초록 ▼

A center heated die plate for an underwater pelletizer radiates heat outwardly to the extrusion orifices and die faces of the die plate thereby maintaining the die plate and extrusion orifices at an elevated temperature to obtain optimum flow of molten polymer through the extrusion orifices. In one

A center heated die plate for an underwater pelletizer radiates heat outwardly to the extrusion orifices and die faces of the die plate thereby maintaining the die plate and extrusion orifices at an elevated temperature to obtain optimum flow of molten polymer through the extrusion orifices. In one embodiment, a centrally located heating plate is mounted in a recess on the upstream face of the die plate inwardly of the nose cone. In a second embodiment, a cylindrical heating coil is placed in a hollow central core of the die plate between the nose cone on the upstream side and an insulation plug or plate on the downstream side. Heating leads extend through a single radial hole in the die plate to provide power to the center heating element.

대표청구항 ▼

What is claimed is: 1. A die plate and heating assembly for a pelletizer, comprising an extrusion die plate having an inner wall that defines a hollow cylindrical center that extends all the way through the die plate from an upstream face to a downstream face thereof, said die plate including a plu

What is claimed is: 1. A die plate and heating assembly for a pelletizer, comprising an extrusion die plate having an inner wall that defines a hollow cylindrical center that extends all the way through the die plate from an upstream face to a downstream face thereof, said die plate including a plurality of orifices surrounding and separate from said hollow center through which molten polymer flows from said upstream face to said downstream face and is extruded to exit at said downstream face as a strand cut into pellets by a moving cutting assembly, and a generally cylindrical coil heating element positioned in said hollow center of said die plate in heat exchange relation to said die plate inner wall to retain said inner wall and the extrusion orifices located adjacent and exterior to said inner wall at an elevated temperature and maintain the polymer passing through the orifices in a molten state as the polymer passes through the orifices. 2. The assembly as claimed in claim 1, wherein said hollow center of the die plate is closed at one end by a nose cone and closed at an other end by an insulation plug to retain heat in the center of the die plate for radiation outwardly toward said orifices. 3. The assembly as claimed in claim 1, wherein said heating element is connected to heating leads which extend through a single radial passageway in said die plate for supplying electrical power to said heating element. 4. A die plate for extruding polymer strands in an underwater pelletizer which comprises a plurality of extrusion orifices oriented in a circular pattern around a periphery of the die plate and extending from an upstream face of the die plate to a downstream face of the die plate, said die plate having an inner wall that defines a hollow cylindrical area also extending from said upstream face to said downstream face to pass all the way through said die plate, said hollow area being substantially centrally located in said die plate and separated from said orifices by said inner wall, said hollow cylindrical area being configured to receive a generally cylindrical coil heating element positioned in heat exchange relation to said inner wall of said die plate which is located inwardly of the circular pattern of said extrusion orifices to radiate heat outwardly to said extrusion orifices through said inner wall to maintain the polymer in a molten state during passage through said orifices. 5. The die plate claimed in claim 4, wherein said heating element is an electric resistance heating element having power supplied thereto by heating leads which connect to said heating element and extend through a single passageway in said die plate to a power source outside said die plate. 6. The die plate as claimed in claim 4, further comprising a nose cone forming a closure for said hollow cylindrical area at the upstream face of the die plate and a closure plate forming a closure for said hollow cylindrical area at the downstream face of the die plate. 7. The die plate as claimed in claim 5, wherein said heating leads are formed integrally with an end of said cylindrical coil. 8. A die plate and heater assembly for extruding polymer strands in an underwater pelletizer which comprises an extrusion die plate having a plurality of extrusion orifices oriented in a circular pattern around a periphery of the die plate and extending from an upstream face of the die plate to a downstream face of the die plate, said die plate having a hollow cylindrical area located radially inwardly of and separate from said extrusion orifices and also extending all the way through said die plate from said upstream face to said downstream face, and a cylindrical coil heater positioned in said hollow cylindrical area in said die plate. 9. The assembly as claimed in claim 8, wherein said coil heater is retained in said hollow cylindrical area by a nose cone forming a closure at said upstream face and an insulation plug forming a closure at said downstream face. 10. The assembly as claimed in claim 9, wherein said nose cone and said insulation plug are held in place by a nose cone anchor bolt which passes through a central hole in said insulation plug and said coil heater and threads into said nose cone. 11. The assembly as claimed in claim 8, further comprising heating leads connected to said coil heater and extending through a single passageway in said die plate for providing power to said coil heater, said heating leads providing the only source for power to said coil heater. 12. The assembly as claimed in claim 8, further comprising heating leads connected to said coil heater and extending through a single passageway in said die plate for providing power to said coil heater, said heating leads being formed integrally with an end of said cylindrical coil heater. 13. The assembly as claimed in claim 8, further comprising heating leads connected to said coil heater and extending through a single passageway in said die plate for providing power to said coil heater, said single passageway extending radially in said die plate. 14. The heating assembly as claimed in claim 1, wherein a portion of said heating element is in full surface contact with said die plate inner wall so that heat from said heating element flows directly to said die plate. 15. The assembly as claimed in claim 8, wherein an outer surface of said cylindrical coil heater is in contact with an inner wall of said die plate that defines said hollow cylindrical area so that heat from said coil heater flows directly to said die plate inner wall. 16. The assembly claimed in claim 1, wherein said heating element is an electric resistance heating element. 17. The assembly as claimed in claim 1, wherein said generally cylindrical coil heating element is in direct abutment with said die plate inner wall under spring tension and surrounds a remaining portion of said hollow area that remains hollow. 18. The assembly as claimed in claim 8, wherein said generally cylindrical coil heating element is in direct abutment under spring tension with an inner wall of said die plate that defines a perimeter of said hollow cylindrical area, a remaining area of said hollow cylindrical area remaining hollow when said coil heating element is in place. 19. The assembly as claimed in claim 1, wherein said hollow center includes an area including a centermost area of said die plate. 20. The assembly as claimed in claim 1, wherein said coil heating element is flexible to enable an outer diameter thereof to be reduced by twisting for insertion of the element into the hollow center, said outer diameter expanding when said coil heating element is released such that an outer surface of said coil heating element seats in direct contact with said die plate inner wall when assembled. 21. The assembly as claimed in claim 15, wherein said coil heater is a flexible element having an outer diameter that is reduced by twisting for insertion of the element into the hollow area, said outer diameter expanding when said element is released so that an outer surface of said heater element seats in direct contact with die plate inner wall when assembled.