Frit production and process control
1. firing Frits, powders mixtures upon heating results in the following changes: the first is evaporation of the water contained in the raw materials and then released the crystal water, such as borax, raising the temperature even emit chemical water, such as boric acid. Decomposed material into oxides. As the temperature continues to rise, low melt substance in powder begins to melt, molten material is due to state specifically to those melting effect, showing raw powder sintering phenomena, those solid materials and that caused softened or melted material glued together and gradually melting. Temperatures continue to rise, alkaline and acidic oxides interact to form silicic acid. Not only to build a simple Portland, also in many frit "eutectic" form. "A total melt" is made up of certain mixtures than its melting point consists of two monomers has a much lower melting point. As the melting point of pure feldspar is 1280 when mixed with the CaO 9:1, the melting point only 1210 c. Refractory CaO and SiO2 combined calcium silicate, calcium silicate, is a fusible material, it is similar to the melting of feldspar. Other basic oxides also produce corresponding changes in the process, such as: K2O, and Na2O, and MgO, and ZnO. Portland formation is more complex, or solidifying the existence in the molten mass which Portland, depends mainly on frit composition, because it is not a separate role of a substance, but a mixture of on overall performance, their composition is only represented by various oxides in proportion with each other. Oxidation and decomposition and combination described above are conducted during the heating process, so good as fully as possible in the oxidation process, combining stages a variety of Portland formed the perfect the better, so that you can get good quality frit. But in the actual production of frit in quality, often with frit furnace structure, fuel type, temperature, atmosphere and method of operation of flame has a close relationship, structure of the frit, frit furnace of the above forms have some weaknesses. Conical Crucible Furnace, powder from the upper joining, melt flow from the lower part, preheating, oxidation, melt compounding is ideal, but often because of the bad quality, the temperature does not meet requirements, melting is not complete, appears caught frit raw impact quality. Again plus Crucible using life short, to production brings must of difficult; back converter due to is intermittent job, from feeding to melting good, natural on formed has by low temperature to high temperature of process, on oxidation decomposition, melting is favourable of, but due to melting time long, low melt material of volatile is inevitable of, addition energy consumption high, feeding Shi dust also bad overcome; pool shaped furnace application more general, due to it of volume small, powder material melting too fierce on oxidation decomposition adverse. Some powder in molten state, it had not been reached with the melt flow, caused by incomplete melting, the furnace outside of high energy consumption, low of volatile soluble substance is more serious, the volatile as the gas flue block, bring some difficulties to the overhaul.
2. melt temperature temperature directly related to glaze the viscosity, starts melting temperature and the glaze firing range. Due to the Frits furnace for small volume, large temperature fluctuations, likely to cause instability in the molten mass, thus melting temperature control block cannot be ignored. Different of melt block composition has different of melting temperature, General fluctuations in 1250~1350℃ Zhijian, temperature of determine main according to glaze surface quality, regardless of application what kiln furnace glaze burn, are hope with firing range wide of glaze material, to adapted kiln furnace Shang, and Xia temperature and firing process in the of temperature fluctuations, especially muffle type tunnel kiln is relies on muffle Board of heat transfer to firing of, its Shang, and Xia temperature on up to as high as mesophile temperature, firing range narrow of glaze material is not adapted of, so glaze burn range should is greater than 60 ℃. Frit relationship between the melting temperature and the viscosity of the glaze very close when Frits melting temperature of 1420 when the glaze flow length of 43mm, when the temperature dropped below the 1320 c, flow length 67mm. This proves that: high temperature, high viscosity, low temperature, low viscosity. As Frits melting temperature, starts melting along with changes in temperature when melting temperature 1260 ° c, melting temperature of 915. When the temperature is increased to 1280 c, began melting temperature is 945. Viscosity of glaze and glaze firing range has narrowed. Glazed appearance, pinhole-free, corrugated and other defects. Viscosity high temperature glaze frit, analyzed the main reasons: low melting substances changed caused by melting blocks excessive volatile. Based on this characteristic, raise or lower the melting temperature to change the viscosity of the glaze. Glaze firing range is less suitable furnace upper and lower when the temperature difference, may be appropriate to reduce the melting temperature, need to enhance glaze began melting temperature, improve the melt temperature can be achieved. Certainly not unprincipled to increase or reduce the temperature, to ensure quality of frit as a precondition. To ensure the quality of frit, operations must be done on time, quantitative feeding by the time tests and record the temperature. Flame atmosphere also has some influence on clinker quality and should be used in oxidizing atmosphere sintering, instead of the reduction flame burning in the furnace, Ikenouchi positive pressure should not be too large, preventing metal oxide reduction affects quality.