Blog Archives - RS Kiln Refractory Bricks

Glass Kiln Lid Bricks used in rolled glass forming can be made from a single piece or from several bricks joined together. The choice between a single brick and several bricks depends on many subjective and objective factors, such as brick quality, brick cost, production cycle, glass specifications, and operator skill level. The basic principle is to ensure product quality, prevent defects during use, and guarantee durability.

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Solid Lid Brick

The length of the solid lip brick is determined by the length of the calendering roll. The advantages of using a solid lip brick are:

Not limited by glass specifications, meeting the cutting needs of various glass sizes;
Good stability during operation, with virtually no displacement or tilting;
Compact, stable, and robust assembly with the support structure.

The disadvantages are: It is prone to breakage, with severe cases showing 4-5 cracks. The brick is relatively long and heavy, and assembly and transportation are inconvenient due to space constraints.

Two Lip Bricks Joined Together

A set of lip bricks consists of two pieces joined together, each piece being half the length of the calendering roll.

The advantages of using two pieces are:

It distributes the various forces acting on the lip brick, reducing the probability of cracking;
Each brick is lighter, making assembly, transportation, and movement easier.

However, using two pieces together has many disadvantages, including:

It is difficult to guarantee the quality of the assembly, mainly due to larger joints between the bricks and the tendency for misalignment to occur on the upper surface of the lip brick, resulting in overall unevenness;
During operation, the brick joints often widen, tilt, shift, or even misalign;
The assembly process is time-consuming and labor-intensive.

There are three methods for splicing two lip bricks together:

Method 1: Make semi-circular grooves downwards on both sides of the splicing surface of the lip bricks, 10mm from the top plane of the lip. After splicing the two bricks, the semi-circular grooves on both sides will form a circular hole. Fill the hole with mortar, ensuring it is completely filled. After fixing both sides, place it near the kiln and bake at high temperature for a period of time. At this point, the refractory mortar inside the hole will have dried and solidified. If the bricks expand when heated, the resulting cylindrical refractory material will not fall off, sealing the joint between the two bricks. Therefore, no air enters, reducing the release of air bubbles and minimizing the impact on the temperature of the surrounding molten glass.
Method 2: Soak ceramic fiber paper (<1mm thick) in molten glass, then apply it to one side of the lip brick, and then align them together. After completion, bake it near the kiln.
Method 3: Dry splicing. Join two well-fitting lip bricks together, ensuring the gap between them is less than 1mm, and then tighten them with screws on both sides before use.

Three-Piece Lip Brick Assembly

A set of lip bricks consists of three pieces joined together. The middle piece is 2-2.2m long, and each of the two ends has a lip brick joint of 250-350mm.

Advantages:

The two joints release more of the compressive force generated by the expansion of the lip bricks, reducing the probability of cracking.
The length of the middle brick can meet the production needs of various glass sizes.

Disadvantages:

The structure is unstable, making it difficult to guarantee the quality of the splicing. Misalignment on the upper surface of the lip bricks at the joints can make expansion and contraction of the glass difficult.
There is a possibility of tilting or displacement during operation.
More fastener installation work is required during online assembly, resulting in a longer cycle time.

Whether used as a single piece or in combination of multiple lip bricks, the lip bricks must be assembled, installed, and fixed to a support frame. Production lines using brick-making calenders initially employed online assembly. However, after a period of trial and error, it was found that online assembly was neither convenient nor guaranteed in terms of quality. Therefore, many companies now use offline assembly, where the assembled bricks are transported to the overflow port by a mobile trolley and installed at the outlet. Production lines using integrated brick-making calenders also use offline assembly, where the lip bricks are assembled and fixed to a support frame outside the production line, and then hoisted and installed as a whole onto the calender frame.

When assembling lip bricks, the upper flat working surface serves as the reference horizontal plane. By processing the brick material or adding leveling shims at the bottom, the lip brick is ensured to be horizontal, with its contact surface with the tail brick perpendicular to the horizontal surface. The joint between lip bricks must be straight and as small as possible, less than 1mm after assembly. There should be no misalignment of the lip brick tips; the tips should be kept in a straight line along the tangent direction. The curved surfaces of the assembled bricks must be on the same plane, without any misalignment or stepped formations. Mullite fiber paper must be used to separate the lip brick from the tail brick, the lip brick from the edge brick, and the lip brick from the support. The center longitudinal direction of the lip brick should be aligned with the production line, the tangent direction parallel to the edge, and the normal direction perpendicular to the top plane of the lip brick.

Online assembly of lip bricks involves high-temperature operation in a confined area. Besides the long operation time (approximately 1-2 hours), the assembly quality of the lip bricks and supports, and the supports and calenders, is inferior to offline assembly. It also negatively impacts the kiln temperature regime.

Offline assembly offers a better working environment, lower labor intensity for workers, and doesn’t interfere with brick-changing time. It allows ample time and space for assembly, enabling precise positioning of the lip brick’s front-to-back and left-to-right spacing with the rollers. If bricks or steel components are unsuitable, they can be processed offline, ensuring the assembly quality of the lip bricks and supports, and the supports and calenders, saving brick loading time. Brick changing can be completed quickly with minimal kiln temperature changes, facilitating rapid production recovery. However, once the integrated brick-making calender is positioned, the relative position of the tail brick cannot be moved, lacking a means to handle defects. In actual production, damage can occur on both sides during the lead-in operation, especially for those accustomed to using a pull-in lead-in system. Once the edge is damaged, the machine must be replaced, and the tail brick must be replaced along with the lead-in brick. Separating the lip brick and tail brick involves long working hours, a poor working environment, and high labor intensity. The heat-resistant steel lip brick support integrated with the brick machine has poor deformation resistance, is prone to bending at high temperatures, and is difficult to restore for reuse after deformation, resulting in waste.

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Jan 17 2026

Lip Bricks for Rolled Glass Production

Lid bricks used in rolled glass production are classified into various types based on their material, including low-porosity clay, zircon mullite, α-β corundum, sillimanite, and fused silica. Currently, most solar rolled glass production lines use lip bricks made of zircon mullite, sillimanite, and α-β corundum.

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Zircon-Mullite Lip Bricks

The main components of zircon-mullite lip bricks are ZrO₂≥6%, Al₂O₃≥75%, SiO₂≤18%, and Fe₂O₃≤0.5%. They are made from industrial alumina (or high-alumina bauxite) and zircon as raw materials, mixed, shaped, dried, and then fired at high temperatures in a shuttle kiln using a reaction sintering process. Zircon-mullite lip bricks possess a dense crystal structure, high mechanical strength at high temperatures, good wear resistance, good thermal shock stability, low reheat shrinkage and high-temperature creep, and extremely high chemical stability and resistance to alkaline media erosion. Their room temperature compressive strength is ≥100MPa, load softening start temperature is ≥1670℃, bulk density is 2.8g/cm³, and air cooling performance is ≥10 cycles. Due to their good wear resistance, long service life, short debubbling time, and minimal impact on the forming after lip wear, zircon-mullite lip bricks offer high cost-effectiveness. Therefore, it is increasingly used in solar rolled glass production lines.

Rongsheng Sillimanite Bricks for Glass Kilns

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Sillimanite Lid Bricks

Sillimanite, with the molecular formula Al₂O₃·SiO₂, has a theoretical chemical composition of 62.93% Al₂O₃ and 37.07% SiO₂. Typically, sillimanite’s mineral composition contains ≥55% Al₂O₃, ≤37% SiO₂, and ≤5% Fe₂O₃, TiO₂, CaO, MgO, Na₂O, K₂O, etc., making it a high-quality, high-alumina raw material. Sillimanite undergoes irreversible transformation into 83.96% mullite (3Al₂O₃·2SiO₂) and 16.04% silicate glass phase during high-temperature sintering at 1500–1750℃, a process known as sillimanization. Mullite-treated sillimanite can be used to prepare high-density clinker with a porosity of less than 3%. This clinker, after being pulverized, can be used to make refractory materials, including lip bricks. Lid bricks made of sillimanite can be used in high-temperature operations up to 1650℃, and have advantages such as high high-temperature strength, low porosity, good volume stability and thermal shock resistance, and resistance to molten glass corrosion. Therefore, sillimanite lip bricks are also used in solar rolled glass production lines.

α-β Alumina Bricks — α-β Corundum Bricks

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α-β Corundum Lip Bricks

Corundum lip bricks are made from raw materials containing ≥94% alumina, ≤1.2% Na₂O, and ≤0.02% Fe₂O₃, through high-temperature alumina melting and casting in an electric arc furnace at temperatures above 2000℃. α-β corundum products consist of α-alumina and β-alumina, with their interlocking crystals forming a very dense microstructure, exhibiting excellent alkali resistance. In temperature ranges below 1350℃, its resistance to glass melt erosion and scouring is better than that of zirconia corundum bricks, possessing excellent mechanical strength and a long service life. Because it contains almost no impurities such as Fe₂O₃ and TiO₂, the matrix glass phase is extremely low, with a porosity ≤2% and a bulk density of 3.4 g/cm³. It produces very few bubbles or other foreign matter when in contact with molten glass, making it the best material for producing lip bricks. However, α-β corundum lip bricks suffer from poor thermal stability, are prone to cracking, and are expensive, limiting their widespread use in solar rolled glass production lines.

Regardless of the lip brick material, its appearance quality must meet the following requirements: the upper surface must be smooth and flat, free of molten holes. The lip brick edge must not have cracks, not gaps, or defects. The working surface and all contact surfaces must be finely ground to a precision of ±0.5mm, and the lip brick’s curvature must be consistent.

Processing Before Lip Brick Assembly

After the lip bricks arrive at the rolled glass manufacturing plant, if their length exceeds the required length or their surface is not smooth, they need to be processed to the required size using a cutting machine or ground.

① First, cut the lower edge of the lip brick. This should be done gradually and repeatedly to ensure a smooth, flat surface with good curvature.
② When processing the upper surface of the lip brick, it should also be done gradually and repeatedly to ensure a smooth, flat surface.
③ The bottom of each lip brick must be flat to maintain the stability of the lip brick and the brick frame support.
④ After pre-assembling the lip bricks, ensure that the contact area between the lip brick tips is less than 1mm. If the connection is not tight, grinding is required. The back of the lip brick should be as tight as possible while ensuring a tight fit, requiring a gap of less than 1.5mm.
⑤ Ensure that the inner dimensional tolerance of the lip brick is no greater than 5mm.
⑥ Based on the condition of the lip brick, use an aluminum alloy ruler and ink lines to clearly mark the areas where the lip brick tips will be processed. ⑦ Place the processed lip bricks near the kiln and bake for at least 72 hours.
⑧ Secure the baked lip bricks with clamps on a lip brick support, install the edge bricks, and fix them in place.
⑨ Precautions for processing lip bricks:

1. When cutting lip bricks, leave approximately 5mm of length for processing.
2. Use a pneumatic brick grinder for rough processing, and an electric angle grinder with a diamond wheel for fine processing.
3. When processing the contact surface of the lip brick, repeated up-and-down finishing is required. Be careful to control the force applied; do not use excessive force.
4. When high precision is required for the contact surface of the lip brick, it must be manually ground with a whetstone; do not use an electric angle grinder.
5. When using a pneumatic angle grinder, pay attention to the orientation of the lip brick to prevent small brick pieces and dust from directly hitting your face. Wear protective gear to prevent facial injury.
6. Handle lip bricks gently, ensuring the lip tip does not touch the ground. Lay cardboard on the ground to prevent damage.
7. Because lip brick processing is delicate work, it takes one to two days. Therefore, the processing of lip bricks must be carried out in a timely manner so that they can be installed and used immediately once the calendering machine is replaced.

Buy high-quality glass kiln lip bricks, such as zircon mullite bricks, sillimanite bricks, α-β Corundum Bricks, etc. Fused AZS Bricks for glass kiln, please feel free to contact Rongsheng Refractory Factory now!

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Jan 2 2026

Production Process of Mullite-Sillimanite Bricks

Rongsheng Refractory Factory lists several production processes, formulas, and molding techniques for mullite refractory brick products. (For reference only)

Mullite-Sillimanite Bricks

Using Shandong calcined shale as aggregate, sillimanite, high-alumina bauxite, and binding clay as fine powders, and sulfite pulp waste liquor as a binder, mullite-sillimanite ceramic kiln furniture can be manufactured.

The raw material composition is as follows: 55% calcined shale clinker particles <3mm; 45% finely ground sillimanite, high-alumina bauxite clinker, and binding clay (<0.088mm). (Of which: 10% sillimanite, 22% high-alumina bauxite, 13% clay); 3% water; 1% sulfite pulp waste liquor (density 1.2g/cm3).

Particle size distribution (%): >5mm, 3; 5~2mm, 25; 2~0.5mm, 24; 0.5~0.088mm, 9.5; <0.088mm, 38.5; Moisture 9.0.

The order of adding materials for clay mixing is: granular material, binder and water, then fine powder. Mixing time is 10 minutes.

After drying, the green body is fired in a downdraft kiln at 1370℃.

The physicochemical properties of the product are as follows: Al₂O₃ 51.9%, SiO₂ 43.9%. Apparent porosity 23%, bulk density 2.27 g/cm³. Compressive strength 38.2 MPa, load softening temperature 1520℃. Thermal shock resistance (1100℃, water cooling) > 20 cycles.

Mullite-sillimanite bricks, used as pusher bricks in a ceramic pusher kiln, show no deformation or wear after approximately 25 uses.

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Sillimanite Bricks

Sillimanite bricks can be manufactured using synthetic mullite, high-alumina bauxite clinker, and coke clinker as aggregates, with Jixi sillimanite as the matrix, employing equipment and processes used for clay brick production.

The raw material proportions are as follows: sillimanite 45-50%, mullite + coke clinker + Grade II high-alumina bauxite 35-50%, Grade I high-alumina bauxite 5-10%, and clay 5-10%. The above raw materials are weighed according to the proportions and mixed in a mixer. Granular materials are added first, followed by the binder, and after thorough mixing, fine powder is added and mixed for 10 minutes. The moisture content of the clay is controlled at 3-3.5%.

Sillimanite bricks are formed using a friction brick press with a capacity of 300t or higher, with the green body density controlled at 2.53g/cm³ or higher. The formed green bodies are then dried in a tunnel drying kiln. The drying kiln inlet temperature is 40-50℃, and the outlet temperature is 150-200℃. Drying time is 8-10 hours, with residual moisture not exceeding 0.5%. The firing temperature of the sillimanite bricks is 1350-1400℃, with a holding time of 8-10 hours.

The main physicochemical properties of the sillimanite bricks are as follows: Al₂O₃ 61.45%; SiO₂ 35.15%. Apparent porosity 15.3%; bulk density 2.58 g/cm³. Compressive strength at room temperature 123.4 MPa; linear change after reheating at 1500℃ for 2 hours +0.17%; creep rate at 1450℃ for 50 hours 0.72%; thermal shock resistance (1100℃ to water cooling) greater than 15 cycles.

Sillimanite Rotary Tube

The rotary tube is the main working component of a glass tube drawing machine. Its working conditions are harsh; it must withstand the erosion and scouring of molten glass at 1150℃, and it must also operate while rotating. Therefore, the product must possess strong resistance to molten glass corrosion.

Sillimanite rotary tubes can be manufactured using Shandong premium grade coke as aggregate, and Jixi sillimanite and purple clay as fine powders.

The ingredient ratio is as follows: coke 60-65%, sillimanite 20-30%, clay 5-10%, plus 1.5% sulfite pulp waste liquor and 4% water.

The mixture is kneaded in a wet mill, with the following order of addition: coke, water, sulfite pulp waste liquor, clay, and sillimanite. The kneading time is 10 minutes. Clay particle size (%): >0.84mm 13-18, 0.84-0.50mm 15-20, 0.50-0.08mm 20-25, <0.08mm 40, Moisture 6%.

Formed by pneumatic hammer tamping, with a working air pressure of 0.39-0.49 MPa. After drying, the residual moisture content of the green body is <1%. The product is fired in a down-draft kiln at a maximum firing temperature of 1370℃ for 48 hours.

The physicochemical properties of the product are as follows: Al₂O₃ 49%, SiO₂ 47%. Apparent porosity 15.7%, load softening temperature 1550℃. Room temperature compressive strength 149.7 MPa. The product is ready for use after polishing.

Sillimanite Bowl

The bowl is the main working component at the bottom of the clarification tank of a glass melting furnace, used for the outlet of molten glass used to produce bottles and jars. Sillimanite bowls can be manufactured using sillimanite concentrate and clay as raw materials.

The raw material ratio is as follows: sillimanite concentrate 3-0.5mm 30-40%, 0.5-0.088mm 20-30%, <0.088mm 20-30%; clay 8-12%, plus 3% sulfite pulp waste liquor.

Mixing is carried out in a mixing mill. According to the clay ratio, first add granular materials and dry mix for 1 minute, then add binder and mix for 3 minutes, then add fine powder and mix for 4-6 minutes. The clay moisture content is controlled at 3-3.5%. The green body is formed under a pressure of 14.7 MPa, dried at 40-60℃ for 3-4 days, and fired at 1450℃.

The main physical properties of the product are as follows: apparent porosity 22.5%, bulk density 2.07 g/cm³, room temperature compressive strength 83 MPa, load softening temperature 1320℃, and thermal shock resistance (1100℃, water cooling) 18 cycles.

Sillimanite Balls

Sillimanite filler balls for blast furnace hot blast stoves can be manufactured using high-alumina bauxite clinker and Jixi sillimanite concentrate as raw materials, and soft clay and sulfite pulp powder as binders.

The raw material ratio is as follows: high-alumina bauxite clinker particles, 0.9-0.5mm, 55%; high-alumina bauxite clinker fine powder, <0.074mm, 15%; sillimanite fine powder, <0.045mm, 20%; binder clay fine powder, <0.074mm, 10%; and added pulp powder, <0.28mm, 5%.

The sillimanite fine powder, high-alumina bauxite clinker fine powder, and clay fine powder are ground together in a vibratory mill for 10-15 minutes according to the ratio. Mixing is carried out in a wet mill. First, add the high-alumina bauxite clinker, then add an appropriate amount of water, mix for 2-3 minutes, and then add the pulp powder. After mixing for 1 minute, add the fine powder and mix for another 7-10 minutes, maintaining a moisture content of 5-17%. Dry the shaped green body at 60-80℃ for 8-10 hours, ensuring residual moisture is <2%. Firing temperature is 1500℃, held for 10-12 hours.

Main physical properties of the product: Apparent porosity 25.41%, bulk density 2.45 g/cm³, room temperature compressive strength 54 MPa, softening temperature under load 1450℃, thermal shock resistance (water cooling at 1100℃) >30 cycles.

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Andalusite Bricks

Andalusite bricks, made from andalusite as aggregate and high-alumina bauxite clinker, sillimanite, and fine clay powder as matrix, can be used to manufacture torpedo iron ladles.

Andalusite is crushed and graded for later use. High-alumina bauxite clinker and clay are mixed and ground finely in a vibrating ball mill. The raw material ratio is as follows: andalusite 50-55%, sillimanite 15-25%, high-alumina bauxite 15-20%, and clay 5-10%. The mixture is kneaded using a roller mill, adding large and medium particles first and dry-mixing for 2-3 minutes, then adding the binder and co-ground powder, with a total kneading time of 15 minutes.

The particle size distribution of the clay is: 3-2mm 25%, 2-1mm 15%, 1-0.5mm 6.5%, 0.5-0.088mm 10.5%, <0.088mm 43%. After being conditioned for 25 hours, the clay was formed using a 630t friction brick press, resulting in bricks with a density of 2.65-2.75 g/cm³. The finished bricks were dried and then fired in a tunnel kiln at a maximum firing temperature of 1350℃ for 8 hours.

The main physical properties of the finished bricks are: bulk density 2.48 g/cm³, apparent porosity 13.7%, room temperature compressive strength 110.8 MPa, load softening temperature 1560℃, creep rate (1350℃, 50h) 15%, reheat linear change (1450℃, 2h) 0.07%, and thermal shock stability (1100℃ water cooling) >30 cycles.

Sillimanite-Silicon Carbide Shelving Bricks

Sillimanite-silicon carbide shelving bricks can be manufactured using silicon carbide sand as aggregate, sillimanite and clay as matrix, and sulfite pulp waste liquor as binder. The formula is as follows: silicon carbide (grade 1) 50-65%, sillimanite 15-35%, clay 10-15%. The particle size distribution of the clay is as follows: 3-2mm 12-20%, 2-1mm 15-24%, 1-0.5mm 10-12%, 0.5-0.088mm 20-25%, <0.088mm 30-35%.

The clay is mixed in a mixing mill. The feeding sequence is: first add silicon carbide particles, then add sulfite pulp waste liquor, mix evenly, and then add the mixed fine powder. Continue mixing for 10 minutes before discharging. The moisture content of the clay should be controlled at 3-4%.

The molding process is carried out on a 500t hydraulic press, with a green body density of not less than 2.65 g/cm³. The green body is dried at 40℃ for 3 days, with residual moisture content less than 1%. Firing can be carried out in a down-draft kiln at 1430℃, with a holding time of 8-16 hours and a total firing time of 90 hours.

The physical properties of the sillimanite-silicon carbide kiln floor bricks are as follows: apparent porosity <21%, bulk density 2.30-2.35 g/cm³, compressive strength >35.2 MPa, load softening temperature >1520℃, and thermal shock resistance (1100℃, water cooling) >8 cycles.

This product can be used as floor bricks in ceramic tunnel kilns fired at 1370℃. It exhibits good thermal conductivity, thermal shock resistance, oxidation resistance, simple production process, and low cost, and can replace high-alumina floor bricks.

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Blog Steel industry refractories

Dec 18 2025

High-Purity Electrofused Mullite Castable Precast Refractory for Steel Rolling Heating Furnaces

The working conditions of certain critical components of industrial kilns, such as high-temperature burner bricks, burner brick upper crossbeams, and the furnace bottom of steel rolling mills, are extremely harsh. The working temperatures of burner bricks and burner brick upper crossbeams often exceed 1500℃, subjecting them not only to high-temperature melting damage but also to the impact of high-speed flame gas flow, their own weight, and the load-bearing capacity. The erosion of iron oxide scale and molten slag mainly damages the furnace bottom of steel rolling mills. In industrial furnaces with frequent start-ups and shutdowns, these components are subjected to stress damage caused by rapid heating and cooling.

Only refractory materials that are both resistant to high temperatures and possess excellent thermal shock stability can meet these requirements. Phosphate castables, high-alumina cement castables, and refractory plastics failed to achieve the desired results. After repeated experiments, high-purity electrofused mullite castable precast refractory achieved satisfactory results.

Theoretical Basis for Material Selection of Precast Refractory Castables in Steel Rolling Heating Furnaces

Why is high-purity electrofused mullite chosen as the main raw material? This is determined by the properties of mullite. Mullite is the only stable compound in the Al₂O₃-SiO₂ binary system. From the Al₂O₃-SiO₂ phase equilibrium, it can be seen that the composition of mullite is between 3Al₂O₃·2SiO₂ and 2Al₂O₃·SiO₂. The composition (by weight) of mullite (A₃S₂) itself is 72.8% Al₂O₃ and 28.2% SiO₂. The composition of the saturated solid solution is 78% Al₂O₃ and 22% SiO₂. That is, the mullite solid solution can contain up to 6% Al₂O₃. Compare the properties of solid solutions in this range below, and the typical composition of mullite 3Al₂O₃·2SiO₂. It has a high melting point (1910℃), high hardness, low high-temperature creep value, and good resistance to chemical corrosion.

Sources of Mullite Raw Materials

Natural mullite is rare among natural minerals. Only extremely small quantities of β-mullite and γ-mullite have been found, and their production is far from meeting the large-scale needs of production. Furthermore, the veins are generally very thin, difficult to mine, and the purity is often insufficient, making them rarely usable.

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There are two methods for the artificial synthesis of mullite: ① sintering method; ② electrofusion method.

The sintering method involves finely grinding the raw materials required for mullite synthesis, forming them into pellets, and then calcining them at high temperatures in a kiln. Impurities inevitably enter during the production process, and it is difficult to reach the ideal high temperature during calcination, resulting in incomplete reactions, poor crystallization, and poor high-temperature stability.

The electrofusion method for producing mullite involves strictly mixing raw materials such as industrial alumina, sintered high-quality bauxite, high-purity silica, and silica in a specific ratio, then loading them into an electric arc furnace. After melting at temperatures above 1850℃, the mixture is slowly cooled and crystallized. Because an electric arc is used as the heat source, very few impurities are introduced during the electrofusion process. As long as the purity of the raw materials is controlled, the product quality is relatively easy to manage, and high-purity electrofused mullite can be produced. The quality of high-purity electrofused mullite raw materials is the guarantee of the quality of the finished product.

Performance of High-Purity Electrofused Mullite Castable Precast Refractory

The main characteristic of high-purity electrofused mullite castable Precast Refractory is its excellent thermal shock resistance. Their thermal shock resistance is significantly better than that of other refractory materials. However, their compressive strength is not high, reaching only 51 MPa, while their thermal shock resistance is several times that of other refractory materials. This may be because the mullite crystal phase forms primary bonds at 850℃, producing a needle-like interstitial layer, which blocks the fracture layer that occurs within the Precast Refractory during surface water cooling tests. Therefore, high-purity electrofused mullite castable Precast Refractory can withstand thermal shock damage when used in steel rolling furnaces.

How to Improve Thermal Shock Resistance in Corundum-Mullite Castables?

Corundum-mullite castables are characterized by high load softening temperature and good creep resistance among high-temperature refractory materials. However, pure corundum products have a relatively large coefficient of thermal expansion, resulting in less than ideal thermal shock resistance. Pure mullite products, on the other hand, have a smaller coefficient of thermal expansion and better thermal shock resistance.

Rongsheng Corundum Mullite Refractory Castable

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Corundum-mullite castables are composed of mullite and corundum phases. When the mass ratio of mullite to corundum is 75:25, it coincides with the eutectic melting point at 1840℃ in the SiO2-Al2O3 phase. Therefore, a mullite to corundum ratio of 75:25 is optimal for improving thermal shock resistance. This is because mullite has a lower coefficient of thermal expansion than corundum, and the coefficient of thermal expansion in composite materials is always greater for the former than the latter. The thermal expansion mismatch between mullite and corundum within the composite material leads to microcracks, increasing the material’s fracture absorption energy and thus improving the castable’s thermal shock resistance.

Using a low eutectic point aggregate composition can negatively impact the creep resistance of castables, as the creep rate is minimized at this point. When the mullite to corundum ratio is approximately 75:25, the aggregate significantly affects the product’s coefficient of thermal expansion and thermal expansion mismatch. When microcracks develop in the castable, they propagate under thermal shock stress, simultaneously causing transgranular fracture of the aggregate and consuming a large amount of energy. This inhibits the propagation of the main crack and also affects the thermal shock stability of the corundum-mullite castable.

Of course, corundum castables also exhibit good thermal shock resistance. This is because the different aggregate-to-binder ratios lead to variations in thermal shock stability. The coefficient of thermal expansion of corundum-mullite castables significantly impacts thermal shock stability; microcracks caused by thermal expansion mismatch can actually improve the castable’s thermal shock resistance.

In summary, a mullite-to-corundum ratio of 75:25 in the process mix provides the best thermal shock stability. An apparent porosity of around 20% is highly beneficial for the thermal shock stability of castables. Therefore, controlling the apparent porosity of corundum-mullite castables to around 20% further enhances thermal shock stability.

Rongsheng Refractory Materials Manufacturer offers environmentally friendly, professional, fully automated monolithic refractory material production lines, specializing in the production of integral refractory castable linings for high-temperature industrial furnaces. Our newly commissioned factory also specializes in producing various precast refractory components. If your industrial furnace requires lining material replacement or lining repair, Rongsheng’s professional technical team can customize a lining material solution based on the actual operating conditions of your industrial furnace. Contact Rongsheng for a free quote and solution.

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Dec 5 2025

Refractory Configuration and Optimization for a 5000t/d Clinker Line (3)

Refractory materials are developing towards environmental friendliness, strong adaptability, and long service life. Rongsheng Refractory Materials Factory supplies refractory materials for kilns used in 5,000 t/d clinker production lines. Rongsheng Refractory Materials Manufacturer leverages its innovative capabilities in refractory castables while focusing on customer needs, aiming to provide high-quality, long-life refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng for free solutions.

Refractory Lining Configuration for a 5,000 t/d Cement Clinker Production Line

This article focuses on the refractory configuration for a 5,000 t/d cement clinker production line. The cement firing system involves a complex chemical process from raw meal to clinker, going through stages such as preheating in the preheater, decomposition in the calciner, high-temperature calcination, and cooling. The refractory materials used in each stage must be adapted to this process.

Analysis of Certain Defects in the Current Configuration and Improvement Plans

(1) Preheater System

Severe scaling at the smoke chamber and precalciner necking, impacting ventilation.

- Cause: The production line was designed to produce 5,000 tons per day, but actual production typically reached 5,500 tons, resulting in an overload of over 10%. This increased the kiln’s thermal load and the likelihood of scaling at the kiln tail. Furthermore, the increased use of anthracite and low-quality coal resulted in less than ideal combustion, increasing the likelihood of incomplete combustion and the rate of scaling. In short, scaling can be caused by a variety of factors, including operational factors, fuel, and raw material issues. In severe cases, it can lead to the cessation of rotary kiln operation.
- Improvement Plan: In actual production, scaling at the kiln tail is not limited to the smoke chamber, but can sometimes extend to the precalciner necking and the fifth-stage drum discharge chute. Therefore, it is recommended to expand the scope of anti-scaling castables, such as using anti-scaling castables throughout the entire section below the fifth-stage drum discharge chute.

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The castables on the top of the cyclone and decomposition furnace are prone to falling off, posing a production safety hazard.

- Causes: Poor anchorage and welding quality, design flaws, and excessively rapid cooling can all cause the top castables to fall off, resulting in numerous fatalities on the production line.
- Improvement Solution: Correct the design flaws, eliminate the calcium silicate board interposition, and use only lightweight castables. Use ceramic anchors and anchor bricks, etc.

The kiln tail tongue is prone to damage.

- Cause: Due to the erosion of high-temperature materials and corrosion from the kiln tail flue gas, the steel plate under the kiln tail tongue is easily damaged, which in turn damages the kiln tail tongue, significantly impacting kiln operation.
- Improvement Solution: Use prefabricated components and eliminate the bottom steel plate to extend service life.

Small-scale repairs are labor-intensive and time-consuming.

- Cause: After two years of operation in a new kiln, some refractory materials in the preheater system may be partially damaged. Because the preheater is hollow, scaffolding must be erected during construction, which reduces maintenance time.
- Improvement plan: Using spray paint for construction can save time and energy, and should be promoted vigorously.

(2) Rotary Kiln System

The kiln mouth castable is easily damaged, resulting in a long construction time.

- Cause: Because the kiln mouth is prone to deformation, the castable is currently cast as a single piece. However, the casting cycle is long, and the baking time may be insufficient. As a result, the kiln mouth refractory cycle is significantly lower than that of other parts of the kiln.
- Improvement: Using plastic castables eliminates the need for formwork, saving construction time. Curing and baking are unnecessary, making it suitable for routine maintenance.

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Firing zone magnesia-chrome bricks does not meet environmental requirements.

- Cause: Magnesia-chrome bricks react easily with sulfur in cement rotary kilns, generating some toxic hexavalent chromium ions, which can cause water pollution. Consequently, European countries have imposed very strict restrictions on the production and use of magnesia-chrome bricks.
- Improvement: Using dolomite bricks, magnesia-iron spinel bricks, and magnesia-alumina spinel bricks.

Spinel bricks have a large thermal conductivity, causing the kiln body temperature to rise.

- Cause: Spinel bricks are currently used near the No. 2 wheel rim and have a good service life. However, their main drawback is their high thermal conductivity, which increases the drum temperature and poses a risk to kiln operation. This also results in significant heat loss.
- Improvement: Use high-quality silica-molybdenum bricks.

Rongsheng Silicon Carbide Mullite Bricks

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(3) Short Burner Head Life

- Cause: Due to the harsh operating environment of the coal injection pipe, such as large temperature differences, a thin refractory layer, a strong reducing atmosphere, and high-temperature radiation, the head has a short service life.
- Improvement: The head is prefabricated and manufactured in advance, with adequate curing and baking, for optimal performance.

(4) The top castable of the kiln hood is prone to partial detachment

Cause: See the top of the preheater.

(5) Cooler System

Susceptible Wear of the Low Wall

- Cause: The high-temperature clinker exiting the rotary kiln is directly rubbed against the low wall during cooling, and the alternating contact between hot and cold air causes rapid wear of the low wall.
- Improvement: Use highly wear-resistant castables.

Susceptible detachment of the top castable

- Cause: See the top of the preheater.

(6) Tertiary air duct bends are prone to wear.

- Cause: The hot air from the kiln head cooler contains a large amount of clinker particles, which rub against the castable at the bend. Typically, castables only last three months.
- Improvement: Use highly wear-resistant castables.

(The end)

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Nov 20 2025

Refractory Configuration and Optimization for a 5000t/d Clinker Line (2)

Refractory Lining Configuration for a 5,000 t/d Cement Clinker Production Line

(3) Kiln Head Hood

The kiln head hood connects the rotary kiln to the cooler and serves as the inlet for kiln air and tertiary air. Air pressure is extremely unstable, making positive pressure a common feature of the entire kiln system. Gas temperatures range from 800-1300°C, with significant temperature fluctuations. Furthermore, the impact of clinker particles is intense, making the top and inlet areas susceptible to damage. Therefore, thermal shock resistance and wear resistance should be considered when selecting materials.

High-Alumina High-Strength Wear-Resistant Castable

Amount: 180 tons

Technical Performance:

Application Location: Round top

Calcium Silicate Board

Amount: 7.2 tons

Technical Performance: See above

Application Location: All refractory linings

(4) Burner

Because the burner is located in the high-temperature gas between the kiln mouth and the cooler, and the pulverized coal burns near the burner head, it is significantly affected by the high-temperature radiation and reducing atmosphere. The chemical composition of coal significantly influences combustion, making the burner head plate susceptible to damage. The refractory material used in this area requires high refractoriness and wear resistance, as well as enhanced thermal shock stability and spalling resistance.

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Mullite Castable

Quantity: 5 tons

Technical Performance:

Application Area: Burner head hood where it enters the kiln

(5) Rotary Kiln

As a rotating drum that calcines raw materials into clinker at high temperatures, the lifespan of its refractory materials often determines the production cycle, making it a key and challenging aspect of refractory material management in cement plants. After preheating and approximately 90% decomposition, the raw material enters the kiln from the kiln outlet, where its temperature gradually rises to over 1450°C, completing the calcination process and entering the cooler. A 74-meter rotary kiln can be broadly divided into five thermal stages. Because the refractory materials within the rotary kiln must be fixed to the continuously rotating drum, the strength of the refractory bricks must not fall below a certain threshold due to the following factors:

There is a certain degree of slippage or sliding tendency between the refractory bricks and the shell, generating friction. The refractory bricks must possess a certain strength to resist damage from this friction.
A rotary kiln is not an absolutely rigid structure when viewed axially. Because the rotary kiln drum has a certain curvature between its support points, it experiences periodic bending in sync with its rotation during operation. Because the three-roller rotary kiln utilizes a statically indeterminate structure, the different expansion rates of each roller group due to temperature differences can cause deviations in the kiln shell’s coaxiality, generating significant additional loads. Furthermore, the 4% inclination of the kiln shell also generates downward stress during rotation.
The shell is not a perfect circle in the radial direction, but rather an elliptical shape. Deformation is greatest at the wheel belts, and this deformation places additional pressure on the refractory bricks. Due to the kiln’s own weight and rotation, the kiln undergoes periodic elliptical deformation, synchronized with the rotation, placing alternating loads on the refractory bricks. When this deformation or elliptical deformation reaches a certain value, it can exceed the internal stresses in the refractory bricks, causing premature failure. Therefore, refractory materials with insufficient strength must be used in rotary kilns; they must meet basic strength requirements.
In addition to the aforementioned mechanical stresses, the refractory materials within the kiln are also subject to the effects of high-temperature gases and liquid clinker. It can be roughly divided into five or six working zones, which require different refractory materials for laying.

Refractory Configuration for a 5,000-ton Rotary Kiln:

Mullite Castable

Usage: 15 tons

Technical Performance: See above (RT-70MC)

Applicable Area: 0-0.6 m

High-Abrasion-Resistant Bricks

Usage: 8 tons

Technical Performance:

Applicable Area: 0.6-1.6 m

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Direct-Bonded Magnesia-Chrome Bricks

Usage: 340 tons

Technical Performance:

Applicable Area: 1.6-25 m/35-45 m

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Spinel Bricks

Usage: 99 tons

Applicable Area: 25-35 m

Anti-Spalling Bricks

Usage: 242 tons

Applicable Area: 45-73.2 m

High-Alumina Castables

Usage: 8.5 tons

Technical Performance: See above

Applicable Area: 73.2-74 m

(6) Cooler

The cooler uses air to cool the hot clinker leaving the kiln from 1400°C to below 80°C. Due to the large temperature difference between the front and rear sections, the most vulnerable parts are concentrated in the front wall and the lower wall. Furthermore, the overhanging beams at the interface with the kiln head are also susceptible to premature damage due to the erosion of high-temperature gases.

Grate coolers are stationary relative to the refractory shell, so insulation materials with low strength but low thermal conductivity can be used on the outer layer. The cooler’s inner surface must withstand thermal erosion and high-temperature abrasion caused by contact with high-temperature clinker at 300-1450°C, so the selected refractory materials must have strong wear resistance. Furthermore, the first stage cooler must also withstand high thermal loads.

Because the grate cooler has large vertical walls, the use of special anchoring refractory bricks is crucial when constructing the refractory brickwork to strengthen the connection between the bricks and the shell to prevent collapse of the vertical walls.

Currently, the most commonly used refractory castables are:

High-strength alkali-resistant castable

Usage: 20 tons

Technical properties: See above (RT-13NL)

Application: Section 3 and top

High-alumina castable

Usage: 106 tons

Technical properties: See above (RT-16)

Application: Section 2 and 3 side walls and parapet

High-heat high-alumina castable

Usage: 183 tons

Application: Cooler front wall and Section 1 parapet

(To be continued…3)

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Nov 5 2025

Refractory Configuration and Optimization for a 5000t/d Clinker Line (1)

Refractory Lining Configuration for a 5,000 t/d Cement Clinker Production Line

(1) Preheater System

This system utilizes kiln exhaust gas to gradually heat the raw meal from ambient temperature in a suspended state to above 750°C before entering the precalciner system for decomposition. The amount of refractory material used in this system accounts for nearly two-thirds of the total refractory material used. Its thermal characteristics are:

60% of the fuel and the preheated raw meal are thoroughly mixed in the precalciner for flameless combustion. Wall and flue gas temperatures are generally controlled below 1000°C. The temperatures of the other cyclones, from the first to the fifth stage, are not higher than 450°C, 650°C, 750°C, 900°C, 1000°C, and 1100°C, respectively.
The preheater system calcines the material with virtually no liquid phase, resulting in minimal agglomeration and sintering, and therefore requires less refractoriness. Furthermore, the overall system temperature is relatively stable, requiring less thermal shock resistance from the refractory material.
The preheater system is a stationary device, but its size is relatively large, requiring insulation materials with low thermal conductivity to reduce the outer shell temperature.
Due to the complex shape of the preheater system, including cones, cyclone inlet and outlet diameter changes, thin feed pipes, and numerous measuring holes, it is more convenient to use on-site formed refractory castables in these areas.
When using raw materials and fuels with high alkali content, the refractory materials in the preheater must withstand not only high-temperature corrosion but also chemical attack from alkali metal oxides.

The aforementioned thermal environment generally determines the configuration of refractory materials for each stage of the preheater, and the following principles should be followed:

Refractory materials with low thermal conductivity, good insulation, and a working surface with sufficient strength and resistance to alkali corrosion should be used.
Castables should be used for sections with complex shapes and a large number of thin pipes, while alkali-resistant bricks should be used for straight tubes and regular sections.
Different materials should be designed for different sections based on the different temperatures of the cyclones and to save costs. For example, for the first and second stage cyclones, a combination of refractory and insulation considerations can be considered, and clay-based alkali-resistant refractory materials can be selected. For preheaters below the third stage, alkali-resistant materials capable of temperatures exceeding 1100°C should be used.
Anti-scaling castables should be used for the refractory castables from the fifth stage to the smoke chamber and below the calciner, as the surface is prone to scaling.

The following is a brief introduction to the selection and dosage of refractory materials for the preheater of a 5000t/d production line:

Alkali Resistant Bricks for Rotary Kiln — Alkali-Resistant Bricks for Rotary Kiln

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RK-H High-Strength Alkali-Resistant Bricks

Quantity: 569 tons

Performance:

Application Areas: Vertical ascending flues, cyclone tubes, and cones

High-Strength Alkali Resistant Castable — High-Strength Alkali-Resistant Castable

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High-strength alkali-resistant castable

Usage: 850 tons

Performance:

Construction method:

Application: Tops of preheater stages 1-4, irregular shapes, etc.

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High-alumina low-cement castable

Usage: 200 tons

Performance:

Application: Precalciner, fifth-stage drum

Anti-scaling castable

Usage: 112 tons

Performance:

Application Area: Kiln tail flue chamber

Calcium Silicate Board

Consumables: 156 tons

Performance:

Application area: All refractory linings

(2) Tertiary Air Ducts

Tertiary air ducts utilize high-temperature, oxygen-rich gases from the kiln head to guide the ducting channels of the precalciner. At temperatures of 800-900°C, these gases contain a large amount of clinker particles, which can severely erode and wear the refractory materials at the bends. Therefore, the system’s alkali resistance and wear resistance must be considered. High-strength alkali-resistant bricks and calcium silicate board are used in the straight sections, while high-wear-resistant castables and calcium silicate board are used in the irregular sections.

Currently, two types of tertiary air ducts are used: parallel ducts and V-shaped ducts. Parallel ducts are arranged almost parallel to the kiln, while V-shaped ducts are V-shaped, with a settling chamber and discharge gate valve located at the lower end of the duct.

Parallel ducts are simple in design, aesthetically pleasing, and require minimal investment. However, to prevent clinker particles from settling in the tertiary duct, higher operating air velocities are required, resulting in greater resistance in the tertiary duct. This higher air velocity also requires higher wear resistance from the refractory materials. The V-type duct is more complicated and requires a large investment. It also requires regular dust discharge from the discharge gate valve. However, the V-type duct can adopt a lower operating wind speed, so the system resistance is low, and the wind speed wear is small.

The refractory material usage and performance requirements are as follows:

RK-H High-Strength Alkali-Resistant Bricks

Usage: 140 tons

Performance: See above

Application: Straight sections of air ducts

Ultra-High-Strength Wear-Resistant Castable

Usage: 70 tons

Performance:

Application Area: Tertiary duct bends and gates

Calcium Silicate Board

Consumables: 17 tons

Performance: See above

Application Area: All refractory linings

( To be continued…2)

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Oct 21 2025

Suitable for Aluminum Alloy Smelting – Unshaped Refractories Medium Temperature Low Cement Castable

The aluminum alloy melting process poses unique and demanding challenges to refractory materials, stemming from the physical and chemical properties of molten aluminum and its alloys. While the combustion chamber of an aluminum melting furnace can reach temperatures of approximately 1200°C, the furnace chamber area in direct contact with the molten aluminum typically only reaches temperatures of 700-800°C (the casting temperature for 6063 aluminum alloy is 720-740°C).

This means that the furnace lining material spends most of its time in a medium-temperature range, rather than a traditionally high-temperature state. In this temperature range, traditional refractories often experience a strength dip due to bonding phase transitions. For example, hydration products (such as CAH₁₀ and C₂AH₈) in cement-bonded Unshaped Refractories Castables begin to dehydrate at 300-400°C, losing their bonding properties while the ceramic bond is not yet fully formed, resulting in a significant drop in strength.

Rongsheng Low Cement Castable for Sale — Rongsheng Low-Cement Castable for Sale

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Low-Cement Castables: Medium- and Low-Temperature Strength Properties

Low-cement castables exhibit unique strength properties in the medium- and low-temperature ranges, distinct from conventional castables. During heating, conventional aluminate cement unshaped refractories castables typically experience a decrease in strength (due to hydrate dehydration) followed by an increase (due to ceramic bonding), with a distinct strength dip occurring in the 800-1000°C range. Low-cement refractory castables, however, exhibit a significant increase in strength at medium temperatures, rather than a decrease in strength.

The research examples in the table below demonstrate that the hot flexural strength of low-cement castables at 800°C is significantly higher than that at room temperature. Low-cement castables made primarily of kyanite-mullite (M45 and M60) exhibit the greatest increase in hot flexural strength with increasing treatment temperature. Low-cement castables made primarily of high-alumina bauxite (M85) exhibit the second-highest increase. Conventional Unshaped Refractories castables using CA-50 cement as a binder exhibit a distinct strength dip after firing at 800°C.

Table: Changes in hot flexural strength after treatment at different temperatures (MPa)

Castable Sample Type	Dry at 110℃	After Sintering at 800℃	After Sintering at 1000℃	After Sintering at 1200℃	Strength Growth Characteristics
M45	8.5	10.2	12.8	15.3	Sustained and stable growth
M60	9.2	11.5	14.2	17.6	Significant increase in medium temperature strength
M85	10.7	12.3	14.9	18.2	High initial strength and stable growth
Traditional CA-50	11.2	8.5	10.3	13.7	The medium temperature strength decreased significantly

The mechanism of this anomaly is that the dehydration of calcium aluminate hydrate in low-cement castables is slow and continuous, with minimal damage to the crystal structure. Simultaneously, the ultrafine powder begins to sinter at moderate temperatures, forming a preliminary ceramic bond.

Core Characteristics and Advantages of Low-Cement Castables

Low-Cement Castables (LCC) are a new generation of unshaped refractory materials developed in the 1980s. Compared to traditional aluminate cement Unshaped Refractories castables, their core characteristic lies in a significant reduction in the amount of calcium cement (typically from 12-20% to 3-8%). Furthermore, through the introduction of ultrafine powder technology and high-efficiency admixtures, they achieve a comprehensive performance optimization of high density, low porosity, and high strength.

The revolutionary breakthrough in low-cement castables stems from the application of ultrafine powder technology. Ultrafine powders (such as reactive SiO₂ powder and α-Al₂O₃ powder) with particle sizes less than 1.0μm can exceed 71%. These ultrafine particles possess an extremely high specific surface area and reactivity, effectively filling the gaps between aggregate particles and achieving the densest packing. It prevents particle size segregation, reduces porosity and pore diameter, ensures the fluidity of the mixture, and improves the density and bonding strength of the Unshaped Refractories castable. More importantly, the high specific surface area and reactivity of ultrafine powder significantly reduce sintering temperatures and promote sintering at medium and low temperatures.

Active SiO₂ ultrafine powder not only improves the fluidity of the castable but is also one of the most effective sintering accelerators. At temperatures above 900°C, SiO₂ ultrafine powder reacts with Al₂O₃ to form mullite (3Al₂O₃·2SiO₂), accompanied by a volume expansion of approximately 10.5%. This volume effect effectively offsets some of the volume shrinkage of the unshaped refractory castable, promoting strength improvement. Furthermore, the mullite phase forms at a relatively low temperature (beginning to form in large quantities at approximately 1000°C), and its needle-shaped or columnar crystal structure forms a cross-linked skeleton, significantly enhancing the material’s strength.

Ultrafine α-Al₂O₃ powder strengthens the material through a different mechanism. It promotes the formation of calcium hexaaluminate (CA₆) from calcium aluminate at high temperatures, along with smaller amounts of mullite, anorthite, CA, and CA₂. These minerals have large molar volumes, which prevent volume shrinkage. Furthermore, CA₆ crystals are small columnar and needle-shaped, while anorthite crystals are fine columnar. Together, they form a cross-linked structure of fine columnar and needle-shaped structures, resulting in a strong and dense structure that can reach strengths of around 100 MPa.

The setting and hardening mechanism of low-cement castables is also fundamentally different from that of traditional Unshaped Refractories castables. Traditional castables primarily derive their strength from hydration products (such as CAH₁₀ and C₂AH₈) produced by cement hydration. However, these hydrates dehydrate and decompose during heating, significantly reducing their strength at medium temperatures. Low-cement castables, on the other hand, rely primarily on a cohesive bonding mechanism: ultrafine powder particles form colloidal particles in water, which form a three-dimensional network structure through van der Waals forces and chemical bonds, tightly binding the aggregate particles together. Cement acts only as a delayed-acting setting accelerator. This cohesive mechanism ensures that the strength of low-cement castables does not decrease due to hydrate decomposition during heating, but instead continues to increase due to sintering.

By carefully controlling the type, particle size distribution, and additive amount of fine powder, low-cement castables achieve an ideal strength development curve within the operating temperature range of aluminum alloy smelting (700-900°C). This avoids the mid-temperature strength trough common in traditional Unshaped Refractories castables while providing sufficient high-temperature performance, perfectly adapting to the unique operating conditions of aluminum melting furnaces.

However, there are downsides. Low porosity and high densification also result in poor air permeability. During baking and heating, steam generated by internal moisture cannot be promptly dissipated, easily building up high pressure within the lining, causing it to spall or crack. Therefore, when using low-cement castables, a reasonable baking system and the addition of explosion-proof agents must be used.

Conclusion

From the “medium-temperature dilemma” of traditional Unshaped Refractories castables to the “precise breakthrough” of low-cement castables, the path to upgrading refractory materials is essentially a matter of precisely matching material properties with operating requirements. For the unique application of aluminum alloy smelting, low-cement castables restructure their strength formation mechanism through ultrafine powder technology. This not only addresses the strength limitations of the medium-temperature range, but also addresses the core requirements of high density and corrosion resistance. This makes them a key material support for the longevity and high efficiency of aluminum industry furnaces.

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Oct 6 2025

How to Improve the Performance Parameters of Zirconium Corundum AZS Bricks?

AZS Bricks, abbreviated as zirconia, are primarily composed of alumina and zirconium oxide, with small amounts of other additives. Their high alumina content and the addition of zirconium oxide impart unique properties. For example, a typical zirconia brick may contain approximately 70% alumina and 30% zirconium oxide. It may also contain trace amounts of additives such as borax and silica sol to improve sintering performance.

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Zirconium-aluminum bricks are primarily used in glass industry tank furnaces, including key areas such as the tank walls, vents, superstructures, hanging walls, and breast walls. In glass furnaces, zirconia-aluminum bricks can withstand temperatures exceeding 1600°C and the corrosive effects of molten glass, ensuring proper furnace operation and high-quality glass production. They are also used in high-temperature industries such as steel smelting furnaces, cement rotary kilns, and non-ferrous metal smelting.

Improving the Performance Parameters of Zirconia-Corundum Bricks

To maximize the performance parameters of Zirconia-Corundum bricks, various performance-enhancing additives are added during production. Nanomaterials exhibit unique size and surface effects, and the introduction of nanoscale additives into Zirconia-Corundum bricks can improve their performance. For example, the addition of nanoparticles such as nanoalumina and nanozirconia can form finer dispersions within the brick, hindering crack propagation and increasing the brick’s toughness and strength. Furthermore, these nanoadditives can synergize with the original components of Zirconia-Corundum bricks to enhance their thermal shock resistance and erosion resistance.

However, due to its high specific surface area and surface energy, nanoalumina is prone to agglomeration. If dispersion issues are not effectively addressed during production, agglomerated nanoalumina particles can form localized defects within the Zirconia-Corundum brick, reducing its overall performance. For example, agglomerates can become stress concentration points, making cracks more likely to form during use, impacting the brick’s strength and durability.

By modifying the nano-alumina, a carbon nanotube core-shell structure is grown in situ on the surface. This core-shell structure prevents direct contact between nano-alumina particles, thereby reducing the possibility of nano-alumina agglomeration. This allows the nano-alumina to be evenly distributed within the corundum monolithic refractory brick, forming a finer dispersed phase within the brick, hindering crack propagation and improving the brick’s toughness and strength.

AZS Refractory Bricks (250 x 124 x 64-mm)

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The technical solution is as follows:

Materials: 55-65 parts alumina powder, 25-35 parts zircon sand, 1-5 parts modified nano-alumina powder, 2-6 parts binder, 1-2 parts chromium oxide, 1-3 parts yttrium oxide, and 1-4 parts flux.

The alumina powder has a particle size of 1-1.5 mm and a purity >99%.

The zircon sand contains 65% zirconium oxide and 34% silicon dioxide, with a particle size of 0.05-2 mm.

The modified nano-alumina powder is nano-alumina modified with in-situ carbon nanotubes. A carbon nanotube core-shell structure is grown on the surface of the modified nano-alumina.

The binder is silica sol. The silica content is approximately 40%, the iron content is <0.01%, the sodium oxide content is <0.5%, the viscosity is 10-20 mPa·s, and the particle size is 20-70 nm.

The flux is borax with a purity of >95%, an iron content of ≤0.005%, and a particle size of 0.15mm.

The production steps are as follows:

Ingredients: Add alumina powder, zircon sand, modified nano-alumina powder, binder, chromium oxide, yttrium oxide, and flux to a mixer in the correct proportions.

Mixing: Stir the ingredients in the mixer at a speed of 120-180 rpm for 90-120 minutes to ensure thorough mixing.

Molding: The mixed ingredients are placed into a mold and molded using a friction press or hydraulic press. The molding pressure is 150-220 MPa, and the holding time is 30-90 seconds, until the bricks reach the desired shape.

Drying: The molded bricks are placed in a drying oven along with the mold to dry and remove moisture. The drying temperature is 110-140°C, and the drying time is 24-72 hours.

Sintering: The dried bricks are placed in an insulated sand box along with the mold and then sintered in a high-temperature kiln at a temperature of 1650-1800°C. The heating rate is 3-5°C/min, and the holding time is 4-8 hours.

Annealing: After the sintered zirconium-alumina refractory bricks and the mold are removed from the insulating flask, the mold is removed. The zirconium-alumina refractory bricks are placed back into the insulating flask for annealing for 24-48 hours. The cooling rate is 2-4°C/min.

Advantages: Nanomaterial modification technology and optimized production processes not only address the problem of nanoparticle agglomeration but also significantly improve the overall performance of the bricks, making them more suitable for high-temperature and highly corrosive working environments. The resulting zirconium-alumina refractory bricks offer high quality, a high forming rate, stable internal stress distribution, and resistance to high temperatures and corrosion.

Differences in Application Between Fused AZS and Fused Corundum Bricks

In float glass furnace design, the optimal combination is determined based on glass quality requirements, furnace service life, refractory properties, and cost. Different refractory types are used in different areas. Parts in contact with the molten glass, such as the tank walls and bottom, have a significant impact on furnace life and glass quality, and therefore require more stringent selection criteria.

With improvements in refractory quality and performance, and increasing demands for furnace lifecycles, fused AZS bricks are currently used for both the melting tank walls and bottom, as well as the neck tank walls and bottom. This is primarily to address chemical erosion caused by batch reactions and erosion from high-temperature molten glass. Fused AZS offers superior high-temperature erosion resistance compared to other refractory materials.

33# oxidation-process fused zirconia-corundum bricks can be used for the cooling tank walls and bottom, but high-quality float glass production lines typically use α-β fused corundum bricks, primarily for glass quality considerations. α-β fused corundum bricks have low porosity and exhibit excellent corrosion resistance at the 1350°C operating temperature of the cooling section, without any glassy phase precipitation. However, fused AZS bricks, due to their high content of SiO2 and alkaline oxides, are prone to glassy phase precipitation, and this volume change can lead to the formation of bubbles. Furthermore, after the zirconium corundum is dissolved by the molten glass, the corrosion-resistant ZrO2 material remains, forming microscopic dendrites. Discharge at the tip triggers an electrochemical reaction, ionizing and reducing the gas components in the glass to form bubbles. Therefore, based on glass quality requirements, kiln runner designs generally use α-β fused corundum bricks for the cooling section walls and floor paving.

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Applications of Fused AZS Bricks and Fused Corundum Bricks

Fused Zirconia Corundum

Grades include: AZS-33 (33% ZrO₂ content), AZS-36 (36% ZrO₂ content), and AZS-41 (41% ZrO₂ content).

The erosion resistance of fused zirconium corundum increases with increasing ZrO₂ content. 33# fused AZS bricks are suitable for the melting pool walls and the breast wall of the material processing area. Corners of the pool walls are more susceptible to erosion by the molten glass, so 36# fused AZS bricks or 41# AZS bricks with higher ZrO₂ content are the best choices.

The production process for fused zirconium corundum is divided into reduction and oxidation methods. Currently, the oxidation method is the primary shrinkage-free casting process. The oxidation melting method eliminates contamination caused by graphite electrodes in the melt, has a low carbon content, and can reduce the bubble content in the glass.

α-β Fused Corundum Bricks

Al2O3 content >98%. Made from high-purity alumina with a small amount of soda ash, it is melted at 2000-2200°C and produced using a shrinkage-free casting method.

The thermal expansion coefficient of fused corundum is 8.6, placing it in the lower-to-medium range for thermal shock resistance. Fused corundum bricks exhibit slightly poor high-temperature corrosion resistance, with resistance to molten glass decreasing rapidly at temperatures above 1600°C. However, at operating temperatures of 1350°C and below, they exhibit strong corrosion resistance and virtually no contamination of the molten glass. They are ideal materials for the cooling tank walls and floors of glass melting furnaces, as well as for float glass launders.

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Sep 21 2025

Alumina Bricks Properties

Different types of alumina bricks (such as β-alumina bricks and hollow alumina sphere bricks) may differ in their specific properties. For example, β-alumina bricks offer better resistance to alkali vapor corrosion, while hollow alumina sphere bricks excel at being lightweight and providing excellent thermal insulation. RS Alumina Bricks Manufacturer supplies high-quality alumina bricks. Contact RS Factory for free samples and quotes.

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Alumina Bricks Have the Following Properties

High-Temperature Resistance

Alumina bricks typically have a refractoriness exceeding 1900°C, maintaining stable physical and chemical properties in high-temperature environments. They are suitable for use in high-temperature industrial furnaces and melting furnaces, where they can withstand long-term high temperatures without deformation or damage.

High Mechanical Strength

They possess high compressive and flexural strengths, reaching approximately 250 MPa at room temperature and maintaining a strength of approximately 150 MPa at 1000°C. They can withstand mechanical and thermal stresses at high temperatures.

Good Chemical Stability

They are chemically stable and highly resistant to corrosion from acids, alkalis, salts, and other chemicals, especially at high temperatures. They are particularly resistant to corrosion from a variety of molten metals and chemicals. They are suitable for applications in chemical and metallurgical industries, where corrosion resistance is critical.

Low Thermal Conductivity

With low thermal conductivity, they offer excellent thermal insulation properties, effectively reducing heat transfer and lowering energy consumption. They are often used as insulation layers in high-temperature furnaces to improve energy efficiency.

Thermal Shock Resistance

High thermal shock resistance allows it to withstand rapid temperature changes without cracking or damage. Suitable for equipment subject to frequent startups and shutdowns or large temperature fluctuations.

High Purity and Low Impurity Content

High-purity alumina bricks (e.g., Al₂O₃ content ≥98%) have low impurity content and greater chemical stability, making them more resistant to chemical reactions and corrosion at high temperatures.

Good Electrical Insulation

With excellent electrical insulation properties, they can be used in the manufacture of high-temperature electrical insulation components, such as spark plug insulators and electronic component substrates.

Why are Alumina Ceramics Both Insulators and Conductors?

Common sense suggests that thermal insulation and thermal conductivity should be two distinct entities. For example, cotton is insulating and can be made into cotton-padded clothes, while iron is conductive and can be used in frying pans. The reverse is not true. However, in the real world of refractory materials, we see a different phenomenon: the same material can be used for seemingly opposite purposes: insulation and thermal conductivity. This is the case with alumina ceramics. Alumina ceramics can be made into insulating bricks for high-temperature kilns and heat sinks for electronic products like LED lights.

To answer this question, we need to consider two aspects.

First, as the question above suggests, the thermal conductivity of materials does vary. The most typical example is the difference in thermal conductivity at different temperatures. Take alumina, for example. As the temperature rises, its thermal conductivity decreases. At 1200°C, its thermal conductivity is only about half that at 400°C. However, alumina’s thermal conductivity is not insignificant: at room temperature, it’s 20-30 W/m•K. Even if this decreases by more than half, it still leaves about 10 W/m•K, which is higher than the thermal conductivity of many materials. Therefore, this small change seems insufficient to explain why alumina can both insulate and conduct heat. A more convincing explanation is needed.

Therefore, we need to consider the second, and most important, aspect. Alumina’s ability to both insulate and conduct heat stems from structural changes. In other words, the internal structure of alumina ceramic differs when used as an insulator and a conductor.

alumina bubble bricks — RS Alumina Bubble Bricks

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When used as an insulator, alumina ceramic’s most significant structural characteristics are its porosity and low density. For example, when made into hollow alumina sphere bricks, the thermal conductivity of air is very low, and so is the thermal conductivity of hollow alumina sphere bricks. Some may ask, since air has a very low thermal conductivity, why bother incorporating air into the alumina material? This is because, while air has a low thermal conductivity, it cannot prevent thermal radiation. Just as the thermal conductivity of a vacuum is zero, heat from the sun still travels through it to Earth. Porous alumina blocks both heat conduction and radiation, effectively providing insulation and heat preservation. For example, a study reported that a type of alumina microporous ceramic has a density of only 0.6g/cm3, a porosity of 85%, and a thermal conductivity of only about 0.3W/m•K at 1200℃.

However, when alumina is made into thermally conductive ceramics, the requirements are completely different. The first requirement is high density—the higher the better. High density reduces pores, allowing the ceramic grains to bond tightly together, facilitating heat conduction. The second requirement is high purity. The higher the purity, the higher the thermal conductivity. For example, a ceramic with a 99% alumina content can achieve a thermal conductivity of ~26 W/m•K, while when the alumina content drops to 95%, the thermal conductivity drops to only ~20 W/m•K. This is because ceramics with low alumina content have a higher glass content, and glass has lower thermal conductivity, resulting in a lower overall thermal conductivity. Of course, cost is also a factor in practical applications. While high-purity alumina ceramics offer high thermal conductivity, they also come at a higher price. Therefore, alumina ceramics should be selected based on the product’s requirements, rather than simply pursuing high purity.

In addition to high purity and a dense structure, alumina ceramics used as heat sinks often have specific requirements for their external shape. For example, when making an LED heat sink, it often has a fin structure to increase the surface area and facilitate heat dissipation into the air, thereby achieving better heat dissipation effects.

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