In the production process of sanitary ceramics, firing is an important stage, and most product defects are produced in the firing stage. In this article, we continue to introduce the defects that are prone to occur in the firing stage of sanitary ceramics and the corresponding solutions.
Crack
Cracks include through cracks (cracking) and non-through cracks (including glaze cracks). During the firing process, due to the unreasonable firing system, excessive heating or improper cooling will cause cracks in the kiln products. For example, when the water content of the products entering the kiln is high, and the temperature rises too fast after entering the kiln, it is easy to cause cracking of the products; for example, improper cooling during the cooling stage (especially slow cooling) is likely to cause glaze cracks. In addition, the billet contains too much plastic raw material or free quartz, which causes stress; improper sieving of the slurry leads to over-screening, which causes particles such as quartz and limestone to be mixed into the slurry; the slurry aging time is insufficient; the mold is too dry or too wet, and the water Uneven; the wet blank dries too fast, and the shrinkage of each part is uneven and other reasons may cause this defect.
The first method to avoid cracks is to adjust and control the firing curve, reduce the temperature difference between the upper and lower sides of the kiln, control the moisture of the products entering the kiln, and appropriately slow down the heating rate of the kiln head and the cooling rate of the slow cooling section. The second is to adjust the billet formula to reduce plastic raw materials and stale system, and improve the content of free quartz; in addition, it is necessary to improve mud preparation,
Smoked
Smoking refers to the fact that the surface of the product is partially or completely gray, brown, black and other different colors due to smoke during firing. The main reason is that the density of the kiln is too high, which makes the gas flow unsmooth; the second is that the firing system is unreasonable and the oxidizing atmosphere in the kiln is insufficient. For example, when the glaze is melted, the temperature rises too fast and there is a relatively thick reducing flue gas in the kiln or a backflow of flue gas is formed at the junction of the firing zone and the quenching section.
Orange glaze
Orange glaze means that the glaze is orange peel-like and has poor luster. The reasons for the occurrence of orange glaze defects in the firing process are as follows: first, the temperature rises too fast or the local temperature is too high when the glaze is melted, which exceeds the maturity temperature of the glaze; second, it is caused by insufficient oxidative atmosphere in the kiln. In addition, improper glaze formulation, poor combination of glaze and glaze; high temperature viscosity of glaze, poor flowability; excessive moisture content of blanks entering the kiln, and thick glaze layer may also produce orange glaze.
Glaze bubble
We believe that the most fundamental reason for the generation of glaze bubbles is that the gas generated during the firing process of the green body cannot escape in time, accumulate with each other, and expand around.
Therefore, the most fundamental method to solve the defects of glaze bubbles: one is to reduce the generation of gas during the firing process of the blank, especially after the liquid phase of the blank appears in large quantities; the other is to make the generated gas escape quickly.
Raw
Raw burning refers to the dull color of the product. The reason is that the sintering temperature is too low. The solution is to strictly control the best or over-densified blanks, and the water absorption rate of this type of product is very high. High sintering temperature, appropriate adjustment of the loading density.