunger 5 becomes zero or small, the push rod 13 advances again by the spring 22 and the guide part 17 engages the sphere 12. To return to the initial state shown in FIG. 2, and waits for the start of the next measuring step. At this time, the engagement between the guide portion 17 and the sphere 12 is performed smoothly because the resin between them is discharged from the escape hole 18.

[0018]

As described above, the backflow prevention device of the pre-plastic injection molding machine of the present invention does not require a drive device for opening / closing such as a slide-type or rotary-type on-off valve. Interaction with the push rod causes the sphere to prevent the flow of the molten resin from flowing and pressure extremely stably and accurately, thereby reliably preventing the backflow of the molten resin from the injection cylinder side to the plasticizing cylinder side. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a pre-plastic injection molding machine to which the present invention is applied.

FIG. 2 is an enlarged cross-sectional view of a backflow prevention device portion along the line AA in FIG. 1;

FIG. 3 is a cross-sectional view showing a state of the device shown in FIG. 2 during a weighing process.

FIG. 4 is a sectional view showing a state of the apparatus shown in FIG. 2 during an injection step.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasticizing cylinder 2 Plasticizing screw 4 Injection cylinder 5 Injection plunger 7a, 7b Connection path 10 Backflow prevention device 12 Sphere 13 Push rod 14 Large diameter part 15 Projection part 16 Valve chamber 17 Guide part 18 Relief hole 20 Cap 22 Spring 23 Seal surface

Claims (1)

[Claims] 1. A backflow prevention device of a pre-plastic injection molding machine in which a plasticizing cylinder and an injection cylinder are connected via a backflow prevention device, wherein a connection for guiding a molten resin plasticized by the plasticizing cylinder to the injection cylinder. A valve chamber provided in the middle of the path, a sphere placed in the valve chamber, a seat surface formed in a pair with the sphere and formed between the valve chamber and a connection path on the plasticizing cylinder side, The sphere is opposed to the seat surface with the sphere positioned therebetween so as to press the sphere against the seat surface so that the sphere is pressed against the seat surface, and the base end extends out of the valve chamber and moves in the direction of pressing the sphere toward the seat surface. A push rod provided freely, and a spring disposed outside the valve chamber and pressing the push rod toward a seat surface, wherein the push rod has a guide portion for receiving the sphere at a tip thereof and a resin for preventing encapsulation of resin. Escape hole or A backflow prevention device for a pre-plastic injection molding machine having a relief groove.