JPH0661836B2 - Vacuum, compressed air and heating method for press-formed synthetic resin sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for heating a synthetic resin sheet used for vacuum forming, pressure forming and press forming a synthetic resin sheet.

[Conventional technology]

Conventionally, when vacuum or pressure molding is performed using a synthetic resin sheet, or during press molding, the synthetic resin sheet is softened in the previous step of bringing the synthetic resin sheet into close contact with the mold, so the upper and lower surfaces of the sheet can be moved. It was heated to a high temperature with a heating device such as a heater.

In the above-mentioned conventional method, when the heating is sufficiently performed, the synthetic resin sheet softens and hangs down, and the distance between the heating device and the synthetic resin sheet changes, so that the temperature of the synthetic resin sheet becomes non-uniform, and the vacuum or pressure molding or When press-molded, there were problems that the thickness of the molded product became extremely uneven and wrinkles were generated.

Therefore, conventionally, many proposals have been made to solve the above problems. For example, in the method for heating a synthetic resin sheet for press molding disclosed in Japanese Patent Laid-Open No. 63-246225, as shown in FIGS. 3 and 4, an airtight box 52 is provided above or below the synthetic resin sheet 51. 53 is provided,
Inner heating device 54 or 55 and outer heating device 5
6 or 57 is moved, while heating the synthetic resin sheet 51 immediately above and below the synthetic resin sheet 51, the pressure in the airtight box 52 or 53 is adjusted by the relationship between atmospheric pressure and positive pressure or atmospheric pressure and negative pressure. The adjusting pressure is configured to prevent the synthetic resin sheet 51 from sagging and maintain a planar state. In FIGS. 3 and 4, 58 is a mold, 59 is a positive pressure source, and 60 is a negative pressure source.

[Problems to be Solved by the Invention]

However, in the technique disclosed in Japanese Patent Laid-Open No. 63-246225, the plane of the synthetic resin sheet being heated is maintained by sandwiching the synthetic resin sheet 51 and balancing the atmospheric pressure with the positive pressure or the negative pressure. However, since one side is atmospheric pressure, even if the pressure is adjusted only on one side of the airtight box 52, it becomes very difficult to adjust the pressure when a synthetic resin sheet having a large thickness and a large area is heated for a long time. Not only that, but when the temperature of the synthetic resin sheet exceeds a certain temperature, the volume of the synthetic resin sheet is unlimitedly expanded, which causes a problem that the thickness of the sheet cannot be controlled. Further, according to the conventional heating method, when a multi-layer sheet other than a thermoplastic resin, a thermosetting resin, or the like is heated, gas foaming occurs, and the multi-layer sheet, the thermosetting resin, or the like cannot be molded.

The present invention was devised in view of the above points, and even if a thick synthetic resin sheet having a large area is heated for a long time, unlimited volume expansion does not occur, and a simple addition structure such as a balance cylinder is provided. It is an object of the present invention to provide a method for heating a synthetic resin sheet for vacuum, pressure, and press molding, in which the thickness can be easily controlled and the molding application range is expanded.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, in the present invention, a synthetic resin sheet is attached in a planar state to a clamp provided on the wall surface in the substantially center of the airtight box, and the airtight box is partitioned into upper and lower chambers. , A compressed gas of the same pressure is flowed into the upper and lower chambers from a pressurized gas source to balance the pressure on both sides of the sheet, and the heating source is moved to directly above and / or below the synthetic resin sheet. It is characterized by heating by heating.

[Action]

By adopting the above method, it is possible to prevent sagging of the softened sheet, particularly thick wall, without causing unlimited volume expansion even if the synthetic resin sheet having a large area is heated for a long time, The wall thickness can be easily controlled with a simple addition of a balance cylinder.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. The drawings are cross-sectional explanatory views of the vacuum, compressed air and press forming apparatus of the present invention. FIG. 1 is an explanatory view showing a state before heating a synthetic resin sheet, and FIG. 2 is an explanatory view showing a state during heating. .

In FIG. 1, 1 is an airtight box, 2 and 2'are clamps,
3, 3'is a heater. Both ends of the synthetic resin sheet 10 are fixed to clamps provided on the wall surface inside the airtight box 1, and the airtight box 1 is placed in the upper chamber 1 at an intermediate position of the airtight box 1.
1, partition into lower chamber 12. Also, synthetic resin sheet 1
A heater storing case 25 is arranged on the side of 0, and heaters 3 and 3'which are movable near the upper and lower sides of the synthetic resin sheet 10 are stored in order to heat and soften the synthetic resin sheet 10. A pipe 26 connected to the pressurized air source 4 via a control valve 6 is connected to the lower chamber 12. A pipe 15 is connected to the upper chamber 11 via a pipe 16 branched by the pipe 26, a control valve 5, and a pipe 27.

A female mold 19 is provided in the lower chamber 12 so as to be vertically movable by a mold moving device 17. Reference numeral 22 denotes a passage for discharging the air inside the cavity when the synthetic resin sheet 10 is pushed into the female mold 19 by the plug 20 described later, and penetrates the center of the mold moving device 17 and is connected to a vacuum source (not shown). It continues to line 21. Further, a plug 20 is provided in the upper chamber 11 so as to be vertically movable by a mold moving device 18.

With this configuration, the control valves 6 and 5 are opened in the upper chamber 11 and the lower chamber 12 partitioned by the synthetic resin sheet 10 at the intermediate position of the airtight box 1, and compressed air of the same pressure is supplied from the pressurized air source. While being fed, the heaters 3 and 3 ′ can be moved from above the heater storage case 25 to near the top and bottom of the synthetic resin sheet 10 to be heated and softened.

When a thick sheet is heated and softened under normal atmospheric pressure, volume expansion occurs due to its own weight, but in the heating method of the present invention, positive pressure compressed air is applied above and below the thick synthetic resin sheet 10. Since it is compressed and heated by heating and softened by compressed air, it is less likely that it will hang down under its own weight compared to normal atmospheric pressure. This is obtained when the present invention is carried out at the material and the heating temperature of the synthetic resin sheet when vacuum, pressure forming or press molding is performed. As described above, in the present invention, even if the synthetic resin sheet 10 is heated and softened at a high temperature, the volume expansion does not occur as compared with the conventional case. Therefore, the thickness of the sheet can be adjusted by an additional configuration such as a balance cylinder.

An example of a simple additional configuration such as a balance cylinder will be described below.

In the balance cylinder 7 shown by the chain double-dashed line in FIG. 1, the right chamber 14 partitioned by the piston 8 communicates with the lower chamber 12, and the lower chamber 13 communicates with the upper chamber 11.

By closing the control valves 5 and 6 in the pipes 26 and 27 and moving the piston 8 left and right by a mechanical external force, the pressures in the upper chamber 11 and the lower chamber 12 of the airtight box 1 are adjusted. Not only can the thickness of the sheet 10 be adjusted, but the synthetic resin sheet 10 can be swelled up or down to a shape close to the shape of the product to facilitate the subsequent vacuum, pressure forming or press forming.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and embodiments can be made without departing from the spirit of the invention.

〔The invention's effect〕

As described above, according to the present invention, with the synthetic resin sheet as a boundary, the airtight box is partitioned into upper and lower chambers, and compressed gas having the same pressure is allowed to flow into the upper and lower chambers to directly above and directly below the synthetic resin sheet. Since heating is performed from either one, the softening sheet is prevented from sagging, and even if a large-scale object is heated for a long time, unlimited volume expansion does not occur. In addition, the wall thickness can be easily managed by a simple additional structure such as a balance cylinder. In addition, the compressed gas of the same pressure (high-pressure compressed air, nitrogen gas, etc.) is pressed against the top and bottom of the sheet to prevent gas foaming due to heating of multi-layer sheets other than thermoplastic resin or thermosetting resin. The sheet can be heated while being kept in a flat state, and the molding application range can be expanded.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view showing a state before heating a synthetic resin sheet of a vacuum, compressed air and press molding apparatus of the present invention, and FIG. 2 is a sectional explanatory view showing a state of the synthetic resin sheet during heating. FIG. 4 is a cross-sectional explanatory view showing a state of heating a synthetic resin sheet of a conventional vacuum, compressed air and press molding apparatus, and FIG. 4 is a cross-sectional explanatory view showing another example of the same. 1 ... Airtight box, 2, 2 '... Clamp 3, 3' ... Heater, 4 ... Pressurized air source 5, 5 '... Control valve, 10 ... Synthetic resin sheet 11 ... Upper chamber, 12 …… Lower chamber 19 …… Female type, 20 …… Plug

Claims (1)

[Claims] 1. A synthetic resin sheet is attached in a flat state to a clamp provided on a wall surface inside the center of an airtight box, and the airtight box is partitioned into upper and lower chambers, and at the same time, in the upper and lower chambers. It is characterized in that compressed gas of the same pressure is introduced from each pressurized gas source to balance the pressures on both sides of the sheet, and the heating source is moved to directly above and / or below the synthetic resin sheet for heating. Vacuum, compressed air and heating method for press-molded synthetic resin sheet.