Kiln furniture refers to the refractory products used in industrial kilns to support or protect the products being fired. It influences the heat distribution in the furnace and the interaction of the load with the atmosphere in the furnace. They are extensively used in daily-use ceramics, building ceramics, sanitary ceramics, and advanced ceramic materials.
If we classify kiln furniture by material, there are generally different types including cordierite, cordierite-mullite, fused silica, mullite, aluminum, aluminum titanate-mullite, silicon carbide, zirconia, corundum-based products, etc.
Based on the different service conditions and functions, kiln furniture can be divided into these major categories:
- Structural Kiln Furniture
- Sintering Vessels
- Kiln Accessories
- Special Kiln Furniture
Structural kiln furniture
Structural kiln furniture is an essential component of industrial kilns. During service, it operates at high temperatures within the kiln, directly exposed to gas flames or receiving heat transfer from heating elements. It typically bears loads heavier than its weight, sometimes several times its weight, without deforming or breaking. This necessitates a certain level of high-temperature mechanical strength and excellent thermal shock stability.
Among these types of kiln furniture, shelves (beams and columns are usually used in conjunction with shelves, with shelves being representative), push plates, and rollers are the main components and have a large market capacity.
1.General Structural Kiln Furniture
1) Kiln Shelves
Kiln Shelves serve as specialized kiln furniture for supporting ceramic pieces during firing and are an important auxiliary material in the ceramics industry. Shelves have a large surface area and thin thickness, making them the most widely used type of kiln furniture both in terms of production and usage. They are highly representative in the field of kiln furniture. Common materials used for shelves in the kiln industry include cordierite-mullite, corundum, OSiC, SiSiC, NSiC, RSiC, etc.
There are also several types, such as extruded batts, plain batts, perforated batts, and grooved batts.
2) Columns/ Supports
Also, known as posts or pillars, are structural components made from a combination of cordierite, mullite, silicon carbide, or other materials. They are usually used in conjunction with shelves.
With various shapes, like I-shaped supports, cubic supports, extruded supports, adjustable supports, and supports with base and splicer.
3) Beams/Supports
Beams apply to the load-bearing structural frame in tunnel kilns, shuttle kilns, and other industrial kilns. They are usually used in conjunction with shelves or directly as structural support in high-temperature processes and metrology equipment.
Beams are available in at least three different materials, SiSiC, NSiC, and RSiC.
4) Support Accessories
Like Fitting Caps/ Collars, Splicer.
5) Push Plates
Push plate kilns are widely used in the ceramics industry, with push plates being their fundamental auxiliary materials. The performance of the push plates typically determines the operational efficiency of the kiln. During the operation of a push plate kiln, the plates must withstand the load of ceramic green bodies or saggars, significant-top pressure, and frictional resistance with the tracks at high temperatures without breaking. They need to endure thermal cycling for dozens or even hundreds of cycles.
Therefore, push plates must have high strength at both room temperature and high temperatures, as well as excellent wear resistance and thermal shock stability. Currently, the commonly used materials for push plates domestically and internationally are silicon carbide and corundum-mullite.
6) Rollers
Roller kilns use the rotation of rollers to transport green bodies, allowing them to pass through preheating, sintering, and cooling zones to complete the firing process. The advantages of roller kilns include uniform temperature within the kiln due to both top and bottom heating, short firing cycles, and low fuel consumption.
Ceramic rollers are critical components of roller kilns and have a high consumption rate. They play a role in bearing and transferring products during continuous high-temperature firing. These rollers must withstand high temperatures and possess resistance to high-temperature creep over long periods of rotation. The primary materials for ceramic rollers include corundum, aluminosilicate, fused silica, and silicon carbide. Silicon carbide rollers are further divided into recrystallized and reaction-bonded silicon carbide.
2. Secondary Structural Kiln Furniture
Secondary kiln furniture usually has specific functions and delicate structures, which are mainly used in tableware and sanitary ware. Many types of them are customized shapes.
The materials are usually cordierite-mullite, mullite, silicon carbide, etc.
1) System for tableware, there are Fish Setters, Profile Setters, Total Foot Support Setters (TFS), T-Cranks, Y-Cranks, Pin Cranks, Cup Rings, Pin Crank Base, Pin Crank Cover, Pin Upright, Pin Cranks-Pins, etc.
2) For sanitary ware, there are Water Basin Setters, W.C Stools, X-Shape W.C Stools, Special Supports, and Special Setters.
etc.
Sintering Vessels
These are specialized kiln furniture used to support ceramic green bodies during firing or to hold powders (such as cathode materials, magnetic powders, and high-purity ceramic materials) for heat treatment in roller kilns, push plate kilns, and tunnel kilns.
Depending on the sintering process used by the manufacturer, these kiln furniture pieces are subjected to different heating conditions. The material of these products depends on the type of sintering body and the heat treatment process.
1. Saggars/Crucibles
Saggars used for holding powders (such as lithium battery cathode materials, magnetic powders, and high-purity ceramic powders) for heat treatment in roller kilns, push plate kilns, and tunnel kilns are typically formed using extrusion, machine pressing, casting, and isostatic pressing techniques. The appropriate forming method is chosen based on the composition and structure of the products.
The most widely used materials for saggars include cordierite-mullite, corundum-mullite, silicon carbide, and graphite, with the synthesis of lithium-ion cathode materials being the most common application field.
2. Setter Plates/ Tray
Setter plates/ Trays are used to support ceramics during firing and must withstand the forces of movement and friction during loading and unloading. They need to be durable through thermal cycling without cracking. To improve the bending strength and crack resistance of setter plates while ensuring good thermal shock resistance is crucial. Additionally, setter plates require excellent chemical inertness to prevent any reactions with the fired products.
The materials used for setter plates include alumina, zirconia, and composite materials. They are mainly applied in fields such as electronic ceramics and specialty ceramics.
Kiln Accessories
This system includes kiln roof systems, kiln wall systems, and kiln car systems for shuttle, tunnel, and roller kilns, etc.
The materials of this category are usually cordierite-mullite, mullite, and silicon carbide.
Kiln accessories include Burners, Hanging Rails, Hanging Cranks, Cover Batts, Burner Blocks, Roller Bricks, Perimeter Blocks, Dry-Lock Bricks, etc.
Special Kiln Furniture
Special kiln furniture refers to kiln accessories customized and designed for unique or specialized applications in the ceramics industry. These pieces are tailored to meet particular needs, such as supporting specific shapes, accommodating high-temperature processes, or protecting delicate ceramic ware during firing.
1.H-cassettes and U-cassettes for the clay roof tile
2. Viaduct Block, Draught Block for bricks
3. Surrounding Edge for foam ceramics
4. Others
Conclusion
With the development of industry, the variety of products being fired has increased, expanding the application fields of kiln furniture. It is now used not only in the ceramics industry but also in fine chemicals, lithium-ion batteries, and other industries. Based on the performance characteristics of the products being fired, the performance requirements for kiln furniture materials are not limited to mechanical strength and thermal shock stability.
In certain fields, kiln furniture is also required to have good corrosion resistance and must not contaminate the products being fired. The requirements for kiln furniture materials vary depending on the corrosive media. For example, in the production of lithium-ion battery cathode materials, kiln furniture materials are required to have good thermal shock stability and resistance to alkaline lithium compounds. In the production of piezoelectric ceramics, kiln furniture materials must resist corrosion by lead and its compounds.
