The influence of impurity iron on the glass melting furnace is as follows:
(1) The impurity iron causes the melting temperature to rise
In the glass melting process, the material absorbs heat from the flame, and the flame transfers the heat to the material by radiation. When the temperature of the melting pool is 1500~1600℃, the radiative heat transfer of the flame and the dome has a maximum value at about 1500nm; in addition, the absorption value of Fe2+ in the soda lime glass is the maximum at 1050nm. Because two can understand that the temperature distribution of the glass deep in the melting pool caused by the radiant heat transfer in the kiln is directly related to the iron content in the glass. According to related measurements, the temperature difference between the surface of the furnace glass and the bottom of the furnace glass is 35℃, and the temperature difference of Fe2O3 reaches 0.51% of the molten glass, and the temperature difference can reach 380℃. It is precisely because of the presence of Fe2O3 and FeO that the temperature difference between the surface and the deep layer of the glass in the kiln is enlarged, which will affect the melting and clarification of the glass liquid. This is due to the strong absorption of heat radiation by iron oxides. caused. Most of the radiant heat is absorbed by the surface glass liquid, forming a temperature difference between the upper and lower melts. If the glass material at the bottom of the glass furnace is melted, the temperature in the entire furnace must be increased. Tests have proved that within the normal melting temperature range, the erosion rate of refractory materials doubles for every 50°C increase in temperature. This not only consumes energy, shortens the service life of the kiln, but also causes uneven temperature in all parts of the glass. It is also easy to cause defects such as ribs on the surface of the glass plate.
(2) Impurity iron causes corrosion of the melting furnace
In recent years, with the development of glass melting technology, the melting capacity per unit area of ??modern glass melting furnaces has been greatly increased. Most of the bottom of the pool adopts a multi-layer structure with good insulation, which greatly reduces heat loss and increases the temperature of the bottom of the pool by 200 ℃. From left to right, the viscosity of the glass liquid is reduced and the flow is intensified, which intensifies the erosion and erosion of the bottom of the pool. Not only that, the molten glass can easily penetrate into the cracks of the poorly sealed bricks, and generate bubbles when interacting with the refractory materials, forming a three-phase interface condition, and causing upward erosion.
The impurity iron brought in with the batch material and broken glass during feeding will cause more serious erosion; especially at the brick joints, the impurity iron will invade the brick joints or pores and generate bubbles, which will erode the bottom of the pool out of the hole, and the glass liquid will affect the fire resistance. The upward undercut on the material contact surface is similar. The erosion of the bottom of the modern glass melting furnace comes from two aspects: first, the direct erosion of the parts contacting the molten glass; second, the erosion of the lower sealing layer (lining), which damages the bottom tiles.
The entire erosion process is divided into four stages: glass liquid or impurities penetrate through the cracks of the bricks; the sealing layer begins to be damaged; the foamed glass liquid penetrates between the paving tiles and the lining at the bottom of the pool; "upward drilling erosion" occurs, causing the pool bottom to be laid. The tiles are damaged.
Therefore, the iron oxides in the glass raw materials are controlled to the lowest allowable limit. Especially for the large amount of silica sand, the iron oxide content is required to be less than 0.2%.
