Shell mold binder composition and method

Abstract

The invention provides a composition that significantly shortens the time necessary to produce a ceramic shell mold. The composition of the invention is used to produce a shell-mold for the investment casting process, providing decreased processing times by reducing the number of shell dips, and better handling and dewaxing through increased green strength. The invention provides a method of forming a shell mold, comprising providing an investment casting shell-mold composition comprising 0.1 to 70 percent by weight inorganic fibers, a binder composition comprising a mixture of 20-98 percent by weight of a colloidal sol comprising particles, and 1-20 percent by weight organic latex polymer.

1 . An investment casting shell-mold composition comprising: 
 a binder composition comprising a mixture of 20-98 percent by weight of a colloidal sol comprising inorganic colloidal particles,    1-20 percent by weight organic latex polymer, and    0.1 to 70 percent by weight of inorganic fibers;    said inorganic colloidal particles having an average particle size that is smaller than 600 mesh, said inorganic fibers having an average length to diameter ratio of more than 30.    
     
     
         2 . The composition according to  claim 1 , wherein said refractory powder is selected from the group consisting of alumino-silicates, fused silica, quartz silica, alumina, zircon, and zirconia.  
     
     
         3 . The composition according to  claim 1  wherein said colloidal sol comprises silica having an average particle diameter of 3 to 100 nanometers.  
     
     
         4 . The composition according to  claim 1  wherein the ratio of colloidal sol to latex polymer is greater than 1:1.  
     
     
         5 . The composition according to  claim 1  wherein a ratio of colloid:latex polymer ranges from 10:1 to 1:1, colloid:latex.  
     
     
         6 . The composition according to  claim 1  wherein said latex polymer includes a blend of acrylic polymers having a pH in the range of from 6 to 11; a viscosity in the range of from 50 to 1000 centipoise; a solids content of from 40 to 65 percent by weight; and an average particle size of from 0.05 to 1.0 microns.  
     
     
         7 . The composition according to  claim 1  wherein the latex polymer is an acrylic latex or a styrene butadiene latex.  
     
     
         8 . The composition according to  claim 1 , further comprising 1 to 98 percent by weight water.  
     
     
         9 . A method of forming a shell mold, consisting essentially of the steps of 
 a) providing an investment casting shell-mold composition comprising: 
 a binder composition comprising a mixture of 20-98 percent by weight of a colloidal sol comprising inorganic colloidal particles,  
 1-20 percent by weight organic polymer, and  
 0.1 to 70 percent by weight of fibers;  
 said inorganic colloidal particles having an average particle size smaller than 600 mesh, said inorganic fibers having an average length to diameter ratio of more than 30,  
   b) providing a disposable pattern,    c) mixing course refractory powder having a particle size of from 120 to 400 mesh, and said binder composition to form a slurry composition,    d) applying said slurry composition to said pattern to form a slurry coating on said slurry coated pattern,    e) applying refractory stucco to said slurry coating to form a slurry and stucco pattern coating,    f) up to thrice repeating steps d and e and    g) melting said disposable pattern.