Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – With internal application of fluid pressure
Reexamination Certificate
1999-03-19
2001-04-24
Davis, Robert (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
With internal application of fluid pressure
C055S385100, C425S130000, C425S546000
Reexamination Certificate
active
06221306
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally pertains to an injection molding apparatus. More specifically, the present invention relates to a gas assisted injection molding apparatus which utilizes a pin-in-sleeve device to direct a gas into a mold cavity.
Gas assisted injection molding has by now become quite popular for its many advantages. These advantages are set forth in, e.g., U.S. Pat. Nos. 4,905,901 dated Mar. 6, 1990; 5,151,278 dated Sep. 29, 1992; 5,164,200 dated Nov. 17, 1992; 5,174,932 dated Dec. 29, 1992 and 5,256,047 dated Oct. 26, 1993. The disclosure of each of these patents is specifically incorporated hereinto in its entirety.
For a pin-in-sleeve arrangement, a pin is positioned in a sleeve such that an annular fluid flow passage is defined between the pin and the sleeve. Pin-in-sleeve arrangements are employed for feeding gas into a mold cavity either through a nozzle, which regulates the flow of plastic into the mold cavity, or spaced from such nozzle. When the pin-in-sleeve device is spaced from the nozzle, the gas is directed into the article. This is termed in-article gas assisted injection molding.
When an in-article gas assisted injection molding device is employed, it is desirable to allow a quick change out of a gas pin of the device. The quick change out feature reduces down time for a molder who would normally have to pull the mold out of the injection molding machine to replace a pin that has become plugged with resin.
Resin plugging of gas injection pins has always been the main problem of gas assisted injection molding. There have been many complicated devices invented to overcome this problem. However, none of these devices have really worked satisfactorily. The pin-in-sleeve design for in-article gas assisted injection molding disclosed herein recognizes the fact that pins without check valves always will plug sooner or later.
Accordingly, it has been considered desirable to develop a new and improved pin-in-sleeve device for in-article gas assisted injection molding which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a pin-in-sleeve device for injecting a non-viscous fluid into a cavity of a mold is provided. The mold includes a socket for receiving the device. The socket has an open end which opens into the mold cavity. The device includes a sleeve, which is received in the socket, and a pin, which extends through the sleeve. The sleeve includes a longitudinally extending bore with an open first end. The bore has a first portion of a first diameter adjacent the bore open end, and a second portion of a second, larger diameter A fluid flow path for the non-viscous fluid is defined between the pin and the bore.
The pin includes a forward section, which is received in the bore first portion, and a base, which is received in the bore second portion. The base has a diameter which is larger than the diameter of the bore first portion. A restraining member is connected with the sleeve for restraining the pin in the sleeve.
In accordance with another aspect of the present invention, an apparatus for use in fluid assisted injection molding of plastic material so as to form an injection molded product is provided. The apparatus includes a pair of mold members defining, when connected, a sealed cavity. A first opening is provided in one of the mold members for admitting the plastic material into the cavity. A second opening is provided in one of the mold members and spaced from the first opening for admitting a fluid into the cavity.
A sleeve extends through the second opening. The sleeve has a longitudinally extending bore opening into the cavity. The bore has a first portion of a first diameter adjacent the cavity, and a second portion of a second, larger diameter spaced from the cavity.
A pin extends through the sleeve. A fluid flow path is defined between the pin and the bore. The pin includes a forward section, which is received in the bore first portion, and a base, which is received in the bore second portion. The base has a diameter which is larger than the diameter of the bore first portion.
In accordance with yet another aspect of the present invention, a method of fluid assisted injection molding of plastic material is provided for forming an injection molded product. The method includes threadably connecting a pin-in-sleeve device, substantially as previously described, to a socket in one of a pair of mold members. The method further includes connecting the mold members together to form a sealed cavity which is defined by the mold members, such that the bore open end communicates with the cavity and injecting the plastic material through a nozzle into the sealed cavity. Further, the method includes injecting a fluid through a fluid flow path defined between the pin and the bore.
One advantage of the present invention is the provision of a pin-in-sleeve device in which the pin is easy to change, the device is easy to disassemble and clean, and the device provides a means whereby resin cannot get beyond the pin assembly and into the gas feeding lines.
Another advantage of this invention is the provision of a self-contained pin-in-sleeve design for in article gas assisted injection molding.
Yet another advantage of the present invention is the provision of a pin-in-sleeve gas injection and withdrawal device for in article gas assisted injection molding which employs a sintered metal filter to prevent any resin from getting behind the pin assembly.
Still another advantage of the present invention is provision of a pin-in sleeve device in which a tip of the pin has a hexagonal cross section with a largest diameter which is substantially equal to the diameter of an adjacent first portion the bore such that the flow path is divided into sectors.
A further advantage of the present invention is provision of a pin-in-sleeve gas injection device having a threaded portion on an exterior surface of the sleeve of the device for threading the device into the mold socket.
A yet further advantage of the present invention is the provision of a pin-in-sleeve device in which an exterior of the sleeve is shaped for engagement by a suitable tool for inserting and removing the device from a socket.
A still yet further advantage of the present invention is the provision of a pin-in-sleeve device with an annular rib or groove for keying into adjacent viscous fluid in the cavity to inhibit the flow of non-viscous fluid around the device and into a socket in which the device is mounted.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon a reading and understanding of the following detailed description of the preferred embodiments.
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Patent Abstracts of Japan, vol. 98, No. 9, Jul. 31, 1998.
Patent Abstracts of Japan, vol. 18, No. 650 (M-1719), Dec. 9, 1994.
Davis Robert
Fay Sharpe Fagan Minnich & McKee LLP
Nitrojection Corporation
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