Molding devices

In order to facilitate the formation of a plastic member with an aperture in a central portion thereof, a ring gating valve arrangement is provided with a multi-piston servo arrangement which enables a specially configured pin (134) to be stepwisely reciprocated back and forth within a molding device. The pin (134) is formed with a land (134a) at one end which is dimensioned and shaped to produce the required aperture. The pin (134) further features a channel structure which includes an annular recess (134d) adapted to permit plastic to flow into the center of the mold cavity area (120) when the pin (134) is thrust to a predetermined location. After the cavity is filled with hot plastic, the pin (134) is retracted to a position wherein the annular recess (134d) is located within a removable gate bushing (116) and the shaped land (134a) is pulled up until it is appropriately located in the mold cavity area (120). As the injected plastic cools and solidifies, the shaped land (134a) acts as the aperture molding pin and forms a clean aperture in the molded part. After solidification, the pin (134) is retracted and the mold is opened to permit the molded part to be ejected.