JPS5973933A - Check valve for injection molding machine - Google Patents

Abstract

PURPOSE:To obtain the check valve, through which a resin is injected under the state in which a resin path is clogged at all times and which can stabilize the weight and shape of a shape, by giving physical righting moment, such as resilient force, magnetic force, etc. CONSTITUTION:Physical righting moment intending to close the check valve, such as magnetic force, resilient force, etc. is given, and the magnitude of the righting moment is made smaller than force forwarding the resin by the revolution of a screw 3, thus forming the aimed check valve 8. When injection is completed, the screw 3 is turned, and a resin material is intended to be forwarded to a void section 5 in front of a screw chip 2 while being plasticized. A spring 7 is compressed by force intending to forward the resin, the valve 8 is moved forward and the resin path 4 is opened that time. When the melted resin forwarded is stored in the void section 5 and the screw 3 is backed, the valve 8 is fast stuck to the nose A of the screw by the righting moment (f) of the spring 7, and the resin path 4 is closed.

Description

DETAILED DESCRIPTION OF THE INVENTION In general, in-line screw injection molding machines are equipped with a backflow prevention valve at the tip of the screw to open and close the resin passage, and when the valve is open or during plasticization, the resin passage is opened and the plasticized resin is When injecting, the opening of the valve closes the resin path and prevents the resin accumulated at the tip of the screw from flowing back toward the screw.

Next, the function and operation will be explained with reference to Figs. 1 and 2. Fig. 1 shows that the non-return valve (1) is pushed by the flow of resin due to the rotation of the non-return valve during plasticization, and the non-return valve (1) The resin passes through the resin path (4) formed between the tip A of the screw (3) and the inside of the heating cylinder (6) in front of the screw tip (2) like a resin flow α. It is accumulated in the gap (5) formed between the wall surface and the wall surface.

FIG. 2 shows the state of the check valve during injection. In Figure 2, plasticization is completed and the screw (3) is ready for injection.
When the valve moves forward (towards the left in the figure), the non-return valve (1) is pushed back by the reaction force of the injection pressure and comes into close contact with the end surface A of the screw (3) as shown in Figure 2, so that the resin The passage (4) is closed, and the resin accumulated in the gap (5) is prevented from flowing back toward the screw.

However, the time during which the check valve (1) is closed varies depending on conditions such as the viscosity of the resin and the injection speed. Further, while the check valve (1) is completely closed, the resin accumulated in the gap (5) flows back. Therefore, if the closing time of the check valve (1) varies, the amount of backflow will also vary, the weight and shape of the molded product will not be constant, there will be a lot of backflow during defective products, and the amount of variation will increase. There were many cases where this occurred.

The purpose of the present invention is to stabilize the weight and shape of a molded product by eliminating the unstable elements of the operation of a check valve when it is closed. By providing the check valve with a force that tends to close the check valve, plasticization is completed, and before the next process of injection, the check valve closes due to the restoring force and the resin passage is closed, so the resin is always It is an object of the present invention to provide a check valve capable of stabilizing the weight and shape of a molded product by performing injection with the passage closed.

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 3 and 4 show a first embodiment of the present invention, in which (2) is a screw tip, (3) is a screw, and (4) is a screw tip. resin road,
(5) is a cavity, and (6) is a heating cylinder, which are the same as the conventional ones shown in FIGS. Only the parts that differ from the diagram will be explained. In Figures 3 and 4, (the force is a compression spring, the non-return valve (8) and the screw tip (2)
), and the check valve (8) is always biased to the right, or the restoring force is selected to be smaller than the force for feeding out the resin due to the rotation of the screw (3).

Next, to explain the operation, FIG. 8 shows the open state of the resin passage (during plasticization), and FIG. 4 shows the closed state of the resin passage (closed by spring force after plasticization is completed). Now, when the injection is completed in Figures 8 and 4, the screw (3)
The screw tip (
2) and tries to send it out to the space (5) in front of it.

At this time, due to the force that is trying to send the resin forward, the spring (force) that is trying to close the check valve (8) is compressed, and the check valve (8) moves forward (to the left in the figure). , the resin path (4) is opened and the molten resin sent out is accumulated in the cavity (5), and the screw (3) is retracted.

When the screw (3) moves back to the specified position and stops,
Since the force trying to send the resin forward is no longer present, the non-return valve (8) comes into close contact with the screw tip A due to the restoring force f of the spring (7).

Next, FIG. 5 shows a second embodiment of the present invention using a non-return valve (9) that uses magnetic force, and FIG. 6 shows a third embodiment of the present invention that uses a pole check valve (10) that uses spring force. shows. In Figure 5, a magnet (1υ) and a screw (
3) shows the case where a magnet (I2) is attached to the tip.

In Fig. 6, the ball check valve 00), which is conventionally known as a ball check valve, is replaced with a spring 03), and these embodiments also have the same effect as the first embodiment. (restoring force) and effect (preliminary caulking before the injection process closes the resin passage to stabilize the injection process). ) As explained in detail above, the present invention includes:
The check valve may have a physical restoring force such as magnetic force or spring force that tries to close the check valve, but the magnitude of this restoring force is smaller than the force that sends out the resin due to the rotation of the screw, so plasticization The resin passage is open inside, but after plasticization is completed, there is no longer any force to feed the resin, so the resin passage is closed due to the restoring force, and the closing operation is prevented due to the reaction force of the injection pressure when the check valve starts advancing forward. By eliminating the stabilizing element, it is possible to stabilize the weight and shape of the molded product.

[Brief explanation of the drawing]

Figures 1 and 2 are side sectional views of the tip of a conventional in-line screw type injection molding machine in different operating states, respectively.
4 and 4 are side sectional views showing different operating states of the check valve part for an injection molding machine according to an embodiment of the present invention, and FIGS. It is a sectional side view of the check valve part for injection molding machines which shows 8th Example. Explanation of the main parts of the figure 2...Screw tip 8...Screw 4゛°' resin path 6...Heating cylinder 7...Compression spring 8...Backflow prevention valve 9...Backflow using magnetic force Prevention valve 10... Pole check valve 11. 12... Magnet 18... Spring patent Applicant: Mitsubishi Heavy Industries, Ltd. Figure 3 Figure 4

Claims (1)

[Claims] It has a physical restoring force such as magnetic force or spring force that tries to close the check valve, and by making the restoring force smaller than the force that sends out the resin due to the rotation of the screw, the resin path is kept closed during plasticization. A backflow prevention valve for an injection molding machine, characterized in that it opens and closes a resin path after plasticization is completed.