When refractory materials are used in glass kilns, they will be severely damaged due to high temperature, flame, powder, atmosphere, air flow and liquid flow, which greatly affects the service life of the kiln. The use of refractory materials in kilns begins from the time of kiln baking. Improper operation will also cause great or even serious damage to refractory materials, so special attention should be paid. Here are some damage situations.
PART.01 Corrosion of refractory materials in glass kilns
Inside the glass kiln, powder, glass liquid and flame gas all pose severe challenges to refractory materials.
First, let's explore the erosion mechanism of powder on refractory materials. Powder releases alkaline vapor in a high temperature environment, which is extremely corrosive to refractory materials. Taking silica bricks as an example, their surface may become uneven due to melting, and even gaps called "rat holes" may appear inside. What is more complicated is that the ultrafine powder will accumulate in the lattice body of the regenerator, forming "tumors" that hinder the airflow. In severe cases, it will block the lattice holes, leading to the collapse and damage of the lattice bricks. It is worth noting that this erosion effect intensifies with the increase of temperature. Generally, the service life of the refractory material may be shortened by about one year for every 50-60℃ increase in the melting temperature. In many key parts of the kiln, such as the front wall, the charging port, and the front of the melting part, they are all threatened by this material powder erosion.
Although the glass liquid is relatively less corrosive to the refractory material, its chemical reaction at the interface with the refractory material is extremely complex. The glass liquid will first dissolve the free SiO2 in the refractory material, followed by mullite and other components. This dissolution process will form a multi-layer structure between the refractory material and the glass liquid, including a mullite layer, a β-Al2O3 layer, etc. As the refractory material dissolves, the viscosity of the glass liquid will increase, and then a protective and difficult-to-move layer will be formed on the surface of the refractory material, which to a certain extent slows down further erosion. However, glass liquid with low viscosity and low surface tension may still penetrate into the interior of the refractory material and cause more serious damage. In particular, high-alkali glass and borosilicate glass, due to their special physical properties, have a more significant erosion effect on refractory materials.
In addition, the corrosive components in the flame gas, such as SO2, V2O5, etc., cannot be ignored. These gases mainly come from the combustion products of coal gas and heavy oil, which will corrode the refractory materials in the flame space, small furnace and regenerator. At the same time, chemical reactions may occur between different furnace materials under high temperature, further aggravating the damage of refractory materials. For example, clay bricks and silica bricks will react violently at high temperatures, resulting in a decrease in material performance.
In the regenerator, the lattice body also faces specific challenges of redox atmosphere. Since the variable valence ions will undergo volume changes in the oxidized and reduced states, this may lead to reduced strength or even cracking of the product, further affecting the service life of the refractory material and the overall performance of the kiln.
PART.02 Burning of refractory materials in glass kilns
Under the long-term action of high-temperature environments, refractory materials in glass kilns are susceptible to melting (also known as burning flow) or softening and deformation, which in turn causes damage. When a certain area in the kiln is locally overheated, or the refractoriness of the refractory materials used does not meet the requirements, the refractory materials will be burned. In addition, even if the refractoriness of the refractory meets the standards, if its load softening temperature is low, the material may still soften and deform during long-term use. This situation will have an adverse effect on the stability of the entire masonry and shorten its service life.
The severity of the burn is closely related to the temperature and the properties of the refractory materials. Specifically, the ignition port arch, small furnace legs, tongue, heat storage chamber arch, melting section kiln arch and breast wall of the small furnace are more susceptible to burns because they are in high-temperature areas or subject to large thermal stresses. In order to ensure the safe and stable operation of the kiln, it is crucial to select refractory materials with appropriate refractoriness and load softening temperature. At the same time, reasonable temperature control and maintenance measures are equally important to slow down the damage rate of refractory materials and extend their service life.
PART.03 Cracks of refractory materials in glass kilns
The cracks of refractory materials in glass kilns mainly occur during the kiln baking stage. During the kiln baking process, a temperature gradient will form inside the refractory bricks, resulting in thermal stress. If the heating rate is too fast and exceeds the ultimate strength that the refractory can withstand, it will cause cracks and even cause the refractory to break. In particular, dense refractory materials that are fused and highly sintered are more susceptible to damage due to their tight internal structure and relatively weak resistance to thermal stress.
In addition to the thermal stress caused by the temperature gradient, the crystal transformation of refractory materials during the heating process will also cause volume changes, thereby generating additional stress. When the heating rate is too fast, the crystal transformation proceeds rapidly, and the volume changes dramatically, resulting in excessive stress, which may eventually cause the refractory to crack. Therefore, during the kiln baking process, it is necessary to strictly follow the pre-established heating curve to ensure a smooth and controllable heating process.
After the kiln is baked, the refractory material will be in a high-temperature working environment for a long time. At this temperature, the mechanical strength of the refractory material will be significantly reduced, far lower than the strength value at room temperature. If the mechanical load on the refractory material is too large at this time, it will cause it to undergo inelastic deformation, similar to the flow behavior of a high-viscosity liquid, which may eventually lead to the destruction of the refractory material. Therefore, in a high-temperature working environment, it is necessary to strictly control the mechanical load acting on the refractory material to ensure its safe and stable operation.
PART.04 Wear of refractory materials in glass kilns
The wear problem faced by refractory materials in glass kilns cannot be ignored. When the glass liquid flows along the surface of the refractory material, its continuous friction and impact will gradually erode the material. This phenomenon is called mechanical wear. Especially in the area where the glass liquid surface contacts the refractory material, the wear is particularly significant. In addition, in areas where the glass liquid circulates, especially in places where the liquid flow state is more turbulent, the wear marks are also clearly visible.
It is worth noting that when the glass liquid surface fluctuates or the liquid flow state changes, such as under the influence of factors such as temperature fluctuations, the wear will be further aggravated. This is because unstable liquid flow will increase the impact force and friction frequency on refractory materials, thereby accelerating the loss of materials.
Therefore, in order to extend the service life of refractory materials, we need to pay close attention to the working conditions in the glass kiln, strive to maintain the stability of the glass liquid flow, and reduce unnecessary fluctuations and turbulence. At the same time, the selection of refractory materials with better wear resistance is also an effective way to reduce wear. Through comprehensive measures, we can effectively reduce the wear of refractory materials and improve the operating efficiency and safety of glass kilns.
The damage of refractory materials in glass kilns is a complex issue involving multiple factors. As an "old glass man", I suggest that when selecting and using refractory materials, we should fully consider the influence of its performance, structure and environmental factors to ensure the stable operation of the kiln and the improvement of glass quality. At the same time, regular inspection and maintenance of the kiln is also an indispensable link. Only in this way can we better extend the service life of the kiln and improve the efficiency of glass production.
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