Abstract: A method and apparatus for gas assisted injection molding which will first inject a shot of molten plastic into a suitable mold, shut off the plastic flow into the mold, and either immediately, or after a delayed time, inject a suitable pressurized gas into the mold at a desired injection pressure. The pressure of the gas in the mold is then controlled by stepping up or stepping down the pressure in the mold in a series of steps to arrive at a second predetermined and precisely controlled pressure. The predetermined pressure is held for a desired time. The setting and holding of pressure is repeated as many times as desired, and is then stepped down to a final pressure. The mold is then opened, and the article is removed.

Abstract: An improved nozzle for gas-assisted injection molding and a method of gas-assisted injection molding using the improved nozzle are provided. This improved nozzle employs a very simple design to vent the gas from the mold cavity once the plastic article has cooled sufficiently to be self supporting. In one especially preferred embodiment of this invention, the improved nozzle contains a separate plastic shut-off valve, a separate gas inlet passage with a check valve, and a separate gas venting passage containing a movable pin. Venting of the pressurized gas occurs by movement of the movable pin so that the pressurized gas can burst through the thin layer of plastic material covering the gas venting passage. The improved nozzle design and method allow for almost continuous operation with minimal operator attention to the nozzle.

Abstract: A method and associated apparatus for gas assisted injection molding wherein a quantity of fluid molding material is injected through a first injection flow path in a gas assisted injection molding nozzle into a mold cavity. The injection is then stopped by interrupting the flow of fluid through the first mold cavity, and introducing a time delay if desired. After any time delay, a quantity of pressurized gas or fluid at a first desired pressure is injected into the mold cavity through a second injection flow path which is isolated from the first injection flow path. The pressure is then reduced to a desired holding pressure, and the pressure is held in the mold while the part cools enough to be self supporting, at which time the pressure is vented from the mold cavity, and the part removed. The apparatus used, by isolating the molding material from the gas passages, is able to be of a simpler construction, avoid clogging of the passages, and use larger gas passages, all without the use of any check valves.

Abstract: A check valve is provided that is especially useful in gas-assisted injection molding wherein pressurized gas is injected into molten plastic material. A tapered or cone-shaped valve member which seats into a correspondingly tapered or cone-shaped valve chamber provides the mechanism by which the valve seals against reverse flow. Any plastic material entering the gas passageway would contact the base end of the tapered or cone-shaped valve member and not any sealing surfaces. By minimizing contact with the sealing surfaces, the useful lifetime of the check valve is significantly increased.

Abstract: Apparatus and methods suitable for controlling and metering thermoplastic material or resin to multiple cavities in a multi-cavity injection molding tool are described, whereby the amount of resin injected into each cavity can be individually controlled. This system minimize overfilling or underfilling of individual article cavities in such a multiple cavity tool and, therefore, allows for the production of more uniform plastic articles from a multiple cavity mold or tool. In practice, a spindle, which is designed to rotate in a reproducible manner as resin flows past it, is inserted into the resin stream feeding each cavity. The amount of resin fed to a particular cavity is determined by measuring the rotation of the spindle. When the amount of resin fed to a particular cavity is equal to the amount appropriate for that cavity (the target amount), the shut-off valve associated with that cavity is activated, thereby terminating the resin flow to that cavity without affecting resin flow to the other cavities.