Investment casting compositions, molds, and related methods

Abstract

Provided are slurry compositions and methods for producing investment casting molds. These compositions include a refractory material, a binder, a solvent, and a thixotropic agent comprising a polymer emulsion. Implementation of these slurry compositions enables a reduction in the number of backup layers in an investment casting shell, while retaining similar viscosity characteristics and similar or greater strength characteristics in the finished investment mold.

1 . A slurry composition for investment casting comprising:
 a refractory material;   a binder;   a solvent; and   a thixotropic agent comprising a polymer emulsion.   
     
     
         2 . The composition of  claim 1 , wherein the polymer emulsion is an aqueous emulsion. 
     
     
         3 . The composition of  claim 1 , wherein the polymer emulsion comprises an alkali-swellable polymer. 
     
     
         4 . The composition of  claim 3 , wherein the alkali-swellable polymer comprises a hydrophobically modified ester of methacrylic acid. 
     
     
         5 . The composition of  claim 1 , further comprising an aluminum phyllosilicate clay. 
     
     
         6 . The composition of  claim 5 , wherein the aluminum phyllosilicate clay is present in an amount ranging from a weight ratio of 1:6 to 4:1 relative to the polymer emulsion. 
     
     
         7 . The composition of  claim 1 , wherein the polymer emulsion is present in an amount ranging from 0.07 weight percent to 0.75 weight percent, based on the overall weight of the composition. 
     
     
         8 . The composition of  claim 1 , wherein the composition has an overall solids content ranging from 50 weight percent to 75 weight percent, based on the overall weight of the composition. 
     
     
         9 . The composition of  claim 1 , wherein the binder comprises colloidal silica. 
     
     
         10 . The composition of  claim 1 , wherein the composition displays a working viscosity of 20 Poise when subjected to a yield stress ranging from 25 dynes/cm 2  to 800 dynes/cm 2 . 
     
     
         11 . The composition of  claim 1 , wherein the binder comprises a styrene-butadiene latex. 
     
     
         12 . The composition of  claim 1 , wherein the binder comprises a polyvinyl butyral resin. 
     
     
         13 . An investment casting mold made using the composition of  claim 1 . 
     
     
         14 . A method of making an investment casting mold comprising:
 coating a sacrificial pattern with a prime layer comprising a first refractory slurry and a first refractory stucco;   at least partially hardening the prime layer;   coating the prime layer with an intermediate layer comprising a second refractory slurry and a second refractory stucco;   at least partially hardening the intermediate layer;   coating the intermediate layer with a backup layer comprising a thixotropic agent, the thixotropic agent including a polymer emulsion; and   at least partially hardening the backup layer.   
     
     
         15 . The method of  claim 14 , wherein the investment casting mold has a non-fired modulus of rupture ranging from 250 psi to 700 psi after fully hardened.