JPS6255115A - Injection apparatus - Google Patents

Abstract

PURPOSE:To make it possible to inject always the weighed resin without shortage, by setting a cylinder reducing the resin pressure of the metering zone in the injection cylinder, close to the check valve at the finishing position of weighing. CONSTITUTION:A cylinder 6 operated by means of oil pressure reducing the resin pressure of the metering zone is set in the injection cylinder 1 at the position close to the check valve 3 at the finishing position of weighing. The piston 8 in the cylinder 6 is thereby operated by operating the changing valve 9 to the backward direction of the plunger 7 at the same time when the injection screw 2 moves forward. A part of the molten resin B is down in by the plunger 7 and the resin pressure thereby decreases. The difference in the resin pressure acting on the front and back surfaces of the check valve 3 therefore occurs and when the injection screw thereby goes forward, the check valve 3 goes backward at one to complete closing. As the result, the back-flowing time of the weighed resin A becomes very short and the decrease in the pouring amount to the mold 10 due to leakage becomes very little.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection device equipped with an injection screw, which is used when injection molding a synthetic resin molded product.

(Prior Art) In general, an injection screw is divided into three zones from the tip: a metering zone, a compression zone, and a feed zone. The resin particles supplied to the rear part of the injection cylinder are preheated in the feed zone, and are transferred to the compression zone as they begin to melt due to the shearing action of the resin and heating from the injection cylinder side. In this combined zone, the resin is further melted by shearing action and external heating, kneaded and pumped to the metering zone. In the metering zone, the molten resin is sufficiently kneaded and homogenized, and the molten resin is needleed into the injection cylinder at the tip of the screw.

Some injection devices equipped with an injection screw are equipped with a check valve at the tip of the screw.

This check valve consists of an annular valve that is fitted around the tip of the screw, and the molten resin that is kneaded and pumped toward the front of the screw by the rotation of the injection screw is
This check valve is pressed in and the liquid accumulates at the front of the cylinder.

When the injection screw is moved forward and the molten resin measured at the front of the cylinder is injected into the mold, this check valve is pushed back by the pressure on the metered resin side that is generated by being pressed by the screw tip. It is designed to close the valve and prevent backflow of resin, which can cause measurement variations.

(Problems to be Solved by the Invention) However, in reality, even if 51 resin groups suitable for the mold are hung, the amount injected into the mold often changes for each injection.

This error in injection amount is thought to be caused by uncertainty in the closing operation of the check valve during injection, but the reason has not yet been elucidated.

(Means for Solving the Problems) Therefore, as a result of repeated research on the opening/closing operation of check valves, the inventors of the present invention discovered that the check valve is capable of preventing resin contact between the il fil side and the metering zone side by the advancement of the injection screw. When a pressure difference occurs, it moves back and closes.
Until a pressure difference occurs, the injection screw moves forward with the injection screw in an open state, and even if the pressure difference occurs, even if the resin is the same, it depends on the state of the resin being pumped from the feed zone to the metering zone, melting and crosstalk. It was discovered that it differs depending on the state and changes for each total a.

Check valve r during injection! It is extremely difficult to constantly control the melting and kneading of the resin in a constant state in order to quickly form the I chain. However, if a sufficient pressure difference is generated before and after the check valve to retract the check valve at the same time as the injection screw advances, the closing operation will be faster than in the past, and the leakage of Ml;fl resin will be reduced.

In view of the above, an object of the present invention is to reduce the pressure on the metering zone side so that the check valve can be closed quickly, thereby ensuring that metered resin is always injected into the mold without shortage. The objective is to provide an injection device that can.

The present invention according to the above-mentioned object is an injection device equipped with an injection screw having a check valve at its tip in an injection cylinder, in which a check valve is disposed near the check valve at a metering completion position.
The gist is that the injection cylinder is provided with a cylinder that reduces the resin pressure in the metering zone.

(Function) In the above injection device, when the cylinder is operated at the same time as the injection screw moves forward and the ram is retracted, a part of the molten resin in the metering zone is drawn into the cylinder side, and the resin in the metering zone is drawn in. The pressure is reduced and a differential pressure is created with the metering resin which is being pressurized. For this reason, the check valve is 1
31! and close the screw tip.

Further, the present invention will be specifically explained with reference to illustrated embodiments.

(Example) In the figure, (1) is an injection cylinder, with an injection screw (2
). At the tip of this injection screw (2),
An annular check valve (3) is fitted around the rear part of the conical tip member (4) with a flow gap provided inside, and is movable back and forth.
) is Mamoru 1. (6) is a hydraulically operated cylinder that reduces the resin pressure in the metering zone, and the injection cylinder (1) is located close to the check valve (3) at the metering completion position.
). The plunge V (7) of the cylinder (6) is movably fitted into a hole bored in the cylinder wall, and connected to the piston (8) to reciprocate within the cylinder wall. (9) is a switching valve for the cylinder (6), (10) is a mold, and (11) is a band heater.

Next, the pressure reduction operation will be explained.

First, the plunger (7) is aligned with the inner surface of the cylinder wall as shown in FIG. 1 from the start to the end of metering. At this time, the resin pressure before and after the check valve is approximately equal, and when the injection screw (2) is moved forward in this state to inject the resin (A) into the mold (10), the check valve (3) also moves forward together with the molten resin (B) in the metering zone. The forward movement of the check valve (3) occurs until the pressure on the metering resin side acts on the check valve (3) due to pressurization by the tip member (4), and during that time, the flow gap causes the metering resin (A) to move forward. part flows back into the metering zone. Due to this backflow, the amount of T-meter resin (A) decreases, and the resin pressure applied to the rear end face of the check valve also increases.

Therefore, in order to press the check valve (3) against the valve seat (5) and complete the closing, an injection screw (°2
) must move forward.

However, if the piston (8) in the cylinder (6) is operated in the direction in which the plunge +7 (7) moves backward by operating the switching valve (9) at the same time as the injection screw (2) moves forward, the result shown in FIG. As shown, part of the molten resin (B) is drawn in by the plunger (7), reducing the resin pressure in the metering zone. For this reason, the check valve (3
), and as soon as the injection screw (2) moves forward, the check valve (3) moves back to complete the closing. As a result, the time for the metering resin (A) to flow back is extremely short, and the mold (1
The decrease in the injection amount to 0) will almost never occur.

(Effects of the Invention) As described above, the present invention includes a cylinder (6) that reduces the resin pressure in the metering zone by the injection cylinder (1).
Provided close to the check valve (3) at the measurement completion position,
As a result, a pressure difference is generated before and after the check valve when the injection screw moves forward, and the check valve can be immediately closed, thereby preventing insufficient injection amount due to leakage of metered resin. Further, since it is only necessary to provide the injection cylinder with a cylinder for depressurization, the structure does not become particularly complicated, and the present invention has the advantage that there is no problem in responding to melt crosstalk.

[Brief explanation of the drawing]

The drawings show an embodiment of the injection device according to the present invention. FIG. 1 is a vertical cross-sectional view of the mold and the tip of the injection device during metering, and FIG. 2 is a vertical cross-sectional view of the injection screw as it advances. It is a diagram. 1... Injection cylinder 2... Injection screw 3... Check valve 6...
Decompression cylinder 7...Plunger

Claims (1)

[Claims] In an injection device equipped with an injection screw having a check valve at its tip inside the injection cylinder, the injection cylinder is provided with a cylinder that reduces the resin pressure in the metering zone in close proximity to the check valve at the metering completion position. Characteristic injection device.