Kiln Furniture

Push plate (corundum mullite, corundum spinel), sagger (cordierite, corundum mullite, corundum spinel), support plate (cordierite, corundum mullite, corundum silicon carbide)

This product is resistant to high temperature, has good thermal stability, corrosion resistance and spalling resistance, and is an ideal high-temperature product for firing various chemical raw materials. This product can also be used in various ceramic kilns, which can effectively reduce product deformation, slag and other defects.

There are various molding methods for kiln furniture, mainly including high-pressure molding, semi-dry pressing molding, extrusion molding, plastic mud pressing molding, grouting molding, etc. The high-pressure molding pressure is generally 400-600kg/cm2, and the press used is a 500-ton, 800-ton, 1000-ton, and 1200-ton hydraulic press; extrusion molding is mainly used for the molding of round tubular pillar bricks; plastic mud molding is mainly used for various types of saggers; grouting molding is mainly used for the molding of various heavy-duty SiC kiln furniture.

 

The trend of kiln furniture structural design is to reduce, thin, and combine. For example, in kiln tools for firing sanitary ceramics, the pillars, column heads and slabs are made of cordierite-mullite, the crossbeams are hollow square tube-shaped thin heavy-duty SiC, the thin plates are heavy-duty silicon carbide or silicon nitride combined with silicon carbide, and the pads are cordierite-mullite pads.

Different types of kiln tools have different performance and development levels of refractory materials, which are described below.

3.1.1 Artificially synthesized violaite and mullite kiln furniture

(1) Violaite-mullite kiln furniture

The violaite and mullite in the violaite-mullite kiln furniture are first artificially synthesized, and then mixed with a binder according to a certain particle size distribution. The production process in Japan is: first synthesize high-quality violaite and mullite separately, and then mix, shape and burn them according to a certain proportion. The production process in Europe and the United States is: the aggregate is artificially synthesized mullite, and the binder is bluestone, which is mixed, molded and burned according to a certain proportion. The latter process is more energy-efficient. The firing is carried out in a special tunnel kiln or shuttle kiln, with a firing temperature of 1350-1380℃ and a firing cycle of 9-10 hours.

The characteristics of violaite-mullite kiln furniture are high strength at high temperature, stable volume, high thermal conductivity and long service life, which can basically solve the problems of sinking, deformation and slag falling during the use of kiln furniture.

(2) Mullite kiln furniture

Synthetic mullite has two types: sintered type and fused type. Sillimanite, andalusite, and kyanite are also used as raw materials or directly as aggregates.

Production process of mullite kiln furniture:

①Raw material selection and processing

The raw materials used in mullite kiln furniture are all artificial synthetic raw materials. The raw material processing is very fine and the requirements are extremely strict. Generally, there are special raw material processing plants to supply various granular raw materials required by the sagger factory. Their performance has reached the expected technical requirements. Therefore, the performance of the sagger made is stable during the firing and use process.

②Molding and drying

Molding adopts semi-dry method and wet pressure molding. The mud material used for wet molding is multi-particle grade ingredients. High-strength plastic clay is selected as a binder, and the moisture content is controlled at a low level to ensure the external dimensions and density of the processed products. In order to ensure the specifications and appearance of the sagger, the design and processing dimensional accuracy of the mold are very strict. If the moisture content of the semi-finished product is higher than 5%, it needs to be dried. The drying temperature adopts different drying systems according to the thickness, size and shape of the product. The maximum drying temperature is 70℃.

③ Firing

The firing temperature of the green body is generally about 50℃ higher than the use temperature. A high-temperature tunnel kiln and gas fuel are used. The maximum temperature difference in the kiln does not exceed 5℃ to ensure the stability of the product during use.

④ Coating

After the fired products are inspected, a layer of alumina slurry containing about 70% alumina is sprayed on the inner surface of the product to increase its service life (generally 240 times).

Mullite super refractory material is a refractory material fired at high temperature with high-purity fused mullite as the main raw material. This material has high refractoriness and high high-temperature strength. The use temperature of the flame contact surface can reach 1750℃, and it has ideal high-temperature volume stability. It is suitable for kiln tools such as furnace materials and pillars of high-temperature kilns.

(3) Cordierite kiln furniture

Cordierite kiln furniture products are mainly used for the production of daily-use ceramics and building sanitary ceramics, with an operating temperature below 1300℃. There are several production processes:

① Semi-dry pressing

This method is generally used for the production of shed boards. According to the size of the product, semi-dry pressing can be performed using presses of different tonnages. The tonnage of the presses is: 250 tons, 500 tons, and a maximum of 2000 tons. The moisture content of the formed blank is 5%. After drying to a moisture content of <1%, it is put into the kiln for firing. Various shed boards are installed vertically on the kiln car and fired in a tunnel kiln. Natural gas is used as fuel and the firing is automatically controlled. The maximum firing temperature is 1380℃ and the firing cycle is 93 hours.

② Extrusion molding

Mainly used for the production of various tubular pillars. First, mix the ingredients and add water, then knead the mud in a vacuum kneading machine, and cut it into mud segments for supply to the tube extruder. The moisture content of the mud material is 16-20% when the tube is extruded. The flat extrusion method is adopted, and the triangular steel track is used for support. The tube length is 600-700mm, and the tube diameter is controlled by the extruder head.

The fired tube is cut into short tubes of various sizes by a diamond cutter.

③ Plastic mud pressing

Mainly produces various types of saggers, which are pressed and formed by a 70-ton press. The moisture content of the plastic mud is 16%.

④ Grouting molding

Small products are molded by grouting, and large-size products are molded by plaster molds with metal plates on the outside. When drying, the plaster mold and the casting are pushed into the drying room together, demolded after drying, and fired in a shuttle kiln.

⑤ Manual molding

It is mainly used to produce saggers for firing sanitary ceramics. Use the well-trained plastic clay to make the bottom of the bowl first, and then add the side to form an integral sagger.

Using cordierite as kiln furniture has a low cost and a service life of 100 to 1000 times.

3.1.2 Silicon carbide kiln furniture

Silicon carbide kiln furniture is made of silicon carbide as the main raw material and various binders fired at high temperature. The varieties include silicate-bonded silicon carbide, nitride-bonded silicon carbide, recrystallized silicon carbide, microcrystalline mullite and corundum-bonded silicon carbide. The following introduces the production of foreign silicate-bonded silicon carbide and nitride-bonded carbon kiln furniture, silicon and recrystallized silicon carbide.

(1) Production process

The main production process of silicon carbide kiln furniture is as follows:

Mixing (using high-speed mixer) → molding (large-tonnage hydraulic press) → drying (using high-pressure steam) → firing (tunnel kiln and bell kiln) → finished product (passing inspection) Molding: mainly using 800-ton, 700-ton, and 350-ton automatic hydraulic presses for pressure molding;

Drying: The moisture content after drying is less than 1%;

Firing: Tunnel kiln and bell kiln are used for firing, and the firing temperature is 1400℃.

Silicon nitride combined with silicon carbide refractory materials is a combination of coarse, medium, and fine silicon carbide with fine silicon nitride. After the kiln furniture is fired, it is heat treated to remove residual carbon and increase the service life of the kiln furniture.

(2) Physical and chemical properties

The chemical composition of the shelf, pillar, and sagger of silicon carbide kiln furniture is as follows: SiC 90.5%, A1203 0.5%, Si02 8.2%, Fe203 0.2%.

The main chemical composition of silicon nitride combined with silicon carbide kiln furniture is as follows: SiC 70-80%, Si2ON2+Si3N4 16-26%.

(3) Usage

In tunnel kilns and shuttle kilns for firing sanitary ceramics, recrystallized silicon carbide is also used as horizontal and vertical beams, which reduces the weight of the kiln furniture system and reduces fuel consumption to 1200kcal/kg and 1800kcal/kg respectively.

3.1.3 New composite kiln furniture

The new composite kiln furniture mainly includes cordierite-aluminum titanate and aluminum titanate mullite.

Aluminum titanate has the highest melting point among the existing low expansion materials and can be used at a temperature of more than 1600°C. It can be composited with cordierite, mullite, etc. and is mainly used in high thermal shock resistance occasions.

Physical and chemical indicators of kiln furniture products

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