High-strength long-life RH dip pipe gunning mix and preparation method thereof

Abstract

The invention relates to a high-strength long-life RH dip pipe gunning mix and a preparation method thereof. The gunning mix is prepared from the following raw materials in parts by weight: 55-70 parts of a waste magnesite-chrome brick reworked material of which the particle size is less than or equal to 5mm, 18-28 parts of fused magnesite skin sand of which the particle size is 180-240 meshes, 3-7 parts of chromium aluminum phosphate, 2-5 parts of a complexing magnesium-aluminum cementing agent, 1-3 parts of activated bentonite, 0.2-0.5 part of calcium lignosulphonate, 0.5-1.5 parts of lanthanum oxide, 0.2-0.6 part of modified carbon fiber and 0.3-0.8 part of polyacrylamide. The RH gunning mix is low in rebound, high in adhesion, rapid in hardening, high in sintering strength, resistant to erosion and scouring, low in cost and long in service life.

Description

Technical Field

[0001] This invention relates to the field of refractory materials for RH vacuum refining, and in particular to a high-strength, long-life RH impregnation pipe spraying material and its preparation method. Background Technology

[0002] The RH vacuum refining furnace is a crucial piece of equipment for external secondary refining, especially for producing ultra-low carbon, high-quality steels such as automotive steel. RH vacuum refining achieves refining effects unmatched by other refining equipment. The RH vacuum refining furnace consists of hot bending tubes, a central trough, a bottom trough, circulating tubes, and impregnation tubes. The service life of the impregnation tubes directly impacts the furnace's utilization efficiency. Due to the extremely harsh working conditions of the impregnation tubes—directly contacting steel and slag while enduring extreme temperatures—the refractory material consumption is very high. Relying solely on the brickwork and castable refractory material of the impregnation tubes to withstand these conditions makes it difficult to achieve a long service life. Generally, repair spraying is used to extend the service life of the impregnation tubes. Currently, some steel mills have the equipment and process conditions to perform spray repair maintenance on weak parts of the immersion tube after refining one heat of steel. However, many steel mills still only have the conditions for spray repair maintenance after the immersion tube has been continuously refined for 5-7 heats. This continuous refining process requires the spray material to have good corrosion resistance and erosion resistance in order to better protect the immersion tube body material, reduce the consumption of the body material, and achieve a long service life for the immersion tube.

[0003] Traditional RH-impregnated pipe spraying materials suffer from problems such as high rebound rate (typically 15%-25%), poor adhesion, long hardening time, low high-temperature strength, poor corrosion resistance, and easy peeling at high temperatures. Generally, the spraying material is basically consumed after processing 3-4 heats of steel, which means that subsequent heats of steel can only consume the impregnated pipe body, resulting in the impregnated pipe not achieving a long service life. At the same time, due to the high rebound rate of the spraying material, the waste of the spraying material is relatively serious, resulting in high cost of using the spraying material. Summary of the Invention

[0004] This invention addresses the technical problems of traditional spray coating materials, such as high rebound rate, low high-temperature strength, poor erosion resistance, and easy peeling. It proposes an RH spray coating material with low rebound, high adhesion, fast hardening, high sintering strength, erosion and scour resistance, low cost, and long service life, as well as its preparation method.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A high-strength, long-life RH-impregnated pipe spraying material is prepared from the following raw materials in parts by weight: 55-70 parts of recycled waste magnesia-chrome brick with a particle size ≤5mm, 18-28 parts of fused magnesia sand with a particle size of 180-240 mesh, 3-7 parts of aluminum chromium phosphate, 2-5 parts of complexed magnesia-alumina binder, 1-3 parts of activated bentonite, 0.2-0.5 parts of calcium lignosulfonate, 0.5-1.5 parts of lanthanum oxide, 0.2-0.6 parts of modified carbon fiber, and 0.3-0.8 parts of polyacrylamide.

[0006] Carbon fibers are modified with an Al2O3 coating to improve their high-temperature resistance. Unmodified carbon fibers typically begin to oxidize at 400℃ and experience significant burn-off above 800℃. Modified carbon fibers can have an oxidation initiation temperature of 800–1000℃ and maintain a stable structure above 1400℃, retaining ≥60% of their residual strength, thus preventing the loss of reinforcing properties due to ablation at high temperatures. Simultaneously, the surface polarity of the modified carbon fibers is significantly increased, and agglomeration is significantly reduced, ensuring excellent uniform dispersion during the mixing of sprayed materials and preventing strength reduction caused by localized defects.

[0007] The physicochemical properties of the raw materials for RH impregnation pipe spraying are shown in Table 1.

[0008] Table 1 Physicochemical properties of the main raw materials for RH impregnation pipe spraying material A method for preparing a high-strength, long-life RH-impregnated pipe spraying compound, the method comprising the following steps: 1) Aggregate pretreatment: After crushing, the recycled material of waste magnesium chrome bricks is graded and screened. It is soaked in 5% dilute hydrochloric acid for 30 minutes to remove impurities, rinsed with clean water until neutral, and dried at 110℃ for 4-5 hours for later use.

[0009] 2) Premixing of binders and additives: In order to ensure the uniformity of the sprayed material mixing, aluminum chromium phosphate, complexed magnesium aluminum binder, activated sodium bentonite, lanthanum oxide, calcium lignosulfonate and polyacrylamide are first fully premixed using a double helix conical premixer for 10-15 minutes to make premixed powder, which is then bagged for later use.

[0010] 3) Use an inclined high-speed mixer for mixing. The mixing sequence is as follows: first add the waste magnesia-chrome brick recycled material and fused magnesia sand and mix for 1 to 3 minutes, then add the premixed powder and modified carbon fiber and mix for another 10 to 15 minutes. The modified carbon fiber should be added in a dispersed manner to avoid agglomeration.

[0011] The mixed dry materials were tested for physicochemical properties according to national or industry standards. The physicochemical properties and service life of the finished product are shown in Table 2.

[0012] Table 2 Physicochemical properties of finished product Compared with the prior art, the beneficial effects of the present invention are: 1) This invention uses aluminum chromium phosphate as a binder, enabling the sprayed material to quickly bond and form a sprayed layer with a certain strength after being sprayed onto the surface of the RH-impregnated pipe. This ensures the bonding strength between the sprayed material and the impregnated pipe, as well as between the particles of the sprayed material itself, preventing the sprayed layer from peeling off during use. Simultaneously, aluminum chromium phosphate undergoes a series of chemical reactions at high temperatures, gradually transforming into a high-temperature resistant ceramic phase. These ceramic phases have high melting points and good thermal stability, thereby improving the high-temperature strength and resistance to deformation of the sprayed material, effectively resisting the high-temperature erosion and scouring of molten steel. Furthermore, the presence of chromium reduces the wetting angle between slag and the sprayed material, reducing slag adhesion and penetration onto the surface of the sprayed material, further improving its erosion resistance and spalling resistance, thus extending the service life of the impregnated pipe. Currently, in a steel group's steelmaking plant, the high-strength sprayed material of this invention has a service life of over 7 heats.

[0013] 2) This invention uses a complexed magnesium-aluminum binder as a reinforcing agent. This binder undergoes a hydration reaction upon contact with water, enabling the sprayed material to quickly form a supportable structure after spraying, improving the room temperature strength of the sprayed material and preventing material collapse. At medium and high temperatures, this material will play a sintering promoting role, promoting the formation of ceramic sintering bonds between the particles inside the sprayed material and the binder itself. Furthermore, the magnesium aluminate in the main body of the binder will form a stable spinel phase, improving the high temperature resistance and corrosion resistance of the sprayed material. At the same time, it can also improve the stability of the sprayed material, reduce the damage to the sprayed layer caused by sudden changes in RH furnace temperature, and extend the service life of the sprayed material.

[0014] 3) This invention employs lanthanum oxide and modified carbon fiber as synergistic functional optimization agents. Lanthanum oxide accumulates and forms second-phase particles at the grain boundaries of the sprayed material, preventing abnormal grain growth through "grain boundary pinholes" and strengthening boundary bonding. Modified carbon fiber acts as a skeleton dispersed in the sprayed material. When cracks occur, the fibers can hinder crack propagation and absorb fracture energy. The synergy of these two agents significantly improves the flexural strength and fracture toughness of the sprayed material, preventing cracking and peeling of the sprayed layer due to thermal stress during RH furnace operations. Simultaneously, lanthanum oxide can compensate for the loss of some elements due to volatilization at high temperatures and can form a stable phase with components in molten steel and slag. Modified carbon fiber synergistically constructs a dense protective layer, inhibiting the inward diffusion of oxidizing gases in the furnace and resisting the erosion of molten steel and slag. The synergy of these two agents reduces the rate of erosion and ablation of the sprayed layer, extending the service life of the sprayed material.

[0015] 4) This invention uses activated bentonite as a plasticizer. It mainly utilizes the fact that after activation, the internal pore structure of bentonite is expanded, the specific surface area is increased, and it is easier to lock in the moisture of the powder. This enhances the adsorption capacity during spraying. At the same time, the activated bentonite optimizes its interlayer structure and enhances the synergistic effect with calcium lignosulfonate, thereby improving the adhesion performance of the spraying material. This makes the spraying material less prone to peeling and cracking during the spraying process, effectively reducing the rebound rate of the spraying material. The rebound rate can be reduced by more than 30% compared with conventional spraying materials, which significantly reduces the spraying and maintenance cost of RH impregnation pipes.

[0016] 5) This invention uses recycled waste magnesia-chrome bricks as aggregate, which is a recycling technology for waste refractory materials, realizing circular economy, energy conservation and emission reduction, and has good economic and social benefits. Detailed Implementation

[0017] The following embodiments are further illustrations of the invention, but the invention is not limited thereto.

[0018] Example 1: The high-strength, long-life RH impregnated pipe spraying material is made from the following raw materials in the following weight ratios: 66 parts of recycled waste magnesia-chrome brick with a particle size ≤5mm, 22 parts of fused magnesia sand with a particle size of 180-240 mesh, 5 parts of aluminum chromium phosphate, 3 parts of complexed magnesia-alumina binder, 2 parts of activated bentonite, 0.3 parts of calcium lignosulfonate, 1 part of lanthanum oxide, 0.4 parts of modified carbon fiber, and 0.3 parts of polyacrylamide.

[0019] Example 2: The high-strength, long-life RH impregnated pipe spraying material is made from the following raw materials in the following weight ratios: 58 parts of recycled waste magnesia-chrome brick with a particle size ≤5mm, 28 parts of fused magnesia sand with a particle size of 180-240 mesh, 6 parts of aluminum chromium phosphate, 5 parts of complexed magnesia-alumina binder, 1 part of activated bentonite, 0.4 parts of calcium lignosulfonate, 0.8 parts of lanthanum oxide, 0.3 parts of modified carbon fiber, and 0.5 parts of polyacrylamide.

[0020] Example 3: The high-strength, long-life RH impregnated pipe spraying material is made from the following raw materials in the following weight ratios: 62 parts of recycled waste magnesia-chrome brick with a particle size ≤5mm, 25 parts of fused magnesia sand with a particle size of 180-240 mesh, 4 parts of aluminum chromium phosphate, 4 parts of complexed magnesia-alumina binder, 3 parts of activated bentonite, 0.5 parts of calcium lignosulfonate, 0.6 parts of lanthanum oxide, 0.5 parts of modified carbon fiber, and 0.4 parts of polyacrylamide.

[0021] Example 4: The high-strength, long-life RH impregnated pipe spraying material is made from the following raw materials in the following weight ratios: 68 parts of recycled waste magnesia-chrome brick with a particle size ≤5mm, 19 parts of fused magnesia sand with a particle size of 180-240 mesh, 7 parts of aluminum chromium phosphate, 2 parts of complexed magnesia-alumina binder, 1 part of activated bentonite, 0.2 parts of calcium lignosulfonate, 1.5 parts of lanthanum oxide, 0.6 parts of modified carbon fiber, and 0.7 parts of polyacrylamide.

[0022] The physicochemical properties of the raw materials for the preparation of RH impregnation pipe spraying materials in Examples 1-4 are shown in Table 3.

[0023] Table 3 Physicochemical properties of raw materials prepared in Examples 1-4 Examples 1-4, the preparation method of RH impregnation pipe spraying material is as follows: 1. Aggregate pretreatment: After crushing, the recycled material from waste magnesium chrome bricks is graded and screened. It is then soaked in 5% dilute hydrochloric acid for 30 minutes to remove impurities, rinsed with clean water until neutral, and dried at 110℃ for 5 hours for later use.

[0024] 2. Premixing of binders and additives: In order to ensure the uniformity of the sprayed material mixing, aluminum chromium phosphate, complexed magnesium aluminum binder, activated sodium bentonite, lanthanum oxide, calcium lignosulfonate and polyacrylamide are first fully premixed using a double helix conical premixer for 12 minutes to make premixed powder, which is then bagged for later use.

[0025] 3. Use the RV19 inclined high-speed mixer for mixing. The mixing sequence is as follows: first add the granular material and magnesia powder and mix for 2 minutes, then add the premixed powder and modified carbon fiber and mix for another 15 minutes. The modified carbon fiber should be added in a dispersed manner to avoid agglomeration.

[0026] 4. The mixed dry materials were tested for physicochemical properties according to national or industry standards. The measured values ​​of the finished product's physicochemical properties and service life are shown in Table 4.

[0027] Table 4 Measured values ​​of finished product physicochemical properties

Claims

1. A high strength long life RH dip-tube gunning mix, characterized in that, The gunning material is configured from the following raw materials in parts by weight: 55-70 parts of waste magnesite-chrome brick regenerative material with particle size ≤5 mm, 18-28 parts of electric smelting magnesite skin sand with particle size of 180-240 mesh, 3-7 parts of aluminum phosphate chromium, 2-5 parts of complex magnesium aluminum cementing agent, 1-3 parts of activated bentonite, 0.2-0.5 parts of calcium lignosulfonate, 0.5-1.5 parts of lanthanum oxide, 0.2-0.6 parts of modified carbon fiber, and 0.3-0.8 parts of polyacrylamide.

2. The high strength long life RH dip-tube gunning mix of claim 1, wherein, The modified carbon fiber has an oxidation starting temperature of 800-1000℃ and maintains a stable structure at a temperature above 1400℃, with a residual strength retention rate ≥60%.

3. The high strength long life RH dip-tube gunning mix of claim 1, wherein, The particle body density of the waste magnesite-chrome brick regenerative material is ≥3.35, MgO is ≥60, and Cr2O3 is ≥18.

4. The high strength long life RH dip-tube gunning mix of claim 1 wherein, The MgO in the electric smelting magnesite skin sand is ≥92, and SiO2 is ≤5.

5. The high strength long life RH dip-tube gunning mix of claim 1 wherein, The Cr2O3 in the aluminum phosphate chromium is 5%-10%, the Al2O3 is 35%-40%, the P2O5 is 45%-50%, and the PH value is 3.5-4.

5.

6. The high strength long life RH tube gunning mix of claim 1 wherein, The MgO in the complex magnesium aluminum cementing agent is ≥48, and the Al2O3 is ≥3.

7. The high strength long life RH dip-tube gunning mix of claim 1 wherein, The physical and chemical indexes of the high-strength long-life RH dip tube gunning material are as follows: MgO+Cr2O3≥70%, high-temperature compression strength at 1450℃×1h ≥35Mpa, thermal shock stability at 1600℃ ≥8 times, and rebound rate ≤10%.

8. A method for preparing the high-strength, long-life RH-impregnated pipe spraying material as described in claim 1, characterized in that, The method comprises the following steps: 1) aggregate pretreatment: after the waste magnesite-chrome brick regenerative material is crushed and classified, it is soaked in 5% dilute hydrochloric acid for 30 min to remove impurities, washed with water until neutral, and dried at 110℃ for 4-5h for standby; 2) premixing of binder and additives: first, the aluminum phosphate chromium, complex magnesium aluminum cementing agent, activated bentonite, lanthanum oxide, calcium lignosulfonate, and polyacrylamide are fully premixed using a double-helix conical premixer; 3) mixing using an inclined high-speed mixer, the mixing sequence is: first, mix the waste magnesite-chrome brick regenerative material and electric smelting magnesite skin sand for 1-3 minutes, then mix the premixed powder and modified carbon fiber for 10-15 minutes, and the modified carbon fiber is dispersedly added to avoid agglomeration.

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