Foundry mold or core compositions and method
AssigneeE. I. Du Pont de Nemours and Company
InventorHoracio E. Bergna
Life of this patent
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Abstract
Compositions and method for producing foundry sand cores or molds of initial high strength but with essentially no strength after casting metals above 700.degree. C. which involves shaping and setting a composition containing foundry sand and a binder comprising sodium, potassium, or lithium silicate and sufficient amorphous silica so that the fraction of the total silica in the binder solution which is present as amorphous silica is from 2 to 75%, the amorphous silica having a particle size in the range from about 2 nanometers to 500 nanometers and the binder having a molar ratio of silica to alkali metal oxide ranging from 3.5:1 to 10.1.
Claims26
A sand core or mold composition comprising of foundary sand, 1-6% by weight of the sand of an aqueous solution or dispersion of a firm-forming resin adhesive and 3 to 15% by weight of the sand of an aqueous binder comprising an aqueous sodium, potassium or lithium silicate solution or mixtures thereof and amorphous silica, the binder characterized by (1) a molar ratio of silica to alkali metal oxide of from 3.5:1 to 10:1;
- (2) a weight fraction of the total silica present as amorphous silica is from 2 to 75%;
- (3) a weight fraction of the total silica present as silicate ions is from 98 to 25% and the amorphous silica has a particle size of from 2 nanometers to 500 nanometers and the sand core or mold possesses a compressive strength sufficiently low to permit easy crushing after said core or mold is used in preparing a metal casting.
A method for making a sand core or a sand mold useful in the casting of molten metal which comprises mixing foundry sand 1-6% by weight of the sand of an aqueous solution or dispersion of a film-forming resin adhesive and 3 to 15% by weight of the sand of a binder which comprises an aqueous sodium, potassium or lithium silicate solution or mixtures thereof and amorphous silica having a particle size of from 2 nanometers to 500 nanometers, the amount of silicate and amorphous silica being adjusted to form a binder with (1) a molar ratio of silica to alkali metal oxide ranging from 3.5:1 to 10:1, (2) the weight fraction of total silica present as amorphous silica of from 2 to 75% and (3) a weight fraction of the total silica present as silicate ions of from 98 to 25%, forming the sand and binder mixtures into the desired shape and setting the formed mixture.
Dependencies are inferred from the claim text.