Gas venting arrangement in injection molding apparatus and method for venting gas in the injection molding apparatus

A gas venting arrangement in a high speed injection molding apparatus which includes a casting sleeve and mold halves defining a mold cavity therebetween, an injected molten metal which is electrically conductive being fed through said casting sleeve and molded within said mold cavity, said gas venting arrangement comprising;

• a gas vent passage formed in said mold halves, said gas vent passage in fluid communication with said mold cavity and positioned downstream thereto;
• a gas vent control valve disposed at a downstream end portion of said gas vent passage;
• a detection member disposed in said gas vent passage, the detection member comprising a means for detecting said injected molten metal in said gas vent passage and generating a detection signal indicative thereof;
• a valve driving mechanism operably connected to said gas vent control valve for selectively driving said gas vent control valve to a first position in which said gas vent control valve is closed and a second position in which said gas vent control valve is open, said valve driving mechanism comprising an electromagnetic change-over valve;
• a pneumatic piston/cylinder drive means connected to said gas vent control valve and operable in response to said change-over operation of said electromagnetic valve for moving said gas vent control valve;
• a vacuum sucking device connected to said gas vent passage and positioned downstream of said gas vent control valve for positively discharging gas from said mold cavity during injection of said molten metal;
• a control means having an electronic circuit means connected between said detection member and said electromagnetic change-over valve, said electromagnetic change-over valve providing change-over operation for selectively actuating said gas vent control valve to said first position in response to said detection signal,
• said electronic circuit means comprising a flip-flop circuit which provides instantaneous operation of said electromagnetic change-over valve upon detection of a leading edge of a detection signal instantaneously generated by the detection of injected molten metal by said detection member.