Hollow injection-molding method and pressurized fluid introducin

Details Hollow injection-molding method and pressurized fluid introducin Hollow injection-molding method and pressurized fluid introducin

1993-08-27

1995-04-25

Tentoni, Leo B.

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

With internal application of fluid pressure

2643287, 2643288, 26432812, 26432813, 425130, 425557, 425562, 425573, B29C 4500, B29D 2200

Patent

active

054096596

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a hollow injection-molding method of forming a hollow portion of molten resin in a mold cavity by introducing a pressurized fluid, and the invention also relates to a pressurized fluid introducing and discharging apparatus therefor. More particularly, the invention relates to a hollow injection-molding method wherein a pressurized fluid is directly introduced into molten resin in a mold such as a sprue, a runner and a mold cavity, and the pressurized fluid in the hollow portion is discharged through the pressurized fluid introducing passage, and the invention also relates to a pressurized fluid introducing and discharging apparatus therefor.


BACKGROUND ART

Conventional hollow injection-molding methods of forming a hollow portion in molten resin in a mold cavity by introducing a pressurized fluid, wherein the pressurized fluid is directly introduced into molten resin in a mold cavity and the pressurized fluid in the hollow portion is discharged through the introducing passage for the pressurized fluid, and a pressurized fluid introducing apparatus therefor are disclosed in Examined Japanese PatentPublications Nos. SHO. 48-41264, and SHO. 59-19017, and U.S. Pat. No. 4,740,150.
Examined Japanese PatentPublication No. SHO. 48-41264 discloses a hollow injection-molding method and a pressurized fluid introducing and discharging apparatus therefor wherein, as shown in FIG. 11, a thin cylindrical projection 102 having a pressurized fluid passage 101 therein is disposed so that it can be projected into and retracted from a mold 103. While the projection 102 is projected into the mold 103, molten resin is injected and a pressurized fluid is introduced from the pressurized fluid passage 101, thereby forming a hollow portion. After cooling and solidification, the pressurized fluid is discharged from the hollow portion through the pressurized fluid passage 101. The projection 102 is retracted from the mold 103, and then the mold article is removed.
Examined Japanese PatentPublication No. SHO. 59-19017 discloses a hollow injection-molding method and a pressurized fluid introducing and discharging apparatus therefor wherein, as shown in FIG. 12, a valve 107 operated by a cylinder 106 to open and close the pressurized fluid passage 101 is disposed in the intermediate portion of a molten-resin passage 105 through which injected molten resin is guided to a mold cavity 104. A pressurized fluid is introduced and discharged through the valve 107 and the pressurized fluid passage 101.
U.S. Pat. No. 4,740,150 discloses an injection-molding method and a pressurized fluid introducing and discharging apparatus therefor wherein a pressurized fluid is introduced into molten resin injected into a mold cavity, through a non-return valve and a nozzle having a pressurized fluid introducing passage which can be communicated with the mold cavity. After the resin solidifies, the nozzle is retracted to open the valve port so that the pressurized fluid in the resin is discharged to the atmosphere.
However, these hollow injection-molding methods and pressurized fluid introducing and discharging apparatuses therefor have following problems.
The hollow injection-molding method and the pressurized fluid introducing and discharging apparatus therefor which are disclosed in Examined Japanese PatentPublication No. SHO. 48-41264 have problems as follows: When molten resin is injected, the molten resin flows back into the pressurized fluid passage 101 in the projection 102, thereby causing the pressurized fluid passage 101 to be clogged. In order to prevent the backflow of molten resin, it may be considered that the bore diameter of the pressurized fluid passage is reduced. However, the time to discharge the pressurized fluid from the hollow portion then increases, thus increasing mold cycle time and reducing mold efficiency.
The hollow injection-molding method and the pressurized fluid introducing and discharging apparatus therefor which are disclosed in Examined Japanese Patent Publication No. SHO. 59-19

REFERENCES:
patent: 4740150 (1988-04-01), Sayer
patent: 5080570 (1992-01-01), Baxi et al.
patent: 5127814 (1992-07-01), Johnson et al.
patent: 5173241 (1992-12-01), Shibuya et al.
patent: 5198177 (1993-03-01), Sugiyama et al.
patent: 5198238 (1993-03-01), Baxi

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