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A sprue bar nozzle assembly for controlling flow of melt through conduits of a mold assembly for injection molding comprises a sprue bar extension and nozzle, the sprue bar extension comprising means for adjusting the overall length of the sprue bar nozzle assembly and the nozzle comprising a nose c

A sprue bar nozzle assembly for controlling flow of melt through conduits of a mold assembly for injection molding comprises a sprue bar extension and nozzle, the sprue bar extension comprising means for adjusting the overall length of the sprue bar nozzle assembly and the nozzle comprising a nose comprising a seating surface for mating engagement with a mating surface of a mating segment of a melt conveying conduit and a slide valve, an open position of the slide valve permitting melt to flow through the sprue bar nozzle assembly and a closed position preventing melt from flowing through the sprue bar nozzle assembly, the slide valve being biased to a closed position by a biasing means and being driven to the open position by forces applied to the nose of the nozzle as a result of closure of an associated mold assembly.

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What is claimed is: 1. A sprue bar nozzle assembly for controlling flow of melt through conduits of a mold assembly, the sprue bar nozzle assembly comprising a sprue bar extension and a nozzle in fluid communication with the sprue bar extension for controlling flow of melt through the sprue bar ext

What is claimed is: 1. A sprue bar nozzle assembly for controlling flow of melt through conduits of a mold assembly, the sprue bar nozzle assembly comprising a sprue bar extension and a nozzle in fluid communication with the sprue bar extension for controlling flow of melt through the sprue bar extension, the sprue bar extension comprising means for adjusting the overall length of the sprue bar nozzle assembly, the nozzle comprising a nozzle valve bore, a nose comprising a seating surface for engagement with a mating surface of a mating segment of a melt conveying conduit, a nozzle slide valve received within the nozzle valve bore and having a valve passage in fluid communication with one of a nozzle inlet and nozzle outlet and terminating in orifices that are covered or exposed according to the location of the slide valve relative to the other of the nozzle inlet and nozzle outlet, an open position of the slide valve permitting melt to flow through the slide valve and nozzle and a closed position preventing melt from flowing through the slide valve and nozzle, an arm projecting from the nozzle slide valve transverse to and passing through an opening in the nozzle, opposed ends of the arm extending beyond the nozzle valve bore, and a biasing means, the biasing means applying a force to the arm in the direction to locate the slide valve to cover the orifices, the nozzle being mounted so that the slide valve is driven to the open position by forces applied to the nose as a result of closure of an associated mold assembly. 2. The assembly according to claim 1 wherein the sprue bar extension comprises a sprue bar base having an extension passage therethrough and an extension stem received within the extension passage so that the extension stem and sprue bar base are slidably engaged. 3. The assembly according to claim 2 wherein the means for adjusting overall length of the sprue bar nozzle assembly further comprises a stem collar fixed to the periphery of the extension stem, a base collar fixed to the periphery of the sprue bar base, at least one pin passing through each of the stem collar and base collar, each pin having an adjustable stop on at least one end projecting beyond a collar and a spring surrounding the pin and interposed between the collars, the adjustable stops, the collars and the pins setting the adjustable limit of separation between the extension stem and sprue bar base, the adjustable limit of separation between the extension stem and sprue bar base establishing the overall length of the sprue bar nozzle assembly. 4. The assembly according to claim 3 wherein the sprue bar extension comprises at least three pins, each having a surrounding spring interposed between the collars, the pins being arranged circumferentially around the sprue bar extension so that axial alignment of the extension stem and sprue bar base is maintained. 5. The assembly according to claim 3 wherein the sprue bar extension comprises at least four pins, each having a surrounding spring interposed between the collars, the pins being arranged circumferentially around the sprue bar extension so that axial alignment of the extension stem and sprue bar base is maintained. 6. The assembly according to claim 1 wherein areas of interior surfaces acted on by melt pressure during mold filling are effective to produce forces additive with the forces exerted by the biasing means acting on the arm and the springs of the adjusting means so that the combined forces are sufficient to overcome forces tending to separate engaged sprue bar segments. 7. The assembly according to claim 1 wherein the seating surface comprises one of the nozzle inlet and nozzle outlet. 8. The assembly according to claim 7 wherein the seating surface comprises one of a convex and concave surface. 9. The assembly according to claim 1 further comprising at least one heater for maintaining melt within the assembly in a flowable condition. 10. The assembly according to claim 9 wherein the heaters comprise at least one cartridge heater received within a bore in a wall of at least one of the nozzle and sprue bar extension. 11. An apparatus for controlling flow of melt through a mold arrangement comprising plural mold assemblies, the apparatus comprising at least one conduit for conveying melt from an injection unit to at least one mold assembly, the conduit comprising mating segments abutted with closure of the mold assemblies and separated with opening of the mold assemblies, at least one of the mating segments comprising a sprue bar nozzle assembly comprising a sprue bar extension and a nozzle in fluid communication with the sprue bar extension for controlling flow of melt through the sprue bar extension, the sprue bar extension comprising means for adjusting the overall length of the sprue bar nozzle assembly, the nozzle comprising a nozzle valve bore, a nose comprising a seating surface for engagement with a mating surface of a mating segment of a melt conveying conduit and a nozzle slide valve received within the nozzle valve bore and having a valve passage in fluid communication with one of a nozzle inlet and nozzle outlet and terminating in orifices that are covered or exposed according to the location of the slide valve relative to the other of the nozzle inlet and nozzle outlet, an open position of the slide valve permitting melt to flow through the slide valve and nozzle and a closed position preventing melt from flowing through the slide valve and nozzle, an arm projecting from the nozzle slide valve transverse to and passing through an opening in the nozzle, opposed ends of the arm extending beyond the nozzle valve bore, and a biasing means, the biasing means applying a force to the arm in the direction to locate the slide valve to cover the orifices, the nozzle being mounted so that the slide valve is driven to the open position by forces applied to the nose as a result of closure of an associated mold assembly. 12. The apparatus according to claim 11 wherein the sprue bar extension comprises a sprue bar base having an extension passage therethrough and an extension stem received within the extension passage so that the extension stem and sprue bar base are slidably engaged, the sprue bar base being attached to a segment of the conduit. 13. The apparatus according to claim 12 wherein the means for adjusting overall length of the sprue bar nozzle assembly further comprises a stem collar fixed to the periphery of the extension stem, a base collar fixed to the periphery of the sprue bar base, at least one pin passing through each of the stem collar and base collar, each pin having an adjustable stop on at least one end projecting beyond a collar and a spring surrounding the pin and interposed between the collars, the adjustable stops, the collars and the pins setting the adjustable limit of separation between the extension stem and sprue bar base, the adjustable limit of separation between the extension stem and sprue bar base establishing the overall length of the sprue bar nozzle assembly. 14. The apparatus according to claim 13 wherein the sprue bar extension comprises at least three pins, each having a surrounding spring interposed between the collars, pins being arranged circumferentially around the sprue bar extension to balance moments acting on the extension stem whereby axial alignment of the extension stem and sprue bar base is maintained. 15. The apparatus according to claim 13 wherein the sprue bar extension comprises at least four pins, each having a surrounding spring interposed between the collars, the pins being arranged circumferentially around the sprue bar extension so that axial alignment of the extension stem and sprue bar base is maintained. 16. The apparatus according to claim 11 wherein interior surfaces of the sprue bar nozzle assembly that are acted upon by melt pressure during mold filling are effective to produce forces additive with the forces exerted by the biasing means acting on the arm and the springs of the adjusting means so that the combined forces are sufficient to overcome forces tending to separate engaged sprue bar segments. 17. The apparatus according to claim 11 wherein the seating surface comprises one of the nozzle inlet and nozzle outlet. 18. The apparatus according to claim 17 wherein the seating surface comprises one of a convex and concave surface. 19. The apparatus according to claim 11 further comprising at least one heater for maintaining melt within the sprue bar nozzle assembly in a flowable condition. 20. The apparatus according to claim 19 wherein the heaters comprise at least one cartridge heater received within a bore in a wall of at least one of the nozzle and sprue bar extension.