JPS5983613A - Method and apparatus for vacuum molding of plastics - Google Patents

Abstract

PURPOSE:To inexpensively obtain a molded product having beautiful finish, by a method wherein a cover lid is placed on a heat softened plastic plate placed on a female mold and, after a female mold side and a cover lid side are simultaneously evacuated, and cover lid side is returned to atmospheric pressure. CONSTITUTION:A preliminarily heat softened plastic plate 6 is placed on a female mold 12 and a cover lid 8 is applied from above to fix said plastic plate 6 so as to hold the same between said female mold and the cover lid 8. Subsequently, valves 20, 18 are opened while valves 19, 22 are closed and a vacuum pump 5 is operated to simultaneously bring the interior 21 of the female mold 12 and the interior 9 of the cover lid 8 to a reduced pressure state. After a vacuum degree is made as high as possible in this state, the valve 18 is closed while the valve 22 is opened and air is introduced into the interior 9 of the cover lid 8 to closely contact the plastic sheet 6 with the female mold 11. In this case, when the molding of the plastic sheet is insufficient only by vacuum molding, the valve 22 is closed while the valve 19 is opened and compressed air is supplied to the interior 9 of the cover lid 8 to perform vacuum pneumatic molding.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel vacuum forming method for plastics, a vacuum forming apparatus, and a vacuum/pressure forming apparatus used in the method.

A vacuum forming method involves placing a plastic plate that has been heated and softened in advance tightly on a female mold, evacuating the inside of the female mold, and attaching plastic to the inner surface of the female mold, or by placing a lid over the female mold. The vacuum/pressure molding method, in which the inside of the female mold is evacuated and the inside of the upper cover is pressurized for molding, can mold larger products than injection molding methods, has a simpler mold structure, and requires only a female mold. It is widely used in the fields of large-scale molding and high-mix, low-volume molding because it requires low mold costs.

Regarding conventional vacuum forming or vacuum/pressure forming,
In both cases, the inside of the female mold is vacuum-suctioned and a softened plastic plate is attached to the inner surface of the female mold, so a small vacuum suction hole of 0.6 to 0.8 mm is formed at the corner or ridge of the female mold. It is necessary to drill a large number of holes, which makes the processing of the female mold extremely complicated and increases the cost of the mold.Furthermore, in some cases, the hollow suction hole part may damage the product and require post-processing. There were drawbacks such as the need for An example of a device used in the conventional method is shown in FIG.
A large number of vacuum suction holes (2) are provided at the corners' and ridges of the female mold (1) at a pitch of approximately 25 to 3 ON, and the bottom chamber (3) of the female mold (1) is vacuumed. Connected to tank (4) and vacuum pump (5). The plastic sheet (6) is clamped around the circumference by a clamping frame (7) and softened by a heater (not shown) that heats the sheet from the top and bottom or one side of the sheet, and then the female mold (1) rises from below. , and comes into contact with the seat (6) at the position shown in FIG.

There is a cover (8) on the top surface of the plastic sheet (6), and the inside (9) of this cover (8) is under atmospheric pressure through an atmosphere communication pipe αO that communicates with atmospheric pressure, or is connected to an air compressor. It is possible to select either connecting to α1) and pressurizing the inside. That is, since the inside (9) of the cover (8) also serves as a pressure chamber, vacuum/pressure forming is performed by suction from below and compressed air from above.

In the vacuum forming method of the present invention, the basic components of the apparatus shown in FIG. Therefore, it is an extremely advantageous method from a Hong Je perspective. The characteristic of the molding method is that a plastic sheet or plate that has been heated and softened in advance is placed on a female mold, a lid is placed on top, the plastic plate is clamped and fixed, and the female mold side and the lid side are separated. The purpose is to reduce the pressure by suction at the same time, and then return the cover side to normal pressure or further compress the air to bring the plastic plate into close contact with the female mold.

FIG. 2 is a piping system diagram showing an example of the apparatus used in the vacuum forming method of the present invention, and the Kamimachi method and apparatus will be specifically explained in detail using this diagram.

As is clear from the female mold 02 compared to the conventional female mold (1), there are no vacuum suction holes in the corners or ridges of the female mold, but instead the product shape on the upper side of the female mold (a) A large suction port 0 [exist] was provided in a part that does not affect the air flow. The suction port 0 east has a step θυ on the upper edge of the female mold 04) as shown in the diagram.
If the side surface between the upper edge and the step is provided with an opening, the molded product will not be damaged.

Since it is no longer necessary to make many vacuum suction holes in this way, the production of the female mold becomes extremely easy. That is, depending on the pattern inside the mold, some holes may not be made even though they are small holes, but the mold of the present invention has no relation to the pattern. In addition, the process of making small holes by thinning the bottom wall and making many thin holes was no longer necessary, resulting in significant savings in mold costs.

The piping system of this device differs from conventional ones in that the female type 0-side vacuum piping OQ and the cover lid (8) side vacuum piping a are communicated via a valve OA (a). These are then connected to a vacuum tank (4) and a vacuum pump (5). On the side of the cover (8), there is a compressed air circuit inside (9).
A pressurized air port (c) is provided at , which is connected to an air compressor aυ via a valve Ql. Therefore, the plastic sheet (6), which has been softened by heating in advance, is placed on the female mold @ together with the clamping frame (7), and in reality, the female mold (6) moves upward to the position of the plastic sheet (6)),
With the lid (8) on top and the plastic sheet (6) sandwiched in place, open the valve (E) and valve (C).
Close valve 01 and valve (c) and turn on the vacuum pump (5)
When activated, the inside of the female mold Qυ and the inside (9) of the cover (8) are separated from their respective suction ports α3 (c), and the pressure is simultaneously reduced, and the pressure is the same on the top and bottom of the plastic sheet (6). The vacuum level is balanced and there is no movement of the sheet itself. In this state, after increasing the degree of vacuum as much as possible, close the valve (to), open the valve (a) and introduce air into the inside of the cover (9), and the plastic sheet (
6) is gathered into the female mold to form a close-contact molded body.

If vacuum forming alone is insufficient, close the valve @, open the valve 0, and supply compressed air from the air compressor aυ to the inside of the lid (9) to perform so-called vacuum/pressure molding.

In addition, in Fig. 2, an example of the cover-side suction port and the compressed air port I2 are shown.
3), the air compressor (li) is connected to the vacuum piping (I″i) on the cover lid side to form a common suction/compression air port, and the atmospheric pressure release valve (221e is attached separately to the cover lid (8)).
It has the same effect even if it is attached to.

The two-dot chain line in the figure shows the entire state in which a two-stage vacuum pull-out circuit and a mold release blower circuit are added.

As detailed above, in the conventional vacuum/pressure molding method, the inside of the female mold is completely evacuated, and the inside of the covering lid on the opposite side of the plastic sheet is fully evacuated, and the plastic sheet is molded in close contact with the inner surface of the female mold. The vacuum or vacuum/pressure forming method of the present invention is a method in which both surfaces of a plastic sheet are evacuated and then air is supplied to the inside of the lid side up to atmospheric pressure, or the air is further compressed with compressed air.

Therefore, on the equipment side, the shape of the mold, which is the most expensive part, is simplified, and excellent effects such as a beautiful finish are obtained because there are no traces of the narrow suction holes left on the surface of the molded product. Ruru.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a female type and a piping system diagram of a conventional device, and FIG. 2 is a sectional view of a female type and a piping system diagram of the device of the present invention. (221 bars) or more Applicant Fuse Shinku Co., Ltd. Agent Patent attorney Hirozo Mori

Claims (1)

[Claims] 1. Place a plastic plate that has been heated and softened in advance on a female mold, cover the top with a lid, clamp and fix the plastic plate, and connect the female mold side and the cover lid side. A method for vacuum forming plastics, characterized in that after simultaneously suctioning and depressurizing the cover, the pressure on the cover side is returned to normal pressure or the pressure is further compressed to bring the plastic plate into close contact with the female mold. 2. A female mold with a suction port provided in a part that will not cause damage to the molded product, and a cover lid that is in the shape of an upside-down plate that covers the periphery of the female mold, has a suction port, and is pressed with a press so as to come into close contact with the female mold. ,
A plastic vacuum forming apparatus comprising vacuum piping, a vacuum tank, and a vacuum pump that connect the female suction port and the cover suction port. 3. A female mold with a suction port provided in a part that will not damage the molded product, and a dish-like shape that covers the female mold and has a suction port and a compressed air port, and is pressed with a press to fit tightly with the female mold. A plastic vacuum/pressure forming apparatus comprising a cover, a vacuum pipe/vacuum tank and a vacuum pump connecting the female mold side suction port and the cover cover side suction port, and an air compressor connected to the compressed air port.