Preparation method of high-temperature-resistant and impact-resistant fluorite balls

Abstract

The invention belongs to the technical field of fluorite ball preparation, and particularly relates to a preparation method of a high-temperature-resistant and impact-resistant fluorite ball, which comprises the steps of raw material preparation, composite binder preparation, material mixing, molding, pre-curing, sintering and cooling. By using the composite binder and the gradient particle grading method, the phenomena of softening and structure loosening at high temperature are avoided, and through the synergistic effect of'coarse particle skeleton supporting-filling coarse particle gaps with medium particles-filling medium particle gaps with fine particles', the void ratio of the fluorite balls is reduced to 8% or below, and the structural integrity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorite ball preparation, and in particular to a method for preparing high-temperature resistant and impact-resistant fluorite balls suitable for high-temperature working conditions in metallurgy, chemical industry, building materials and the like. Background Art

[0002] Fluorite (mainly composed of Due to its excellent fluxing properties, chemical stability, and optical properties, fluorite is widely used in the metallurgical industry (as a flux for steelmaking and a raw material for continuous casting mold slag), the chemical industry (for the production of hydrofluoric acid and fluorides), and the building materials industry (for fluxing glass and ceramics). In practical applications, fluorite is often processed into spherical structures (fluorite balls) to reduce transportation losses and improve material fluidity and reaction efficiency under working conditions. However, existing fluorite ball production technology has significant deficiencies in high-temperature resistance and impact resistance, making it difficult to meet the long-term use requirements of high-temperature and harsh working conditions (such as steelmaking converters and cement rotary kilns, where operating temperatures often reach 800-1200°C).

[0003] The existing fluorite ball preparation process mainly uses silicate cement as a binder, which can make the fluorite ball compressive strength reach more than 20MPa at room temperature. However, under high temperature environment above 800℃, the silicate cement Dehydration will occur, producing Easy to react with impurities in fluorite powder (such as 、 ) reacts to form a low melting point glass (such as , melting point 1544°C, but begins to soften at 1000°C), resulting in a loose structure and a sharp drop in strength of the fluorite spheres. Experimental data showed that after being held at 1000°C for 2 hours, the patented product's impact strength was only 1.2 MPa, and its cracking rate was as high as 30%, making it unsuitable for use in high-temperature environments such as steelmaking converters. Organic resin binders (such as phenolic resin) carbonize and burn above 300°C, completely losing their adhesive properties and making them unsuitable for high-temperature applications. Summary of the Invention

[0004] In order to make up for the deficiencies of the prior art and solve the above technical problems, the present invention proposes a method for preparing high-temperature resistant and impact-resistant fluorite balls.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing a high-temperature resistant and impact-resistant fluorite ball according to the present invention comprises the following steps: Raw material preparation: selection Fluorite powder with a purity of ≥95%, wherein the fluorite powder is graded by mass percentage, with coarse particles (1-3 mm) 25-35%, medium particles (0.1-1 mm) 45-55%, and fine particles (≤0.1 mm) 15-25%; a composite binder is prepared, wherein the composite binder is composed of 80-90% modified calcium aluminate cement, 8-12% nano inorganic particles, and 2-5% silane coupling agent. The dosage is 2%; Raw material pretreatment: drying the gradient-graded fluorite powder in a drying oven at 105-110°C for 2-3 hours to reduce the moisture content of the fluorite powder to ≤0.5%; mixing the nano-inorganic particles with deionized water at a solid-liquid mass ratio of 1:5, and ultrasonically dispersing the mixture at a power of 300-500W for 10-20 minutes to form a nano-particle dispersion; Preparation of composite binder: adding the modified calcium aluminate cement, nanoparticle dispersion, and silane coupling agent into a stirring kettle, stirring at 300-500 r / min for 15-30 min to obtain a paste-like composite binder; Material mixing: Add the pretreated fluorite powder and the paste-like composite binder into a double-screw mixer at a mass ratio of 85:15-90:10, add deionized water to adjust the material humidity to 10-15%, and stir at 200-300 r / min for 20-30 minutes to obtain a uniform mixture; Molding: placing the mixed material in a spherical mold, applying a pressure of 20-30 MPa using a hydraulic molding machine, and maintaining the pressure for 5-10 seconds to obtain a fluorite ball green body; Pre-curing: placing the fluorite ball green body in a constant temperature and humidity curing box, curing for 20-28 hours at a temperature of 50-70°C and a relative humidity of 75-85%; Sintering: Place the pre-cured green body in a roller kiln, heat it to 1000-1200℃ at 5-10℃ / min, and keep it at this temperature for 2-4h; Cooling: The sintered fluorite balls are cooled to room temperature along with the furnace, with a cooling rate of ≤10℃ / min to obtain high temperature resistant and impact resistant fluorite balls.

[0006] Preferably, the nano inorganic particles are nano or nano , the nano The particle size is 20-50nm, the nano The particle size is 30-60nm.

[0007] Preferably, when the nano inorganic particles are nano When the composite binder is composed of 85% modified calcium aluminate cement, nano 10%, silane coupling agent KH-5505%.

[0008] Preferably, when the nano-inorganic particles are nano , the composite binder is composed of modified calcium aluminate cement 88%, nano 9%, silane coupling agent (KH-550) 3%.

[0009] Preferably, in the raw material preparation step, the gradient grading of the fluorite powder is that coarse particles (1-3mm) account for 30%, medium particles (0.1-1mm) account for 50%, and fine particles (≤0.1mm) account for 20%.

[0010] Preferably, in the composite binder preparation step, the power of ultrasonic dispersion is 400W, and the dispersion time is 15min.

[0011] Preferably, in the molding step, the molding pressure is 25MPa, and the pressure maintaining time is 8s; in the pre-curing step, the pre-curing temperature is 60℃, the relative humidity is 80%, and the curing time is 24h.

[0012] Preferably, in the sintering step, the heating rate is 8℃ / min, the sintering temperature is 1100℃, and the holding time is 3h; in the cooling step, the cooling rate is 8℃ / min.

[0013] The advantages of the present application are as follows: 1. The present application provides basic bonding force and high-temperature resistant framework through a composite binder system composed of modified calcium aluminate cement (80-90%), nano-inorganic particles (8-12%), and silane coupling agent (2-5%), wherein the modified calcium aluminate cement (modified by adding 2% of , to improve high-temperature resistance) provides basic bonding force and high-temperature resistant framework, the nano-inorganic particles (nano or nano ) fill micro gaps and enhance interface bonding, and the silane coupling agent (such as KH-550) improves the interface compatibility of the binder and the fluorite powder; the modified calcium aluminate cement is converted into anhydrous aluminate (CaAl2O4, , , with melting points of 1535℃ and 1455℃, respectively) at high temperature, the nano particles react with the fluorite powder and the cement components to generate high-temperature stable phases (CaAl4O7, , , with melting points all greater than 1500℃), so that the fluorite ball has no softening and no structural loose phenomenon in the range of 800-1200℃.

[0014] 2. The present invention adopts a gradient particle grading method, with the mass percentage being 25-35% of coarse particles (1-3mm), 45-55% of medium particles (0.1-1mm), and 15-25% of fine particles (≤0.1mm). This grading can reduce the void ratio of fluorite balls to below 8% and improve structural integrity through the synergistic effect of "coarse particles supporting the skeleton - medium particles filling the gaps between coarse particles - fine particles filling the gaps between medium particles". BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is a flowchart of Example 1; Figure 2 The figures are experimental data of Examples and Comparative Examples. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example 1 ( Particles Please combine Figure 1 , a method for preparing high-temperature resistant and impact-resistant fluorite balls, comprising the following steps; 1. Raw material preparation: Fluorite powder: Purity 96.5%, impurities 1.8%, 0.9%; by mass ratio, coarse particles (1-3mm) 30%, medium particles (0.1-1mm) 50%, fine particles (≤0.1mm) 20%; Composite binder: modified calcium aluminate cement ( Dosage 2%) 85kg, nano (particle size 20-50nm) 10kg, silane coupling agent (KH-550) 5kg.

[0019] 2. Raw material pretreatment The fluorite powder was dried at 105℃ for 2.5h to reduce the moisture content to 0.4%. The free water in the fluorite powder was removed to avoid the cracking of the green body caused by the evaporation of water after molding. nanometer Add 50kg deionized water and disperse ultrasonically for 15min at 400W power to form nanoparticles. The function of the dispersion is to break up the agglomeration of nanoparticles, ensure that they are evenly dispersed in the binder, and give full play to their microscopic filling effect.

[0020] 3. Preparation of Composite Binder Modified calcium aluminate cement, nano The dispersion and KH-550 were added into the stirring kettle and stirred at 400 r / min for 20 min to obtain a paste-like binder, so that the binder components were fully mixed, the nanoparticles were evenly distributed, and the silane coupling agent fully coated the cement particles and nanoparticles, laying the foundation for the subsequent interface bonding with fluorite powder.

[0021] 4. Material mixing Take 900 kg of pretreated fluorite powder and add it into a double-screw mixer, add 100 kg of composite binder, and at the same time add deionized water to adjust the humidity to 12%, stir at 250 r / min for 25 minutes to obtain a uniform mixture, ensure that the composite binder evenly covers the fluorite powder particles, and humidity control can ensure the formability of the material, avoiding over-drying resulting in loose green body or over-wetting resulting in uneven shrinkage after forming.

[0022] 5. Molding The material is placed in a spherical mold with a diameter of 8 mm, a pressure of 25 MPa is applied, and the pressure is maintained for 8 seconds to obtain a fluorite ball green body. The pressure makes the material tightly combined to form a spherical structure with a certain initial strength.

[0023] 6. Pre-curing The green body is cured in a curing box at 60℃ and 80% relative humidity for 24h to promote the full hydration of modified calcium aluminate cement and generate stable hydration products ( ), so that the green body forms a dense initial structure, avoiding cracking caused by rapid evaporation of water during subsequent high-temperature sintering; at the same time, the hydration products form a preliminary synergistic combination with the nanoparticles and silane coupling agent, thereby improving the strength of the green body.

[0024] 7. Sintering The green body is placed in a roller kiln and heated to 1100℃ at a rate of 8℃ / min and kept warm for 3 hours. Slow heating can avoid thermal stress cracking of the green body caused by sudden temperature rise. The sintering temperature of 1000-1200℃ can further convert the hydration products of modified calcium aluminate cement into high temperature resistant anhydrous aluminate (such as 、 ), while the nanoparticles react with the fluorite powder and cement components (such as nano and Reaction generation , and cement Reaction generation ), forming a dense high-temperature stable phase, improving the high-temperature resistance and structural strength of the fluorite ball. The specific reaction steps are as follows; Step 1: Nano + → + ↑ (provide reaction raw materials ); Step 2: Respectively 、 Reaction generation 、 (basal stable phase); Step 3: + + → (Double salt stable phase, highest melting point).

[0025] 8. Cooling Cool down to room temperature with the furnace at a cooling rate of 8℃ / min. Slow cooling can avoid thermal stress in the fluorite balls due to excessive temperature difference and prevent cracking.

[0026] Example 2 ( Particles Comparative Example 1, as another embodiment of the present invention; the method for preparing a high-temperature resistant and impact-resistant fluorite ball, with other steps remaining unchanged: Raw material pretreatment: Fluorite powder was dried at 105℃ for 2.5h, and the moisture content was reduced to 0.4%; nanometer Add 27kg deionized water and disperse ultrasonically for 15min at 400W power to form nanoparticles. dispersion.

[0027] Composite adhesive preparation: Modified calcium aluminate cement, nano The dispersion and KH-550 were added into the stirring kettle and stirred at 350 r / min for 25 min to obtain a paste-like adhesive.

[0028] Example 3 Comparative Example 1, as another embodiment of the present invention; the method for preparing a high-temperature resistant and impact-resistant fluorite ball, with other steps remaining unchanged: In the raw material preparation step, the fluorite powder is composed of 15% coarse particles (1-3mm), 50% medium particles (0.1-1mm), and 35% fine particles (≤0.1mm) by mass.

[0029] Example 4 Comparative Example 1, as another embodiment of the present invention; the method for preparing a high-temperature resistant and impact-resistant fluorite ball, with other steps remaining unchanged: In the raw material preparation step, the fluorite powder is composed of 20% coarse particles (1-3mm), 50% medium particles (0.1-1mm), and 30% fine particles (≤0.1mm) by mass.

[0030] Example 5 Comparative Example 1, as another embodiment of the present invention; the method for preparing a high-temperature resistant and impact-resistant fluorite ball, with other steps remaining unchanged: In the raw material preparation step, the fluorite powder is composed of 25% coarse particles (1-3mm), 50% medium particles (0.1-1mm), and 25% fine particles (≤0.1mm) by mass.

[0031] Example 6 Comparative Example 1, as another embodiment of the present invention; the method for preparing a high-temperature resistant and impact-resistant fluorite ball, with other steps remaining unchanged: In the raw material preparation step, the mass ratio of fluorite powder is 35% of coarse particles (1-3mm), 50% of medium particles (0.1-1mm), and 15% of fine particles (≤0.1mm).

[0032] Example 7 Comparative Example 1, as another embodiment of the present invention; the method for preparing a high-temperature resistant and impact-resistant fluorite ball, with other steps remaining unchanged: In the raw material preparation step, the fluorite powder is composed of 40% coarse particles (1-3mm), 50% medium particles (0.1-1mm), and 10% fine particles (≤0.1mm) by mass.

[0033] Comparative Example 1 Using conventional technology Fluorite powder: single particle size (1-3mm), Purity is about 96%; Binder: Portland cement (P.O42.5); Process: Mix fluorite powder + 15% silicate cement, add water to disperse, shape at 20MPa, cure at room temperature for 24h, and sinter at 1000℃ for 2h.

[0034] Comparative Example 2 (missing nanoparticles in the composite binder) Fluorite powder: same as example one (gradient grading: coarse 30% + medium 50% + fine 20%); Binder: only modified calcium aluminate cement (85%) + silane coupling agent KH-550 (5%), remove nano-SiO2, fluorite powder and binder mass ratio 90:10; The rest of the process: same as example one (105℃ drying 2.5h→ binder stirring→ 25MPa forming→ 60℃ / 80% humidity pre-curing 24h→ 1100℃ sintering 3h→ 8℃ / min cooling).

[0035] Comparative example three (missing gradient particle grading, using two-level grading) Fluorite powder: two-level grading (coarse particles 1-3mm 60% + fine particles ≤0.1mm 40%), no medium particles, Purity same as example one; Binder: same as example 1 (modified calcium aluminate cement 85% + nano 10% + KH-550 5%); The rest of the process: same as example one.

[0036] Comparative example four (missing silane coupling agent in composite binder) Fluorite powder: same as example one; Binder: only modified calcium aluminate cement (90%) + nano (10%), remove silane coupling agent KH-550; The rest of the process: same as example one.

[0037] Comparative example five (using ordinary calcium aluminate cement instead of modified calcium aluminate cement) Fluorite powder: same as example one; Binder: ordinary calcium aluminate cement (85%) + nano (10%) + KH-550 (5%), no Modification; The rest of the process: same as example one.

[0038] After performance testing of impact strength, cracking rate, porosity and compressive strength indicators, the experimental data comparison table is shown in Figure 2 : When example 1 and example 2 use the same gradient particle grading, the impact strength of inorganic particles as alumina is slightly higher than that of silicon oxide, the cracking rate is slightly lower than that of silicon oxide, and the compressive strength is slightly higher than that of silicon oxide.

[0039] By comparing Example 1 and Examples 3-7, it can be seen that different gradient particle gradations will lead to different void ratios. The actual values ​​of the gaps in Examples 1, 5 and 6 are all below 7%. If the medium particles are quantitatively controlled to be 50%, the large particles and small particles are optimally in the range of 25-35% and 15-25%, respectively.

[0040] Comparative Example 2: Missing Nano After that, the microscopic gaps cannot be effectively filled, the interfacial bonding force is weakened, resulting in an increase in porosity and a significant decrease in impact strength and high-temperature compressive strength, proving that the "microscopic densification" role of nanoparticles is indispensable.

[0041] In Comparative Example 3, the two-graded pairing lacks medium particles to fill the gaps between coarse and fine particles, the void ratio increases significantly (from 6.2% to 12.1%), the structural integrity decreases, and the impact resistance weakens, proving the key role of the "coarse-medium-fine" three-level gradient grading in reducing the void ratio and improving structural stability.

[0042] Combined with Comparative Example 4, the silane coupling agent can improve the interface compatibility between the binder and the fluorite powder (the interface shear strength decreases by 40%). After its absence, the interface bonding force is weakened and interface cracks are easily generated, proving its key role in "interface strengthening".

[0043] In Comparative Example 5, ordinary calcium aluminate cement is easily decomposed at high temperature (C3A retention rate is only 50% at 1200℃), while Modification can improve the high-temperature stability of cement (C3A retention rate reaches 90%). Without modification, the high-temperature skeleton collapses and the performance decreases significantly, proving the "high-temperature skeleton support" role of modified calcium aluminate cement.

[0044] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0045] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for preparing high-temperature resistant and impact-resistant fluorite balls, characterized in that: The following steps are involved: S1: Select fluorite powder, which is graded by mass percentage and consists of 25-35% coarse particles (1-3mm), 50% medium particles (0.1-1mm), and 15-25% fine particles (≤0.1mm). Select a composite binder, which includes 80-90% modified calcium aluminate cement and 8-12% nano inorganic particles. The dosage is 2%; S2: drying the fluorite powder in a drying oven to reduce the moisture content of the fluorite powder to ≤0.5%; mixing the nano inorganic particles with deionized water to form a nano particle dispersion; S3: adding the modified calcium aluminate cement, nanoparticle dispersion, and silane coupling agent into a stirring tank to obtain a paste-like composite binder; S4: Add the pretreated fluorite powder and the paste-like composite binder in a mass ratio of 85:15-90:10 into a double-screw mixer, and add deionized water to adjust the material humidity to 10-15% to obtain a uniform mixture; S5: placing the mixed material in a spherical mold, using hydraulic molding to obtain a fluorite ball green body, placing the fluorite ball green body in a constant temperature and humidity curing box for curing, placing the pre-cured green body in a roller kiln for insulation for 2-4 hours, and cooling the sintered fluorite ball to room temperature with the furnace to obtain a high temperature resistant and impact resistant fluorite ball.

2. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 1, characterized in that: The S1 selection Fluorite powder with a purity of ≥95%, in S2, the nano inorganic particles are mixed with deionized water at a solid-liquid mass ratio of 1:5, and ultrasonically dispersed at a power of 300-500W for 10-20 minutes.

3. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 1, characterized in that: The S4 double-screw mixer stirs at 200-300 r / min for 20-30 minutes to obtain a uniformly mixed material. The hydraulic molding machine in S5 applies a pressure of 20-30 MPa and maintains the pressure for 5-10 seconds to obtain a fluorite ball green body. The fluorite ball green body is placed in a constant temperature and humidity curing box and cured for 20-28 hours at a temperature of 50-70°C and a relative humidity of 75-85%. The pre-cured green body is placed in a roller kiln, heated to 1000-1200°C at 5-10°C / min, kept warm for 2-4 hours, and cooled to room temperature at a cooling rate of ≤10°C / min.

4. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 1, characterized in that: The nano inorganic particles are nano or nano , the nano The particle size is 20-50nm, the nano The particle size is 30-60nm.

5. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 2, characterized in that: When the nano inorganic particles are nano When the composite binder is composed of 85% modified calcium aluminate cement, nano 10%, and the composite adhesive further comprises 5% silane coupling agent.

6. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 2, characterized in that: When the nano inorganic particles are nano When the composite binder is composed of 88% modified calcium aluminate cement, nano 9%, and the composite adhesive also includes 3% silane coupling agent.

7. A method for preparing high-temperature-resistant and impact-resistant fluorite balls according to any one of claims 1 to 6, characterized in that: In S1, the gradient gradation of the fluorite powder is as follows: coarse particles (1-3 mm) account for 30%, medium particles (0.1-1 mm) account for 50%, and fine particles (≤0.1 mm) account for 20%.

8. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 1, characterized in that: In S2, the ultrasonic dispersion power is 400 W and the dispersion time is 15 min.

9. The method for preparing high-temperature-resistant and impact-resistant fluorite balls according to claim 1, characterized in that: In S5, the molding pressure is 25 MPa, the holding time is 8 seconds, the pre-curing temperature is 60° C., the relative humidity is 80%, and the curing time is 24 hours.

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