Preparation device and method of magnesia refractory bricks

Abstract

The application discloses a preparation device and method of magnesia refractory bricks, and belongs to the technical field of refractory material preparation. The application designs a preparation process of ingredient mixing, vibration-assisted multi-stage variable-pressure forming, drying, atmosphere feedback self-adaptive sectional sintering and partitioned speed control cooling, cooperatively introduces rare earth composite sintering additives, nano spinel additives and surface-activated stabilized zirconia additives in the ingredients, and respectively realizes low-temperature densification, grain pinning refinement and phase change toughening. The forming process adopts a three-stage variable-pressure procedure of pre-pressing, vibration degassing and main pressing, and closed-loop control is carried out based on a pressure distribution uniformity coefficient to ensure the uniformity of the body density; the sintering process dynamically adjusts the heating rate by online detection of the carbon monoxide concentration; and the cooling process controls the cooling rate in sections to ensure uniform phase change. The product obtained by the application has the advantages of high density, excellent strength, good thermal shock resistance and high qualified rate.

Description

Technical Field

[0001] This invention belongs to the field of refractory material preparation technology, specifically relating to an apparatus and method for preparing magnesia refractory bricks. Background Technology

[0002] Magnesia refractory bricks are alkaline refractory materials widely used in steelmaking converter linings, ladle bottoms, and other high-temperature metallurgical equipment. As steel metallurgical processes develop towards higher efficiency, ultra-high temperature, and longer service life, more stringent performance requirements are being placed on the density, high-temperature mechanical strength, thermal shock resistance, and fracture toughness of magnesia refractory bricks.

[0003] However, existing methods for preparing magnesia refractory bricks still have unresolved technical problems in each of the forming, sintering, and cooling processes. In forming, traditional hydraulic brick presses typically use a unidirectional, single-stage pressing method. During pressing, due to the bridging effect and friction between particles, the pressure transmission of the mixture within the mold exhibits a significant attenuation from the pressing end to the distal end along the pressing direction. This results in uneven density distribution of the green body along its height. Simultaneously, closed air bubbles between particles are difficult to fully expel during a single pressurization, remaining inside the green body. These uneven density distributions and residual porosity defects easily lead to warping, delamination, and other defects during subsequent sintering, reducing the batch firing pass rate. Furthermore, existing forming processes lack online real-time evaluation methods for the uniformity of the green body density distribution, making it impossible to promptly identify and correct substandard green bodies during the forming stage. In sintering, most existing processes use preset fixed heating curves, with the heating rate remaining unchanged throughout the sintering process regardless of the actual atmosphere within the kiln. Within the pyrolysis temperature range of the organic binder, the decomposition of organic matter generates a large amount of gas. Due to differences in binder dosage, body thickness, and kiln loading density, the actual gas production rate varies significantly between different batches of green bodies. A fixed heating curve cannot accommodate these batch-to-batch differences, easily leading to a gas production rate exceeding the safe gas escape capacity of the green body. This results in gas pressure buildup inside the green body, causing cracking defects. Regarding cooling, traditional processes typically shut off the heating elements after sintering, allowing the green body to cool naturally. The cooling rate is not precisely controlled, especially within the critical temperature range for the phase transformation of stabilized zirconia. Excessive cooling rates and uneven temperature distribution cause inconsistent degrees of phase transformation in different parts of the green body, resulting in localized volumetric strain differences and thermomechanical stress concentration. This not only weakens the toughening effect of the phase transformation but may also induce microcracks, reducing the fracture toughness and thermal shock resistance of the finished product. In terms of raw material formulation, traditional magnesia refractory bricks mainly rely on increasing the sintering temperature to achieve densification. Higher sintering temperatures lead to increased energy consumption, and at high temperatures, magnesia grains are prone to abnormal growth. The coarse grain structure is detrimental to improving thermal shock resistance. While existing technologies include methods for adding sintering aids or toughening additives individually, there are still shortcomings in the synergistic effect of multiple functional additives and the uniform dispersion of additives in the matrix, which limits the further improvement of the overall performance of magnesia refractory bricks.

[0004] Therefore, designing a preparation apparatus and method for magnesia refractory bricks that solves the above problems is of great significance. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a method for preparing magnesia refractory bricks, comprising the following steps:

[0006] S1: Ingredient mixing: After high-purity fused magnesia is graded according to particle size, rare earth composite sintering aid, nano MgAl2O4 spinel powder, surface-activated stabilized ZrO2 powder and organic binder are added in sequence and mixed evenly to obtain the mixture.

[0007] S2: Vibration-assisted multi-stage variable pressure molding involves adding the compound to a pressing mold and sequentially executing a pre-pressing stage, a vibration venting stage, and a main pressing stage. During the pressure holding period in the main pressing stage, pressure at each measuring point is collected in real time using a pressure sensor array arranged at different height layers of the pressing mold, and the pressure distribution uniformity coefficient is calculated. When the pressure distribution uniformity coefficient is lower than a set threshold, the process returns to the vibration venting stage and repeats the vibration venting stage and main pressing stage sequentially until the pressure distribution uniformity coefficient is not lower than the set threshold, at which point the mold is removed to obtain the billet.

[0008] S3: Dry the green body until the residual moisture content meets the sintering requirements to obtain a dried green body;

[0009] S4: Atmosphere feedback adaptive segmented sintering, the dried green body is loaded into a sintering kiln with online gas detection function, and sintering is completed in sequence through a low-temperature drying section, an organic matter decomposition section, a degassing and temperature stabilization section, a high-temperature sintering section and a heat preservation section; in the organic matter decomposition section, the CO concentration in the kiln is detected in real time by an online gas analyzer, and the heating rate of this section is dynamically adjusted according to the detected CO concentration.

[0010] S5: Zoned controlled cooling. After sintering, the refractory bricks are cooled sequentially in three temperature zones: high-temperature slow cooling zone, critical slow cooling zone, and low-temperature fast cooling zone, according to the corresponding cooling rates, to obtain the finished magnesia refractory bricks.

[0011] Furthermore, step S1 includes the following steps:

[0012] S11: Particle size distribution. High-purity fused magnesia with MgO content of not less than 97wt% is selected and weighed according to four particle size ranges: coarse, medium, fine and fine powder. The coarse particles form the skeleton and the medium and fine particles fill the gaps step by step to obtain graded magnesia.

[0013] S12: Add rare earth composite sintering aid. A rare earth composite sintering aid composed of CeO2 powder and La2O3 powder is added to the graded magnesia. The mass ratio of CeO2 to La2O3 is 1:1 to 2:1, and the total amount of the rare earth composite sintering aid added is 0.5 to 1.5 wt% of the total mass of the graded magnesia. During the sintering process, CeO2 and La2O3 segregate and enrich at the periclase grain boundaries, synergistically purifying the grain boundaries and inhibiting the formation of low-melting-point silicate phases to obtain the first mixture.

[0014] S13: Add nano-spinel powder to the first mixture, adding particles with a particle size of [missing information]. Nano-sized MgAl2O4 spinel powder with a diameter not greater than 0.5 μm is added at an amount of 1 to 3 wt% of the total mass of the graded magnesia. During the sintering process, the nano-MgAl2O4 forms a dispersed pinning phase at the periclase grain boundaries, which inhibits the abnormal growth of periclase grains, thus obtaining the second mixture.

[0015] S14: Add stabilized zirconia micro powder. Add Y2O3 stabilized ZrO2 micro powder that has undergone surface activation treatment to the second mixture. The amount added is 0.5 to 2.0 wt% of the total mass of the graded magnesia. The surface activation treatment makes the ZrO2 micro powder uniformly dispersed in the matrix during the mixing and molding stages, so that it undergoes uniform phase transformation and toughening during sintering and cooling to obtain the third mixture.

[0016] S15: Add binder and mix. Add modified calcium lignosulfonate solution to the third mixture. The amount added is 2.5 to 3.5 wt% of the total mass of the graded magnesia. Mix evenly with wet mix to obtain the mixture.

[0017] Furthermore, step S2 includes the following steps:

[0018] S21: Pre-compression section: After adding the mixture into the pressing mold, pre-compression pressure is applied and maintained to initially compact the mixture and discharge the free gas in the large gaps between particles, thus obtaining a pre-compressed material.

[0019] S22: Vibration exhaust section, which reduces the pre-compression pressure to zero and activates the vibration excitation mechanism to apply vibration along the pressing direction, causing fine powder particles to migrate and fill the gaps between coarse particles and drive closed air bubbles to escape, thereby improving the particle packing density.

[0020] S23: Main pressure section, applying and maintaining the main pressure; during the pressure holding period, the pressure sensor array continuously collects the pressure at each measuring point, and takes the average value of no less than 5 consecutive sampling points as the representative value of the pressure at each measuring point, and calculates the pressure distribution uniformity coefficient according to the following formula. :

[0021] ;

[0022] In the formula, This is the pressure distribution uniformity coefficient, with a value range of [0,1]. The closer the value is to 1, the more uniform the pressure distribution at each measuring point. The standard deviation (MPa) of the representative pressure values ​​at all measuring points; It is the arithmetic mean (MPa) of the representative pressure values ​​at all measuring points.

[0023] when When the pressure distribution is not lower than the set threshold, the uniformity of pressure distribution is deemed acceptable, and the mold is removed to obtain the blank; when When the pressure drops below the set threshold, return to step S22 and repeat the vibration exhaust section and main pressure section sequentially. This supplementary cycle is performed a maximum of 3 times until... After the material is removed from the mold when it is not lower than the set threshold, a blank is obtained.

[0024] Furthermore, step S4 includes the following steps:

[0025] S41: Low-temperature drying section, the kiln temperature rises from room temperature to 200°C, removing residual moisture from the dried billet to obtain a preheated billet;

[0026] S42: Organic matter decomposition section, kiln temperature rises from 200℃ to 650℃; the CO volume concentration in the kiln is monitored in real time by an online gas analyzer, and the current heating rate is dynamically adjusted according to the following rules: when the CO volume concentration does not exceed the concentration threshold, the temperature is increased normally at the baseline heating rate; when the CO volume concentration exceeds the concentration threshold but is lower than the upper concentration limit, the heating rate is reduced according to the following formula:

[0027] ;

[0028] In the formula The current dynamic heating rate is adjusted (°C / min). The reference heating rate (°C / min) for the organic matter decomposition section; The CO volume concentration (ppm) inside the kiln is detected in real time by an online gas analyzer. CO concentration threshold (ppm) to trigger temperature rate regulation; To trigger the upper limit of CO concentration (ppm) for isothermal maintenance.

[0029] When the CO volume concentration is not lower than the upper limit of the concentration, the heating is stopped and the kiln temperature is kept constant. After the CO volume concentration drops below the concentration threshold, the heating is resumed at the baseline heating rate to complete the decomposition of organic matter.

[0030] S43: Degassing and temperature stabilization section, the kiln temperature rises from 650℃ to 1000℃, removing residual decomposition gases of organic matter and making the temperature of the billet more uniform.

[0031] S44: High-temperature sintering section, where the kiln temperature rises from 1000℃ to the maximum sintering temperature to complete densification sintering;

[0032] S45: Heat preservation section, the temperature is kept constant at the highest sintering temperature. The heat preservation time is determined according to the maximum thickness of the billet and the target bulk density. The thicker the billet or the higher the target density, the longer the heat preservation time is taken. After the heat preservation is completed, proceed to step S5.

[0033] Furthermore, step S5 includes the following steps:

[0034] S51: High-temperature slow cooling zone, cooling from the highest sintering temperature to 1200℃, controlling the cooling rate to prevent thermal stress cracks from forming in the billet due to excessive internal and external temperature differences.

[0035] S52: Critical slow cooling zone, cooling from 1200℃ to 800℃, controlling the cooling rate to a level lower than that of the high-temperature slow cooling zone; at the same time, by monitoring the temperature of each temperature measuring point in the kiln, adjusting the speed of the cooling fan in each cooling section to control the temperature difference between each temperature measuring point in the kiln.

[0036] S53: Low-temperature rapid cooling zone, cooling from 800℃ to room temperature, with a cooling rate higher than that of the critical slow cooling zone, yielding magnesia refractory brick finished product after exiting the kiln.

[0037] Furthermore, the surface activation treatment in step S14 includes the following steps:

[0038] The Y2O3-stabilized ZrO2 micro powder was dispersed in anhydrous ethanol, a silane coupling agent was added, and the mixture was stirred under heating conditions, then filtered and dried to obtain surface-activated ZrO2 micro powder.

[0039] This invention also provides a magnesia refractory brick preparation apparatus, including a vibration-assisted multi-stage variable pressure molding machine, an atmosphere feedback sintering kiln, and an integrated control system;

[0040] The vibration-assisted multi-segment variable pressure molding machine includes a hydraulic pressurizing unit, a vibration excitation mechanism, a pressing die, a pressure sensor array, and a molding control unit. The hydraulic pressurizing unit is connected to a hydraulic cylinder via a proportional servo valve. The piston rod of the hydraulic cylinder is connected to an upper press head, which is positioned directly above the pressing die. The vibration excitation mechanism is connected to the upper press head or the die frame of the pressing die and is used to apply vibration along the pressing direction. The pressure sensor array is installed on the inner wall of the pressing die and distributed at different heights along the pressing direction. The signal output terminals of each sensor are connected to the signal input terminals of the molding control unit. The control output terminals of the molding control unit are connected to the control terminals of the hydraulic pressurizing unit and the vibration excitation mechanism, respectively. The molding control unit has a built-in real-time calculation module for the pressure distribution uniformity coefficient and a multi-segment variable pressure logic control module.

[0041] The atmosphere feedback sintering kiln includes a multi-section electrically heated kiln body, an online gas analysis module, a multi-zone temperature control module, a cooling rate control unit, and a sintering control unit. The online gas analysis module is installed at the exhaust port of the kiln chamber corresponding to the organic matter decomposition temperature zone, and its signal output terminal is connected to the signal input terminal of the sintering control unit. The control output terminal of the sintering control unit is connected to the multi-zone temperature control module, which is connected to the heating element of each temperature control zone. The control output terminal of the cooling rate control unit is connected to the cooling fan, and its signal input terminal receives the detection signal from the temperature sensor inside the kiln. The sintering control unit has a built-in dynamic heating rate calculation module for the organic matter decomposition section.

[0042] The integrated control system interconnects the forming control unit and the sintering control unit through a communication network. The forming control unit automatically transmits the measured green bulk density data to the sintering control unit for use in determining the holding time.

[0043] In a preferred embodiment, the vibration excitation mechanism includes a variable frequency eccentric vibration motor and an elastic vibration isolation pad. The variable frequency eccentric vibration motor is installed on the side of the upper pressure head, and the vibration direction is axial vibration along the pressing direction. Both the vibration frequency and amplitude are adjustable. In the vibration exhaust section, an axial periodic disturbance force is applied to the mixture to promote the migration of fine powder particles into the gaps between coarse particles. The elastic vibration isolation pad is set between the vibration excitation mechanism and the frame to prevent vibration from being transmitted to the frame and affecting the pressure control accuracy of the hydraulic pressurization unit.

[0044] The pressure sensor array is divided into upper, middle and lower layers along the inner wall of the pressing mold. Pressure sensors are evenly arranged in each layer along the circumferential direction of the cross section to capture the pressure distribution of the blank along the pressing direction and the cross section direction. The pressing mold is also equipped with an axial displacement sensor, which is installed on the drive shaft of the hydraulic cylinder and connected to the forming control unit to measure the displacement of the upper pressure head in real time to monitor the amount of blank compression.

[0045] The multi-section electrically heated kiln body contains multiple independent temperature control zones, each equipped with heating elements and temperature detection elements, and thermal insulation structures are provided between adjacent temperature control zones; the online gas analysis module uses non-dispersive infrared spectroscopy to detect CO concentration; the cooling rate control unit includes cooling air ducts arranged along the top and side walls of the kiln, variable frequency speed-regulating cooling fans connected to the cooling air ducts, and a cooling controller; each cooling section has an independent air duct and a corresponding variable frequency speed-regulating cooling fan, and thermal insulation partitions are provided between adjacent cooling sections; the signal input terminal of the cooling controller is connected to the kiln temperature sensor, and the control output terminal is connected to the variable frequency speed-regulating cooling fan of each section, independently controlling the cooling rate in the high-temperature slow cooling zone, the critical slow cooling zone, and the low-temperature fast cooling zone.

[0046] The beneficial effects achieved by this invention are as follows:

[0047] This invention introduces vibration-assisted multi-stage variable pressure molding technology into the molding process. After pre-pressurization, axial vibration venting is added under depressurization conditions. Periodic vibration breaks down the bridging structure in particle accumulation, prompting fine particles to migrate and fill the gaps between coarse particles. Simultaneously, it drives closed air bubbles to escape to the surface of the green body, improving particle density and reducing closed pores in the green body. Based on this, the invention proposes an online closed-loop feedback control method based on a pressure distribution uniformity coefficient. During the pressure holding period in the main pressing stage, a pressure sensor array arranged at different heights of the mold collects the pressure at each measuring point in real time and calculates the pressure distribution uniformity coefficient. When this coefficient falls below a set threshold, a supplementary cycle is automatically triggered, gradually improving the uniformity of the green body's density distribution during the cycle. This ensures that the density distribution of each green body meets the set uniformity requirements from the source of the molding stage, reducing the probability of warping and delamination defects caused by excessive density gradients in the fired products, and significantly improving the batch firing pass rate.

[0048] This invention synergistically introduces three functional components into the feedstock system: a rare earth composite sintering aid, a nano-spinel additive, and a surface-activated stabilized zirconia additive. These three components exert different strengthening mechanisms during sintering and form a synergistic effect. The cerium oxide and lanthanum oxide in the rare earth composite sintering aid have a small lattice mismatch with magnesium oxide, preferentially segregating and enriching at the periclase grain boundaries during sintering. Their combined action purifies grain boundary impurities and inhibits the formation of low-melting-point silicate phases at grain boundaries, improving the high-temperature strength and creep resistance of the sintered body. Simultaneously, the eutectic point of the two rare earth oxides is lower than their melting temperatures when they exist individually, allowing for the formation of a suitable amount of grain boundary liquid phase at a lower sintering temperature to drive particle rearrangement and eliminate porosity, achieving low-temperature, high-efficiency densification. During sintering, nano-spinel additives form a metallurgical bond with the magnesium oxide matrix, creating a dispersed spinel pinning phase at grain boundaries. This pinning mechanism inhibits abnormal growth of periclase grains, resulting in more uniform and refined grain sizes, enhanced grain boundary bonding, and consequently improved room-temperature mechanical strength and high-temperature creep resistance of the sintered body. Stabilized zirconia micropowder, surface-activated with a silane coupling agent, achieves uniform dispersion in the matrix. During sintering and cooling, it undergoes a uniform martensitic transformation from tetragonal to monoclinic phase. The volume expansion generated by this transformation creates a compressive stress zone at the crack tip to dissipate crack propagation energy. Through the synergistic effect of transformation toughening and microcrack toughening mechanisms, the fracture toughness and thermal shock resistance of the product are significantly improved.

[0049] This invention introduces dynamic adjustment of the heating rate based on real-time detection of carbon monoxide concentration in the kiln during the organic matter decomposition stage of the sintering process, achieving adaptive matching between the rate of escape of organic pyrolysis gases and the heating rate. An online gas analyzer installed at the flue gas outlet continuously monitors the carbon monoxide concentration in the kiln. The sintering control unit calculates and outputs dynamic heating rate commands in real time according to the detected concentration value using a proportional adjustment strategy. When the carbon monoxide concentration increases, the heating rate is automatically reduced to decrease the gas production per unit time. When the concentration exceeds the safety limit, heating is automatically paused and the kiln temperature is maintained constant. Normal heating resumes after the concentration returns to normal. This proportional adjustment strategy achieves a continuous and smooth transition from normal heating to heating cessation, avoiding sudden changes in the heating rate caused by single-threshold switch control. It minimizes the heating time while ensuring that the green body does not suffer from delamination or bursting defects due to gas pressure accumulation, effectively balancing sintering safety and production efficiency.

[0050] This invention proposes a zoned, rate-controlled cooling method in the cooling process. The cooling process after sintering is divided into three stages based on temperature ranges: a high-temperature slow cooling zone, a critical slow cooling zone, and a low-temperature rapid cooling zone. Each stage is independently controlled according to different cooling rate requirements. The critical slow cooling zone is the key to cooling control. Within this temperature range, stabilized zirconia undergoes a martensitic phase transformation, and the periclase grain boundary glass phase solidifies. By strictly limiting the cooling rate and supplementing it with real-time monitoring of the temperature difference within the kiln, the uniformity of the phase transformation across the entire cross-section is ensured. This avoids localized volumetric strain inconsistencies and thermomechanical stress concentrations caused by excessively rapid cooling leading to large differences in the degree of phase transformation in different regions. This allows the phase transformation toughening effect to be fully realized, significantly improving the fracture toughness and thermal shock cycle life of the finished product. Attached Figure Description

[0051] Figure 1 The graphs show the comparison of pressure distribution uniformity coefficient Kd and firing pass rate between Examples 1-3 and Comparative Examples 1-3, where (a) is a stem graph of Kd values ​​for each group and (b) is a stem graph of firing pass rate for each group.

[0052] Figure 2 The graphs show a comparison of the densification index and mechanical properties after firing of Examples 1-3 and Comparative Examples 1-3. (a) is a bar chart of the bulk density after firing, (b) is a bar chart of the apparent porosity, (c) is a bar chart of the compressive strength at room temperature, and (d) is a bar chart of the flexural strength at room temperature.

[0053] Figure 3 This is a comparison chart of the thermal shock stability of Examples 1-3 and Comparative Examples 1-3, showing the number of thermal shock cycles for each group under water cooling conditions at 1100℃ in the form of a broken line scatter plot.

[0054] Figure 4This is a comparison graph of the dynamic heating rate response of CO concentration feedback in the organic matter decomposition section of Example 1 and Comparative Example 1. (a) is a curve of heating rate VT changing with kiln temperature, and (b) is a curve of CO volume concentration in the kiln changing with kiln temperature.

[0055] Figure 5 This is a schematic diagram of the structural composition of a magnesia refractory brick preparation device according to the present invention. Detailed Implementation

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] This invention designs a method for preparing magnesia refractory bricks, which is implemented in the following order: batching and mixing (S1), vibration-assisted multi-stage variable pressure molding (S2), drying (S3), atmosphere feedback adaptive segmented sintering (S4), and zoned controlled-speed cooling (S5). There are transmission and connection relationships between process parameters in each step. In particular, the measured bulk density of the green body in step S2 is transmitted as a key parameter to step S4 for determining the holding time, forming a collaborative control logic for the entire process from molding to sintering.

[0058] Step S1: Ingredient mixing; Step S1 is carried out in the following order, and each sub-step is completed within the ingredient mixing framework of Step S1.

[0059] Step S11 involves particle size distribution. High-purity fused magnesia with an MgO content of not less than 97 wt% is selected as the main material. It is graded into four particle size ranges: coarse particles (3–5 mm), medium particles (1–3 mm), fine particles (0.1–1 mm), and fine powder (less than 0.088 mm). The mass fractions of the four particle sizes are 38–42 wt%, 22–26 wt%, 18–22 wt%, and 12–16 wt%, respectively, with a total mass of 100 wt%. In this gradation scheme, coarse particles form the skeleton of the green body, medium particles fill the primary pores between coarse particles, and fine particles and fine powder progressively fill smaller gaps. The particle size distribution design follows a progressive filling principle, which helps to maximize the initial bulk density of the mixture and reduce the residual porosity in the green body. The graded magnesia is then ready for use.

[0060] Step S12 involves adding rare earth composite sintering aids. These aids are added to the graded magnesia. powder and Rare earth composite sintering aids composed of powder. and The mass ratio is 1:1 to 2:1, and the total amount of rare earth composite sintering aid added is 0.5 to 1.5 wt% of the total mass of graded magnesia. powder and Particle size of powder All are no larger than 1 μm. Particle size This refers to the particle size value corresponding to when the cumulative particle size distribution in a powder particle group reaches 50%, i.e., the median diameter. The size of no more than 1 μm ensures the uniform distribution of rare earth additives at the microscale. and With relatively small mismatch with MgO lattice, it preferentially segregates and enriches at the periclase grain boundaries during sintering. By purifying grain boundary impurities and suppressing the precipitation of low-melting-point silicate phases at grain boundaries, it improves the mechanical strength and creep resistance of the sintered body under high-temperature conditions. When the two rare earth oxides are used in combination, they synergistically exert a liquid-phase-assisted densification effect over a wider temperature range. Moreover, the eutectic point of the two is lower than the melting temperature of each when they exist alone, which is conducive to forming an appropriate amount of liquid phase at a lower sintering temperature, driving particle rearrangement and eliminating porosity.

[0061] Step S13 involves adding nano-spinel powder. Nano-spinel powder is added to the mixture obtained in step S12. Spinel micro powder, its particle size The nanoparticle size is no larger than 0.5 μm, and the added amount is 1–3 wt% of the total mass of the graded magnesia. During sintering, it forms a metallurgical bond with the MgO matrix, resulting in dispersed spinel second-phase particles at the periclase grain boundaries. This suppresses abnormal periclase grain growth through the Zener pinning mechanism. The Zener pinning mechanism refers to the pinning resistance of dispersed second-phase particles to grain boundary migration, reducing the driving force for grain growth, thereby refining the grains and achieving a more uniform grain size distribution. This improves the thermal shock resistance of the green body while enhancing the room-temperature flexural strength and high-temperature creep resistance of the sintered body. It is recommended that the above-mentioned grain size be met. Under the premise of meeting the requirements, nanoparticles with a concentrated particle size distribution should be selected as much as possible. Products are designed to ensure consistent nailing results.

[0062] Step S14 involves adding surface-activated and stabilized zirconia micropowder. 3 mol% of the surface-activated zirconia micropowder is added to the mixture obtained in step S13. Stablize Micronized powder, hereinafter referred to as Y-PSZ, has a particle size The particle size is no larger than 1 μm, and the amount added is 0.5–2.0 wt% of the total mass of graded magnesia. The specific steps of the surface activation treatment are as follows: Y-PSZ micro powder is dispersed in anhydrous ethanol, and 0.5–1.0 wt% of silane coupling agent KH-560 is added. The mixture is stirred at 50–60 °C for 30–60 min, filtered, and dried at an appropriate temperature to obtain surface-activated Y-PSZ micro powder. KH-560, namely γ-epoxypropoxypropyltrimethoxysilane, after hydrolysis in an alcohol-water mixed medium, its silanol groups undergo a condensation reaction with the hydroxyl Zr-OH groups on the surface of Y-PSZ particles to form stable Si-O-Zr chemical bonds, thereby constructing an organosilane modified layer on the particle surface and introducing epoxy functional groups. This organic layer improves the wettability between Y-PSZ micropowder, magnesia particles, and calcium lignosulfonate binder, inhibiting the agglomeration of Y-PSZ particles during mixing and molding, and ensuring their uniform dispersion in the matrix. The phase transformation toughening mechanism of Y-PSZ is based on the following principle: After stabilization Existing in a metastable tetragonal phase at room temperature, Y-PSZ induces a martensitic transformation from the tetragonal phase to the monoclinic phase when cracks propagate in the matrix. This transformation is accompanied by a volume expansion of approximately 3–5%, forming a compressive stress zone at the crack tip, which consumes crack propagation energy and thus improves fracture toughness. During sintering and cooling, Y-PSZ undergoes this phase transformation uniformly, achieving uniform transformation toughening and microcrack toughening, synergistically improving the fracture toughness and thermal shock resistance of the product. Furthermore, due to the uniform distribution of Y-PSZ in the green body, the spatial consistency of the transformation effect is guaranteed.

[0063] Step S15 involves adding a binder and completing the mixing process. A modified calcium lignosulfonate solution with a solid content of not less than 50 wt% is added to the mixture obtained in step S14. The amount added is 2.5–3.5 wt% of the total mass of the graded magnesia. Wet mixing is performed for 6–10 minutes to ensure the binder evenly coats the surface of particles of all sizes, resulting in the final mixture. The modified calcium lignosulfonate is obtained through oxidative modification of sulfite pulp waste liquor. The sulfonic acid groups in its molecular chain give it good water solubility and wetting and adsorption properties for magnesia particles, providing temporary bonding force between particles during the green body forming stage, while also giving the green body sufficient strength to support drying and kiln loading operations. A solid content of not less than 50 wt% helps reduce the total amount of moisture that needs to be removed during the subsequent drying stage, reducing the risk of drying cracking. The wet mixing time should be adjusted appropriately according to the uniformity and flowability of the mixture. A shorter wet mixing time may lead to uneven distribution of the binder, while a longer time may cause the material to become too sticky, which is not conducive to mold filling.

[0064] Step S2: Vibration-assisted multi-segment pressure forming; Step S2 is performed in the following order, and the pressure distribution uniformity coefficient calculated at the end of Step S23 is used as the basis for the calculation. The size of the value determines whether to return to step S22 to execute the supplementary loop.

[0065] Step S21 is the pre-compression stage. After the mixture obtained in step S1 is added to the pressing mold, a pre-compression pressure of 20-35 MPa is precisely applied by the hydraulic pressurization unit through a proportional servo valve and held for 5-8 seconds. The pre-compression stage initially compacts the mixture, expelling free gas from the large pores between particles, and simultaneously provides a basic compacted state for the subsequent vibration venting stage, preventing the mixture from loosening and splashing during intense vibration. The pre-compression pressure should not be too high to avoid the particle bridging effect solidifying and affecting the particle rearrangement effect during the vibration venting stage.

[0066] Step S22 is the vibration venting section. After pre-compression, the pressure is released to zero, and the vibration excitation mechanism is activated to apply axial vibration along the pressing direction at a frequency of 30-50Hz and an amplitude of 0.5-2.0mm for 3-5s. The core principle of the vibration venting section is that the contact force between particles is greatly reduced under depressurization, and the particle mobility is increased. The axial periodic vibration force applied along the pressing direction causes fine powder particles to overcome the friction between particles and migrate to fill the gaps between coarse particles. At the same time, it destroys the bridging structure in the particle pack and drives closed air bubbles to escape to the surface of the particle pack, thereby improving the particle packing density and reducing closed pores in the green body. If the vibration frequency is too low, the particle disturbance is insufficient; if it is too high, it may cause fine particle separation and stratification. It is recommended to select the optimal frequency within the range of 30-50Hz according to the specific gradation of the material. If the amplitude is too small, the bubble expulsion effect is limited; if it is too large, it may destroy the already compacted particle packing. It is recommended to select the appropriate amplitude within the range of 0.5-2.0mm in combination with the material properties and mold size.

[0067] Step S23 is the main pressure stage. After vibration venting, a main pressure of 130–180 MPa is applied and held for 15–25 seconds to allow the billet to complete densification. At the end of the holding period, a pressure sensor array continuously collects pressure data at each measuring point. The average value of at least five consecutive sampling points is taken as the representative pressure value for each measuring point. Using the average value instead of the instantaneous value eliminates signal fluctuations caused by residual local vibration or hydraulic pulsation. Based on the representative pressure values ​​of all measuring points, the pressure distribution uniformity coefficient is calculated using the following formula. :

[0068] ;

[0069] In the formula, This is the pressure distribution uniformity coefficient, with a value range of [0,1]. The closer the value is to 1, the more uniform the pressure distribution at each measuring point, which indirectly reflects the uniformity of the density distribution of the billet. The standard deviation (MPa) of the representative pressure values ​​at all measuring points; It is the arithmetic mean (MPa) of the representative pressure values ​​at all measuring points.

[0070] In the above formula, The coefficient of variation (CV) of the pressure at each measuring point is a dimensionless statistic that characterizes the relative dispersion of the data. =1-CV, where CV=0 when the pressure at all measuring points is exactly the same. =1; the greater the pressure dispersion at each measuring point, the larger the CV. The smaller the value, the better. During hydraulic pressing, the pressure transmission inside the material column attenuates from the pressurized end to the far end along the pressing direction. The pressure representative values ​​of the measuring points of the pressure sensing array at the upper, middle, and lower height layers can indirectly characterize the forming pressure experienced by the blank in the corresponding height region, thereby reflecting the uniformity of the density distribution of the blank along the height direction.

[0071] when When the pressure distribution is not lower than the set threshold, the uniformity of pressure distribution is deemed acceptable, and the mold is removed to obtain the blank; when If the pressure drops below the set threshold, return to step S22 to re-execute the vibration exhaust section and main pressure section, repeating the cycle up to 3 times until... After reaching the set threshold, the mold is removed to obtain the blank. It is recommended to... The set threshold is 0.93, which can be adjusted within a reasonable range according to the product's operating conditions and quality requirements. For products requiring higher density uniformity, the threshold can be appropriately increased. Through the above closed-loop feedback control mechanism, the uniformity of the green body density distribution is gradually improved during the supplementary cycle, effectively reducing the probability of warping and delamination of the fired product due to excessive density gradient.

[0072] Step S3: Drying; Transfer the green body obtained in step S2 to a drying device and dry it at an appropriate temperature until the residual moisture content of the green body is no higher than 0.5 wt%, thus obtaining a dried green body. The purpose of the drying stage is to remove free water and most of the bound water from the green body to prevent cracking caused by the steam pressure generated by rapid evaporation of moisture exceeding the structural capacity of the green body during the initial heating stage of the subsequent low-temperature drying section. A residual moisture content of no more than 0.5 wt% is a necessary condition to ensure safe heating in the initial stage of subsequent segmented sintering. The basis for determining this is that below this moisture content, the gas pressure generated by moisture evaporation is insufficient to damage the green body structure.

[0073] Step S4: Atmosphere Feedback Adaptive Segmented Sintering; Step S4 is executed sequentially according to the following steps. The core of this step lies in the introduction of a dynamic adjustment mechanism for the heating rate based on real-time detection of CO concentration in the kiln in step S42, which achieves adaptive matching between the escape rate of organic pyrolysis gas and the heating rate.

[0074] Step S41 is the low-temperature drying section. The kiln temperature rises from room temperature to 200℃ at a rate of 1.5–2.5℃ / min. The main task of this section is to remove residual moisture from the billet while ensuring a slow and uniform temperature increase. This reduces the temperature gradient between the inside and outside of the billet, preventing micro-cracks caused by asynchronous heating of the surface and interior of the billet, thus laying the foundation for safe heating in the organic matter decomposition section.

[0075] Step S42 is the organic matter decomposition section. The kiln temperature rises from 200℃ to 650℃. Within this temperature range, the organic binder-modified calcium lignosulfonate in the green body continuously produces gases such as CO, CO2, and water vapor during pyrolysis, and the gas generation rate increases with increasing temperature. If the heating rate is too fast, the amount of gas generated by pyrolysis per unit time exceeds the rate at which it diffuses outward from the inside of the green body, causing gas pressure to accumulate inside the green body. When this exceeds the limit that the green body structure can withstand, it will cause delamination or bursting defects. If the heating rate is too slow, energy consumption will increase and production efficiency will decrease.

[0076] To address the aforementioned contradiction, this step utilizes an online gas analyzer installed at the flue gas outlet of the kiln chamber corresponding to the organic matter decomposition temperature zone to monitor the CO volume concentration inside the kiln in real time. The CO concentration at the flue gas outlet shows a strong correlation with the CO content in the kiln atmosphere, reflecting the intensity of organic matter pyrolysis gas production per unit time, thus indirectly characterizing the risk of gas pressure accumulation inside the green body. Based on the detected... The sintering control unit dynamically adjusts the current heating rate according to the following segmentation rules. :

[0077] when No more than At that time, maintain = The temperature is increased normally at the reference rate;

[0078] when Exceed And lower than When, use the following formula to exist Linearly reduce between 0 and 0:

[0079] ;

[0080] when Not less than At that time, stop heating and maintain a constant kiln temperature. =0), waiting Down to After that, restore the button. Temperatures continue to rise.

[0081] In the above formulas, The current dynamic heating rate is adjusted (°C / min). The reference heating rate (°C / min) for the organic matter decomposition section is taken as 2.5–3.5°C / min; The CO volume concentration (ppm) inside the kiln is detected in real time by an online gas analyzer. The CO concentration threshold (ppm) for triggering the temperature rise rate regulation is set to 200–400 ppm. To trigger the upper limit of CO concentration (ppm) for isothermal maintenance, use 1500-2500 ppm.

[0082] Explanation of the formula for linearly lowering the middle section: Let the adjustment ratio f = ( - ) / ( - ),when = When f=0, the heating rate is not adjusted. = ;when Approaching As f approaches 1, the heating rate approaches 0, meaning heating almost completely stops. By proportionally decreasing the baseline heating rate with f as a weight, continuous and smooth adjustment from normal heating to heating cessation is achieved, avoiding sudden changes in the heating rate caused by single-threshold on / off control, and ensuring that the gas generation rate remains within the safe gas escape capacity of the billet. The physical meaning of this control strategy is: CO concentration relative to... The greater the degree of CO exceedance, the more intense the pyrolysis of organic matter, and the greater the corresponding decrease in the heating rate. The adjustment range is directly proportional to the degree of CO exceedance, which is essentially a proportional adjustment strategy based on atmosphere feedback. and The value should be adapted to the process based on the type of binder, the thickness of the green body, and the kiln loading density. For cases with thicker green bodies or higher kiln loading densities, the value should be appropriately reduced. The value of is chosen to allow for a greater safety margin.

[0083] Step S43 is the degassing and temperature stabilization section. The kiln temperature rises from 650℃ to 1000℃ at a rate of 3-4℃ / min. The main task of this section is to remove residual decomposition gases from organic matter and to stabilize and unify the temperature of the green body before it enters the high-temperature sintering section, thus avoiding uneven densification in the subsequent high-temperature sintering section due to localized temperature unevenness.

[0084] Step S44 is the high-temperature sintering section. The kiln temperature is increased from 1000℃ to 1580-1650℃ at a rate of 4-5℃ / min. Within this temperature range, the rare earth composite sintering aid added in step S12 (… and A suitable amount of liquid phase forms at the grain boundaries. This liquid phase generates capillary forces in the interparticle spaces, driving particle rearrangement and filling pores, thus promoting the liquid-assisted densification process; nano Metallurgical bonding is achieved with the MgO matrix at high temperatures, and dispersed spinel pinning phases form at grain boundaries, inhibiting abnormal periclase grain growth while ensuring uniform grain growth during densification. The recommended maximum sintering temperature is within the range of 1580–1650℃. The amount of additives and the target density of the green body are selected. When the amount added is high, the maximum sintering temperature can be appropriately reduced, while still achieving a high degree of densification.

[0085] Step S45 is the heat preservation stage. The green body is held at a constant temperature of 1580–1650℃ for 2–4 hours to ensure uniform heat distribution within the green body and consistent densification along its thickness. The holding time needs to consider three factors: the maximum thickness of the green body, the difference between the target post-firing bulk density and the measured green body bulk density in step S2. A larger maximum thickness requires more time for heat to conduct into the green body, thus requiring a longer holding time. Similarly, a higher target bulk density or lower green body bulk density requires a greater amount of densification to be achieved during the holding stage, also necessitating a longer holding time. Conversely, the holding time can be appropriately shortened within the 2–4 hour range. The specific holding time should be calculated and selected based on the three parameters using pre-established process data relationships or empirical formulas. After the heat preservation is completed, the green body completes densification sintering and proceeds to step S5.

[0086] Step S5: Zoned speed-controlled cooling; Step S5 implements differentiated cooling rate control in three temperature zones in the following order. The cooling rate settings of the three zones are gradually relaxed from high temperature to low temperature, reflecting the differences in the thermal stress resistance and phase transformation behavior of the billet in different temperature zones.

[0087] Step S51 is the high-temperature slow cooling zone. Cooling is performed from the highest sintering temperature to 1200℃, with a cooling rate not exceeding 5℃ / min. Within this temperature range, the entire billet is at a relatively high temperature, the grain boundary glass phase still possesses a certain degree of viscous fluidity, the material's elastic modulus is relatively low, and the thermal stress relaxation rate is relatively fast. Limiting the cooling rate aims to prevent excessive temperature differences between the inside and outside of the billet, keeping the internal and external thermal stress differences within a safe range and avoiding the initiation of cracks in the high-temperature zone.

[0088] Step S52 is the critical slow cooling zone. Cooling from 1200℃ to 800℃ at a rate not exceeding 3℃ / min, while simultaneously adjusting the cooling fan speed by monitoring temperatures at various points within the kiln, ensures that the temperature difference between these points does not exceed 30℃, guaranteeing uniform cooling of the entire billet. This temperature range is crucial for cooling control in this method for two reasons: First, the Y-PSZ added in step S14 undergoes a martensitic phase transformation from tetragonal to monoclinic phase within this range. This phase transformation is highly sensitive to both cooling rate and temperature uniformity. Excessive cooling rate or uneven temperature distribution across the billet can lead to significant differences in the degree of phase transformation in different regions, causing inconsistent local volumetric strain and resulting in thermomechanical stress concentration, which in turn induces microcracks. Second, the periclase grain boundary glass phase transforms and solidifies within this range. If the cooling rate is too fast, the shrinkage during glass phase solidification will not match the thermal shrinkage rate of the matrix grains, also generating additional stress at the grain boundaries. If the combined stresses of the two stresses exceed the fracture toughness limit of periclase, irreversible microcrack initiation and propagation will occur, significantly reducing the thermal shock stability of the finished product. Therefore, this step ensures uniform phase transformation by strictly limiting the cooling rate and supplementing it with real-time temperature difference monitoring, thereby improving the fracture toughness and thermal shock cycle life of the finished product.

[0089] Step S53 is the low-temperature rapid cooling zone. Cooling from 800℃ to room temperature at a rate not exceeding 15℃ / min, the resulting magnesia refractory brick is obtained after exiting the kiln. Below 800℃, the martensitic phase transformation of Y-PSZ is essentially complete, the periclase grain boundary glass phase is fully solidified, and the green body structure tends to be stable. This significantly reduces the requirement for a high cooling rate; appropriately increasing the cooling rate helps shorten the sintering cycle and improve production efficiency.

[0090] This invention relates to an apparatus for preparing magnesia refractory bricks, with reference to... Figure 5 The system comprises three parts: a vibration-assisted multi-stage variable pressure molding machine, an atmosphere feedback sintering kiln, and an integrated control system. The vibration-assisted multi-stage variable pressure molding machine includes a hydraulic pressurizing unit, a vibration excitation mechanism, a pressing die, a pressure sensor array, and a molding control unit. The hydraulic pressurizing unit is connected to a hydraulic cylinder via a proportional servo valve. The piston rod of the hydraulic cylinder is connected to an upper pressure head, which is positioned directly above the pressing die. The hydraulic cylinder drives the upper pressure head to apply precisely adjustable pressure to the mixture within the die. The introduction of the proportional servo valve gives the hydraulic system continuous pressure regulation capability, ensuring precise switching and stable maintenance of the target pressure in each of the three pressure-changing stages: the pre-pressurization stage, the vibration exhaust stage (pressure reduced to zero), and the main pressure stage.

[0091] The vibration excitation mechanism consists of a variable frequency eccentric vibratory motor and elastic vibration isolation pads. The variable frequency eccentric vibratory motors are fixedly mounted on the side of the upper pressure head, with at least two symmetrically arranged. This symmetrical arrangement cancels out the horizontal component of the force, ensuring that the vibration excitation force is output vertically along the pressing direction, effectively acting on the rearrangement and venting of the compound particles along the pressing direction. The vibration frequency and amplitude of the variable frequency eccentric vibratory motors can be independently adjusted to adapt to the process requirements of different gradations. Elastic vibration isolation pads are placed between the vibration excitation mechanism and the frame, typically made of elastomer material with high damping characteristics. These pads isolate the vibration transmission from the excitation mechanism to the frame, preventing frame vibration from interfering with the pressure control accuracy of the hydraulic system and ensuring that the pressure sensor array's acquisition signal is not affected by the vibration background noise during the main pressure holding period. The vibration excitation mechanism is activated only in the vibration venting section and is closed in the pre-pressing and main pressure sections.

[0092] A pressure sensor array is installed on the inner wall of the pressing die, distributed along the pressing direction in three height layers: upper, middle, and lower. Each layer has at least three pressure sensors evenly arranged circumferentially along the cross-section to capture the non-uniformity of pressure distribution within the cross-section. The spacing of the sensors in the height direction should be rationally designed according to the height of the billet to ensure sufficient characterization of the pressure gradient distribution along the pressing direction. The signal output terminals of each sensor are connected to the signal input terminals of the forming control unit via acquisition cables, enabling real-time parallel acquisition of pressure data at each measuring point. The pressing die is also equipped with an axial displacement sensor, mounted on the hydraulic cylinder drive shaft and connected to the forming control unit. This sensor measures the axial displacement of the upper pressure head in real time, and then, combined with the die dimensions, calculates the compression amount of the billet, providing basic data for process parameter recording and billet size monitoring.

[0093] The molding control unit is the core control component of the vibration-assisted multi-segment variable pressure molding machine. Its control output is connected to the control terminals of the hydraulic pressurization unit and the vibration excitation mechanism, respectively, while its signal input receives real-time signals from the pressure sensor array and the axial displacement sensor. The molding control unit has a built-in pressure distribution uniformity coefficient. The real-time calculation module, based on the pressure data collected by the pressure sensor array at each measuring point, calculates according to... =1- The pressure representative values ​​at each measuring point are calculated in real time, and the calculation results are compared with the set threshold for judgment. The molding control unit also has a built-in three-stage pressure change logic control module, which automatically drives the hydraulic pressurization unit and vibration excitation mechanism to complete the action switching according to the timing logic of the pre-compression stage step S21, the vibration exhaust stage step S22, and the main pressure stage step S23; when When the voltage drops below the set threshold, the three-stage transformer logic control module automatically issues a trigger command to return to step S22, starts a supplementary loop, and counts the number of supplementary loops, which can be executed up to 3 times.

[0094] The atmosphere feedback sintering kiln includes a multi-section electrically heated kiln body, an online gas analysis module, a multi-zone temperature control module, a cooling rate control unit, and a sintering control unit.

[0095] The multi-section electric heating kiln body contains 7 to 9 independent temperature control zones. Each temperature control zone is equipped with heating elements and temperature detection elements. There is a heat insulation structure between adjacent temperature control zones to reduce thermal crosstalk between adjacent sections, ensure that each temperature control zone independently and accurately executes the heating rate command, and achieves a reasonable temperature gradient distribution between sections at different sintering stages.

[0096] The online gas analysis module is installed at the flue gas outlet of the kiln chamber corresponding to the organic matter decomposition temperature zone, and uses non-dispersive infrared spectroscopy (NDIR) to detect CO concentration. The working principle of NDIR is based on the selective absorption of CO molecules by infrared radiation of a specific wavelength, approximately 4.67 μm. According to the Lambert-Bohr law, the absorbance of a gas is proportional to the product of its concentration and optical path length. By measuring the intensity attenuation of infrared light before and after passing through the gas sample, the CO volume concentration can be calculated. NDIR has advantages such as fast response speed, good selectivity for CO, and low maintenance, making it suitable for continuous online monitoring of kilns. The signal output terminal of the online gas analysis module is connected to the signal input terminal of the sintering control unit, transmitting the real-time detected CO concentration. The value is continuously transmitted to the sintering control unit.

[0097] The control input terminal of the multi-zone temperature control module receives dynamic heating rate commands from the sintering control unit. Its control output terminal is connected to the heating element of each temperature control zone. By adjusting the heating power of each temperature control zone, the actual heating rate of each temperature control zone can be adjusted in real time. Command value. The sintering control unit has a built-in dynamic heating rate calculation module for the organic matter decomposition section, which calculates the value based on the received command value. The detected value is calculated in real time according to the segmentation logic and formula described in step S42. The calculation results are then output to the multi-zone temperature control module in the form of control commands.

[0098] The cooling rate control unit includes cooling ducts arranged along the top and side walls of the kiln, variable frequency speed-regulating cooling fans connected to the cooling ducts, and a cooling controller. Each cooling section has an independent duct and a corresponding variable frequency speed-regulating cooling fan. Insulation baffles are installed between adjacent cooling sections to ensure that the cooling rate of each section can be independently adjusted without interference. The signal input terminal of the cooling controller is connected to the temperature sensor inside the kiln to receive real-time temperature signals from each measuring point. Its control output terminal is connected to the variable frequency speed-regulating cooling fan in each section. By independently adjusting the speed of the cooling fan in each section, the cooling rate in the high-temperature slow cooling zone, the critical slow cooling zone, and the low-temperature fast cooling zone is controlled respectively, ensuring that the actual cooling rate of each cooling section meets the requirements of step S5. The cooling controller corresponding to the critical slow cooling zone also calculates the temperature difference between each measuring point inside the kiln in real time. When the temperature difference exceeds the set value, the speed of the cooling fan in the corresponding section is automatically adjusted to reduce the temperature difference and ensure uniform cooling of the billet.

[0099] The integrated control system interconnects the forming control unit and the sintering control unit via a communication network. After completing step S2, the forming control unit automatically transmits the measured green bulk density data to the sintering control unit via the communication network. Upon receiving this data, the sintering control unit uses it as the input value for the green bulk density parameter in the holding time calculation in step S45. Combined with the maximum green body thickness and target post-sintering bulk density parameters input by the operator, it automatically determines the holding time for this batch of green bodies and generates a personalized sintering process curve accordingly. This automatic data transmission mechanism directly incorporates the actual measurement results of the forming process into the calculation of sintering process parameters, eliminating errors that may be caused by manual parameter input. It achieves full-process digital collaborative control from forming to sintering, providing targeted process parameter matching for product batches with different specifications and densification requirements.

[0100] Example 1: In this example, standard-sized magnesia refractory bricks for use as linings in steelmaking converters were prepared. The green body size was 230mm×115mm×65mm, and the sintering temperature was 1620℃. The process parameters were taken as the median values ​​within the range of each step of the present invention, which were used to verify the baseline of the comprehensive performance of the method of the present invention.

[0101] Step S1, batching and mixing, is performed sequentially from S11 to S15. In S11, high-purity fused magnesia with an MgO content of not less than 97wt% is weighed out according to the following proportions: 40wt% coarse particles, 24wt% medium particles, 20wt% fine particles, and 16wt% fine powder, totaling 100wt% to obtain graded magnesia. In S12, a rare earth composite sintering aid composed of CeO2 and La2O3 in a mass ratio of 1:1 is added, with a total addition amount of 1.0wt% of the total mass of the graded magnesia. The particle sizes of the two powders are... All particles are no larger than 1 μm. In S13, particles with a diameter of [missing value] are added. 2.0 wt% of nano-MgAl2O4 spinel powder with a particle size not greater than 0.5 μm was added to S14. 3 mol% of surface-activated Y2O3-stabilized ZrO2 powder, abbreviated as Y-PSZ, was also added. (Particle size...) The powder has a particle size not exceeding 1 μm, an added amount of 1.0 wt%, and KH-560 dosage of 0.8 wt% of the ZrO2 micro powder mass. The mixture is stirred at 55℃ for 45 min, filtered, and dried to obtain surface-activated Y-PSZ micro powder. In S15, 3.0 wt% modified calcium lignosulfonate solution (50 wt% solids content) is added and wet-mixed for 8 min to obtain a compound with a loose bulk density of [missing information]. =1.82g / cm 3 .

[0102] Step S2 Vibration-Assisted Multi-Segment Pressure Molding: S21 Pre-compression stage, apply pressure of 30MPa, hold pressure for 6s; S22 Vibration venting stage, depressurize to zero, activate the vibration excitation mechanism, apply axial vibration along the pressing direction at a frequency of 40Hz and an amplitude of 1.0mm for 4s; S23 Main compression stage, apply pressure of 155MPa, hold pressure for 20s, at the end of the pressure holding stage, the pressure at each measuring point is collected by the upper, middle and lower three-layer pressure sensor array, according to the formula specified in step S23 of this invention. Calculation, initial =0.914, which is lower than the set threshold of 0.93. Return to S22 and execute one supplementary loop. =0.961, meeting the threshold requirement, demolding yields the green body; the molding control unit automatically records and transmits the measured green body bulk density. =3.026g / cm 3 To the sintering control unit.

[0103] Step S3 Drying: The green body is dried at 110℃ for 20 hours, with a residual moisture content of 0.38wt%, which meets the requirement of not exceeding 0.5wt%.

[0104] Step S4: Atmosphere Feedback Adaptive Segmented Sintering: S41 Low-Temperature Drying Section, heating from room temperature to 200℃ at a rate of 2.0℃ / min; S42 Organic Decomposition Section, reference heating rate. =3.0℃ / min, CO concentration trigger threshold =300ppm, upper limit of constant temperature =2000ppm, the online NDIR analyzer detects the CO volume concentration in the kiln in real time, and the sintering control unit follows the formula in step S42 of this invention. The heating rate was dynamically adjusted, and the measured CO peak was approximately 1100 ppm, occurring at approximately 360°C. The sintering control unit then adjusted accordingly. The temperature was reduced to approximately 1.6℃ / min, with no cracking of the billet throughout the process; in the S43 degassing and temperature stabilization section, the temperature was increased from 650℃ to 1000℃ at a rate of 3.5℃ / min; in the S44 high-temperature sintering section, the temperature was increased from 1000℃ to 1620℃ at a rate of 4.5℃ / min; and in the S45 heat preservation section, the temperature was maintained at 1620℃ for 3 hours.

[0105] Step S5: Zoned controlled cooling: S51 High-temperature slow cooling zone, cooling from 1620℃ to 1200℃ at 4℃ / min; S52 Critical slow cooling zone, cooling from 1200℃ to 800℃ at 2.5℃ / min, with the cooling controller monitoring in real time and controlling the temperature difference between each temperature measuring point in the kiln to within 30℃; S53 Low-temperature rapid cooling zone, cooling from 800℃ to room temperature at 12℃ / min, yielding the finished magnesia refractory bricks after exiting the kiln.

[0106] Example 2: This example increases the proportion and total amount of CeO2 in the rare earth additives and lowers the sintering temperature compared to Example 1. The differences from Example 1 are as follows: In S12, the mass ratio of CeO2 to La2O3 is adjusted to 2:1, and the total added amount is increased to 1.5wt%; in S13, the amount of nano-MgAl2O4 added is increased to 3.0wt%; in S14, the amount of Y-PSZ added is increased to 1.5wt%, and the amount of KH-560 is 0.5wt%, treated at 50℃ for 30 min. In S22, the vibration exhaust section parameters are adjusted to 35Hz, 0.8mm amplitude, and 4s; in S23, the main pressure section pressure is 150MPa, held for 18s, and initially... =0.957, which meets the threshold; no additional loop is needed. =3.035g / cm 3 . S42 in =2.5℃ / min, =400ppm, =1500ppm; the maximum sintering temperature of S44 was reduced to 1580℃; S45 was held at the temperature for 2.5h. Due to the increased CeO2 content, the liquid phase densification efficiency was improved, and the volumetric density target could be met at a lower temperature. The zoned cooling parameters were the same as in Example 1.

[0107] Example 3: This example prepares large-format, thick-body magnesia refractory bricks for the bottom of steel ladles, with a green body size of 300mm × 150mm × 80mm. The differences from Example 1 are as follows: In S11, the proportion of coarse particles is increased to 42wt%, medium particles are reduced to 22wt%, fine particles to 20wt%, and fine powder to 16wt%, to improve the skeleton strength; in S15, the wet mixing time is extended to 10min. In S22, the vibration parameters are adjusted to 45Hz, 1.5mm amplitude, and 5s; in S23, the main pressure section pressure is 170MPa, held for 25s, and initially... =0.908, after 2 replenishment cycles =0.943, which meets the threshold. =3.018g / cm 3 . S42 in Reduced to 200ppm =1800ppm, to cope with the case of thicker billets and longer gas escape paths, the measured CO peak value is about 1200ppm. The minimum temperature drop is approximately 1.1℃ / min, with no cracking throughout the process. The holding time for S45 is set at 4 hours to ensure uniform heat distribution within the 80mm thick billet. The cooling rate for the S51 high-temperature slow cooling zone is set at 3.5℃ / min, and the cooling rate for the S52 critical slow cooling zone is set at 2.0℃ / min to meet the requirements for temperature uniformity inside and outside the cross-section of the large-section billet.

[0108] Comparative Example 1 used the same S1 feedstock as Example 1, but the molding, sintering, and cooling were all performed using conventional methods, serving as a benchmark for comprehensive performance comparison using a fully conventional process. Molding was performed using a hydraulic brick press with unidirectional, single-stage pressurization at 155 MPa, holding pressure for 20 seconds, with no vibration or venting. Closed-loop control, actual measurement =0.872, =2.993g / cm 3 Drying was the same as in Example 1. Sintering used a fixed temperature rise profile: from room temperature to 200°C at a rate of 2.0°C / min; from 200°C to 650°C at a fixed rate of 3.0°C / min without CO concentration feedback adjustment; from 650°C to 1000°C at a rate of 3.5°C / min; from 1000°C to 1620°C at a rate of 4.5°C / min; and a holding time of 1620°C for 4 hours. Cooling was performed by natural heat dissipation after the heating elements were turned off. The average cooling rate was approximately 8°C / min in the 1200°C to 800°C range, without zoned speed control.

[0109] Comparative Example 2, based on Comparative Example 1, only introduces vibration-assisted multi-stage pressure forming. Its S2 step is exactly the same as in Example 1. =0.942, which meets the threshold. =3.014g / cm 3 However, the sintering still uses the fixed heating curve of Comparative Example 1, and the cooling still uses natural cooling.

[0110] Comparative Example 3, based on the single-stage hydraulic forming method of Comparative Example 1, introduces the same S4 ​​atmosphere feedback adaptive segmented sintering and S5 zoned speed-controlled cooling processes as in Example 1, resulting in vibration-free exhaust and... Closed-loop control, actual measurement =0.876, =2.996g / cm 3 .

[0111] Experimental Example 1, Comparison of values ​​and firing pass rates; This experimental example uses the methods of Examples 1 to 3 and Comparative Examples 1 to 3 to compare and analyze the effect of vibration-assisted multi-segment variable pressure forming on the pressure distribution uniformity coefficient. The influence of batch firing pass rate, experimental results are as follows Figure 1 As shown. According to the formula specified in step S23 of this invention Calculation, where The standard deviation of the representative pressure values ​​at all measuring points. The arithmetic mean is used, and the pressure representative value is the average of at least 5 consecutive sampling points. The firing pass rate is statistically analyzed on a batch-by-batch basis, and the pass criteria are no delamination, warping exceeding 2mm, or surface cracks wider than 0.2mm after firing.

[0112] Figure 1 The groups are presented in stem diagram form. Value and firing pass rate. From Figure 1 As can be seen from Example (a), Examples 1 to 3 and Comparative Example 2 employ the vibration exhaust step S22 and the closed-loop control step S23 of the present invention. The values ​​were 0.961, 0.957, 0.943, and 0.942, respectively, all higher than the set threshold of 0.93; Comparative Examples 1 and 3, which did not use vibration-assisted molding, The values ​​were only 0.872 and 0.876 respectively, significantly lower than the threshold. From Figure 1 From (b), we can see that the firing pass rate of each group is related to... The distribution patterns of the values ​​are basically consistent, with Examples 1 to 3 showing a pass rate of 96% to 98%, which is superior to all comparative examples. It is worth noting that the pass rate of Comparative Example 3 is 95%, higher than that of Comparative Example 2 (91%). Comparative Example 3 introduced a CO concentration feedback sintering mechanism, which effectively prevented the green body from cracking caused by excessively rapid gas production in the organic matter decomposition section. This shows that crack prevention sintering control also has an independent and important contribution to improving the pass rate.

[0113] It can be seen that the S22 vibration venting step of the present invention, by applying axial periodic disturbance force to the particles in the depressurized state, disrupts the bridging structure in the accumulated particles, promoting the migration and filling of fine powder into the gaps between coarse particles. The direct mechanism of the enhancement. Step S23 of this invention is based on The online calculation results are used to judge the molding uniformity in real time and... When the threshold is not met, a supplementary cycle is triggered to ensure that the density distribution of each blank meets the set uniformity requirements. This reduces warping and delamination defects caused by excessive density gradient in the fired products from the source of the forming stage, thereby improving the firing qualification rate.

[0114] Experimental Example 2: Comparison of post-firing densification index and mechanical properties; This experimental example uses the methods of Examples 1 to 3 and Comparative Examples 1 to 3 to prepare finished magnesia refractory bricks. The experimental results are as follows: Figure 2 As shown. The compressive strength specimen size is 50mm×50mm×50mm, and the loading rate is 0.15MPa / s; the flexural strength specimen size is 25mm×25mm×150mm, the support span is 125mm, and the loading rate is 0.15MPa / s.

[0115] from Figure 2 (a) and Figure 2 As can be seen from (b), the post-calcination bulk densities of Examples 1 to 3 are 3.05, 3.07, and 3.03 g / cm³, respectively. 3 The apparent porosities were 9.8%, 9.2%, and 10.5%, respectively, all superior to those of Comparative Examples 1 to 3. Particularly noteworthy is Example 2, which achieved a porosity of 3.07 g / cm³ at a sintering temperature of 1580 °C. 3 It exhibits a high bulk density and a low apparent porosity of 9.2%, while Comparative Example 1 has a bulk density of only 2.98 g / cm³ at a higher temperature of 1620 °C. 3 The apparent porosity of 14.2% indicates that the CeO2 and La2O3 composite additive introduced in step S12 of this invention achieves a higher degree of densification while reducing the sintering temperature. CeO2 and La2O3 co-segregate at the grain boundaries, and their eutectic point is lower than their melting temperature when they exist alone. At a lower temperature, a suitable amount of grain boundary liquid phase can be formed. The capillary force generated by the liquid phase drives the particles to rearrange and fill the pores, thereby achieving low-temperature and efficient densification. In contrast, Comparative Examples 1, 2, and 3 do not contain rare earth additives or the additive effect is not fully utilized, resulting in a significantly lower degree of densification.

[0116] from Figure 2 (c) and Figure 2 As can be seen from (d), the room temperature compressive strength of Examples 1 and 2 reached 62 MPa and 65 MPa, respectively, which were 41% and 48% higher than the 44 MPa of Comparative Example 1; the room temperature flexural strength reached 12.5 MPa and 13.2 MPa, respectively, which were 47% and 55% higher than the 8.5 MPa of Comparative Example 1. The significant improvement in mechanical properties can be explained from two aspects: on the one hand, the vibration venting step S22 of this invention improved the initial packing density and density uniformity of the green body, reduced the number of defects in the sintering precursor, and laid the foundation for the formation of a high-strength sintered body; on the other hand, in step S13 of this invention, nano-MgAl2O4 formed a dispersed spinel second phase at the periclase grain boundaries through the Zener pinning mechanism during sintering, which suppressed abnormal grain growth, made the grain size tend to be uniform and refined, enhanced the grain boundary bonding force, and thus improved the room temperature mechanical strength.

[0117] Experimental Example 3: Magnesia refractory bricks prepared using the methods of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to thermal shock stability testing using the water quenching method. The test temperature was 1100℃, and after holding at this temperature for 30 minutes, the bricks were immersed in flowing water for quenching. Failure was defined as the appearance of cracks wider than 0.5 mm or a mass loss exceeding 20%. The number of thermal shock cycles until failure was recorded. The experimental results are as follows: Figure 3 As shown.

[0118] from Figure 3 It can be seen that the number of thermal shock cycles in Examples 1, 2, and 3 were 17, 19, and 15 respectively, all significantly higher than those in the comparative examples. Comparative Example 1 had the lowest number, only 6 cycles; Comparative Example 2 had 9 cycles, and Comparative Example 3 had 12 cycles. The order of the number of thermal shock cycles from low to high is: Comparative Example 1 < Comparative Example 2 < Comparative Example 3 < Example 3 < Example 1 < Example 2. Comparing Comparative Example 2 and Comparative Example 3, it can be found that the number of thermal shock cycles in Comparative Example 3 (12 cycles) is higher than that in Comparative Example 2 (9 cycles), indicating that the contribution of the S52 critical slow cooling zone step of the present invention to the improvement of thermal shock stability is greater than the contribution of vibration-assisted molding alone.

[0119] The S52 critical slow cooling zone step of this invention strictly controls the cooling rate within the 1200℃ to 800℃ range to within 3℃ / min, which is a key technical means to significantly improve thermal shock stability. The Y-PSZ introduced in step S14 of this invention and uniformly dispersed after surface activation treatment undergoes a tetragonal-to-monoclinic martensitic phase transformation in the 1200℃ to 800℃ range. This phase transformation is accompanied by approximately 3% to 5% volume expansion, forming a compressive stress zone at the crack tip to consume crack propagation energy, thereby improving fracture toughness. However, to fully realize the toughening effect of this phase transformation, the phase transformation must occur uniformly throughout the entire cross-section of the billet. If the cooling rate in this temperature range is too fast, the temperature gradient in different parts of the billet increases, the difference in the degree of phase transformation in different regions intensifies, causing inconsistent local volumetric strain and thermomechanical stress concentration. This not only fails to effectively exert the toughening effect but also induces new microcracks. In step S52 of this invention, the temperature difference inside the kiln is controlled within 30°C in real time by a cooling controller, which ensures the uniformity of phase transformation across the entire cross section and allows the phase transformation toughening effect to be fully utilized. Ultimately, the number of thermal shock cycles in the embodiment is increased to more than 15, which is more than twice that of the 6 cycles in Comparative Example 1.

[0120] Experiment Example 4: Dynamic Heating Rate Response of CO Concentration Feedback in Organic Matter Decomposition Section; This experiment uses the S42 organic matter decomposition section of the present invention in Example 1 as the research object. The kiln temperature within the organic matter decomposition zone is used as the abscissa, and the CO volume concentration inside the kiln, detected in real time by an online NDIR analyzer, is recorded. The heating rate is dynamically adjusted by the sintering control unit accordingly. The process of kiln temperature change is shown, and the fixed temperature rise curve of Comparative Example 1 for the same temperature range and the corresponding... Draw the outline together Figure 4 As a control, the experimental results are as follows: Figure 4 As shown.

[0121] from Figure 4 From (a), it can be seen that the heating rate in Example 1 is... The temperature is continuously and dynamically adjusted according to changes in kiln temperature, at approximately 360°C within the peak CO concentration range. The rate dropped to a minimum of approximately 1.6 °C / min, significantly lower than the baseline heating rate. =3.0℃ / min; while Comparative Example 1 The temperature was maintained at a constant 3.0℃ / min, and was not adjusted regardless of changes in the kiln atmosphere. Figure 4 From (b), it can be seen that in Example 1 The peak value is approximately 1100 ppm, lower than The set threshold of 2000 ppm did not trigger the protection action to stop heating throughout the process; in Comparative Example 1, due to the fixed heating rate, the organic matter underwent violent pyrolysis during the rapid heating process. The peak value reached approximately 2350 ppm, exceeding =2000ppm, indicating that the rate of organic gas generation at this fixed heating rate has exceeded the safe gas escape capacity of the green body. As a result, batch 1 in the comparative example experienced cracking and was scrapped, reducing the firing pass rate to 85%. Figure 4 (b) Exceeding The results directly match.

[0122] It can be seen that the dynamic speed regulation formula used in step S42 of this invention With online real-time detection As a feedback signal, the heating rate is closely coupled with the actual gas production intensity of organic matter pyrolysis within the kiln. When When it rises, By proportionally reducing the gas production rate, the gas output per unit time decreases accordingly, maintaining the gas production rate within the safe gas escape capacity of the billet and effectively preventing the gas pressure inside the billet from accumulating to the critical value for cracking; when Down to After that, Automatically restore to This ensures overall heating efficiency. The proportional adjustment strategy achieves a smooth and continuous transition from normal heating to heating cessation, avoiding sudden changes in the heating rate caused by single-threshold switch control, and minimizing heating time while preventing cracking of the billet. In step S42 of this invention, the analyzer uses non-dispersive infrared spectroscopy to detect CO concentration, with a response time of no more than 10 seconds, meeting the requirements of real-time feedback control for sensor response speed.

[0123] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing magnesia refractory bricks, characterized in that, Includes the following steps: S1: Ingredient mixing: After high-purity fused magnesia is graded according to particle size, rare earth composite sintering aid, nano MgAl2O4 spinel powder, surface-activated stabilized ZrO2 powder and organic binder are added in sequence and mixed evenly to obtain the mixture. S2: Vibration-assisted multi-stage variable pressure molding involves adding the compound to a pressing mold and sequentially executing a pre-pressing stage, a vibration venting stage, and a main pressing stage. During the pressure holding period in the main pressing stage, pressure at each measuring point is collected in real time using a pressure sensor array arranged at different height layers of the pressing mold, and the pressure distribution uniformity coefficient is calculated. When the pressure distribution uniformity coefficient is lower than a set threshold, the process returns to the vibration venting stage and repeats the vibration venting stage and main pressing stage sequentially until the pressure distribution uniformity coefficient is not lower than the set threshold, at which point the mold is removed to obtain the billet. S3: Dry the green body until the residual moisture content meets the sintering requirements to obtain a dried green body; S4: Atmosphere feedback adaptive segmented sintering, the dried green body is loaded into a sintering kiln with online gas detection function, and sintering is completed in sequence through a low-temperature drying section, an organic matter decomposition section, a degassing and temperature stabilization section, a high-temperature sintering section and a heat preservation section; in the organic matter decomposition section, the CO concentration in the kiln is detected in real time by an online gas analyzer, and the heating rate of this section is dynamically adjusted according to the detected CO concentration. S5: Zoned controlled cooling. After sintering, the refractory bricks are cooled sequentially in three temperature zones: high temperature slow cooling zone, critical slow cooling zone, and low temperature fast cooling zone, according to the corresponding cooling rates, to obtain the finished magnesia refractory bricks. Step S1 includes the following steps: S11: Particle size distribution. High-purity fused magnesia with MgO content of not less than 97wt% is selected and weighed according to four particle size ranges: coarse, medium, fine and fine powder. The coarse particles form the skeleton and the medium and fine particles fill the gaps step by step to obtain graded magnesia. S12: Add rare earth composite sintering aid. A rare earth composite sintering aid composed of CeO2 powder and La2O3 powder is added to the graded magnesia. The mass ratio of CeO2 to La2O3 is 1:1 to 2:1, and the total amount of the rare earth composite sintering aid added is 0.5 to 1.5 wt% of the total mass of the graded magnesia. During the sintering process, CeO2 and La2O3 segregate and enrich at the periclase grain boundaries, synergistically purifying the grain boundaries and inhibiting the formation of low-melting-point silicate phases to obtain the first mixture. S13: Add nano spinel powder. Add nano MgAl2O4 spinel powder to the first mixture. The amount added is 1 to 3 wt% of the total mass of the graded magnesia. During the sintering process, the nano MgAl2O4 forms a dispersed pinning phase at the periclase grain boundaries, which inhibits the abnormal growth of periclase grains and obtains the second mixture. S14: Add stabilized zirconia micro powder. Add Y2O3 stabilized ZrO2 micro powder that has undergone surface activation treatment to the second mixture. The amount added is 0.5 to 2.0 wt% of the total mass of the graded magnesia. The surface activation treatment makes the ZrO2 micro powder uniformly dispersed in the matrix during the mixing and molding stages, so that it undergoes uniform phase transformation and toughening during sintering and cooling to obtain the third mixture. S15: Add binder and mix. Add modified calcium lignosulfonate solution to the third mixture. The amount added is 2.5 to 3.5 wt% of the total mass of the graded magnesia. Mix evenly with wet to obtain the mixture. Step S2 includes the following steps: S21: Pre-compression section: After adding the mixture into the pressing mold, pre-compression pressure is applied and maintained to initially compact the mixture and discharge the free gas in the large gaps between particles, thus obtaining a pre-compressed material. S22: Vibration exhaust section, which reduces the pre-compression pressure to zero and activates the vibration excitation mechanism to apply vibration along the pressing direction, causing fine powder particles to migrate and fill the gaps between coarse particles and drive closed air bubbles to escape, thereby improving the particle packing density. S23: Main pressure section, applying and maintaining the main pressure; during the pressure holding period, the pressure sensor array continuously collects the pressure at each measuring point, and takes the average value of no less than 5 consecutive sampling points as the representative value of the pressure at each measuring point, and calculates the pressure distribution uniformity coefficient according to the following formula. : ； In the formula, This is the pressure distribution uniformity coefficient, with a value range of [0,1]. The closer the value is to 1, the more uniform the pressure distribution at each measuring point. The standard deviation of the representative pressure values ​​at all measuring points; This is the arithmetic mean of the representative pressure values ​​at all measuring points; when When the pressure distribution is not lower than the set threshold, the uniformity of pressure distribution is deemed acceptable, and the mold is removed to obtain the blank; when If the pressure falls below the set threshold, return to step S22 and repeat the vibration exhaust section and main pressure section sequentially until... After the material is not lower than the set threshold, the mold is removed to obtain the blank. Step S4 includes the following steps: S41: Low-temperature drying section, the kiln temperature rises from room temperature to 200°C, removing residual moisture from the dried billet to obtain a preheated billet; S42: Organic matter decomposition section, kiln temperature rises from 200℃ to 650℃; the CO volume concentration in the kiln is monitored in real time by an online gas analyzer, and the current heating rate is dynamically adjusted according to the following rules: when the CO volume concentration does not exceed the concentration threshold, the temperature is increased normally at the baseline heating rate; when the CO volume concentration exceeds the concentration threshold but is lower than the upper concentration limit, the heating rate is reduced according to the following formula: ； In the formula To dynamically adjust the heating rate; The reference heating rate for the organic matter decomposition section; The volume concentration of CO inside the kiln is detected in real time by an online gas analyzer; The CO concentration threshold that triggers temperature rise rate regulation; To trigger the upper limit of CO concentration for isothermal maintenance; When the CO volume concentration is not lower than the upper limit of the concentration, the heating is stopped and the kiln temperature is kept constant. After the CO volume concentration drops below the concentration threshold, the heating is resumed at the baseline heating rate to complete the decomposition of organic matter. S43: Degassing and temperature stabilization section, the kiln temperature rises from 650℃ to 1000℃, removing residual decomposition gases of organic matter and making the temperature of the billet more uniform. S44: High-temperature sintering section, where the kiln temperature rises from 1000℃ to the maximum sintering temperature to complete densification sintering; S45: Heat preservation section, constant temperature heat preservation at the highest sintering temperature, the heat preservation time is determined according to the maximum thickness of the green body and the target bulk density, the thicker the green body or the higher the target density, the longer the heat preservation time is taken; after the heat preservation is completed, proceed to step S5. Step S5 includes the following steps: S51: High-temperature slow cooling zone, cooling from the highest sintering temperature to 1200℃, controlling the cooling rate to prevent thermal stress cracks from forming in the billet due to excessive internal and external temperature differences. S52: Critical slow cooling zone, cooling from 1200℃ to 800℃, controlling the cooling rate to a level lower than that of the high-temperature slow cooling zone; at the same time, by monitoring the temperature of each temperature measuring point in the kiln, adjusting the speed of the cooling fan in each cooling section to control the temperature difference between each temperature measuring point in the kiln. S53: Low-temperature rapid cooling zone, cooling from 800℃ to room temperature, with a cooling rate higher than that of the critical slow cooling zone, yielding magnesia refractory brick finished product after exiting the kiln.

2. The preparation method according to claim 1, characterized in that, The surface activation treatment in step S14 includes the following steps: The Y2O3-stabilized ZrO2 micro powder was dispersed in anhydrous ethanol, a silane coupling agent was added, and the mixture was stirred under heating conditions, then filtered and dried to obtain surface-activated ZrO2 micro powder.

3. An apparatus for preparing magnesia refractory bricks for implementing the preparation method of claim 1, characterized in that, This includes a vibration-assisted multi-stage variable pressure molding machine, an atmosphere feedback sintering kiln, and an integrated control system; The vibration-assisted multi-segment variable pressure molding machine includes a hydraulic pressurizing unit, a vibration excitation mechanism, a pressing die, a pressure sensor array, and a molding control unit. The hydraulic pressurizing unit is connected to a hydraulic cylinder via a proportional servo valve. The piston rod of the hydraulic cylinder is connected to an upper press head, which is positioned directly above the pressing die. The vibration excitation mechanism is connected to the upper press head or the die frame of the pressing die and is used to apply vibration along the pressing direction. The pressure sensor array is installed on the inner wall of the pressing die and distributed at different heights along the pressing direction. The signal output terminals of each sensor are connected to the signal input terminals of the molding control unit. The control output terminals of the molding control unit are connected to the control terminals of the hydraulic pressurizing unit and the vibration excitation mechanism, respectively. The molding control unit has a built-in real-time calculation module for the pressure distribution uniformity coefficient and a multi-segment variable pressure logic control module. The atmosphere feedback sintering kiln includes a multi-section electrically heated kiln body, an online gas analysis module, a multi-zone temperature control module, a cooling rate control unit, and a sintering control unit; The online gas analysis module is installed at the exhaust port of the kiln chamber corresponding to the organic matter decomposition temperature zone, and its signal output terminal is connected to the signal input terminal of the sintering control unit; the control output terminal of the sintering control unit is connected to the multi-zone temperature control module, and the multi-zone temperature control module is connected to the heating element of each temperature control zone; the control output terminal of the cooling rate control unit is connected to the cooling fan, and its signal input terminal receives the detection signal from the temperature sensor in the kiln; the sintering control unit has a built-in dynamic heating rate calculation module for the organic matter decomposition section. The integrated control system interconnects the forming control unit and the sintering control unit through a communication network. The forming control unit automatically transmits the measured green bulk density data to the sintering control unit for use in determining the holding time.

4. The preparation apparatus according to claim 3, characterized in that: The vibration excitation mechanism includes a variable frequency eccentric vibration motor and an elastic vibration isolation pad. The variable frequency eccentric vibration motor is installed on the side of the upper pressure head, and the vibration direction is axial vibration along the pressing direction. The vibration frequency and amplitude are adjustable. In the vibration exhaust section, an axial periodic disturbance force is applied to the mixture to promote the migration of fine powder particles into the gaps between coarse particles. The elastic vibration isolation pad is set between the vibration excitation mechanism and the frame to prevent vibration from being transmitted to the frame and affecting the pressure control accuracy of the hydraulic pressurization unit. The pressure sensor array is divided into upper, middle and lower layers along the inner wall of the pressing mold. Pressure sensors are evenly arranged in each layer along the circumferential direction of the cross section to capture the pressure distribution of the blank along the pressing direction and the cross section direction. The pressing mold is also equipped with an axial displacement sensor, which is installed on the drive shaft of the hydraulic cylinder and connected to the forming control unit to measure the displacement of the upper pressure head in real time to monitor the amount of blank compression. The multi-section electrically heated kiln body contains multiple independent temperature control zones, each equipped with heating elements and temperature detection elements, and thermal insulation structures are provided between adjacent temperature control zones; the online gas analysis module uses non-dispersive infrared spectroscopy to detect CO concentration; the cooling rate control unit includes cooling air ducts arranged along the top and side walls of the kiln, variable frequency speed-regulating cooling fans connected to the cooling air ducts, and a cooling controller; each cooling section has an independent air duct and a corresponding variable frequency speed-regulating cooling fan, and thermal insulation partitions are provided between adjacent cooling sections; the signal input terminal of the cooling controller is connected to the kiln temperature sensor, and the control output terminal is connected to the variable frequency speed-regulating cooling fan of each section, independently controlling the cooling rate in the high-temperature slow cooling zone, the critical slow cooling zone, and the low-temperature fast cooling zone.

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