Thermally insulated die plate assembly for underwater pelletizing and the like

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 downstream face, a portion of said downstream face being cut out to form a recess or a cavity that is centrally positioned in said downstream face;
• (b) a cover plate sized to mate with and fit over said cavity, said cover plate and said cavity together forming and defining a thermally insulating air chamber in said die plate assembly adjacent said cutting face, said air chamber in direct communication with a surrounding atmosphere outside the die plate assembly to keep air in said chamber at atmospheric pressure;
• 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
• (d) a plurality of individual orifice protrusions extending outwardly from said raised circular ridge, distal ends of said protrusions being attachedly connected to said cover plate adjacent said cover plate openings, said raised circular ridge and said orifice protrusions through-penetrating said air chamber and being surrounded and insulated by said air chamber to provide continuous heating along a length of said extrusion orifice extensions and to prevent heat loss from the process melt adjacent the cutting face.

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 and cooled by cooling water on a downstream side of said cutting face, in which the die plate assembly comprises:

• (a) a die plate body having a downstream face that includes a center section and a generally circular periphery, said center section of said downstream face having a generally circular cutout formed therein, said circular cutout being inset from and generally concentric with said periphery of said die plate body downstream face and extending across said downstream face center section;
• (b) 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 said cutting face;
• and
• (c) a circular cover plate sized to mate with and fit over said circular cutout, said cover plate having holes that receive distal ends of said extrusion orifice extensions, said cover plate and said cutout together forming and defining an air chamber inset into the downstream face of the die plate body and closed by said cover plate, said air chamber surrounding and thermally insulating said extrusion orifice extensions and said die plate body from heat loss that could otherwise occur due to a temperature of the cooling water adjacent said die face.

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;
• said die plate body having a portion of its downstream face cut out to form a recess or a cavity that is centrally positioned in said downstream face;
• at least one ring of extrusion orifice extensions in said recess or cavity in said downstream face through which said extrusion orifices extend;
• a cover plate sized to fit over said recess or cavity and having openings which mate with said extrusion orifices, said cover plate being attached to said die plate body over said recess or cavity in said downstream face to form said cutting face;
• said cover plate and said recess or cavity forming and defining a thermally insulating air chamber adjacent said cutting face, said air chamber surrounding said extrusion orifice extensions to insulate said extrusion orifice extensions and provide continuous heating along a length of said extrusion orifices, said insulation provided by said air chamber surrounding said extrusion orifice extensions configured to prevent heat loss of the process melt adjacent the cutting face due to a temperature of the cooling water in the cutting chamber.

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 process melt is extruded to exit at a cutting face, said die plate body having a downstream face that includes a center section and a generally circular periphery, said center section of said downstream face having a generally circular cutout formed therein, said circular cutout being inset from and generally concentric with said periphery of said die plate body downstream face and extending across said downstream face center section;
• a rotary cutter blade assembly in opposed relation to the cutting face on a downstream side of said die plate body, 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;
• at least one ring of extrusion orifice extensions encasing said extrusion or through which the process melt is carried from said die plate body to said cutting face;
• a circular cover plate having holes matching said extrusion orifice extensions and sized to mate with and fit over said circular cutout and ends of said extrusion orifice extensions, said cover plate and said cutout together forming and defining a generally circular air chamber inset into the downstream face of the die plate body and closed by said cover plate, said air chamber surrounding said extrusion orifice extensions and thermally insulating said die plate body from said cutting face to provide continuos heating along a length of the orifice extensions and to prevent heat loss from the process melt adjacent the cutting face;
• and
• 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.