| 摘要 |
<p>This invention relates generally to a method and apparatus for molding a centrally apertured part, such as a video disc. Prior art molding techniques are deficient in that extremely tight hole centering tolerances could not be met, and likewise thickness tolerance caused excessive birefringence of a light beam used in reading the disc. The present invention overcomes these deficiencies by providing an improved molding technology In accordance with the invention heated material is injected into an annular cavity, defined by a pair of mold halves, through a sprue passage, defined by a sprue bushing and an end portion of a punch. The annular cavity and the sprue passage form, respectively, the centrally apertured part and a sprue. After partial cooling of the heated material, the punch is locked in place while the annular cavity is displaced relative to the sprue passage so that the sprue is severed from the part along the peripheral surface of the punch end portion. The mold halves are separated to open the annular cavity while the sprue is resting on the punch end portion, and while the part is held by the punch end peripheral surface. After the mold halves are separated, a sprue ejector member is actuated to eject the sprue from the punch end portion. The finished video disc is then removed, carried by the moving platen of the moving mold assembly. An improved injection gate is also provided, as well as a unique manner of cooling the mold assembly.</p> |
