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 are specially configured to 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 . 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) a die plate body having a cutout formed centrally in a downstream side of said body;   (b) at least one ring of extrusion orifice extensions in said cutout through which said extrusion orifices extend;   (c) a cover plate sized to fit over said cutout and having openings which mate with said extrusion orifices therethrough to form said cutting face, said cover plate attached to said die plate body over said cutout to form a thermally insulating air chamber in said assembly adjacent said cutting face and surrounding said orifice extensions, said air chamber equilibratingly vented to atmosphere outside of said die plate assembly; and   (d) at least one chemical, corrosion, abrasion or wear-resistant surface treatment applied to an outside surface of said cover plate including said cutting face.   
   
   
       2 . The assembly as claimed in  claim 1 , 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. 
   
   
       3 . The assembly as claimed in  claim 1 , 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. 
   
   
       4 . The assembly as claimed in  claim 3 , wherein said removable insert and said die plate outer ring are independently thermally regulated by at least one of electrical resistance, induction, steam, or thermal transfer fluid. 
   
   
       5 . The assembly as claimed in  claim 1 , wherein the cutting face is a raised annular plane through which penetrate the multiplicity of extrusion orifices and a lower peripherally plane about each side of said raised annular plane, said raised annular plane being at least about 0.025 millimeters higher than the peripherally plane. 
   
   
       6 . A pelletizer having a die plate assembly as claimed in  claim 1 . 
   
   
       7 . The pelletizer as claimed in  claim 6 , wherein the pelletizer is an underwater pelletizer. 
   
   
       8 . The assembly as claimed in  claim 1 , wherein the surface treatment 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, and spray coating. 
   
   
       9 . The assembly as claimed in  claim 1 , 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. 
   
   
       10 . The assembly as claimed in  claim 9 , 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 to said cover plate. 
   
   
       11 . The assembly as-claimed in  claim 10 , wherein said raised circular ridge is configured to channel heat to said orifice protrusions. 
   
   
       12 . The assembly as claimed in  claim 10 , wherein said raised circular ridge has a cross-section of trapezoidal shape. 
   
   
       13 . The assembly as claimed in  claim 10 , wherein said cover plate counter-bore is sized so that the thermally insulating air chamber follows the contour of the raised circular ridge. 
   
   
       14 . The assembly as claimed in  claim 1 , wherein the cover plate contains at least one circumferential expansion groove on at least one face. 
   
   
       15 . The assembly as claimed in  claim 14 , wherein the cover plate contains a multiplicity of circumferential expansion grooves on both faces in a staggered and alternating configuration. 
   
   
       16 . The assembly as claimed in  claim 1 , wherein the cover plate is made of a nickel steel and is weldingly attached by nickel steel. 
   
   
       17 . The assembly as claimed in  claim 1 , wherein the cover plate is weldingly attached to said die plate body at a peripheral groove circumferentially about said cover plate and to distal ends of said orifice protrusions at the openings in said cover plate. 
   
   
       18 . The assembly as claimed in  claim 1 , wherein the atmospherically equilibrated air chamber is at least 0.05 millimeters in depth. 
   
   
       19 . The assembly as claimed in  claim 10 , wherein the orifice protrusions are through-penetrated by a multiplicity of extrusion orifices arranged in at least one of groups, pods, and clusters. 
   
   
       20 . The assembly as claimed in  claim 10 , wherein the orifice protrusions can be at least one geometry including oval, round, square, triangular, rectangular, polygonal, or combinations thereof, can be arranged concentrically alternating, staggeredly, linearly, or combinations thereof, can be parallel to the arc of the cutting face or perpendicular to the arc, and can be of a kidney- to comma-shaped configuration. 
   
   
       21 . The assembly as claimed in  claim 10 , wherein the orifice protrusions are separate elements attachedly connected to the raised circular ridge on the die plate body. 
   
   
       22 . The assembly as claimed in  claim 1 , wherein the extrusion orifice outlets can be of any geometry including round, oval, square, rectangular, triangular, pentagonal, hexagonal, polygonal, slotted, radially slotted and any combination thereof. 
   
   
       23 . 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 moving cutting assembly which comprises:
 (a) a die plate body having a cutout formed in a downstream side of said body;   (b) a cover plate welded around its periphery to said die plate body to fit over said cutout and form a thermally insulating chamber in said assembly adjacent said cutting face; and   (c) at least one ring of extrusion orifice extensions encasing said extrusion orifices through which the process melt is carried from said die plate body to openings in said cover plate to form said cutting face, said extrusion orifice extensions configured as a raised circular ridge continuous and unitary with said die plate body and individual orifice protrusions extending from said raised ridge and welded to said cover plate adjacent said cover plate openings.   
   
   
       24 . The assembly as claimed in  claim 23 , wherein said thermally insulating chamber is equilibriatingly vented to atmosphere outside of said die plate assembly. 
   
   
       25 . The assembly as claimed in  claim 23 , 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. 
   
   
       26 . A pelletizer having a die plate assembly as claimed in  claim 23 . 
   
   
       27 . The pelletizer as claimed in  claim 26 , wherein the pelletizer is an underwater pelletizer. 
   
   
       28 . The assembly as claimed in  claim 23 , wherein said raised circular ridge is configured to channel heat to said orifice protrusions. 
   
   
       29 . The assembly as claimed in  claim 28 , 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 chamber follows the contour of the raised circular ridge. 
   
   
       30 . The assembly as claimed in  claim 23 , wherein the thermally insulating chamber has a depth of at least 0.30 millimeters. 
   
   
       31 . The assembly as claimed in  claim 23 , wherein said die plate body and said cover plate include complementary abutting surfaces where said cover plate is welded around its periphery to said die plate body. 
   
   
       32 . The assembly as claimed in  claim 31 , wherein said cover plate and said orifice protrusions include complementary abutting surfaces where said orifice protrusions are welded to said cover plate adjacent said cover plate openings.