Efeitos das condições de queima e densidade aparente sobre a sobrequeima em porcelanatos
Abstract
The phenomenon of overfiring manifests in porcelain tiles and other
products with high degree of vitrification, as a consequence of the expansion of
gases trapped in closed pores, in the final stages of sintering. When it is not
properly controlled, it generates swelling of the pieces and then they present
dimensional problems, damages in the mechanical properties and low stain
resistance in polished products. Porcelain tiles are products with strict
requirements, water absorption ≤0.5% for glazed and ≤0.1% for technical ones,
moreover the ceramics industries, nowadays, use firing cycles increasingly
faster, which allows significant productivity increases and costs reductions.
Associate both avoiding the phenomenon of overfiring is not an easy task. The
aim of this study was to evaluate the effects of the green bulk density and the
firing curve (heating rate and soaking time at the maximum temperature) on the
characteristics of the final product and on the development of this phenomenon.
To achieve the objectives, a factorial design of experiments (DOE) was used.
The differences between the firing temperatures necessary to produce 0.5% of
water absorption and to achieve the maximum bulk density were considered to
determine the firing range before overfiring the porcelain tiles. The results
indicate that the firing range is strongly influenced by the time the samples were
kept at the maximum temperature of the firing cycle. At the same time, they also
indicate the importance of the bulk density of the green bodies as a way to
reduce the closed porosity of the fired bodies and consequently to prevent the
production of overfired porcelain tiles.