Use of a coating composition containing an acid in the foundry industry

Abstract

The present invention describes the use of a coating composition, comprising an aqueous phase having a pH of at most 5 and one or more refractories, in the foundry industry and also coated, waterglass-bound foundry molding elements, especially foundry molds and/or foundry cores, which each comprise such an aforementioned coating composition. The invention further describes a method for producing a coated, waterglass-bound foundry molding element. The invention likewise describes a kit whose contents include an aforementioned coating composition, comprising aqueous acid and one or more refractories.

1 . The method of a coating composition comprising
 (a) one or more refractories, and   (b) an aqueous phase having a pH of at most 5,   
       for producing a coating on a waterglass-bound mold or on a waterglass-bound core, for use in the foundry, where the waterglass-bound mold or the waterglass-bound core comprises particulate, amorphous silicon dioxide. 
     
     
         2 . The method as claimed in  claim 1 , where the coated, waterglass-bound mold or the coated, waterglass-bound core, in comparison to a coated, waterglass-bound comparative mold or a coated, waterglass-bound comparative core produced, under otherwise identical conditions, using a comparative coating composition obtained from the coating composition by adding sodium hydroxide until a pH of 7 is reached,
 possesses a flexural strength which decreases less on drying   
       and/or
 possess an increased storage stability. 
 
     
     
         3 . The method as claimed in  claim 1 , where the aqueous phase (b) comprises
 (b1) water, and   (b2) one or more acids, preferably having a pKa<5, more preferably having a pKa<4,   
       where preferably the ratio of the mass of constituent (b1) to the mass of constituent (b2) is in the range from 10:1 to 200:1, more preferably in the range from 10:1 to 100:1, 
       and/or 
       where preferably the ratio of the mass of constituent (b1) to the total mass of the aqueous phase (b) is greater than 50%, more preferably greater than 70%, very preferably greater than 90%, 
       and/or 
       where preferably the aqueous phase possesses a pH of at most 4. 
     
     
         4 . The method as claimed in  claim 3 ,
 where the constituent (b2) comprises one or more acids which are selected from the group consisting of inorganic and organic acids,
 where the organic acids are preferably selected from the group consisting of mono-, di-, and tricarboxylic acids, preferably mono-, di-, and tricarboxylic acids which are solid at 25° C. and 1013 mbar, more preferably citric acid and oxalic acid, 
 and/or 
 where the inorganic acids are preferably selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, and acidic phosphates, more preferably from the group consisting of hydrochloric acid, nitric acid, and phosphoric acid, 
 and/or 
 where the ratio of the total mass of inorganic and organic acids of constituent (b2) to the total mass of the coating composition is in the range from 0.1 to 10%, preferably in the range from 0.5 to 5%, more preferably in the range from 1 to 5%, very preferably in the range from in the range from 1 to 3.5%, and especially preferably in the range from 2.5 to 3.5%. 
   
     
     
         5 . The method as claimed in  claim 1 , where the constituent (a) comprises
 particulate, amorphous silicon dioxide,
 preferably particulate, amorphous silicon dioxide whose primary particles (i) are spherical and/or (ii) possess a D90<10 μm, preferably a D90 of <1 determined by laser diffraction, 
 more preferably particulate, amorphous silicon dioxide which comprises as a secondary constituent (i) zirconium dioxide and/or (ii) a Lewis acid, 
   and/or   one or more substances selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, phyllosilicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide, and bauxite.   
     
     
         6 . The method as claimed in  claim 1 , where the coating composition comprises one or more or all of the following constituents:
 one or more biocides,   one or more wetting agents,   one or more rheological additives, and   one or more binders, preferably polyvinyl alcohol.   
     
     
         7 . The method as claimed in  claim 1 , where the coating composition possesses a solids content of less than 80 wt %, preferably less than 45 wt %, based on the total mass of the coating composition,
 and/or   where the coating composition comprises one or more binders, preferably comprising polyvinyl alcohol, in a total amount of not more than 2 wt %, preferably in an amount in the range from 0.05 to 0.80 wt %, based on the total mass of the coating composition.   
     
     
         8 . The method as claimed in  claim 1 , where the coating composition is applied to a waterglass-bound mold or a waterglass-bound core for use in the casting of a metal melt with a temperature >900° C., preferably >1250° C., preferably for use in the casting of a metal melt comprising iron and/or steel,
 and/or 
 where the coating composition is applied to a waterglass-bound mold or a waterglass-bound core for use in the casting of iron or steel 
 and/or 
 where the coating composition is applied to a waterglass-bound mold or a waterglass-bound core at a temperature of the waterglass-bound core or the waterglass-bound mold of >50° C., preferably >70° C., more preferably at a temperature <100° C. 
 
     
     
         9 . The method of acid for setting a pH of at most 5 in the aqueous phase of a coating composition for application to a waterglass-bound mold or a waterglass-bound core. 
     
     
         10 . The method as claimed in  claim 9 ,
 where the acid is selected from the group consisting of inorganic and organic acids,
 where the organic acids are preferably selected from the group consisting of mono-, di-, and tricarboxylic acids, preferably mono-, di-, and tricarboxylic acids which are solid at 25° C. and 1013 mbar, more preferably citric acid and oxalic acid, 
 and/or 
 where the inorganic acids are preferably selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, and acidic phosphates, more preferably from the group consisting of hydrochloric acid, nitric acid, and phosphoric acid, 
   and/or   where the waterglass-bound mold or the waterglass-bound core comprises particulate, amorphous silicon dioxide, where the acid is used preferably for setting a pH of at most 4.   
     
     
         11 . A process for producing a coated, waterglass-bound mold with high storage stability, or a coated, waterglass-bound core with high storage stability, for use in the foundry, comprising the following steps:
 (1) providing or producing a coating composition as defined in  claim 1 ,   (2) providing or producing an uncoated, waterglass-bound mold or an uncoated, waterglass-bound core, and   (3) applying the provided or produced coating composition from step (1) to the provided or produced mold or the provided or produced core.   
     
     
         12 . The process as claimed in  claim 11 , where the provided or produced mold or the provided or produced core comprises particulate, amorphous silicon dioxide. 
     
     
         13 . The process as claimed in  claim 11 , where application to the mold takes place at a temperature of the core or of the mold of >50° C., preferably >70° C., more preferably at a temperature <100° C. 
     
     
         14 . A coated mold or coated core for use in the foundry, in each case comprising
 (X) a waterglass-bound mold or a waterglass-bound core, and   (Y) a coating comprising a coating composition as defined in  claim 1 .   
     
     
         15 . A coated mold or coated core, producible by the process as claimed in  claim 11 . 
     
     
         16 . The coated mold or coated core as claimed in  claim 14 , where the waterglass-bound mold and/or the waterglass-bound core comprises particulate, amorphous silicon dioxide. 
     
     
         17 . The coated mold or coated core as claimed in  claim 14  for use in the casting of a metal melt having a temperature >900° C., preferably for use in the casting of a metal melt comprising iron and/or steel. 
     
     
         18 . A kit including in separate components
 (U) a coating composition comprising
 (a) one or more refractories, and 
 (b) an aqueous phase having a pH of at most 5 
   
       for producing a coating on a waterglass-bound mold or a waterglass-bound core, for use in the foundry,
 (V) a binder comprising waterglass, and 
 (W) particulate, amorphous silicon dioxide. 
 
     
     
         19 . A kit,
 comprising as component (U) a coating composition, where the coating composition is as defined in  claim 1 ,
 (V) a binder comprising waterglass, and 
 (W) particulate, amorphous silicon dioxide.