Coated sand, manufacturing method for same, and manufacturing method for mold

Abstract

Purposes of the present invention are to provide a dry coated sand having a high degree of fluidity at the room temperature, a method of advantageously producing the coated sand, and a method of producing a casting mold having excellent properties, by using the coated sand. The dry coated sand is obtained by mixing an aqueous solution of a water glass used as a binder, with a heated refractory aggregate, whereby water in the aqueous solution is evaporated, and a coating layer of the binder is formed on surfaces of the refractory aggregate. A moisture percentage in the thus obtained dry coated sand is controlled so as to be not more than 0.5% by mass. The intended casting mold is obtained by filling a molding cavity of a forming mold, with the dry coated sand, and passing a steam through the coated sand, to solidify or cure the coated sand.

1 . A coated sand which is in a dry state and which has fluidity at the room temperature, the coated sand being obtained by mixing an aqueous solution of a water glass used as a binder, with a heated refractory aggregate, to evaporate water in the aqueous solution of the water glass, for thereby forming a coating layer of the binder on surfaces of the refractory aggregate, the coated sand being characterized in that its moisture percentage is controlled so as to be not more than 0.5% by mass. 
     
     
         2 . The coated sand according to  claim 1 , characterized in that the coated sand includes not more than 3% by mass of lumps which do not pass through a 20-mesh screen. 
     
     
         3 . The coated sand according to  claim 1 , characterized in that the aqueous solution of the water glass contains an alkali metal silicate as its major component. 
     
     
         4 . The coated sand according to  claim 3 , characterized in that the alkali metal silicate has a molar ratio of silicon dioxide to an alkali metal oxide, which molar ratio is not smaller than 1.0 and smaller than 3.0. 
     
     
         5 . The coated sand according to  claim 3 , characterized in that the alkali metal silicate is sodium silicate. 
     
     
         6 . The coated sand according to  claim 5 , characterized in that the sodium silicate has a molar ratio SiO 2 /Na 2 O of not smaller than 1.0 and smaller than 3.0. 
     
     
         7 . The coated sand according to  claim 1 , characterized in that a nonvolatile content in the aqueous solution of the water glass is 20-45% by mass. 
     
     
         8 . The coated sand according to  claim 1 , characterized in that the aqueous solution of the water glass is used in an amount of 0.1-2.5 parts by mass, in terms of its solid content, with respect to 100 parts by mass of the refractory aggregate. 
     
     
         9 . A method of producing the coated sand according to  claim 1 , characterized in that the refractory aggregate and the aqueous solution of the water glass are mixed together such that the water in the aqueous solution of the water glass is evaporated within 5 minutes after addition of the aqueous solution of the water glass to the refractory aggregate, to obtain the coated sand having the moisture percentage of not more than 0.5% by mass. 
     
     
         10 . A method of producing a casting mold, characterized in that the casting mold is obtained by filling a molding cavity of a forming mold which gives the casting mold, with the coated sand according to  claim 1 , and then passing a steam through the coated sand, to solidify or cure the coated sand within the forming mold. 
     
     
         11 . The method of producing the casting mold according to  claim 10 , characterized in that a dry air, a heated dry air, a nitrogen gas or an argon gas is further passed through a filling phase of the coated sand filling the molding cavity of the forming mold, simultaneously with or after passing the steam through the coated sand. 
     
     
         12 . The method of producing the casting mold according to  claim 10 , characterized in that at least one of a carbon dioxide gas, an ester gas and a carbonate gas is passed through a filling phase of the coated sand filling the molding cavity of the forming mold, simultaneously with or after passing the steam through the coated sand. 
     
     
         13 . The method of producing the casting mold according to  claim 10 , characterized in that a pressure within the molding cavity of the forming mold is reduced before passing the steam through the coated sand. 
     
     
         14 . The method of producing the casting mold according to  claim 10 , characterized in that the coated sand is preheated to a temperature not lower than 30° C., and then the molding cavity of the forming mold is filled with the preheated coated sand. 
     
     
         15 . The method of producing the casting mold according to  claim 10 , characterized in that the forming mold is preheated and kept at an elevated temperature. 
     
     
         16 . A method of producing a casting mold, characterized in that the casting mold is formed by multilayer molding using the coated sand according to  claim 1 .