Gas venting arrangement incorporated into a mold

In a gas venting arrangement incorporated into a mold formed of stationary and movable mold halves together defining a cavity to be filled with a melt, said gas venting arrangement comprising:

• (a) a valve chamber including an enlarged forward portion formed in said mold and a constricted rear portion formed in a member separate from said mold, and a valve seat formed between said forward and rear portions;
• (b) a gas vent passage formed in said mold connected to said cavity and to the forward end of said forward portion of said valve chamber;
• (c) a gas discharge passage formed in said mold and opening on an inner side surface of said rear portion of said valve chamber to communicate with the outside of said mold;
• (d) at least one by-pass passage formed in said mold branching from a point on said gas vent passage to an opening on an inner side surface of said forward portion of said valve chamber;
• (e) a valve slidably received in said forward portion of said valve chamber for movement between a first position, wherein said valve cooperates with said valve chamber to prevent said gas vent passage from communicating with said gas discharge passage through said forward portion of said valve chamber and to permit said by-pass passage to communicate therewith through said valve chamber, and a second position, wherein said valve rests against said valve seat and cooperates with said valve chamber to prevent both said by-pass passage and said gas vent passage from communicating with said gas discharge passage through said valve chamber;
• (f) first means for biasing said valve into said first position and permitting movement of said valve into said second position under axial impingement against said valve of a portion of said melt injected into said cavity and forced to flow through said gas vent passage into said forward portion of said valve chamber, said first biasing means being adjusted and said by-pass passage being dimensioned and configured to permit movement of said valve into said second position before a second portion of said melt reaches said forward portion of said valve chamber through said by-pass passage;
• (g) second means for biasing said valve into said second position after said valve is forced to move from said first position to said second position by an initial impingement of said melt;
• and
• (h) first means for releasing said valve from said second biasing means to return from said second position to said first position, the improvement consisting in that:
• (A) said gas venting arrangement comprises a pneumatic piston-cylinder device in such arrangement that said rear portion of said valve chamber has a closed rear end and extends rearward to form said cylinder at its rear end portion, and said valve has a rearward extension co-axially therewith and extending slidably thereinto, said valve extension forming said piston at its rear end portion;
• (B) said first biasing means is that for releasably securing said valve in said first position to said rear portion of said valve chamber against the force of said second biasing means;
• (C) said second biasing means is that for constantly urging said piston rearward relative to said rear portion of said valve chamber;
• (D) said piston-cylinder device functions as said first releasing means in such manner that said device actuates said piston to move forward against the force of said second biasing means;
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• (E) said piston-cylinder device further functions as second means for releasing said valve from said first biasing means to move from said first position to said second position in such manner that said device actuates said piston to move rearward against the force of said first biasing means.