System and method for preserving valve member travel in a multi-nozzle extruder
An extruder has a valve assembly configured to move pins to open and close the nozzles in a multi-nozzle extruder head independently. The pins of the valve assembly that are driven by actuators into and out of engagement with nozzles in the extruder head are positioned within sleeves that extend between the valve assembly and the extruder head. A gap is provided between the extruder head and the end of the sleeves proximate the extruder head to enable thermoplastic material leaking from the extruder that contacts the pins to remain in a melted or plastic state so the thermoplastic material does not interfere with the movement of the pins.
1. An extruder comprising:
an extruder head having a seal, a chamber for holding a volume of thermoplastic material and a plurality of nozzles fluidically connected to the chamber;
a plurality of actuators;
a plurality of elongated solid members that are operatively connected to the actuators in a one-to-one correspondence, each elongated solid member extending from the respective actuator associated with the respective elongated solid member through the seal in the extruder head and through the chamber in the extruder head to enable the respective actuator to push and pull a distal end of the respective elongated solid member into and out of engagement, respectively, with one of the nozzles in the extruder head in a one-to-one correspondence between the elongated solid members and the nozzles to enable and disable flow of thermoplastic material from the chamber through the nozzles independently;
a plurality of hollow members, each hollow member being positioned about one of the elongated solid members in a one-to-one correspondence and each hollow member extending from the respective actuator to a position short of the extruder head to form a gap between a distal end of the hollow member and an upper surface of the extruder head; and
at least one hollow member support platform having a plurality of openings, each opening being configured to receive one of the hollow members in a one-to-one correspondence, the at least one hollow member support platform being positioned between the plurality of actuators and the extruder head.
2. The extruder of claim 1 wherein the seal is a planar member having a plurality of openings, each opening in the seal receiving one of the elongated solid members in a one-to-one correspondence.
3. The extruder of claim 1 , the extruder head further comprising:
a plurality of O-rings, each O-ring being positioned within a surface of the extruder head and each O-ring being configured to receive one of the elongated solid members in a one-to-one correspondence.
4. The extruder of claim 1 wherein the hollow members bend from the plurality of actuators toward a center of the at least one hollow member support platform and the hollow members bend from the at least one hollow member support platform toward a center of the extruder head.
5. The extruder of claim 4 , the extruder head further comprising:
a planar member, each nozzle in the plurality of nozzles being positioned within the planar member and a distal end of each nozzle is flush with the planar member to enable the planar member to spread thermoplastic material emitted from the nozzles in the planar member.
6. The extruder of claim 5 wherein the gap between the distal end of each hollow member and the extruder head is approximately 1 mm or less.
7. The extruder of claim 6 wherein the distal end of each elongated solid member is rounded.
8. The extruder of claim 7 wherein each hollow member consists essentially of metal.
9. The extruder of claim 8 wherein the metal consists essentially of a low thermally conductive metal.
10. The extruder of claim 9 wherein the metal consists essentially of stainless steel.
11. The extruder of claim 9 , each elongated member further comprising:
a coating having a low coefficient of friction to facilitate movement of the respective elongated member within the respective hollow member.
12. The extruder of claim 7 wherein each hollow member is configured to reduce friction between an interior surface of each hollow member and the respective elongated solid member moving within the respective hollow member.
13. The extruder of claim 12 further comprising:
a lubricant within each hollow member to facilitate movement of the respective elongated member within the respective hollow member.
14. The extruder of claim 8 wherein each actuator in the plurality of actuators is a pneumatic actuator.
15. The extruder of claim 8 further comprising:
a controller operatively connected to the plurality of actuators, the controller being configured to operate the plurality of actuators independently to control flow of thermoplastic material from the nozzles of the extruder head independently.
16. The extruder of claim 15 , the extruder head further comprising:
an upper member having a plurality of recessed openings, a portion of each hollow member and a portion of each elongated solid member being positioned within one of the recessed openings in a one-to-one correspondence between the recessed openings in the upper member of the extruder head and the plurality of hollow members and the plurality of elongated solid members.
17. The extruder of claim 16 wherein each hollow member includes a sleeve and each sleeve is shorter than a length of each elongated solid member extending from the respective actuator configured to move the respective elongated solid member to a surface of the upper member within the respective recessed opening.
18. The extruder of claim 17 wherein each hollow member is configured to slide longitudinally along the respective elongated solid member within the respective hollow member.
19. The extruder of claim 18 further comprising:
a cooler configured to direct air flow toward the plurality of hollow members.