Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means between charger and mold to cut off flow of...
Reexamination Certificate
2002-07-01
2004-09-21
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means between charger and mold to cut off flow of...
C425S572000
Reexamination Certificate
active
06793480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a valve apparatus for gas-assisted injection molding. More particularly, the present invention relates to a fluid assisted shutoff nozzle valve.
2. Description of the Prior Art
The use of pressurized gas to assist in injection molding of resinous material is known in the art. It is important in injection molding processes to control the flow of the resinous material while minimizing the back flow of the resinous material from the molded article.
U.S. Pat. No. 3,295,169 to Moslo discloses a spring pressed shutoff for an injection nozzle for use in connection with a plastic injection molding machine. The nozzle of the Moslo invention includes a hollow elongated body that is open at the rear end and closed at the forward end except for a small discharge opening. The body has a generally cylindrical internal diameter for the major portion of its length except at the forward end where it tapers in generally conical shape toward the discharge opening.
A shutoff pin is slidably mounted in the hollow body. This pin has a nose adapted to close the discharge opening. A helical spring is provided biasing the pin toward its closed position. The shutoff pin includes a central passageway and a plurality of diverging passageways in fluid communication with the central passageway. The plurality of diverging passageways are evenly spaced about the central axis of the shutoff pin so the pressure in the passageways will balance in a radial direction and the shutoff pin will slide easily in the nozzle body. A discharge pocket is defined in an area between the forward end of the nozzle body and the nose portion of the shutoff pin.
When the injection material under pressure is forced through the passageways and into the discharge pocket at the start of an injection operation, pressure will build against an effective area at the forward end of the nozzle body to overcome the pressure against an effective area at the rear end of the nozzle body, thereby causing rearward movement of the pin which overcomes the bias and compresses the helical spring. This will open the nozzle so that the melt or injection material will pass through the discharge pocket into a mold cavity downstream of the nozzle body. As soon as the molding operation ceases, the spring will again bias the shutoff pin forwardly so that the nose of the pin will close the discharge opening.
The Moslo disclosure relies on differential pressure to begin actuation of the injection nozzle after overcoming the bias of the helical spring for the shutoff. The reliance on differential pressure actuation taught by Moslo necessitates a complex design with a system of passageways and cavities such that the pressure is properly balanced and does not restrict the motion of the shutoff pin. Furthermore, regulation of the proper pressure differential is a delicate process in which a slight pressure imbalance can result in premature shutoff or backflow. Finally, the Moslo disclosure is not adapted to accommodate a valve for the introduction of gas in a gas-assisted injection-molding operation.
U.S. Pat. No. 4,010,903 to Sakuri et al., discloses a plug-in type nozzle with a valve gate for molding of thermoplastic materials. The nozzle of the Sakuri et al. disclosure includes a cylinder, a differential moving piston and a spring.
The interior of the cylinder forms a cylindrical piston chamber. An inlet is provided through the rear end of the cylinder, and is connected to a conventional molding machine. A gate is provided in the front end of the cylinder along the axis of the cylinder, and is connected to a mold cavity. A front portion of the piston chamber and a rear portion of the piston chamber are interconnected with a passage.
The differential moving piston is disposed in the piston chamber slidably in the axial direction of the cylinder. The differential moving piston includes a front piston, a rear piston and a piston rod. A needle protrudes forward from the front end of the front piston. When the differential moving piston is in the front position, the needle couples with the gate and when the differential moving piston is in the rear position, the needle is apart from the gate. The spring is disposed in the rear portion of the piston chamber pressing the rear end of the rear piston forward.
Molten resin is introduced from a connected molding machine flows through the gate, fills the rear portion of the piston chamber, the passage, and the front portion of the piston chamber. When the pressure of molten resin exceeds a predetermined value, the excess pressure generates reversely directed forces acting on the differential moving piston to slide the piston backward against the forward biased spring. As a result, the gate opens automatically to inject the resin in the piston chamber to the mold cavity. When the pressure of the molten resin decreases, the gate closes automatically
The Sakuri et al. disclosure is similar to the Moslo disclosure in that both rely on differential pressure to actuate the injection nozzle, and a spring for the shutoff. Therefore, Sakuri et al. has many of the disadvantages inherent in the differential pressure systems discussed in reference to Moslo. Specifically, regulation of the proper pressure differential is a delicate process requiring very tight tolerances on the associated parts. Furthermore, a slight pressure imbalance in a differential pressure system can result in premature shutoff or backflow. Again as in Moslo, the Sakuri et al. disclosure is not adapted to accommodate a valve for the introduction of gas in a gas-assisted injection-molding operation.
U.S. Pat. No. 5,273,417 to Nelson discloses an injection nozzle for gas assisted injection molding. The nozzle of the present invention contains a separate gas entry passageway with a check valve for injection of the gas into the molten plastic stream and a separate gas exit passageway containing a movable pin or arm for venting the gas back through the plastic passageway in the nozzle.
The check valve in the gas entry passageway allows pressurized gas to be injected into the plastic material in the mold cavity but prevents gas from passing back through the gas entry passageway.
The movable pin in the gas exit passageway travels from a first or closed position to a second or open position. The movable pin is normally maintained in the closed position during injection of both the molten plastic and the pressurized gas, such that neither pressurized gas or plastic can enter the gas exit passageway. Once the plastic article has cooled sufficiently to be self-supporting, the movable pin is moved to the open position whereby the gas is allowed to vent.
In the closed position, the end or tip of the movable pin provides support for the thin layer of plastic covering the gas exit passageway. In the open position, however, the support for the thin layer of plastic is effectively removed. Therefore, upon moving the pin to the open position, the pressurized gas punctures the thin, unsupported layer of plastic covering the gas exit passageway and then vents to atmosphere.
The injection nozzle disclosed in Nelson does not include an automatic plunger or piston valve system. Nelson teaches a “push-push” or “push-pull” plastic shutoff valve that must be coordinated with each injection operation. Actuation of the plastic shutoff valve is mechanical and requires additional means for providing power, thereby adding cost and complexity to the apparatus as compared to an automatic system. Furthermore, the potential for failure of an injection operation resulting from improper actuation and/or timing of the plastic shutoff valve is introduced into the system taught by Nelson.
Finally, Nelson does not teach a means for maintaining the check valve in the closed position in the absence of pressure. Therefore, it is possible that during an injection operation, the check valve will improperly seat thereby permitting molten plastic to flow into and plug the gas entry passageway.
U.S. Pat. No. 3,4
Heitbrink Tim
VanOphem & VanOphem P.C.
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