Patent ID: 8006745

Claim:
A molding material mixture for foundry purposes, comprising the following components: a mold sand; 0.1 to 10 percent by weight of a sodium hydroxide aqueous solution; 0.1 to 5 percent by weight of an alkali-silicate binding agent; and 0.1 to 3 percent by weight of an additive suspension; wherein: said mold sand comprises mold sand particles having a grain size of 0.1 to 1 mm; said sodium hydroxide aqueous solution comprises a concentration of 20 to 40 percent by weight of sodium hydroxide; said alkali-silicate binding agent comprises 20 to 70 percent by volume of alkali-silicate; said additive suspension comprises 30 to 70 percent by volume of amorphous, spherical SiO 2 particles; each of said amorphous, spherical SiO 2 particles having one of: a first grain size in the range of between 1 and 5 micrometers; and a second grain size in the range of between 0.01 and 0.05 micrometers; and the volumetric amount of amorphous, spherical SiO 2 particles having the first grain size is in the range of 0.8 to 1.2 times the volumetric amount of amorphous, spherical SiO 2 particles having the second grain size.