Magnesium-based ceramic core formula based on photocuring technology and preparation method

Abstract

The invention discloses a magnesium-based ceramic core formula based on a photocuring technology and a preparation method, and relates to the technical field of ceramic core material forming, the magnesium oxide ceramic core comprises the following components by mass: 55-65 wt% of magnesium oxide ceramic slurry, 30-40 wt% of photosensitive resin, 1-3 wt% of a dispersant, and 0.5-2 wt% of a photoinitiator; according to the preparation technology of the magnesium oxide ceramic core, the stability of high-solid-content slurry is improved and the agglomeration and sedimentation of the slurry are inhibited through silane coupling hydration modification in combination with size-graded particle matching; through cooperative regulation and control of a mineralizer and a sintering process, the pore structure, the mechanical strength of a blank and thermal expansion matching performance are optimized, and the depoling efficiency and the casting supporting requirement can be improved; by strictly regulating and controlling the component content of the slurry, it is ensured that the mold core has the chemical inertness that the mold core does not react with stainless steel at high temperature; and the photocuring 3D printing technology is combined with an optimized slurry formula, forming of a complex micro runner structure is achieved, high-precision manufacturing is achieved, and the obtained mold core is good in comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of ceramic core material forming technology, and in particular to a magnesium-based ceramic core formulation and preparation method based on photopolymerization technology. Background Technology

[0002] In the field of precision casting, industries such as aerospace and high-end equipment have an increasing demand for castings with complex internal structures, such as cooling channels for aero-engine blades and internal flow channels for servo valves. The forming accuracy of these castings is highly dependent on the structural complexity and dimensional stability of the casting core. However, traditional core preparation technologies face severe challenges. For example, the wax pattern cores widely used in investment casting are difficult to realize micron-level complex structures, such as multi-channel holes and cross-connecting holes in servo valves. Furthermore, the dewaxing process is prone to deformation or residual wax due to thermal stress, resulting in dimensional deviations in the castings. Photopolymer 3D printing technology, with its micron-level resolution and near-net-shape forming capability, has become a suitable choice for manufacturing complex ceramic parts. It can directly and integrally form complex structures without molds and with high material utilization, providing a feasible solution for the fabrication of high-precision ceramic cores. Currently, ceramic core materials are mainly alumina and fused silica, but both have significant limitations in high-performance castings, especially stainless steel castings: although aluminum-based ceramic cores have excellent high-temperature resistance, they are prone to chemical reactions in corrosive casting environments containing sulfur and chlorine, leading to powdering of the core surface and a sharp drop in strength; silicon-based ceramic cores have lower costs and better core removal performance, but when they come into contact with casting materials such as stainless steel and high-temperature alloys, they are prone to forming brittle phases due to silicon diffusion, causing interface contamination of the casting and affecting the mechanical properties of the product.

[0003] Magnesium-based ceramic cores have become an ideal choice for core materials due to their advantages such as high temperature resistance and no interfacial reaction with stainless steel. However, existing technologies face three major bottlenecks: However, existing technologies face three major bottlenecks: Poor slurry stability: Magnesium-based slurries with high ceramic phase content are prone to sedimentation and stratification due to particle agglomeration, and the scattering of ultraviolet light by ceramic particles during photocuring can lead to incomplete curing. Performance coordination and control is difficult: the core needs to simultaneously meet the requirements of apparent porosity, room temperature flexural strength and appropriate expansion coefficient, and the existing formula cannot balance the three. Insufficient high-temperature chemical compatibility: During sintering or casting, the core composition needs to be further optimized to avoid reaction with stainless steel, which would affect the quality of the casting. Summary of the Invention

[0004] The main objective of this invention is to propose a magnesium-based ceramic core formulation and preparation method based on photocuring technology, aiming to solve the problem of magnesium-based ceramic cores.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention proposes a magnesium-based ceramic core formulation based on photocuring technology, comprising a magnesium oxide ceramic core, wherein the magnesium oxide ceramic core slurry (magnesium-based ceramic slurry) comprises the following components by mass percentage: 55-65 wt% magnesium oxide ceramic particles, 30-40 wt% photosensitive resin, 1-3 wt% dispersant, and 0.5-2 wt% photoinitiator.

[0006] In one embodiment, the material includes magnesium oxide ceramic particles, which comprise 85-95 wt% surface-modified magnesium oxide powder and 5-15 wt% mineralizer.

[0007] In one embodiment, the material further includes magnesium oxide powder, which comprises three particle sizes: 5~10 μm, 2~5 μm, and 0.5~2 μm, wherein 5~10 μm accounts for 15~30 wt%, 2~5 μm accounts for 40~60 wt%, and 0.5~2 μm accounts for 20~40 wt%.

[0008] In one embodiment, the magnesium oxide ceramic core meets the following performance indicators: apparent porosity of 15~25%; room temperature flexural strength ≥25 MPa; coefficient of thermal expansion of 10~13×10⁻⁶ MPa. -6 / ℃ (25~800 ℃); It has high-temperature chemical inertness and does not react chemically with stainless steel alloys at temperatures below 1600 ℃ during the casting stage.

[0009] In one embodiment, the magnesium-based ceramic core is formed layer by layer by photopolymerization technology, wherein the photopolymerization technology is any one of digital light processing (DLP) photopolymerization, stereolithography (SLA) photopolymerization, or liquid crystal display (LCD) photopolymerization.

[0010] In one embodiment, the surface modification step of the magnesium oxide powder is to form a protective layer on the powder surface using a silane coupling agent; The silane coupling agent is selected from silanes containing one or more functional groups selected from amino, epoxy, vinyl, methacryloxy, and mercapto groups; the amount of the silane coupling agent is 0.3 to 3 wt% of the magnesium oxide powder, and the proportion of a single type of silane coupling agent in the total mass of the modifier is ≤60 wt%.

[0011] In one embodiment, the mineralizer, based on a total mass of 100%, comprises 7-15 wt% yttrium oxide, 20-30 wt% zirconium oxide, 15-25 wt% alumina, 10-20 wt% low-melting-point borosilicate glass powder, and 10-30 wt% auxiliary mineralizer. The auxiliary mineralizer is selected from one or more of silicon carbide powder, zirconium carbide powder, and silicon nitride powder, and the proportion of a single component is ≤15 wt% (based on the total mass of the mineralizer). The yttrium oxide has a particle size of 0.5~2 μm, the zirconium oxide has a particle size of 1~3 μm, the alumina has a particle size of 1~3 μm, the low melting point borosilicate glass powder has a particle size of 1~3 μm, and the auxiliary mineralizer has a particle size of 1~5 μm. The low-melting-point borosilicate glass powder contains ≤10 wt% silicon dioxide (SiO2), and its addition to the mineralizer results in the total proportion of SiO2 in the total mass of the core being ≤0.1 wt%.

[0012] In one embodiment, the photosensitive resin system comprises, by total mass, 50-70 wt% acrylate monomers and 30-50 wt% acrylate oligomers.

[0013] In one embodiment, the dispersant comprises 60-70 wt% oleic acid and 30-40 wt% polyoxyethylene castor oil, based on a total mass of 100%.

[0014] In one embodiment, the photoinitiator comprises, by weight 100%, 60-80 wt% of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 20-40 wt% of ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L).

[0015] Secondly, the present invention provides a method for preparing a magnesium-based ceramic core based on photopolymerization technology, comprising the following steps in sequence: Step 1: Mix the surface-modified magnesium oxide powder, mineralizer, and acrylate photosensitive resin system to prepare a stable magnesium-based ceramic slurry; Step 2: Place the magnesium-based ceramic slurry into a vacuum pump for degassing to remove internal air bubbles; Step 3: Place the degassed magnesium-based ceramic slurry into the material tank of the photopolymerization printing equipment, and print the magnesium-based ceramic core blank according to the preset model parameters; Step 4: The magnesium-based ceramic core blanks are subjected to degreasing and sintering treatments in sequence to obtain magnesium-based ceramic cores.

[0016] In one implementation, In step one, the preparation method of the magnesium-based ceramic slurry includes the following steps in sequence: The surface modification treatment of magnesium oxide powder is carried out as required, specifically: the powder is dispersed in an ethanol solution containing 0.5~3 wt% silane coupling agent, ultrasonically dispersed for 30~60 min, filtered and dried for later use; Prepare the surface-modified magnesium oxide powder, mineralizer, photosensitive resin, acrylate oligomer, dispersant, and photoinitiator according to the preset requirements; Add a dispersant to the acrylate mixture, continue stirring for 10-20 min, then add a photoinitiator, stir in the dark for 15-25 min to obtain a premix; Add the mineralizer to the premixed liquid, transfer it to a ball mill, use zirconia balls as the grinding medium, and ball mill at 300~400 r / min for 20~30 min; Magnesium oxide powder is added in stages: first, powder with a particle size of 0.5~2 μm is added, and ball milling is performed at 300~400 r / min for 20~30 min; then, powder with a particle size of 2~5 μm is added, and ball milling is performed at 300~400 r / min for 30~40 min; finally, powder with a particle size of 5~10 μm is added, and ball milling is performed at 300~400 r / min for 40~60 min to obtain a magnesium-based ceramic slurry; the slurry is then subjected to a shearing at 25 ℃ and a shear rate of 100 s. - The viscosity under the given conditions is 3000~6000 mPas; In step two, the process parameters for the vacuum degassing treatment are: stirring and degassing under a vacuum of 0.01~0.04 MPa (absolute pressure), holding pressure for 15~30 min, and stopping after observing until no more bubbles overflow. In step three, the key process parameters for the photopolymerization 3D printing are: The curing light source wavelength was set to 385~405 nm; the curing power was set to 10~15 mW / cm²; the curing time for a single layer was set to 4~8 s; and the curing thickness for a single layer was set to 30~80 μm. In step four, the degreasing and sintering process is as follows: Degreasing stage (tube furnace, air atmosphere): Heating from room temperature to 250℃: heating rate 1~2℃ / min, hold for 1~2 h; heating from 250℃ to 400~450℃: heating rate 0.5~1℃ / min, hold for 2~3 h; heating from 450℃ to 650℃: heating rate 1~2℃ / min, hold for 2~3 h. Sintering stage (tube furnace, vacuum or inert protection with oxygen content below 200 ppm): Heating from 650 ℃ to 1200 ℃: heating rate 2~3 ℃ / min; heating from 1200 ℃ to 1500 ℃: heating rate 1~2 ℃ / min, holding for 4~6 h; cooling from 1500 ℃ to 800 ℃: cooling rate 2~3 ℃ / min, holding for 1~2 h; cooling from 800 ℃ to room temperature, cooling with the furnace.

[0017] The technical solution of the present invention has the following significant advantages: Excellent slurry stability: Through the synergistic effect of hydrophobic modification of silane coupling agent and three-level particle size matching of magnesium oxide ceramic particles, the viscosity change rate of high ceramic content slurry is ≤15% after 7 days, the dispersion uniformity is improved by 30%, and the problem of agglomeration and sedimentation of magnesium oxide ceramic slurry is solved.

[0018] Synergistic and controllable performance: The mineralizer and sintering process are synergistically controlled to ensure that the core simultaneously meets the requirements of 15~25% apparent porosity, core release and collapse resistance, room temperature bending strength ≥25 MPa, and casting support requirements. Furthermore, the coefficient of thermal expansion is adjusted accordingly by the component content in the mineralizer to reduce cracking caused by casting stress.

[0019] Good high-temperature chemical compatibility: The total SiO2 content is strictly controlled to be ≤0.1 wt%. There is no interfacial reaction with stainless steel below 1600 ℃, no brittle phase is generated, and the qualified rate of ceramic cores is increased to over 95%.

[0020] Strong ability to form complex structures: Photopolymer 3D printing technology, combined with optimized magnesium oxide ceramic slurry and process parameters, can form complex flow channel structures with pore sizes in the millimeter range, with a dimensional accuracy of ±0.1 mm, which is better than the dimensional accuracy of complex structures of traditional processes. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 Flowchart of the preparation method for magnesium-based ceramic cores Figure 2 This is a schematic diagram of the three-dimensional structure of the magnesium-based ceramic core in Example 2. Figure 3 This is a schematic diagram of the viscosity-time curves of the slurry in Examples 1 and 2 (shear rate is 100 s). -1 ) Figure 4 The image shows the microstructure of the core after sintering in Example 1. Figure 5 The image shows the microstructure of the core after sintering in Example 2. Explanation of icon numbers: The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that if directional indicators (such as up, down, left, right, front, back, etc.) are involved in the embodiments of this invention, these directional indicators are only used to explain the relative positional relationships and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly. Unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0025] Furthermore, if the embodiments of the present invention involve descriptions using terms such as "first," "second," etc., these descriptions are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Furthermore, the use of "and / or" or "and / or" throughout the text includes three parallel options; for example, "A and / or B" includes option A, option B, or options where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0026] Magnesium-based ceramic cores are formed layer by layer using photopolymerization technology. The cores consist of the following components by weight percentage: 55-65 wt% magnesium oxide ceramic slurry, 30-40 wt% photosensitive resin, 1-3 wt% dispersant, and 0.5-2 wt% photoinitiator. The magnesium oxide ceramic slurry comprises 85-95 wt% surface-modified magnesium oxide powder and 5-15 wt% mineralizer. Magnesium oxide powder includes three particle sizes: 5~10 μm, 2~5 μm, and 0.5~2 μm. The mass percentages of each particle size in the magnesium oxide powder are as follows: 5~10 μm: 15~30 wt%; 2~5 μm: 40~60 wt%; 0.5~2 μm: 20~40 wt%. Magnesium oxide ceramic cores must meet the following requirements: apparent porosity of 15-25%, room temperature flexural strength ≥25 MPa, dimensional accuracy ≤±0.10 mm, and coefficient of thermal expansion of 10-13×10⁻⁶. -6 It does not react chemically with stainless steel alloys below 1600℃ (25~800℃).

[0027] Photopolymerization 3D printing technology includes one of the following: digital light processing photopolymerization, stereolithography photopolymerization, and liquid crystal display photopolymerization.

[0028] The surface modification of magnesium oxide powder is achieved by forming a protective layer on the powder surface through a silane coupling agent. The silane coupling agent is selected from silanes containing one or more functional groups, such as amino, epoxy, vinyl, methacryloxy, and mercapto. The amount of silane coupling agent used is 0.3~3 wt% of the magnesium oxide powder, and the single type of silane coupling agent accounts for 30~80 wt% of the total mass of the modifier; Surface modification must ensure that: the modified magnesium oxide powder does not react adversely with the mineralizer or photosensitive resin, and that after photocuring-debinding-sintering, the physical properties of the core still meet the requirements of claim 1. The mineralizer components, based on 100% of total mass, are as follows: Yttrium oxide 7-15 wt%, zirconium oxide 20-30 wt%, alumina 15-25 wt%, low melting point borosilicate glass powder 10-20 wt%, and auxiliary mineralizers (accounting for 10-30 wt% of the total mass of mineralizers); The auxiliary mineralizer is selected from one or more of silicon carbide powder, zirconium carbide powder, and silicon nitride powder, and the proportion of a single component is ≤15 wt% (based on the total mass of the mineralizer). Yttrium oxide has a particle size of 0.5~2 μm, zirconium oxide has a particle size of 1~3 μm, alumina has a particle size of 1~3 μm, low melting point borosilicate glass powder has a particle size of 1~3 μm, and auxiliary mineralizer has a particle size of 1~5 μm. The SiO2 content in the low melting point borosilicate glass powder is ≤10 wt%, and its addition to the mineralizer makes the total proportion of SiO2 in the total mass of the core ≤0.1 wt%.

[0029] The photosensitive resin system, based on a total mass of 100%, includes 50-70 wt% acrylate monomers and 30-50 wt% acrylate oligomers. The dispersant, by total mass of 100%, includes 60-70 wt% oleic acid and 30-40 wt% polyoxyethylene castor oil.

[0030] The photoinitiator, based on 100% of total mass, includes 60-80 wt% TPO and 20-40 wt% TPO-L.

[0031] The magnesium-based ceramic core prepared by photopolymerization technology includes the following steps in sequence: Step 1: Mix the surface-modified magnesium oxide powder, mineralizer, and acrylate photosensitive resin system to prepare a stable magnesium-based ceramic slurry; Step 2: Place the magnesium-based ceramic slurry into a vacuum pump for degassing to remove internal air bubbles; Step 3: Place the degassed magnesium-based ceramic slurry into the material tank of the photopolymerization 3D printing equipment, and print the magnesium-based ceramic core blank according to the preset model parameters; Step 4: The magnesium-based ceramic core blank is subjected to degreasing and sintering treatment in sequence to obtain the magnesium-based ceramic core.

[0032] In step one, the preparation method of magnesium-based ceramic slurry includes the following steps in sequence: The surface modification treatment of magnesium oxide powder is carried out as required, specifically: the powder is dispersed in an ethanol solution containing 0.5~3 wt% silane coupling agent (KH550, KH560, etc.), ultrasonically dispersed for 30~60 min, filtered and dried for later use.

[0033] Prepare the surface-modified magnesium oxide powder, mineralizer, acrylate monomers, acrylate oligomers, dispersant, and photoinitiator according to the preset requirements; Place the acrylate monomers and acrylate oligomers into a mixing container and stir for 15-30 min to form a homogeneous liquid mixture; add a dispersant to the liquid mixture and continue stirring for 10-20 min; then add a photoinitiator and stir in the dark for 15-25 min to form a premixed liquid. Add the mineralizer to the premixed liquid, transfer it to a ball mill, use zirconia balls as the grinding medium, and ball mill at 300~400 r / min for 20~30 min; Magnesium oxide powder was added in stages: first, powder with a particle size of 0.5–2 μm was added, and ball milling was performed at 300–400 r / min for 20–30 min; then, powder with a particle size of 2–5 μm was added, and ball milling was performed at 300–400 r / min for 30–40 min; finally, powder with a particle size of 5–10 μm was added, and ball milling was performed at 300–400 r / min for 40–60 min to obtain a magnesium-based ceramic slurry; the slurry was then subjected to a shearing at 25 ℃ and a shear rate of 100 s⁻¹. - The viscosity under the given conditions is 3000~6000 mPa・s.

[0034] In step two, the process parameters for vacuum degassing are as follows: stirring and degassing under a vacuum of 0.01~0.04 MPa (absolute pressure) for 15~30 min, and stopping after observing until no more bubbles overflow.

[0035] In step three, the key process parameters for photopolymer 3D printing are: curing light source wavelength: 385~405 nm; curing power: 8~15 mW / cm²; single-layer curing time: 4~8 s; single-layer curing thickness: 30~80 μm; printing environment: humidity ≤40%.

[0036] In step four, the degreasing and sintering process is as follows: In a tube furnace under air atmosphere, degreasing treatment was carried out as follows: heating from room temperature to 250 ℃ at a rate of 1~2 ℃ / min and holding for 1~2 h (removal of small molecule volatiles); heating from 250 ℃ to 400~450 ℃ at a rate of 0.5~1 ℃ / min and holding for 2~3 h (decomposition of acrylic resin); heating from 450 ℃ to 650 ℃ at a rate of 1~2 ℃ / min and holding for 2~3 h (complete removal of residual carbon). When performing argon-protected sintering in a tube furnace, the oxygen content inside the furnace must be controlled below 200 ppm. Heating from 650 ℃ to 1200 ℃: heating rate 2~3 ℃ / min; heating from 1200 ℃ to 1500 ℃: heating rate 1~2 ℃ / min, holding for 4~6 h (to promote diffusion sintering of magnesium oxide and mineralizer); cooling from 1500 ℃ to 800 ℃: cooling rate 2~3 ℃ / min, holding for 1~2 h (to relieve internal stress); cooling from 800 ℃ to room temperature: cooling with the furnace (to avoid rapid cooling cracking).

[0037] A magnesium-based ceramic core based on photopolymerization 3D printing, formed layer by layer through photopolymerization technology, has the following core features: Composition design: Composed of magnesium oxide ceramic slurry (55~65 wt%), photosensitive resin (30~40 wt%), dispersant (1~3 wt%), and photoinitiator (0.5~2 wt%); The magnesium oxide ceramic slurry contains surface-modified magnesium oxide powder (85~95 wt%) and mineralizer (5~15 wt%). The magnesium oxide powder adopts a three-level particle size distribution (5~10 μm accounts for 15~30 wt%, 2~5 μm accounts for 40~60 wt%, and 0.5~2 μm accounts for 20~40 wt%). After modification with silane coupling agents (including amino, epoxy, etc.), the water wetting angle is ≥90°, which improves the compatibility with organic phases. The mineralizers include yttrium oxide (7~15 wt%), zirconium oxide (20~30 wt%), alumina (15~25 wt%), low-melting-point borosilicate glass powder (10~20 wt%), and auxiliary mineralizers (10~30 wt%). The auxiliary mineralizers are selected from one or more of silicon carbide, zirconium carbide, and silicon nitride (single component ≤15 wt%). The SiO2 content in the low-melting-point borosilicate glass powder (≤10 wt%) and the total SiO2 content in the core (≤0.1 wt%) are strictly controlled to avoid the formation of harmful phases by reaction with MgO at high temperatures. The photosensitive resin is composed of acrylate monomers (50~70 wt%, including dipropylene glycol diacrylate, etc.) and oligomers (30~50 wt%, including polyurethane acrylate, etc.), matched with photoinitiators (TPO and TPO-L) to ensure curing efficiency under high ceramic solid content.

[0038] Performance indicators: Apparent porosity 15~25%, room temperature flexural strength ≥50 MPa, coefficient of thermal expansion 10~13×10 -6 / ℃ (25~800 ℃), and has no chemical reaction with stainless steel below 1600 ℃.

[0039] A method for preparing a magnesium-based ceramic core based on photopolymerization 3D printing includes the following steps: Preparation of magnesium-based ceramic slurry: Surface modification of magnesium oxide powder: Disperse the powder in an ethanol solution containing 0.5~3wt% silane coupling agent (e.g., KH550, KH560), ultrasonically disperse for 30~60 min, filter and dry for later use, to improve the hydrophobicity and dispersibility of the powder; Preparation of premix: Mix acrylate monomers and oligomers in proportion, stir for 15-30 min to form a homogeneous liquid, add dispersant (60-70 wt% oleic acid + 30-40 wt% polyoxyethylene castor oil) and continue stirring for 10-20 min, then add photoinitiator (60-80 wt% TPO + 20-40 wt% TPO-L) and stir in the dark for 15-25 min; Ball milling: Add the mineralizer to the premixed liquid and transfer it to a ball mill (zirconia balls as the medium). Ball mill at 300~400 r / min for 20~30 min. Add magnesium oxide powder in stages (first 0.5~2 μm, then 2~5 μm, and finally 5~10 μm), and continue ball milling for 40~60 min to prepare a slurry with a viscosity of 3000~6000 mPas.

[0040] Degassing treatment: Place the slurry in a vacuum device and stir at 100-200 r / min for 15-30 min at 0.01-0.04 MPa (absolute pressure) until no bubbles overflow, to avoid the generation of hole defects during printing.

[0041] Photopolymerization printing: A 385~405 nm ultraviolet light source is used, and the curing power is set to 8~15 mW / cm². The curing power is set higher according to the higher the ceramic content, which helps to meet the light penetration requirements under high ceramic content. The curing time of a single layer is 4~8 s and the thickness is 50~100 μm. The core blank is printed in an environment with humidity ≤40%.

[0042] The material is placed in a tube furnace and degreased in an air atmosphere: Heating from room temperature to 250℃: heating rate 1~2℃ / min, holding for 1~2 h, to remove small molecule volatiles; heating from 250℃ to 400~450℃: heating rate 0.5~1℃ / min, holding for 2~3 h, to decompose acrylate resin; heating from 450℃ to 650℃: heating rate 1~2℃ / min, holding for 2~3 h, to completely remove residual carbon. When performing argon-protected sintering in a tube furnace, the oxygen content inside the furnace must be controlled below 200 ppm: Heating from 650 ℃ to 1200 ℃: heating rate 2~3 ℃ / min; heating from 1200 ℃ to 1500 ℃: heating rate 1~2 ℃ / min, holding for 4~6 h, during which the mineralizer promotes the densification of magnesium oxide grains; cooling from 1500 ℃ to 800 ℃: cooling rate 2~3 ℃ / min, holding for 1~2 h to eliminate internal stress; cooling from 800 ℃ to room temperature: cooling with the furnace to avoid cracking caused by rapid temperature changes.

[0043] The following description, using a preferred embodiment, illustrates the content related to the above embodiments: Example 1 According to a preferred embodiment of the magnesium-based ceramic core based on photopolymerization 3D printing of the present invention, the following table shows the percentage of each substance in the magnesium-based ceramic core by mass: This formula is a magnesium oxide ceramic slurry system, and its components and proportions are as follows: Magnesium oxide ceramic slurry (60 wt%): composed of magnesium oxide powder and mineralizer, with magnesium oxide powder accounting for 88% and mineralizer accounting for 12%; the magnesium oxide powder has 20% of 5–10 μm, 50% of 2–5 μm, and 30% of 0.5–2 μm, all modified with KH550 silane; the mineralizer includes yttrium oxide (10%), zirconium oxide (20%), alumina (25%), borosilicate glass powder (15%, B2O3-ZnO system), silicon carbide powder (15%), and zirconium carbide powder (15%), with the particle size of each mineralizer controlled within 1–3 μm.

[0044] Photosensitive resin (35 wt%): composed of acrylate monomers and oligomers, with acrylate monomers accounting for 60% and oligomers accounting for 40%; the acrylate monomers are a blend of dipropylene glycol diacrylate (60%), isobornyl acrylate (25%) and isobornyl methacrylate (15%); the oligomers are a combination of polyurethane acrylate (70%) and silicone-modified polyurethane acrylate (30%) to balance the hardness and toughness after curing.

[0045] Dispersant (3 wt%): a mixture of oleic acid (6 5%) and polyoxyethylene castor oil (35%) to ensure uniform and stable dispersion of ceramic particles in the resin system.

[0046] Photoinitiator (2 wt%): a compound of TPO (70 %) and TPO-L (30 %), optimized for initiation efficiency at UV curing wavelengths.

[0047] Graded magnesium oxide powder was dispersed in an ethanol solution containing 1 wt% KH550 silane coupling agent, ultrasonically dispersed for 45 min, filtered, and dried at 120 ℃ for 2 h for later use. Then, acrylate monomers and oligomers were weighed according to the formula and placed in a stirred tank in a 30 ℃ constant temperature water bath. The mixture was stirred at 500 r / min for 20 min to form a homogeneous liquid mixture. A dispersant was added, and the mixture was stirred at 500 r / min for 15 min. A photoinitiator was then added, and the mixture was stirred at 400 r / min for 20 min under light-protected conditions to form a premix. A mineralizer was added to the premix, and the mixture was transferred to a ball mill. Using zirconia balls as the medium, the mixture was ball-milled at 350 r / min for 25 min with a ball-to-material ratio of 4:1. Finally, modified magnesium oxide powder was added in stages: first, 0.5–2 μm powder was added and ball-milled at 350 r / min for 25 min; then, 2–5 μm powder was added and ball-milled at 350 r / min for 35 min; finally, 5–10 μm powder was added and ball-milled at 350 r / min for 35 min. The magnesium-based ceramic slurry was obtained by ball milling at r / min for 50 min. Its properties were then tested at 25 ℃ and a shear rate of 100 s. -The viscosity at ¹ is 5632 mPa·s. Under constant temperature, constant humidity, and sealed, light-proof storage conditions, the viscosity change rate is 16% over 7 days.

[0048] Transfer the slurry into a vacuum degassing tank, set the absolute pressure to 0.03 MPa, and stir and degas at 150 r / min at 25 ℃ for 20 min. Observe until no bubbles overflow, then stop and set aside for later use.

[0049] Using a DLP photopolymerization device, the following parameters were set: curing power: 10 mW / cm²; single-layer curing time: 8 s; single-layer thickness: 40 μm; a preset 3D model of an engine valve core was printed, which contains 3 intersecting flow channels and a minimum aperture of 3 mm, to obtain a core blank with a dimensional accuracy of ±0.1 mm.

[0050] Degreasing was performed in a tube furnace under air atmosphere, with the following temperature increases: from room temperature to 250 °C at a rate of 1.5 °C / min, holding for 1.5 h; from 250 °C to 420 °C at a rate of 0.8 °C / min, holding for 2.5 h; and from 420 °C to 650 °C at a rate of 1.5 °C / min, holding for 2 h. When performing argon-protected sintering in a tube furnace, the oxygen content inside the furnace must be controlled below 150 ppm: Heating from 650 ℃ to 1200 ℃: heating rate 2.5 ℃ / min; heating from 1200 ℃ to 1500 ℃: heating rate 1.5 ℃ / min, holding for 5 h; cooling from 1500 ℃ to 800 ℃: cooling rate 2.5 ℃ / min, holding for 1.5 h; cooling from 800 ℃ to room temperature: cooling with the furnace.

[0051] Performance tests showed the following: apparent porosity: 17%; room temperature flexural strength: 42 MPa; coefficient of thermal expansion: 11.5 × 10⁻⁶. -6 / ℃ (25~800 ℃); High-temperature compatibility: After contact with 304 stainless steel at 1600 ℃ for 2 h, no reactive phase was formed at the interface. Microstructure diagram of the core surface is shown below. Figure 4 As shown. Example

[0052] This embodiment relates to a magnesium-based ceramic core prepared by photopolymerization 3D printing technology, used for casting complex flow channels in hydraulic servo valves, such as... Figure 2 As shown, the servo valve housing has a cavity for housing the valve core, an oil discharge inlet is provided in the cavity, an oil discharge outlet is provided on the inner wall of the return port, and an oil discharge channel is provided between the oil discharge inlet and the oil discharge outlet. The diameter of the oil discharge channel is less than 1 mm. Therefore, this embodiment can efficiently form complex three-dimensional structures, including fine flow channels with a diameter of less than 1 mm.

[0053] First, three-gradient magnesium oxide powders (0.5~2 μm, 2~5 μm, 5~10 μm) were ultrasonically dispersed for 45 min in an ethanol solution containing 2 wt% KH550 silane coupling agent. The composite mineralizer system contained yttrium oxide, zirconium oxide, borosilicate glass powder, and zirconium carbide, with the SiO2 content controlled to ≤0.08 wt% to avoid interfacial reactions with stainless steel.

[0054] Secondly, the magnesium-based ceramic slurry composition of this embodiment is as follows: acrylate monomer / oligomer accounts for 37.5 wt%; modified magnesium oxide powder accounts for 55 wt%; mineralizer accounts for 5 wt%; dispersant accounts for 1.5 wt%; and photoinitiator accounts for 1.0 wt%.

[0055] Magnesium oxide powder was added in three stages, from smallest to largest particle size. After ball milling at each stage, the slurry viscosity remained stable, ensuring uniform particle dispersion and preventing sedimentation and stratification. The final photocurable magnesium oxide slurry for printing achieved a maximum viscosity of 4856 mPa·s. Under constant temperature, constant humidity, and sealed, light-protected storage conditions, the viscosity change rate after 7 days was ≤13%. The viscosity-time curve is shown below. Figure 3 As shown.

[0056] The DLP printing parameters for this embodiment are: wavelength 405 nm; single-layer curing time 6 s; thickness 50 μm; printing a servo valve core preform (e.g., for printing valve body flow channels (minimum orifice diameter 1.0 mm)). Figure 2 ).

[0057] Then, a three-step heating method (250 ℃ / 420 ℃ / 650 ℃) was adopted, with a heating rate ≤1.5 ℃ / min, to thoroughly remove organic matter. In the argon-protected sintering low-temperature section (heating from 650 ℃ to 1200 ℃), rapid heating (2.5 ℃ / min) suppressed abnormal grain growth; in the high-temperature section (heating from 1200 ℃ to 1500 ℃), slow heating (1.5 ℃ / min) promoted spinel phase formation, and the temperature was held for 5 h; in the controlled cooling section (cooling from 1500 ℃ to 800 ℃), the cooling rate was 2.5 ℃ / min to reduce thermal stress cracking. The microstructure of the servo valve flow channel core surface is shown in the figure. Figure 5 As shown, the apparent porosity is 14%.

[0058] Finally, the core is embedded in the silica sol shell and the firing temperature is set to 1160 ℃; then 304 stainless steel is poured in, cooled, shot blasted to remove sand, and then core is removed by circulating blasting with 40% acetic acid solution at 80 ℃ to remove core residue.

[0059] It should be understood that the terms "one embodiment" or "one example" throughout the specification mean that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of the invention. Therefore, "in one embodiment" or "in one example" appearing throughout the specification do not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Those skilled in the art should also recognize that the embodiments described in the specification are optional embodiments, and the actions and modules involved are not necessarily essential to the invention.

[0060] In various embodiments of the present invention, it should be understood that the sequence number of each process does not necessarily imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0061] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It is particularly important to note that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0062] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A magnesium-based ceramic core formulation based on photocuring technology, characterized by: The magnesium oxide ceramic core slurry (magnesium-based ceramic slurry) comprises the following components by mass percentage: 55-65 wt% of magnesium oxide ceramic particles, 30-40 wt% of photosensitive resin, 1-3 wt% of dispersant, and 0.5-2 wt% of photoinitiator.

2. A magnesium-based ceramic core formulation based on photocuring technology according to claim 1, characterized in that: The magnesium oxide ceramic particles comprise 85-95 wt% of surface-modified magnesium oxide powder and 5-15 wt% of mineralizer.

3. A magnesium-based ceramic core formulation based on photocuring technology as claimed in claim 1, wherein: The magnesium oxide powder comprises three grades of particle size: 5-10 μm, 2-5 μm, and 0.5-2 μm, wherein 5-10 μm accounts for 15-30 wt%, 2-5 μm accounts for 40-60 wt%, and 0.5-2 μm accounts for 20-40 wt%.

4. A magnesium-based ceramic core formulation based on photocuring technology according to claim 1, characterized by: The magnesium oxide ceramic core satisfies the following performance indexes: apparent porosity is 15-25%; room temperature bending strength is greater than or equal to 25 MPa; thermal expansion coefficient is 10-13*10 -6 / ℃ (25-800 ℃); has high-temperature chemical inertness, and does not chemically react with a stainless steel alloy at a temperature below 1600 ℃ in a pouring stage.

5. A magnesium-based ceramic core formulation based on photocuring technology according to claim 1, characterized in that: The magnesium-based ceramic core is formed layer by layer through a light curing technology, which adopts any one of digital light processing (DLP) light curing, stereolithography (SLA) light curing, and liquid crystal display (LCD) light curing.

6. A magnesium-based ceramic core formulation based on photocuring technology as claimed in claim 3, wherein, The surface modification step of the magnesium oxide powder is to form a protective layer on the surface of the powder by using a silane coupling agent; The silane coupling agent is selected from silanes containing one or more functional groups such as amino, epoxy, vinyl, methacryloyloxy, and mercapto; the amount of the silane coupling agent is 0.3-3 wt% of the mass of the magnesium oxide powder, and the proportion of a single type of silane coupling agent in the total amount of the modifier is ≤60 wt%.

7. A magnesium-based ceramic core formulation based on photocuring technology as claimed in claim 2, wherein: The mineralizer comprises, based on a total mass of 100%, 7-15 wt% of yttrium oxide, 20-30 wt% of zirconium oxide, 15-25 wt% of aluminum oxide, 10-20 wt% of low-melting-point boron glass powder, and 10-30 wt% of auxiliary mineralizer; The auxiliary mineralizer is selected from one or more of silicon carbide powder, zirconium carbide powder, and silicon nitride powder, and the proportion of a single component is ≤15 wt% (based on the total mass of the mineralizer); The particle size of the yttrium oxide is 0.5-2 μm, the particle size of the zirconium oxide is 1-3 μm, the particle size of the aluminum oxide is 1-3 μm, the particle size of the low-melting-point boron glass powder is 1-3 μm, and the particle size of the auxiliary mineralizer is 1-5 μm; The content of silicon oxide (SiO2) in the low-melting-point boron glass powder is ≤10 wt%, and the addition amount of the low-melting-point boron glass powder in the mineralizer is such that the total proportion of SiO2 in the total mass of the core is ≤0.1 wt%.

8. A magnesium-based ceramic core formulation based on photocuring technology according to claim 1, characterized by: The photosensitive resin system comprises, based on a total mass of 100%, 50-70 wt% of acrylate monomer and 30-50 wt% of acrylate oligomer.

9. A magnesium-based ceramic core formulation based on photocuring technology according to claim 1, characterized by: The dispersant comprises, based on a total mass of 100%, 60-70 wt% of oleic acid and 30-40 wt% of polyoxyethylene castor oil.

10. A magnesium-based ceramic core formulation based on photocuring technology according to claim 1, characterized by: The photoinitiator comprises, based on a total mass of 100%, 60-80 wt% of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide (TPO) and 20-40 wt% of 2,4,6-trimethylbenzoyl phenyl phosphonic acid ethyl ester (TPO-L).

11. A method for the production of a magnesium-based ceramic core based on light-curing technology, characterized in that: The method for preparing the magnesium-based ceramic core according to any one of claims 1-10 comprises the following steps in the following order: Step one: mix the surface-modified magnesium oxide powder, mineralizer and acrylate photosensitive resin system to prepare a stable magnesium-based ceramic slurry; Step two: place the magnesium-based ceramic slurry into a vacuumizing device for defoaming treatment to remove internal bubbles; Step three: place the defoamed magnesium-based ceramic slurry into the trough of a photocuring printing device, and print a magnesium-based ceramic core blank according to the preset model parameters; Step four: sequentially perform debinding and sintering treatment on the magnesium-based ceramic core blank to obtain a magnesium-based ceramic core.

12. The magnesium-based ceramic core preparation method based on photocuring technology according to claim 11, characterized in that: In step one, the preparation method of the magnesium-based ceramic slurry comprises the following steps in sequence: The surface of the magnesium oxide powder is modified according to requirements, specifically: the powder is dispersed in an ethanol solution containing 0.5-3 wt% silane coupling agent, ultrasonic dispersion is performed for 30-60 min, and the powder is filtered and dried for standby; The surface-modified magnesium oxide powder, mineralizer, photosensitive resin, acrylate oligomer, dispersant and photoinitiator are prepared according to preset requirements; The dispersant is added to the acrylate mixture, and stirring is continued for 10-20 min, then the photoinitiator is added, and stirring is performed in the dark for 15-25 min to obtain a premix; The mineralizer is added to the premix, and the premix is transferred into a ball mill, zirconia balls are used as grinding media, and ball milling is performed at 300-400 r / min for 20-30 min; The magnesium oxide powder is added in stages: first, 0.5-2 μm particle size powder is added, and ball milling is carried out at 300-400 r / min for 20-30 min; then, 2-5 μm particle size powder is added, and ball milling is carried out at 300-400 r / min for 30-40 min; finally, 5-10 μm particle size powder is added, and ball milling is carried out at 300-400 r / min for 40-60 min, to obtain a magnesium-based ceramic slurry; the slurry is subjected to shearing at 25 ℃ and a shearing rate of 100 s - viscosity under the condition of 1 is 3000-6000 mPa·s; In step two, the process parameters of the vacuum defoaming treatment are as follows: defoaming is performed under a vacuum degree of 0.01-0.04 MPa (absolute pressure), the pressure holding time is 15-30 min, and the process is stopped after no bubbles overflow during observation; In step three, the key process parameters of the photocuring 3D printing are as follows: The curing light source wavelength is set to 385-405 nm, the curing power is set to 10-15 mW / cm², the single-layer curing time is set to 4-8 s, and the single-layer curing thickness is set to 30-80 μm; In step four, the process system of debinding and sintering is as follows: Debinding stage (tubular furnace, air atmosphere): From room temperature to 250 ℃: heating rate 1-2 ℃ / min, holding for 1-2 h; from 250 ℃ to 400-450 ℃: heating rate 0.5-1 ℃ / min, holding for 2-3 h; from 450 ℃ to 650 ℃: heating rate 1-2 ℃ / min, holding for 2-3 h; Sintering stage (tubular furnace, vacuum or inert protection, oxygen content lower than 200 ppm in the atmosphere): From 650 ℃ to 1200 ℃: heating rate 2-3 ℃ / min; from 1200 ℃ to 1500 ℃: heating rate 1-2 ℃ / min, holding for 4-6 h; from 1500 ℃ to 800 ℃: cooling rate 2-3 ℃ / min, holding for 1-2 h; from 800 ℃ to room temperature, cooling with the furnace.

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