JPS6357214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) The present invention relates to a screw head of an in-line screw injection molding machine and a method of operating a check valve using the screw.

(Prior Art) To explain the check valve, as shown in FIGS. 1 and 2, the check valve 10 has a screw 11.
A cylindrical screw having an inner diameter surface such that a sufficient gap 13 is formed between the small diameter portion 12a of the screw head 12 attached to the tip of the screw head 12, and attached to the conical portion 12b of the screw head 12 and the tip surface of the screw 11. It is fitted into the inner diameter surface of the heating cylinder 15 so as to be able to move back and forth in the axial direction between the spacers 14 by a predetermined interval. In addition, the claw 16 provided at the front end of the check valve 10 is connected to the conical portion 12b of the screw head.
The screw 11 and the check valve 10 are engaged with a recess 17 provided in the screw head so that the screw 11 and the check valve 10 rotate together. When the screw head comes into contact with the conical portion 12b of the screw head, a gap 18 is formed between the conical portion 12b of the screw head and the plurality of projections 10a, and a gap 13 is formed between the screw head small diameter portion 12a.
, the gap 18 , and the rear end surface B of the check valve 10 .
The gap S formed between the spacer 14 and the spacer 14 is connected to form a resin flow path.

With the above structure, when the screw 11 rotates during the plasticizing process, the resin material melted and transferred from upstream of the screw 11 pushes the check valve 10 forward (towards the left in the figure) and causes the screw head to move forward. As a result of contacting the conical portion 12b, the arrow a
The resin material flows through the resin flow path and accumulates in front of the screw head 12 as shown in FIG. Next, when a predetermined accumulated amount is measured, the plasticizing process ends, and the screw 11, which is at the retraction limit, moves forward (moves to the left in the figure) to inject the measured amount of resin material, and the check valve 10 closes to the screw head. The spacer 12 is pushed back by the resin accumulated in front of the spacer 12, and the gap S formed between the rear end surface B and the surface of the spacer 14 moves backward.
The resin passage is closed.

(Disadvantages of Prior Art) However, the operation of the check valve 10 to close the gap S during injection is very unstable, and varies depending on the frictional resistance with the inner diameter surface of the heating cylinder 15 or the viscosity of the resin. Especially when the gap S is large,
The closing action is unstable. Therefore, the unstable operation of the check valve 10 causes variations in the amount of resin injected, which affects the molded product.

(Structure of the Invention) The present invention allows the non-return valve to operate quickly even when the gap S between the non-return valve and the spacer, which is one of the unstable factors in the resin flow path closing operation of the non-return valve, is large, and the resin flow is prevented. It is an object of the present invention to provide a screw head that closes a flow passage and a method of operating a check valve using the screw head.

In order to operate the above-mentioned check valve, the present inventor has proposed that a concave portion provided in the screw head, which engages with a convex portion provided at the front end of the check valve, be inserted from the insertion opening of the convex portion of the check valve. The screw head is formed by slanting the side wall surface of the concave portion on the opposite side to the screw rotation direction with respect to the axis so that the width becomes narrower as the plasticizing process is completed. When the screw reaches an arbitrary retracted position, the discharge pressure is reduced by decreasing the screw rotation speed, and the check valve is moved toward the screw to close the resin passage or to a position on the verge of closing. The prevention valve operation method has been changed.

(Example) Next, an example of the present invention will be described with reference to FIG.

Components that are the same as the conventional example have the same configuration and operation as the conventional example, so they are given the same numbers and explanations will be omitted. Only the members used in the present invention will be described. 20 is a screw head and a convex portion at the front end of the check valve 10. A recess 21 with which the claw 16 engages is provided, and the side wall surface c of the recess 21 on the side opposite to the screw rotation direction b has an axis line that becomes narrower as it goes beyond the insertion side entrance of the claw 16. tilted against.

Since the screw head has the concave portion 21 constructed as described above, if the angle of inclination is θ with respect to the axis, the screw rotates in the direction of arrow b, and the pawl 16 hits the side wall surface c of the concave portion 21, and the rotational force _F1 causes the screw head to rotate in the direction of arrow b. A component force F ₂ is applied, and the check valve 10 is pushed backward (toward the spacer) by a force F ₂ due to screw rotation, or if the rotation speed is large and the discharge resin pressure is high, this force F ₂ can be overcome. The check valve 10 has been pushed forward. However, when the discharge pressure decreases by decreasing the rotational speed, the component force _F2 becomes larger and the balance that has been maintained until now is lost.
The check valve 10 closes the gap S or retreats to the point where it closes. Then comes the next step, the injection process.
When the screw moves forward, the gap S is zero or very narrow, so the resin passage is quickly closed, and the dispersion caused by the closing operation as in the prior art is eliminated, and the molded product does not become defective.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between a conventional screw head and a check valve. FIG. 2 is an axial cross-sectional view of FIG. 1. FIG. 3 is a diagram showing one embodiment of the present invention. 10...Return prevention valve, 11...Screw, 1
2, 20... Screw head, 13... Gap, 1
4...Spacer, 16...Claw, 17, 21...Recess.

Claims (1)

[Claims] 1. Provided between the screw tip and the screw head, during the plasticizing process, the molten resin path is opened and the molten resin passes to the screw head side, but during injection, it moves to the screw side and closes the resin path. A recess provided in the screw head that engages the protrusion provided on the front end of the screw head side of the check valve configured to have the same shape as that shown in FIG. A screw head characterized in that the side wall surface of the recess on the opposite side to the screw rotation direction is inclined with respect to the axis. 2. A recess provided in the screw head that engages the protrusion provided at the end of the screw head side of the check valve is moved in the direction of rotation of the screw so that it becomes a clamp as it goes from the insertion opening of the protrusion of the check valve. On the other hand, by using a screw head in which the side wall surface of the recess on the opposite side is inclined with respect to the axis, the discharge pressure can be reduced by reducing the screw rotation speed at any time immediately before the completion of the plasticizing process or when the screw is in the retracted position. A method for operating a check valve, comprising: closing the resin passage or moving the check valve toward the screw to a position on the verge of closing.