Thermally insulated die plate assembly for underwater pelletizing and the like

Abstract

An insulated die plate assembly for use in underwater pelletizing and other granulation processes includes a thin, continuous air chamber formed across the plate assembly generally parallel to the die face such that the heated upstream portion of the die plate assembly is thermally insulated from the downstream portion. The air chamber is atmospherically equilibrated by venting the air chamber to the atmosphere. The plurality of extrusion orifices, either individually or in groups, are formed in extrusion orifice extensions that extend through the insulation chamber so that the process melt to be granulated can pass therethrough. The orifice extensions and the components forming the air chamber around the orifice extensions channel heat along said extensions to maintain the process melt therein at a desired temperature, to help rigidify the die plate assembly and to better seal the air chamber.

1 - 19 . (canceled) 
     
     
         20 . A thermally insulated extrusion die plate assembly for a pelletizer including a plurality of extrusion orifices through which process melt is extruded to exit at a cutting face as a strand to be cut into pellets by a moving cutting assembly which comprises:
 a die plate body having a downstream face, a portion of said downstream face being cut out to form a recess or cavity in said downstream face;   said extrusion orifices having a plurality of extrusion orifice extensions that extend through said cavity; and   a cover plate attached to said die plate body to form said cutting face, said cover plate fitted over and enclosing said cavity to form and define a thermally insulating air chamber in said assembly adjacent said cutting face, said orifice extensions through-penetrating said air chamber and said cover plate having openings therethrough which mate with said extrusion orifices extensions, said air chamber surrounding and insulating said orifice extensions to prevent heat loss from the process melt adjacent the cutting face.   
     
     
         21 . The assembly as claimed in  claim 20 , wherein the die plate body is a single-body construction that is thermally regulated by at least one of electrical resistance, induction, steam, and thermal transfer fluid. 
     
     
         22 . The assembly as claimed in  claim 20 , wherein the die plate body is a two-piece construction including a removable insert and a die plate outer ring that are thermally regulated by at least one of electrical resistance, induction, steam, or thermal transfer fluid. 
     
     
         23 . The assembly as claimed in  claim 20 , wherein said cover plate has a counter-bore which conforms to a shape of said extrusion orifice extensions to further define said thermally insulating air pocket. 
     
     
         24 . The assembly as claimed in  claim 23 , wherein said extrusion orifice extensions are configured as a raised circular ridge continuous and unitary with said die plate body, and individual orifice protrusions extend from said raised ridge to said cover plate. 
     
     
         25 . The assembly as claimed in  claim 24 , wherein said raised circular ridge is configured to channel heat to said orifice protrusions. 
     
     
         26 . The assembly as claimed in  claim 24 , wherein said cover plate counter-bore is sized so that the thermally insulating air chamber follows the contour of the raised circular ridge. 
     
     
         27 . The assembly as claimed in  claim 24 , wherein the orifice protrusions are separate elements attachedly connected to the raised circular ridge on the die plate body. 
     
     
         28 . A thermally insulated extrusion die plate assembly for a pelletizer including a plurality of extrusion orifices through which process melt is extruded to exit at a cutting face as a strand to be cut into pellets by a moving cutting assembly which comprises:
 a die plate body having a downstream face;   a cover plate attached to the downstream face to form said cutting face;   a thermally insulating air chamber formed between said downstream face and said cover plate upon attachment of said cover plate to said die plate body; and   a plurality of extrusion orifice extensions through-penetrating said air chamber and said die plate body, said extrusion orifice extensions being surrounded and insulated by said air chamber to provide continuous and more uniform heating along a length of said extrusion orifice extensions.   
     
     
         29 . The assembly as claimed in  claim 28 , wherein said air chamber is in direct communication with a surrounding atmosphere outside the die plate assembly to keep air in said chamber at atmospheric pressure. 
     
     
         30 . The assembly as claimed in  claim 29 , wherein a portion of said downstream face of the die plate body is cut out to form a recess or cavity, said air chamber being formed and defined by said cavity and said cover plate attached to the downstream face. 
     
     
         31 . The assembly as claimed in  claim 30 , wherein said extrusion orifice extensions are configured as a raised circular ridge continuous and unitary with said die plate body, said raised circular ridge being configured to channel heat to said orifice protrusions and said cover plate having a counter-bore which conforms to a shape of said extrusion orifice extensions and is sized so that the thermally insulating chamber follows the contour of the raised circular ridge. 
     
     
         32 . The assembly as claimed in  claim 28 , wherein said assembly includes a vent configured to equilibriatingly vent said thermally insulating chamber to an ambient atmosphere outside of said die plate assembly to prevent pressure build up and/or vacuum formation in said air chamber. 
     
     
         33 . The assembly as claimed in  claim 20  in combination with an underfluid pelletizer. 
     
     
         34 . The assembly as claimed in  claim 28 , wherein said air chamber extends between and on either side of the extrusion orifice extensions, said extrusion orifice extensions dividing the air chamber into an outer section and an inner section. 
     
     
         35 . An underwater pelletizer for extruding and cutting a process melt into pellets comprising:
 a die plate body with a plurality of extrusion orifices formed therein through which the process melt is carried from said die plate body to a cutting face on a downstream side of said die plate body;   a rotary cutter blade assembly in opposed relation to said cutting face, said cutter blade assembly having a hub and at least one cutter blade mounted on said hub and capable of moving in a plane generally parallel to and closely adjacent said cutting face to cut strands of process melt extruded through said orifices into pellets;   a water box having a cutting chamber enclosing said cutting face and cutter blade assembly, said water box including a water inlet for introducing cooling water into the cutting chamber and an outlet for discharge of water and pellets entrained in the water;   a die plate body having a downstream face;   a cover plate attached to the downstream face to form said cutting face;   a thermally insulating air chamber formed between said downstream face and said cover plate upon attachment of said cover plate to said die plate body;   a plurality of extrusion orifice extensions through-penetrating said air chamber and being surrounded and insulated by said air chamber to provide continuous and more uniform heating along a length of said extrusion orifice extensions, said cover plate having openings therethrough which mate with said extrusion orifices extensions, distal ends of said extrusion orifice extensions being attachedly connected to said cover plate adjacent said cover plate openings.   
     
     
         36 . The underwater pelletizer as claimed in  claim 35 , wherein a portion of said downstream face of the die plate body is cut out to form a recess or cavity, said air chamber being formed and defined by said cavity and said cover plate attached to the downstream face. 
     
     
         37 . The underwater pelletizer as claimed in  claim 36 , wherein said extrusion orifice extensions are configured as a raised circular ridge continuous and unitary with said die plate body and individual orifice protrusions extending from said raised ridge, distal ends of said orifice protrusions being attachedly connected to said cover plate. 
     
     
         38 . The underwater pelletizer as claimed in  claim 37 , wherein said cover plate has a counter-bore which conforms to a shape of said extrusion orifice extensions and is sized so that the thermally insulating air chamber follows a contour of the raised circular ridge, said raised circular ridge dividing said air chamber into a generally annular outer section and a generally circular inner section. 
     
     
         39 . The underwater pelletizer as claimed in  claim 35 , further comprising radial electric heaters positioned in radial slots in said die plate body, said die plate body channeling heat from said heaters to said extrusion orifice extensions. 
     
     
         40 . The underwater pelletizer as claimed in  claim 35 , wherein said air chamber is vented to an atmosphere outside the die plate assembly to prevent pressure build up and/or vacuum formation in said air chamber. 
     
     
         41 . The assembly as claimed in  claim 28 , wherein said thermally insulating air chamber is equilibriatingly vented to atmosphere outside of the die plate assembly. 
     
     
         42 . The assembly as claimed in  claim 28 , wherein said cutting face has a surface treatment applied thereto that includes at least one of nitriding, carbonitriding, electroplating, electroless plating, electroless nickel dispersion treatments, flame spraying including high velocity applications, thermal spraying, plasma treatment, electrolytic plasma treatments, sintering, powder coating, vacuum deposition, chemical vapor deposition, physical vapor deposition, sputtering techniques, spray coating, and vacuum brazing of carbides. 
     
     
         43 . The assembly as claimed in  claim 28 , wherein an outside surface of said cover plate including said cutting face has at least one chemical, corrosion, abrasion or wear-resistant surface treatment applied thereto. 
     
     
         44 . The assembly as claimed in  claim 28 , wherein said plurality of extrusion orifice extensions are configured as a raised circular ridge continuous and unitary with said die plate body and individual orifice protrusions extending from said raised ridge to said cover plate, said orifice protrusions being through-penetrated by a multiplicity of extrusion orifices that are arranged in at least one of groups, pods, and clusters. 
     
     
         45 . The assembly as claimed in  claim 44 , wherein the orifice protrusions have at least one geometry selected from the group consisting of oval, round, square, triangular, polygonal, and combinations thereof; said orifice protrusions have an arrangement selected from the group consisting of concentrically alternating, staggeredly, linearly, and combinations thereof; said orifice protrusions are parallel to the arc of the cutting face or perpendicular to the arc; and said orifice protrusions have a kidney- to comma-shaped configuration. 
     
     
         46 . The assembly as claimed in  claim 44 , wherein said cover plate has openings therein which mate with said extrusion orifices, said cover plate being attached to distal ends of said orifice protrusions at the openings in said cover plate. 
     
     
         47 . The assembly as claimed in  claim 28 , wherein said cover plate contains a multiplicity of circumferential expansion grooves on both faces in a staggered and alternating configuration. 
     
     
         48 . The assembly as claimed in  claim 28 , wherein said cover plate is made of nickel steel and is weldingly attached by nickel steel. 
     
     
         49 . The assembly as claimed in  claim 28 , wherein outlets of said extrusion orifice extensions at said cutting face have a geometry selected from the group consisting of round, oval, square, rectangular, triangular, pentagonal, hexagonal, polygonal, slotted, radially slotted and any combination thereof.