Patent ID: 6227840
Filing Date: 2001-05-08
Classification: B29C,B29L,B62D,Y10T

Abstract:
An apparatus for molding a relatively large article comprising:first and second mold halves defining a mold cavity therebetween in a shape of an article to be produced when the mold halves are clamped together in a closed relationship at a selected clamping pressure;first injection conduit in one of the mold halves for injecting molten thermoplastic resin into the mold cavity at a first location;a first gate valve connected to the first injection conduit for controlling the flow of thermoplastic resin through the first injection conduit to the mold cavity;a second injection conduit in one of the mold cavities for injecting molten thermoplastic resin into the mold cavity at a second location spaced from the first location;a second gate valve connected to the second injection conduit for controlling the flow of thermoplastic resin through the second injection conduit to the mold cavity;a sensor in the mold to sense the arrival of the molten thermoplastic resin at the second location;a controller connected to the first and second gate valves for controlling the opening and closing of the first and second gate valves, the controller being programmed to open the first gate valve and to close the second gate valve during an initial period of time in which molten thermoplastic resin is injected under pressure into the mold cavity through the first injection conduit and to open the second gate valve substantially simultaneously with the arrival of the molten thermoplastic resin at the second injection conduit from the first injection conduit in response to the sensed arrival of the thermoplastic resin at the second location and to thereafter close the first gate valve to terminate the flow of molten thermoplastic resin into the mold cavity from the first injection conduit all while the mold halves are maintained in the closed relationship at least at the selected claiming pressure;a gas-injection conduit with a gas control valve and connected to a mold cavity for injecting an inert gas under pressure into the mold cavity to force the molten thermoplastic resin to the edges of the mold cavity; andthe controller is connected to the gas control valve and is further programmed to open the gas control valve to inject inert gas under pressure into the mold cavity at a time interval after the first gate valve is closed and while the mold halves are maintained in the closed relationship at least at the selected clamping pressure.