Apparatus for fluid compression of injection molded plastic material

In an injection molding apparatus including first and second mold sections which close together to define a parting line and form a mold cavity for molding an article, a first inlet for introducing hot plastic material into the mold cavity, a second inlet for introducing pressurized gas into the mold cavity and between a first surface of the plastic material and the surface of the mold section adjacent thereto whereby to move the plastic material at that position and the outer surface thereof away from the adjacent mold section towards the other mold section, the improvement wherein

• said mold cavity includes first and second cavity surfaces which form, at least in part, the outer and inner surfaces of the article to be molded, said first cavity surface being formed with a series of interconnected gas passages,
• said fluid injection means comprises a gas inlet opening on said first cavity surface and in communication with said gas passages, said gas inlet for communicating said pressurized gas to at least one of said gas passages, and
• sealing means for preventing said pressurized gas from escaping from said mold cavity and maintaining a predetermined fluid pressure on said plastics material for a predetermined time sufficient for the plastic material to solidify.

In an injection molding apparatus including first and second mold sections which close together to define a parting line and form a mold cavity for molding an article, a first inlet for introducing hot plastic material into the mold cavity, a second inlet for introducing pressurized gas into the mold cavity, a second inlet for introducing pressurized gas into the mold cavity and between a first surface of the plastic material and the surface of the adjacent mold section whereby to move the plastic material at that position and the outer surface thereof away from the adjacent mold section towards the other mold section, the improvement comprising

• sealing means for preventing said pressurized gas from escaping from said mold cavity and maintaining a predetermined fluid pressure on said plastic material for a predetermined time sufficient for the plastic material to solidify, and
• said fluid injection means comprises a cylindrical recess in the surface of said mold section, and a plurality of generally concentric C-shaped wall sections in said recess, the wall sections forming a plurality of cylindrical gas passages with the ends of each of said C-shaped wall sections forming a throat for communicating fluid between the gas passages formed on each side of the wall section,
• said second inlet for communicating said pressurized gas to at least one of said gas passages.

An apparatus for producing an injection molding of plastic material comprising means defining a first inlet for introducing plastic material into a mold space, and means including a second inlet for applying at at least one selected position an external pressure on one surface of the plastic material which moves the plastic material at that position inwardly of the mold space away from the adjacent mold surface and for maintaining the external pressure until the plastic material is self supporting, characterized by

• said first inlet for introducing plastic material being separate from said second inlet, and
• seal means for inhibiting external gas once injected into the mold space from migrating around the plastic material and reaching the outer surface thereof,
• said seal means including an undercut encircling said second inlet being adapted to receive a portion of the plastic material whereby during cooling of the plastic material a seal ring is formed which prevents gas from escaping from the mold space.