JPH0471815A - Check valve for resin molded screw - Google Patents

Abstract

PURPOSE:To obtain many advantages such as longer effective length of a screw, remarkable improvement of kneading properties and the like by a method wherein a check valve is tiltably provided with hinges between screw flights at the axial tip of a screw main body. CONSTITUTION:A check valve 16 is tiltably connected with hinges at its lower end to a screw main body 22, and tilts to the direction opposite to the direction of rotation of a screw as the screw rotates at metering and stands upright by the backward pressing force developed by the advancement of the screw main body 22 at injection. Accordingly, at the metering, the clearance between the check valve 16 and a heating cylinder 1 becomes larger, resulting in smoothly flowing molten resin. At the injection, larger flow resistance develops when the resin flows backwards or from a screw head 23 side to the screw main body 22 side, resulting in allowing to realize rapid checking.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The object of the present invention is to quickly and reliably perform a check operation of a check mechanism at the start of an injection operation.

[Conventional technology]

FIG. 4 shows a longitudinal section of the main part of the most common conventional check ring.

In FIG. 4, the check ring 5 is attached to the shaft 4 in a small diameter assembly with the screw spatula 3 fixed to the front end of the screw body 2.
A cylindrical check ring 5 is fitted loosely into the heating cylinder 1 with an outer diameter that can prevent leakage of molten resin between the heating cylinder 1 and the heating cylinder 1, and is fitted so as to be slidable in the front and rear directions. When assembled, a direct communication path 7 is provided between the inner circumferential surface of the retaining ring 5 and the circumferential surface of the shaft 4, so that the molten resin can flow from the screw body 2 side to the front of the screw head 3. ing.

In addition, protrusions 1 are provided at predetermined intervals on the front end surface 9 of the check ring 5.
Several zeros are provided so that even if the reverse ring 5 is pressed against the screw hend 3, the communication path 7 will not be blocked.

The opening of the communication path 7 in the rear end surface 11 of the check ring 5 is arranged so that its entire area faces the screw front surface 12 of the screw body 2, so that the rear end surface 11 of the check ring 5 is in contact with the screw front surface 12. In some cases, it becomes completely occluded.

When the molten resin is plasticized and metered backwards (hereinafter referred to simply as metering backwards), the check ring 5 is pressed forward by the flow resistance of the molten resin, and the rear communication port 13, the communication path 7, and the front communication port are 14 and is pushed out to the front of the screw head 3.

At the time of injection, the screw body 2 and the screw head 3 move forward together, while only the check ring 5 remains to close the rear communication port 13 and prevent the molten resin from flowing back.

[Problems to be Solved by the Invention] However, in reality, when the viscosity of the molten resin is low or the injection speed is slow, the degree of backflow of the molten resin increases until the rear communication port 13 is closed. This will cause variations in the injection amount.

For this reason, if the backflow of molten resin results in insufficient metering and filling, or if the backflow of molten resin is measured in anticipation of the backflow of molten resin, overfilling may result in defective products, and the mold may become stiff due to overfilling. There was a serious drawback that it caused damage.

As a means to eliminate these inconveniences, check ring 5
There are measures to reduce the fitting gap between the outer circumferential surface of the heating cylinder 1 and the inner circumferential surface of the heating cylinder 1, and to reduce the operating stroke of the check ring 5, but the former prevents galling and the latter prevents the resin from forming. The flow path was narrow (and the measurement time increased due to the increase in flow resistance), so there was a limit and it could not be an essential solution.

[Means for Solving the Problems] In order to solve these problems, a screw groove in the front end of the screw body, which is rotatably installed in the heating cylinder and can move forward and backward, is fitted. Therefore, a check valve that prevents the backflow of resin is arranged in a freely tiltable manner.

6 Effects] The check valve is provided with a hinge between the screw flights at the tip of the screw body in the axial direction so that it can be tilted freely, which increases the effective length of the screw and greatly improves crosstalk. It has the following advantages.

〔Example〕

1 to 3 show one embodiment of a check valve for a screw for resin molding according to the present invention, FIG. 1 is a longitudinal cross-sectional view of the front part of an injection device, and FIG. The configuration is shown, FIG. 2(a) is a front view, FIG. 2(b) is a plan view, and FIG. 2(C)
is a sectional view taken from A-A in Figure 2(a), Figure 3 shows the state of the check valve, Figure 3(a) is during measurement, Figure 3(b) is
indicates the time of injection.

The present invention provides a screw head 23 at the front end of a straight rod-shaped screw body 22 which is rotatably assembled to the heating cylinder 1 and is movable forward and backward, and has a screw flight Is on its circumferential surface.
is installed.

The terminal groove portion 17 of the screw body 22 has the screw body 2
A check valve 16 is provided in the axial direction of 2.

The present invention has a configuration having three major features.

(1) Screw flight 1 at the tip of the screw body 22
A check valve 16 is provided using the groove 17 between the screw head 23 and the screw body 2, as in the conventional case.
The effective length of the screw can be longer than that in which a check ring 5 is provided between the tips of the two screws.

(2) The lower end of the check valve 16 is rotatably connected to the screw body 22 via a hinge.

During metering, the check valve 16 tilts in the opposite direction to the rotational direction as the screw rotates, and during injection, the check valve 16 stands up due to the backward pressing force of the screw body 22 as the screw body 22 moves forward. Therefore, backflow of the molten resin into the groove portion 17 can be completely prevented.

(3) As shown in Fig. 3(a), the check valve 16 is tilted during metering, and the groove of the screw body 17 is carved and deepened (as shown in Fig. 3). (Side A), it is susceptible to flow resistance due to backflow of molten resin when switching from metering to injection.

By using the check mechanism having the configuration (1) or 3) described above, the back pressure against the injection pressure of the molten resin acts on the check valve 16 during injection, so the check valve 16 quickly closes ( It stands up and presses against the engraved screw body 24, achieving a quick check.

In the present invention, although not shown, the screw head 23 is screwed into the screw body 22.
3, the protrusion 16b of the check valve and the screw body 22 are connected rearward from the end of the screw body 22 by an insertion shaft (not shown), and the check valve 16 body is It is rotatably supported by a shaft 16a.

The tilting angle θ of the check valve 16 varies depending on the viscosity of the molten resin. Usually, when the viscosity is small, the tip of the check valve 16 and the heating cylinder 1 are The gap α between the inner walls may be small.

This means that when changing from metering to injection, the check valve 16 quickly stands up in a short time due to the back pressure of extrusion pressure caused by the backflow of resin, closes the check valve 16, and moves the screw body 22 toward the tip. This is due to the fact that backflow of resin toward the rear end must be completely prevented.

On the other hand, when the viscosity is large, the gap α between the tip of the check valve 16 and the inner wall of the heating cylinder 1 increases when the check valve 16 is tilted.
It is necessary to make the flow resistance as small as possible by increasing it.

As mentioned above, since the gap between the check valve 16 and the heating cylinder 1 can be made large during metering, the molten resin can easily flow smoothly, and during injection there is a large flow resistance when it flows backward from the screw head 23 side to the screw body 22 side. As a result, quick check can be achieved.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, the screw body engages with the screw groove at the front end of the screw body, which is rotatably installed in the heating cylinder so that it can move forward and backward, so that the resin can flow backward. The structure is simple, with a check valve that can be tilted freely, making it easy to change colors and materials. Also, during injection, it is susceptible to flow resistance of molten resin and back pressure from injection pressure. Therefore, backflow of resin can be quickly and completely prevented.

Furthermore, the effective length of the screw becomes longer, and the crosstalk property is greatly improved.

[Brief explanation of the drawing]

1 to 3 show one embodiment of a check valve for a screw for resin molding according to the present invention, FIG. 1 is a sectional view of the front joint of an injection device, and FIG. The configuration is shown, FIG. 2(a) is a front view, FIG. 2(b) is a plan view, and FIG. 2(C)
is a cross-sectional view taken from A-A in Fig. 2(a), Fig. 3 shows the state of the check valve, Fig. 3(a) shows the state of the check valve, and Fig. 3(b) shows the state of the check valve.
4 shows the state at the time of injection, and FIG. 4 shows a reduced cross section of the main part of the most common conventional check ring. 1...Heating tube, 2.22...Screw body, 3,2
3...Screw head, 5...Check ring, 15.
...Screw light, 16...Check valve, 17...
Screw groove, θ...Tilting angle of check valve, α...Gap. Figure 1

Claims (1)

[Claims] A check valve is rotatably installed in the heating cylinder and prevents the backflow of resin by engaging with the screw groove at the front end of the screw body, which is rotatably installed in the heating cylinder so that it can move forward and backward. Characteristic check valve for resin molded screws.