A mullite fiber modified ceramic formwork and a method for manufacturing the same
By adding mullite fibers to the ceramic mold shell and adopting a reasonable calcination process, the problems of insufficient strength and permeability of the ceramic mold shell at high temperatures were solved, and a highly efficient casting effect was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG XINMIAO AVIATION POWER CO LTD
- Filing Date
- 2026-04-01
- Publication Date
- 2026-06-26
AI Technical Summary
Existing ceramic mold shell materials struggle to balance strength and permeability at high temperatures, and traditional modification methods suffer from fiber softening, melting, and delamination issues, affecting casting quality and production efficiency.
A method for preparing mullite fiber modified ceramic mold shells was developed. By adding mullite fibers to the surface and back layers of the slurry and combining it with a reasonable calcination process, a high-strength and highly permeable ceramic mold shell was prepared.
It improves the bending strength and high-temperature stability of the mold shell, reduces the amount of raw materials used, shortens the production cycle, reduces costs, and meets the requirements of high-temperature casting.
Smart Images
Figure CN122277271A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of mold shell material preparation technology, and relates to a mullite fiber modified ceramic mold shell and its preparation method. Background Technology
[0002] Currently, the internal components of aero-engines and gas turbines are mainly obtained through high-temperature alloy investment casting. In the casting process, mold shell making is an essential step, and the quality of the mold shell directly affects the surface quality and dimensional accuracy of the casting. High-quality mold shells need to have high strength and heat dissipation at both room temperature and high temperature, especially for large, thin-walled complex hollow blades and guide vanes, etc., high-temperature alloy castings. Traditional mold shell materials and preparation processes are no longer sufficient to meet the requirements of casting processability.
[0003] In traditional processes, to balance the structural strength and permeability of the mold shell, the thickness of the mold shell is usually increased or the mold shell material is modified through composite processes. However, increasing the thickness of the mold shell significantly reduces its thermal conductivity, affecting the heat dissipation efficiency during the solidification process of the casting, which in turn has an adverse impact on grain size and control. At the same time, the thick-shell process also prolongs the shell-making cycle, increases material consumption, and leads to an increase in the defect rate during drying and firing, reducing production efficiency.
[0004] To improve the mechanical properties of mold shells while maintaining good air permeability and heat dissipation, existing research mostly employs the method of adding reinforcing phases to ceramic slurries. Among these methods, glass fiber is widely used due to its low cost and significant reinforcing effect. However, the softening point of glass fiber is typically below 800℃. During the high-temperature calcination of the mold shell and alloy casting, the fiber softens, melts, or even fails, leading to a sharp decrease in the interfacial bonding strength between the fiber and the ceramic matrix. Furthermore, thermal expansion mismatch during temperature changes can easily cause delamination and peeling. In addition, with increasing fiber content, the fiber is prone to aggregation, entanglement, and even agglomeration in the slurry, forming highly irregular aggregates that reduce the strength of the mold shell. Therefore, existing glass fiber-reinforced mold shell modification technologies are limited by the fiber's own temperature resistance, high-temperature compatibility with the matrix, and insufficient dispersion processes, making it difficult to maintain a stable reinforcing effect under high-temperature conditions, thus restricting their application in high-end investment casting.
[0005] In summary, there is an urgent need to develop a method for preparing ceramic molds that can balance the strength and permeability of the ceramic mold while ensuring high-temperature stability. Summary of the Invention
[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a mullite fiber modified ceramic mold shell and its preparation method, which can improve the structural strength of the ceramic mold shell and maintain good air permeability and high temperature stability, while significantly reducing the amount of raw materials used.
[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a mullite fiber modified ceramic mold shell, the method comprising the following steps: (1) The wax model is placed in the surface slurry and then coated with sand to obtain the surface mold shell; the raw materials of the surface slurry include silica sol, mullite fiber, cobalt aluminate and zircon powder; (2) The surface mold shell obtained in step (1) is placed in the back layer slurry and then coated with sand to obtain the back layer mold shell; the raw materials of the back layer slurry include silica sol, mullite fiber and zircon powder; (3) After dewaxing the back layer mold shell obtained in step (2), it is calcined to obtain the mullite fiber modified ceramic mold shell.
[0008] The method for preparing mullite fiber modified ceramic mold shell provided by the present invention adds mullite fiber as an additive to the surface layer slurry and the back layer slurry, which can prepare a ceramic mold shell with high strength, while ensuring that the mold shell has good air permeability, greatly reducing the amount of raw materials used for shell making, shortening the production cycle of the mold shell, and saving production costs.
[0009] Material fracture is usually caused by the propagation of microcracks inside the specimen. When the microcracks come into contact with mullite fibers, they deflect and can effectively dissipate the fracture energy. In addition, mullite fibers have a melting point of 1850℃ and are not easy to soften and decompose at high temperatures. They have strong high-temperature stability, which can ensure the dimensional stability of the mold shell at high temperatures and guarantee the accuracy of the casting.
[0010] Preferably, the wax model in step (1) is cleaned.
[0011] Preferably, the preparation steps of the surface slurry in step (1) specifically include: adding cobalt aluminate and mullite fiber into silica sol for a first stirring, and then adding zircon powder for a second stirring to obtain the surface slurry.
[0012] Preferably, the mass ratio of mullite fiber to zircon powder is (1-2):5, for example, it can be 1:5, 1.2:5, 1.3:5, 1.5:5, 1.8:5 or 2:5, but is not limited to the listed values. Other unlisted values within the range are also applicable, preferably 1.3:5.
[0013] Preferably, the mass ratio of mullite fiber to cobalt aluminate is (3-10):1, for example, it can be 3:1, 5:1, 6:1, 8:1 or 10:1, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0014] Preferably, the length of the mullite fiber is 2-3 mm, for example, it can be 2 mm, 2.2 mm, 2.5 mm, 2.8 mm or 3 mm, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0015] Preferably, the solid content of the surface slurry is 80-85 wt%, for example, it can be 80 wt%, 81 wt%, 82 wt%, 83 wt% or 85 wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0016] Preferably, the first stirring speed is 750-850 rpm / min and the time is 25-35 min.
[0017] The first stirring speed is 750-850 rpm / min, for example, it can be 750 rpm / min, 780 rpm / min, 800 rpm / min, 820 rpm / min or 850 rpm / min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0018] The first stirring time is 25-35 minutes, for example, it can be 25 minutes, 28 minutes, 30 minutes, 32 minutes or 35 minutes, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0019] Preferably, the second stirring speed is 550-650 rpm / min and the time is 110-130 min.
[0020] The second stirring speed is 550-650 rpm / min, for example, it can be 550 rpm / min, 580 rpm / min, 600 rpm / min, 620 rpm / min or 650 rpm / min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0021] The second stirring time is 110-130 min, for example, it can be 110 min, 115 min, 120 min, 125 min or 130 min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0022] Preferably, both the first stirring and the second stirring are carried out in a planetary multi-layer paddle mixer.
[0023] Preferably, the time for coating the slurry in step (1) is 60-90s, for example, it can be 60s, 65s, 70s, 80s or 90s, but is not limited to the listed values. Other unlisted values within the range are also applicable, with 80s being the preferred value.
[0024] Preferably, the sand used in step (1) includes 70-100 mesh corundum sand, for example, it can be 70 mesh, 75 mesh, 80 mesh, 90 mesh or 100 mesh, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0025] Preferably, step (1) includes a natural drying step after sand rinsing.
[0026] Preferably, the preparation steps of the backing slurry in step (2) specifically include: adding zircon powder and mullite fiber to silica sol in sequence and stirring to obtain the backing slurry.
[0027] Preferably, the mass ratio of mullite fiber to zircon powder is (2-3):5, for example, it can be 2:5, 2.2:5, 2.4:5, 2.6:5 or 3:5, but is not limited to the listed values. Other unlisted values within the range are also applicable, preferably 2.6:5.
[0028] Preferably, the solid content of the backing slurry is 80-85 wt%, for example, it can be 80 wt%, 81 wt%, 82 wt%, 83 wt% or 85 wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0029] Preferably, the stirring speed is 550-650 rpm / min and the stirring time is 110-130 min.
[0030] The stirring speed is 550-650 rpm / min, for example, it can be 550 rpm / min, 580 rpm / min, 600 rpm / min, 620 rpm / min or 650 rpm / min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0031] The stirring time is 110-130 min, for example, it can be 110 min, 115 min, 120 min, 125 min or 130 min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0032] Preferably, the mixing is carried out in a planetary multi-layer paddle mixer.
[0033] Preferably, the time for coating the slurry in step (2) is 30-70s, for example, it can be 30s, 40s, 50s, 60s or 70s, but is not limited to the listed values. Other unlisted values within the range are also applicable, preferably 50s.
[0034] Preferably, the sand used in step (2) includes 30-70 mesh molybdenum sand, for example, it can be 30 mesh, 40 mesh, 50 mesh, 60 mesh or 70 mesh, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0035] Preferably, step (2) includes a natural drying step after sand rinsing.
[0036] Preferably, the steps of slurry application and sand application in step (2) are repeated 5-7 times to obtain the back layer mold shell, for example, 5 times, 6 times or 7 times.
[0037] Preferably, the dewaxing in step (3) is carried out in a dewaxing kettle.
[0038] Preferably, the roasting in step (3) includes a first heating stage, a second heating stage, and a constant temperature roasting stage performed sequentially.
[0039] Preferably, the first heating stage is: heating from room temperature to 590-610℃ at a rate of 4-6℃ / min.
[0040] The heating rate of the first heating stage is 4-6℃ / min, for example, it can be 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min or 6℃ / min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0041] The room temperature refers to a temperature between 15 and 30°C, such as 15°C, 20°C, 22°C, 25°C, or 30°C, but is not limited to the listed values. Other unlisted values within the range also apply.
[0042] The heating endpoint of the first heating stage is 590-610℃, for example, it can be 590℃, 595℃, 600℃, 605℃ or 610℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0043] Preferably, the second heating stage is characterized by heating from 590-610℃ to 900-1100℃ at a rate of 18-22℃ / min.
[0044] The heating rate of the second heating stage is 18-22℃ / min, for example, it can be 18℃ / min, 19℃ / min, 20℃ / min, 21℃ / min or 22℃ / min, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0045] The heating endpoint of the second heating stage is 900-1100℃, for example, it can be 900℃, 950℃, 1000℃, 1050℃ or 1100℃, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0046] Preferably, the constant temperature calcination section is calcined at 900-1100℃ for 60-120 minutes, and more preferably at 1000℃ for 90 minutes.
[0047] The calcination temperature of the constant temperature calcination section is 900-1100℃, for example, it can be 900℃, 950℃, 1000℃, 1050℃ or 1100℃, but is not limited to the listed values. Other unlisted values within the range are also applicable, and 1000℃ is preferred.
[0048] The calcination time of the constant temperature calcination section is 60-120 min, for example, it can be 60 min, 75 min, 90 min, 105 min or 120 min, but is not limited to the listed values. Other unlisted values within the range are also applicable, with 90 min being the preferred value.
[0049] Preferably, the thickness of the mullite fiber modified ceramic mold shell in step (3) is 5-8 mm, for example, it can be 5 mm, 6 mm, 7 mm or 8 mm, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0050] This invention employs a suitable high-temperature sintering process to produce high-strength ceramic mold shells.
[0051] Secondly, the present invention provides a mullite fiber modified ceramic mold shell, which is prepared by the preparation method of the mullite fiber modified ceramic mold shell described in the first aspect.
[0052] The mullite fiber content in the mullite fiber modified ceramic mold shell is 8-12 wt%, for example, it can be 8 wt%, 9 wt%, 10 wt%, 11 wt% or 12 wt%, but is not limited to the listed values. Other unlisted values within the range are also applicable.
[0053] The mullite fiber-modified ceramic mold shell provided by this invention is prepared by adding mullite fibers and using a reasonable calcination process. It achieves a flexural strength of up to 11.3 MPa and an air permeability of 35.3 m at 1000℃. 4 / (N·min), which balances the strength and breathability of the mold shell.
[0054] The numerical range described in this invention includes not only the point values listed above, but also any point values within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values included in the range.
[0055] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing mullite fiber modified ceramic mold shells. By adding mullite fiber as an additive to both the surface and back layers of the slurry, a high-strength ceramic mold shell can be prepared. Simultaneously, the mold shell maintains good air permeability and dimensional stability at high temperatures, significantly reducing the amount of raw materials used, shortening the production cycle, and saving production costs. The resulting mullite fiber modified ceramic mold shell has a flexural strength of up to 11.3 MPa, and an air permeability of 35.3 m at 1000℃. 4 / (N·min), which can meet the requirements of precision casting process. Attached Figure Description
[0056] Figure 1 This is the XRD pattern of mullite fiber provided in Embodiment 1 of the present invention.
[0057] Figure 2 This is an optical image of the surface mold shell provided in Embodiment 1 of the present invention.
[0058] Figure 3 This is an optical image of the back layer mold shell provided in Embodiment 1 of the present invention.
[0059] Figure 4 This is a cross-sectional SEM image of the mullite fiber modified ceramic mold shell sample provided in Embodiment 1 of the present invention. Detailed Implementation
[0060] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0061] Example 1 This embodiment provides a mullite fiber modified ceramic mold shell, wherein the mullite fiber content is 10wt%, the mullite fiber length is 2.5mm, and the XRD pattern of the mullite fiber is shown below. Figure 1As shown in the figure, the material is composed of three phases: mullite (3Al2O3·2SiO2), corundum (Al2O3), and cristobalite (SiO2). This three-phase load structure gives the material significant performance advantages: the mullite skeleton provides high-temperature stability, the corundum phase enhances mechanical properties, and the cristobalite toughens through a phase transformation mechanism.
[0062] The preparation method of the mullite fiber modified ceramic mold shell includes the following steps: (1) Place the silica sol in a planetary multi-layer paddle mixer, add cobalt aluminate and mullite fiber to the silica sol, and stir for the first time at a speed of 800 rpm / min for 30 min; then add zircon powder and stir for the second time at a speed of 600 rpm / min for 120 min to obtain a surface slurry with a solid content of 82 wt%; the mass ratio of mullite fiber to zircon powder is 1.3:5; the mass ratio of mullite fiber to cobalt aluminate is 5:1.
[0063] After cleaning, the wax model is immersed in the surface slurry for 80 seconds, followed by sanding with 90-mesh corundum sand to obtain the surface mold shell. The optical image is shown below. Figure 2 As shown.
[0064] (2) Place the silica sol in a planetary multi-layer paddle mixer, add zircon powder and mullite fiber to the silica sol in sequence, and stir at a speed of 600 rpm / min for 120 min to obtain a back layer slurry with a solid content of 82 wt%; the mass ratio of mullite fiber to zircon powder is 2.6:5.
[0065] The surface mold shell obtained in step (1) is placed in the back layer slurry and coated for 50 seconds, followed by sand application. The sand is 50-mesh Molecat sand. The coating and sand application steps are repeated 6 times to obtain the back layer mold shell. The optical image is shown below. Figure 3 As shown.
[0066] (3) The back layer mold shell obtained in step (2) is dewaxed in a dewaxing kettle and then calcined. The calcination includes: heating from room temperature to 600°C at a rate of 5°C / min, then heating from 600°C to 1000°C at a rate of 20°C / min, and calcining at 1000°C for 90 min to obtain a mullite fiber modified ceramic mold shell with a thickness of 7 mm.
[0067] SEM images of cross-sections of mullite fiber modified ceramic mold shell specimens are shown below. Figure 4 As shown in the figure, the mullite fibers are distributed irregularly and interwovenly, forming a three-dimensional network structure. The fibers overlap and interweave with each other, and are relatively uniformly dispersed in the matrix without large-area agglomeration, indicating that the preparation process has achieved good uniform dispersion of the fibers. At the same time, the interface between the fibers and the matrix is clear, and the matrix can be seen wrapping the fibers in some areas, indicating that there is a certain degree of bonding between the two.
[0068] Example 2 This embodiment provides a mullite fiber modified ceramic mold shell, wherein the mullite fiber content is 8wt% and the length of the mullite fiber is 2mm.
[0069] The preparation method of the mullite fiber modified ceramic mold shell includes the following steps: (1) Place the silica sol in a planetary multi-layer paddle mixer, add cobalt aluminate and mullite fiber to the silica sol, and stir for the first time at a speed of 750 rpm / min for 35 min; then add zircon powder and stir for the second time at a speed of 550 rpm / min for 130 min to obtain a surface slurry with a solid content of 80 wt%; the mass ratio of mullite fiber to zircon powder is 1:5; the mass ratio of mullite fiber to cobalt aluminate is 3:1.
[0070] After cleaning, the wax model is placed in the surface slurry and coated for 60 seconds, then sand is poured on it. The sand is 70-mesh corundum sand, thus obtaining the surface mold shell.
[0071] (2) Place the silica sol in a planetary multi-layer paddle mixer, add zircon powder and mullite fiber to the silica sol in sequence, and stir at a speed of 550 rpm / min for 130 min to obtain a back layer slurry with a solid content of 80 wt%; the mass ratio of mullite fiber to zircon powder is 2:5.
[0072] The surface mold shell obtained in step (1) is placed in the back layer slurry and coated for 30 minutes, then sand is poured on. The sand is 30 mesh molybdenum sand. The coating and sand pouring steps are repeated 7 times to obtain the back layer mold shell.
[0073] (3) The back layer mold shell obtained in step (2) is dewaxed in a dewaxing kettle and then calcined. The calcination includes: heating from room temperature to 590°C at a rate of 4°C / min, then heating from 590°C to 900°C at a rate of 18°C / min, and calcining at 900°C for 120 min to obtain a mullite fiber modified ceramic mold shell with a thickness of 8 mm.
[0074] Example 3 This embodiment provides a mullite fiber modified ceramic mold shell, wherein the mullite fiber content is 12wt% and the length of the mullite fiber is 3mm.
[0075] The preparation method of the mullite fiber modified ceramic mold shell includes the following steps: (1) Place the silica sol in a planetary multi-layer paddle mixer, add cobalt aluminate and mullite fiber to the silica sol, and stir for the first time at a speed of 850 rpm / min for 25 min; then add zircon powder and stir for the second time at a speed of 650 rpm / min for 110 min to obtain a surface slurry with a solid content of 85 wt%; the mass ratio of mullite fiber to zircon powder is 2:5; the mass ratio of mullite fiber to cobalt aluminate is 10:1.
[0076] After cleaning, the wax model is placed in the surface slurry and coated for 90 seconds, then sand is poured on it. The sand is 100-mesh corundum sand, thus obtaining the surface mold shell.
[0077] (2) Place the silica sol in a planetary multi-layer paddle mixer, add zircon powder and mullite fiber to the silica sol in sequence, and stir at a speed of 650 rpm / min for 110 min to obtain a back layer slurry with a solid content of 85 wt%; the mass ratio of mullite fiber to zircon powder is 3:5.
[0078] The surface mold shell obtained in step (1) is placed in the back layer slurry and coated for 70 seconds, then sand is poured on. The sand is 70 mesh Molecule kaolin. The coating and sand pouring steps are repeated 5 times to obtain the back layer mold shell.
[0079] (3) The back layer mold shell obtained in step (2) is dewaxed in a dewaxing kettle and then calcined. The calcination includes: heating from room temperature to 610°C at a rate of 6°C / min, then heating from 610°C to 1100°C at a rate of 22°C / min, and calcining at 1100°C for 60 min to obtain a mullite fiber modified ceramic mold shell with a thickness of 5 mm.
[0080] Example 4 This embodiment provides a mullite fiber modified ceramic mold shell. The preparation method of the mullite fiber modified ceramic mold shell differs from that of Embodiment 1 in that the zircon powder, cobalt aluminate, and mullite fiber described in step (1) are added together to the silica sol and stirred for 150 minutes at a speed of 800 rpm / min. The rest is the same as that of Embodiment 1.
[0081] Example 5 This embodiment provides a mullite fiber modified ceramic mold shell. The difference between the preparation method of the mullite fiber modified ceramic mold shell and that of Embodiment 1 is that the mass ratio of mullite fiber to zircon powder in step (1) is adjusted to 0.5:5, and the rest is the same as that of Embodiment 1.
[0082] Example 6 This embodiment provides a mullite fiber modified ceramic mold shell. The difference between the preparation method of the mullite fiber modified ceramic mold shell and that of Embodiment 1 is that the mass ratio of mullite fiber to zircon powder in step (1) is adjusted to 2.5:5, and the rest is the same as that of Embodiment 1.
[0083] Example 7 This embodiment provides a mullite fiber modified ceramic mold shell. The preparation method of the mullite fiber modified ceramic mold shell differs from that of Embodiment 1 in that the calcination in step (3) is adjusted to: heating from room temperature to 1000℃ at a rate of 20℃ / min, and calcining at 1000℃ for 90min. The rest is the same as that of Embodiment 1.
[0084] Example 8 This embodiment provides a mullite fiber modified ceramic mold shell. The preparation method of the mullite fiber modified ceramic mold shell differs from that of Embodiment 1 in that the calcination in step (3) is adjusted to: heating from room temperature to 1000℃ at a rate of 5℃ / min, and calcining at 1000℃ for 90min. The rest is the same as that of Embodiment 1.
[0085] Comparative Example 1 This comparative example provides a mullite fiber modified ceramic mold shell, which differs from Example 1 in that the mullite fiber content in the mullite fiber modified ceramic mold shell is adjusted to 5 wt%, while the rest is the same as Example 1.
[0086] Comparative Example 2 This comparative example provides a mullite fiber modified ceramic mold shell, which differs from Example 1 in that the mullite fiber content in the mullite fiber modified ceramic mold shell is adjusted to 15wt%, while the rest is the same as Example 1.
[0087] Comparative Example 3 This comparative example provides a mullite powder modified ceramic mold shell. The difference from Example 1 is that the mullite fibers are replaced with mullite powder with a particle size of 240 mesh, while the rest is the same as Example 1.
[0088] Comparative Example 4 This comparative example provides a glass fiber modified ceramic mold shell, which differs from Example 1 in that the mullite fibers of equal mass and length are replaced with glass fibers, while the rest are the same as in Example 1.
[0089] The mullite fiber modified ceramic mold shells provided in Examples 1-8 and Comparative Examples 1-2, the mullite powder modified ceramic mold shell provided in Comparative Example 3, and the glass fiber modified ceramic mold shell provided in Comparative Example 4 were subjected to mechanical property tests using HB 5321.1 "Mechanical properties test of high temperature alloys for aviation - Part 1: Tensile test" and permeability tests using HB 5352.4 "Performance test method for investment casting mold shells - Part 4: Determination of permeability". The results are shown in Table 1.
[0090] Table 1 As can be seen from Table 1, the mullite fiber modified ceramic mold shell provided by the present invention has high flexural strength and good air permeability. At the same time, the mullite fiber is not easy to soften and decompose at high temperature, which ensures the dimensional stability of the mold shell at high temperature.
[0091] A comparison of Examples 1 and 4 shows that adding all raw materials together and stirring at the same speed during the preparation of the surface slurry leads to uneven fiber dispersion and a decrease in the flexural strength of the mold shell. A comparison of Examples 1 and Examples 5 and 6 shows that a low mass ratio of mullite fiber to zircon powder leads to mullite powder crowding the fiber skeleton space, resulting in a decrease in the flexural strength of the mold shell; a high mass ratio leads to weaker connections between fibers, resulting in a decrease in the flexural strength of the mold shell. A comparison of Examples 1 and Examples 7 and 8 shows that using a high heating rate to directly heat to the calcination temperature leads to a decrease in the glass phase content inside the mold shell, resulting in a decrease in the flexural strength of the mold shell; using a low heating rate to directly heat to the calcination temperature leads to an increase in the glass phase content inside the mold shell, resulting in a decrease in the air permeability of the mold shell.
[0092] A comparison of Example 1 with Comparative Examples 1 and 2 shows that insufficient addition of mullite fibers leads to voids within the matrix, reducing the flexural strength of the mold shell; excessive addition leads to fiber agglomeration, also reducing the flexural strength. A comparison of Example 1 with Comparative Examples 3 and 4 shows that replacing mullite fibers with mullite powder reduces both the air permeability and flexural strength of the mold shell. This is mainly because mullite powder fills the pores in the matrix, reducing air permeability and decreasing the proportion of the reinforcing phase in the matrix, thus lowering the flexural strength. Replacing mullite fibers with glass fibers also reduces the flexural strength of the mold shell, primarily because high-temperature calcination damages the fiber skeleton structure of the glass fibers.
[0093] In summary, the method for preparing mullite fiber modified ceramic mold shells provided by this invention, by adding mullite fiber as an additive to both the surface and back layers of the slurry, can produce ceramic mold shells with high strength while ensuring good air permeability and dimensional stability at high temperatures. This significantly reduces the amount of raw materials used, shortens the production cycle, and saves production costs. The resulting mullite fiber modified ceramic mold shell has a flexural strength of up to 11.3 MPa and an air permeability of 35.3 m at 1000℃. 4 / (N·min), which can meet the requirements of precision casting process.
[0094] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A method for preparing a mullite fiber modified ceramic mold shell, characterized in that, The preparation method includes the following steps: (1) The wax model is placed in the surface slurry and then coated with sand to obtain the surface mold shell; the raw materials of the surface slurry include silica sol, mullite fiber, cobalt aluminate and zircon powder; (2) The surface mold shell obtained in step (1) is placed in the back layer slurry and then coated with sand to obtain the back layer mold shell; the raw materials of the back layer slurry include silica sol, mullite fiber and zircon powder; (3) After dewaxing the back layer mold shell obtained in step (2), it is calcined to obtain the mullite fiber modified ceramic mold shell.
2. The preparation method according to claim 1, characterized in that, The preparation steps of the surface slurry in step (1) specifically include: adding cobalt aluminate and mullite fiber into silica sol for the first stirring, and then adding zircon powder for the second stirring to obtain the surface slurry.
3. The preparation method according to claim 2, characterized in that, The mass ratio of mullite fiber to zircon powder is (1-2):5, preferably 1.3:5; Preferably, the mass ratio of mullite fiber to cobalt aluminate is (3-10):1; Preferably, the length of the mullite fiber is 2-3 mm; Preferably, the solid content of the surface slurry is 80-85 wt%.
4. The preparation method according to claim 2 or 3, characterized in that, The first stirring speed is 750-850 rpm / min, and the time is 25-35 min; Preferably, the second stirring speed is 550-650 rpm / min and the time is 110-130 min.
5. The preparation method according to any one of claims 1-4, characterized in that, The time for applying the slurry in step (1) is 60-90 seconds, preferably 80 seconds; Preferably, the sand used in step (1) includes 70-100 mesh corundum sand.
6. The preparation method according to any one of claims 1-5, characterized in that, The preparation steps of the backing slurry in step (2) specifically include: adding zircon powder and mullite fiber to silica sol in sequence and stirring to obtain the backing slurry.
7. The preparation method according to claim 6, characterized in that, The mass ratio of mullite fiber to zircon powder is (2-3):5, preferably 2.6:5; Preferably, the solid content of the backing slurry is 80-85 wt%; Preferably, the stirring speed is 550-650 rpm / min and the stirring time is 110-130 min.
8. The preparation method according to any one of claims 1-7, characterized in that, The time for applying the slurry in step (2) is 30-70 seconds, preferably 50 seconds; Preferably, the sand used in step (2) for sand rinsing includes 30-70 mesh molybdenum sand; Preferably, the steps of slurry application and sand application in step (2) are repeated 5-7 times to obtain the back layer mold shell.
9. The preparation method according to any one of claims 1-8, characterized in that, The roasting in step (3) includes a first heating stage, a second heating stage, and a constant temperature roasting stage performed sequentially; Preferably, the first heating stage is: heating from room temperature to 590-610℃ at a rate of 4-6℃ / min; Preferably, the second heating stage is: heating from 590-610℃ to 900-1100℃ at a rate of 18-22℃ / min; Preferably, the constant temperature calcination section is calcined at 900-1100℃ for 60-120 minutes, and more preferably at 1000℃ for 90 minutes; Preferably, the thickness of the mullite fiber modified ceramic mold shell in step (3) is 5-8 mm.
10. A mullite fiber modified ceramic mold shell, characterized in that, The mullite fiber modified ceramic mold shell is prepared by the preparation method of the mullite fiber modified ceramic mold shell according to any one of claims 1-9; The mullite fiber content in the mullite fiber modified ceramic mold shell is 8-12 wt%.