PROCEDURE FOR IMPROVING THE PROPERTIES OF GYPSUM SHAPED PIECES

• Advantages / Applications: The present invention covers a procedure for improving the stability of items fabricated from plaster of Paris through additive manufacturing techniques involving binder jetting. It achieves enhanced strength and reduces the presence of volatiles in plaster items. This procedure consists of the application of different heat treatments in combination with a vacuum infiltration process of a solution of magnesium sulfate heptahydrate (Epsom salt) in distilled water. Unlike furans commonly used in the manufacture of plaster molds, Epsom salt is a compound that is harmless to health and the environment. The principal advantage afforded by the present invention relative to the methods habitually used is that it achieves improvements in the mechanical properties of solid prefabricated items, together with a reduction in the volatile compounds present in them. Such enhanced characteristics imply that there is an increase in the number of applications for which the items manufactured by this process can be employed. Possible applications are the production of molds for low melting point metals or for injecting plastics, where the amounts of volatiles present in items is crucial, decorative parts, medical prostheses or construction elements. • Main differential points that provide the patent 1) The patent presents a procedure that allows parts or molds to be manufactured directly, without the need to use previous models that are expensive. This first phase of modeling, typical of traditional sand molding processes, is avoided. For this, additive manufacturing techniques or computer-aided 3D printing are used, avoiding typical manual modeling or machining processes, which allows reducing operating time and reducing waste. 2) The method habitually uses curing substances that achieves improvements in the mechanical properties of solid prefabricated items, together with a reduction in the volatile compounds present in them. In contrast with other curing substances used in the current state of the art, magnesium sulfate speeds up the setting of plaster of Paris. It is, moreover, a substance that is effectively harmless for health and the environment. 3) Unlike some of the approaches in the present state of the art, the procedure described here permits curing time to be reduced from weeks down to days, or even hours, but with considerably enhanced penetration by the magnesium sulfate solution in comparison with other methods currently employed. 3) The process consists of several stages of heat treatment that give rise to several possibilities in terms of properties of the obtained parts (strength, moisture content, etc.). Differing from some processes in the current state of the art, the use of heat treatments to reduce capillary humidity and remove part of the water of crystallization permits improvements in properties, as well as increasing the strength of plaster items. In particular, it reduces the quantity of volatiles present in pieces. This allows to increase the range of applications of the obtained product depending on whether a higher level of resistance, greater porosity, etc. is required.