Metal-ceramic composite low-cost heat preservation riser tube and preparation method thereof

Abstract

The invention relates to a metal-ceramic composite low-cost heat preservation liquid rising pipe and a preparation method thereof, belongs to the technical field of ceramic materials, and solves the problems that an existing composite liquid rising pipe is complex in preparation process, low in production efficiency, high in liquid leakage risk caused by assembly gaps, integrally scrapped due to local damage and high in cost. The method comprises the following steps: preparing a metal cylindrical shell which is provided with a truncated cone-shaped inner cavity with a large upper part and a small lower part; processing a wood mold, wherein the wood mold has a circular truncated cone shape; according to the big-end-up direction, the wood mold is placed into the circular-truncated-cone-shaped inner cavity, a gap exists between the wood mold and the shell, and ceramic slurry is injected into the gap; and standing, drying and sintering are conducted, and the metal shell and ceramic lining composite riser tube is obtained. By combining wood mold forming and an integrated sintering process, the metal shell and the ceramic lining of the riser tube are seamlessly combined, so that the strength, thermal shock resistance and heat preservation performance of the riser tube are improved, the liquid leakage risk is reduced, the production efficiency is improved, and the cost and energy consumption are reduced.

Description

Technical Field

[0001] This invention relates to the field of ceramic composite materials technology, and in particular to a low-cost metal-ceramic composite heat-insulating liquid riser and its preparation method. Background Technology

[0002] Riser pipes are crucial components in casting furnaces used in low-pressure casting, differential pressure casting, and vacuum casting, connecting the melting furnace and the mold. For example, iron riser pipes are mostly used in the pouring processes of aluminum alloys, copper alloys, and magnesium alloys. Due to equipment limitations, the riser pipes cannot be locally heated, which can easily lower the temperature of the molten metal during transport. This results in the molten metal actually being poured into the mold cavity at a lower temperature than expected. If iron riser pipes are used, their high thermal conductivity can severely reduce the temperature of the molten metal during transport, leading to problems such as cold shuts and linear defects in the casting.

[0003] Currently, to address the issue of excessive temperature drop in molten metal due to its transport via riser pipes, improvements include localized heating of the riser pipes to reduce heat loss, and the use of low thermal conductivity ceramic / graphite riser pipes or composite riser pipes to further reduce heat dissipation. However, localized heating of the riser pipe requires space, is complex to operate, and carries significant safety risks; while riser pipes made solely of low thermal conductivity materials cannot fully meet the requirements. For example, pure ceramic riser pipes are brittle and have poor thermal shock resistance; traditional graphite riser pipes are prone to oxidation and cracking, resulting in a short lifespan.

[0004] To address the shortcomings of existing single-material riser pipes, riser pipes composed of components made of different materials have been increasingly researched and used. These composite riser pipes can leverage the strengths of both materials and significantly improve casting quality. However, existing composite riser pipes are mostly manufactured using a split or modular approach, often employing a nested assembly of a metal liner and a prefabricated ceramic shell. On one hand, the difference in thermal expansion coefficients between the metal and ceramic materials complicates assembly and reduces production efficiency. On the other hand, the high thermal conductivity of the metal liner still significantly impacts the temperature of the molten steel being transported, particularly affecting the production of thin castings. Furthermore, localized damage to the composite riser pipe can lead to complete scrapping, further increasing costs.

[0005] Therefore, there is an urgent need to develop a composite riser tube with superior performance and its preparation method. This would not only effectively improve the quality of castings and extend their service life during subsequent use, but also simplify the preparation process of the composite riser tube, improve production efficiency, and reduce costs. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a low-cost metal-ceramic composite insulated riser pipe and its preparation method, in order to solve at least one of the problems in the prior art of composite riser pipe preparation process, low production efficiency, high risk of leakage due to assembly gaps, local damage causing overall scrap, and high cost.

[0007] On one hand, embodiments of the present invention provide a method for preparing a low-cost, metal-ceramic composite heat-insulating riser tube, the method comprising: (1) Prepare a metal cylindrical shell, wherein the shell has a frustum-shaped inner cavity, which is larger at the top and smaller at the bottom; (2) Processing wooden molds, wherein the wooden molds have a frustum shape; (3) Place the wooden mold into the frustum-shaped inner cavity in a direction that is larger at the top and smaller at the bottom. There is a gap between the wooden mold and the outer shell. Ceramic slurry is injected into the gap. (4) Let stand, dry and sinter to obtain a heat-insulating liquid riser with a metal shell and ceramic lining.

[0008] Furthermore, in step (1), the angle between the generatrix of the frustum-shaped inner cavity and the central axis is 0.5°-2°.

[0009] Furthermore, in step (2), the angle between the generatrix of the wooden mold and the central axis is 0.5°-2°.

[0010] Furthermore, in step (2), the diameter of the large bottom surface of the wooden mold is smaller than the diameter of the large bottom surface of the frustum-shaped inner cavity; the diameter of the small bottom surface of the wooden mold is smaller than the diameter of the small bottom surface of the frustum-shaped inner cavity.

[0011] Furthermore, in step (2), the height of the wooden mold is greater than or equal to the height of the outer shell.

[0012] Furthermore, in step (3), before placing the wooden mold into the frustum-shaped inner cavity, a high-temperature release oil is applied to the surface of the wooden mold.

[0013] Furthermore, in step (3), the ceramic slurry contains, by weight percentage, 40wt%~60wt% mullite powder, 40wt%~60wt% coal gangue powder, 8~15wt% silica sol and 0.5wt%~3wt% sodium salt.

[0014] Furthermore, the solid content of the ceramic slurry is 60%-90%.

[0015] Furthermore, in step (4), the settling time is 2-4 hours.

[0016] Furthermore, the drying process involves ventilating and drying at a temperature of 20-40°C for 6-12 hours.

[0017] Furthermore, the sintering is segmented sintering.

[0018] Furthermore, the segmented sintering specifically involves sintering at 200-400℃ for 2-4 hours, followed by sintering at 830-870℃ for 2-4 hours.

[0019] On the other hand, embodiments of the present invention also provide a low-cost, heat-insulating riser pipe made of metal and ceramic composite. The riser pipe is prepared by the above method and includes a metal shell and a ceramic liner. There is no gap between the metal shell and the ceramic liner. The thickness of the metal shell is 3-8 mm, the thickness of the ceramic liner is 10-30 mm, and the height of the ceramic liner is 1-2 mm higher than the height of the metal shell.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. Unlike existing technologies that use separate or combined methods to prepare composite riser tubes, this invention innovatively uses an integrated molding process to prepare composite riser tubes. By combining wood mold forming with an integrated sintering process, on the one hand, the metal shell and ceramic lining of the riser tube are seamlessly bonded, which effectively improves the strength, thermal shock resistance, and heat insulation performance of the riser tube, extends its service life, and reduces the risk of leakage; on the other hand, the integrated molding process can improve production efficiency and reduce production costs and energy consumption.

[0021] 2. This invention adjusts the angle between the generatrix and the central axis of the wooden mold with a frustum shape, the angle between the generatrix and the central axis of the frustum-shaped inner cavity of the metal cylindrical shell, and the dimensional relationship between the wooden mold and the frustum-shaped inner cavity. While ensuring the successful fabrication of the composite riser pipe and its stability in subsequent use without affecting the metal liquid transport, it facilitates the smooth removal of the wooden mold during the integrated fabrication process. This ensures a tight, seamless bond between the metal shell and the ceramic lining of the composite riser pipe, as well as the integrity and uniformity of the ceramic lining. This effectively improves the thermal shock resistance and insulation performance of the riser pipe, and enhances the quality of the castings produced in practical applications.

[0022] 3. The present invention adjusts the relative height between the wooden mold and the metal shell, so that the height of the ceramic liner is 1-2 mm greater than the height of the metal shell. The outlet surface of the ceramic liner is basically flat, which helps to avoid contact between the molten metal and the metal shell. A certain pressure is maintained between the ceramic liner and the metal shell of the riser pipe to prevent leakage and pressure loss. At the same time, this design presses the flexible contact material such as ceramic fiber felt placed between the casting and the riser pipe more tightly to prevent pressure loss during the casting process.

[0023] 4. The present invention regulates the composition of the ceramic slurry, which can reduce the thermal conductivity of the composite riser tube ceramic lining and improve its thermal shock performance. By regulating the solid content of the ceramic slurry, not only is its fluidity ensured so that it can fill the pores between the metal shell and the wooden mold during casting, but it can also prevent the green body from having too low density after casting and large shrinkage deformation during solidification. By regulating the content of the coagulant in the ceramic slurry, the ceramic sintering temperature can be reduced and the density of the ceramic lining can be increased.

[0024] 5. The present invention regulates the processing technology after the casting of ceramic slurry, including the sequential static initial setting, removal of wooden mold, drying and curing, and segmented sintering, which can prevent deformation and damage during the forming process of ceramic lining, suppress the generation of defects such as bubbling, reduce the internal stress of ceramic and the stress between ceramic and metal, and avoid stress deformation or cracking caused by uneven heating of the mold shell.

[0025] 6. The method of this invention enables a seamless bond between the metal shell and the ceramic liner of the composite riser tube. Combined with the structural design of the composite riser tube, including the thickness of the metal shell and the ceramic liner, and their relative height, it can effectively improve the strength, thermal shock resistance, and heat insulation performance of the riser tube, extend its service life, and reduce the risk of leakage. The ceramic liner is intact with a porosity of <5%; the thermal conductivity of the riser tube is <0.7W / (m·K); no interface leakage occurs in the initial stage of molten metal transportation (70 heats); and the casting life is >100 heats.

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 This is a process flow diagram for the preparation of the metal-ceramic composite riser tube of the present invention; Figure 2 This is a schematic diagram of the structure of the present invention using the wood mold forming process; Figure 3 This is a schematic cross-sectional view of the composite riser tube fabricated according to the present invention. Figure label: 1-Metal outer shell; 2-1-Ceramic slurry; 2-2-Ceramic inner lining; 3-Wooden mold; 4-Positioning base; 5-Liquid lifting channel. Detailed Implementation

[0028] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0029] As a crucial component connecting the melting furnace and the mold, the riser pipe requires high standards for airtightness, mechanical strength, high-temperature resistance, and chemical stability. However, existing riser pipes made of single materials present various problems in practical use. For instance, the high thermal conductivity of iron riser pipes significantly reduces the temperature of the molten metal during transport, resulting in a lower-than-average temperature of the molten metal poured into the mold cavity. This can lead to problems such as cold shuts and linear defects in the casting. While locally heating the iron riser pipe to reduce heat loss is a space-consuming, complex, and safety-risk-prone method, it is also problematic. Furthermore, riser pipes made of single low-thermal-conductivity materials cannot fully meet the requirements. For example, pure ceramic riser pipes are brittle and have poor thermal shock resistance, while traditional graphite riser pipes are prone to oxidation and cracking, resulting in a short lifespan. To overcome the problems of existing single-material riser pipes, riser pipes composed of components made of different materials are increasingly being researched and used. These composite riser pipes can leverage the strengths of different materials and significantly improve the quality of castings.

[0030] However, the inventors discovered in their research that existing composite riser tubes are mostly manufactured using a split or modular approach, often employing a metal outer shell and a prefabricated ceramic inner tube for nested assembly. Due to the difference in thermal expansion coefficients between metal and ceramic materials, the assembly process is complex and production efficiency is low. The nested assembly also introduces a high risk of leakage due to the gap between the outer shell and the inner tube. Furthermore, the composite riser tube may become unusable due to localized damage, further increasing costs.

[0031] Therefore, the present invention provides a method for preparing a low-cost, metal-ceramic composite heat-insulating riser tube, the method comprising: (1) Prepare a metal cylindrical shell, wherein the shell has a frustum-shaped inner cavity, which is larger at the top and smaller at the bottom; (2) Processing wooden molds, wherein the wooden molds have a frustum shape; (3) Place the wooden mold into the frustum-shaped inner cavity in a direction that is larger at the top and smaller at the bottom. There is a gap between the wooden mold and the outer shell. Ceramic slurry is injected into the gap. (4) Let stand, dry and sinter to obtain a heat-insulating liquid riser with a metal shell and ceramic lining.

[0032] It should be noted that, in order to improve the mechanical strength of the composite riser tube, the present invention uses a metal cylinder as the supporting frame for the riser tube.

[0033] Specifically, in step (1), a metal cylindrical shell is prepared by traditional rolling forming method, stamping forming method or spinning forming method, wherein the shell has a cylindrical or frustum-shaped inner cavity.

[0034] According to some preferred embodiments of the present invention, the metal cylindrical outer shell of the present invention has a frustum-shaped inner cavity, which is larger at the top and smaller at the bottom.

[0035] It should be noted that, in order to ensure the integrity and uniformity of the ceramic lining and to ensure the stability of metal liquid transportation in the actual application of the composite riser pipe, the present invention needs to define the shape of the frustum-shaped inner cavity of the metal cylindrical shell.

[0036] More specifically, in step (1), the angle between the generatrix of the frustum-shaped inner cavity and the central axis is 0.5°-2°, which can be 0.5°, 1°, 1.5°, or 2°. If the angle is too large, it can easily lead to a large difference in thickness between the upper and lower ends of the ceramic liner, as well as a reduction in the cross-sectional area of ​​the molten metal flow in the riser tube.

[0037] It should be noted that, in order to facilitate the removal of the shaped wooden mold after the slurry is poured and initially set, and to ensure the integrity and uniformity of the ceramic lining, and to ensure the stability of the metal liquid transport in the actual application of the composite riser pipe, the present invention needs to limit the shape and size of the wooden mold.

[0038] Specifically, in step (2), a shaped wooden mold is processed. The wooden mold has a frustum shape, with one end of the frustum being larger than the other. This structure helps the ceramic slurry, which is seamlessly bonded to the inner wall of the metal shell, to be successfully removed from the prefabricated composite riser tube after initial solidification.

[0039] More specifically, in step (2), the angle between the generatrix of the wooden mold and the central axis is 0.5°-2°, which can be 0.5°, 1°, 1.5°, or 2°. If the angle is too large, the cross-sectional area of ​​the molten metal inlet of the riser pipe will be significantly smaller than the cross-sectional area of ​​the outlet, which will easily affect the filling stability of the casting.

[0040] More specifically, when the outer shell has a cylindrical inner cavity, in step (2), the diameter of the large base of the wooden mold is smaller than the diameter of the bottom surface of the cylindrical inner cavity; when the outer shell has a frustum-shaped inner cavity, in step (2), the diameter of the large base of the wooden mold is smaller than the diameter of the large base of the frustum-shaped inner cavity; and the diameter of the small base of the wooden mold is smaller than the diameter of the small base of the frustum-shaped inner cavity. Wherein, when the wooden mold is placed into the inner cavity of the metal cylindrical outer shell, the gap structure formed between the wooden mold and the inner wall of the metal cylinder is the structure of the ceramic lining to be cast.

[0041] According to some preferred embodiments of the present invention, the metal cylindrical outer shell has a frustum-shaped inner cavity. The diameter of the large base of the wooden mold is 10-30 mm smaller than the diameter of the large base of the frustum-shaped inner cavity, and the diameter of the small base of the wooden mold is 10-30 mm smaller than the diameter of the small base of the frustum-shaped inner cavity. That is, the thickness of the ceramic lining to be cast is 10-30 mm. Because ceramic materials have poor thermal conductivity, if the thickness is too large, cracks will occur due to uneven heating during the preparation and use process, causing damage.

[0042] It should be noted that in order to successfully obtain a composite riser pipe with a metal outer shell structure and a ceramic inner lining structure, the present invention needs to define the placement direction and position of the molded wooden mold in the metal outer shell.

[0043] Specifically, in step (3), when the metal shell has a frustum-shaped inner cavity, the wooden mold with a frustum shape from step (2) is placed into the frustum-shaped inner cavity in a direction that is larger at the top and smaller at the bottom. There is a gap between the wooden mold and the shell, and ceramic slurry is injected into the gap.

[0044] More specifically, in step (3), the wooden mold is placed in the center of the inner cavity of the metal shell, so that the central axis of the wooden mold overlaps with the central axis of the inner cavity of the metal shell, so as to promote the integrity and uniformity of the ceramic liner preparation process.

[0045] It should be noted that the present invention uses a positioning chassis to fix the metal shell and the wooden mold, such as Figure 2 As shown.

[0046] It should be noted that, in order to easily fix the wooden mold and easily remove the wooden mold after the ceramic is shaped, and to make the height of the ceramic liner greater than the height of the metal shell, the present invention needs to limit the relative height between the wooden mold and the metal shell.

[0047] Specifically, in step (2), the height of the wooden mold is greater than or equal to the height of the outer shell. Preferably, the height of the wooden mold is at least 1 mm higher than the height of the outer shell, and more preferably 1-2 mm higher.

[0048] It should be noted that in step (3), before placing the wooden mold into the frustum-shaped inner cavity, a high-temperature release oil is applied to the surface of the wooden mold, which is beneficial to promoting the subsequent demolding effect.

[0049] It should be noted that in order to reduce the thermal conductivity of the composite riser tube ceramic lining and improve its thermal shock resistance and insulation performance, the present invention requires limiting the ceramic composition.

[0050] Specifically, in step (3), the ceramic composition includes refractory aggregate (40% to 60% of mullite powder, coal gangue powder or a mixture thereof), silica sol and sodium salt coagulant.

[0051] More specifically, in step (3), the ceramic slurry contains 40wt%~60wt% mullite powder, 40wt%~60wt% coal gangue powder, 8wt%~15wt% silica sol, and 0.5wt%~3wt% sodium salt by weight percentage. If the content of refractory aggregates such as mullite powder and coal gangue powder is too high, the ceramic slurry will have poor fluidity, insufficient bonding strength, and large fluctuations in the quality of the ceramic lining. If the content of refractory aggregates such as mullite powder and coal gangue powder is too low, the film formed by silica sol will be too thick, the shrinkage stress will be concentrated, the ceramic lining will be prone to cracks, and the cracks will be more likely to propagate at high temperatures, resulting in weak resistance to erosion and corrosion of the ceramic lining.

[0052] It should be noted that, in order to reduce the sintering temperature of the ceramic and increase the density of the resulting ceramic lining, the present invention requires controlling the content of the coagulant in the ceramic slurry.

[0053] Specifically, in step (3), the content of the sodium salt co-solvent is 0.5wt%~3wt%, and can be 0.5wt%, 0.8wt%, 1wt%, 1.3wt%, 1.5wt%, 1.8wt%, 2.1wt%, 2.4wt%, 2.7wt%, or 3wt%. This invention controls the content of the sodium salt co-solvent in the ceramic, which not only reduces the sintering temperature of the ceramic but also increases the density of the ceramic lining.

[0054] More specifically, the sodium salt co-solvent is sodium chloride.

[0055] It should be noted that, in order to ensure the fluidity of the ceramic slurry so that it can fill the pores between the metal shell and the wooden mold during casting, and to prevent excessive shrinkage and deformation during solidification due to the low density of the green body after casting, the present invention needs to limit the solid content of the ceramic slurry.

[0056] Specifically, in step (3), the solid content of the ceramic slurry is 60%-90%, which can be 60%, 63%, 65%, 67%, 70%, 72%, 75%, 78%, 80%, 83%, 85%, 88%, or 90%. If the solid content is too high, the viscosity of the slurry will increase and the fluidity will be poor, making it difficult to fill the gap between the metal shell and the wooden mold. If the solid content is too low, the ceramic blank obtained after casting will have low density, large shrinkage, and be prone to deformation and cracking.

[0057] In order to ensure that the composite riser tube can be formed by integral molding of the metal shell and the ceramic liner, so that the two can be seamlessly connected, the present invention needs to control the process of processing the composite riser tube preform made by molding with wooden mold.

[0058] Specifically, in step (4), the composite riser pipe preforms obtained after the wooden mold is formed are subjected to static standing, mold removal, drying and sintering in sequence to obtain a heat-insulating riser pipe with a metal shell and ceramic lining.

[0059] It should be noted that, in order to smoothly remove the wooden mold after the ceramic slurry has been poured, the present invention requires that the ceramic body obtained after pouring undergo initial setting and have a certain strength.

[0060] More specifically, in step (4), the settling is carried out at room temperature for 2-4 hours, which can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. If the settling time is too short, the strength of the ceramic body after initial setting will be insufficient, which may cause the ceramic body to separate from the metal shell when removing the mold, or may damage the integrity of the ceramic body; if the settling time is too long, it will be difficult to remove the wooden mold, and forcibly removing it may damage the ceramic body.

[0061] It should be noted that in order to accelerate the solidification of the ceramic blank and avoid internal defects such as stress and blistering, the ceramic blank needs to be dried before sintering.

[0062] Specifically, in step (4), the drying process involves ventilating and drying at a temperature of 20-40℃ for 6-12 hours. The drying time can be 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours at temperatures of 20℃, 25℃, 30℃, 35℃, and 40℃, respectively. The drying temperature should not be too high, as higher temperatures accelerate drying efficiency, making it difficult for internal moisture to escape and easily causing cracks. The drying time should not be too short, as this will result in excessive internal moisture, which will rapidly vaporize during firing, leading to cracking and bulging of the ceramic lining. However, it should not be too long either, as excessive drying and shrinkage can cause stress accumulation, easily resulting in surface cracks, which will lead to crack propagation during subsequent firing and casting.

[0063] To avoid stress deformation or defects in the ceramic lining during sintering, the present invention performs segmented sintering of the ceramic blank.

[0064] Specifically, in step (4), the sintering is as follows: first, a first-stage sintering is carried out at a low temperature to further remove free water and avoid excessive evaporation of water at high temperature, which would cause stress deformation and defects in the ceramic lining; then, a second-stage sintering and heat preservation treatment is carried out at a high temperature to obtain a ceramic lining with high density and no deformation or cracking, so as to achieve a seamless combination with the metal shell.

[0065] More specifically, the first-stage sintering refers to sintering at a temperature of 200-400℃ for 2-4 hours, which can be sintering at temperatures of 200℃, 220℃, 250℃, 280℃, 300℃, 330℃, 350℃, 380℃, and 400℃ for 2 hours, 2.5 hours, 3 hours, 3.5 hours, and 4 hours, respectively. The first-stage sintering temperature should not be too high, otherwise it will cause the residual moisture to evaporate rapidly and the ceramic lining to crack. If it is too low, the sintering time will be prolonged, increasing the preparation cycle. If the time is too long, the preparation cycle will be increased. If the time is too short, the residual moisture will not dry completely, and the moisture will vaporize violently when the temperature is raised later, causing cracks in the ceramic lining.

[0066] More specifically, the two-stage sintering involves sintering at 830-870℃ for 2-4 hours, which can be sintering at 830℃, 840℃, 850℃, 860℃, or 870℃ for 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, respectively. The two-stage sintering temperature cannot be too high or the sintering time cannot be too long, otherwise the ceramic lining will become brittle and have poor thermal shock resistance. Conversely, the sintering temperature cannot be too low or the sintering time cannot be too short, otherwise the silica sol conversion will be incomplete, the high-temperature strength of the ceramic lining will be insufficient, microcracks will not be eliminated, and the erosion resistance will be weak.

[0067] Unlike existing technologies that use separate or combined methods to prepare composite riser tubes, this invention innovatively employs an integrated molding process to prepare composite riser tubes. By combining wood mold forming with an integrated sintering process, on the one hand, the metal outer shell and ceramic lining of the prepared riser tube are seamlessly bonded, which effectively improves the strength, thermal shock resistance, and thermal insulation performance of the riser tube, extends its service life, and reduces the risk of leakage; on the other hand, the integrated molding process can improve production efficiency and reduce production costs and energy consumption.

[0068] On the other hand, embodiments of the present invention also provide a low-cost metal-ceramic composite insulated riser pipe, which is prepared by the above method and includes a metal shell and a ceramic liner. There is no gap between the metal shell and the ceramic liner. The thickness of the metal shell is 3-8 mm, the thickness of the ceramic liner is 10-30 mm, the density is <5%, and the height of the ceramic liner is 1-2 mm higher than the height of the metal shell.

[0069] It should be noted that, in order to reduce the cost of preparation, commonly used 45 steel can be used. However, this invention selects a metal shell material as the composite riser tube. To extend the service life and reduce metal corrosion caused by high temperature, heat-resistant stainless steel can be used.

[0070] In order to achieve uniform temperature distribution during the process of conveying molten metal, the present invention requires that the thickness of the metal shell be limited to 3-8mm, which can be 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, or 8mm.

[0071] It should be noted that, due to the poor thermal conductivity of ceramic materials, excessive thickness can easily lead to cracks and damage due to uneven heating. Therefore, the thickness of the ceramic liner of the composite riser tube in this invention is limited to 10-30mm, which can be 10mm, 12mm, 15mm, 18mm, 20mm, 23mm, 25mm, 27mm, or 30mm.

[0072] It should be noted that in order to ensure the high strength of the ceramic liner and prevent pressure leakage and cracking, the composite riser tube ceramic liner of this invention needs to have high density and a porosity of <5%. If the porosity is too high, it will lead to low strength of the ceramic liner.

[0073] To ensure no pressure or air leakage during the anti-gravity casting process, the height of the ceramic lining of the composite riser pipe of this invention is 1-2 mm higher than the height of the metal outer shell, and can be 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, or 2 mm.

[0074] The composite riser tube provided by this invention features a seamless connection between its metal outer shell and ceramic liner. Combined with the structural design of the composite riser tube, including the thickness of the metal outer shell and the ceramic liner, and their relative height, it effectively improves the riser tube's strength, thermal shock resistance, and insulation performance, extends its service life, and reduces the risk of leakage. This composite riser tube is particularly suitable for casting aluminum alloys, copper alloys, and magnesium alloys.

[0075] The technical solution of the present invention will be further explained and illustrated below through examples and comparative examples.

[0076] Example 1 A method for preparing a metal-ceramic composite riser tube, comprising: (1) A 304 stainless steel cylindrical shell with a thickness of 8 mm was prepared by rolling forming method, and the angle between the generatrix of the frustum-shaped inner cavity and the central axis was 1°. (2) Processing the wooden mold, the wooden mold has a frustum shape, the angle between the generatrix of the wooden mold and the central axis is 1°, the diameter of the large bottom surface of the wooden mold is 10 mm smaller than the diameter of the large bottom surface of the frustum-shaped inner cavity in step (1), and the diameter of the small bottom surface of the wooden mold is 10 mm smaller than the diameter of the small bottom surface of the frustum-shaped inner cavity. (3) Following the direction of larger at the top and smaller at the bottom, place the wooden mold obtained in step (2) into the frustum-shaped inner cavity of step (1), as shown. Figure 2As shown, the central axis of the wooden mold overlaps with the central axis of the frustum-shaped inner cavity. Ceramic slurry is injected into the gap between the wooden mold and the outer shell to obtain a composite riser preform containing a ceramic liner. The ceramic slurry has a solid content of 90%, and by weight percentage, the ceramic container contains 60wt% 325-mesh mullite powder, 40wt% 200-mesh coal gangue powder, 8wt% silica sol, and 2wt% NaCl. (4) The composite riser pipe preform obtained in step (3) is left to stand at room temperature for 2 hours, and the wooden mold is taken out; it is dried in a ventilated environment at 24℃ for 12 hours; it is sintered at 200℃ for 2 hours and then sintered at 850℃ for 2 hours to obtain a metal shell ceramic liner composite riser pipe.

[0077] Testing revealed that the composite riser tube ceramic liner prepared in Example 1 had a porosity of 3% and a thermal conductivity of 0.69 W / (m·K) at 700℃. No aluminum melt was found to penetrate into the interface between the metal shell and the ceramic liner during the initial use period, and the low-pressure casting life was >100 heats.

[0078] Examples 2-6, Comparative Examples 1-6 Using the same method as in Example 1, except that in Examples 2-6 and Comparative Examples 1-6, the process conditions in the preparation of the composite riser tube were changed, including the shape of the wooden mold, the gap and relative height between the wooden mold and the outer shell, the content of the coagulant, the standing time, and the sintering process conditions, and finally, a metal shell ceramic liner composite riser tube was obtained. The preparation process conditions of Examples 2-6 and Comparative Examples 1-6 are shown in Table 1.

[0079] The structural performance parameters, application in aluminum alloy casting, and lifespan of the composite riser tubes prepared by Examples 1-6 and Comparative Examples 1-6 are shown in Table 2.

[0080] Table 1. Preparation process conditions of Examples 1-6 and Comparative Examples 1-6

[0081] Table 2 Structural performance parameters of the composite riser tubes in Examples 1-5 and Comparative Examples 1-6

[0082] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a low-cost, metal-ceramic composite heat-insulating riser pipe, characterized in that, The method includes: (1) Prepare a metal cylindrical shell, wherein the shell has a frustum-shaped inner cavity, which is larger at the top and smaller at the bottom; (2) Processing wooden molds, wherein the wooden molds have a frustum shape; (3) Place the wooden mold into the frustum-shaped inner cavity in a direction that is larger at the top and smaller at the bottom. There is a gap between the wooden mold and the outer shell. Ceramic slurry is injected into the gap. (4) Let it stand, take out the mold, dry and sinter to obtain a heat-insulating liquid-lifting pipe with a metal shell and ceramic lining.

2. The method according to claim 1, characterized in that, In step (1), the angle between the generatrix of the frustum-shaped inner cavity and the central axis is 0.5°-2°.

3. The method according to claim 1, characterized in that, In step (2), the angle between the generatrix of the wooden mold and the central axis is 0.5°-2°.

4. The method according to claim 1, characterized in that, In step (2), the diameter of the large bottom surface of the wooden mold is smaller than the diameter of the large bottom surface of the frustum-shaped inner cavity; the diameter of the small bottom surface of the wooden mold is smaller than the diameter of the small bottom surface of the frustum-shaped inner cavity.

5. The method according to claim 1, characterized in that, In step (2), the height of the wooden mold is at least 1 mm higher than the height of the outer shell.

6. The method according to claim 1, characterized in that, In step (3), before placing the wooden mold into the frustum-shaped inner cavity, a high-temperature release oil is applied to the surface of the wooden mold.

7. The method according to claim 1, characterized in that, In step (3), the ceramic slurry contains, by weight percentage, 40wt%~60wt% mullite powder, 40wt%~60wt% coal gangue powder, 8~15wt% silica sol, and 0.5wt%~3wt% sodium salt; And / or, the solid content of the ceramic slurry is 60%-90%.

8. The method according to claim 1, characterized in that, In step (4), the settling time is 2-4 hours; And / or, the drying is performed by ventilation drying at a temperature of 20-40°C for 6-12 hours; And / or, the sintering is segmented sintering.

9. The method according to claim 8, characterized in that, The segmented sintering process specifically involves sintering at 200-400℃ for 2-4 hours, followed by sintering at 830-870℃ for another 2-4 hours.

10. A low-cost, heat-insulating, riser pipe made of metal and ceramic composite material, characterized in that, The riser tube is prepared by the method according to any one of claims 1-9, comprising a metal shell and a ceramic liner, wherein there is no gap between the metal shell and the ceramic liner, the thickness of the metal shell is 3-8 mm, the thickness of the ceramic liner is 10-30 mm, the density is <5%, and the height of the ceramic liner is 1-2 mm higher than the height of the metal shell.

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