Injection molding flow control apparatus and method

A method of controlling the rate of flow of fluid through a flow channel communicating with a gate of a mold in an injection molding apparatus, the apparatus including a valve pin having a selected longitudinal length that is slidably mounted in a housing that is adapted for back and forth axial movement of the pin through the flow channel, the method comprising:

• forming the pin with a protrusion at a selected position along its length wherein the protrusion has an upstream end having a selected curvilinear surface and a downstream end having a selected curvilinear surface,
• mounting the pin such that the protrusion is controllably drivable back and forth within the channel,
• forming the protrusion with a maximum diameter outer circumferential surface between its upstream and downstream ends;
• forming the channel with an interior surface area portion which is complementary to the maximum diameter circumferential surface such that the maximum diameter outer circumferential surface of the protrusion is matable with the interior surface area portion of the channel to stop flow of the fluid through the channel during driving of the pin;
• controlling driven movement of the pin through the channel to selectively position the pin at selectable positions where:
• the downstream end of the protrusion is positionable relative to the interior surface area portion of the channel such that the rate of flow of fluid is controllably variable and
• the upstream end of the protrusion is positionable relative to the interior surface area portion of the channel such that the rate of flow of fluid is controllably variable and
• the maximum diameter circumferential surface of the protrusion is positionable relative to the interior surface area portion of the channel such that the rate of flow of the fluid through the channel is stopped.