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

A gas venting arrangement in an injection molding apparatus which includes a casting sleeve, mold halves defining a mold cavity therebetween, an injected molten metal being fed through the casting sleeve and molded within the mold cavity, the mold halves being formed with a gas vent passage in fluid communication with the mold cavity and positioned downstream with respect thereto, and a gas vent control valve disposed at a downstream end portion of the gas vent passage, the gas venting arrangement comprising:

• a detection member for detecting molten metal and generating a detection signal;
• a control circuit connected to the detection member, the control circuit generating a high voltage drive signal in response to the detection signal;
• a valve driving mechanism having one end connected to the control circuit and another end connected to the gas vent control valve, the valve driving mechanism comprising:
• a pneumatic source;
• an electromagnetic valve connected to the pneumatic source and performing change-over operation in response to the high voltage drive signal;
• a pneumatically operated valve connected to the pneumatic source and having one end connected to the electromagnetic valve and having another end;
• and
• a valve driving cylinder having one end connected to said other end of the pneumatically operated valve and having another end connected to the gas vent control valve, the pneumatically operated valve performing change-over operation in response to the change-over operation of the electromagnetic valve for applying a pneumatic pressure in the pneumatic source to the valve driving cylinder to move the gas vent control valve to its closed position.