The application prospects of ceramic fibers in high-temperature kilns are expanding. The high temperature of refractory felts and blankets made of ceramic fibers can reach 1430 °C. It has the characteristics of good heat insulation effect, easy use and small heat storage, and is widely used in various kilns, which greatly shows high energy saving efficiency.
1. Variety and performance
The more important indicators of ceramic refractory fibers are the diameter and thermal stability of the fibers. Commonly used in the ceramic industry are Al2O3 and SiO2 fibers, which are divided into different application ranges according to the content of Al2O3, and Cr2O3 materials are also introduced into them to improve their refractory and anti-oxidation properties. Generally, fiber products with high alumina content and low content of iron oxide and other impurities are pure white, and the fibers introduced with chromium oxide are in the color of custard yellow. The average diameter of the ceramic fibers is 22-33 microns. Those with fine fibers, low density and low thermal conductivity have higher operating temperatures. If the fiber is thick and the density is high, the effect is not ideal. The thermal stability index of the fiber is more important. The linear shrinkage range of various products of Al2O3-SiO2 fiber at 1260℃ is between 35-88%. The amount of shrinkage also directly affects thermal stability.
Due to the low thermal conductivity, low density and light weight of fibers, lighter steel frame support structures are used in the design and construction of kilns, so that the development of ceramic kilns has entered the era of “lightweight kilns”. The fiber has small heat storage and is suitable for rapid heating and cooling firing methods. The fibers are flexible and can be processed into products with grooves or openings, and have good resistance to mechanical vibration and impact, as well as good chemical stability. development plays an important role in promoting.
At present, ceramic fiber products include: felt, blanket, block, bulk fiber, fiber paper and various products of vacuum forming.
Loose fibers can be classified into two types: those with or without lubricants; those with long and short fibers mixed together, etc. Several fibers can also be used in blends. Uncleaned fibers are less expensive and can be used as fillers for filling joints. The fiber products added with lubricant are easy to operate and construct, and the dust is small. Although the dust scattered into the air when installing the fiber is not very toxic, it will cause itching of the skin or stinging of the throat, so pay attention to protection during construction.
2. Masonry methods and precautions
Refractory fiber felt, suitable for furnace lining, can greatly improve energy-saving efficiency. Typically, organic binders are used to roll fibers into tubular or sheet-like fabrics. After the inner wall of the kiln is built with high-temperature and light-weight refractory bricks, it can be pasted with ceramic fiber refractory felt to form an inner lining. After firing, the fiber felt or plate becomes relatively rigid and has satisfactory recovery ability, and can bounce back when cooled. Tighten the seams.
There are usually two methods for masonry fibers: one is to apply the blanket layer by layer, and then riveted with bolts. Generally, temperature-resistant metal bolts are used below 1222 °C, and ceramic riveting parts are used above 1223 °C. Fill with loose fiber and heat-resistant cement at one end near the hot surface. The use of ceramic rivets also prevents fiber deterioration caused by carbon deposition. The second method is to use prefabricated assemblies, that is, preforms that are stacked with felts or 305mm wide felts folded into accordion-style preforms. Compared with the two, the latter has higher energy-saving efficiency but higher cost due to the same material from the furnace shell to the hot surface.
When the temperature rises, the joints formed by the masonry of the fiber prefabs need to be inlaid with elastic fibers. Installation with prefabricated assemblies is easy, quick and easy to maintain, requiring replacement of damaged parts.
In terms of thermal efficiency, layer-by-layer application is significantly better than prefabricated assemblies. Because the fiber direction of the former is perpendicular to the heat flow, and the fiber direction of the stacked prefabricated assembly is parallel to the heat flow, the difference in thermal conductivity between the two is about 20-40%. For example, the accordion-shaped prefabricated assembly is between the two. , its fiber orientation is both parallel and perpendicular to the heat flow.
3. Development Prospects
As energy prices continue to rise, fuel costs will become a bottleneck restricting the development of the ceramic industry, and energy conservation is becoming more and more important. People are more and more concerned about the heat loss of the kiln, and some directly paste a layer of refractory ceramic fiber on the surface of the original refractory lining to improve the thermal efficiency. The obvious cracks or peeling parts on the kiln wall must be repaired before sticking. However, insulating refractory bricks and refractory fibers cannot be abused arbitrarily. So far, the linings of alkaline oxygen-blown steel furnaces, cement rotary kilns, etc. cannot be temporarily lined with fibers due to severe chemical erosion at high temperatures.
For continuous heating equipment such as ceramic tunnel kilns, refractory ceramic fibers have long been used as the lining of continuous heating equipment. According to relevant data reports, the use of refractory ceramic fibers in rapid push-plate kilns and tunnel kilns has significant energy-saving effects. Especially in ultra-high temperature heating, such as kilns with a firing temperature of 1538℃-1649℃, the energy saving effect of using refractory fibers is better.