JPH0423890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for preventing molten resin from remaining in an injection molding machine.

(Prior art) Conventionally, when molding synthetic resin products using an injection molding machine, a valve that can be opened and closed is provided in the nozzle part that jets out molten resin, and the speed of the jet flow is controlled by the degree of opening of this valve. is being carried out.

Therefore, as a molding condition, injection may be performed without fully opening the nozzle valve.

(Problems to be Solved by the Invention) In the above-mentioned injection molding, if the injection speed is high due to the molding conditions, defects such as burrs and dierites will occur in the molded product. This is because the phenomenon often does not improve.

For example, in the case of a rotary valve type valve, unless the rotary valve is fully opened, a vortex will form in the molten resin flow path inside the injection molding machine and if it stagnates, the resin will decompose, causing black spots and other problems in the molded product. There were problems such as the occurrence of defective silver stripes.

In view of this, the present invention has been made for the purpose of providing a method for preventing molten resin from remaining in an injection molding machine, which solves the problems of the prior art by providing a shot self-cleaning effect during continuous molding. be.

(Means for Solving the Problems) In order to achieve the above object, the present invention aims to complete the post-injection pressure holding process in the process of continuously molding a molded product using an injection molding machine equipped with a throttle valve that can be opened and closed in the nozzle part. The present invention is characterized by a method for preventing molten resin from remaining in an injection molding machine, in which a throttle valve is fully opened at times to provide a shot self-cleaning effect.

(Example) Hereinafter, the present invention will be explained with reference to the example shown in FIGS. 1 to 3.

The injection molding machine to which the method for preventing molten resin retention according to the present invention is applied is configured as follows.

That is, as shown in FIG. 1, a screw shaft 2 is housed in a cylindrical barrel 1, a nozzle part 3 is provided at the tip of the barrel 1, and a throttle valve 4 that can be opened and closed is provided in the nozzle part 3. There is.

Further, the barrel 1 is provided with a hopper 5 at the top for receiving raw materials such as resin, and the molten resin in the barrel 1 is sent to the nozzle part 3 by the screw shaft 2, but the molten resin is returned In order to prevent this, a check valve 6 is provided in the barrel 1 at a position close to the nozzle portion 3.

A screw position detector 7 and a rod 9 of an injection cylinder 8 are connected to the rear end of the screw shaft 2, and a hydraulic motor 10 for driving the injection cylinder 8 is provided at the rear of the injection cylinder 8.

A lever 11 and a link 12 are connected to the outside of the throttle valve 4, and the link 12 is connected to an opening/closing drive device 13 for the throttle valve 4.

The opening/closing drive device 13 is also electrically connected to a throttle valve control device 14, and the throttle valve control device 14 is electrically connected to an injection molding machine control device 15.

This injection molding machine control device 15 controls the operation of the injection molding machine, and is designed to control the operation of the next injection molding process based on arbitrary values set by the operator.

In other words, the injection molding process repeats the cycle of mold closing → mold drawing → injection → holding pressure → cooling (during which the raw material is plasticized by rotation of the screw shaft) → mold closing → product ejection → mold closing.

During this time, the throttle valve 4 is in a fully closed state except during the injection and pressure holding processes, and during the injection and pressure holding processes, the throttle valve 4 is limited to an arbitrary throttle opening suitable for the molded product.

In the present invention, in such a process, the throttle valve 4 is always fully opened along with a signal indicating completion of pressure holding.

That is, the condition in which the throttle valve 4 does not need to be closed in the above molding cycle is when the nozzle portion 3 is in contact with the mold into which injection is to be performed and the injection is still in progress, the pressure is held, or the mold is being cooled.

During injection and pressure holding, the throttle valve 4 is in the open state, which is a control condition that matches the molded product, so the timing when the throttle valve 4 can be fully opened is when the screw shaft 2 is rotating and the nozzle is This is only while the part 3 is in contact with the mold.

However, at the moment when the pressure retention is completed, the nozzle part 3 is in contact with the mold, and the throttle valve part 4 aims at this.
A full open signal is sent, and in this embodiment, the opening is made only for a minute period of about 0.5 to 1 second.

At the same time, at the moment when the pressure holding is completed, the molten resin pressure in the throttle valve 4 is also reduced from the pressure during the pressure holding process, so that the elastic compression amount of the molten resin is recovered, and the resin in this area also undergoes a slight flow change.

As a result, the position of the vortex flow of the molten resin in the throttle valve 4 portion also moves as the throttle valve 4 is fully opened.

Since the vortex thus moved is injected during the next shot molding, the vortex is self-cleaned after each molding cycle.

Further, since this vortex stays in only one shot, problems such as resin decomposition due to the stay do not occur.

According to experimental results, black spots appeared after about 3,000 shots when acrylic resin was continuously molded with slow filling in the conventional method, and this was due to resin retention in the four throttle valves.

However, with the method according to the present invention, such problems did not occur at all even after continuous operation of 100,000 shots.

In addition, when changing the color of the material, there is no material retention, and for example, changing from red to white for ABS material can be reduced from 15 shots to 3 shots, which saves material and reduces time during setup. It also became possible.

(Effects of the Invention) As explained above, the present invention includes a fully opening process of the throttle valve at the completion of the post-injection pressure holding process in the process of continuously molding a molded product using an injection molding machine equipped with a throttle valve that can be opened and closed in the nozzle part. Since the shot is provided with a self-cleaning effect, it is possible to prevent the conventional stagnation, and as a result, the occurrence of black spots, silver, etc. that have conventionally occurred in molded products can be prevented.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the structure and control system of an injection molding machine to which the present invention is applied, Fig. 2 is an enlarged cross-sectional view of the nozzle portion of Fig. 1, and Fig. 3 is a state of vortex flow retained in the throttle valve portion. FIG. DESCRIPTION OF SYMBOLS 1... Barrel, 2... Screw shaft, 3... Nozzle part, 4... Throttle valve, 13... Throttle valve driving device, 14... Throttle valve braking device, 15...
...Injection molding machine control device.

Claims (1)

[Claims] 1. In the process of continuously molding molded products using an injection molding machine equipped with a throttle valve that can be opened and closed in the nozzle part, a fully open throttle valve step is provided at the completion of the post-injection pressure holding process to provide a shot self-cleaning effect. A method for preventing molten resin from stagnation in an injection molding machine.