Binder composition and method of forming foundry sand cores and molds

Abstract

A cost-effective starch/water-based binder composition and related method for forming silica sand cores and molds for foundries, wherein the sand grains are pre-coated with starch having additives making the coated sand effective for blowing said cores and molds. One or more additives are included with the starch; preferably sodium tripolyphosphate and silicon or Silres BS16. The preferred starch is a tapioca starch. The binder of the invention is highly competitive due to its low cost and effectiveness for forming silica-sand cores and molds, being particularly effective for use in aluminum foundries for the automotive industry.

1 . A method of forming silica sand cores and molds for foundries utilizing a starch-water-based binder comprising mixing silica sand grains with starch in a suitable mixer, adding water to said sand and starch mixture and continue mixing said sand, starch and water so that the sand grains are coated with starch; drying the starch-coated sand grains and treating them in a mill for destroying lumps formed during the starch-coating step; adding water to said coated sand grains and screening said sand grains for homogenizing and loosening said grains; adding at least one additive selected from the group consisting of sodium tripolyphosphate, silicon and a concentrated water solution of 1-5% potassium hydroxide plus 40-70% potassium methyl siliconate; and blowing said cores and molds utilizing said starch-coated sand grains. 
     
     
         2 . The method according to  claim 1 , wherein said silica sand is mixed with starch in a proportion of from about 0.5% to 2% by weight on the basis of the sand weight. 
     
     
         3 . The method according to  claim 1 , wherein said sand grains and starch are mixed in a paddle mixer for a period of time from about 30 seconds to about 120 seconds. 
     
     
         4 . The method according to  claim 1 , wherein water is added to the sand-starch mixture in a proportion from about 5% to 10% by weight on the basis of the sand weight. 
     
     
         5 . The method of forming silica sand cores and molds according to  claim 1 , wherein said starch-coated sand grains are allowed to dry naturally. 
     
     
         6 . The method of forming silica sand cores and molds according to  claim 5 , wherein said starch-coated sand grains are dried in a drying furnace for increasing productivity. 
     
     
         7 . The method of forming silica sand cores and molds according to  claim 1 , wherein the dry starch-coated sand is treated in a ball mill or a vibratory shaker. 
     
     
         8 . The method of forming silica sand cores and molds according to  claim 1 , further comprising screening the starch-coated sand and thereafter mixing said starch-coated sand with water in a proportion of at least 2% by weight on the basis of the sand weight. 
     
     
         9 . The method of forming silica sand cores and molds according to  claim 1 , wherein said additive is sodium tripolyphosphate, which is added in a proportion of from about 0.1% to about 0.2% by weight on the basis of the sand weight; and a further additive is silicon being also added in the same proportion. 
     
     
         10 . The method of forming silica sand cores and molds according to  claim 1 , wherein said additive is sodium tripolyphosphate, which is added in a proportion of from about 0.1% to about 0.2% by weight on the basis of the sand weight; and a further additive is iron oxide is also added in the same proportion. 
     
     
         11 . The method of forming silica sand cores and molds according to  claim 1 , further comprising heating said sand to a temperature in the range from about 110° C. to about 130° C. prior to mixing said sand with water and starch. 
     
     
         12 . The method of forming silica sand cores and molds according to  claim 1 , wherein said starch is artificially modified tapioca starch. 
     
     
         13 . The method of forming silica sand cores and molds according to  claim 1 , wherein said starch is native tapioca starch. 
     
     
         14 . The method of forming silica sand cores and molds according to  claim 11 , wherein said starch is native tapioca starch. 
     
     
         15 . A starch-water-based binder composition suitable for forming silica sand cores and molds for foundries, comprising more than about 80% starch; sodium tripolyphosphate and silicon. 
     
     
         16 . A starch-water-based binder composition suitable for forming silica sand cores and molds for foundries, comprising from about 1.0% to about 1.5% by weight of starch; from about 0.1% to about 0.2% by weight of sodium tripolyphosphate; and from about 0.1% to about 0.2% by weight of silicon; all on the basis of the sand weight. 
     
     
         17 . A starch-water-based binder composition suitable for forming silica sand cores and molds for foundries, comprising more than about 70% of starch; from about 0.1% to about 0.2% by weight of sodium tripolyphosphate; and from about 0.1% to about 0.2% by weight of Silres-BS16; all on the basis of the sand weight. 
     
     
         18 . A starch-water-based binder composition according to  claim 15 , suitable for forming silica sand cores and molds for foundries, wherein said starch is tapioca starch. 
     
     
         19 . A starch-water-based binder composition according to  claim 15 , suitable for forming silica sand cores and molds for foundries, wherein said starch is artificially modified tapioca starch. 
     
     
         20 . A starch-water-based binder composition according to  claim 15 , suitable for forming silica sand cores and molds for foundries, wherein said starch is native-tapioca starch.