Frangible mold core for metal casting, production and use

Abstract

The invention concerns the production of frangible ceramic mold cores for metallic casting, their production and use. In general, by the conventional debindering of the green ceramic, a substantial mechanical weakening of the cast mold occurs. Thus is particularly true in the case of awkward component geometry, such that a destruction of fine structures or freely projecting mold parts can occur during casting. It is thus the task of the invention to provide a geometrically complex mold core of slip-ceramic for metal casting, which exhibits a sufficiently high structural stability, in order to survive removal from pre-molds, as well as to survive metal casting without damage, and which thereafter can be removed in simple manner from the cast part. The task is solved in that the mold core includes ceramic microparticles, as well as a stable outer skin in which the microparticles are joined with each other by sintered nanoparticles.

1 . A frangible mold core for metallic casting, containing ceramic microparticles, 
 wherein the mold core exhibits a stable outer skin, in which skin the microparticles are joined to each other by sintered nanoparticles.    
   
   
       2 . The mold core according to  claim 1 , 
 wherein the microparticles and/or nanoparticles are comprised of refractory oxides, carbides or nitrides.    
   
   
       3 . A process for producing a frangible mold core for metallic casting comprising the steps: 
 providing a pre-mold,    providing a slip, containing ceramic microparticles,    filling the pre-mold with the slip,    freezing the slip to form into a green mold core,    removing the green mold core from the pre-mold,    freeze-drying the green mold core,    comprising: 
 applying colloidal nanoparticles upon the green mold core,  
 heating:  
 for off-gassing organic components of the green mold core and,  
 for sintering the colloidal nanoparticles, with formation of a stable outer skin of the mold core.  
   
   
   
       4 . The process for producing a mold core according to  claim 3 , 
 wherein the heating reaches a maximal temperature of between 750 and 1200° C.,    and wherein the maximal temperature is maintained constant for 30 to 120 minutes.    
   
   
       5 . The process for producing a mold core according to  claim 4 , 
 wherein the maximal temperature is reached by a continuous thermal increase of between 100 and 150° C./h.    
   
   
       6 . The process for producing a mold core according to  claim 3   wherein off-gasses are vented during heating.    
   
   
       7 . The process for producing a mold core according to  claim 3   wherein the application of the nanoparticles is accomplished by spraying or brushing or dipping with a dispersion.    
   
   
       8 . A process for casting components for internal combustion engines of steel or light metal, said process comprising: 
 (a) providing a frangible mold core for metallic casting, the core comprising a core and an outer skin, wherein the core of the mold core contains ceramic microparticles, and wherein the skin is rendered more stable than the core by applying nanoparticles onto the mold core and heating sufficiently to partially or completely melt the nanoparticles thereby joining the microparticles to each other to form a stable outer skin on the mold core,    (b) introducing said mold core into a mold to produce a ceramic casting mold,    (c) casting a molten metal into said casting mold to form a cast component,    (d) cooling the cast component to cause shrinkage and application of tension on said mold core, reducing the stability of said outer skin, and    (e) breaking up and removing the mold core from said cast component.    
   
   
       9 . The process as in  claim 8 , wherein said ceramic casting mold is comprised of an assembly of multiple components.  
   
   
       10 . The mold core according to  claim 2 , wherein the microparticles are zirconium silicate.  
   
   
       11 . The mold core according to  claim 2 , wherein the nanoparticles are silicone dioxide.  
   
   
       12 . The process for producing a mold core according to  claim 7 , wherein the application of the nanoparticles is accomplished by spraying or brushing on, or dipping in, an aqueous dispersion of the nanoparticles.