Valve pin and nozzle configuration and method of control

An injection molding apparatus comprising:

• a manifold having a manifold channel that receives an injection fluid,
• a nozzle having a nozzle channel having an axis receiving the injection fluid from the manifold channel, the nozzle having a distal tip in fluid communication with a gate to a mold cavity,
• the distal tip of the nozzle being comprised of a heat conductive insert and an insulation cap that is substantially less heat conductive than the insert, mounted coaxially within the nozzle channel in nested contact with each other,
• the heat conductive insert and the insulation cap each having a downstream end portion containing a fluid exit aperture that are aligned with each other enabling flow of injection fluid through the nozzle channel downstream into the mold cavity,
• the downstream end portion of the insulation cap being disposed between the gate and the downstream end portion of the heat conductive insert forming a fluid seal around the gate,
• a valve pin interconnected to an actuator adapted for controllably driven reciprocal movement of the valve pin coaxially through the nozzle flow channel,
• the valve pin having a distal end portion having a downstream-most circumferential surface complementary to an axially interior surface of the gate and a downstream surface portion around the circumference of a bulbous portion of the valve pin immediately upstream of the downstream-most circumferential surface that mates with a guide surface of the insert to stop flow of injection fluid upstream of the axially interior surface of the gate, downstream surface portion having a gap enabling circumferential surface around the circumference of the bulbous portion of the valve pin,
• the actuator being adapted to controllably drive the distal end portion of the valve pin along a drive path extending between one or more upstream positions where the injection fluid flows through the gate and a downstream gate closed position where the distal end portion of the valve pin mates with the axially interior surface of the gate to stop flow of injection fluid through the gate,
• wherein when the valve pin is in the gate closed position, an axially interior surface of the fluid exit aperture of the insulation cap surrounds the gap enabling circumferential surface of the valve pin forming a spatial gap immediately upstream of the gate and downstream of the guide between the interior surface of the fluid exit aperture of the insulation cap and the gap enabling circumferential surface around the circumference of the bulbous portion of the valve pin.