METODO PER RICUPERARE SABBIE DA MISCELE USATE DI FONDERIA E SISTEMA PER ESEGUIRE LO STESSO

A method for recovering sand from used foundry mixtures comprising exposing the grains of sand to heat treatment at a temperature between 310 and 900 degree C. Sorting and mechanical treatment are performed in cycles with a sand grain speed of between 5 and 50 m/sec, at least one of the cycles being performed in aqueous medium. The method provides for heat treatment of the sand at a temperature between 310 and 490 degree C and its subsequent exposure to mechanical treatment in an aqueous medium. In accordance with the invention mechanical treatment of the sand is performed in an aqueous medium followed by heat treatment at a temperature between 700 and 900 degree C, in which the mechanical treatment is performed in an aerated medium at a grain movement velocity of between 30 and 50 m/sec. The system for performing the method is provided with lines for the preparation of sands for moulds and cores, and also a line for processing sand wastes for moulds and cores, the lines being interconnected with each other by conveyor lines. The wastes treatment line comprises means to separate impurities from the surfaces of the sand grains, the said means comprising a calcining furnace with a cooler, a machine for hydraulic abrasion, a hydraulic sorter, a dewatering device and drier. The means for separating impurities from the surfaces of the sand grains comprise a machine for hydraulic abrasion mounted in series with a hydraulic sorter, a dewatering machine and a calcination furnace with a cooler and a machine for dry abrasion with an extractor system, a pneumatic generator divided into sections being used as the machine for dry abrasion.