| 摘要 |
The invention relates to a moulding material mixture for foundry purposes, consisting of a mould sand, a sodium hydroxide solution, a binding agent based on alkal i silicate and additives, wherein the mould sand particles comprise a grain size of 0.1 to 1 mm. The moulding material mixture contains 0.1 to 10 percent by weight of sodium hydroxide solution with reference to the weight of the sand and 0.1 to 5 % o f binding agent based on alkali silicate with a solid matter percentage of 20 to 70 %, wherein the moulding material mixture, as the additive, contains 0.1 to 3 percent by weight of a suspension with a solid matter percentage of 30 to 70% of amorphous, spherical SiO2. The amorphous, spherical SiO2 is contained in the suspension in two grain size classifications with a first grain size classification A containing SiO2 particles with a grain size ranging between 1 and 5 micrometers and with a second grain size classification B containing SiO2 particles with a grain size ranging between 0.01 and 0.05 micrometers. For the volume percentages of the two grain size ranges A, B, the following distribution rule applies: 0.8 to 1.0-1.2 to 1. Furthermore, the invention relates to a moulded part for foundry purposes and to a process of producing said moulted part.
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