초록 ▼

A hot sprue assembly is provided for controlling flow of molten material into the mold cavity of an injection molding machine. The hot sprue assembly is particularly designed for use with an injection molding machine for molding centrally apertured record discs, such as video information discs. The

A hot sprue assembly is provided for controlling flow of molten material into the mold cavity of an injection molding machine. The hot sprue assembly is particularly designed for use with an injection molding machine for molding centrally apertured record discs, such as video information discs. The hot sprue assembly includes a hot sprue bushing cooperating with a dispersion head to define an open and relatively narrow annular gate through which molten material is injected into the mold cavity, and a central die plug within the mold cavity for cooperating with the dispersion head to mold a central aperture into the disc. Valving of the molten material through the gate is achieved by heating the sprue assembly to create a temperature differential which, during solidification of the material within the mold cavity, permits the material within the mold cavity to solidify up to the gate without substantial solidification of material within the sprue assembly. The gate is disposed at a plane recessed slighty from the general plane of the solidified disc to prevent any surface discontinuities arising by retraction of the sprue assembly when the mold cavity is opened from projecting above the general plane of the disc.

대표청구항 ▼

In an injection molding machine for producing centrally apertured record discs, apparatus for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue assembly forming an open and relatively narrow gate for passage of the molten disc-forming material into

In an injection molding machine for producing centrally apertured record discs, apparatus for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue assembly forming an open and relatively narrow gate for passage of the molten disc-forming material into the mold cavity, said gate being disposed in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity; said sprue assembly including a sprue bushing having a central bore formed therein for passage of the molten disc-forming material toward the mold cavity, and dispersion means having a plurality of relatively small extrusion passages formed therein, said dispersion means being mounted generally within the end of said bore adjacent said mold cavity for passage of the molten disc-forming material through said extrusion passages prior to passage through said gate; and heater means for controlled elevation of the temperature of said sprue assembly to create a preselected temperature gradient between said sprue assembly and the mold cavity for permitting solidification of the disc-forming material within the mold cavity up to the gate without substantial solidification of disc-forming material within said sprue assembly.