Properties of Fused-Cast Z80 Bricks. Linear Thermal Expansion Rate: The linear thermal expansion rate is one of the key parameters for evaluating the performance of refractory materials. It reflects the dimensional changes a material undergoes in response to temperature fluctuations. This parameter is crucial for the selection of furnace body materials in fused-cast furnaces, as it directly impacts the structural stability and crack resistance of the furnace.
A comparison of the linear thermal expansion rates of Fused-Cast Z80 bricks and Fused-Cast AZS41# bricks reveals that the rates for both materials are quite similar at 1400°C. However, the variation in the linear thermal expansion rate of Fused-Cast Z80 bricks across different temperature ranges is significantly smaller. Consequently, Fused-Cast Z80 bricks present a lower risk of cracking during heating cycles or rapid temperature changes (thermal shock). By selecting Fused-Cast Z80 bricks as the refractory material, it is possible to more effectively mitigate structural damage to glass furnaces caused by temperature fluctuations, thereby enhancing the safety and reliability of fused-cast furnaces throughout their operational cycles.
Bubble Generation Rate. The bubble generation rate of Fused-Cast Z80 bricks stands at 0% at 1300°C and 0.1% at 1500°C—levels considered extremely low. Fused-Cast Z80 bricks exhibit the lowest bubble generation rate among comparable materials, demonstrating excellent efficacy in suppressing bubble defects in glass products caused by the refractory lining. This superior performance is attributed to the uniform elemental composition and density distribution of Fused-Cast Z80 bricks; as they undergo no changes in their phase structure, they are able to consistently maintain an exceptionally low bubble generation rate.
Physicochemical Properties of Fused-Cast Z80 Bricks
As a refractory material utilized in glass melting furnaces, the physicochemical properties of fused-cast Z80 bricks are of paramount importance. A comparative analysis against fused-cast AZS33#, AZS41#, and fused-cast 95% high-zirconia bricks reveals that the Z80 variety is characterized by a low impurity content, as well as high uniformity in apparent porosity and density. During service, the material exhibits no formation of glass phases, bubbles, or needle-like defects; furthermore, it possesses a relatively low coefficient of thermal expansion. Consequently, it demonstrates excellent resistance to corrosion, erosion, and thermal shock. Its comprehensive performance significantly surpasses that of fused-cast AZS33# and AZS41# bricks, placing it on par with fused-cast 95% high-zirconia bricks. However, given that its cost is lower than that of fused-cast 95% high-zirconia bricks, it offers an optimal balance between extending the service life of glass furnaces and managing investment costs.
Microstructure of Fused-Cast Z80 Bricks
The grain size of fused-cast Z80 bricks is significantly smaller than that of fused-cast 95% high-zirconia bricks—a characteristic that exerts multifaceted influences on the material’s overall performance.
First, a smaller grain size results in a higher density of grain boundaries. As key pathways for diffusion, grain boundaries effectively impede ion migration within high-temperature environments, thereby enhancing the material’s corrosion resistance and chemical stability. During the vitrification process of fly ash, fused-cast Z80 bricks demonstrate superior corrosion resistance, thereby minimizing material loss.
Second, a fine and uniformly distributed grain structure contributes to improved overall strength and toughness. Compared to materials with coarse grains, fine-grained materials exhibit reduced internal stress concentration and possess more tortuous crack propagation paths. Consequently, fused-cast Z80 bricks offer superior thermal shock stability and mechanical strength, resulting in a lower risk of fracture. In summary, the fine-grained microstructure of fused-cast Z80 bricks makes them an ideal choice for the refractory lining configurations of fly ash vitrification furnaces.
Fused-cast Z80 bricks possess exceptional resistance to thermal shock and exhibit favorable thermal penetration characteristics. During the furnace heat-up and commissioning process, fused-cast Z80 bricks remain free from cracking caused by thermal shock or linear thermal expansion variations; moreover, their efficient thermal penetration minimizes thermal shock-induced damage to the adjacent outer refractory layers.
Performance of Electrofused Z80/AZS Composite Bricks
Compared to electrofused AZS bricks, electrofused Z80 bricks exhibit superior resistance to corrosion and erosion, as well as excellent reheat performance; however, they come at a higher cost. Conversely, electrofused AZS bricks possess commendable mechanical strength and thermal stability. To extend furnace service life and reduce refractory material costs, a composite brick—comprising electrofused Z80 as the working face material and electrofused AZS as the backing support—has been developed. To ensure a robust bond between the two materials, a method combining physical structural design with the use of a high-temperature binder was adopted. During fabrication, mechanical interlocking was achieved through the precise control of interfacial roughness and geometry, while a high-temperature binder with a zirconia (ZrO₂) content of 90% by mass was selected to fill and reinforce the interface. Upon drying and curing at 200°C, this binder forms a strong bonding layer that enhances the structural integrity of the assembly and improves the composite material’s resistance to thermal shock and chemical attack.
In practical applications, the electrofused Z80/AZS composite brick has demonstrated excellent performance when compared against the electrofused AZS41# bricks and fused-cast 95# high-zirconia bricks produced by a renowned domestic manufacturer. The electrofused Z80/AZS composite brick offers several significant advantages in real-world usage:
(1) It resolves the inherent challenge faced by single-material refractories—namely, the difficulty of simultaneously balancing manufacturing costs with performance requirements.
(2) Through rational material pairing and optimized design, it enhances the cost-effectiveness of the refractory lining configuration, enabling users to achieve a longer furnace service life with a lower initial investment.
(3) It reduces the frequency of maintenance and material replacements, thereby minimizing furnace downtime and generating substantial economic benefits for enterprises.
Binders play a pivotal role in the production of Al₂O₃-SiC-C bricks (alumina-silicon carbide-carbon bricks), significantly influencing the mixing and forming properties of the green mix, as well as the microstructure of the final product. The primary requirements for binders used in Al₂O₃-SiC-C bricks are as follows:
(1) They must exhibit excellent wettability with the Al₂O₃-based refractory aggregates and matrix materials.
(2) They should contain no—or minimal—components that are harmful to human health.
(3) The properties of the mixed batch should remain relatively stable over time, and the extent of chemical reaction with the aggregates should be minimal.
(4) During the heating process of the product, the binder should maintain a high residual carbon yield; furthermore, the polymer structure formed after carbonization must possess excellent high-temperature strength.
Good wettability between the binder and the refractory aggregates and graphite—combined with appropriate viscosity—can significantly enhance the bulk density and mechanical strength of the final product. Moreover, excellent wettability with graphite facilitates the uniform dispersion of graphite particles throughout the product, ideally forming a continuous network structure. Upon carbonization, this network evolves into a continuous carbon-bonded skeleton, thereby substantially improving both the mechanical strength and high-temperature slag resistance of the product. Consequently, the selection of an appropriate binder is of paramount importance. In the manufacture of Al₂O₃-SiC-C bricks, phenolic resins and aluminum dihydrogen phosphate are frequently selected as the binders.
Phenolic resins are synthesized through a polycondensation reaction involving phenolic compounds (such as cresol, phenol, xylenol, and resorcinol) and aldehyde compounds (such as formaldehyde and furfural), catalyzed by acids or bases. In the refractory industry, phenolic resins are widely utilized in the production of carbon-containing refractories due to their high carbon yield, excellent bonding strength—which enhances product mechanical strength—low emission of harmful volatile organic compounds, and high thermal stability. Based on their thermal behavior and structural morphology, they are primarily classified into two categories: thermosetting phenolic resins and thermoplastic phenolic resins.
In the fabrication of Al2O3-SiC-C bricks, thermosetting phenolic resins are typically selected as the binder; they are generally added at a concentration of approximately 5%, resulting in refractory products with relatively low porosity after molding. When subjected to heat in a neutral or reducing atmosphere, phenolic resins undergo thermal decomposition, generating gaseous products such as CO2, CO, CH4, H2, and H2O.
Within the temperature range of 200°C to 1000°C, phenolic resins continuously decompose to generate gases. As these gases volatilize, they create open pores, thereby increasing the apparent porosity of the refractory material and negatively impacting the mechanical strength, oxidation resistance, and slag resistance of carbon-containing refractory products. Consequently, to ensure the optimal performance of refractory products, two key measures must be taken: firstly, selecting a resin binder characterized by low gas evolution and a high carbon yield; and secondly, determining and utilizing an appropriate addition level for the resin.
Aluminum Dihydrogen Phosphate
Aluminum phosphate is widely utilized in the preparation of refractory materials. One of its primary advantages as a binder for refractories is that the resulting bonded structure exhibits excellent properties at intermediate temperatures. Aluminum phosphate is typically synthesized through the reaction of aluminum hydroxide with phosphoric acid. Depending on the degree of neutralization during this reaction, three distinct products can be formed: aluminum dihydrogen phosphate [Al(H₂PO₄)₃], aluminum hydrogen phosphate [Al₂(HPO₄)₃], and aluminum orthophosphate [AlPO₄]. For refractory applications, aluminum dihydrogen phosphate is the preferred choice of binder; its primary mechanism involves the polymerization of reaction products upon heating to a specific temperature, thereby enhancing the intermediate-temperature performance of the refractory product. At room temperature, aluminum dihydrogen phosphate is water-soluble; however, when heated to a certain temperature, it decomposes into aluminum pyrophosphate and aluminum metaphosphate, simultaneously undergoing polymerization reactions.
The formation and polymerization of aluminum metaphosphate [Al(PO₃)₃]n generate strong adhesive forces, thereby imparting strength to the refractory material at intermediate temperatures. As the temperature continues to rise, the aluminum metaphosphate decomposes to yield AlPO₄ and P₂O₅. The P₂O₅ can further react with the Al₂O₃ present in the refractory material to form additional AlPO₄, thereby further enhancing the intermediate-temperature strength of the refractory product.
Below 500°C, the aluminum dihydrogen phosphate primarily undergoes a dehydration process as the temperature increases. As the free water within the refractory product is expelled, the product undergoes shrinkage. During this dehydration phase—prior to reaching 500°C—the overall volume of the product remains relatively stable; however, the porosity of the binder phase increases, while its bulk density decreases. At this stage—due to the gradual precipitation of AlPO₄ and the subsequent formation and polymerization of aluminum pyrophosphate and aluminum metaphosphate—the density of the bonded structure may decrease slightly, yet its mechanical strength increases significantly.
When the temperature exceeds 500°C, the dehydration process within the bonded structure diminishes, and the product’s weight loss becomes negligible. Prior to the onset of high-temperature ceramic bonding within the material, there are no significant changes observed in the product’s porosity or density.
For refractory specimens utilizing aluminum dihydrogen phosphate as a binder, the cold-state strength begins to decline once the temperature surpasses a turning point of approximately 500°C; the strength does not begin to rise again until high-temperature ceramic bonding is established within the interior of the specimen. In contrast to its cold strength, the hot strength of the specimen increased continuously, reaching a maximum value at a temperature of 900°C. This increase in hot strength with rising temperature is likely attributable to the formation of compounds such as AlPO4 and Al(PO3)3 during the heating process; furthermore, the thermal expansion of the material fills the pores, resulting in a denser structure.
Between 900°C and 1000°C, the material’s hot strength declined significantly. This decline may be attributed to two factors: on one hand, the P2O5—generated from the decomposition of aluminum phosphate and aluminum pyrophosphate within the product—begins to volatilize; on the other hand, it may be related to the crystallographic phase transformation of AlPO4. As the temperature rises, AlPO4 undergoes a series of phase transformations: the low-temperature quartz form (low-temperature berlinite) transforms into the high-temperature quartz form (high-temperature berlinite) at 586°C. The high-temperature berlinite form can further transform into the tridymite form at 815°C, and the tridymite form transforms into the cristobalite form at 1025°C. During these phase transformations, the various crystalline forms of AlPO4 undergo volume expansion or contraction; this disrupts the product’s structural integrity, induces cracking, and consequently reduces the product’s bonding strength. When the temperature exceeds 1000°C, aluminum dihydrogen phosphate completely decomposes to yield AlPO4 and P2O5 (note that AlPO4 itself does not undergo decomposition to form M2O3 and P2O5 until reaching 1760°C); once the P2O5 has volatilized, only AlPO4 remains. Calculations based on solid-solution formulas indicate that, at high temperatures, AlPO4 can react vigorously with SiO2 to produce mullite and P2O5.
Overview of Refractory Linings in Gasifiers. Refractory bricks designed for GE coal-water slurry gasification systems constitute a critical component of the gasifier’s reaction chamber; they are required to meet stringent criteria regarding high-temperature resistance and resistance to erosion. These materials are characterized by their corrosion resistance, high mechanical strength, absence of toxic substance leaching, and long service life. The hot-face refractory materials must be capable of withstanding slag attack and corrosion by high-temperature syngas under the normal operating temperature conditions of the gasifier’s reaction chamber. Furthermore, they must endure the erosive forces of high-temperature syngas—as well as the abrasion caused by flowing molten coal slag—should the reaction chamber’s operating temperature rise to 1500°C.
Refractory materials for GE coal-water slurry gasifiers represent one of the key consumable items that significantly impact the long-term, economical operation of the gasifier. However, many gasifiers of this type encounter numerous issues regarding the application of refractory materials. This often results in shortened service lives for the furnace bricks and, in extreme cases during normal production, leads to unplanned system shutdowns caused by localized overheating of the furnace’s steel shell—a direct consequence of refractory lining failure—thereby posing substantial risks to both production continuity and equipment safety. With a specific focus on the application of refractory linings, this discussion examines various aspects—including material selection, masonry requirements, furnace drying and cooling procedures, normal operational protocols, and the root causes of material degradation—and proposes specific improvement measures aimed at extending the service life of the refractory lining.
Refractory Lining Structure of the Gasifier Combustion Chamber
The combustion chamber of the gasifier features a vertical structural arrangement; extending from the furnace throat down to the slag tap, the refractory lining covers various sections, including the dome, the cylindrical shell, and the conical section.
Dome Section
The refractory lining in the dome section consists of three layers, arranged from the interior outward: a hot-face refractory brick layer, a layer of chrome-corundum castable, and a layer of refractory fiber plastic materials. The installation ports for the process burners at the furnace throat are constructed from two layers of refractory material, arranged from the interior outward: an inner layer of high-chrome bricks and an outer layer of alumina hollow-sphere bricks. A thick layer of refractory fiber felt is placed as a cushion between the refractory materials at the furnace throat and the large flange at the furnace head.
Cylindrical Shell Section
The refractory lining in the cylindrical shell section consists of four layers, arranged from the interior outward: a hot-face refractory brick layer—specifically, high-chrome refractory material that interacts directly with the process gas and molten slag generated by the gasification reaction; a layer of chrome-corundum bricks, positioned immediately adjacent to the outer side of the hot-face refractory layer; a layer of alumina hollow-sphere bricks; and a layer of refractory fiber plastic refractory, which serves to fill the space between the alumina hollow-sphere bricks and the steel shell of the gasifier cylinder.
Chrome Corundum Bricks for Refractory Linings in Gasifiers
The refractory lining in the conical section consists of two layers, arranged from the interior outward: a hot-face layer composed of high-chrome bricks; and a layer of chrome-corundum castable positioned between the high-chrome bricks and the conical furnace shell. This castable material is primarily utilized to fill the irregular void spaces situated behind the hot-face refractory bricks.
Material Selection and Masonry Requirements for Refractory Linings
When selecting raw materials for the hot-face bricks (facing the heat source), high-quality materials with a high Cr₂O₃ content must be utilized. The resulting hot-face refractory bricks must meet specific densification standards, exhibiting low porosity, a fine-grained microstructure, and a high bulk density. Furthermore, they must demonstrate exceptional resistance to slag corrosion and superior chemical stability at high temperatures to ensure the overall quality of the refractory lining.
For the back-side lining of the hot-face bricks in the dome and conical sections, chrome-alumina castables should be employed; these materials must possess superior strength, density, and effective insulating properties. During the furnace heat-up phase, this configuration facilitates the formation of a monolithic furnace roof structure, thereby preventing localized overheating and mitigating the risk of “narrow-gas” phenomena (localized flow constriction).
During the masonry construction of the gasifier, refractory expansion joints must be provided in accordance with specified requirements, and all technical parameters—particularly those pertaining to the dome and cylindrical sections—must be strictly adhered to.
The primary technical specifications for refractory brick masonry are as follows: horizontal joints must be <1.0 mm, vertical joints <1.8 mm, vertical alignment (plumbness) within ±5 mm, horizontal alignment (levelness) within ±4 mm, and concentricity within ±5 mm.
Given the unique nature of the reaction media and process conditions within the gasifier, the refractory lining—including expansion joints, nozzle ports, temperature measurement ports, pressure measurement ports, and brick-support areas—requires meticulous design and specialized treatment to ensure the safe, reliable, and long-term operation of the gasifier.
During the masonry process, a specific clearance must be maintained between adjacent refractory lining sections. This intermediate gap should be filled with compressible refractory fiber or plastic refractory material to ensure that adjacent lining sections remain free from compressive stress—and are able to undergo relatively free differential movement—during high-temperature thermal expansion. Additionally, the gaps between adjacent refractory lining sections should be lined with an organic film separator. The joints between hot-face bricks (or those in the insulating/thermal-retention layers) and their immediate lateral neighbors must not form continuous straight lines in the longitudinal direction. Furthermore, the corresponding vertical and horizontal joints across the various layers of the refractory lining—from the innermost hot-face layer outward—must not align to form continuous straight lines that traverse the entire lining structure. The precision of the refractory brickwork at the process burner location must be strictly controlled in accordance with technical specifications. The centerline and concentricity of the process burner must be aligned with the centerline of the furnace body, with a permissible deviation of no more than ±2 mm. The diameter deviation at any given cross-section shall not exceed ±6 mm; the straightness deviation of the furnace lining centerline shall be within ±3 mm; and the total height deviation shall not exceed ±6 mm.
Waterproofing measures must be applied to the interface between the refractory bricks and the castable material to prevent the bricks from absorbing moisture.
Upon completion of refractory brick masonry, the structure must undergo natural ventilation and drying for 2 to 3 days. For newly laid refractory bricks, the initial temperature rise—the “bake-out” process—must strictly adhere to the original prescribed heating curve. This process serves to eliminate free water, crystalline water, and residual chemically bound water present within the refractory bricks and mortar. During the bake-out, improper operation or failure to follow the heating curve can lead to cracking of the refractory lining, a reduction in its structural strength, or even spalling (flaking) of the lining material.
If material charging is to commence immediately after the bake-out, the temperature may be raised from 800°C to the designated charging temperature at a heating rate of less than 50 K/h. If, however, the gasifier requires cooling to ambient temperature after the bake-out, the cooling process must not be abrupt; the rate of temperature decrease should be controlled at no more than 20 K/h. When initiating the bake-out by ignition, one must strictly avoid raising the furnace temperature too rapidly, as this risks cracking the furnace lining. The bake-out procedure must be conducted in strict accordance with operational protocols; specifically, the temperature differential between the upper and lower sections of the gasifier’s combustion chamber must be maintained below 80 K. Should an excessive temperature differential arise, it can be corrected by increasing the induced draft volume to adjust the furnace’s negative pressure, thereby elongating the flame and effectively controlling the temperature distribution. In the event of a flameout, the fuel supply must be immediately cut off, and negative pressure (draft) maintained for 5 minutes. Once analysis confirms that the concentration of combustible gases within the combustion chamber is within safe limits, re-ignition may proceed according to operational protocols. The furnace temperature should be raised at a rate of no more than 30 K/h until it reaches the temperature recorded just prior to the flameout, after which heating should continue in accordance with the prescribed heating curve. Upon completion of the gasifier bake-out, the internal furnace temperature should be measured using a temperature gun; the water supply to the quench ring may be shut off—allowing the furnace to cool naturally—only when the internal temperature has dropped below 140°C.
During a standard bake-out procedure, a heating rate of 40 to 50 K/h is required. The temperature is to be raised to the specified target of 1250°C, followed by a period of constant-temperature holding. Throughout the heating phase, raising the temperature too rapidly is strictly prohibited; furthermore, precautions must be taken to prevent excessive temperatures that could lead to slag accumulation and blockage of the slag tap. In the event of a flameout, immediately close the fuel control valve and the shut-off valve. After fully opening the preheating burner damper and maintaining a negative pressure draft for 5 minutes, reignite the burner. Then, increase the temperature at a rate of less than 50 K/h until the temperature prior to the flameout is reached; only then may the temperature be raised to the charging temperature in accordance with the prescribed heating rate.
The Impact of Process Operations on Furnace Bricks and Measures to Extend Their Service Life
Refractory bricks—particularly those on the hot face—experience wear during operation primarily due to mechanical erosion by coal ash and slag, spalling caused by thermal and chemical stresses, chemical corrosion, high-temperature ablation, and gradual thinning resulting from normal use. This section analyzes the actual operational conditions of refractory bricks.
An analysis of the multifaceted forms of wear experienced by refractory bricks—specifically those on the hot face—during operation reveals the following:
(1) Mechanical Erosion: Molten ash and slag flow across and erode the furnace bricks, leading to severe scouring, deformation, and even detachment of the bricks, often exacerbated by thermal stresses.
(2) Thermal Stress Spalling: Thermal expansion generates circumferential stresses within the hot-face bricks; this causes creep deformation in the refractory material on the hot-face side, subsequently leading to crack formation and spalling.
(3) Joint Erosion: When the gaps between refractory bricks are excessively wide, the refractory mortar within the joints shrinks. Consequently, these gaps become vulnerable to erosion by flowing ash and slag, as well as corrosion and ablation by high-temperature gases. The refractory bricks are gradually eroded—starting from these weak joint areas—resulting in “groove-like” or “pitted” forms of damage.
(4) Impact of Oxygen-to-Coal Ratio: An excessively high oxygen-to-coal ratio prevents the formation of a protective slag layer on the surface of the furnace bricks, thereby negating the “slag-against-slag” protective effect.
(5) Chemical Corrosion by Ash and Slag: Various elements present in the ash and slag react with different parts of the refractory bricks, thereby corroding them. For instance, K and Na tend to accumulate and react on the surface; Al and Fe react at the interface; while Ca and Si react within the interior of the brick structure.
(6) Impact of Coal Type: Different types of coal exhibit distinct viscosity-temperature characteristics. Consequently, the corrosive and penetrative effects of the various constituents within the ash and slag on the refractory bricks also vary. Notably, SiO₂ and CaO possess stronger corrosive potential toward refractory bricks than do FeO and Al₂O₃; therefore, changes in the type of coal utilized have a profound impact on the service life of the bricks.
The interior of the gasifier is dominated by reducing gases—specifically H₂ and CO—meaning that the entire hot-face lining of the refractory structure is in constant contact with these reducing gases. Gases permeate into the interior of the refractory bricks through pores or cracks, reacting with the silicon (Si) and iron (Fe) present within the bricks; this reaction causes the cracks to widen, thereby damaging the structural integrity of the bricks.
During the frequent start-up and shutdown cycles of a gasifier, the furnace chamber’s temperature and pressure undergo drastic fluctuations. During the feeding process, the sudden ignition of the coal slurry leads to a rapid surge in gas volume, subjecting the furnace bricks to significant thermal and mechanical shock. Furthermore, frequent adjustments to the operational load—whether increasing or decreasing it—impose similar stresses on the furnace bricks. When the quality of the coal feedstock is unstable, frequent adjustments to the oxygen-to-coal ratio become necessary. An excessively high oxygen-to-coal ratio can result in an abnormal elevation of chromium levels within the furnace slag. In the event of system anomalies—such as a sudden and drastic rise or fall in pressure—the service life and performance of the refractory bricks are significantly compromised.
Following a gasifier shutdown, when the process burner is being extracted, the rate of temperature decline must be strictly controlled. This control can be achieved by covering the furnace opening with a lid to facilitate a slow, “smothered” cooling process, while simultaneously utilizing an induced draft fan to regulate the negative pressure within the chamber.
The refractory bricks situated in different sections of the gasifier exhibit distinct wear characteristics during operation. Generally, the bricks in the furnace dome (arch) demonstrate a lower rate of erosion and enjoy a longer service life. However, during prolonged periods of low-load operation—or when the volatile matter content of the coal is excessively high—the operational conditions for the dome bricks deteriorate, making them highly susceptible to issues such as spalling (detachment) and cracking. If the process burner is poorly designed, or if the gasifier is operated beyond its rated capacity—resulting in an excessively high velocity of oxygen flow into the furnace—the erosive scouring of the bricks on the hot face (the surface exposed to the flame) is significantly exacerbated. The combustion reaction between the excess oxygen and the coal slurry releases a massive amount of heat, causing the dome to remain under extreme thermal stress for extended periods, thereby accelerating the thermal erosion of the dome bricks. Following the installation of the gasifier’s process burner, a significant annular gap often remains between the burner’s outer diameter and the furnace opening. During the initial stages of feeding, this gap facilitates the formation of intense gas vortices within the dome area; these vortices channel high-temperature gases toward the furnace head, causing the large flange at the furnace head to overheat. This overheating compromises equipment safety and adversely affects the service life of both the furnace-opening bricks and the dome bricks. As operational time accumulates, fly ash or coal slag gradually fills this gap; the resulting reduction in the gap size attenuates the vortex phenomenon, allowing the temperature of the large flange at the furnace head to return to normal levels. To mitigate this issue, measures can be implemented—such as encasing the outer diameter of the burner with castable refractory material or wrapping it with refractory fiber insulation—to effectively reduce the gap between the process burner’s outer surface and the furnace opening. The barrel bricks are significantly influenced by the central oxygen flow, coal ash content, and gasifier load; their erosion rate falls between that of the dome bricks and the cone-bottom bricks. If burner misalignment occurs during operation, or if the gasifier’s concentricity deviates from the controlled range, high operating temperatures can lead to severe localized or generalized erosion, thereby compromising the overall service life of the barrel bricks. The cone-bottom bricks exhibit the highest erosion rate—particularly the slag-tap bricks. In the cone-bottom channel, where the cross-sectional area narrows abruptly and flow velocity increases, the volume of molten ash slag contacting the refractory bricks per unit of time is significantly higher; consequently, erosive wear is most severe in this region, necessitating the highest frequency of replacement. The actual service duration of refractory bricks in various sections of the gasifier is heavily dependent on the specific production conditions and operational practices of each facility, resulting in considerable variations in service life. The extent of refractory damage can be assessed and diagnosed by analyzing the chromium content in the coarse slag; a higher chromium content indicates more severe erosive wear.
Furnace temperature can be inferred by analyzing parameters such as the particle size of discharged coarse slag, the extent of slag stringing, the residual carbon content in fine slag, and the composition of process gas (specifically, the content of effective gas components and methane). Where conditions permit, the furnace chamber temperature can be monitored directly; however, thermometers installed in a molten environment are prone to damage due to erosion by slag and gas flows. Additionally, after a scheduled shutdown, the wear on the furnace lining can be measured and evaluated to facilitate adjustments to process operating conditions, thereby ensuring the stable performance of the refractory bricks.
The precision of equipment installation also significantly impacts the furnace lining. Factors such as the vertical alignment of the gasifier vessel, the levelness of the large flange at the gasifier mouth, the concentricity between the process burner and the gasifier, and the concentricity between the burner’s large flange and the furnace mouth all directly determine whether the burner nozzle experiences off-center spraying during operation.
During normal operation, inspections conducted after each shutdown require the replacement of the furnace lining whenever the overall hot-face brick thickness is found to have diminished to one-third of its original design thickness; this measure prevents the furnace wall from overheating during subsequent operation. The hot-face bricks within the cylindrical section typically suffer from severe localized erosion and corrosion—particularly in the vicinity of the furnace chamber thermometer—rendering them unfit for continued use. However, if the surface condition and thickness of the bricks across a large area remain suitable for continued operation, localized patching and repair techniques can be employed to extend the overall service life of the hot-face lining. The bricks within the conical section are categorized numerically from #1 to #9, starting from the slag tap and extending toward the furnace wall; typically, the bricks most severely affected by erosion and corrosion are those located near the slag tap (bricks #1 through #4). By selectively replacing specific rings of bricks based on their individual condition, the overall service life of the entire conical lining can be effectively extended.
Most existing domestic production facilities prioritize economic efficiency, leading to a continuous drive to increase production output and operational load. Furthermore, newly constructed facilities are trending toward larger scales, resulting in ever-increasing coal feed rates. Under the combined influence of complex coal quality, high ash content, variable slag compositions, and high ash fusion temperatures, the refractory lining is subjected to intensified erosion, corrosion, and slag penetration, consequently shortening the service life of the refractory bricks. Consequently, overcoming the technical challenges associated with refractory materials—and thereby enabling long-duration, continuous operation—has emerged as a central focus of attention within the industry.
Extending the Service Life of Refractory Bricks in Gasifier Linings
Within a coal-water slurry gasifier, coal undergoes combustion reactions at operating temperatures exceeding the ash melting point. The resulting slag assumes a molten, liquid state, flowing downward along the inner walls of the furnace chamber and exiting through the slag tap. Should the furnace bricks or other refractory materials suffer any failure—such as gas channeling, brick dislodgment, or structural damage—localized overheating of the furnace’s steel shell may ensue. This, in turn, can trigger unplanned shutdowns and even pose safety risks involving potential equipment damage. Consequently, the service life of refractory bricks is primarily governed by factors such as material selection, furnace construction, kiln drying, startup and shutdown procedures, load adjustments, post-shutdown cooling protocols, and operator handling practices.
Currently, numerous domestic manufacturers are engaged in the development of refractory materials. Through continuous optimization of both refractory brick compositions and manufacturing processes, product quality has been significantly enhanced and reliably assured. Against the backdrop of fierce competition among peer enterprises—all striving to achieve “energy conservation and consumption reduction” as well as “safe, stable, high-capacity, and optimized operations”—extending the service life of refractory bricks has emerged as a central focus of shared interest among users and a critical direction for ongoing research.
The types and materials of refractory materials used in the glass industry differ from those used in the steel industry. Glass furnace refractory are mainly divided into casting materials, silica materials, and magnesium metal materials, such as silica bricks, clay bricks, high-alumina bricks, sillimanite bricks, mullite bricks, fused mullite bricks, zirconia-corundum bricks, fused corundum bricks, and zirconium-containing refractory bricks, etc. When used in glass furnaces, refractory materials are severely damaged by high temperatures, flames, powder, atmosphere, airflow, and liquid flow, significantly affecting the furnace’s service life. The use of refractory materials in the furnace begins from the start of firing. Improper operation can cause significant, even severe, damage to the refractory materials, requiring special attention. The types of erosion that refractory materials in glass tank furnaces experience during production include:
The powdered feedstock, molten glass, and flame gases within the kiln all corrode refractory materials at high temperatures. Soda ash, sodium sulfate, borates, fluorides, and oxides in the batch react with the refractory surface at high temperatures, forming eutectic or porous substances. These substances then continue to penetrate and diffuse into the brick body through the pores of the refractory material itself or through interfacial replacement reactions, gradually dissolving, peeling off, thinning, deteriorating, and recrystallizing the refractory material. The corrosion mechanisms of the various salts and compounds mentioned above are different; sodium sulfate is much more corrosive than soda ash.
The corrosive effect of the powdered feedstock on refractory materials is mainly manifested in the erosion of the refractory material by the alkaline vapors emitted from the powder at high temperatures. Examples include the melting and corrosion of the surface of silica bricks, internal “rat holes,” and the de-nephelineization in checker bricks. Furthermore, ultrafine powder particles accumulate in the regenerator checker, forming nodules that block the checker pores, and in severe cases, causing the checker bricks to collapse and be damaged, requiring hot repairs. The corrosive effect intensifies with increasing temperature; every 50-60°C increase in melting temperature shortens the service life by approximately one year. The front wall, charging port, front space of the melting section, pool walls, small furnace, and upper grid of the regenerator are all susceptible to corrosion from the refractory powder.
The corrosive effect of molten glass on refractory materials is much smaller than that of molten glass. The phase reaction at the interface between molten glass and refractory materials is complex. Molten glass first dissolves free SO₂ in the refractory material. Mullite dissolves at a slower rate, accumulating at the interface between the molten glass and refractory material. Although small mullite crystals dissolve, larger mullite crystals may even grow during use. After the refractory material is eroded, the molten material in contact with it gains SO₂ and Al₂O₃. The molten material then diffuses into the rest of the molten glass. During diffusion, the composition of the molten material changes, with increased SO₂ and alkali content, while β-Al₂O₃ crystals aggregate at the interface. Therefore, at the interface between the refractory material and the molten glass, the first layer is mullite, followed by the β-Al₂O₃ layer, and then the uncorroded refractory material. The dissolution of the refractory material increases the viscosity of the molten glass, promoting the formation of a more difficult-to-move protective layer on the refractory surface, thus reducing further erosion.
Burn-off
Under prolonged exposure to high temperatures, refractory materials can be damaged by melting (also known as burn-through) or softening and deformation. Localized overheating in a part of the kiln or insufficient refractoriness of the refractory material can cause it to melt. Sometimes, even if the refractoriness is acceptable, a low load softening temperature can lead to softening and deformation over long-term use, affecting the stability and service life of the entire masonry. The severity of burn-off depends on the temperature and the properties of the refractory material. Small furnace burner arches, small furnace legs, tongues, regenerator arches, melting section kiln arches, and breast walls are prone to burn-off.
Cracking
Cracking mainly occurs during the kiln firing stage. During firing, a temperature difference exists within the refractory bricks, generating corresponding mechanical stress. If the heating rate is too rapid, exceeding the allowable ultimate strength of the refractory material, cracks will appear, even breaking into fragments. Electrofused, highly sintered, dense refractory materials are most susceptible to damage. Besides stress caused by temperature differences, the expansion or contraction resulting from changes in the crystal structure of refractory materials also generates stress. When the temperature rises too quickly, the crystal structure changes rapidly, and the volume change is too drastic, generating excessive stress and causing the refractory material to crack. Therefore, the temperature must be increased according to a pre-defined firing curve during kiln firing. After firing, the refractory material is under high temperature for a long time, and its mechanical strength at this operating temperature is much lower than at room temperature. If the mechanical load acting on the refractory material is too large, it will undergo inelastic deformation (similar to the flow of a highly viscous liquid), leading to failure.
Abrasion
When molten glass flows along the refractory material, it has a “dripping water wears away stone” effect, grinding grooves into the refractory material; this is mechanical wear. The main wear area is at the surface of the molten glass. Additionally, it is also clearly visible in areas of circulating liquid flow (especially in turbulent areas). Wear is exacerbated by fluctuations in the liquid surface and changes in liquid flow (such as those caused by temperature fluctuations).
Chemical Erosion
Chemical erosion mainly includes the following four types:
① Erosion caused by the reaction between molten glass and refractory materials.
This type of erosion is exemplified by the wall bricks of the pool that come into contact with molten glass. The most important type of glass is soda-lime-silica glass. Common bottle and jar glass and flat glass belong to this category. This type of glass is mainly composed of SO₂ (approximately 70%), Na₂O (approximately 15%), CaO (approximately 10%), and small amounts of Al₂O₃ and MgO. To improve the performance of the glass, oxides such as K₂O, L₂O, BaO, and PbO can be introduced based on soda-lime-silica glass. Although there are many types of glass, they can all be simplified to consider the SO₂ content, the alkali metal oxide (Na₂O + K₂O + L₂O) content, and the alkaline earth metal oxide (CaO + MgO + BaO) content. As long as the contents of these three oxides are basically the same, the chemical erosion effect on the refractory materials will also be basically the same. However, the chemical erosion of refractory materials by borosilicate glass differs from that of soda-lime-silica glass. Especially low-alkali or alkali-free borosilicate glass, which has a high content of acidic oxides and a high melting temperature, requires the use of special refractory materials.
② Erosion caused by the chemical reaction between glass batch dust and refractory materials.
This chemical erosion mainly occurs in the upper structure of the melting pool and the regenerator in the furnace. The composition of batch dust varies in different locations. The batch dust near the charging port has a composition basically the same as that of the glass. Due to the high density of silica sand particles, the SO₂ content in the batch dust decreases the further away from the charging port. The amount of batch dust is related to many factors. For the same type of glass batch, the amount of dust is greatly related to the raw material density, particle size, and charging method. Adding water, pressing into cakes, or forming into balls can significantly reduce the amount of batch dust.
③ Chemical erosion caused by the reaction between volatiles in the glass batch and refractory materials.
Volatile substances from glass and batch materials are present in the upper space of the furnace and the middle of the regenerator, chemically eroding the refractory materials in these areas. The volatile components are mainly compounds of alkali metal oxides and boron, as well as fluorides, chlorides, and sulfur compounds. These volatiles react chemically with the refractory materials not only in the gaseous phase but also condense into a liquid phase at low temperatures, reacting with the refractory materials. Sodium compounds, in particular, condense at 1400℃. These condensed liquids penetrate into the pores of the refractory materials through wetting and diffusion. This is especially damaging when the upper structure masonry has cracks or incompletely filled mortar joints.
④ Chemical erosion caused by the chemical reaction between fuel ash and combustion products and the refractory materials.
When burning heavy oil and natural gas, ash is virtually non-existent. While V₂O₅ and NO severely corrode refractory materials, their content in heavy oil is generally very low, having little impact on furnace production. Sulfur in heavy oil and producer gas generates SO₂ during combustion, which reacts with R₂O in volatile components to form sodium sulfite. Sodium sulfite reacts strongly with refractory materials, and this influencing factor must be taken into account during glass production.
Physical Erosion
Physical erosion is highly dependent on time and temperature. The most significant physical erosion effects are the scouring action of the molten glass flow and the gravitational force of the refractory material under load. In high-temperature zones, the scouring action of the molten glass flow can multiply the rate of chemical erosion. In low-temperature zones, chemical erosion is minimal, with physical erosion primarily caused by the scouring action of the molten glass flow. In the high-temperature zone of the melting pool, the glass viscosity is low, and the flow is intense. This is especially true with the use of electric flux and bubbling, which further intensifies the flow. The combination of intense scouring and chemical erosion can cause significant damage to the refractory material. Gravity-induced damage mainly occurs in the regenerator checker bricks. With advancements in pool furnace technology, the height of the regenerator has increased, resulting in significant pressure from the checker bricks and grate arches due to the weight of the checker. When chemical erosion damages these checker bricks, stress concentration at the damaged areas leads to further collapse, ultimately causing the entire checker to collapse.
As an alumina-silica refractory material, silica mullite bricks possess superior thermal shock resistance, a high load softening temperature, and excellent erosion resistance, which are key reasons why they can be used in all sections of cement kilns except the firing zone.
Of course, compared to high-alumina bricks, the superior properties of silica-mullite bricks are due to the presence of silicon carbide components. Silicon carbide, as a non-oxide material, has excellent high-temperature mechanical properties, combining erosion resistance and thermal shock resistance. The main raw materials used in silica mullite bricks are as follows:
High-Alumina Bauxite
High-alumina bauxite is an important mineral resource with significant strategic and practical value worldwide. China has bauxite reserves of 2.5 billion tons, accounting for 2.4% of the world’s total, indicating abundant reserves. China’s bauxite is mainly of the gibbsite-kaolinite type. The ore has high Al₂O₃ and SiO₂ content and low Fe₂O₃ content, making it suitable as a refractory raw material. The mineral composition of high-alumina bauxite is mainly gibbsite and kaolinite. Gibbsite has the chemical formula AlO(OH), belongs to the orthorhombic crystal system, has a density of 3.3~3.5 g/cm³, and a Mohs hardness of 6~7. Kaolinite has the chemical formula Al₂O₃·2SiO₂·2H₂O, is a triclinic silicate mineral, and is also a type of clay mineral. It has strong water absorption, good plasticity, a density of 2.60~2.63 g/cm³, and a hardness of 2~2.5. The structural characteristics of high-alumina bauxite are described below.
Currently, approximately 65% of refractory materials in my country are alumina-silicon-based products, and about 65% of these products use high-alumina bauxite as raw material. Therefore, high-alumina bauxite is an extremely important raw material for the production of Al2O3-SiO2-based refractory materials. The phase composition of high-alumina bauxite clinker consists of corundum, mullite, and cristobalite. Its chemical composition, bulk density, water absorption rate, and mineral uniformity have a decisive influence on the performance of the high-alumina refractory materials produced. High-alumina bauxite clinker is classified into nine grades according to its different physicochemical properties.
Silicon Carbide
Silicon carbide (SiC) is a covalent compound with atoms bonded by covalent bonds. Due to its strong covalent bonds, this material possesses excellent physical properties at both room temperature and high temperatures. Silicon carbide has high refractoriness, reaching 2600℃ in a reducing atmosphere. It has high hardness (Mohs hardness 9~9.5), high thermal conductivity (64.4 W/(m·K) at 500℃), and a low coefficient of thermal expansion of 5.68×10⁻⁶/℃ (1000~2400℃). It also possesses excellent resistance to corrosion, impact, and oxidation.
Although silicon carbide has very good performance at both room temperature and high temperatures, it is extremely rare in nature. Industrially required silicon carbide is mainly synthesized artificially. There are five main methods for artificially preparing silicon carbide:
1) Carbothermic reduction of silicon dioxide.
2) Elemental synthesis of silicon carbide.
3) Molten salt method for producing silicon carbide.
4) Preparation of silicon carbide from gaseous compounds.
5) Preparation using steam-liquid-solid phase methods, etc.
Among these, silicon carbide used in the industrial production of refractory materials is often prepared using the SiO2 carbon reduction method. When reducing SiO2 with carbon in an electric resistance furnace, below 1250℃, the generated CO cannot oxidize silicon carbide. At higher temperatures, the generated CO then reacts with SiO2, further reducing SiO2 and precipitating free carbon on the crystal surface.
When silicon carbide is introduced into aluminosilicate refractories, it partially oxidizes during firing to form SiO2, creating a glassy phase of a certain thickness on the surface of the product. Due to the oxidation of the surface silicon carbide, a weak reducing atmosphere is created inside the brick. The internal silicon carbide is activated and oxidized, generating SiO gas. When SiO diffuses to the interface, it is re-oxidized back to SiO2. This SiO2, along with other impurities, forms a glassy phase that blocks pores, inhibits further oxidation, and slows down erosion. In addition, some of the SiO2 generated by the oxidation of silicon carbide will also react with the excess Al2O3 in the material at a certain temperature to form mullite.
Silicon carbide also possesses high thermal conductivity, which, when added, improves the material’s thermal conductivity. Furthermore, silicon carbide has a low coefficient of thermal expansion, very close to that of mullite, significantly reducing internal stress generated during rapid temperature changes. This greatly promotes the improvement of the material’s thermal shock resistance. On the other hand, excessive SiC oxidation leads to an excessively thick oxide layer. The oxidation process also generates SiO gas; increased internal gas production weakens the material’s internal structure, potentially damaging it. Excessive silicon carbide oxidation not only reduces the material’s density but also produces more SiO2, whose crystal transformation is highly temperature-sensitive, negatively impacting thermal shock resistance. Therefore, in certain operating environments, adding an appropriate amount of antioxidant is essential to prevent excessive SiC oxidation. One commonly used antioxidant is Si powder. Si, as an element, is highly reactive and oxidizes before SiC to form SiO2. Therefore, as the amount of Si added increases, the oxide layer thickness tends to decrease. However, when the amount of Si added continuously increases beyond 2%, the amount of SiO2 generated by its oxidation increases, leading to excessive secondary mullitization in the material, excessive volume expansion, resulting in a loose material structure, reduced bulk density, and increased porosity. Another commonly used antioxidant is metallic Al powder. Similarly, metallic Al powder will be oxidized to Al2O3 earlier than SiC, inhibiting silicon carbide oxidation. The Al2O3 and SiO2 generated by the oxidation of metallic Al and SiC respectively will begin the mullitization reaction at around 1400℃.
Furthermore, adding metallic aluminum and elemental silicon simultaneously as antioxidants to the product is extremely effective in inhibiting the over-oxidation of SiC. Although elemental Si has a high melting point of 1414℃, its eutectic temperature with metallic Al is only 577℃. Therefore, when both are added as antioxidants in combination, a liquid phase is generated at a lower temperature, which is conducive to ion diffusion and transfer, thereby reducing the reaction formation temperature.
Mullite-High-Silica Glass Multiphase Material
Due to the low sintering temperature of clay clinker, its phase composition generally contains 10%–25% cristobalite. In the last century, foreign countries began to explore ways to dissolve cristobalite from aluminosilicate refractory clinker into the glass phase, resulting in mullite-high-silica glass multiphase materials with a mullite network structure, by focusing on preparation processes and the introduction of additives.
Mullite-high-silica glass multiphase materials are a new type of refractory material composed of crystalline mullite and an amorphous silica-rich glass phase. They possess excellent properties such as a high load softening temperature, a low coefficient of thermal expansion, and excellent thermal shock resistance. Based on the content of alkali metal oxide impurities, mullite-high-silica glass multiphase materials can be divided into two main categories: high impurity content (R₂O 0.2%–2.0%) and low impurity content (R₂O < 0.2%). As a high-SiO₂ content mullite composite, its phase does not contain cristobalite. Furthermore, its tightly bound mullite network structure and high-viscosity silica-rich glass phase significantly improve the material’s performance at high temperatures, particularly its thermal shock resistance.
A mullite-high silica glass multiphase material was prepared using natural kyanite mineral. The sintering temperature was 1500–1600℃, resulting in large mullite grains and a high mullite content. In this material, the mullite content was 75%–80%, and the glass phase was 20%–25%, with relatively uniform phase distribution. The prepared kyanite-based mullite had a bulk density of 1.99–2.11 g/cm³. However, its room-temperature compressive strength reached 163–264 MPa, significantly outperforming similar materials made from kaolin or high-alumina bauxite.
By introducing appropriate additives, clay was calcined to produce a quartz-free mullite-high silica glass phase material. Experiments have shown that using potassium- and sodium-rich natural minerals like feldspar as additives is more beneficial for the synthesis of mullite-high silica glass phase materials. This is because these minerals enable clay to sinter at lower temperatures, are inexpensive and readily available, and help maintain the stability of the mixture’s composition. However, the amount added should not be too large, otherwise it will reduce the material’s refractory properties.
Kyanite-based mullite (KBM) is a type of mullite-high silica glass multiphase material. In China, it is produced by using kyanite ore as the starting material, adding additives, wet grinding, pressure filtration, vacuum extrusion molding, and finally calcination at 1500℃~1650℃. Based on the different Al2O3 contents of the synthesized kyanite-based mullite, it can be divided into series such as KBM45, KBM50, KBM55, and KBM60.
Among them, the basic raw material used for synthesizing KBM45 and KBM50 is low-grade kyanite ore with an Al2O3 content of about 45%. KBM50 incorporates a small amount of industrial alumina to adjust its composition, and its synthesis temperatures are 1500℃ and 1600℃, respectively. KBM55 and KBM60 use medium-grade kyanite ore with an Al2O3 content of approximately 50% as raw material. Different amounts of industrial alumina are added to adjust the Al2O3 content, along with different amounts of composite sintering aids. Their synthesis temperatures are 1600℃ and 1650℃, respectively. Partial physical properties of the four kyanite-based mullite raw materials are also described.
Guangxi White Clay
Guangxi white clay is a type of soft kaolin clay. Its main chemical components are: SiO2 content 45.3%~51.6%, Al2O3 content 26.0%~36.8%, Fe2O3 content 0.65%~2.20%, and K2O+Na2O <1.50%. The main mineral composition of Guangxi white clay is disordered kaolin, sometimes reaching 90%, followed by quartz, generally below 30%. It also contains trace amounts of ilmenite and other minerals. As a binder in refractory materials, Guangxi white clay possesses excellent fluidity, plasticity, and binding properties, making it the highest quality soft refractory clay discovered in my country to date. Guangxi white clay is widely used in the refractory materials industry, including in the production of clay-bonded castables, sprayed refractory materials, refractory bonding clays, and gunning compound additives.
In the high-temperature smelting process of an electric arc furnace with intense charge movement, the refractory lining of the furnace is an essential guarantee for the normal operation of the process. Based on the type of slag and the properties of the refractory materials used, electric arc furnaces can be divided into acidic slag electric arc furnaces and basic slag electric arc furnaces. Most of the aforementioned electric arc furnaces used in steelmaking are basic slag electric arc furnaces, with a slag basicity greater than 1. Since acidic slag does not have desulfurization and dephosphorization effects, the application of acidic slag electric arc furnaces is currently limited in my country. Currently, the furnace linings mostly use basic refractories with good resistance to basic slag, such as magnesia-carbon bricks and magnesia-chrome bricks. Therefore, my country produces a very large amount of basic slag as a byproduct each year. It is estimated that in 2019, the slag produced in my country’s electric arc furnace steelmaking production was approximately 0.2 billion tons. Such a large accumulation of slag, if not properly handled, could cause environmental pollution due to the heavy metals such as chromium, lead, and cadmium it contains, posing a significant potential threat to biological health and the balance of the ecological environment.
Refractory Materials for Electric Arc Furnace
Refractory Materials for Lining Acidic Slag-Based Electric Arc Furnaces
The slag in acidic slag-based electric arc furnaces is acidic, and the lining uses acidic or neutral refractory materials. Compared to basic slag, acidic slag is more environmentally friendly. When the SiO2 content in acidic slag is high, it forms acidic silicate slag with a microstructure similar to glass. This is an amorphous, non-crystallizing material that cools slowly, i.e., glassy slag (hereinafter referred to as “glass slag”). Some studies suggest that when amorphous silicate materials are corroded in an acidic environment, the inconsistent dissolution of oxides causes the silicate surface to form a silicon-rich protective layer. This fixes harmful metals in the slag, and the higher the degree of vitrification (amorphous material content), the better the fixation effect. This significantly reduces the risk of environmental pollution and harm to animal and plant health. Based on this characteristic, many industrial waste treatment processes, such as leather industry waste treatment and waste incineration fly ash treatment, are suitable for this high-temperature vitrification process, which is an effective method for fixing metal pollutants. Meanwhile, this glass slag can also be reused as a raw material for preparing microcrystalline glass. The vitrification process of acidic slag has been proven to be a successful example of the harmless treatment and reuse of waste resources.
Acidic slag-based electric arc furnace smelting can be used for the recovery and harmless treatment of valuable metals in secondary resources. One very important smelting process is the electric arc furnace smelting of waste automotive exhaust purification catalysts. Waste automotive exhaust purification catalysts mainly consist of a carrier component (composed of oxides such as γ-Al₂O₃ or cordierite) and an active component (composed of three precious metals: platinum, palladium, and rhodium). After crushing and finely grinding the catalyst, it is mixed with trapping metals, flux, and a small amount of coke, granulated, and then smelted in an electric arc furnace. This utilizes the principle that trapping metals such as iron or copper have a strong affinity for platinum group metals in the catalyst at high temperatures (above 1420 °C). This process enriches the precious metal active components in the catalyst within the molten metal, while the catalyst support components, along with added fluxes such as SiO2 and CaO, form slag that enters the glass slag, achieving efficient and harmless recovery of valuable metal resources. Depending on the attractant and flux composition, the electric arc furnace operates at varying temperatures, reaching up to 1600 °C. At this temperature, the scouring motion of the furnace charge on the refractory material is quite intense. Furthermore, carbon is added during smelting to reduce the oxides of the target metal, creating a reducing atmosphere in the furnace, thus placing high performance requirements on the furnace lining refractory material of the electric arc furnace. Existing refractory materials have a short service life in the aforementioned electric arc furnaces; in pilot-scale small electric arc furnaces, the lining needs to be replaced approximately every two months, limiting the industrial application of this process. This paper addresses the problem of short lining service life in electric arc furnace smelting of acidic slag-based refractory materials, analyzing the mechanism of acidic glass slag corrosion of refractory materials. It also reviews the development and research of refractory materials suitable for high-temperature acidic slag-based electric arc furnaces both domestically and internationally in recent years. The feasibility of these materials in high-temperature acidic slag-based electric arc furnaces was analyzed, and the future development trend of refractory materials for acidic slag-based smelting furnaces was prospected.
The Corrosion Mechanism of Acidic Glass Slag on Refractory Materials
The corrosion of refractory materials by molten slag is a complex process involving many influencing factors. These include the chemical composition and pH of the molten slag and refractory materials, the viscosity and surface properties of the molten slag, the melting atmosphere, the physical properties of the refractory materials (porosity, high-temperature flexural strength, etc.), and the solubility limits of their components in the molten slag (i.e., the concentration of refractory components in the molten slag at saturation). Furthermore, unlike other melting furnaces, electric arc furnaces use a high-temperature electric arc to heat the furnace charge, and the resulting electromagnetic field significantly affects the properties of the molten slag. For example, it alters the wettability and penetration kinetics of the molten slag on refractory materials, influencing the formation and distribution of different phases, thus affecting the erosion of refractory materials by the molten slag. Currently, there is little research, both domestically and internationally, on the influence of the electromagnetic field of electric arc furnaces on the erosion of refractory materials by acidic glassy molten slag. The erosion of refractory materials by glass slag can be divided into two types: penetration erosion and chemical corrosion.
Current Status of Research on Refractory Materials for Acidic Slag-Based Electric Arc Furnaces
Currently, research on the slag erosion resistance of refractory materials largely relies on high-temperature erosion resistance tests to simulate the erosion of refractory materials by molten slag during industrial production, in addition to using refractory materials that have failed in actual industrial production. The quality of refractory material’s slag resistance is evaluated using indicators such as the rate of mass change before and after the test, the erosion rate of the molten slag, and the penetration rate. High-temperature erosion resistance tests can be divided into two types: static and dynamic methods. The difference lies in whether an external force is applied to keep the molten slag flowing relative to the refractory material. The most widely used static method is the static crucible method. This method requires simpler equipment and operation, and the molten slag only statically penetrates and dissolves the refractory material. It is suitable for refractory materials whose erosion is mainly caused by the dissolution of components in the molten slag. Dynamic erosion resistance tests are more suitable for refractory materials with more complex erosion processes.
Application of Refractory Materials in High-Temperature Acidic Slag-Based Electric Arc Furnaces (1600 ℃)
Based on the corrosion mechanism of acidic glassy molten slag (glass slag) on refractory materials, and assuming their potential application in acidic slag-based electric arc furnaces, this paper reviews the research results on the resistance of several refractory materials (Al2O3-SiO2 materials, Al2O3-SiO2-ZrO2 composite materials, chromium-containing materials, densified zirconium (chromium)-containing materials, carbonaceous and carbide materials) to glass slag corrosion, summarizing their advantages and disadvantages. The feasibility of applying these refractory materials in high-temperature acidic slag-based electric arc furnaces (1600 ℃) was discussed, and the following conclusions were drawn:
(1) Al2O3-SiO2 refractory materials have poor high-temperature corrosion resistance and are not suitable for high-temperature acidic slag-based electric arc furnaces.
(2) Chromium-containing refractory materials have excellent resistance to glass slag corrosion, but due to the toxicity of Cr, which can easily cause environmental hazards, their use should not be expanded.
(3) Carbonaceous and carbide refractories have high thermal conductivity and poor insulation performance, which can lead to a significant increase in energy consumption of electric arc furnaces.
(4) Al2O3-SiO2-ZrO2 composite refractories have good resistance to glass slag corrosion, and the densification process further enhances their corrosion resistance. In addition, the feasibility of using 41# (containing 41% ZrO2) fused cast zirconia-corundum bricks in high-temperature acidic slag-based electric arc furnaces (1600 ℃) has been preliminarily demonstrated.
Currently, with the gradual increase in public awareness of environmental protection and the strict implementation of national environmental protection policies, researchers will focus on improving and developing environmentally friendly and energy-saving refractory materials without affecting service life. The structure and properties of the slag in high-temperature acidic slag-based electric arc furnaces are similar to those of the glass melt in glass melting furnaces and other vitrification furnaces. The development of refractory materials for high-temperature acidic slag-based electric arc furnaces can fully draw on the industrial application experience of both. It is foreseeable that, represented by 41# fused cast zirconium corundum refractory, densified zirconium-containing materials with excellent resistance to glass melt corrosion will become a widely used furnace lining material for high-temperature acidic slag-based electric arc furnaces.
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A seat brick is a refractory brick installed at the bottom of a steel ladle to fix the nozzle brick. The well block refractory brick is square in shape, hence also called a square brick. Its functions are to fix the nozzle position, facilitate nozzle removal and installation, support the lower end of the stopper rod during pouring, and ensure that the stopper rod slides along the curved surface towards the nozzle after pouring to cut off the flow.
Application and Classification of Well Block Refractory Bricks
Well block refractory bricks are mainly used in conjunction with nozzles in continuous casting tundishes. They are mostly used at the bottom of the ladle and tundish to protect the internal nozzles and permeable bricks. Well block refractory bricks have high corrosion resistance and are used in conjunction with zirconium sizing nozzles.
Initially, well block refractory bricks could be made of clay, high-alumina, or unfired high-alumina materials. Later, well block refractory bricks were classified according to changes in the usage environment and the materials used:
(1) Al2O3-Cr2O3 well block refractory bricks. Original high-alumina well block refractory bricks had poor heat spalling resistance. Using corundum as the main raw material, adding appropriate amounts of alumina, spinel, chromium oxide, etc. to the matrix can produce Al2O3-Cr2O3 well block refractory bricks with good heat spalling resistance and strong corrosion resistance. This material has a long service life and can be used synchronously with the ladle. Currently, most well block refractory bricks used are Al2O3-Cr2O3 well block refractory bricks.
(2) Magnesia well block refractory bricks. Precast well block refractory bricks were prepared by adding fused corundum powder (below 1μm) and magnesium oxide to the original alumina base material. Because the material is an alumina castable containing magnesium oxide, the cement content is extremely low, increasing the service life by 40%. The main reasons are: the fine corundum powder containing magnesium oxide densifies the matrix, improving erosion resistance; the matrix density and low cement content increase the material’s high-temperature strength, enhancing its resistance to thermal shock and mechanical spalling; and the magnesium oxide and alumina in the matrix largely form spinel at high temperatures, thus inhibiting slag penetration and improving erosion resistance. The magnesia base bricks are precast, reducing brick joints and simplifying construction.
Characteristics of Nozzle Well Block Refractory Bricks
High-Temperature Corrosion Resistance: Refining steel ladles requires extremely strict temperature and time control, often exceeding 1750℃.
High-Temperature Abrasion Resistance: Forced stirring is used in various ladle refining methods, which severely impacts the high-temperature abrasion resistance of the well block refractory bricks.
Well Block Refractory Bricks Installation
Before installing the well block refractory bricks at the taphole, the bottom should be leveled with ramming material to ensure the taphole cylinder and the masonry layer are on the same plane. When laying separate well block refractory bricks, the mating surfaces of each brick must be evenly coated with mortar. The inner holes of the well block refractory bricks must be uniform; on-site correction is necessary if required to ensure proper installation of the taphole tube bricks. Considering that the well block refractory bricks consist of multiple pieces, ramming material should be filled from both sides simultaneously around the taphole well block refractory bricks to prevent rotation.
Main Components of Permeable Bricks, Nozzle Well Block Refractory Bricks, and Castables
In the steelmaking industry, steelmakers commonly use refractory materials such as permeable bricks, nozzle well block refractory bricks, electric furnace covers, castables, guide sand, and magnesia-carbon bricks in their ladles and refining furnaces. These refractory materials differ significantly in their main components and additives. Chemically, refractory materials are composed of minerals, such as corundum, mullite, and magnesia. Their main components include alumina and magnesia.
The main components of refractory materials are the matrix components that constitute their refractory properties and form the basis of their characteristics, directly determining the properties of the finished refractory product. For example, permeable bricks require high-quality ore and are manufactured through strict and reasonable processes to ensure that the service life of the permeable bricks used by steelmakers meets requirements. The main components of refractory materials can be oxides (alumina and magnesia, etc.) or elements or non-oxide compounds (carbon, silicon carbide, etc.).
Based on the properties of their main components, refractory materials can be classified into three categories: acidic, neutral, and basic. Acidic refractories mainly contain acidic oxides such as silicon dioxide, with silicic acid or aluminum silicate as the primary components. They will form salts under high temperatures and alkaline conditions. Basic refractories mainly contain magnesium oxide and calcium oxide. Common refractory products include guide sand and ladle slide plates. Neutral refractories are strictly speaking carbonaceous and chromium-based refractories. High-alumina refractories (alumina content greater than 45%) tend towards acidic neutrality. Chromium-based refractories are alkaline but tend towards neutrality. Common high-alumina refractories include permeable bricks, nozzle well block refractory bricks, and electric furnace covers.
Rongsheng Refractory Materials Factory researches, develops, produces, and sells permeable bricks, nozzle well block refractory bricks, castables, and other refractory materials. With patented formulas, unique designs, and strict adherence to every process standard, we provide high-quality refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng to get free samples and quotes.
Glass Kiln Lip Bricks are a relatively special type of irregularly shaped refractory material. Their service life is affected by every aspect, including the raw material composition, forming and manufacturing process, and assembly. Especially during the hammering and ignition processes, the bricks must withstand temperature differences of hundreds of degrees Celsius. Therefore, whether using a single brick or combining several lip bricks, cracking is a potential problem. The causes of cracking in lip bricks and preventative measures are listed below.
① The brick material itself has low compressive strength, poor thermal stability, and a high coefficient of thermal expansion. When subjected to thermal shock, the tensile strength of the brick is less than the expansion thermal stress, causing it to break. To eliminate this factor, in addition to designing a good formula and selecting good materials, the contact surfaces between the fixing screws and the retaining iron used to fix the lip brick and the lip brick should be padded with flexible material, and the iron parts should not directly contact the brick body.
② The firing temperature is low, and the dehydration stage of crystal water is short. During the high-temperature dehydration process of the crystal water inside the brick body, the original structure is destroyed and new minerals are generated. To avoid this situation, in addition to avoiding components with a large amount of mineral structural water when determining the lip brick formula, the brick blank must be fully dried after casting before being fired in the kiln. Furthermore, the heat preservation time should be increased in the dehydration temperature range of crystal water according to the mineral composition.
③ The lip brick is backed by the tail brick, and there are fixing screws on the front and sides acting on the brick body. When heated, forces from four directions act on the local area of the brick body. The fixing screws restrict the expansion and movement of the brick body, but they can also easily cause the brick body to crack under external forces. Preventive Measures: After the lip brick is fixed to the overflow port support, secure the support with jacking screws and bolts, but do not tighten it completely; leave an expansion gap. Then, heat it with fire, slowly raising the temperature to above 700℃ to allow the lip brick to fully expand. Tighten the jacking screws again before the lead-in.
④ Insufficient pre-use baking time prevents the removal of free water from the brick. To eliminate this factor, place the lip brick in a high-temperature environment before use to fully remove free water, or preheat the kiln during on-site construction.
⑤ Using deformed lip brick supports may cause cracks or even breakage of the lip brick. Therefore, deformed lip brick supports, especially those with deformed contact surfaces with the lip brick, should not be used.
Lip Brick Replacement
After a period of operation in a rolled glass production line, if defects appear in the glass due to erosion or wear of the lip brick, it needs to be replaced.
Before replacing the lip brick, it must be baked at a high temperature for at least 72 hours to remove free water remaining in the brick due to processing, transportation, or other reasons. Baking can be done using a natural drying method: the brick is placed next to the kiln, relying on the heat emitted by the kiln for baking. Because it is natural baking, it requires a long time and can only remove some free water, so the baking is not thorough. Alternatively, a preheating furnace baking method can be used. A kiln is built with refractory materials, and the lip brick is heated according to a heating curve, baked at 200-300℃ for 24 hours, and then assembled to the overflow port. After the calender is positioned and installed, the temperature is further increased to 1100℃ for the lead-in operation. This method requires specialized hoisting and installation tools. It is also more difficult to operate at high temperatures, but it ensures that the lip brick will not crack. Online baking can also be used: after the lip brick and calender are positioned and installed at the forming port, they are baked using a spray gun. This method uses gradual heating, allowing sufficient time for the free water and crystal water in the lip brick to be fully drained. This method reduces the probability of the lip brick cracking or even shattering.
Before replacing the lip brick, prepare the following tools: pipe wrench, Allen wrench, wrench, pliers, level, measuring tape, 1-3mm sheet metal, square timber, mullite fiber paper, etc.
When removing the lip brick from the calender, first use a sledgehammer and pneumatic hammer to remove the old lip brick. Then, use an electric scraper to clean the tail brick thoroughly, ensuring there is no residual glass or unevenness on the surface. After applying a 3-5mm thick layer of high-temperature mullite fiber paper to the contact surface of the tail brick, assemble the lip brick on the lip brick support as required, or install the lip brick already assembled on the support at the tail brick location. Finally, push the calender into position, check for any problems, and then slowly heat the lip brick to the guide plate with a spray gun to complete the replacement operation.
Glass Kiln Lip 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.
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.
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.
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.
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.
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:
When cutting lip bricks, leave approximately 5mm of length for processing.
Use a pneumatic brick grinder for rough processing, and an electric angle grinder with a diamond wheel for fine processing.
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.
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.
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.
Handle lip bricks gently, ensuring the lip tip does not touch the ground. Lay cardboard on the ground to prevent damage.
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.
