10 common problems with burning defects of ceramic tableware

Why do ceramic tableware often have defects in the firing process? Today, the editor of the ceramic tableware manufacturer summarized the common defects of the top 10 ceramic firing processes for you, allowing you to seek advantages and avoid disadvantages, and minimize the number of firing defective chinaware ceramic. 1. Deformation: The firing deformation of the product is the most common and serious defect in the ceramic industry, such as distorted and out-of-round caliber, and irregular changes in geometry. The main reason is improper method of kiln installation. If the saggar column is not correct, the bottom of the saggar or the gasket is not flat, the kiln car will vibrate, which will affect the deformation of the product. In addition, when the product is sintered, when the green body is preheated and the temperature rises quickly, the temperature difference is large and it is easy to deform. The firing temperature is too high or the holding time is too long will also cause a large number of deformation defects. The poor high-temperature strength of the sagger used or the uneven paint will also cause the deformation of the fired product. 2. Cracking: Cracking refers to cracks of different sizes on the product. The reason is that the water content of the green body into the kiln is too high (more than 2%), and the preheating and cooling are too fast, resulting in uneven shrinkage of the product inside and outside. In some cases, the green body has been collided with internal injuries before loading the bowl. Uneven thickness of the blank, excessive weight of accessories (such as pot handles, spouts, etc.) or poor bonding can also cause the product to crack. The preventive measures are: (1) The water content of the kiln body is less than 2%, and the vehicle speed should be appropriately reduced in cooling capacity. (2) Be cautious when installing the kiln, and the gasket and the green body have the same formula. Fitting size, weight and bonding position are appropriate. Some add 10-15% of the glaze to the bonding slurry, which can make the nozzle and the main body firmly welded together, so that cracking defects can be overcome. 3. Foaming: There are two types of foaming for fired products: green foam and glaze foam. There are two types of green bubbles: oxidized bubbles and reduced bubbles. Oxidized bubble refers to the glaze layer on the outside of the blank bubble, the section is gray-black, and is mostly formed in the low temperature part of the kiln. The main reason is that the decomposition products in the porcelain body and the glaze are not fully oxidized, and the burning loss is not completely eliminated. The preheating temperature rises quickly, the oxidation decomposition stage time is short, the temperature in the kiln is too low at the end of the oxidation, and the temperature difference between the upper and lower sides is too large. In the blank glaze, carbonate. Sulfate and more organic impurities are the main causes of product foaming. In addition, attention should be paid to reasons such as improper density of fashion cars and high moisture entering the kiln. The reduction bubble is also called the overfire bubble, which breaks and turns yellow, and it mostly occurs in the products near the vent of high temperature. It is mainly caused by insufficient reduction of sulfate and high-valent iron in the body, insufficient strong reducing atmosphere and excessively high firing temperature. The deposited charcoal and decomposition products of the glaze bubble system cannot be burnt and volatilized before the glaze is melted, and the gas is prevented from forming in the glaze layer. It can be solved if the glaze melting time is prolonged or the flat firing is appropriate. 4. Yin yellow: the surface of the product becomes yellow or spotted yellow, and some sections also have yellowing phenomenon, which mostly occurs at high fire positions. The main reason is that the temperature rises too fast, the glaze melts too early, and the reducing atmosphere is insufficient, so that the fe2o3 in the porcelain body cannot be reduced to feo. In addition, if the pot column is too low, the product temperature on the top of the kiln is too high and the reduction is insufficient. Too high content of tio2 in the product raw materials will also cause the product to turn yellow. If a small amount of coo is added to the blank, the yellow color of the product can be covered. 5. Smoke: Smoke will occur no matter what kind of fuel is used. Smoke refers to the appearance of gray or impure white on the surface of the product. Mainly due to incomplete oxidation or premature reduction of the green body, the carbon, organic matter or low-temperature carbon in the green body cannot be burnt before the glaze layer is sealed. Sometimes the backflow of smoke will erode the glaze. If the calcium content in the glaze is too high, it is easy to form smoke defects. 6. Pinhole: Refers to tiny dents or small holes on the glaze of the product. One such defect is the organic matter in the blank. The content of carbon and iron oxide is relatively high. When the temperature rises quickly, the burning loss cannot be completely burnt out and volatilized, and it will not escape the glaze until the later high temperature stage, forming pinholes like microscopic volcanoes. In addition, the reducing atmosphere of the high-temperature furnace is too weak, and the product at the vent is oxidized again, which will also cause pinholes. Furthermore, pinhole defects can also occur when the glaze has poor fluidity or the glaze is too thin. 7. Orange glaze: The glaze of the product is uneven and has an orange peel shape. Generally occurs in plates, dishes or porcelain white porcelin dinnerware tile products. The main reason is that the heating of the glaze is too fast during waveization, and the sintering temperature is too high to cause the glaze to boil. In addition, uneven thickness of the glaze slurry, poor high-temperature fluidity, and poorly ground glaze are the crux of the formation of orange glaze defects. 8. Shocking glaze: There are thick hairline cracks on the glaze of the product. The main reason is that the expansion coefficient of the blank and the glaze are quite different. This requires re-adjustment of the billet. Glaze ingredients recipe. In addition, the firing temperature is too high, the cooling system is unreasonable, or the glaze layer is too thick can also cause glaze defects. 9. Burning and overburning: the appearance of burnt products is yellow, the water absorption rate is high, the glaze is poor and rough, the intensity is low, and the sound is turbid when hit. When over-firing, the product deforms and the glaze blisters or flows. The main reason is that the firing temperature is too high or low, the high temperature holding time is not properly controlled, the loading density is unreasonable, or the firing temperature difference is large, etc., which may cause local overburning or raw burning. 10. Matte: also known as Xiaoyan. The reason for the glaze matt is the formation of fine bodies on the glaze surface and poor fusion of the glaze layer, so the glaze matt defect is formed. Quick cooling can be adopted at the initial stage of cooling to prevent chromatographic crystals on the glaze surface. Improve glaze gloss.

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