Product firing deformation is the most common and most serious defect in the ceramic industry, such as aperture distortion, irregular geometric shape change. The main reason is improper kiln loading method. If the saggar column is not straight, the saggar bottom or the gasket is uneven, the kiln car will be shaken and the deformation of the product will be affected. In addition, the product is prone to deformation when the preheating and heating of the blank body are fast in the firing process. Too high firing temperature or too long holding time will also cause a large number of deformation defects. The poor strength of the saggar used at high temperature, or the uneven coating will also cause the deformation of the burned product.
2, Yin yellow:
The surface of the product is yellow or spotty yellow, and some sections also have yellow phenomenon, which mostly appears in high fire position. The main reason is that the temperature rises too fast, the glaze melts too early, the reduction atmosphere is insufficient, and the Fe2O3 in the porcelain can not be reduced to FeO. In addition, the loading column is too low, the local product temperature of the kiln top is high and the reduction is insufficient, which will also form Yin and yellow defects. The TiO2 content in the raw material of the product is too high, it will also lead to the yellow of the product, if the trace CoO is added to the blank, the yellow of the product can be covered.
Smoke will occur regardless of the fuel used. Smoky refers to the product surface is gray or non-pure white. Due to incomplete oxidation or premature reduction of the body, the carbon, organic matter or low temperature carbon in the body failed to burn up before the glaze layer was closed. Sometimes the backflow of smoke can corrode the glaze. If the calcium content in the glaze is high, it is easy to form smoke defects.
4. Raw and overcooked:
The appearance of raw cooked products is yellow, the water absorption rate is high, the glaze is poor and rough, the strength is low, and the sound is cloudy when beating. The product deforms when it is overburned, and the glaze bubbles or flows. The main reasons are high or low firing temperature, improper control of high temperature holding time, unreasonable loading density or large firing temperature difference, resulting in local overburning or raw burning.
5, no light:
Also known as Xiaoyan. The cause of the dull glaze is the formation of fine glaze and poor melting of glaze layer, so the dull glaze defect is formed. Rapid cooling can be taken during the initial cooling period to prevent the glaze from being stratified. Improves glaze gloss.
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