Curvature Evolution of Porcelain Tile during Firing

Abstract

Planarity is one of indispensable attribute of a ceramic tile quality. During the firing changes on curvature may be permanent causing damage on quality and productivity. The objective was to evaluate curvature evolution on porcelain tile during heating stage of firing. Effects of engobe and glaze coating were evaluated. The performance of two compositions of porcelain tile was studied on industrial (1000 mm x 500 mm x 10 mm) and laboratorial (100 mm x 50 mm x 6 mm) scale. Industrial test pieces were fired at 950 and 1200 °C. Final curvature was measured by conventional dial indicator. Curvature evolution of laboratorial test pieces was evaluated by thermal fleximetry from 25 to 1200 °C. This characterization was capable to identify very significant positive curvature deflection on temperature range from 930 to 1200 °C, directly associated to permanent planarity defects. Differences on composition affect significantly the curvature evolution.

Effect of Feldspar Substitution by Basalt on Pyroplastic Behaviour of Porcelain Tile Composition

“…It can be observed that, approximately, from a temperature of 900 °C, the studied compositions began to show a negative deformation, i.e., concavity, owing to the beginning of the formation of a liquid phase from the fusion of clay minerals and the action of gravity [ 21 ]. Between 975 and 1025 °C, the increase in the deformation was interrupted by the formation of mullite at 1005 °C, which stabilised the structure, as shown in the DSC graph of the studied compositions in Figure 12 .…”

“…The test consisted of an arrangement of a standardised specimen (3 mm × 5 mm × 80 mm) supported on two points. With warm-up, it was expected that this body would form an arrow shape, owing to the effect of gravity [ 21 ]. This test was performed on composition samples C0, C1, C2, and C3 in an optical fleximeter (Expert System Solutions, model Misura Flex ODLT, Modena, Italy) at a heating rate of 10 °C/min.…”