초록 ▼

A mold apparatus and method is used to form a solid injection molded plastic part having no internal voids, a Class A finish, a sink-free exterior appearance surface, and unevenly distributed structural detail extending from the opposite surface, the detail including free-standing reinforcement ribs

A mold apparatus and method is used to form a solid injection molded plastic part having no internal voids, a Class A finish, a sink-free exterior appearance surface, and unevenly distributed structural detail extending from the opposite surface, the detail including free-standing reinforcement ribs, attachment bosses, and the like. In sequence, a seal groove in the mold cavity is reduced to a pressure below atmospheric (i.e., negative), a charge of hot thermoplastic is introduced into the mold cavity and seal groove whereby to form a gas seal ring, and pressurized gas is injected into the mold cavity. The pressurized gas forces the hot plastic from one mold half against the other mold half, and the gas seal formed by the plastic prevents gas on one side of the thermoplastic from reaching the appearance surface of the part.

대표청구항 ▼

1. A method of producing an injection molded article, the article having a finished outer surface, the method comprising, in sequence,clamping together the mating faces of a pair of mold portions having respective article forming surfaces whereby to define a mold cavity, the article forming surface

1. A method of producing an injection molded article, the article having a finished outer surface, the method comprising, in sequence,clamping together the mating faces of a pair of mold portions having respective article forming surfaces whereby to define a mold cavity, the article forming surface of one of said mold portions including a continuous sealing groove; sealing said mold cavity to form a substantially sealed condition; evacuating the air in the sealing groove through a first gas port subsequent to the step of sealing said mold cavity to a reduced pressure which is substantially equal to or higher than about 0.9 atmospheres but below atmospheric pressure; introducing molten thermoplastic material into the evacuated mold cavity and sealing groove; applying a pressurized gas at least through said first gas port onto at least one surface of the thermoplastic material to force said molten thermoplastic material away from one mold portion and against the other mold portion to form the finished outer surface of the article; allowing the material to cool and solidifying in a cooling phase; and separating the mold portions and removing the injection molded article.