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In this paper is described the investigation process and development of a new mixture for foundry cores, in which a factorial complete at two levels experimental design for mixtures with relationships between the components and an operation variable is used. The mixture that is developed uses the traditional process sodium silicate - CO2 and a new element has been employed: the carbonaceous schist as to facilitate the breaking down of the pieces from de moulds. A nomogram was made, in which it is represented the region where the relationships between components show the best properties, as resistance to the compression and breaking down. Also, it was carried out the integral hygroscopic characterization of the mixture selected as the best, which show excellent hygroscopic properties, compared with the similar ones that use for breaking down the cores, mixtures with sugary compounds.En este artículo se describe el proceso de investigación y desarrollo de una nueva mezcla para machos de fundición, en el que se emplea un diseño de experimento para mezclas, factorial completo a dos niveles con relaciones de componentes y variable de operación. La mezcla que se desarrolla utiliza el tradicional proceso silicato de sodio (vidrio líquido) - CO2 y como elemento novedoso se tiene el empleo de los esquistos carbonosos como aditivo desarenante. Se confecciona un nomograma que presenta la región donde las relaciones entre componentes muestran las mejores propiedades de resistencia a la compresión y desmoldeabilidad para la mezcla en estudio. Además, se realizó la caracterización higroscópica integral de la mezcla seleccionada como de mejores propiedades, la cual mostró excelentes propiedades higroscópicas, comparada con sus similares que emplean desarenantes del tipo azucarado.

The moisture diffusion in molding mixtures employing in foundry processes is described. Using gravimetric techniques the humectation kinetic behavior of different types of molding mixtures for foundry cores were registered. The mixture higroscopicity is compared using the porcentual increase in wet mass. The kinetic study is ending with the calculations effective coefficients of diffusion of the atmospheric water in the mixtures to different bleakness. For this goal the fitting through non lineal methods was used. The influences of the agglutinative and draw materials in the hygroscope properties of these were analyzed too.Se describe la difusión de humedad en mezclas de moldeo utilizadas en los procesos de fundición. Empleando técnicas gravimétricas se registra el comportamiento de la cinética de humectación de diferentes tipos de mezclas de moldeo para machos de fundición. La higroscopicidad de las mezclas es comparada usando el criterio del incremento porcentual en masa húmeda. El estudio cinético se concluye con los cálculos de los coeficientes efectivos de difusión del agua atmosférica en las mezclas a distintas intemperies. Para este propósito se emplean métodos de ajuste no lineal. También se analiza la influencia de los materiales aglutinantes y desarenantes en las propiedades higroscópicas de estas mezclas.

The article presents information on a comparative study in which the reaction kinetics of a mixture of sugar cane straw with 20 and 30% of clay, burned at 800 and 1000 degree Celsius, and hydrated lime, calcium hydroxide, is described with the help of different kinetic models. The models applied for the description includes Jander, Jander Modified and Zuravlev. A comparison of these models have been made with a kinetic-diffusive model previously published.

The kinetics of the pozzolanic reaction between lime (calcium hydroxide) and sugar cane straw ash (SCSA) with 20% and 30% of clay burned at 800 and 1000 °C is studied. A simple experimental technique was used in which the conductivity is the experimental variable. For correlating the conductivity with the concentration of calcium hydroxide (CH), a calibration curve was established. We elaborated a mathematical model that allows us to describe the process in either kinetic or kinetic–diffusive regimes. The fitting of the model by computerized methods enables us determine the parameters that characterize the process: i.e. the diffusion coefficient and reaction rate constant. The pozzolanic activity is evaluated according to the obtained values of the reaction rate constant. The results show that SCSA has a good pozzolanic activity comparable to that of the rice husk ash (RHA). [Copyright &y& Elsevier]

Abstract: The reaction kinetics of a mixture of sugar cane straw with 20% and 30% of clay burned at 800 and 1000 °C and lime (calcium hydroxide) is studied. A direct method (accelerated chemical method) based on the measurement of the amount of lime reacted as the reaction proceeds is applied. A kinetic–diffusive model published in a previous paper by some authors of this research is used. The fitting of the model by computerized methods allows determining the kinetic coefficients that characterize the process: in particular, the reaction rate constant. The index of pozzolanic activity evaluated according to the obtained values of the reaction rate constant permits to characterize the pozzolanic activity of these materials in a rigorous way. The results are compared with the results obtained applying an indirect method (conductometric method). The kinetic results obtained in the current paper allow affirming that the kinetic–diffuse model used in order to evaluate the pozzolanic reaction is valid, independently of the method used for the evaluation of the pozzolanic activity. [Copyright &y& Elsevier]