Method of dry coating sand cores

Abstract

A method for applying a refractory coating to a sand core, to be used for a metal casting, in a dry state, without the use of a liquid carrier. The coating may be applied by pressing the coating into a mixture of refractory material and impacting media fluidized in a vibratory bed such that the core floats in the mixture, and then rotating the core to coat the surfaces that will be in contact with the molten metal in the casting process.

1 . A method of applying a dry coating to a sand core, comprising allowing the core to bear against a fluidized mixture of an impacting media and a coating powder, said mixture fluidized such that said core floats in said mixture with a desired degree of submersion. 
     
     
         2 . The method of  claim 1 , further comprising moving the core with respect to said fluidized mixture with the core bearing against said mixture. 
     
     
         3 . The method of  claim 2 , wherein said moving comprises rotating said core about its primary axis. 
     
     
         4 . The method of  claim 3 , wherein said core is rotated about its primary axis at a predetermined angle to the surface of the fluidized mixture to limit the areas of the sand core to which the coating is applied. 
     
     
         5 . The method of  claim 1 , further comprising pressing said coating into the surface of said core. 
     
     
         6 . The method of  claim 1 , wherein said fluidized mixture is fluidized with a vibratory drive that imparts a circulatory flow in said fluidized mixture. 
     
     
         7 . The method of  claim 1 , wherein the desired degree of submersion corresponds to a depth sufficient to coat only those portions of the sand core that will form a surface of the metal casting. 
     
     
         8 . The method of  claim 1 , wherein the impacting media and coating powder have refractory properties and the coating powder has a mesh size of not greater than 325 and a melt point not less than 2000 C. 
     
     
         9 . The method of  claim 1 , wherein the coating is applied at a rate of about 0.0002 to 0.004 pounds per square inch of coated surface area of the core. 
     
     
         10 . A method of applying a dry powder coating to a sand core, comprising:
 (a) fluidizing in a tub with a vibratory drive a mixture of an impacting media and a coating powder sufficiently to impart a circulatory flow to said mixture in said tub;   (b) submerging the sand core in said mixture to a predetermined extent;   (c) allowing the core to bear against the mixture.   
     
     
         11 . The method of  claim 10 , further comprising rotating said core about its primary axis while it is bearing against the mixture. 
     
     
         12 . The method of  claim 11 , wherein said core is rotated about its primary axis at a predetermined angle to the surface of the fluidized mixture to limit the areas of the sand core to which the coating is applied. 
     
     
         13 . The method of  claim 10 , wherein said mixture is fluidized such that said core floats in said mixture with a desired degree of submersion. 
     
     
         14 . The method of  claim 13 , wherein the desired degree of submersion corresponds to a depth sufficient to coat only those portions of the sand core that will form a surface of the metal casting. 
     
     
         15 . The method of  claim 13 , wherein said core is rotated about its primary axis at a predetermined angle to the surface of the fluidized mixture to limit the areas of the sand core to which the coating is applied. 
     
     
         16 . The method of  claim 10 , wherein the coating is applied at a rate of about 0.0002 to 0.004 pounds per square inch of coated surface area of the core. 
     
     
         17 . (canceled) 
     
     
         18 . (canceled)