Alternative pressure control for a low constant pressure injection molding apparatus
A low constant pressure injection molding machine forms molded parts by injecting molten thermoplastic material into a mold cavity at low constant pressures of 6,000 psi and lower. As a result, the low constant pressure injection molding machine includes a mold formed of easily machineable material that is less costly and faster to manufacture than typical injection molds.
1. A melt pressure regulating mechanism for an injection molding apparatus having a melt holder for pressurizing molten plastic prior to injection into a mold, the molten plastic having a melt pressure, and an injection element for advancing the molten plastic from the melt holder through a nozzle and into the mold, the melt pressure regulating mechanism comprising:
a pressure regulating device, disposed between the melt holder and the mold but separate from the nozzle, the pressure regulating device configured to maintain molten plastic within a mold cavity of the mold at a substantially constant melt pressure, the pressure regulating device comprising at least one of a fluid pressure regulating valve and a pressure relief valve.
2. The melt pressure regulating mechanism of claim 1 , wherein the pressure regulating device is a fluid pressure regulating valve.
3. The melt pressure regulating mechanism of claim 1 , wherein the molten plastic passageway is substantially straight between the molten plastic inlet and the molten plastic outlet.
4. The melt pressure regulating mechanism of claim 1 , wherein the pressure regulating device is a pressure relief valve.
5. The melt pressure regulating mechanism of claim 4 , wherein the pressure relief valve is configured with a set point, such that, when molten plastic on a melt holder side of the pressure relief valve has a melt pressure that is greater than the set point of the pressure relief valve, the pressure relief valve is configured to maintain molten plastic on mold side of the pressure relief valve at a melt pressure that is substantially constant, at the set point.
6. The melt pressure regulating mechanism of claim 5 , wherein the pressure relief valve includes a pressure relief outlet and the pressure relief valve is configured, such that, when molten plastic at the pressure relief valve has a melt pressure that is greater than the set point the pressure relief valve diverts a portion of the molten plastic out through the pressure relief outlet.
7. The melt pressure regulating mechanism of claim 6 , wherein the pressure relief valve is configured, such that, when molten plastic at the pressure relief valve has a melt pressure that is greater than the set point, the pressure relief valve diverts the portion of the molten plastic into a return circuit that is configured to return the molten plastic to the melt holder of the injection molding apparatus.
8. The melt pressure regulating mechanism of claim 1 , wherein the pressure regulating device comprises both the fluid pressure regulating valve and the pressure relief valve, oriented in series.
9. The melt pressure regulating mechanism of claim 1 , wherein the pressure regulating device is disposed adjacent to a mold gate of the injection molding apparatus.
10. The melt pressure regulating mechanism of claim 2 , wherein the fluid pressure regulating valve comprises:
a valve body having a molten plastic inlet and a molten plastic outlet connected by a molten plastic passageway having an orifice;
a valve plug connected to a valve stem;
a valve seat disposed within the orifice; and
an actuator connected to the valve stem, the actuator moving the valve stem and valve plug towards or away from the valve seat to control molten plastic flow through the orifice,
wherein the actuator moves the valve stem to control an amount of fluid moving through the orifice so that a melt pressure of the molten plastic that is downstream of the orifice is maintained at a substantially constant pressure is disposed in a feed system of the injection molding apparatus.
11. The melt pressure regulating mechanism of claim 2 , wherein the fluid pressure regulating valve is disposed between the nozzle and a feed system of the injection molding apparatus.
12. The melt pressure regulating mechanism of claim 2 , wherein the fluid pressure regulating valve is disposed in a feed system of the injection molding apparatus.
13. The melt pressure regulating mechanism of claim 2 , wherein the fluid pressure regulating valve is disposed between the nozzle and a manifold of the injection molding apparatus.
14. The melt pressure regulating mechanism of claim 2 , wherein the fluid pressure regulating valve is disposed in a manifold of the injection molding apparatus.
15. The melt pressure regulating mechanism of claim 8 , wherein the fluid pressure regulating valve is disposed upstream of the pressure relief valve.
16. An injection molding machine including the melt pressure regulating mechanism and the injection molding apparatus of claim 1 .
17. The injection molding machine of claim 15 , wherein the machine does not include a closed loop control system for controlling a melt pressure of the molten plastic.
18. A melt pressure control mechanism for an injection molding apparatus having a melt holder for pressurizing molten plastic prior to injection into a mold, the molten plastic having a melt pressure, and an injection element for advancing the molten plastic from the melt holder through a nozzle and into the mold, the melt pressure control mechanism comprising:
a pressure relief valve, disposed separate from the nozzle and downstream from the injection element in the melt holder.
19. An injection molding machine including the melt pressure regulating mechanism and the injection molding apparatus of claim 18 .
20. The injection molding machine of claim 17 , wherein the machine does not include a closed loop control system for controlling a melt pressure of the molten plastic.