Salt-based cores, method for the production thereof and use thereof

Abstract

Cores that are inserted into the mold during the die casting of workpieces from metal in order to keep the cavities provided in the workpieces free during the filling of the molds with the melt have to meet demanding requirements with regard to the dimensional stability and suitability thereof for removal from the cavities. Therefore, salt-based cores which can be produced by molding and compressing a core material mixture are provided according to the invention, the core materials thereof being selected from at least one salt, at least one binder system comprising a combination of binder/binding agent and optionally auxiliary substances such as additives, fillers, wetting agents and catalysts, wherein the salt, the binder system and the optionally used auxiliary substances of the core material mixture are inorganic, and these core materials are soluble with water as the solvent.

1 - 47 . (canceled) 
     
     
         48 . Salt-based cores comprising a core material mixture;
 wherein the core material mixture comprises a salt and a binder system;   said binder system comprising a binder and a drying agent;   wherein the salt and the binder are inorganic; and   wherein the core material mixture is shaped into the salt cores and compacted via a dry pressing method.   
     
     
         49 . The salt-based cores according to  claim 48 , wherein salts are used which have a decomposition or melting point above the temperature of the liquid metal that is poured around the cores. 
     
     
         50 . The salt-based cores according to  claim 48 , wherein the salt is selected from the group consisting of an alkali chloride, an alkaline earth chloride, a sulfate of an alkali element, a sulfate of an alkaline earth element, a nitrate of an alkali element and a nitrate of an alkaline earth element. 
     
     
         51 . The salt-based cores according to  claim 48 , wherein the salt is selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride sulfates and nitrates of the alkali elements and alkaline earth elements, in particular potassium sulfate and/or magnesium sulfate, ammonium salts, in particular ammonium sulfate, or mixtures of these salts. 
     
     
         52 . The salt-based cores according to  claim 48 , wherein the salt is sodium chloride. 
     
     
         53 . The salt-based cores according to  claim 48 , wherein the salt has a grain size in the range from 0.01 mm to 2 mm. 
     
     
         54 . The salt-based cores according to  claim 48 , wherein the salt is present in a bimodal or trimodal grain size distribution. 
     
     
         55 . The salt-based cores according to  claim 48 , wherein the salt has a grain size distribution of from 0.01 to 0.29 mm. 
     
     
         56 . The salt-based cores according to  claim 48 , wherein the salt has a grain size distribution of from 0.3 to 1.3 mm. 
     
     
         57 . The salt-based cores according to  claim 48 , wherein the salt has a grain size distribution of from 1.31 to 2.0 mm. 
     
     
         58 . The salt-based cores according to  claim 48 , wherein the binder comprises at least one compound selected from the group consisting of an inorganic phosphate, an inorganic borate and a silicate compound which can be removed with water without leaving any residue. 
     
     
         59 . The salt-based cores according to  claim 58 , wherein the binder is selected from the group consisting of an alkali phosphate, ammonium phosphate, monoaluminum phosphate, boron phosphate, trisodium phosphate, tetrapotassium pyrophosphate and sodium polyphosphate. 
     
     
         60 . The salt-based cores according to  claim 58 , wherein the binder is a water-soluble silicate compounds. 
     
     
         61 . The salt-based cores according to  claim 48 , wherein the binder is a water glass having a water glass module of from 1 to 5. 
     
     
         62 . The salt-based cores according to  claim 48 , wherein the content of binder is between 0.5% by weight and 15% by weight, based on the salt. 
     
     
         63 . The salt-based cores according to  claim 48 , wherein the content of the binder is between 0.5% by weight and 15% by weight, based on the salt. 
     
     
         64 . The salt-based cores according to  claim 48 , wherein water glass is present as the binder in a content of 0.5% by weight to 15% by weight, based on the salt that is used, as a function of the grain size distribution and tailored to the water glass module. 
     
     
         65 . The salt-based cores according to  claim 48 , wherein the binder is tetrapotassium pyrophosphate. 
     
     
         66 . The salt-based cores according to  claim 48 , wherein the binder is tetrapotassium pyrophosphate in liquid form. 
     
     
         67 . The salt-based cores according to  claim 48 , wherein the binder is tetrapotassium pyrophosphate in an aqueous 60% solution. 
     
     
         68 . The salt-based cores according to  claim 48 , wherein the binder used in the binder system is tetrapotassium pyrophosphate in an aqueous 60% solution and in an amount of from 1 to 5% by weight, based on the amount of the salt. 
     
     
         69 . The salt-based cores according to  claim 48 , wherein the binder is tetrapotassium pyrophosphate in an aqueous 60% solution and in amount of from 1 to 5% by weight, and tetrapotassium pyrophosphate in solid form is present in the same amount or in a larger amount. 
     
     
         70 . The salt-based cores according to  claim 48 , wherein the binder is present in the binder system in a content of 1 to 15% by weight, based on the amount of the salt, and the drying agent is present in a content of 0.3 to 4.5% by weight, based on the amount of the salt. 
     
     
         71 . The salt-based cores according to  claim 48 , wherein hydrophilic substances which are able to reversibly bind water are used in the binder system as drying agents. 
     
     
         72 . The salt-based cores according to  claim 48 , wherein the drying agent is selected from the group consisting of silicic acid, silica gel, a zeolite, an anhydrous sodium sulfate and magnesium sulfate. 
     
     
         73 . The salt-based cores according to  claim 48 , further comprising a catalyst. 
     
     
         74 . The salt-based cores according to  claim 48 , wherein the catalyst is particularly fine-grained salt, and preferably powdered salt having a particle size of less than 100 nm. 
     
     
         75 . The salt-based cores according to  claim 48 , wherein the salt is sodium chloride, which is preferably present in a bimodal or trimodal grain size distribution, particularly preferably in a grain size distribution of 0.01 to 0.29 mm, 0.3 to 1.3 mm and/or 1.31 to 2.0 mm, the binder system is composed of the combination of water glass as the binder and Aerosil as the drying agent, the catalyst is particularly fine-grained salt, and preferably powdered salt having a particle size of less than 100 nm, optionally further auxiliary substances such as additives, fillers, wetting agents and/or further catalysts are present, and the mixture of the core materials is free-flowing. 
     
     
         76 . The salt-based cores according to  claim 48 , wherein the cores are heat-treated after shaping. 
     
     
         77 . The salt-based cores according to  claim 48 , wherein, after shaping, the cores are heat-treated at a temperature up to 600° C., preferably at temperatures of 500 to 600° C., and preferably at a temperature of 580° C. 
     
     
         78 . The salt-based cores according to  claim 48 , wherein the shaped cores have a density of 1.5 g/cm 3  to 2.1 g/cm 3 . 
     
     
         79 . The salt-based cores according to  claim 48 , wherein the shaped cores have a porosity of 10% to 40%. 
     
     
         80 . The salt-based cores according to  claim 48 , wherein the shaped cores have a flexural strength between 400 N/cm 2  and 1500 N/cm 2 . 
     
     
         81 . A method for producing salt-based cores comprising the steps of:
 homogenously mixing the core material mixture;   shaping the core material mixture into shaped cores; and   compacting the shaped cores view dry pressing to form the salt-based cores;   wherein the core material mixture comprises a salt and a binder system;   said binder system comprising a binder and a drying agent;   wherein the salt and the binder are inorganic.   
     
     
         82 . A method according to  claim 81 , wherein salt having grain sizes with differing distribution curves, preferably in a bimodal or trimodal grain size distribution, is used and mixed. 
     
     
         83 . A method according to  claim 81 , wherein the salt is selected from the group consisting of an alkali chloride, an alkaline earth chloride, a sulfate of an alkali element, a sulfate of an alkaline earth element, a nitrate of an alkali element and a nitrate of an alkaline earth element. 
     
     
         84 . A method according to  claim 81 , wherein the binders/binders used in the binder system are inorganic phosphates, inorganic borates or silicate compounds which can be removed without leaving any residue, using water, or mixtures of these binders/binders. 
     
     
         85 . A method according to  claim 81 , wherein the binder comprises at least one member selected from the group consisting of an alkali phosphate, ammonium phosphate, monoaluminum phosphate, boron phosphate, trisodium phosphate, tetrapotassium pyrophosphate and sodium polyphosphate which can be removed with water without leaving any residue. 
     
     
         86 . A method according to  claim 81 , wherein the binder is a water-soluble silicate compound. 
     
     
         87 . A method according to  claim 81 , wherein the binder in the binder system is water glass having a water glass module of 1 to 5, and/or a mixture of water glasses having differing water glass modules. 
     
     
         88 . A method according to  claim 81 , wherein hydrophilic substances which are able to reversibly bind water are used in the binder system as drying agents. 
     
     
         89 . A method according to  claim 81 , wherein the drying agent is selected form the group consisting of a silicic acid, silica gel, a zeolite, an anhydrous sodium sulfate and magnesium sulfate. 
     
     
         90 . A method according to  claim 81 , wherein a catalyst is added as an auxiliary substance. 
     
     
         91 . A method according to  claim 81 , wherein the catalyst is particularly fine-grained salt, and preferably powdered salt having a particle size of less than 100 nm. 
     
     
         92 . A method according to  claim 81 , wherein the salt is sodium chloride, which is present in a bimodal or trimodal grain size distribution, the binder system is composed of the combination of water glass as the binder and Aerosil as the drying agent, the catalyst is particularly fine-grained salt, and preferably powdered salt having a particle size of less than 100 nm. 
     
     
         93 . A method according to  claim 81 , wherein the core materials are homogeneously mixed, shaped into a core, and compacted in a dry pressing method. 
     
     
         94 . A method according to  claim 81 , wherein the core materials have a grain size ranging from 0.01 mm to 2 mm. 
     
     
         95 . A method according to  claim 81 , wherein the cores are heat-treated after shaping. 
     
     
         96 . A method according to  claim 81 , wherein, after shaping, the cores are heat-treated at a temperature up to 600° C. 
     
     
         97 . A method comprising providing the salt-based cores according to  claim 48  as cavity placeholder in a mold during production of metal cast part. 
     
     
         98 . A method according to  claim 81 , wherein the salt-based cores are heat treated. 
     
     
         99 . The salt-based cores according to  claim 48 , wherein the binder is a mixture of water glasses having differing water glass modules. 
     
     
         100 . The salt based cores adoring to  claim 48 , wherein the binder is a water glass. 
     
     
         101 . The salt-based cores according to  claim 48 , further comprising an auxiliary substance. 
     
     
         102 . A method according to  claim 81 , wherein the binder is a water glass. 
     
     
         103 . A method according to  claim 81 , wherein the salt is sodium chloride, which is present in a bimodal or trimodal grain size distribution, particularly preferably in a grain size distribution of 0.01 to 0.29 mm, 0.3 to 1.3 mm and/or 1.31 to 2.0 mm, the binder system is composed of the combination of water glass as the binder and Aerosil as the drying agent, the catalyst is particularly fine-grained salt, and preferably powdered salt having a particle size of less than 100 nm, optionally further auxiliary substances such as additives, fillers, wetting agents and/or further catalysts are present, and the mixture of the core materials is free-flowing.