Coated pelletizing extrusion dies and method for making the same

Abstract

A pelletizing extrusion die comprising a die body contains a plurality of extrusion holes. Each of the extrusion holes is defined by a defining surface of the die body wherein at least a portion of the defining surface has a low-friction coating deposited thereon. A method for applying the low-friction coating to the defining surface wherein the applying step occurs at a temperature equal to less than about 520° C.

What is claimed is: 
     
         1 . A method of coating a defining surface of a pelletizing extrusion die body contains a plurality of extrusion holes, and wherein each of the extrusion holes being defined by the defining surface of the die body, the method comprising the steps of:
 applying a low-friction coating to at least a portion of the defining surface at a temperature equal to less than about 520° C.   
     
     
         2 . The method according to  claim 1  wherein pelletizing extrusion die plate comprising any one of the following: steels, stainless steels, and superalloys. 
     
     
         3 . The method according to  claim 1  wherein the low-friction coating comprising any one of the following: metal, ceramic or composite. 
     
     
         4 . The method according to  claim 1  wherein the low-friction coating has coefficient of friction equal to less than about 0.5. 
     
     
         5 . The method according to  claim 1  wherein the die body having a inner face and an outer face, the defining surface having a generally frusto-conically shaped entrance section adjacent to the inner face and an exit section extending from the entrance section to the outer face, and wherein the applying step applies the low-friction coating to only the entrance section of the defining surface, 
     
     
         6 . The method according to  claim 1  wherein the pelletizing extrusion die body has an inner face, and the applying step further included applying the low-friction coating to at least a portion of the inner face. 
     
     
         7 . A method of coating at least a portion of a defining surface of a cylindrical pelletizing extrusion body having an inner cylindrical face and an outer face, and the cylindrical pelletizing extrusion die body further containing a plurality of extrusion holes extending radially through the cylindrical pelletizing extrusion die body, and wherein each of the extrusion holes being defined by the defining surface of the cylindrical extrusion die body wherein the defining surface having a generally frusto-conically shaped unobstructed entrance section adjacent to the inner cylindrical face and an exit section extending from the entrance section to the outer face, the method comprising step of:
 applying a metallurgically-bonded low-friction coating having a substantially constant thickness, on the entrance section of the defining surface and the exit section of the defining surface.   
     
     
         8 . The method according to  claim 7  wherein the meteallurgically-bonded low-friction coating has coefficient of friction equal to less than about 0.5. 
     
     
         9 . The method according to  claim 7  wherein the metallurgically-bonded low-friction coating being on at least a part of the inner cylindrical face. 
     
     
         10 . The method according to  claim 7  wherein the cylindrical die body comprising any one of the following: steel. stainless steel and superalloy. 
     
     
         11 . The method according to  claim 7  wherein the metallurgically-bonded low-friction coating comprising any one of the following: metal, ceramic or composite. 
     
     
         12 . The method according to  claim 7  wherein the metallurgically-bonded low-friction coating has a thickness equal to be between about 20 microns and about 200 microns. 
     
     
         13 . A method of coating at least a portion of a defining surface of a cylindrical pelletizing extrusion body having an inner cylindrical face and an outer face, and the cylindrical pelletizing extrusion die body further containing a plurality of extrusion holes extending radially through the cylindrical pelletizing extrusion die body, and wherein each of the extrusion holes being defined by the defining surface of the cylindrical extrusion die body wherein the defining surface having a generally frusto-conically shaped unobstructed entrance section adjacent to the inner cylindrical face and an exit section extending from the entrance section to the outer face, the method comprising step of:
 applying a metallurgically-bonded low-friction coating having a substantially constant thickness, on the exit section of the defining surface.