Regenerated mullite powder and preparation method of thin-wall high-strength shell for precision casting

Abstract

The invention discloses regenerated mullite powder and a preparation method of a thin-wall high-strength shell for precision casting, and belongs to the technical field of precision casting. The modified regenerated mullite powder is prepared by carrying out grain size grading (20-30% of coarse powder, 50-75% of medium powder and 5-20% of fine powder) on regenerated mullite powder according to a specific proportion, and adding 5-10% of a composite reinforcing agent (such as a compound of nano silicon dioxide, a catalyst and nano aluminum oxide). The modified regenerated mullite powder is adopted as a main refractory material, and a ceramic shell with the total layer number being only three and a half can be prepared through a specific slurry preparation and coating process. Compared with a traditional new ore mullite sand powder four-layer half shell, the thickness of the shell is reduced by 25%-27%, and the wet strength and the high-temperature molten steel impact resistance strength are improved by 10% or above on the contrary. According to the method, high-value utilization of waste resources is achieved, the production cost and energy consumption are remarkably reduced, the technological process is simplified, and meanwhile the comprehensive performance of the shell is improved.

Description

Technical Field

[0001] This invention relates to the field of precision casting technology, specifically to a ceramic mold shell for investment casting, and more particularly to a thin-walled, high-strength mold shell made from a specific recycled mullite powder material and its preparation method. Background Technology

[0002] In investment casting (also known as lost-wax casting), preparing a ceramic shell with sufficient strength is crucial for obtaining high-quality precision castings. The shell needs to withstand the thermal and mechanical shocks during dewaxing, firing, and pouring of molten metal. Traditional shell casting processes commonly use newly mined mullite ore powder (referred to as new mullite powder) as the main refractory aggregate and filler. Due to the limited strength of new mullite powder itself, to ensure sufficient room-temperature strength, high-temperature strength, and resistance to molten steel erosion during casting, it is usually necessary to construct at least four and a half layers (i.e., at least four layers of sand and four and a half layers of coating) of shell. This multi-layered structure results in a large overall shell thickness, leading to a series of problems: high material consumption and production costs; bulky shells, inconvenient operation; long drying and firing times, resulting in high energy consumption; and excessively thick shells are more prone to cracking due to uneven expansion and contraction during dewaxing and cooling, affecting the precision of the casting.

[0003] With the deepening of the concepts of circular economy and sustainable development, the resource utilization of foundry waste has received attention. The cost of recycled mullite powder (obtained from the recycling and processing of waste mold shells) is much lower than that of new ore mullite powder, but its performance is generally considered to be unstable or lower than that of new materials. Therefore, it is mostly used for low-requirement castings or as an auxiliary material, and it is difficult to replace new ore mullite powder as the main material in high-requirement precision casting.

[0004] Therefore, how to modify recycled mullite powder to make its performance surpass that of new ore mullite powder, and based on this, develop a shell preparation process with fewer layers, thinner thickness, but higher strength, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a method for preparing recycled mullite powder and thin-walled, high-strength molded shells for precision casting. By scientifically distributing the particle size of recycled mullite powder and modifying it with composite reinforcing agents, this invention enables the preparation of three-and-a-half-layer molded shells that, while significantly reducing thickness, exhibit superior overall strength compared to four-and-a-half-layer molded shells prepared from traditional new ore mullite sand powder.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a modified recycled mullite powder for precision casting mold shells, comprising a recycled mullite powder matrix, a composite reinforcing agent, and optional additives; wherein the particle size distribution of the recycled mullite powder satisfies the following mass percentages: Coarse powder with a particle size of 150–200 mesh: 20%–30% Medium-sized flour with a particle size of 100–200 mesh: 50%–75% Fine powder with a particle size of 200 mesh or larger: 5%–20% The amount of the composite reinforcing agent added is 5% to 15% of the total mass of the regenerated mulberry powder.

[0007] Preferably, the composite reinforcing agent is composed of silica sol, alumina sol and nano alumina powder in a mass ratio of (3-5):(1-2):(0.1-0.5).

[0008] Secondly, the present invention provides a method for preparing the above-mentioned modified recycled mulle powder, characterized by comprising the following steps: S1. The recycled waste ceramic shells are crushed and magnetically separated to remove iron; S2. Grind and classify the material processed in step S1 to obtain recycled mulley sand powder of different particle sizes; S3. According to the particle size distribution ratio described in claim 1, weigh the regenerated mulberry powder in each particle size range, mix them evenly, and obtain the regenerated mulberry powder matrix; S4. Add the composite reinforcing agent to the regenerated mullet powder matrix obtained in step S3, and perform thorough mixing and homogenization to obtain the modified regenerated mullet powder.

[0009] Thirdly, the present invention provides a method for preparing a thin-walled, high-strength precision casting shell, using the modified recycled mullite powder as the main refractory material, characterized by comprising the following steps: (1) Preparation and application of surface slurry: Fine-grained refractory powder (such as corundum powder, zircon powder) and silica sol binder are mixed in proportion to prepare surface slurry. The surface slurry is applied to the wax model, and surface sand (such as zircon sand) is sprinkled on it and dried. (2) Preparation and coating of transition layer slurry: The modified recycled mullite powder and silica sol binder are prepared into a transition layer slurry. The transition layer slurry is dipped onto the dried surface layer, and the modified recycled mullite sand is sprinkled as the transition layer sand. The surface layer is then dried. (3) Backing slurry preparation and coating: The modified recycled mullite powder and silica sol binder are prepared into a backing slurry. The backing slurry is dipped and coated at least twice on the dried transition layer and sand is sprinkled. Each time the sand is sprinkled, the coarse sand part of the modified recycled mullite sand powder is used as the backing sand. Each layer is fully dried after coating. The shell has a total of three and a half layers, namely: one surface layer, one transition layer, and at least one and a half back layers.

[0010] Fourthly, the present invention provides a thin-walled high-strength precision casting shell prepared by the above-mentioned preparation method, characterized in that the total thickness of the shell is reduced by 25% to 27% compared with the total thickness of a four-and-a-half-layer shell prepared using traditional new ore mullite powder, and its wet bending strength and high-temperature molten steel impact strength are both more than 10% higher than those of the traditional four-and-a-half-layer shell.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) Through unique particle size distribution and composite reinforcing agent modification, the performance of recycled mulberry powder is fundamentally improved. The three-and-a-half shell prepared by it has a significantly reduced thickness (25%~27%), and its comprehensive strength exceeds that of the traditional four-and-a-half shell by more than 10%, thus achieving "weight reduction and efficiency improvement".

[0012] (2) The core material is recycled molasses powder, which has a significantly lower raw material cost than new mineral sand powder, in line with the concept of green manufacturing.

[0013] (3) The number of shell layers was reduced from four and a half layers or more to three and a half layers, which simplified the process, shortened the production cycle (the drying time of each layer was reduced cumulatively), and reduced energy consumption and labor costs.

[0014] (4) Thin-walled shells have less thermal stress during dewaxing and baking, reducing the risk of cracking. At the same time, the thermal conductivity of the shells is relatively improved, which is conducive to the optimization of the solidification structure of the molten metal and may improve the internal quality of the casting.

[0015] (5) It has achieved high-value recycling of waste shells, reduced solid waste emissions and consumption of primary mineral resources, and has significant environmental benefits. Attached Figure Description

[0016] Figure 1 This is a schematic diagram comparing the thickness of the shells prepared in Examples 1 and 3 of the present invention with that in Comparative Example 1 (conventional process).

[0017] Figure 2 This is a comparison chart of the wet bending strength test results of the shells prepared in Examples 1 and 2 of the present invention and Comparative Example 1.

[0018] Figure 3 These are comparative photographs showing the morphology of the shells prepared in Example 1 and Comparative Example 1 after a high-temperature molten steel erosion test. Detailed Implementation

[0019] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0020] 1. Preparation of modified recycled mulberry powder: Waste mold shells are recycled, crushed, magnetically separated, and then ground and graded to obtain recycled mullite powder of different particle sizes. The powder is graded according to the following mass ratio: 30% coarse sand (16-30 mesh), 10% medium sand (30-60 mesh), and 60% fine powder (150-2500 mesh). A composite reinforcing agent is added at 5%-15% of the total mass of the recycled mullite powder. The graded powder and composite reinforcing agent are mixed evenly in a high-speed mixer and then sealed and aged for 24 hours before use.

[0021] 2. Preparation of the three-and-a-half-layer shell: (1) Surface layer: After cleaning the wax model, immerse it in zircon powder-silica sol surface layer slurry, remove it and drain it, sprinkle 80-100 mesh zircon sand, and dry it for 6 hours at a temperature of 23±2℃ and a humidity of 60%±5%.

[0022] (2) Transition layer: The modified recycled mullite powder obtained in step 1 is mixed with silica sol to form a slurry, which is then dipped onto the dried surface layer. The medium sand portion (30-60 mesh) of the modified recycled mullite sand powder is sprinkled on as the transition layer sand, and dried for 6 hours under the same conditions.

[0023] (3) Back layer: Prepare a back layer slurry by mixing all the modified recycled mullite powder obtained in step 1 with silica sol binder (mass ratio 2:1). On the dried transition layer, perform two complete "slurry dipping ~ sand sprinkling (using 16-30 mesh coarse sand) ~ drying (8 hours each time)" operations to form two back layers. Then dip and coat the back layer slurry again (without sprinkling sand), and seal it after drying to obtain a "three-and-a-half layer" structural shell (1 surface layer + 1 transition layer + 2 back layers + half layer slurry). Example 2

[0024] The difference from Example 1 lies in the particle size distribution of the modified recycled mulberry powder and the amount of composite reinforcing agent.

[0025] The particle size distribution is as follows: 30% coarse sand (16-30 mesh), 10% medium sand (30-60 mesh), and 60% fine powder (above 150 mesh).

[0026] The amount of composite reinforcing agent added is 5% of the total mass of the recycled mulberry powder.

[0027] The shell preparation process is the same as in Example 1. Example 3

[0028] The difference from Example 1 lies in the particle size distribution of the modified recycled mulberry powder and the amount of composite reinforcing agent.

[0029] The particle size distribution is as follows: 20% coarse powder (150-200 mesh) and 80% fine powder (200-2500 mesh).

[0030] The amount of composite reinforcing agent added is 10% of the total mass of the regenerated mulberry powder.

[0031] The shell preparation process is the same as in Example 1.

[0032] Comparative Example 1 (Traditional Process)

[0033] Commercially available new ore mullite powder (without special gradation or reinforcement treatment) was used as the backing material. The shell was prepared according to the traditional four-and-a-half-layer process: one surface layer (zircon powder / sand), one transition layer (new ore mullite fine powder / medium sand), and the backing layer (new ore mullite powder / coarse sand) was coated and sprinkled with sand at least three times (forming three backing layers), and finally a half-layer of slurry was coated. The drying time for each layer was comparable to that in the example.

[0034] Performance Testing and Comparative Analysis The performance of the shells prepared in Examples 1-3 and Comparative Example 1 was tested: Thickness measurement: Ten shells prepared from the same type of wax mold were randomly selected, and their average total thickness was measured. The results are as follows: Figure 1 As shown, the average shell thickness of Examples 1-3 is 3.6-3.8 mm, while the average shell thickness of Comparative Example 1 is 5 mm. The shell thickness of the Examples is reduced by approximately 24%-28%.

[0035] Wet flexural strength: Standard test strips were prepared from the dried shell sheets, and their wet (dry but not fired) flexural strength was tested using a universal testing machine. Results are as follows: Figure 2 As shown, the shells of Examples 1-3 have a strength of 5.8-6.2 MPa, while the shell of Comparative Example 1 has a strength of 5.2 MPa. The shell strength of the Examples is increased by approximately 11%-19%.

[0036] High-Temperature Molten Steel Impact Simulation Test: A baked mold shell was simplified into a specific shape, and molten 304 stainless steel was poured into it at 1650℃. The corrosion, erosion, and cracking of the inner wall of the mold shell were observed. Figure 3 As shown, the inner walls of the shells in Examples 1-3 are intact with only a slight sintered layer; while the inner wall of the shell in Comparative Example 1 shows localized peeling and fine cracks. Quantitatively, by measuring the amount of peeling per unit area, the impact resistance of the shells in the Examples is more than 10% better than that of the Comparative Example.

[0037] The above experimental results show that the three-and-a-half-layer shell preparation process based on modified recycled mulberry powder provided by the present invention successfully achieves the "thin-wall" and "high-strength" properties of the shell, and its comprehensive performance surpasses that of traditional processes.

[0038] It should be noted that 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 limitation, 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.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A recycled mullite powder for use in precision casting molds, characterized in that, It consists of a recycled mulle powder matrix and a composite reinforcing agent; wherein the particle size distribution of the recycled mulle powder matrix satisfies the following mass percentages: Coarse powder with a particle size of 150-200 mesh: 20%-30%, Medium-sized flour with a particle size of 100-200 mesh: 50%-75%, Fine powder with a particle size of 200 mesh or larger: 5%–20%; The amount of the composite reinforcing agent added is 5% to 15% of the total mass of the regenerated mulberry powder matrix.

2. The recycled mulberry powder according to claim 1, characterized in that, The composite reinforcing agent is composed of nano-silica, catalyst and nano-alumina powder.

3. The recycled mulberry powder according to claim 2, characterized in that, The mass ratio of the nano-silica, catalyst, and nano-alumina powder is (3-5):(1-2):(0.1-0.5).

4. A method for preparing the regenerated mulberry powder according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Crush and remove iron from the recycled waste ceramic shells; S2. Grind and classify the material processed in step S1 to obtain recycled mulley sand powder of different particle sizes; S3. According to the particle size distribution ratio described in claim 1, weigh the regenerated mulberry powder in each particle size range, mix them evenly, and obtain the regenerated mulberry powder matrix; S4. Add the composite reinforcing agent to the regenerated mullet powder matrix obtained in step S3, and perform mixing and homogenization treatment to obtain the modified regenerated mullet powder.

5. A method for preparing a thin-walled, high-strength precision casting shell, characterized in that, Using the recycled mullite powder according to any one of claims 1-3 as the main refractory material, the method includes the following steps: (1) Preparation and application of surface slurry: Prepare the surface refractory powder and binder into a surface slurry, apply the surface slurry onto the wax mold, sprinkle surface sand, and dry; (2) Preparation and application of transition layer slurry: The modified recycled mullite powder and binder are prepared into a transition layer slurry, which is then dipped onto the dried surface layer. The modified recycled mullite sand is then sprinkled on as the transition layer sand and dried. (3) Preparation and application of back layer slurry: The modified recycled mullite powder and binder are prepared into a back layer slurry. The back layer slurry and sand-spreading operation are performed at least twice on the dried transition layer. The modified recycled mullite sand is used as the back layer sand for each sand-spreading operation. Each layer is dried after application. The shell has a total of three and a half layers.

6. The preparation method according to claim 5, characterized in that, The adhesive used in steps (2) and (3) is silica sol.

7. The preparation method according to claim 5, characterized in that, The three-and-a-half-layer structure specifically includes: a surface layer formed in step (1), a transition layer formed in step (2), at least one complete back layer formed in step (3), and a final slurry layer without sand.

8. The preparation method according to any one of claims 5-7, characterized in that, In step (3), two dip-coating operations of the backing slurry and sand spreading are performed to form two complete backing layers.

9. A thin-walled, high-strength precision cast shell prepared by the preparation method according to any one of claims 5-8.

10. The thin-walled, high-strength precision-cast shell according to claim 9, characterized in that, The total thickness of the shell is reduced by 25% to 27% compared to the total thickness of a four-and-a-half-layer shell made from traditional new ore mullite powder, and its wet bending strength and high-temperature molten steel impact strength are both more than 10% higher than those of the traditional four-and-a-half-layer shell.

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