1. Cracking:
Cracking refers to cracks of different sizes on the product. The reason is that the moisture of the billet into the kiln is too high (more than 2%), and the preheating and cooling are too fast, resulting in uneven internal and external shrinkage of the product. In some cases, the body has suffered internal injuries before loading. Uneven body thickness, accessories (such as pot handle, nozzle, etc.) too much weight or poor bonding will also cause product cracking.
The way to prevent is: (1) the kiln body must be dry; (2) When the kiln is installed, the operation of the set is cautious, and the formula of the gasket and the blank body is consistent. Fitting size, weight and bonding position are appropriate. Some add 10-15% of the glaze in the bonding mud, which can make the nozzle and the main body firmly fused together, so as to overcome the cracking defect.
2. Foaming:
There are two kinds of “blank bubble” and “glaze bubble”. Billet bubbles are divided into “oxidation bubble” and “reduction bubble” two kinds. Oxidized bubble refers to the billet bubble covered with glaze layer, the cross section is gray black, mostly formed in the low-temperature part of the kiln. The main reason is that the decomposition in the porcelain and glaze is not fully oxidized, and the lost goods are not completely eliminated. The preheating is fast, the time of oxidation decomposition is short, the temperature in the kiln is too low at the end of oxidation, and the temperature difference between upper and lower is too large. In the blank glaze, carbonate. Sulfates and organic impurities are the main cause of foaming products. In addition, the reasons for improper density of fashion kilns and high moisture into kilns should also be noted. Reduction bubble is also known as the fire bubble, broken and yellow, mostly in high temperature near the fire outlet products. It is mainly caused by insufficient reduction of sulfate and high price iron in billet, insufficient strong reduction atmosphere and high sintering temperature. The deposited carbon and decomposition of the glaze bubble are not burned and volatilized before the glaze melts, and the gas is blocked in the glaze layer to form. It can be solved if the glaze melting time is prolonged or flat burning is appropriate.
3. Pinhole:
Refers to the appearance of small dents or holes in the glaze of the product. The formation of such defects is the organic matter in the billet. The content of carbon and iron oxide is high, and when the temperature rises fast, the lost goods cannot be completely burned and volatilized, and only escape from the glaze in the late high temperature stage, forming a micro-volcanic pinhole. In addition, the reduction atmosphere of the high temperature furnace is too weak, and the product at the nozzle is oxidized again, which will also cause pinholes. In addition, pinhole defects can also occur when the glaze fluidity is poor or the glaze is too thin.
4, orange glaze:
Products glazed uneven, orange peel. It generally occurs in plates, dishes or porcelain tile products. The main reason is that the temperature rises too fast when the glaze waves, and the sintering temperature is too high, which causes the glaze to boil. In addition, the glaze thickness is uneven, the high temperature fluidity is poor and the glaze grinding is not fine, etc., are the crux of the formation of orange glaze defects.
5. Shock glaze:
The glaze of the product has hair-thick cracks. The main reason is that the expansion coefficient of billet and glaze is relatively different. This requires readjustment of the blank. Glaze ingredients recipe. In addition, the firing temperature is too high, the cooling system is unreasonable or the glaze layer is too thick will also form the glaze defect.
Post time: Jul-07-2023