Coating compositions for inorganic casting molds and cores and use thereof and method for sizing

Abstract

The invention relates to coating compositions, comprising specific clays, an aqueous carrier fluid and refractory materials in powder form, and to the use thereof for casting molds and cores, in particular those that are produced using water glass as a binder. The invention further relates to a method for producing the sizing agents and for applying same to inorganically bound casting molds and cores.

1 . A sizing composition comprising
 (A) at least the following clays:
 (A1) 1 to 10 parts by weight of palygorskite, which is a magnesium-aluminum hydrosilicate, present in the form of rod-shaped crystals with particle dimensions of 1 to 3 μm in length and of 1 to 5 nm in diameter; 
 (A2) 1 to 10 parts by weight of hectorite; and 
 (A3) 1 to 20 parts by weight of sodium bentonite, based on the ratio of the components (A1), (A2) and (A3) relative to one another; 
   (B) a carrier fluid comprising water that can be fully evaporated at up to 160° C. and 1013 mbar; and   (C) refractory materials different from (A).   
     
     
         2 . The sizing composition according to  claim 1 , comprising, independently of one another:
 (A1) 1 to 5 parts by weight of palygorskite   (A2) 1 to 5 parts by weight of hectorite and   (A3) 1 to 10 parts by weight of sodium bentonite.   
     
     
         3 . The sizing composition according to  claim 1 , wherein the total clay content A1, A2 and A3 of the sizing agents combined amounts to 0.1 to 4.0% by weight, based on the solids content of the sizing composition. 
     
     
         4 . The sizing composition according to  claim 1 , wherein the carrier fluid comprises more than 50% by weight of water. 
     
     
         5 . The sizing composition according to  claim 1 , wherein the solids content of the sizing composition amounts to 20 to 90% by weight. 
     
     
         6 . The sizing composition according to  claim 1 , wherein the sizing composition comprises 10 to 85% by weight of refractory material, based on the solids content of the sizing composition. 
     
     
         7 . The sizing composition according to  claim 1 , wherein the refractory materials are selected from the group consisting of: quartz, aluminum oxide, zirconium dioxide, aluminum silicates, zirconium sands, ziconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, kaolinite, metakaolinite, iron oxide, bauxite and mixtures thereof. 
     
     
         8 . The sizing composition according to  claim 1 , in which the refractory materials have particle sizes of 0.1 to 500 μm, measured by light scattering according to DIN/ISO 13320. 
     
     
         9 . The sizing composition according to  claim 1 , wherein the sizing composition comprises 0.1 to 20% by weight, of at least one binder, based on the solids content of the sizing composition. 
     
     
         10 . The sizing composition according to  claim 1 , wherein the sizing composition is used as a concentrate and the fraction of the refractory solid (C) in the sizing composition is more than 70% by weight, based on the solids fraction of the sizing composition. 
     
     
         11 . (canceled) 
     
     
         12 . A method for sizing molds and cores cured with an inorganic binder, comprising the steps of:
 a) providing a sizing composition by combining at least:
 (A) the following clays:
 (A1) 1 to 10 parts by weight of palygorskite, which is a magnesium-aluminum hydrosilicate, present in the form of rod-shaped crystals with particle dimensions of 1 to 3 μm in length and of 1 to 5 nm in diameter; 
 (A2) 1 to 10 parts by weight of hectorite; and 
 (A3) 1 to 20 parts by weight of sodium bentonite, based on the ratio of the components (A1), (A2) and (A3) relative to one another; 
 
 (B) a carrier fluid comprising water that can be fully evaporated at up to 160° C. and 1013 mbar; and 
 (C) refractory materials different from (A)
 and 
 
   b) sizing molds and cores with the sizing composition, wherein the molds and cores consist of molding material mixtures cured with an inorganic binder.   
     
     
         13 . (canceled) 
     
     
         14 . The method according to  claim 12 , wherein:
 the binder is water glass; and   the molding material mixtures comprise particulate silicon dioxide, particulate aluminum oxide, particulate titanium oxide, particulate zinc oxide and mixtures thereof.   
     
     
         15 . The sizing composition according to  claim 3 , wherein the total clay content A1, A2 and A3 of the sizing agents combined amounts to 0.5 to 3.0% by weight, based on the solids content of the sizing composition. 
     
     
         16 . The sizing composition according to  claim 3 , wherein the total clay content A1, A2 and A3 of the sizing agents combined amounts to 1.0 to 2.0% by weight, based on the solids content of the sizing composition. 
     
     
         17 . The sizing composition according to  claim 4 , wherein the carrier fluid further comprises at least one alcohol, including polyalcohols and polyether alcohols. 
     
     
         18 . The sizing composition according to  claim 5 , wherein the solids content of the sizing composition amounts to 80 to 85% by weight. 
     
     
         19 . The sizing composition according to  claim 8 , in which the refractory materials have particle sizes of 1 to 200 μm, measured by light scattering according to DIN/ISO 13320. 
     
     
         20 . The sizing composition according to  claim 9 , wherein the sizing composition comprises 0.5 to 5% by weight, of at least one binder, based on the solids content of the sizing composition. 
     
     
         21 . The sizing composition according to  claim 10 , wherein the sizing composition is used as a concentrate and the fraction of the refractory solid (C) in the sizing composition is more than 80% by weight, based on the solids fraction of the sizing composition. 
     
     
         22 . The sizing composition according to  claim 10 , wherein the total clay content A1, A2 and A3 of the sizing agents combined amounts to 0.1 to 4.0% by weight based on the solids content of the sizing composition. 
     
     
         23 . The sizing composition according to  claim 10 , wherein the solids content of the sizing composition amounts to 20 to 90% by weight.