Kiln furniture provides the basis for uniform firing and therefore optimal product quality. Which includes: extruded batts, setter plates, push plates, square beams, supports, pillars, rollers, kiln car system, kiln roof and kiln wall system, saggers, crucibles, and other related refractory products,
Modern production technology enables us to manufacture thin-walled, lightweight, and high-temperature resistant kiln furniture, which depends on its design and the selected materials.
The most common raw materials of kiln furniture include cordierite, mullite, corundum, and silicon carbide. Because the color of silicon carbide is easier to distinguish, but the first three materials, you may certainly be easily confused.
1， the English name
2， The content of Alumina(Al2O3)
The three refractory materials have different alumina contents; the order is corundum> mullite> cordierite.
The thermal properties order is also corundum> mullite> cordierite.
However, depending on the alumina content of the three, their withstand temperatures will also vary. (The higher the alumina content, the higher the withstand temperature)
3， Comparative Analysis
4, How to choose kiln furniture with the correct material?
A more critical point is whether the client’s use conditions are consistent or follow the established standard operating procedure.
For example: heating curve, holding time, cooling curve, load per unit area, stacking method, and chemical composition of burnt material. These factors will affect the working time of the kiln furniture as well.
So, based on the working conditions, we can choose kiln furniture with different materials.
1)Cordierite-Mullite
The thermal expansion coefficients of cordierite and mullite in cordierite-mullite slabs at room temperature to 1000℃ are 1.1×10-6℃-1 and 5.3×10-6℃-1 respectively. It can be seen that the expansion coefficients of the two materials are quite different. The composite preparation of the two materials forms microcracks at the interface of the two phases, which can effectively reduce the thermal stress caused by rapid temperature changes, thereby improving thermal shock stability.
In principle, if the required temperature is less than 1300℃, cordierite and mullite products can meet most of the needs. Like, as the ceramic industry, powder calcination, powdered metal, crystallized glass panel, heavy clay, food processing industries, etc.
2)Corundum-Mullite
With the development of high-temperature functional ceramics such as soft magnetic materials and electronic insulating ceramics, the application of traditional cordierite-mullite slabs has been limited to a certain extent.
However, the ratio of mullite or even corundum raw materials will increase relatively, because of their excellent high-temperature strength, thermal shock resistance, high operating temperature (1700°C), and good chemical stability.
Pure corundum products have high load softening temperatures and good creep resistance, but due to the large thermal expansion coefficient, the thermal shock resistance is not ideal. The thermal expansion coefficient of mullite is significantly lower than that of corundum, and it can be used as the sub-crystalline phase or bonded phase of products.
The combination of mullite and corundum combines the properties of the two materials, making its thermal shock resistance relatively high. Compared with pure corundum, it is greatly improved. It is used in push plate kilns for firing high-temperature ceramic materials, and its service life is up to more than 100 times.
Anyway, if the ratio of mullite or even corundum raw materials increases relatively, naturally the product price cost will also rise accordingly.
3)Corundum
Corundum ceramics have become widespread due to such physical and mechanical properties as high strength, hardness, wear resistance, refractory resistance, thermal conductivity, chemical resistance, and high electrical strength.
Corundum setter refers to high-end kiln furniture with α-Al2O3 as the main crystal phase. It has excellent properties such as high strength, corrosion resistance, high-temperature resistance, and wear resistance. It has small deformation at high temperatures (＞1650℃), but the sintering temperature is high and the thermal shock stability is poor. During the firing process of lead zirconate titanate piezoelectric ceramics, the corundum setter faces central warping, surface-layered powdering, and peeling.
Corundum saggers are mainly used for calcining some high-purity powders in an environment with low thermal shock conditions and high operating temperatures. For example, for calcining high-purity alumina powders, the saggers need to be sintered at 1800°C. They are produced using alumina active powder with an Al2O3 content of 99.9wt% and low-sodium white corundum. The binder uses low ash (Ash≤0.01wt%) to ensure effective control of impurities in the entire raw material control and achieve a low thermal expansion coefficient after sufficient high-temperature sintering.
5, Conclusion
With the development of industry, the types of products being fired have increased, and the application areas of kiln furniture are expanding. It is not only used in the ceramic industry but also in fine chemicals, lithium-ion batteries, and other industries.
According to the performance characteristics of the fired products, the performance requirements for kiln furniture materials are not limited to mechanical strength and thermal shock stability. In some fields, kiln furniture is also required to have good corrosion resistance and not pollute the fired products. Different erosion media have different requirements for kiln furniture materials.
Each material, with its unique composition and unparalleled properties, stands ready to elevate your projects and products to new heights of performance and durability.
Firller Refractories is dedicated to providing cutting-edge solutions that meet the evolving needs of kiln furniture worldwide.
For detailed information, please feel free to reach out to Firller Refractories info@firller.com
