Hot sprue sleeve valve assembly for an injection molding machine

In an injection molding machine for producing centrally apertured record discs, a valve assembly for controlling flow of molten disc-forming material through a sprue bushing into a disc-shaped mold cavity, comprising:

• a dispersion head secured to the end of the sprue bushing adjacent the mold cavity and including means for guiding the molten disc-forming material from the sprue bushing is a generally radially outward direction with substantially uniform radial distribution into the mold cavity;
• a sleeve valve carried about the sprue bushing for sliding movement between a first position retracted from the mold cavity to allow the material to flow from the sprue bushing past said dispersion head into the mold cavity, and a second position advanced into the mold cavity in seated engagement upon a portion of said dispersion head for separating material within said valve from material within the mold cavity to prevent flow of the material into the mold cavity, said sleeve valve and said dispersion head cooperating to mold a central aperture in the record disc;
• and
• means for controlling movement of said sleeve valve between said first and second positions,
• said control means moving said sleeve valve to said second position prior to solidification of said disc-forming material within the mold cavity,
• said control means comprising a spring for biasing said sleeve valve toward said second position, said sleeve valve further including an annular pressure face extending from said valve seat in a radially inward direction axially away from the mold cavity in spaced relation with said dispersion head when said sleeve valve is in said second position, said pressure face being responsive to the pressure of material within the sprue bushing for movement of said sleeve valve to said first position when the pressure exceeds a predetermined magnitude.

A mold assembly for an injection molding machine, comprising:

• first and second mold halves movable toward each other to define a disc-shaped mold cavity, and movable away from each other to allow a molded disc to be removed from said mold cavity;
• a sprue bushing mounted on said first mold half and including a central bore for passage of molten material in a direction toward the mold cavity generally along a central axis of the mold cavity;
• a dispersion head secured to the end of the sprue bushing adjacent the mold cavity and including means for guiding the molten disc-forming material from the sprue bushing in a generally radially outward direction with substantially uniform radial distribution into the mold cavity;
• a sleeve valve carried about the sprue bushing for sliding movement between a first position retracted from the mold cavity to allow the material to flow from the sprue bushing past said dispersion head into the mold cavity, and a second position advanced into the mold cavity in seated engagement upon a portion of said dispersion head for separating material within said valve from material within the mold cavity to prevent flow of the material into the mold cavity, said sleeve valve and said dispersion head cooperating to mold a central aperture in the record disc;
• and
• means for controlling movement of said sleeve valve between said first and second positions,
• said control means moving said valve to said second position prior to solidification of said disc-forming material within the mold cavity,
• said control means comprising a spring for urging said sleeve valve toward said second position,
• said sleeve valve including an angularly set pressure face at its end adjacent the mold cavity and oriented for communication with disc-forming material within the sprue bushing, said sleeve valve being responsive to the pressure of the material within the sprue bushing acting upon said pressure face for movement against said spring to said first position when the pressure reaches a predetermined magnitude.