Longitudinally expansible and contractible hydrostatic mold gate

In a multiple cavity mold system, a plurality of gates each of said mold gates comprising:

• a molding compound inlet conduit defining an outer end for communication with a source of molding compound and an inner end for communication with the mold cavity, a plunger member mounted in said molding compound inlet conduit and adapted to prevent flow through said conduit in a first longitudinal position, and to permit flow through said conduit in a second longitudinal position, said plunger member defining a transversly enlarged sealing end proportioned to prevent said flow through the conduit in the first position, said sealing end defining a mold cavity-facing surface which is of larger cross-sectional area than the surface of the plunger opposed to said mold chamber and subject to contact with pressurized molding compound in the conduit, said plunger member comprising a sealed tubular metal wall, at least a portion of said tubular wall defining annular convolution means to provide a longitudinally expansible and contractible characteristic to the plunger member, said tubular wall being immovably secured adjacent one end thereof whereby relatively pressurized molding compound in the conduit, relative to pressure in the mold cavity, causes said enlarged sealing end to longitudinally expand to spontaneously open into a second longitudinal position by the action of pressure on said opposed surface, the relative equalization of elevated pressures in the mold cavity and the conduit causing said enlarged sealing end to longitudinally contract to spontaneously close to its first longitudinal position.