Method for producing molds and cores for metal casting and molds and cores produced according to this method

Abstract

The invention relates to a method for producing casting molds and cores, in which a foundry base material comprising at least one refractory material and a binder curable by CO 2 , preferably based on water glass, is cured by gassing with CO 2 and flushing with a second gas. The invention further relates to molds and cores produced according to this method.

1 . A method for producing casting molds and cores, comprising the steps of:
 preparing a molding mixture comprising at least one refractory molding base material and an inorganic binder,   introducing the molding mixture into a mold, and   flushing the molding mixture while the molding mixture is curing in the mold, through the steps of:
 flushing with a first gas, being gaseous carbon dioxide or containing gaseous carbon dioxide; and 
 flushing with a second gas, the second gas having a lower percentage of carbon dioxide, including no carbon dioxide, than the first gas. 
   
     
     
         2 . The method of  claim 1 , wherein:
 for introducing the molding mixture into the mold, a core-shooting machine with compressed air is used, where the mold is a molding tool that is flushed with the first and second gas.   
     
     
         3 . The method of  claim 1 , wherein the mold either is not heatable or is heated to temperatures of less than 70° C., preferably less than 60° C. and especially preferably less than 40° C. 
     
     
         4 . The method of  claim 1 , wherein the inorganic binder is water glass, especially water glass with a SiO 2 /M 2 O molar ratio of 1.6 to 4.0, preferably 2.0 to less than 3.5 with M is selected from the group consisting of: lithium, sodium, potassium, and mixtures thereof. 
     
     
         5 . The method of  claim 1 , wherein the molding mixture contains a maximum of 1 wt %, preferably a maximum of 0.5 wt % and particularly preferably a maximum of 0.2 wt % organic compounds. 
     
     
         6 . The method of  claim 1 , wherein the second gas contains less than 10 vol % CO 2 , especially less than 2 vol % CO 2 , and especially is air or nitrogen or a mixture thereof. 
     
     
         7 . The method of  claim 1 , wherein the first gas contains at least 25 mol % CO 2 , especially at least 50 mol % CO 2  and preferably at least 80 mol % CO 2 . 
     
     
         8 . The method of  claim 1 , wherein at least one of the first and the second gas is applied at a gas flow that amounts to 0.5 to 600 L/min (standard liters), preferably to 0.5 to 300 L/min and particularly preferably 0.5 L/min to 100 L/min. 
     
     
         9 . The method of  claim 1 , wherein at least one of the first and the second gas is used at a gas flow that amounts to 0.5 to 30 L/min (standard liters), preferably to 0.5 to 25 L/min and particularly preferably 0.5 L/min to 20 L/min, preferably at a gas temperature of 15 to 40° C. 
     
     
         10 . The method of  claim 1 , wherein at least one of the first and the second gas is at a charging pressure with reference to the mold that is between 0.5 bar and 10 bar, preferably between 0.5 bar and 8 bar and particularly preferably between 0.5 and 6 bar. 
     
     
         11 . The method of  claim 1 , wherein the first gas relative to the second gas is applied at a ratio of gassing times of 2:98 to 90:10, preferably 2:98 to 20:80 and particularly preferably 5:95 to 30:70 and especially with the first gas amounts maximally to 60% of the sum of the gassing time with the first and second gas. 
     
     
         12 . The method of  claim 1 , wherein the refractory molding base material has a mean particle diameter in the range of from 100 to 600 μm, preferably from 150 to 500 μm, and is selected from the group consisting of: quartz-, zirconium- or chrome ore sand, olivine, vermiculite, bauxite, fireclay and combinations thereof. 
     
     
         13 . The method of  claim 1 , wherein the binder, especially water glass, is contained in the refractory molding base material at up to 0.5 to 5 wt %, preferably 1 to 3.5 wt %, based on the refractory molding base material, in the case of water glass, based on a solids fraction of 25 to 65 wt %, preferably 30 to 60 wt %. 
     
     
         14 . The method of  claim 1 , wherein the molding mixture further comprises amorphous SiO 2 , especially synthetic amorphous SiO 2  and preferably with a mean particle size of between 0.05 μm and 10 μm, especially between 0.1 μm and 5 μm, particularly preferably between 0.1 μm and 2 μm, and independently thereof, the amorphous SiO 2  has a BET surface area amounting to 1 to 200 m 2 /g, especially 1 to 50 m 2 /g and particularly preferably 1 to 30 m 2 /g. 
     
     
         15 . The method of  claim 14 , wherein the amorphous SiO 2  is present in the range of 0.1 to 2 wt %, preferably 0.1 to 1.5 wt %, in each case based on the refractory molding base material and independently thereof, based on the weight of the binder with 2 to 60 wt %, particularly preferably 4 to 50 wt %. 
     
     
         16 . The method of  claim 1 , wherein
 in the flushing step, the first gas is introduced into the mold at a temperature of 15 to 120° C., preferably from 15 to 100° C. and particularly preferably from 25 to 80° C., and independently thereof, the second gas is introduced into the mold at a temperature within the same temperature interval or a temperature of 40 to 250° C., and preferably the temperature of the second gas upon introduction into the mold is greater than that of the first gas.   
     
     
         17 . The method of  claim 14 , wherein: wherein the amorphous SiO 2  has a water content of less than 15 wt %, especially less than 5 wt % and particularly preferably less than 1 wt % and independently of this is used especially as a powder. 
     
     
         18 . The method of  claim 1 , wherein:
 the first gas and the second gas are introduced into the mold for flushing in any arbitrary order and number of introduction processes, but at least temporarily separate from one another, wherein preferably the second gas is conducted through the mold last, and especially first and only once the first gas and subsequently the second gas is conducted through the mold.   
     
     
         19 . A mold or core produced according to  claim 1 .