ES369899A1 - Foundry moulding sand compositions - Google Patents

Abstract

A foundry moulding sand composition comprises a particulate refractory material admixed with an aqueous fluid, which fluid comprises, in solution, or in stable suspension or dispersion, an alkali metal silicate, a water-soluble oxidizing agent compatible with the metal silicate, and from 9-40%, by weight, on the weight of the fluid, of a readily oxidizable organic material, which is compatible with the alkali metal silicate and the oxidizing agent. The alkali metal silicate used is preferably sodium silicate and of these that having a SiO 2 : Na 2 O weight ratio of 2À0- 3.3 is advantageously used. The aqueous fluid preferably contains from 50-80% by weight, particularly 60-75%, of the commercial sodium silicate solution, whilst the amount of oxidizing agent is preferably 1-15% by weight. The water-soluble oxidizing agent should be compatible with the alkali metal silicate in the sense that it does not prevent the alkali metal silicate from exercizing its function as a sand binding agent and examples of such oxidizing agents are the nitrates, chromates, dichromates, permanganates and chlorates of alkali metals, particularly of sodium and potassium. Mixtures of such agents may be used. Examples of the readily oxidizable materials are starches, dextrine, celluloses, gums, natural resins, sugars and carbohydrate materials, ligneous materials, synthetic polymers, e.g. polyethylene and polystyrene, and hydrocarbon materials, e.g. coal-tars pitch and wood tars and these materials may be used separately or in admixture. Sucrose is a preferred material and a preferred composition includes sucrose and a mixture of a major proportion of sodium chlorate and a minor proportion of sodium dichromate as the oxidizing agent. The aqueous fluid preferably contains from 6-10% of added water but percentages above or below this range are also envisaged. The term # and is used to cover particulate refractory materials in general, e.g. silica, zircon, chrome, olivine or sillimanite. The aqueous fluid may be added to the sand in a wide range of proportions, e.g. 2-8 parts by weight per 100 parts by weight of sand. Small amounts 0À5-2À0% by weight, of bentonite and soluble dextrine may be added to the sand to improve its green strength.