The application prospects of ceramic fibers in high-temperature firing kilns are expanding day by day. The refractory felt and blanket products made of ceramic fibers can reach a higher temperature of 1430 ° C. It is widely used in various kilns with the characteristics of good thermal insulation effect, easy use and small heat storage, which greatly shows high energy-saving efficiency.

Variety and performance

The most important indicators of ceramic refractory fibers are the diameter and thermal stability of the fibers. Al2O3 and SiO2 fibers are commonly used in the ceramic industry. They are divided into different application ranges according to the content of Al2O3. Cr2O3 materials are also introduced into them to improve their refractory and oxidation resistance properties. Generally, fiber products with high alumina content and low impurity content such as iron oxide are pure white, and fibers with introduced chromium oxide are pinned and creamy. The average diameter of ceramic fibers is 22-33 microns. Those with fine fibers, low density and low thermal conductivity have high operating temperatures. If the fibers are thick and dense, the use 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 ° C is between 35-88%. The amount of shrinkage also directly affects the 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". Fibers have small heat storage and are suitable for rapid heating and cooling and firing. Fibers are flexible and can be processed into products with grooves or openings, and have good resistance to mechanical vibration and shock, and have good chemical stability. These advantages are important for the development of new kilns and affect the development of ceramic technology and industry.

At present, ceramic fiber products include: felts, blankets, blocks, bulk fibers, fiber paper and vacuum-formed products. The working range is generally 871-1430 ° C. In special cases, it can be used at high temperatures above the limit temperature for a short period of time.

There are two types of loose fibers: those with or without lubricant; those with long and short fibers mixed together, etc. Several fibers can also be mixed and used. Uncleared fibers are cheaper and can be used to fill fillers at joints. Fiber products with lubricant are easy to operate and construct, and the dust is small. Although the dust scattered into the air when installing fibers is not very toxic, it will cause itchy skin or stinging throat, so pay attention to protection during construction.

Masonry methods and precautions

Refractory fiber felt, suitable for kiln lining, can greatly improve energy saving efficiency. Generally, organic binders are used to make fiber rolls into cylindrical or sheet-shaped fabrics. After the inner wall of the kiln is built with high-temperature lightweight refractory bricks, it can be pasted into the lining with ceramic fiber refractory felt. After firing, the fiber felt or board forms a relative rigidity and has a satisfactory recovery ability. When cooled, it can spring back to tighten the seams.

There are usually two methods for masonry fibers: one is to apply the felt blanket layer by layer, and then rivet it with bolt rods. Generally, temperature-resistant metal bolt rods are used below 1222 ° C, and ceramic riveting parts are used above 1223 ° C. One end of the hot surface is filled with loose fibers and heat-resistant cement. The use of ceramic riveting parts can also prevent fiber deterioration caused by carbon deposition. The second method is to use prefabricated components, that is, prefabricated parts stacked with felt blankets or folded into accordion-style prefabricated parts with a 305mm wide felt blanket. Compared with the two, the latter has higher energy saving efficiency and higher cost because it is the same material from the furnace shell to the hot surface.

When the temperature rises, the joints formed by the masonry of the fiber preform need to be inlaid with stretchable fibers. The prefabricated assembly is easy to install, fast and easy to maintain, and the damaged part needs to be replaced.

In terms of thermal efficiency, the layer-by-layer application method is significantly better than the prefabricated assembly. 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 heat conduction between the two is about 20-40%. For example, the accordion-folded prefabricated assembly is in between, and its fiber direction is both parallel and perpendicular to the heat flow.

Development Prospects

Due to the rising energy prices, fuel costs will become a bottleneck in the development of the ceramic industry, and energy saving will become more and more important. People are more and more concerned about the heat loss of kilns, and some directly add a layer of refractory ceramic fibers to the surface of the original refractory lining to improve thermal efficiency. Before adding, the obvious cracks or peeling parts on the kiln wall must be repaired. However, heat-insulating refractory bricks and refractory fibers cannot be abused arbitrarily. So far, linings such as alkaline oxygen-blowing steel furnaces and cement rotary kilns cannot be used as linings for the time being due to serious high-temperature chemical erosion.

For continuous heating equipment such as ceramic tunnel kilns, the use of refractory ceramic fibers as the lining of continuous heating equipment has long been realized. According to relevant data reports, the energy saving effect of refractory ceramic fibers in fast push plate kilns and tunnel kilns is very significant. Especially for ultra-high temperature heating, such as kilns with firing temperature of 1538 ℃ -1649 ℃, the energy saving effect of using refractory fibers is better.