Self-propelling sprue bar shutoff device

An injection mold shutoff assembly comprising:

• an integral injection molding machine nozzle tip having a beveled forward end, the forward end terminating forwardly with an abutting surface;
• an assembly block defining a chamber;
• an exterior seat in the assembly block, the exterior seat sealing to the injection molding machine nozzle tip when the nozzle tip is in an engaged position and spaced from the nozzle tip when the nozzle tip is in a nonengaged position;
• a first opening in the assembly block providing fluid communication from the exterior seat to the chamber through an entry wall of the chamber, a first sealing surface of the entry wall surrounding the first opening;
• a movable body reciprocally movable within the chamber between a rear position proximate to the entry wall and a forward position remote from the entry wall, the movable body having a second sealing surface which seals with the first sealing surface when the movable body is in the rear position;
• an exit wall of the chamber including a second opening formed therein and being in fluid communication with a receiving unit;
• the abutting surface of the nozzle tip contacting the movable body when the nozzle tip is in the engaged position so as to prevent the movable body from being in the rear position;
• and
• the movable body biased toward the rear position, such that when the nozzle tip is in the nonengaged position, the second sealing surface seals with the first sealing surface, closing the first opening.

An injection molding shutoff assembly, comprising:

• an injection molding machine nozzle tip having a forward end formed around an axis, the forward end terminating in an abutting surface, a side surface of the forward end of the nozzle tip extending rearwardly from the abutting surface, the side surface formed as a noncylindrical surface of rotation around the axis and having a radius which decreases continuously and monotonically in an axial forward direction, the side surface having an axial length;
• an assembly block defining a chamber with a rear end and a forward end, an entry wall disposed at the rear end of the chamber and an exit wall disposed at the forward end of the chamber, a first opening formed in the entry wall of the chamber and disposed on the axis, a first sealing surface of the entry wall formed around the first opening;
• the assembly block having an exterior surface, an exterior seat formed in the exterior surface to be coaxial with and communicating with the first opening, a forward section of the exterior seat formed as a noncylindrical surface of rotation which is matable to the side surface of the forward end of the nozzle tip;
• a movable body reciprocable within the chamber between a rear position and a forward position, the movable body having a second sealing surface matable to the first sealing surface of the entry wall when the movable body is in the rear position;
• the forward section of the exterior seat of the assembly block having an axial length which is less than said axial length of the side surface of the forward end, such that when the forward end is mated with the forward section of the exterior seat, the forward surface of the nozzle tip extends forwardly into the chamber, propping the movable body toward the forward position.

A method for connecting and disconnecting an injection molding machine nozzle to and from a shutoff assembly having a chamber, comprising the steps of:

• biasing a movable body within the chamber with a magnetic force toward a rear position proximate a first opening in the chamber;
• connecting the injection molding machine nozzle to the assembly, the step of connecting including the substeps of:
• mating a tip of the nozzle of the injection molding machine to an exterior seat in the assembly, the seat in fluid communication with the chamber through a first opening extending from the seat to the chamber, a first sealing surface surrounding the first opening;
• concurrently with said substep of mating, contacting an abutting surface of a forward end of the nozzle tip with the movable body and pushing the movable body from the rear position proximate to the first opening toward a forward position remote from the first opening;
• flowing molten polymer through the first opening to a second opening in the chamber and thence to at least one receiving unit in fluid communication with the second opening;
• decompressing the receiving unit, said step of decompressing comprising the substeps of:
• ceasing the flow of the molten polymer from the first opening toward the second opening;
• maintaining contact between the abutting surface of the nozzle tip and the movable body;
• and
• allowing molten polymer to flow from the second opening toward the first opening;
• disconnecting the injection molding machine nozzle tip from the assembly, said step of disconnecting including the substeps of:
• withdrawing the forward end of the nozzle tip from the chamber through the first opening;
• concurrently with said substep of withdrawing, moving the movable body to the rear position by means of at least one of the magnetic force and molten polymer flowing back from the second opening toward the first opening;
• and
• sealing the second sealing surface with the first sealing surface.