Method for constructing molds and cores layer by layer by means of a binder containing water glass, and a binder containing water glass

Abstract

The invention relates to a binder, which contains water glass and further a phosphate or a borate or both. The invention further relates to a method for constructing molds and cores layer by layer, the molds and cores comprising a construction material mixture, which at least comprises a refractory molding base material, and the binder. In order to produce the molds and cores layer by layer in 3-D printing, the refractory molding base material is applied layer by layer and is selectively printed with the binder layer by layer, and consequently a body corresponding to the molds or cores is constructed and the molds or cores are released after the unbonded construction material mixture has been removed.

1 . A method for constructing bodies layer by layer, comprising at least the following steps:
 a) providing a refractory molding base material as a component of a construction material mixture;   b) spreading a thin layer of the construction material mixture with a layer thickness of 0.05 mm to 3 mm, preferably 0.1 mm to 2 mm and particularly preferably 0.1 mm to 1 mm;   c) printing selected areas of the thin layer with a binder having a dynamic viscosity at 25° C. of greater than 1 mPas and less than 25 mPas, comprising:
 water glass in the form of an aqueous alkali silicate solution, and 
 at least one phosphate or at least one borate or phosphate and borate; and 
   d) repeatedly repeating steps b) and c).   
     
     
         2 . The method according to  claim 1 , further comprising the step of curing the printed areas, in particular by temperature increase, preferably effected by microwaves and/or infrared light. 
     
     
         3 . The method according to  claim 2 , wherein the curing of the printed areas takes place in each case after constructing 1 to 10 printed layers of the construction material mixture, preferably 3 to 8 printed layers. 
     
     
         4 . The method according to  claim 2 , further comprising the following steps:
 i) curing the body after completion of the layer by layer construction in a furnace or by means of a microwave, and subsequent   ii) removing the unbonded construction material mixture from the at least partially cured casting mold.   
     
     
         5 . The method according to  claim 1 , wherein the refractory molding base material comprises quartz, zirconium or chromium ore sand, olivine, vermiculite, bauxite, fire clay, glass beads, glass granules, hollow aluminum silicate microspheres and mixtures thereof, and preferably consists of more than 50% by weight of quartz sand, based on the refractory molding base material. 
     
     
         6 . The method according to  claim 1 , wherein more than 80% by weight, preferably greater than 90% by weight, and particularly preferably greater than 95% by weight, of the construction material mixture is refractory molding base material. 
     
     
         7 . The method according to  claim 1 , wherein the refractory molding base material has average grain diameters from 50 μm to 600 μm, preferably between 80 μm and 300 μm, determined by sieving analysis. 
     
     
         8 . The method according to  claim 1 , wherein the water glass, including solvent/diluent, is used in an amount of between 0.5% by weight and 7% by weight, preferably between 0.75% by weight and 6% by weight, and particularly preferably between 1% by weight and 5.0% by weight, based on the molding base material. 
     
     
         9 . The method according to  claim 1 , wherein an inorganic curing agent for water glass-based binders is added to the construction material mixture, and the inorganic curing agent is preferably a phosphate. 
     
     
         10 . The method according to  claim 9 , wherein the proportion of the curing agent relative to the binder is greater than or equal to 5 to less than 25% by weight, preferably greater than or equal to 8 to less than 20% by weight, particularly preferably greater than or equal to 10 to less than 15% by weight. 
     
     
         11 . The method according to  claim 9 , wherein between 0.05% by weight and 2% by weight of the inorganic curing agent is used, preferably between 0.1% by weight and 1% by weight, particularly preferably between 0.1% by weight and 0.6% by weight, in each case based on the molding base material. 
     
     
         12 . The method according to  claim 1 , wherein the printing is carried out with a printing head having a plurality of nozzles, the nozzles preferably being individually selectively controllable. 
     
     
         13 . The method according to  claim 12 , wherein the print head is movable in at least one plane controlled by a computer, and the nozzles apply the liquid binder layer by layer. 
     
     
         14 . The method according to  claim 12 , wherein the print head is a drop-on-demand print head with bubble-jet or piezo technology. 
     
     
         15 . The method according to  claim 1 , wherein the at least one phosphate is at least water-soluble at 25° C. and is preferably an alkali phosphate, particularly preferably sodium polyphosphate or sodium metaphosphate or both. 
     
     
         16 . The method according to  claim 1 , wherein the binder contains phosphates, preferably in a molar ratio of P 2 O 5 /SiO 2  (calculated as P 2 O 5  and relative to SiO 2  in the binder) of greater than 0.01 and less than 0.5. 
     
     
         17 . The method according to  claim 1 , wherein the binder contains borates and preferably the molar ratio of B 2 O 3 /SiO 2  (calculated as B 2 O 3  and SiO 2  in the binder) is from 0.01 to 0.5. 
     
     
         18 . The method according to  claim 1 , wherein the at least one borate is at least water-soluble at 25° C. and is preferably an alkali borate, more preferably disodium tetraborate decahydrate. 
     
     
         19 . A mold or core, producible according to  claim 1 , for metal casting, in particular iron, steel, copper or aluminum casting. 
     
     
         20 . A binder, comprising
 water glass with a molar ratio of Na 2 O/M 2 O of greater than 0.4, preferably greater than 0.5 and more preferably greater than 0.6 and particularly preferably greater than 0.7, and a molar modulus SiO 2 /M 2 O of greater 1.4 to less than 2.8, preferably greater than 1.6 to less than 2.6, preferably greater than 1.8 to less than 2.5 and more preferably greater than 1.9 and less than 2.4,   wherein in each case M 2 O is the sum of the molar amounts of lithium, sodium and potassium calculated as oxide, based on the amorphous alkali silicates, alkali oxides, alkali hydroxides, alkali phosphates and/or alkali borates contained in the binder; and   wherein any particulate constituents in the binder have a D90 value of less than 70 μm;   the binder contains at least one phosphate or at least one borate or phosphate and borate; and   the binder has a dynamic viscosity at 25° C. of greater than 1 mPas and less than 25 m Pas.   
     
     
         21 . The binder according to  claim 20 , wherein the binder has a solids content of greater than 22 to less than 40% by weight, preferably greater than 24 to less than 38% by weight, preferably greater than 26 to less than 36% by weight, particularly preferably greater than 28 to less than 35% by weight. 
     
     
         22 . The binder according to  claim 20 , wherein particles, if any, in the binder
 have a D90 value of less than 40 μm, preferably less than 30 μm, particularly preferably less than 25 μm, and more preferably less than 20 μm, and/or   have a D100 value of less than 250 μm, preferably less than 120 μm, preferably less than 50 μm, more preferably less than 40 μm, particularly preferably less than 35 μm, and more preferably less than 30 μm.   
     
     
         23 . The binder according to  claim 20 , wherein the at least one phosphate is at least water-soluble at 25° C., preferably is an alkali phosphate, particularly preferably sodium polyphosphate or sodium metaphosphate or both. 
     
     
         24 . The binder according to  claim 20 , wherein the binder contains phosphates, preferably in a molar ratio of P 2 O 5 /SiO 2  (calculated as P 2 O 5  and relative to the SiO 2  in the binder) of greater than 0.01 and less than 0.5. 
     
     
         25 . The binder according to  claim 20 , wherein the binder contains borates and preferably the molar ratio B 2 O 3 /SiO 2  (calculated as B 2 O 3  and SiO 2  in the binder) is from 0.01 to 0.5. 
     
     
         26 . The binder according to  claim 20 , wherein the at least one borate is at least water-soluble at 25° C. and is preferably an alkali borate, particularly preferably disodium tetraborate decahydrate. 
     
     
         27 . The binder according to  claim 20 , wherein the binder further contains surface-active substances, preferably surfactants, in particular between 0.01 and 4.0% by weight, preferably between 0.1 and 3.0% by weight. 
     
     
         28 . (canceled)