JPH0262218A - Method for molding plastic - Google Patents

Abstract

PURPOSE:To improve the escape of air and gas by a method wherein a space between a backing plate and a bottom plate is enclosed under the condition that molds are closes and evacuated during the injection of plastic. CONSTITUTION:An ejector plate upper 5 and an ejector plate lower 6 are arranged in a space between a backing plate 10 and a bottom plate 11, which is enclosed by a spacer block 9, a plate 13 and a ring 14. A hose attaching port 15, through which a vacuum generating device 16 is connected, is provided on the side of the plate 13. When molds are closed, a solenoid valve 18 is opened by means of a sequence timer 19 so as to generate vacuum and, after that, injection is started. The air in cavities and generated gas are sucked through clearances between ejector pins 8 and a movable retainer plate 2 in a vacuumized space between the backing plate 10 and the bottom plate 11. After the finish of injection, mold closing is done. At that time, before the start of the pushing-up of the ejector plate lower 6 by an ejector rod 7, the solenoid valve 18 is closed by means of the sequence timer 19, resulting in stopping the actuation of the vacuum generating device 16 so as to release vacuum. The removal of a product from the molds can not be hindered by vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for molding plastic.

BACKGROUND ART Conventionally, as a molding method of this type, the one shown in FIG. 3 has been generally used. FIG. 3 is an example of the most common and simple mold for injection molding, and the explanation will focus on the parts related to the present invention.The fixed side mold plate 1 and the movable side mold plate 2 Molten plastic is injected through a sprue 3 into a cavity formed between the two, and is cooled and solidified to obtain a molded product 4.

After that, move the movable template 2 in the direction of the arrow, and then move the upper ejector plate 6 and the lower ejector plate 6.
is moved in the opposite direction to the arrow A by the ejector rod 7, and the product 4 is pushed off from the movable mold plate 2 by the ejector pin 8. Reference numeral 9 designates a pair of spacer blocks, which are attached to the movable side template 2. Receiving plate 10. The spacer block 8 is fixed to the plate 11 on the movable side.

The other parts are extremely common, so their explanation will be omitted.

Problem to be Solved by the Invention However, in such a conventional configuration, when molten plastic is injected into the cavity, the air in the cavity and the gas generated from the molten plastic flow into the fixed side. There may be a slight gap between the template 1 and the movable template 2, or the ejector bin 8 and the movable template 2 (actually the core 12 in this case, but for convenience, the core 12 is
(also referred to as the movable mold plate 2) is discharged from the mold through a minute gap between the movable mold plate 2 and the movable mold plate 2.

At this time, the clearance between each part should be 0.0 to prevent the occurrence of cracks.
Since it is set to about 01m+n, it is difficult for air and gas to escape, and therefore, the cavity is not filled with plastic sufficiently, resulting in a so-called short shot.

However, the air inside the cavity is adiabatically compressed and reaches high temperatures, which can cause burning of the plastic and corrosion of the mold surface.

Furthermore, the gas passing between the ejector bin 8 and the movable mold plate 2 cools and turns into a tar-like substance that fills the gap, so it is necessary to disassemble and clean the mold.

In order to solve these problems, K has conventionally known a method of creating negative pressure in the cooling water pipe (not shown) in the mold; A special structure is required, making it difficult to use existing molds. Equipment for separating water from gas, etc. taken into the water pipes was still expensive.

Also, the use of a vacuum pump can solve this problem.
For example, ``Basics and Applications of Injection Molds - Expanded and Revised Board'' (Japan Plastic Processing Industry Association, published September 1, 1980,
Although it is introduced in literature such as PO2), the specific method is not shown.

Means for Solving the Problems In order to solve this problem, the present invention provides a structure in which the space between the receiving plate and the movable side mounting plate is sealed at least when the mold is closed, and the space between the receiving plate and the movable side mounting plate is sealed. While this is being carried out, the space is kept in a vacuum (pressure lower than atmospheric pressure).

Operation: With this configuration, air or gas in the cavity can quickly flow out into the space through between the ejector pin and the movable mold plate. Also, I don't have time to get cold and stale on the way. Furthermore, since the vacuum has been released when the ejector pin pushes out the product, there is no problem in preventing the product from leaving the movable mold plate.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. Note that the same numbers are used for parts corresponding to those in the conventional example, and explanations of overlapping parts are omitted.

FIG. 1 is a side view of a mold for injection molding according to an embodiment of the present invention, with a portion shown in cross section. In FIG. 1, the space between the receiving plate 1o and the movable side mounting plate 11 is on the ejector plate 6. Ejector pout 6 is arranged, spacer block 9. It is sealed by a plate 13 and a song 14.

However, this is the state when the mold is closed, and when the mold is opened and the ejector rod 7 lifts the lower ejector plate 6, the ring 14 and the lower ejector plate 6 are separated, and the ejector rod 7 and the movable side mounting Outside air flows in through the gap between the space and the plate 11, and the vacuum in the space is released.

A hose attachment port 15 is provided on the side surface of the plate 13, and the hose connection port 15 is connected to a vacuum generator 16 using an air flow. 1
7 is an air compressor, 18 is a solenoid valve, and 19 is a sequence timer for setting the operation of the molding machine. Hose attachment port 15
The vacuum source connected to is not limited to the one mentioned above.

Next, to explain the operation of this device, first, when the mold is closed, the solenoid valve 18 is activated by the sequence timer 19.
opens to create a vacuum and then injects molten plastic into the cavity. Gas generated from the air and plastic in the cavity passes through the gap between the ejector bin 8 and the movable mold plate 2, and rapidly reaches the receiving plate 1o.
and the movable side attachment are sucked out into the vacuum space between the plates 11 and further led to the vacuum generator 16.

When the injection is completed and the injected plastic cools down and solidifies to form a molded product, the movable side mounting plate 11 is moved along the arrow A.
The mold is opened by moving it in the direction of . Then, before the ejector rod 7 starts pushing up the lower ejector plate 6, the sequence timer 19 closes the solenoid valve 18 to stop the operation of the vacuum generator 16, and the atmospheric pressure causes the air to flow back into the space. It flows into the vacuum and the vacuum is released.

In this way, when the ejector bin 8 starts to push out the product 4, the vacuum has been released, so the product 4
The removal of the movable mold plate 2 is not hindered by the vacuum.

Note that if the inside of the space is made to have a positive pressure, the product 4 can be pushed out more smoothly, and this can be easily achieved in the present invention. That is, compressed air may be sent into the space from the air compressor 17 via the electromagnetic valve.

Details of the ejector bin 8 are shown in FIG. In FIG. 2, the ejector bin 8 is provided with one or several scraped portions 8a by scraping with a glider or the like. Further, the circumferential portion 8b is also left to prevent rattling between the movable mold plate 2 and the movable mold plate 2.

Effects of the Invention As described above, according to the present invention, the conventional mold is sealed with the plate 13 and the ring 14, the side surface of the ejector bin 8 is shaved off, and compressed air commonly used in factories is used. Ordinary inexpensive vacuum generator 16, solenoid valve 18. The release of air and gas can be improved by the economical method of using the sequence timer 19 attached to the molding machine. As a result, defective phenomena such as short shiggot can be prevented. In addition, the generation of tar is significantly reduced, and it is virtually unnecessary to disassemble and clean the mold.

[Brief explanation of the drawing]

FIG. 1 is a side view of a mold and a layout diagram of piping used in a plastic molding method according to an embodiment of the present invention, and FIG.
The figure is an enlarged view of a part thereof, and FIG. 3 is a side sectional view of a mold used in a conventional molding method. 5......on the ejector plate, 6......
Ejector plate bottom, 8...Ejector bin,
8a...Shaving off part, 10...Receiving plate,
11...The movable side is mounted on a plate. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 5 - Ejector plate lower 6 - Ejector plate lower 8 - Garlic gubin k...Old domain ζ part 10 - Ukesu slope n -1 Possible Young I

Claims (3)

[Claims] (1) The space between the receiving plate in which the upper and lower ejector plates of the plastic injection mold are housed, and the movable mounting plate is sealed, at least when the mold is closed, and plastic injection is carried out. A method for molding plastics, characterized in that the space is evacuated during the molding process. (2) The plastic molding method according to claim 1, wherein the vacuum is released when the product begins to be pushed out of the movable mold plate by the ejector pin. (3) The method for molding plastics according to claim 1 or 2, wherein the ejector pin is provided with a cut-off portion, which is a gas passage, in the middle of the ejector pin in its longitudinal direction.