Valve-gate bushing for gas-assisted injection molding

Details Valve-gate bushing for gas-assisted injection molding Valve-gate bushing for gas-assisted injection molding

1998-10-13

2001-06-26

Nguyen, Nam (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Means feeding fluent stock from plural sources to common...

C264S572000, C425S546000, C425S564000

Reexamination Certificate

active

06250903

ABSTRACT:

TECHNICAL FIELD
The present invention relates to devices, such as mold bushings or nozzles, for gas-assisted injection molding systems.
BACKGROUND ART
There are many processes and techniques today for gas-assisted injection molding. Gas-assisted injection molding processes have added new flexibility to the design and manufacture of plastic parts with their ability to produce partially hollow, lightweight, rigid parts with minimal sink marks and less tendency to warp. These processes can reduce material requirements, as well as equipment costs and cycle time, and thus have advantages over conventional injection molding processes and techniques in many applications.
In general, gas-assisted injection molding systems utilize a fluid or gas, such as nitrogen, under pressure to expand the plastic material in the mold and conform it to the mold cavity details. The fluid or gas can be introduced into the mold in several ways, such as through a bushing, nozzle, or machine nozzle in one or more cavities, or in more than one location.
With gas-assisted injection molding techniques, care must be taken to ensure that the gas delivery orifices into the mold do not become plugged or clogged with plastic material and, at the same time, it is necessary that the gas be directed into the mold cavity and not back into the bushing, runner system, or plastic injection system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved nozzle or bushing for use with a gas-assisted injection molding process. It is also an object of the present invention to provide an improved gas-assist bushing or nozzle for introduction of plastic material and gas into one or more cavities and at one or more locations.
It is another object of the present invention to provide an improved valve-gate bushing or nozzle for use with a gas-assisted injection molding process. It is a further object of the present invention to provide a nozzle or bushing with a movable gate pin which can close off the entry of plastic material into the mold, and at the same time allow entry of gas therein.
It is a still further object of the present invention to provide a gas-assisted injection molding system having orifices or openings into the mold cavity which do not become plugged or clogged with plastic material and which prevents the gas from entering back into the bushing, runner system, or plastic source.
The present invention overcomes prior difficulties with valve-gate type bushings or nozzles and fulfills the objects and purposes noted above. The present invention provides a pin-type valve-gate device which effectively blocks off the flow of plastic material into the mold as desired, allows the entry of the gas into the mold cavity, prevents the plastic material from plugging or clogging the gas orifices, and prevents the gas from flowing or entering back into the bushing and plastic material supply.
In particular, the bushing preferably includes a movable shut-off pin mechanism which selectively allows plastic material to enter the mold cavity and at the same time has a series of small slits, apertures or openings in the pin, body or components which allow gas or fluid to pass therethrough, but are too small to allow plastic material from entering. The small slits or openings can be positioned to allow gas flow in an axial direction, in a direction transverse to the longitudinal axis, or both. The slits or openings can be produced by machining techniques, or by a combination of parts with predefined spaces between them, and can have diverging, converging or parallel cross-sections. The slits or openings also can be used to exhaust the gas or fluid from the part cavity after the injection process is complete.
These and other objects, purposes, benefits and advantages of the present invention will become apparent from the following detailed description of the invention, when taken together in view of the accompanying drawings and appended claims.


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