JPH0548167B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an in-mold vacuum injection molding machine.

(Prior art) It is known that when filling a cavity in a mold with molten plastic, if the air in the cavity is not completely exhausted, defects in molded products may occur due to air entrainment. . For this purpose, an in-mold vacuum injection molding machine has been proposed that prevents defects by removing air from the mold cavity to create a vacuum state and then filling it with plastic. -194523 is an example. The first example of the in-mold vacuum forming machine proposed in this publication is provided with a suction hole communicating with the cavity on the movable template side, and a vacuum device is communicated with this suction hole, and the cavity and the suction hole are connected. The space between the sprue ejector pin and the sprue ejector pin is connected by a valve formed by reducing the diameter near the tip of the sprue ejector pin and a hemispherical receiving part formed at the tip, and the sprue ejector pin is not fixed to the ejector plate. It is in a free state, and its forward movement is performed by the forward movement of the ejector plate, but its backward movement is performed by pushing back the pin by applying the pressure of the filling plastic to the receiving part during plastic filling. To explain the forming method in this example, as the ejector plate advances, the rear end of the sprue ejector pin is pressed, and the tip protrudes into the cavity, and this pin does not follow the retreat of the ejector plate. When the protruding position is secured and the mold is closed, the tip of the pin contacts the sprue, and at this time, the cavity and the suction hole are in communication. After the mold clamping is completed, the vacuum device is activated to bring the cavity and sprue to a high vacuum state, and then the sprue is filled with plastic. The plastic hits the receiving part and pushes back the ejector pin, and the ejector pin comes into contact with the ejector plate. At the retracted position, the cavity and the suction hole are blocked by the receiving part. After filling is completed, the movable mold plate is opened and demolded.

The above-mentioned publication also shows another example. In this example, in a mold structure in which the sprue ejector pin cannot be used, an independent advancing/retracting rod is provided in the mold plate, and a special hydraulic circuit for operating this rod is installed. established in
It creates a high vacuum state by operating the rod.

(Problem to be Solved by the Invention) In the former example, the ejector pin is retracted while applying the pressure of the plastic to be injected to the hemispherical receiver, but the injected plastic tends to leak to the outside of the receiver, resulting in insufficient pressing force. This may prevent the pin from retracting smoothly, and the plastic leaking to the outside may adhere to the back side of the receiving part, becoming integrated with the plastic of the molded product and making it difficult to release from the mold. It also adheres around the valve and seals the gap between the valves, resulting in the inconvenience that the cavity and suction hole are always in a "closed" state.

In the latter example, there are drawbacks such as the need to provide an independent hydraulic circuit, which increases the number of parts and complicates the structure.

An object of the present invention is to provide an in-mold vacuum injection molding machine in which the pin can be smoothly retracted, the cavity and the suction path can always be connected reliably, and the structure is not complicated.

(Means for Solving the Problems) The present invention provides a fixed side mold plate and a movable side mold plate, a cavity formed between opposing surfaces when the two mold plates are clamped, and a cavity formed on the movable side mold plate side. An ejector plate provided so as to be movable back and forth, a return pin attached to the ejector plate, a pin attached to the ejector plate and equipped with a valve at its tip, and a pin formed on the movable side mold plate. and a pin hole through which a pin equipped with the valve is inserted, and a tip of this pin hole,
A communication hole communicating with the cavity and into which the valve can be inserted, and an air suction path formed on the movable template side connected to the communication hole and communicating with the vacuum device. This is what we are doing.

The pin provided with the valve has an elongated portion having a diameter smaller than the diameter of the pin formed on the outer periphery of the rear portion of the valve. The valve can be opened and closed by moving the communication hole back and forth by a predetermined distance, and the communication hole is opened at a position protruding forward from the communication hole, so that the communication hole, the cavity, and the air suction path are in communication with each other. This is the result.
The length of the return pin is set so that the tip of the pin is located a predetermined distance behind the abutment surface of the movable template, and this predetermined distance is a distance for opening and closing the valve with respect to the communication hole. It is equal to the distance traveled.

(Operation) After mold clamping is completed, move the ejector plate forward, move the pin forward, set the valve to the protruding position in front of the communication hole, open the communication hole, and connect the cavity and the air suction path. After that, operate the vacuum device to remove the air in the cavity and when the desired degree of vacuum is reached, the pin is retracted by the ejector plate and the valve is returned to its original position. After closing the communication hole, injection of plastic into the cavity is started, and after filling, the plastic is cooled, hardened, and then released from the mold.

(Example) A first embodiment will be described with reference to FIGS. 1 to 3.

As shown in FIG. 1, of the templates 1 and 2, the upper template 1 is a stationary template and is attached to a stationary mounting plate 3. A sprue bush 4 is inserted into a mounting hole provided through the mounting plate 3 and template 1. Sprue bushing 4 sprue 5
The nozzle 22 abuts on the upper end opening of the sprue, the lower end surface forms the same plane as the surface facing the movable mold plate 2, and the lower part of the sprue extends to the movable mold plate. In addition,
The gap between the outer peripheral surface of the sprue bush 4 and the mounting hole is sealed by a ring.

A cavity 6 is formed between the movable mold plate 2 and the facing surface of the fixed mold plate 1, and this cavity communicates with the gate 7 on the left side as shown in FIGS. 2 and 3.
This gate communicates with the runner 8, which in turn communicates with the sprue 5. A spacer block 10 is disposed below the movable mold plate 2 via a receiving plate 9, and this spacer block is attached to a movable mounting plate 11. An ejector plate 12 is arranged in the space within the spacer block 10 so as to be movable up and down. Ejecta plate 1
2 is screwed to the tip of a push-up rod 23 that passes through the mounting plate 11, and moves forward and backward as the rod moves up and down. An ejector pin 13, a sprue lock pin 14, and a return pin 15 are respectively erected on the ejector plate 12.

The molded product inside the cavity 6 can be ejected with the tip of the ejector pin 13. A valve 141 is formed at the tip of the sprue lock pin 14, and the outer periphery of the lower part of the valve is an elongated portion 142 shorter than the diameter of the sprue lock pin 14. As the sprue lock pin 14 moves up and down, the valve 141 moves up and down in the communicating hole 161 that forms the tip of the pin hole 16. As shown in FIG. When closed and in the forward position as shown in FIG.
1 is opened by the gap between the elongated portion and the hole wall, so that the sprue 5, runner 8, and cavity 6 communicate with the communicating hole 161. Therefore, the valve 141 opens and closes the communicating hole 161 by moving back and forth by a distance D (FIG. 3). The tip of the return pin 15 is at a distance Da from the contact surface of the movable mold plate 2 (Fig. 1)
This distance is set equal to the travel distance D for opening and closing the valve 141.

In addition, an air suction path 17 is formed in the horizontal direction in the movable mold plate 2, and one end of the suction path is connected to a communication hole 16.
1, and the other end is connected to a vacuum pump 18 constituting a vacuum device, and the suction force is adjusted by a solenoid valve 19.

In addition, between the opposing surfaces of templates 1 and 2, pins 13 to 15
The outer peripheral surfaces of each are sealed by a ring.

Next, the molding method will be explained.

First, after the mold clamping is completed, the ejector circuit of the molding machine starts the push-up rod 23 to raise the ejector plate 12, thereby advancing the sprue lock pin 14 by a predetermined distance D, and then electrically connecting the ejector circuit to the ejector circuit. Open the electromagnetic valve 19 that is electrically connected to the vacuum pump 18 and remove the air from the cavity 6 by operating the vacuum pump 18. Sprue lock pin 1
When the sprue 4 is in the protruding position shown in FIG. All of the air is exhausted toward the suction path 17. When the desired degree of vacuum is reached in the cavity 6, the push-up rod 23 is operated to retract the sprue lock pin 14 via the ejector plate 12, and the valve 141 is returned to its original position by retracting the distance D. Upon return, the valve closes the communication hole 161 and at this point the injection of molten plastic from the nozzle 22 into the sprue bushing 4 begins, injecting the plastic into the cavity and allowing it to cool and solidify after being filled. After cooling and solidifying, open the mold and place ejector plate 1.
2 is moved forward, and the molded product is released from the mold using the ejector pin 13.

The sprue lock pin advancement process, air suction process, and injection process performed from the mold clamping process to the mold releasing process are all electrically controlled through a control circuit, and switching timings are automatically performed.

Note that during the injection process, the pump 18 is operated to suck air inside the cavity 6 and gas generated from the molten plastic through the suction path 17.
Continue to emit.

The pin provided with the valve is not limited to the sprue lock pin, but may be an ejector pin 13a as shown in FIG. In this example, ejector pin 13
The valve 131a formed at the tip of the valve 131a opens a communication hole 161 that communicates with the cavity 6 as the valve 131a moves back and forth.
a is opened and closed, and this opening and closing operation connects the cavity and the suction path 17. 132a is an elongated portion. Other configurations are substantially the same as the above example,
Corresponding parts are given the same reference numerals as in the first embodiment.

FIG. 5 shows an example of application to a pinpoint type molding machine, in which a valve 131 is attached to the tip of the valve pin 13b.
b and an elongated portion 132b. The valve 131b of the ejector pin 13b can protrude into the runner and sprue 20, and in the protruding position, the runner and sprue, the communication hole 161b, and the suction path 17 connected to the communication hole are in communication. At the rear position of the valve 131b, the communicating hole 161b is closed. 21 is ejectapine. The tip of the return pin 15 is set back by a distance Da from the contact surface of the movable mold plate 2a. Other configurations are
This embodiment is substantially the same as the first embodiment, and corresponding parts are given the same reference numerals as in the first embodiment.

(Effects of the Invention) According to the present invention, since the forward and backward movement of the pin having the valve is linked to the movement of the ejector plate, the valve can move forward and backward smoothly, and a special It does not require an actuation means, does not have a complicated structure, does not have the problems of leakage and is difficult to release from the mold, and does not have the problem of sealing the hole where the valve goes in and out. By moving, communication between the cavity and the suction path can be reliably interrupted. The communicating hole constitutes the tip of the pin hole through which the pin with the valve is inserted, and since the pin has an elongated portion at the rear of the valve, the communicating hole can be opened and closed by simply moving the pin slightly. , the efficiency of air removal work is improved accordingly. Since the elongated portion is formed on the outer periphery of the pin, the suction direction is not limited to one direction, so that instantaneous air suction can be performed smoothly and the configuration is simple.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view, Fig. 2 is an explanatory drawing showing an enlarged injection process, Fig. 3 is an explanatory drawing showing an enlarged air suction process, and Fig. 4 is a partial enlarged cross-section of another embodiment. FIG. 5 is a sectional view of still another embodiment. 1... Fixed side template, 2, 2a... Movable side template, 6...
Cavity, 12... Ejector plate, 13
a, 13b, 14...pin, 131a, 131b,
141...Valve, 132a, 132b, 142...Slender part, 15...Return pin, 161, 161a, 1
61b...Communication hole, 17...Air suction path, 18, 19
...vacuum device, D...movement distance of valve for opening and closing,
Da…Retraction distance of the tip of the return pin.

Claims (1)

[Scope of Claims] 1. A fixed side mold plate and a movable side mold plate, a cavity formed between opposing surfaces when the two mold plates are clamped, and a cavity provided on the movable side mold plate side so as to be movable back and forth. an ejector plate; a return pin attached to the ejector plate; a pin attached to the ejector plate and equipped with a valve at its tip; a pin hole through which the provided pin is inserted; a communication hole that constitutes the tip of the pin hole and communicates with the cavity and into which the valve can be inserted; and the movable template side. and an air suction path connected to the communication hole and communicating with the vacuum device, and the pin equipped with the valve has an elongated part with a diameter shorter than the pin diameter on the outer periphery of the rear part of the valve. The valve can be opened and closed by moving the communicating hole back and forth a predetermined distance, and the communicating hole is opened at a position protruding forward from the communicating hole, and the communicating hole, the cavity, and the air suction are connected to each other. The length of the return pin is set so that the tip of the pin is located a predetermined distance behind the contact surface of the movable mold plate, and this predetermined distance is An in-mold vacuum injection molding machine characterized in that the distance traveled for opening and closing the valve relative to the communication hole is equal to the travel distance for opening and closing the valve.