Factors affecting the creep of porcelain tiles should be related to the microstructure of the tiles. These pores are usually aggregated and consist of decomposition of specific impurities. The origin of the microcracks are varies, though in particular as a result of the discrepancy between the residual quartz particles and the glass matrix and the spray dryer powder granule junctions that did not deform during the full press.
The creep is very high in porcelain tile pieces due to the growth of microcracks in the tile when the tile is exposed to tensile stress. Therefore, the factors that create these microcracks determine the creep in these types of tiles. Thus increasing the amount of quartz, such as particle size, creates microstructures with a larger number of microcracks, which probably increases the tile creep. This can also happen when the compound is not sufficiently milled.
The effect of dry coloring on creep is that the piece over time is subjected to creep, which is very rapid at the beginning and is fixed over time. The piece with pigment has a significantly higher tension than the piece without pigment, indicating that the deformation capacity under pressure is much higher for the colored piece.
The pieces with pigment have a higher creep that can be attributed to the microstructure of this type of tile where particles pigments are concentrated in certain areas of the piece.
These areas can act as microtransfer defects when higher percentages of pigments are used, those growth under certain stresses can create more creep. There are, of course, color patterns that show no delayed curvature. However, despite the asymmetric residual stresses on the tiles, and other equal factors, the tiles that exhibit the highest creep are likely to withstand time changes.
The evolution of curvature over the time for glazed porcelain tiles, when the minimum curvature of the glazing tile was observed (24 h, 0.37 mm) practically is simultaneous with the maximum curvature in the tile without glaze detected in the (23 h, 1.02 mm). This behavior may be due to the different expansion rates between the top and the bottom of the tile, since the tiles are firing with the same cycle of the kiln and therefore the residual stresses due to cooling must be similar. The same behavior has been observed in porcelain tiles without coating, which seems to indicate a very high effect of glaze evolution of curvature over the time.
The cooling stage in industrial roller kiln has rapid initial cooling by injecting air into the kiln at ambient temperature. This type of cooling produces a high temperature gradient between the surface and the inner part of the tile, resulting in residual stresses that can cause delayed curvature In symmetric cooling (segment in vertical possition), both sides of the segment cool equally.
And in asymmetric cooling (the piece is placed horizontally on a refractory board) in this case, cooling is basically done from above. In both cases, the two surfaces of the parts are subjected to compressive stress, while the inner part of the part is under pressure, which is the same situation in ceramic materials. Cooling also has a significant effect on the stress diagram. Therefore, when the test piece is cooled equally on both layers (the cooled piece in a vertical position), the stress diagram is symmetric, while the piece is on a horizontal position on the refractory slab (asymmetric cooling) displays asymmetric diagram. This results in a difference in the amount of cooling through the top and the bottom of the segment, which can lead to asymmetric diagram.