JPS59201816A - Double-side vacuum molding apparatus of plastic plate - Google Patents

Abstract

PURPOSE:To prevent deformation prior to molding by further uniformizing and equilibrating the vacuum degree between a mold box and a pressure forming box, by connecting the arranged pipe of a mold box side and the arranged pipe of a pressure forming box side to a vacuum source through a balance valve. CONSTITUTION:The arranged pipe 4 of a mold box side and the arranged pipe 5 of a pressure forming box are connected to a vacuum source through a balance valve 6 to constitute a double-side vacuum/pressure forming apparatus of a plastic plate. As the aforementioned balance valve, a piston equilibrium type or a diaphragm equilibrium type can be utilized and the piston equilibrium balance valve has such a structure that a piston valve 11 balanced by coil springs 10, 10 is provided in a cylindrical valve case 9 and the passage 12 to the arranged pipe 4 of a mold box side provided to the lower part of the cylindrical valve case 9 and the passage 13 to the arranged pipe 5 of a pressure forming box side provided to the upper part thereof are used as slide holes through which valve stems 14, 15 are, in turn, inserted to move the piston valve 11 up and down.

Description

[Detailed Description of the Invention] The present invention relates to an improvement in a vacuum forming apparatus for heat-softened plastic plates, and has been developed specifically for the purpose of more effective forming by applying vacuum from both sides of the plastic plate. It is something.

The method of heating and softening a plastic plate or sheet by placing it in a mold, shaping it while it is still soft, and cooling it to make a molded product is called plastic forming, and is used for thick material molding and high-mix low-volume production. Since it is suitable for

In general, the curve of tensile strength and elongation depending on the heating temperature of plastic materials is shown in Figure 1. Since water flux and molding stretch the material, the temperature (a) at which the elongation rate is maximum is the molding condition. However, in vacuum forming, even if the elongation rate is slightly lowered, the unit area pressure (k
, g/c♂), mold reproducibility is improved by heating the material to a temperature at which the tensile strength decreases. However, the average elongation of the molding material is impaired,
Unbalanced meat becomes more likely to occur. Therefore, even in the temperature range (c) lower than the elongation peak (a) in which thermal decomposition or thermal alteration of the material does not occur, the pressure greater than atmospheric pressure (usually gauge pressure 2 ~ko, nig /
c++i) Vacuum/pressure forming can generate a vacuum differential pressure of 1i, and even if the tensile strength is large, it is possible to perform molecular forming.
It was found that uneven thickness was less likely to occur, and a special application was filed in 1983-1.
．． 93 (i (proposed in issue i2).

However, when forming under the conditions (c), a slight temperature drop increases the tensile strength and reduces the elongation, so quick forming is required, and the vacuum shown in Figure 2 is required. - In the compressed grass molding device, the air inside the mold box (2) below the plastic plate (1) and the compressed air box (3) above must be rapidly and evenly vacuumed.

The present invention is a double-sided direct air forming apparatus from a plastic plate that satisfies these requirements, and includes
! It is characterized in that the pipe (4) and the compressed air box side piping (5) are connected to a vacuum source via a balance valve (6).

When the balance valve (6) draws air from the vacuum source consisting of the vacuum tank (7) and the vacuum pump (8)'7J1, the air in the mold box (2) and the air in the compressed air box (3) are connected to both chambers. Breathe evenly by minimizing pressure fluctuations 13
This valve is designed to sense the movement of air in both chambers and open/close the valve or change the opening level using the eye movement. An example of that structure is the 3rd Iill! I, 4th
As shown in the figures, FIG. 3 shows a flat piston type, and FIG. 4 shows a diaphragm balanced type. In addition, suitable types of balance valves such as shirt 1 to le balanced types can be used.

The piston-balanced balance valve shown in Fig. 3 has a cylindrical valve box (
9) A piston valve (11) balanced by a coil spring (10) (10) is provided inside the cylindrical valve box (9) and a passage (12) to the mold box side piping (4) below the cylindrical valve box (9).
The piston valve (1) is moved upward by inserting the valve rods (1, 4) and (1, 5) into the passage (13) to one of the compressed air box side piping (5) as a sliding hole. Valve stem (14) (15)
It has grooves to facilitate air circulation. The piston valve (11) also has two circumferential grooves (16) around it.
(17), which communicates with the valve chamber (18) (1, 9). The two circumferential grooves (16) and (17) are arranged so that they communicate with the suction port (20) provided on the side of the cylindrical valve box (9) during balance, and when unbalanced, the pressure increases. It is provided so that suction can be carried out only from the upper side or from the higher side. Therefore, the valve chamber (18)
By sensitively sensing the pressure between the valve chamber (19) and the piston valve (
11), the pressure inside both valve chambers, that is, the pressure inside the mold box (2) and the pressure inside the compressed air box (3) can be automatically adjusted so that they are always at the same pressure.

The Daryaphram balance type valve shown in Figure 4 operates in the same way as the screw one balance type valve shown in Figure 3.
A diaphragm valve (24) is provided with a diaphragm (22) sandwiched and supported in the center of the diaphragm (22), and a valve body (23) is provided at the center of the diaphragm (22). (4) and the entrance of the passage (13) to the compressed air box side piping (5) to the valve seat (25) (26
). 5 pipe bra A on the mouth surface of the valve box (21),
A suction port (27) is provided in which the top and bottom of C22) communicate with each other,
The movement of both chambers is balanced by the diaphragm valve (24) which moves in the same way as the piston 4-j (] 3 ) in Figure 3. Here, as mentioned above, the mold box (2) It is also necessary to approximate the internal volumes of the compressed air box (3) and the compressed air box (3) as closely as possible. In addition, the mold box (2) is the mold (28)
The mold (28) is placed inside the mold box (2), and the space between the circumferential gap (29) and the bottom gap (3o) between the two forms a suction passage. The aim is to increase speed, simplify the mold, and reduce cost.

The device of the present invention helps to more evenly balance the degree of vacuum between both boxes, thereby suppressing the deformation of the softened plastic plate before molding that is too far to one side, and quickly producing high-quality molded products. It is possible.

[Brief explanation of drawings]

FIG. 1 is a graph showing the temperature dependence of tensile strength and elongation of plastic materials. FIG. 2 is a schematic diagram of a vacuum/one-air molding arrangement, and FIGS. 3 and 4 are exemplary cross-sectional views of a balance valve. (1) Plastic counter (2) Mold box (3) Compressed air box (4) Molding box side piping (5) Compressed air box side piping (6) Balance valve (9) Cylindrical valve box (11) Piece 1 - valve (2]) valve box (22) diaphragm
(23) Valve body (24) R'1'Yaphram valve and above outlet/reservoir A11 Vacuum well water ceremony meeting A'2 Agent Patent attorney Synthesis 3rd Department 1st same high mouth low - 2nd Pl crawler → Hatake Figure 2

Claims (1)

[Claims] ■ When connecting the inside of the molding mold Nomux and the inside of the compressed air box to a vacuum source by sandwiching the heat-softened plastic plate between the mold box and the compressed air box from both sides, the piping on the mold box side A double-sided vacuum forming device made from a plastic plate, characterized in that: and a compressed air box side piping are connected to a vacuum source via a balance valve. 2. The double-sided vacuum forming apparatus from a plastic plate according to claim 1, wherein the balance valve is a round piston balanced by a spring in a force box. 3 The balance valve is a diaphragm balanced in the valve box.
.