Injection molding system having offset valve pin biasing mechanism

Claim 1

In a valve gated center entry hot runner injection molding apparatus having a heated nozzle which is secured to a heated manifold, the heated nozzle being received in a cavity plate, said nozzle having a central bore and a forward nose portion which extends through an opening in the cavity plate to a cavity, the central bore of the nozzle having a rear portion and a forward portion which extends through the nose portion of the nozzle to form a gate forming a forward mouth, an elongated valve member which extends through the central bore in the nozzle and reciprocates longitudinally between a retracted closed position and a forward open position, the valve member having a forward portion, a central portion, and a rear portion, the central portion of the valve member extending through the rear portion of the central bore, the rear portion of the valve member extending into a central opening the manifold, and a melt passage to convey pressurized melt from a central inlet in the manifold to the gate, the melt passage extending through the manifold and nozzle around the rear portion of the valve member to join a space which leaks to the gate, the space extending around the forward portion of the valve member in the forward portion of the central bore, the central portion of the valve member fitting in the rear portion of the central bore to prevent substantial leakage of the pressurized melt around the reciprocating valve member, the improvement wherein: the valve member has an enlarged forward end which seats in the mouth of the gate in the retracted closed position, and (a) at least one biasing mechanism is mounted in the manifold, the at least one biasing mechanism including a compression spring mounted in the manifold and lever means extending to receive a force from the compression spring and apply a force to the valve member in a rearward direction.